**Solid Waste Processing and Resource Recovery Workshop Report -- Volume
I**

Engineering Directorate

Crew and Thermal Systems Division

CTSD-ADV-474

March 1, 2001

> ![](media/image1.png){width="1.0673611111111112in"
> height="1.1493055555555556in"}

National Aeronautics and Space Administration

Lyndon B. Johnson Space Center

Houston, Texas 77058

![](media/image2.png)

**SOLID WASTE PROCESSING AND RESOURCE RECOVERY WORKSHOP REPORT**

**TABLE OF CONTENTS**

Page Number

1\. PREFACE 1

2\. EXECUTIVE SUMMARY 2

3\. INTRODUCTION 4

4\. RESULTS & DISCUSSION 6

4.1 Pre- and Post-Processing Technologies 6

4.2 Biological Technologies 19

4.3 Physicochemical Technologies 35

4.4 Conclusions 55

5\. SUMMARY ANALYSIS 56

6\. FUTURE DIRECTIONS 68

7\. ACRONYM LIST 70

8.  REFERENCES 71

9\. ACKNOWLEDGEMENT 74

**SOLID WASTE PROCESSING AND RESOURCE RECOVERY WORKSHOP REPORT**

# 1. PREFACE 

The mission of the Biological and Physical Research Enterprise is to use
the synergy between physical, chemical and biological research in space
to acquire fundamental knowledge and generate applications for space
travel and Earth applications. It is the intended long-term objective of
the Human Exploration and Development of Space (HEDS) Enterprise of the
National Aeronautics and Space Administration (NASA) to establish a
human presence on the Moon, Mars, or elsewhere in the Inner Solar
System. In order to attain this objective, it will be essential to
develop a closed-loop life support system that relies on minimal or no
re-supply. The strategy, therefore, is to develop regenerative
physicochemical and biological technologies that will reduce the
system's mass, power, and volume requirements on the entire mission. To
have a truly closed-loop system, it is necessary to produce and process
food and recover resources from wastes while providing clean air and
water. NASA recognizes the particular challenges of solid waste
processing and resource recovery for its proposed long-term space
missions. Over the years considerable effort has been directed towards
storage and safe handling of wastes due to the nature of the missions.
As NASA plans for more long-duration missions, the focus broadens from
storage to resource recovery.

There is a plethora of waste processing technologies on Earth. The use
of a specific waste processing technology is often dictated by the level
of pollution abatement and, more often than that, the economics of the
operation. To direct NASA's efforts in the area of solid waste
processing, it is important to realize the full potential of these
technologies and relate them to the critical requirements of the various
exploration mission scenarios.

A workshop titled "Solid Waste Processing and Resource Recovery (SWPRR)"
was held in Houston on April 4 - 6, 2000. The main objective of the
SWPRR workshop was to assess these technologies to develop a research
and technology development strategy for SWPRR in NASA's Advanced Life
Support (ALS) program. Evaluations included assessments of the
technology readiness and their suitability for use in space-based life
support systems. Various pre- and post-processing and resource recovery
technologies were evaluated for their mass, power, and volume
requirements and their particular strengths and shortcomings.
Specialists from industry, government and academia participated in this
event. Data on each technology relevant to the technology's development
and use for waste processing were pooled and evaluated based on their
applications for various operating scenarios. Technology assessments and
an attendee's list with contact information are located in the Volume II
(Solid Waste Processing and Resource Recovery Workshop Report Appendix),
along with other pertinent information that describes the mission
scenarios and the waste model.

At the time of these assessments it was understood that many of the
technologies were not mature enough to fully recognize their strengths
and weaknesses. Also, the technology assessment forms that were used
could not be fully completed at the time of the workshop, as some of the
information sought at the time of the meeting was either too speculative
or unavailable.

The experts were encouraged to identify the critical research and
technology development needs as part of the technology assessment. In
instances where they were unsure of the data that was sought, the
attendees were asked to give estimates that would be accurate to within
an order of magnitude.

NASA realizes that this document may not provide a true technology
assessment in all the research areas, but the intent is to have a
dynamic document that the research community will be able to access to
understand the areas that require research.

# 2. EXECUTIVE SUMMARY

## 2.1 Workshop Planning And Development Of Pre-Workshop Documents

Weekly teleconferences were held between Johnson Space Center (JSC),
Ames Research Center (ARC), and NASA Headquarters (HQ) to develop the
technology assessment documents based on five mission scenarios. The
Systems Modeling and Analysis Project (SMAP) led the development of
these documents. The intent was to gather as much data as possible on
solid waste processing technologies. These documents were sent to the
workshop participants a month in advance for them to do an individual
preliminary analysis. The completed documents were compiled according to
the different technology types and made available to the participants
prior to the workshop.

## 2.2 Panelists

An effort was made to bring together the top waste treatment experts in
the nation, along with currently funded NASA researchers in the area of
solid waste processing. Expertise was drawn from national laboratories,
small-scale industries, aerospace industry, academia, consulting firms,
and the federal government. The intent was to bring about a thorough
exchange of ideas and draft a thorough technology evaluation document
for each of the technologies.

## 2.3 Invited Talks

Dr. Donald Henninger (Chief Scientist & Deputy Manager, Advanced Life
Support Program) gave an overview of NASA's Advance Life Support (ALS)
program to the participants. This was an educational presentation about
the status of research and development in ALS.

Dr. Joan Vernikos (Director of NASA Office of Life and Microgravity
Science and Applications Division) advised the participants about the
need for a waste treatment strategy for long-term space missions. In her
address, she also gave a perspective of the nascent stage of development
in waste collection and treatment aboard the short-duration space
missions.

Dr. Shannon Lucid (astronaut aboard MIR and various shuttle flights)
spoke to the workshop participants about the state of the art on the US
and Russian space-flight operations. Her talk focused on solid waste
collection devices and storage of wastes on MIR and the shuttle. She
also spoke about the problems in microgravity and mitigation procedures
to overcome microgravity effects for efficient collection of wastes in
orbit.

## 2.4 Workshop Structure And Function

The participants were divided into three working groups
(Pre-Processing/Post-Processing, Physicochemical Processing, Biological
Processing). Each working group was headed by an external expert and
assisted by a NASA scientist.

Pre-Processing/Post-Processing

The charge to this group was to take input from the other two working
groups on pre- and post-processing needs for the different waste
treatment technologies. Once this information was provided, this group
identified 20 generic pre-processing technology areas applicable to the
pre- and post-processing needs. Of these 20 technologies, twelve main
categories of technologies for detailed assessments were selected and
placed into three technological groupings. These groupings included
particle size reduction, drying/mixing, and transport/conveyance.

# Physicochemical (PC) Processing 

The main charge for this group was to examine the PC technologies that
are currently used (activated carbon manufacture, incineration,
pyrolysis, lyophilization, supercritical water oxidation, peroxide
oxidation, electrochemical oxidation, plasma arc thermal destruction,
gasification and biomass acid hydrolysis) and study their potential
application in satisfying NASA's needs as defined in the five mission
scenarios.

**Biological Processing**

Like the charge to the PC group, this group was charged to evaluate the
potential of currently used biological processing technologies for NASA
applications. The technologies this working group considered were the
following: composting, anaerobic digestion, single cell protein (SCP)
production, paper-making as an intermediate product, and methods for
recovering inorganic nutrients for preparation of plant growth
hydroponics solutions.

The panelists discussed the different technology assessment forms that
were submitted prior to the workshop and refined their preliminary
assessments. The goal was to create a single technology assessment form
with all the available information for each technology assessed. To
accomplish this, panelists were instructed to give realistic information
on the basis of the current knowledge that exists in the literature.

At the end of the two days of assessments, each working group presented
a summary of their findings to the entire workshop.

## 2.5 Open Discussion

At the end of the workshop there was a two-hour open discussion
addressing different aspects of solid waste treatment. One of the focal
points of this discussion was the BIO-Plex project and its use as a test
bed for testing various waste processing technologies.

**2.6 [Summary of Findings]{.underline}**

A total of thirty-one technologies were assessed - eleven pre-processing
technologies, thirteen physicochemical and seven biological. Results
showed that all technologies are below TRL 5, with the exception for
storage equipment. Particular areas that require significant research
and technology development include the following: 1) development of
integrated waste processors for end-to-end automated operation; 2)
assessment of technologies for gravity dependence; 3) optimization of
pre-Processing, physicochemical and biological processes; and 4) testing
and validation in relevant environments. Methods for collection and
storage of solid wastes have been flight demonstrated in the Shuttle,
Russian Space Station and previous missions. These methods will require
evaluation for use in transit and planetary missions.

# 3. INTRODUCTION

## 3.1 Background and Purpose of the Workshop

Successful long duration missions will require regeneration of life
support resources from wastes generated in space-based habitats. Losses
of resources vital to life support due to wastes (i.e. consumables) that
cannot be processed and recovered will require resupply. A loss in
essential life-supporting elements could jeopardize crew performance and
well being, whereas any resupply from Earth will be cost prohibitive.
Thus, resource recovery from wastes becomes a critical component to
closure in future ALS systems (1)\*. Utility of waste processing
technologies is a function of the resources bound to the wastes that can
be recovered and mission duration. Mission duration will be a
determining factor in resource recovery requirements. Without recycling
needed resources, resupply cost will increase more for a longer mission
than a shorter mission (2).

Assessment of potential technologies and development of a strategy for
development of solid waste processing hardware for collection,
pre-processing, processing, post-processing, and storage of unusable
residues / unprocessed solid waste residues are essential to having
mature technologies for space-based habitats on the Moon and Mars (2).

\* Numbers in parentheses represent references.

The ALS team at NASA invited a team of experts from academia and
industry to contribute to a research and technology development roadmap
for solid waste processing and resource recovery. Along with the
specific technology assessment forms the workshop participants were
given a broad charter to seek the information.

## 3.2 Charter to the Workshop

Advanced life support (ALS) systems will be required for long duration
human missions of the future. Recycling of air and water, production of
crops and processing into storable items or food, and solid waste
processing are key elements of an ALS. Solid waste processing and
resource recovery (SWPRR) can be more aptly stated as recovery and
recycling of useful resources from solid wastes.

The goal of the proposed SWPRR workshop is to provide input to NASA to
develop a research and technology development strategy for SWPRR.
Candidate waste processing technologies for possible use in future
space-based human life support systems would be assessed at this
workshop. Each candidate solid waste processing technology will be
independently assessed in terms of established criteria including mass,
power, volume, reliability, use of expendables, technology readiness
level, and operational scenarios (e.g., microgravity vs. hypogravity;
vehicle vs. planetary surface applications). Evaluations will also
include an assessment of the technology readiness and its suitability
for use in space-based ALS in the context of specific mission scenarios.

The workshop will be structured into four functional components of solid
waste processing: 1) collection, transport, storage and pre-processing;
2) physico-chemical primary processing; 3) biological primary
processing; and 4) post-treatment and disposition of 'unprocessed'
wastes.

Waste models that will describe the components and quantities of wastes
expected for specific elements of the mission scenarios will be
provided. It is expected that a technology assessment will be done on
the basis of these waste models. Tools will be provided to record data
needed on each technology. Assessment of the technologies will include
identification of limitations of the technology in the context of NASA
mission applications and possible approaches to overcoming these
limitations. Finally, new technologies, which might be potentially
applicable to space-based life support systems, will be solicited.

The recommendations and findings of this workshop are expected to serve
as a guideline to solicit and conduct research in ALS in the area of
SWPRR.

# 

# 

# 

# 

# 4. RESULTS & DISCUSSION

## 4.1 Pre- and Post-Processing Technologies

### 4.1.1 Introduction

The pre- and post-processing (PPP) working group identified and analyzed
pre-processing and post-processing technologies that could support the
physicochemical (PC) and biological (Bio) conversion systems being
considered at the workshop. With reference to the ALS program,
pre-processing technologies are those that prepare solid waste for PC or
Bio processing. An example of pre-processing technology is size
reduction, i.e., shredding (or synonymously, grinding), that may be
required by a primary processing system to provide for adequate
treatment (i.e. physicochemical or biological conversion of the wastes
to a resource). Pre-processing includes: 1) processes that select or
separate the wastes into a feedstock that can be processed by a primary
processing system, 2) preparation of the wastes into a physical form
(e.g., dried, micron-sized particles, a slurry) that is optimal for the
primary processing system, and 3) transport of the waste.
Post-processing generally refers to those operations that refine a
material to a higher quality or to another physical form so that it may
be used, treated further, or disposed. Examples of post-processing
include processing of the solid residues for particle size separation
and treatment of some of the secondary products (ash, slurry). The water
and gases recovered as by-products from any of these processes would be
further treated by a water recovery system designed for the application,
or by the air revitalization system, respectively.

With regard to throughput rates and processing flexibility, PPP
technologies may be designed to operate in batch, continuous, or both
modes of processing. Articles and books that discuss handling and
preparation of wastes for solid waste processing are references (3-7).

### 4.1.2 Major Activities of the PPP Working Group

-   Definition of the governing characteristics of the waste and solid
    product streams from the PC and Bio conversion systems that might
    have to be post-processed

-   Definition of the universe of applicable generic PPP technologies
    for solid wastes

-   Narrowing of the universe to those technologies selected as being
    more relevant to PC and Bio primary processing systems

-   Description of the characteristics of the selected technologies,
    analysis of the technologies, and estimation of their TRLs

### 4.1.3 Selection of Relevant PPP Technologies

The initial work of the working group revolved around the need to secure
waste stream properties, both on a wet and dry weight basis, and the
waste characteristics desired by the PC and Bio technologies. A summary
of the waste input information received from the PC and Bio conversion
system working groups is given in Table 1. Prior to receiving the waste
input information for the other two working groups, the PPP working
group identified about 20 generic areas of PPP technology. The areas are
summarized in Table 2.

From the list of PPP technologies presented in Table 2, the working
group selected twelve main categories or subcategories for detailed
analysis. The technologies were selected based primarily on the
estimated processing rates, the raw (i.e., as collected) solid waste
characteristics, and the required input feedstock characteristics of the
PC and Bio technologies, as identified and analyzed by their respective
working groups. A secondary consideration was the applicability of the
technologies to post-processing of the solid by-products generated by
the PC and Bio systems.

The twelve selected technologies were coalesced into three technological
groupings. An assessment group (i.e., subgroup of members of the PPP
working group) was established subsequently to conduct the evaluation of
the technologies within a particular technological grouping. The names
of the technological groupings were as follows:

Transport, Conveyance, and Phase Separation;

Drying and Mixing; and

Particle Size Reduction and Control.

For each technology within the technology groupings, the assessment
groups analyzed the advantages and disadvantages, the potential effect
of micro- and hypogravity, and the current technology readiness level
(TRL). Additionally, each assessment group selected one or two
technologies in their grouping for further analysis in terms of the
specific technical tasks that would be required in order to develop the
technology to a status of TRL 5 (reference 2). A summary of the results
of these analyses is given in Tables 3 through 5, respectively, for each
of the three technology groupings and their subcategories of
technologies.

#### 4.1.3.a Pre- and Post-Processing Requirements 

**Table 1. Pre- and Post-Processing Requirements for PC and**

**Bio Conversion Systems Configured for Resource Recovery**

+----------+------+----+-------+----------+----------+---------------+
|          | **   |    |       |          |          | ## Po         |
|          | Pre- |    |       |          |          | st-Processing |
|          | Proc |    |       |          |          |               |
|          | essi |    |       |          |          |               |
|          | ng** |    |       |          |          |               |
+==========+======+====+=======+==========+==========+===============+
| **Solid  | **   | ** | *     | **Items  | **Items  | ## Products   |
| Waste    | Requ | Bu | *Desi | Te       | Te       |               |
| Techno   | ired | lk | rable | chnology | chnology |               |
| logies** | Part | D  | or    | WILL     | WILL NOT |               |
|          | icle | en | Accep | P        | P        |               |
|          | Si   | si | table | rocess** | rocess** |               |
|          | ze** | ty | Moi   |          |          |               |
|          |      | ** | sture |          |          |               |
|          |      |    | Cont  |          |          |               |
|          |      |    | ent** |          |          |               |
+----------+------+----+-------+----------+----------+---------------+
| ####     |      |    |       |          |          |               |
| Physicoc |      |    |       |          |          |               |
| hemical  |      |    |       |          |          |               |
+----------+------+----+-------+----------+----------+---------------+
| Freeze   | 100  | 0  | nor   | feces    |          | need to store |
| Drying   | m to | .5 | mally | and      |          |               |
|          | 0.3  | g/ |       | biomass  |          |               |
|          | cm   | cc | \> 10 |          |          |               |
|          |      |    | %     |          |          |               |
+----------+------+----+-------+----------+----------+---------------+
| Super    | [\<] | 1  | [nor  | like a   | 1,500    | organic free  |
| Critical | {.un | g/ | mally | puree;   | ppm HCl  | oxides;       |
| Wet      | derl | cc | 75 to |          | or       | salts;        |
| O        | ine} |    | 95    | 7% to    | H        | oxides;       |
| xidation | 100  |    | %]{.  | 10%      | ~2~SO~4~ | CO~2~, O~2~,  |
|          | m    |    | under | organic, |          | N~2~, and     |
|          |      |    | line} | 2% to 3% |          | some N~2~O;   |
|          |      |    |       | i        |          | moisture      |
|          |      |    |       | norganic |          | [\<           |
|          |      |    |       |          |          | ]{.underline} |
|          |      |    |       |          |          | 50%           |
+----------+------+----+-------+----------+----------+---------------+
| Inci     | [\<] |    | [     | anything | remove   | CO~2~, ash;   |
| neration | {.un |    | \<]{. | that can | alkali   | trace organic |
| --       | derl |    | under | be       | and      | compounds,    |
| F        | ine} |    | line} | ground   | c        | HCl           |
| luidized | 0.6  |    | 50%   | to small | hlorides |               |
| Bed      | cm   |    | to    | size     |          |               |
|          |      |    | 70%   |          |          |               |
+----------+------+----+-------+----------+----------+---------------+
| Inci     | [\<] |    | lower | none if  | minimize | CO~2~, ash;   |
| neration | {.un |    | is    | small    | alkali,  | trace organic |
| -- Batch | derl |    | b     |          | ch       | compounds,    |
|          | ine} |    | etter |          | lorides, | HCl           |
|          | 5.0  |    |       |          | and      |               |
|          | cm   |    |       |          | i        |               |
|          |      |    |       |          | norganic |               |
|          |      |    |       |          | nitrogen |               |
+----------+------+----+-------+----------+----------+---------------+
| Inci     | n/a  |    |       | comb     | metals   | CO~2~,        |
| neration |      |    |       | ustibles | or glass | nitrates;     |
| --       |      |    |       |          |          | NO~x~         |
| Plasma   |      |    |       |          |          |               |
+----------+------+----+-------+----------+----------+---------------+
| Indirect | 0    |    | high  | soluble  | flu      | CO~2~, trace  |
| Electro  | (    |    | co    | organic  | orinated | volatile      |
| chemical | solu |    | ntent | m        | p        | organic       |
| R        | ble) |    | is    | aterials | lastics, | compounds,    |
| eduction | up   |    | b     |          | c        | Cl~2~ and HCl |
|          | to   |    | etter |          | hlorides |               |
|          | [\<] |    | but   |          |          |               |
|          | {.un |    | not   |          |          |               |
|          | derl |    | nece  |          |          |               |
|          | ine} |    | ssary |          |          |               |
|          | 10 m |    |       |          |          |               |
+----------+------+----+-------+----------+----------+---------------+
| Carbo    | 0.05 |    | [     | c        | human    | activated     |
| nization | to   |    | \<]{. | ellulose | waste    | carbon;       |
|          | 1.0  |    | under | waste    |          | pyrolysis gas |
|          | cm   |    | line} |          |          | or synthesis  |
|          |      |    | 50%   |          |          | gas (CO,      |
|          |      |    |       |          |          | CH~4~, H~2~O, |
|          |      |    |       |          |          | H~2~ and      |
|          |      |    |       |          |          | volatile      |
|          |      |    |       |          |          | organic       |
|          |      |    |       |          |          | compounds)    |
|          |      |    |       |          |          | =\> energy    |
+----------+------+----+-------+----------+----------+---------------+

Table 1. Pre- and Post-Processing Requirements for PC and

**Bio Conversion Systems Configured for Resource Recovery (cont.)**

+-----------+-----+----+------+----------+----------+---------------+
|           | **P |    |      |          |          | ## Po         |
|           | re- |    |      |          |          | st-Processing |
|           | Pro |    |      |          |          |               |
|           | ces |    |      |          |          |               |
|           | sin |    |      |          |          |               |
|           | g** |    |      |          |          |               |
+===========+=====+====+======+==========+==========+===============+
|           | *   | ** | **D  | **Items  | **Items  | ## Products   |
|           | *Re | Bu | esir | Te       | Te       |               |
|           | qui | lk | able | chnology | chnology |               |
|           | red | D  | or   | WILL     | WILL NOT |               |
|           | Pa  | en | Ac   | P        | P        |               |
|           | rti | si | cept | rocess** | rocess** |               |
|           | cle | ty | able |          |          |               |
|           | Siz | ** | Mois |          |          |               |
|           | e** |    | ture |          |          |               |
|           |     |    | C    |          |          |               |
|           |     |    | onte |          |          |               |
|           |     |    | nt** |          |          |               |
+-----------+-----+----+------+----------+----------+---------------+
| Hydrogen  | [   |    | 0%   | paper,   | water or | CO~2~, ash;   |
| Peroxide  | \<] |    |      | p        | oil      | energy from   |
| Oxidation | {.u |    |      | lastics, |          | steam         |
|           | nde |    |      | inedible |          |               |
|           | rli |    |      | biomass, |          |               |
|           | ne} |    |      | human    |          |               |
|           | 15  |    |      | waste,   |          |               |
|           | cm  |    |      | and food |          |               |
+-----------+-----+----+------+----------+----------+---------------+
| Pyrolysis | n/a | 0  | [\<] | batch or | no       | A range of    |
|           |     | .5 | {.un | co       | fluorine | solids: 20%   |
|           | [   | g/ | derl | ntinuous | or       | to 35% by     |
|           | \<] | cc | ine} |          | c        | weight;       |
|           | {.u |    | 80%  |          | hlorine; | liquids 0% to |
|           | nde |    |      |          | metal or | 50% by        |
|           | rli |    |      |          | ceramic  | weight; gas   |
|           | ne} |    |      |          |          | 30% to 80% by |
|           | 10  |    |      |          |          | volume. This  |
|           | cm  |    |      |          |          | split alters  |
|           |     |    |      |          |          | due to        |
|           |     |    |      |          |          | temperature   |
+-----------+-----+----+------+----------+----------+---------------+
| Gas       | [   |    | any  | high     |          | Produce a     |
| ification | \<] |    |      | heat     |          | solid,        |
|           | {.u |    |      | value    |          | liquid,\      |
| (steam    | nde |    |      | m        |          | and a gas;    |
| r         | rli |    |      | aterials |          | range of      |
| eforming) | ne} |    |      |          |          | solids: 20%   |
|           | 0.1 |    |      |          |          | to 35% by     |
|           | cm  |    |      |          |          | weight;       |
|           |     |    |      |          |          | liquids 0% to |
|           | ([  |    |      |          |          | 50% by        |
|           | \<] |    |      |          |          | weight; gas   |
|           | {.u |    |      |          |          | 30 to 80% by  |
|           | nde |    |      |          |          | volume. This  |
|           | rli |    |      |          |          | split alters  |
|           | ne} |    |      |          |          | due to        |
|           | 10  |    |      |          |          | temperature.  |
|           | cm) |    |      |          |          |               |
+-----------+-----+----+------+----------+----------+---------------+
| # [Biolo  |     |    |      |          |          |               |
| gical]{.u |     |    |      |          |          |               |
| nderline} |     |    |      |          |          |               |
+-----------+-----+----+------+----------+----------+---------------+
| C         | 0.5 |    | 40%  | biode    | n        | produce       |
| omposting | to  |    | to   | gradable | on-biode | solid, liquid |
|           | 5.0 |    | 70%  |          | gradable | (water),      |
|           | cm  |    |      |          |          | leachate      |
|           |     |    |      |          | (p       | (high         |
|           |     |    |      |          | lastics, | organic), gas |
|           |     |    |      |          | metals,  | (CO~2~,       |
|           |     |    |      |          | tapes,   | H~2~O, and    |
|           |     |    |      |          | etc.)    | NH~3~ plus    |
|           |     |    |      |          |          | trace organic |
|           |     |    |      |          |          | compounds)    |
+-----------+-----+----+------+----------+----------+---------------+
| Slurrying | [   | 1  | [\>] | separate | n        | produce       |
|           | \<] | g/ | {.un | bi       | on-biode | solid, liquid |
|           | {.u | cc | derl | ological | gradable | (water),      |
|           | nde |    | ine} | and      | (p       | leachate      |
|           | rli |    | 90%  | non-bi   | lastics, | (high         |
|           | ne} |    |      | ological | metals,  | organic), gas |
|           | 0.5 |    |      | co       | tapes,   | (CO~2~,       |
|           | cm  |    |      | mponents | etc.)    | H~2~O, and    |
|           |     |    |      |          |          | NH~3~ plus    |
|           |     |    |      |          |          | trace organic |
|           |     |    |      |          |          | compounds)    |
+-----------+-----+----+------+----------+----------+---------------+
| Leaching  | [   | 1  | [\<] | inedible | n        | Leachate with |
|           | \<] | g/ | {.un | biomass  | on-biode | high organic  |
|           | {.u | cc | derl |          | gradable | content +     |
|           | nde |    | ine} |          | (p       | inorganic     |
|           | rli |    | 10%  |          | lastics, | nutrient +    |
|           | ne} |    |      |          | metals,  | microbial     |
|           | 10  |    |      |          | tapes,   | cells and     |
|           | cm  |    |      |          | etc.)    | trace NH~3~   |
|           |     |    |      |          |          | gas           |
+-----------+-----+----+------+----------+----------+---------------+

#### 4.1.3.b Technology Areas

Table 2. Universe of Technology Areas for Pre- and Post-Processing of
Solid Wastes

+-----------------------------------------------------------------------+
| 1.  Source separation (i.e., manual separation)                       |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 2.  Storage (using various types of containers or bins)               |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 3.  Drying:                                                           |
+-----------------------------------------------------------------------+
| 1.  freeze drying                                                     |
+-----------------------------------------------------------------------+
| 2.  thermal drying                                                    |
+-----------------------------------------------------------------------+
| 3.  vacuum drying                                                     |
+-----------------------------------------------------------------------+
| 4.  air drying                                                        |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 4.  Compaction (bulk compaction; product is a large, dense unit       |
|     (e.g., bale))                                                     |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 5.  Pelletization (or densification; product is a small, dense unit   |
|     (e.g., pellet))                                                   |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 6.  Size reduction:                                                   |
+-----------------------------------------------------------------------+
| 1.  wet (defined as size reduction of wastes with a moisture content  |
|     greater than 60%, or slurry or pulping of the waste)              |
+-----------------------------------------------------------------------+
| 2.  dry (defined as size reduction of wastes with a moisture content  |
|     less than or equal to 60%)                                        |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 7.  Transport and conveyance:                                         |
+-----------------------------------------------------------------------+
| 1.  fluidic:                                                          |
+-----------------------------------------------------------------------+
| 1.  gas working fluid                                                 |
+-----------------------------------------------------------------------+
| 2.  liquid working fluid                                              |
+-----------------------------------------------------------------------+
| 2.  mechanical (e.g., belt or screw conveyors)                        |
+-----------------------------------------------------------------------+
| 3.  manual (e.g., using containers)                                   |
+-----------------------------------------------------------------------+
| 8.  Mixing:                                                           |
+-----------------------------------------------------------------------+
| 1.  liquid/solid (to dissolve solids or to slurry them)               |
+-----------------------------------------------------------------------+
| 2.  solid/solid (to achieve homogenous a mixture of two or more       |
|     different types of solids)                                        |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 9.  Phase separation (physical, e.g., sieving of different sized      |
|     particles)                                                        |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 10. Air classification (gas (e.g., air) is the working fluid          |
|     affecting separation of two or more solid phases)                 |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| 11. Metal separation (e.g., ferrous and non-ferrous)                  |
+-----------------------------------------------------------------------+

#### 4.1.3.c Mixing and Drying Technologies

**Table 3. Summary of Analysis of Selected Mixing and Drying
Technologies**

+-----------+-------------+----------------------+--------------+----+
| **Tec     | **A         | **Disadvantages**    | **Gravity    | *  |
| hnology** | dvantages** |                      | Issues**     | *C |
|           |             |                      |              | ur |
|           |             |                      |              | re |
|           |             |                      |              | nt |
|           |             |                      |              | T  |
|           |             |                      |              | RL |
|           |             |                      |              | ^\ |
|           |             |                      |              | *^ |
|           |             |                      |              | ** |
+===========+=============+======================+==============+====+
| A. Force  | -           | -   Mass/volume/size | -   Needs to | 3  |
| Air       |   Principle |     of major/minor   |     be       | or |
| Thermal   |     concept |     components not   |              | 4  |
| C         |     is      |     known            |   determined |    |
| onvection |     proven  |                      |              |    |
|           |             | -   May produce      | -   May be   |    |
| B. Forced | -   Minimal |     volatile         |              |    |
| Air       |             |     contaminants     |   restricted |    |
| Drying    |  complexity |                      |     to batch |    |
|           |             | -   Not proven in    |              |    |
| C.        | -           |     this application |    operation |    |
| Thermal   |   Scaleable |     (needs           |              |    |
| Vacuum    |             |     validation in    | -   Material |    |
| Drying    |             |     relevant         |     probably |    |
|           |             |     environment,     |     will     |    |
| D. Freeze |             |     micro- and       |     need to  |    |
| Vacuum    |             |     hypogravity)     |     be fixed |    |
| Drying    |             |                      |     in       |    |
|           |             |                      |     position |    |
+-----------+-------------+----------------------+--------------+----+
| E.        | -           | -   Mass/volume/size | -   Needs to | 2  |
| So        |   Principle |     of major/minor   |     be       | or |
| lid/Solid |     concept |     components not   |              | 3  |
| Blender   |     is      |     known            |   determined |    |
|           |     proven  |                      |              |    |
|           |             | -   Not proven in    | -   May need |    |
|           | -           |     this application |     to test  |    |
|           | Flexibility |     (needs           |     concept  |    |
|           |     of      |     validation in    |     in       |    |
|           |             |     relevant         |     relevant |    |
|           |   operation |     environment,     |              |    |
|           |             |     micro- and       |  environment |    |
|           |   (throttle |     hypogravity)     |              |    |
|           |             |                      |              |    |
|           |    process) | -   May produce dust |              |    |
|           |             |     with dry feeds   |              |    |
|           | -           |                      |              |    |
|           |   Scaleable |                      |              |    |
|           |             |                      |              |    |
|           | -           |                      |              |    |
|           |    Handling |                      |              |    |
|           |     of wide |                      |              |    |
|           |     variety |                      |              |    |
|           |     of      |                      |              |    |
|           |     wastes  |                      |              |    |
|           |             |                      |              |    |
|           | -   Less    |                      |              |    |
|           |     energy  |                      |              |    |
+-----------+-------------+----------------------+--------------+----+
| F.        | -           | -   Mass/volume/size | -   Needs to | 2  |
| Sol       |   Principle |     of major/minor   |     be       | or |
| id/Liquid |     concept |     components not   |              | 3  |
| Blender   |     is      |     known            |   determined |    |
|           |     proven  |                      |              |    |
|           |             | -   Not proven in    |              |    |
|           | -           |     this application |              |    |
|           | Flexibility |     (needs           |              |    |
|           |     of      |     validation in    |              |    |
|           |             |     relevant         |              |    |
|           |   operation |     environment,     |              |    |
|           |             |     micro- and       |              |    |
|           |   (throttle |     hypogravity)     |              |    |
|           |             |                      |              |    |
|           |    process) |                      |              |    |
|           |             |                      |              |    |
|           | -           |                      |              |    |
|           |   Scaleable |                      |              |    |
|           |             |                      |              |    |
|           | -           |                      |              |    |
|           |    Handling |                      |              |    |
|           |     of wide |                      |              |    |
|           |     variety |                      |              |    |
|           |     of      |                      |              |    |
|           |     wastes  |                      |              |    |
+-----------+-------------+----------------------+--------------+----+

\*See Volume II (Appendix) for definitions of TRLs.

**[Technical Tasks to Achieve TRL 5 for Solid/Liquid
Mixers]{.underline}**

1.  Evaluate and select best mixing concept for micro- and hypogravity

2.  Select major/minor components

3.  Size and design system

4.  Build breadboard system

5.  Performance test (validation in relevant environment) and make
    modifications as required

**Development Time:** 2 years

**Cost to Achieve TRL 5:** \$150,000 to \$200,000

#### 4.1.3.d Transport, Conveyance and Separation Technologies

Table 4. Summary of Analysis of the Selected Transport, Conveyance, and
Separation Technologies

+-------------+----------------+----------------+------------+-------+
| **T         | **Advantages** | **D            | **Gravity  | **Cu  |
| echnology** |                | isadvantages** | Issues**   | rrent |
|             |                |                |            | TR    |
|             |                |                |            | L\*** |
+-------------+----------------+----------------+------------+-------+
| Vacuum      | -   Handles    | -   Requires a | -   Ma     | 4     |
| transfer    |     wide range |     "receiver  | terial/gas |       |
|             |     size and   |     tank"      |            |       |
|             |     moisture   |     (pumped    | separation |       |
|             |     content    |     down)      |     in     |       |
|             |                |                |            |       |
|             | -   Good for   | -   Sewage     |   receiver |       |
|             |                |     becomes    |     tank   |       |
|             |   intermittent |     anaerobic  |            |       |
|             |     operation  |     in tank if |            |       |
|             |                |     left in    |            |       |
|             |                |     tank for   |            |       |
|             |                |     any length |            |       |
|             |                |     of time    |            |       |
|             |                |                |            |       |
|             |                | -   Needs      |            |       |
|             |                |     validation |            |       |
|             |                |     in         |            |       |
|             |                |     relevant   |            |       |
|             |                |                |            |       |
|             |                |    environment |            |       |
+-------------+----------------+----------------+------------+-------+
| Slurry pump | -   Simple,    | -   Separation | -          | 4     |
|             |     commercial |     and        |   Requires |       |
|             |     technology |     settling   |            |       |
|             |                |     in         |   positive |       |
|             |                |     transfer   |     feed   |       |
|             |                |     line       |            |       |
|             |                |                |            |       |
|             |                | -   Large      |            |       |
|             |                |     hold-up    |            |       |
|             |                |     volume     |            |       |
|             |                |                |            |       |
|             |                | -   Need for   |            |       |
|             |                |     flush or   |            |       |
|             |                |     recycle    |            |       |
|             |                |                |            |       |
|             |                | -   Needs      |            |       |
|             |                |     validation |            |       |
|             |                |     in         |            |       |
|             |                |     relevant   |            |       |
|             |                |                |            |       |
|             |                |    environment |            |       |
+-------------+----------------+----------------+------------+-------+
| Dry         | -   Simple,    | -   Potential  | -          | 4     |
| pneumatic   |     commercial |     static     |  Gas/solid |       |
|             |     technology |     charge and |            |       |
|             |                |     dust       | separation |       |
|             | -   Good for   |     reactions  |            |       |
|             |                |                |   (cyclone |       |
|             |   intermittent | -   Potential  |     on     |       |
|             |     operation  |     for clogs  |            |       |
|             |                |                |  receiver) |       |
|             |                | -   Requires   |            |       |
|             |                |     separator  |            |       |
|             |                |     and filter |            |       |
|             |                |                |            |       |
|             |                | -   Needs      |            |       |
|             |                |     validation |            |       |
|             |                |     in         |            |       |
|             |                |     relevant   |            |       |
|             |                |                |            |       |
|             |                |    environment |            |       |
+-------------+----------------+----------------+------------+-------+
| Screw       | -   Simple,    | -   Potential  | -          | 4     |
| conveyor    |     commercial |     for jams   |   Requires |       |
|             |     technology |                |            |       |
|             |                | -   Large      |   positive |       |
|             |                |     hold-up    |     feed   |       |
|             |                |     volume     |            |       |
|             |                |                |            |       |
|             |                | -   Needs      |            |       |
|             |                |     validation |            |       |
|             |                |     in         |            |       |
|             |                |     relevant   |            |       |
|             |                |                |            |       |
|             |                |    environment |            |       |
+-------------+----------------+----------------+------------+-------+

\*See the Volume II (Appendix) for definitions of TRLs.

Technical Tasks to Achieve TRL 5 for Vacuum Transfer

1.  Build unit of required scale

2.  Operate with representative waste stream (validation in relevant
    environment)

**Development time:**

Specify, procure, and fabricate 5 months

Set up 1 month

Test 6 months

Cost to Achieve TRL 5: \$150,000

Technical Tasks to Achieve TRL 5 for Dry Pneumatic Transfer

1.  Build unit of required scale

2.  Operate with representative waste stream (validation in relevant
    environment)

**Development time:**

Specify, procure, and fabricate 5 months

Set up 1 month

Test 6 months

**Cost to Achieve TRL 5:** \$150,000

**4.1.3.e Particle Size Reduction and Control Technologies**

Table 5. Summary of Analysis of the Selected Particle Size Reduction and
Control Technologies

+-------------+----------------+--------------+--------------+-------+
| ########    | **Advantages** | **Dis        | **Gravity    | **Cu  |
|  Technology |                | advantages** | Issues**     | rrent |
|             |                |              |              | TRL** |
+-------------+----------------+--------------+--------------+-------+
| Dry         | -   Much       | -   Product  | -   Sizing   | 3     |
| particle    |                |     size     |     process  |       |
| size        |    terrestrial |     limited  |     is       |       |
| reduction   |     experience |     to 0.1   |     gravity  |       |
| and control |                |     cm       |              |       |
|             | -   Short time |              |    dependent |       |
|             |     constant   | -   Dust and |              |       |
|             |                |     noise    | -   Unknown  |       |
|             | -   Throughput |              |     effect   |       |
|             |                |   generation |     of       |       |
|             |    flexibility |              |     gravity  |       |
|             |                | -            |     on size  |       |
|             | -   Low energy |   Validation |              |       |
|             |                |     in       |    reduction |       |
|             |    requirement |     relevant |     process  |       |
|             |                |              |              |       |
|             |                |  environment |              |       |
+-------------+----------------+--------------+--------------+-------+
| Wet         | -   Can        | -   High     | -   C        | 3     |
| particle    |     produce    |     water    | ompatibility |       |
| size        |     product    |              |     with     |       |
| particle    |     sizes less |  requirement |              |       |
| reduction   |     than 0.1   |              | microgravity |       |
| and control |     cm         | -   U        |              |       |
|             |                | npredictable |              |       |
|             | -   Compatible |              |              |       |
|             |     with       |   liquid/gas |              |       |
|             |                |     problems |              |       |
|             |   slurry-based |     in       |              |       |
|             |     back-end   |              |              |       |
|             |     systems    | microgravity |              |       |
|             |                |              |              |       |
|             |                | -   Energy   |              |       |
|             |                |              |              |       |
|             |                |    intensive |              |       |
|             |                |              |              |       |
|             |                | -            |              |       |
|             |                |  Reliability |              |       |
|             |                |              |              |       |
|             |                | -            |              |       |
|             |                |   Validation |              |       |
|             |                |     in       |              |       |
|             |                |     relevant |              |       |
|             |                |              |              |       |
|             |                |  environment |              |       |
+-------------+----------------+--------------+--------------+-------+

Technical Tasks to Achieve TRL 5 for Dry Particle Size Reduction and
Control

1.  Select best particle size reduction technology for feed stream and
    particle size goal

2.  Review microgravity considerations

3.  Design and fabricate breadboard system

4.  Test under terrestrial conditions (validation in relevant
    environment)

5.  Optimize system

**Development Time:** 3 years

**Cost to Achieve TRL 5:** \$900,000

### 4.1.4 Summary

Conclusions of the PPP working group are as follows:

-   Many of the PPP technologies have potential applications for the
    different mission scenarios. The list of technologies in this
    document should be scrutinized further to encompass some PPP
    technologies that may not have been mentioned in this workshop.
    (References 3-7)

-   As per the requirements of the PC and Bio technologies discussed in
    this document it is imperative that the waste streams as envisioned
    should undergo pre-processing for size reduction and drying
    (moisture contents range from air dry to 80% water content for
    different technologies).

-   The successful application of any of the PPP technologies requires
    that they be integrated with the other processing unit operations;
    the integration requires material transport (i.e., conveyance)
    systems.

-   Four generic processing technologies were selected to meet the
    compatibility criterion, namely particle size reduction and control,
    mixing and drying, transport/conveyance, and phase separation.

The working group also identified the following issues and potential
problems associated with the selected PPP technologies and their
application in space:

-   Waste quantities and characteristics: The successful design and
    operation of pre-processing technologies are strongly dependent upon
    the rate of processing and the characteristics of the waste. Thus,
    the analysis of the solid waste generated by space missions and
    mission simulations should be ongoing. The methods and procedures of
    the waste sampling and laboratory analysis program should
    specifically be designed such that the results of the analysis are
    relevant to pre-processing technologies.

-   Effect of waste generation rates: The waste generation rates during
    crewed flight missions and planetary surface stays are estimated to
    be low in the early years of exploration. This important fact must
    be considered when designing PPP systems, including the advantages
    and disadvantages of batch and continuous processing of waste. The
    low waste generation rates (and, therefore, average processing
    rates) may limit some technological options for pre- and
    post-processing.

-   The effect of micro- and hypogravity: The results of the analysis
    among all of the selected PPP technologies indicate that the effect
    of micro- and hypogravity on the technologies is difficult to
    determine with any degree of certainty without actual testing of the
    technologies in the appropriate gravitational environment. It is
    recommended that all of the technologies be analyzed for
    gravitational dependency, the functional relationship of the
    dependency, and whether or not any control systems, methods of
    engineering, or both can be designed to facilitate the abilities of
    the technologies to operate successfully in micro- and hypogravity
    environments. The following are some of the issues identified by the
    workshop team for the transport/conveyance and mixing/drying
    technologies: 1) forced-air convection drying may require fixing the
    waste materials in place; 2) a slurry pump and a screw conveyor may
    require the provision for a positive feed (i.e., a mechanical means
    for introducing wastes into the conveyor or pump); and 3) a vacuum
    transfer technology may require a means of separating the gas from
    the solid waste in the receiver tank.

-   Maximum particle size requirements of the PC and Bio conversion
    systems: The currently available, terrestrial, solid waste size
    reduction technologies likely cannot meet the more stringent
    particle size requirements of some of the primary processing
    systems. Some primary processing systems require a particle size of
    10 microns or less and it is doubtful that conventional size
    reduction equipment can meet this fine particle size requirement in
    a feasible manner without technological improvements.

-   Engineering and operational problems: Historically, the transport
    (conveyance) of raw and processed solid waste in terrestrial solid
    waste processing systems has generated substantial problems,
    including, for example, jamming of screw feeders, pneumatic
    pipelines, and hydraulic piping. This circumstance must be
    considered prominently in the design and testing of PPP technologies
    for application in space.

Based on the results of the analysis, the following three technologies
are recommended for further study based on perceived need for crewed
space missions.

High Priority:

1\. Transport and Conveyance

Detailed study of candidate transport and conveyance technologies is
required because they are a necessary and integral part of any type of
solid waste processing system. Most of the systems for transport and
conveyance of solid waste on earth depend explicitly or implicitly on
the earth's gravity and a transporting medium, e.g., conveyor belt or
fluid (such as air or water). The lack of the equivalent of Earth's
gravity and of working fluids for the near-term space missions (or,
conversely, the provision of the resources to meet the requirements of
the systems) must be taken into consideration when selecting transport
and conveyance systems. Thus, a recommendation is made that an analysis
be conducted of the gravitational and fluidic dependence of the various
transport and conveyance systems (listed in Table 3) and of the
preliminary feasibility of the various systems. These analyses can be
performed using theoretical or semi-empirical methods since the
scientific and engineering bases of these transport/conveyance systems
are well known. The successful design and operation of solid waste
transport/conveyance systems on Earth also are critically dependent on
the rate of processing and on the composition and other properties of
the waste. Thus, the analysis recommended above must also present the
findings in terms of the throughputs and characteristics of processed
solid waste that are expected from space missions. In terms of priority,
the analyses should be conducted simultaneously for belt, pneumatic, and
screw conveyors. If the results of the preliminary feasibility study of
potential gravitational limitations and resource supply are positive,
then the design and bench-scale testing of these three technologies is
indicated and should be the subject of a dedicated research and
development program.

2\. Particle Size Reduction and Control

There are a variety of particle size reduction processes, each with its
own set of governing physical principles. Many of the commercially
available, terrestrial technologies are dependent to one degree or
another on Earth's gravity. In terrestrial waste processing systems,
particle size reduction equipment is bulky, has a large mass, and has a
high specific energy and wear requirement. Basic research and
development in size reduction is recommended because: 1) the need for
some degree of size reduction of the input feedstock was common among
all of the PC and Bio conversion systems identified in the workshop; 2)
the large number of variables that affect the design, operation, and
performance of size reduction equipment make judgments of equipment
feasibility extremely risky without the benefit of experimental testing;
and 3) the supporting resource requirements may be substantial. Both wet
(e.g., pulping processes) and dry size reduction processes should be the
subjects of detailed study. To the extent that size reduction equipment
cannot meet the requirements for certain particle size distributions,
research and development is warranted for analysis of screening
(particle size separation) equipment. Screening technologies are subject
to many of the same governing parameters and conditions that have been
described above in the subsection, Transport and Conveyance. Based on
prevalence and performance in terrestrial waste processing, the research
and development priorities for particle size control technologies should
be: flat-bed vibratory, trommel (rotating cylindrical screen), and disc
screens. Screening technologies other than those mentioned in the
preceding sentence (e.g., cyclone separators) may also be warranted for
certain applications.

Moderate Priority:

3\. Mixing and Drying

Mixing and drying are given a lower priority than the two preceding
technology groupings. The reasons for the lower ranking are that mixing
and drying technologies are well developed on Earth, and the
technologies are considered transferable to space missions without
requiring substantial modifications. Mixing systems may be required in
space missions to homogenize materials of different compositions. Based
on terrestrial experience in solid waste processing, mechanical mixers
(e.g., with rotating elements) are the most prevalent mixing technology
and would be a candidate for application in space missions. The mixing
process is highly dependent on the characteristics of the materials to
be mixed. Thus, research in mixing would be particularly warranted if
the materials have proven to be difficult to mix on Earth (examples of
such feedstocks would include stringy materials), or would be difficult
to mix in micro- or hypogravity environments. Both wet and dry mixing
technologies should be investigated.

Drying systems generally have not been used in terrestrial waste
processing systems because of the energy cost and because the processed
feedstocks generally have an inherently acceptable moisture content.
Drying was an important aspect of some early, but limited in number,
fuel preparation systems that produced a densified refuse-derived fuel
(dRDF). The typical system used convective drying. Research and
development in the areas of convective or vacuum drying of organic
wastes may be warranted by NASA if a dry feedstock would be required for
primary processing systems. For example, an incineration system would
provide better performance with a dry feedstock.

### 

### 4.1.5 Conclusion

> Regardless of the PPP technologies that are selected for further
> study, each must be subjected to testing under conditions relevant to
> space missions. This testing would normally occur after the
> technologies have been identified and their preliminary feasibility
> determined. The relevant operating conditions should include the
> appropriate gravitational force and the use of solid wastes
> characteristic of those generated in space missions.

## 4.2 Biological Technologies

### 4.2.1 Introduction

#### 4.2.1.a Background

Biological treatment is a very common approach to handling waste in
Earth systems. Waste (i.e., unused materials), such as residues from
plant and animal systems, biodegrades and recycles nutrients for the
next generation of organisms. Large-scale systems process biosolids
(sludge) using anaerobic/aerobic digesters (liquid), or more recently,
large composting systems (solid). They also process other residue
streams such as yard and food wastes. Removal of non-biodegradable
materials from the waste stream will increase system performance while
producing a product that is useable with positive impacts. This is born
out by experiences in Europe in the 1980s and North America in the
1990s.

Biological treatment systems can be constructed using organisms at all
size levels and complexities. {An example is a food residue processing
system using large animals and microorganisms, i.e., swine eating food
residue and microorganisms processing swine manure.} However, those
using microorganisms are the simplest systems in terms of components and
process control requirements. These systems handle highly variable
biodegradable waste streams and often require minimal preprocessing.
Considerations of set points for temperature, moisture content, oxygen,
volatile solids, carbon, nitrogen, pH and particle size are the major
controllable factors. Output products to be considered are organic
residue, biomass, water (liquid and gas), heat, and gases of CO~2~,
CH~4~, volatile organic compounds (VOCs), NO~x~ and NH~3~, to name the
most common.

#### 4.2.1.b Determination of Waste Stream Constituents Suitable for Biological Processing

Not all components of the given waste model are biodegradable. Given the
current state of materials technology, it was assumed that plastics of
all types and tape are non-biodegradable and therefore excluded from the
biological processing system waste stream. It is recommended that
further efforts be conducted with regard to the development and/or
testing of biodegradable packaging and other consumables (e.g., air
filters) where appropriate.

Although it is possible to treat urine and/or urine solids using certain
biological solid waste processing technologies, the working group
concluded that urine/urine solids would best be treated by other systems
(gray-water processing) and are therefore not included in the solid
waste stream. A primary reason involves the high concentration of salts
in the process residue if urine was added, which can severely hinder
further utilization and resource recovery (i.e., extraction for plant
nutrients). Additionally, the high nitrogen loading imposed by the
addition of urine will promote microbial ammonification with a
consequent increase in pH and ammonia volatilization. This will result
in nitrogen loss from the system, and ammonia volatilization could
impose substantial demands on downstream trace air contaminant control
systems.

Biological systems universally require water for growth, metabolism,
solute transport, and other functions. Each biological waste processing
technology requires specific moisture conditions, ranging from the lower
moisture contents of 50-70% for solid-phase systems such as composting,
to upper levels of \~98% for aqueous systems. Because of these
constraints, the moisture content of the waste stream components is
important, both in relation to the individual waste and to average of
the overall wastes. This is particularly true for systems that employ
low moisture such as composting, in that excessive moisture will impede
treatment. Materials that are high in moisture (e.g., certain inedible
plant biomass) may require some pre-drying or can be mixed with drier
materials (e.g., paper) to render suitable average moisture content.

Table 6 is a summary of the identified waste stream for NASA scenario 3,
a 6-member space mission crew. This stream consists of both
biodegradable and non-biodegradable constituents. The biodegradable flow
rate was 8.13 kg~db~/day or 29.18 kg~wb~/day (72.1% water content) and
the non-biodegradable flow rate was 2.42 kg~db~/day.

Table 6. Waste Stream for a 6-Person Space Mission (One Growth Chamber)

+----------------+------------+------------+------------+------------+
| Waste          | Waste      | Biological | Biological | Other      |
| Component      | Stream^1^  | Tr         | Tr         | Tr         |
|                |            | eatment^1^ | eatment^2^ | eatment^1^ |
|                | (k         |            |            |            |
|                | g~db~/day) | kg~db~/day | (k         | kg~db~/day |
|                |            |            | g~wb~/day) |            |
+----------------+------------+------------+------------+------------+
| Daily Feces    | 0.180      | 0.180      | 1.200      | 0          |
|                |            |            |            |            |
| Urine          | 0.360      | 0          | 1.200      | 0.360      |
|                |            |            |            |            |
| Shower/Hand    | 0.060      | 0.060      | 2.400      | 0          |
| wash           |            |            |            |            |
|                | 0.120      | 0.120      | 21.800     | 0          |
| Sweat          |            |            |            |            |
|                | 5.450      | 5.450      | 0.618      | 0          |
| Inedible Plant |            |            |            |            |
| Biomass        | 0.556      | 0.556      | 0.667      | 0          |
|                |            |            |            |            |
| Trash          | 2.017      | 0.600      | 1.164      | 1.417      |
|                |            |            |            |            |
| Packaging      | 1.164      | 1.164      | 1.293      | 0          |
| Material       |            |            |            |            |
|                | 0.246      |            |            | 0.246      |
| Paper          |            |            |            |            |
|                | 0.326      |            |            | 0.326      |
| Tape           |            |            |            |            |
|                | 0.069      |            |            | 0.069      |
| Filters        |            |            |            |            |
|                |            |            |            |            |
| Miscellaneous  |            |            |            |            |
| (Teflon, PVC)  |            |            |            |            |
+----------------+------------+------------+------------+------------+
| Total          | 10.548     | 8.130      | 29.178     | 2.418      |
+----------------+------------+------------+------------+------------+

^1^ = dry matter basis ^2^ = wet basis

Table 7. Estimated Chemical Composition and Density for Waste Stream for
a 6-Person Space Mission

  -------------------- --------- ------ ------ ------------- ---------- ---------
  ITEM                 Ash%      C%     N%     C/N           Moisture   Density

                                               (available)   \% w.b.    kg/m^3^

  Feces                0.43      42     8      5.1           85         949

  Urine                0.56      18     22     0.8           0          1009

  Shower/.../Sweat     0.50      25     4      6.3           95         1009

  Inedible Plant       0.15      34     4      9.0           75         300
  Biomass (1)                                                           

  Trash                0.02      45     1      90.0          10         148

  Packaging Material   0.05      44     4      11.0          10         148
  (2)                                                                   

  Paper                0.02      45     1      90.0          10         148

  Tape                           0      0      0.0           0          148

  Filters                        0      0      0.0           0          148

  Miscellaneous                  0      0      0.0           0          148

  Recycled compost               26     2      13.0          49         550

  Composite mixture              37     3      11.6          72         308
  -------------------- --------- ------ ------ ------------- ---------- ---------

#### 4.2.1.c Safety Considerations 

Biological waste treatment systems are typically operated at
near-ambient temperatures, pressures, and pH, and therefore pose little
threat due to explosions, fires, or acute corrosivity. Areas of
potential safety concern include by-product formation and pathogenic or
undesired microbial growth. Anaerobic biological waste treatment systems
by design produce significant amounts of methane, while aerobic systems
produce methane only if aeration is not uniform. While methane can
potentially be separated and utilized as a fuel, it simultaneously poses
an explosive risk. Other potentially harmful gaseous by-products include
various volatile organic and inorganic compounds. These will require
treatment to avoid accumulation in the cabin atmosphere.

Any waste treatment system utilized will need to provide reliable human
(and possibly plant) pathogen control. Biological systems typically do
not sanitize the waste stream and will require post-treatment pathogen
destruction, preferably in conjunction with the waste-processing unit.
An exception is composting: the inherent microbial self-heating can be
controlled to elevate matrix temperatures to levels that effectively
destroy both human and plant pathogens. Pathogen dissemination can also
occur through the production of airborne bio-aerosols, which may require
capture and treatment prior to release to cabin atmosphere. This is true
of most, if not all, biological solid, liquid, and gaseous treatment
systems.

#### 4.2.1.d Pre-Processing Requirements

Each biological technology exerts variable pre-processing demands.
Composting systems will require little to no drying, with minimal
particle size reduction requirements (1-5cm). The aqueous systems will
require nearly complete drying of the material to allow the size
reduction required to obtain optimal system performance (0.5 cm).
Complex pre-treatment may be required in the case of bio-conversion
technologies such as paper-making, including size reduction, heating, or
chemical addition.

#### 4.2.1.e Batch vs. Continuous Systems

Biological systems can be designed to operate in either batch or
continuous mode. The batch mode will likely require greater system
volume and mass than continuous systems, as matrix volume reduction
during processing will create unused space within the reactor. In
contrast, continuous systems will likely exert greater mechanical
requirements, due to increased material translocation and mixing
requirements. Process control/stability may also be a significant factor
in whether a batch or continuous process is more desirable.

Another factor that strongly influences whether batch or continuous
systems should be employed involves the immediate waste loading
requirements. For instance, harvesting and/or processing a large crop
will create a large plug of inedible biomass waste. This waste must
either be stored and fed incrementally to a continuous system, or
alternatively fed to properly sized batch reactors. Additionally, the
impact of batch reactors must be assessed with regard to demands exerted
on air revitalization systems and other mass buffering systems; e.g.,
biological batch processing will transiently require high amounts of
oxygen supply and carbon dioxide removal.

### 4.2.2 Candidate Biological Solid Waste Treatment Technologies

The potential biological waste treatment technologies examined during
this workshop included:

Aerobic Composting

Anaerobic Composting

Continuously Stirred Tank Reactor

Fixed Film Bioreactor

Conversion Technologies (production of single cell protein, ethanol,
blotter paper)

Each system possesses specific criteria for operation. The following are
brief descriptions of each technology. Detailed analyses are presented
in Volume II (Appendix).

#### 4.2.2.a Composting

Composting is the accelerated biological decomposition process of
organic materials in a predominantly aerobic environment. The process is
carried out in a solid matrix (moisture generally \< 75%) as opposed to
a water-based system (moisture generally \> 90%). During the process,
bacteria, fungi and other microorganisms (including microarthropods)
break down organic materials to stable, usable organic substances called
composts. The process consumes oxygen and releases heat, water, and
CO~2~ (8). The compost that remains resembles humus and may be used as a
soil conditioner, organic fertilizer or as a food base for
microorganisms for disease control. Composting reduces the volume of the
parent materials and many pathogens are destroyed if the process is
controlled properly (T~compost~ \> 55^o^C for \>3 days). Efficient
composting requires the control of many factors to avoid nuisance
problems such as odors and dust.

Under controlled conditions, composting is accomplished in two main
phases: a composting phase and a curing phase (9). The typical batch
composting phase involves three subphases: 1) an initial phase, when
mesophilic microorganisms degrade constituents such as sugars, starch,
proteins, etc., and compost temperature rises rapidly; 2) a high-rate
thermophilic phase, in which temperatures rise above 40^o^C and fats,
hemicellulose, cellulose and some lignins are degraded (also pathogens
are destroyed at this time); and 3) a stabilization phase during which
the temperature declines and further degradation of cellulose,
hemicellulose and lignins occurs. The high rate phase is accompanied by
high rates of O~2~ uptake, CO~2~ and biological heat production.
Excessive production of NH~3~ and other gases (VOCs) may occur if the
process is not effectively controlled. During the curing phase,
mesophilic organisms recolonize the compost.

The ideal water content of the compost during the curing phase is 45-50%
wet weight basis. The length of field operation curing time typically
represents a minimum of 1 month and generally lasts 3 to 6 months (9).
The length of time for any one phase of composting or curing is affected
by the composition of the parent materials, processes temperature,
oxygen levels, C/N ratio, particle size, turning frequency, and many
other factors (see Appendix Accession Number B-05, Sequential Batch
Anaerobic Composting). During the curing stage, specific microorganisms
that control plant diseases can be inoculated into the compost to
produce "designer" composts (10). Commercial-scale inoculation of
composts with beneficial microflora is beginning to take place. Numerous
articles and books that review factors affecting composting (11, 12, 13,
14, 15, 16, 17, 18, and 19).

A process termed anaerobic composting is somewhat similar to (aerobic)
composting with the major difference being operation in the absence of
oxygen. Operating conditions include moisture contents of 65-75%,
temperatures of 45-50^o^C, and microbial production of substantial
amounts of methane gas.

**Aerobic Composting - ALS Systems**

Figure 1 illustrates material and gas flow in a top-fed, plug-flow
composting system designed for solid waste treatment in ALS systems. For
this process, wastes are shredded and blended with limited recycled
compost to achieve acceptable ranges for particle size, initial C/N, and
moisture before the mix is charged to the reactor. The matrix is
agitated at a frequency determined by the operational requirements of
the system. In this design, air is forced through the compost to control
temperature and keep the pile supplied with oxygen. Additionally, air is
recycled through the system to maximize decomposition rates by
minimizing temperature gradients in the system. Water in the recycled
air stream is condensed, constituting a major output from the system.
Process gas recirculation significantly decreases the demand for fresh
air and can decrease overall emission both in respect to total gas as
well as trace contaminants. This stage is anticipated to run 21 days and
yield a 50% mass and volume reduction. At termination of treatment
(little or no heat output is observed), the material is moved to a
second reactor, which serves as a biofilter for treatment of process air
(remove VOCs, NH~3~) and allows the compost to recolonize with
mesophilic microorganisms (curing stage). This stage may allow microbial
nitrification in order to transform NH~3~/NH~4~^+^. The length and
necessity of curing operations will be based upon the final
utilization/disposition of the process residue. At the completion of
this cycle, this strategy proposes that the compost be used within the
biomass production unit as a plant growth medium. Other composting
treatment strategies exist, including treating the waste only to the
point that effective nutrient extraction and subsequent utilization of
the extract for plant growth is allowed (initial prediction \~7 days).
While this significantly decreases treatment time and reactor size/mass
requirements, further extraction operations will be necessary.
Regardless of the strategy utilized, both human and plant pathogens will
be effectively destroyed, as the process is carried out at 55-60^o^C
over an extended period (12).

![](media/image3.wmf){width="6.379861111111111in"
height="4.154861111111111in"}

**Figure 1. Aerobic Composting - ALS Systems**

**Advantages Identified for Aerobic Composting:**

-   Well-established operational theory and experience

-   Operate in batch or continuous operation

-   Minimal pre-processing requirements

-   Near ambient temperature and pressure conditions

-   Minimal mass/water requirements

-   Resistant to loading and control perturbations

-   Low power requirements

-   Very effective human and plant pathogen destruction

-   Can transform NH~3~ to NO~3~ (preferred plant N form)

-   Effective integrations: Compost can be utilized for plant nutrient
    recovery, growth medium, and biofilter material

Disadvantages:

-   Significant residue production (\~50%)

-   Large reactor volume requirements -- retention time dependent

-   Exhaust can contain VOCs, NH~3~, NO~x~, CH~4~

-   Requires hardware development for material translocation

Microgravity Considerations for Aerobic Composting:

Composting is seen as having limited application in a microgravity
environment unless specialized equipment is developed to move material.
Also, such an operation would most likely require specialized air-water
separation equipment.

Technical Readiness Level of Aerobic Composting:

The current level of development is a TRL of 4. To complete development
to a TRL 5 would cost \$500,000 and take 2-3 years.

Research and Development Steps Needed to Fully Develop Aerobic
Composting Technology:

-   Develop and test individual system components

-   Integrate composting and biofilter components

-   Optimize completed system with appropriate feedstock

-   Pathogen, perturbation, and product studies

######### **Anaerobic Composting-Sequential Batch Anaerobic Composting**

The high-solids sequential batch anaerobic composting process
(SEBAC^TM^)\* is a treatment method for conversion of wastes into
methane, carbon dioxide, and compost (Figure 2). The process involves
maceration and three stages of digestion, which occur sequentially as
conversion proceeds. Wastes are macerated by adding enough liquid waste
and recycled water to make the water content \>65% and passing the mix
through a high-solids macerator pump. Once in the digester, the waste is
not moved but goes through the various stages of treatment in the same
reactor; that is, there are four 0.8 m^3^ reactors and different stages
of treatment at all times. The shredded waste (7 days inventory) is
placed into the new reactor. Recirculation of leachate between reactors
at the new and final stages inoculates and adds inorganic matter needed
for startup. Volatile acids formed during startup are conveyed from the
new to the final reactor for conversion. After startup (7 days) the
reactor is mature and leachate is recycled upon itself to keep the
system moist. For the third stage the final stage is recycled with a new
stage for startup. If well insulated, this three-reactor system will
operate at 50^o^C and affect 60-90% (depends on quality of paper used)
conversion of the volatile solids. Note that this system is on a
seven-day cycle, i.e., it is fed every 7 days. The waste is collected
for 7 days; the digester residence time is 21 days.

After anaerobic digestion is complete (21 days), the remaining solids
are aerated with ambient air for 3 (1-7) days to remove lingering
reduced compounds and dewatered to 50%. The compost will act as a
biofilter to purify the air. The effluent air must be filtered to remove
particles, chemicals and microorganisms. The solids will be used for
compost and the wastewater will be used for required process recycling
and plant growth. The biogas is collected

\* Does not imply NASA endorsement.

and stored under pressure. It can be used directly as an energy source;
some cleanup may be necessary to remove hydrogen sulfide, if present.

**Figure 2. High-Solids Sequential Batch Anaerobic Composting Process
(SEBAC^TM^)**

**Advantages Identified for Anaerobic Composting:**

-   Dry biodegradable feeds without pretreatment

-   Produces methane and compost and conserves nutrients

-   Does not require oxygen

-   Low energy requirements

-   Operates at low temperatures and pressures

-   Produces minimal microbial biomass

-   Sanitizes wastes

-   Simple design and operation

-   Proven technology

Disadvantages:

-   Limited to feed batch operation with design modification

-   Long residence time (large reactor)

-   Conversion is limited (50-90%; depends on feedstock)

-   Effluent solids may require storage or further treatment if not used
    as compost

Microgravity Considerations for Anaerobic Composting:

High-solids sequential batch anaerobic composting process (SEBAC^TM^) is
seen as having limited application in a microgravity environment unless
specialized liquid recycle and gas collection equipment are developed.

Technical Readiness Level of Anaerobic Composting:

The current level of development is a TRL of 4. To complete development
to a TRL 5 would cost \$500,000 and take 2-3 years.

**Research and Development Steps Needed to Fully Develop Anaerobic
Composting Technology:**

-   Design and operation for microgravity

-   Test proposed feeds

-   Test uses of effluent for plant growth and air purification

-   Analysis of biogas for micro contaminants

#### 4.2.2.b Continuous Stirred Tank Reactor (CSTR)

Biological processing of ALS solid wastes in a continuous stirred tank
reactor (CSTR) utilizes a suspension of aerobic, heterotrophic
microorganisms (bacteria, fungi, and microfauna\--protists such as
ciliates, amoebae, and flagellates, rotifers, nematodes, etc.) to
degrade soluble and/or particulate organic materials. This process is
most similar to a typical activated sludge process commonly used
worldwide to bioprocess dilute solutions of human fecal wastes. It has
also be termed suspended growth culture, to differentiate it from
fixed-film bioreactors and from 'solid-state fermentation' such as
composting. For ALS solid waste applications, the CSTR-suspension
culture process has been adapted to receive oven- or freeze-dried,
milled (\> 2 mm dia.) crop residues -- leaves, stems, roots, etc. --
with typically higher solids loading rates than used for conventional
activated sludge sewage treatment systems on Earth. Substrate addition
to a CSTR is usually continuous, so maintenance of microbial metabolic
activities is relatively constant with time. Compared to composting,
this process can operate at vastly accelerated hydraulic retention times
(HRT). Soluble organic compounds/monosaccharides and some oligo- and
polysaccharides can be completely biodegraded within 3 to 6 hours CSTR
retention time. Other polysaccharides, cellulose and hemicelluloses, can
be approximately 50% biodegraded within a hydraulic retention time of 8
to 10 days. Very long retention times of 24 to 48 days will give 60 to
80% bioconversion of these polymers to CO~2~ and H~2~O. The stabilized
particulate end product, sludge, consists of microbial cells,
extracellular microbial matrix material, and undegraded crop residues
and human waste solids. These solids resemble humus and could be used as
a soil conditioner or as an input to a composter or combustion
apparatus. At longer HRT, a curing stage is probably not needed for use
of bioprocessed solids as a soil conditioner.

Integration of CSTR bioprocessing of ALS solid wastes has been well
demonstrated. Crop residues from ALS crop growth chambers have been fed
into CSTR suspension culture bioreactors. Crop growth chamber condensate
water has been used for the water source in these bioreactors. Most
important, CSTRs have successfully been used to recycle inorganic
nutrients from the crop residues back to hydroponic crop production
systems. Over a wide range of hydraulic retention times (1 to 48 days),
upwards of 80% of the inorganic nutrient mass contained in crop residues
can be recovered in CSTR bioreactor effluent. These effluents have been
used successfully at both laboratory (3 month studies) and breadboard
(418 days) scales to replenish at least 50% of nutrients for crop
hydroponic solutions in a number of integrated studies with crop
production (*Garland et a. 1993 (20); Mackowiack et al 1996 (21); and
Mackowiack et al. 1997 (22)*). Bioreactor oxygen has been supplied by
O~2~ generated in ALS plant growth chambers. CSTR biologically generated
CO~2~ in the offgas has been recycled back to the plant growth chamber.
CSTR filter retentate solids have been tested as a feed source in
NASA-funded research on fluidized bed incinerators and other combustion
devices. CSTR bioreactor solids have been tested, on a limited basis, as
a solid seed germination support/matrix.

Aerobic microbial oxidation of biodegradable organics including soluble
and particulate components from crop residues, inedible biomass, paper
waste, trash, food remains, and human solid wastes (feces, urine solids,
shower/hand wash solids, and sweat) could be processed in a CSTR.
Soluble organics can be taken as primarily carbohydrates. Using this
assumption the balanced stoichiometric reaction (assuming no net
accumulation of microbial biomass is: CH~2~O + O~2~ CO~2~ + H~2~O.
Particulate organics can be taken as primarily carbohydrates (high
molecular weight polysaccharides, cellulose, hemicellulose). Using this
assumption the balanced stoichiometric reaction (assuming no net
accumulation of microbial biomass) is: C~12~H~10~O~5~ + 12 O~2~
12CO~2~ + 5 H~2~O.

The additional step involved in degradation of particulate organics
involves depolymerization, usually carried out through hydrolysis
reactions. The hydrolysis reactions are not oxidation/reduction
reactions so their stoichiometry is not important here. The difference
between the reactions for soluble and particulate organics can be
accounted for kinetically as demonstrated in the rate equations.
Additional reactions that are potentially favorable can occur in the
reactor. The extent and rate of these reactions depend on environmental
conditions (e.g., temperature, dissolved oxygen, pH) and operating
parameters (e.g., solids residence time, hydraulic residence time).
Microbial oxidation of ammonia by autotrophic nitrifiers can occur,
i.e., nitrification (ammonia is released from the degradation of
proteins, amino acids, and other nitrogen containing organic compounds):
NH~4~^+^ + 2 O~2~ NO~3~^-^ + H~2~O + 2 H+. The actual reaction is
carried out in two steps by different classes of nitrifiers. Both steps
are carried out with oxygen as the terminal electron acceptor (aerobic
reaction). Ammonia oxidizers oxidize ammonia to nitrite; nitrite
oxidizers oxidize nitrite to nitrate: NH~4~^+^ + 1.5 O~2~ NO~2~^-^ +
H~2~O + 2 H+, and NO~2~^-^ + 0.5 O~2~ NO~3~^-^. Microbial oxidation of
organic compounds with nitrate as the terminal electron acceptor can
also occur, i.e., heterotrophic denitrification: CH~2~O + 0.8 NO~3~^-^ +
0.8 H+ CO~2~ + 1.4 H~2~O + 0.4 N~2~. Potential undesirable side
reactions include the formation of NO and N~2~O as gaseous intermediates
in the formation of N~2~ during denitrification.

**Advantages Identified for Continuous Stirred Tank Reactors:**

-   Previously demonstrated in integrated ALS tests at various scales

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-   Easily controlled (e.g., change process parameters like temperature,
    hydraulic & solids retention times)

-   Recovers majority of plant nutrients in a form directly compatible
    with various plant production systems

-   Low power requirements

-   Near ambient operating conditions

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-   ![](media/image4.wmf){width="5.995833333333334in"
    height="4.913888888888889in"}Not limited by mode of operation, can
    function in either batch or continuous operational modes.

**Figure 3. Continuous Stirred Tank Reactor**

**Disadvantages:**

-   Incomplete carbon degradation

-   Large volume/mass (water) requirements

-   Solid/liquid separation issues at post-harvest

-   Some pretreatment (i.e., size reduction) necessary

-   Pathogen survival/exposure issues if human waste added

Microgravity Considerations for Continuous Stirred Tank Reactors:

Continuous stirred tank reactor is seen as having limited application in
a microgravity environment unless specialized two-phase separation
(liquid, gas) equipment is developed.

Technical Readiness Level of Continuous Stirred Tank Reactors:

The current level of development is a TRL of 3. To complete development
to a TRL 4 would cost \$300,000 and take 2-3 years.

Research and Development Steps Needed to Fully Develop Continuous
Stirred Tank Reactor Technology:

-   Integration with other ALS components has been well documented for
    crop residues Other solid wastes -- human feces, paper trash, etc.,
    in combination with crop residues, need to be tested and optimized

-   Current pre-processing and post-processing components are
    undesirable, thus need to develop and test better individual
    components for these steps

-   Develop automation (reduce crew interactions) of feeding, harvesting
    and post-processing

-   Pathogen, perturbation, and product studies

#### 4.2.2.c Fixed-film Bioreactor (FFB)

Fixed-film bioreactors (FFBs) are a mature technology with widespread
uses. The use of FFBs in space ALS has been proposed and studied.
AlliedSignal Corp., in conjunction with the Johnson Space Center, has
designed, built, and operated an immobilized cell graywater processor
*(Nacheff-Benedict et al. 1994 (23); and Edeen et al. 1995 (24). Miller
et al. 1991 (25)* showed that a packed bed, fixed film bioreactor,
operating at a 27-hour retention time, could remove up to 99.8% of
phenol in a 100 PPM phenol-laced waste stream. KSC has utilized FFBs for
the dual use of total organic carbon (TOC) reduction and nitrification
*(Strayer et al. (26)).* Steady-state TOC reduction and nitrification
rates of 80% and 98% respectively, were demonstrated during the
experiment. Effluent from the bioreactor was successfully used in a
concurrent plant growth experiment.

The major advantage of fixed-film designs is retention of high
concentrations of decomposer microbes in the attached biofilms. This
advantage would enable the reactor to have lower volume, mass, and
probably power requirements than CSTR. Disadvantages relate to
diffusion-limited transfer of dissolved oxygen into biofilms with a
resulting potential for denitrification, which is undesired in ALS
(*Stutte 1996 (27)).* Also, fixed film bioreactors are generally
designed to process soluble, or low particulate waste streams, thus
upstream particle/liquid separation would be needed. Because bacterial
or greater sized pathogens would be removed by the particle/liquid
separation step, operation of the fixed-film bioreactor will not have to
be concerned over exposure to these pathogens.

The input to a fixed film bioreactor would have to be soluble, since
particulate solids would clog the void volume between attachment media.
Thus, this bioreactor would have the limited function of rapidly
bioprocessing soluble biodegradable compounds from aqueous extraction
(i.e., leached) of crop residues and human solid wastes (generally,
carbohydrates \-- soluble monosaccharides and
polysaccharides/hemicelluloses). The reaction for generalized
carbohydrate would be CH~2~O + O~2~ CO~2~ + H~2~O (equation NOT
balanced). Significant side reactions would include denitrification, if
low oxygen conditions were allowed: NO~3~^-^ + CH~2~O N~2~ + H~2~O +
CO~2~ (equation NOT balanced), or NO~3~^-^ + CH~2~O NH~3~ + H~2~O +
CO~2~ is also possible (again, equation NOT balanced).

![](media/image5.wmf){width="5.9944444444444445in"
height="5.596527777777778in"}

**Figure 4. Biological Processing, Fixed-Film Bioreactor**

To integrate an FFB in an ALS, crop residues from crop growth chambers
would undergo a leachate pretreatment step to produce a liquid stream
for input to the fixed-film bioreactor. Crop growth chamber condensate
water can be used for water source in fixed-film bioreactors. Filtered
(to remove biofilm-sloughed material) FFB effluent would be recycled
back to the crop hydroponic production system to replenish crop
nutrients. FFB oxygen would be supplied by plant growth chamber
generated O~2~. Bioreactor-generated CO~2~ in the offgas would be cycled
back to the plant growth chamber. Filter retentate solids may be used as
feed material for composters, fluidized bed incinerators and other
combustion devices. Filtration solids may also be useful as a solid seed
germination support/matrix.

**Advantages Identified for Fixed-Film Bioreactors:**

-   Recovers the majority of plant nutrients in a form directly
    compatible with various plant production systems

-   Rapid processing rates equate to low mass/volume requirements

-   Microbial biofilms are very resistant to stress

-   Produces solid stream with low inorganic content

-   Minimal size reduction required in preprocessing

-   May utilize dual-function bioreactor (solid waste and wastewater)

-   Minimal solid-liquid separation (post-harvest)

**Disadvantages:**

-   Some pretreatment (i.e., drying) needed

-   Minimal organic degradation (\~20%)

-   Only addresses one solid waste stream (although it is the largest
    waste stream)

-   Limited to continuous operation modes (but can withstand variable
    rates)

-   Need to develop continual crop residue leaching component

Microgravity Considerations for Fixed-Film Bioreactors (FFB):

FFB is seen as having limited application in a microgravity environment
unless specialized two-phase separation (liquid, gas) equipment is
developed.

Technical Readiness Level of FFB:

The current level of development is a TRL of 2-3. To complete
development to a TRL 4 would cost \$300,000 and take 2-3 years.

Research and Development Steps Needed to Fully Develop FFB:

-   Develop and test individual system components

```{=html}
<!-- -->
```
-   Integrate fixed-film bioreactor components with crop production and
    crew fecal production inputs -- leaching step required and
    bioreactor effluent and gas stream outputs

-   Optimize completed system with appropriate feedstock

-   Pathogen, perturbation, and product studies

**4.2.2.d Single Cell Protein (SCP) and Paper Manufacture**

Lignocellulosic biomass can be used as a feedstock for biologically
based processing into other consumable products on board. The feedstream
would include paper and inedible biomass but would need to be segregated
from human waste due to pathogen concerns.

The workshop participants discussed two major types of bioproducts from
this biomass feedstream: fermentation products (e.g., ethanol, organic
acids, amino acids) for use as solvents, cleaners or even as food
supplements; and single cell protein (SCP) as a highly nutritive food
supplement. For the fermentation products, ethanol will be used as the
model product; with minor modifications other products could be made
(acetic acid, lysine, etc.). It should be noted that these methods as
applicable to space missions would not give 100% conversion of biomass
into usable products; 50% to 80% conversion of the biomass is a more
reasonable target.

The core of the processes is pretreatment, bioconversion, and
post-treatment (e.g., separation and concentration). The process
equipment could be adapted to these other bioproducts. The processes
have been extensively studied on Earth for commodity chemical production
with technological success but without a current commercial operation.
The challenge for this report and for adaptation into a space mission is
to assess and evaluate the wide variety of workable approaches and to
optimize the process into a low lift mass, low energy input
configuration. Each of the pieces of a terrestrial process would have
advantages and disadvantages.

The fermentation ethanol process:

Pretreatment will partially break the biomass and paper into its sugars.
Size reduction is required. The two most reliable hydrolysis methods are
steam explosion and acid hydrolysis.

Steam explosion is simple but high energy and will require a pressure
vessel (high mass and safety). Dilute acid hydrolysis requires acid
(0.2M sulfuric) and moderate temperatures.

Conversion:

The bioconversion/fermentor will be a simple, ambient temperature,
controlled, mixed vessel. Gas addition and disengagement are the
technical challenges in microgravity operation. Oxygen or air will be
required for SCP production while significant coproduction of carbon
dioxide will occur in either SCP growth or anaerobic ethanol production.
This means that a conventional stirred tank is not likely to work. A
recycle loop attached to the vessel via pumps can also be used to
accomplish the mixing. The gas disengagement may then be accomplished in
this sidestream via a membrane system. This adds another unit but all
units can be made of low weight plastics capable of withstanding
sterilization. Low-level waste heat will be produced in the
fermentation. The key element is the microbial catalyst. Several
genetically engineered microbes exist to convert both pentose and hexose
sugars. Cellulolytic enzymes will also be required to improve the
fermentation. These can also be produced microbially from the same
feedstocks. This could require a second vessel, but more simply a
two-stage fermentation process: 1) a longer slower growth of the
cellulolytic microbe or fungi followed by 2) the addition of the rapid
fermentative microbe to produce ethanol.

Separation:

On Earth distillation is the standard unit of operation; for space or
Mars application, the participants felt that the vacuum resource should
be exploited. Vacuum distillation of dilute ethanol or acetic acid
solution should allow concentration to 90% purity, which should be
sufficient for most mission applications. Pervaporation (vacuum via a
membrane) might be used directly with the conversion step to
preconcentrate the ethanol and improve the conversion. Freeze drying may
be effective for the nutrients or the SCP protein after a simple
centrifugation step to remove the bulk water.

SCP production:

The method shown could be performed after the pretreatments discussed
above or just after size reduction. There is a proposed three-stage
bioconversion: an anaerobic cellulolytic stage to produce a "cleaned
solids" and a rich organic aqueous stream that is used to grow yeast for
SCP. The clarified liquid effluent from the SCP production will be rich
in soluble minerals that can be run through a biodenitrification
reaction to yield recycled water rich in fertilizer minerals and nitrate
to be used for the crop growth. Again these conversions will require
mixed fermentors with gas disengagement. The first two will be high
solids. The approaches discussed above should apply here.

The main unit operation is solid/liquid separation or dewatering after
the pretreatment, after the anaerobic conversion to separate the
recalcitrant solids and after the yeast production to remove the SCP.
This could be accomplished via either a simple centrifugal separator or
via a membrane system.

**Advantages Identified for Single Cell Protein and Paper Manufacture:**

-   Batch operation as needed

-   Process units adaptable to a limited variety of products: ethanol,
    acetic acid, SCP with mostly just a change in microbial catalysts

-   Most fermentation units could be built of plastic

-   Provides consumables currently used on mission from planned waste
    product-- ethanol is not the best solvent or degreaser but it is
    effective and safe. SCP is an effective nutrition supplement

-   Generally simple operation and equipment

**Disadvantages:**

-   Requires technical skills (maintenance of several microbial
    cultures)

-   Intermediate analysis of process steams may be limited

-   Pretreatment requires some moderate hazard conditions (steam or acid
    at greater temperatures of 200 C or 150 C respectively)

-   Incomplete conversion -- will still have some wet biosolids to deal
    with

-   Pumping and pumps add energy and weight

-   If membranes used, membrane replacement adds to consumables. Some
    porous steel membranes do work for dewatering.

**Recommendations** (for both the "ethanol" and the SCP product
streams):

-   Assessment activity of the technologies

-   Assessment of units/ rates/ conversions

-   Equipment mass, power, consumable, volumes, added CO~2~ loads, etc.

-   Potential radiation effects, microgravity on the processes

-   Potential uses of the products within the recycle system

Then, some confirmatory integrated experimentation can be done, perhaps
using waste biomass from ALS plant growth studies. After that, perhaps
innovative approaches will be solicited to improve/solve this base
system of biomass to bioproducts.

## 

## 4.3 Physicochemical Processes

### 4.3.1 Introduction

Physicochemical (PC) processes are very commonly used to handle waste;
combustion is a common example. PC processes can rapidly convert waste
to products either completely or partially. PC processes can also
produce useful products including carbon dioxide, water, inorganic
nutrients, activated carbon, fuels, organic chemicals, solvents, and
paper.

Combustion is perhaps the most widely used PC process used to treat
waste. Combustion has been used by farmers to burn crop residues in the
field in order to rapidly return the nutrients to the soil. Cities and
towns commonly use combustion in incinerators to burn waste. Industry
uses incinerators to destroy hazardous wastes. Many small-scale
incinerators are used to destroy wastes in hospitals, on ships, and in
remote locations. Advantages for combustion include rapid conversion of
waste to carbon dioxide, water, and inorganic minerals.

PC processes other than incineration can also completely convert the
wastes. Supercritical water oxidation oxidizes waste to the same
products as combustion, but without the contaminants produced by
combustion. Pyrolysis and gasification completely convert complex
hydrocarbon wastes to solid, liquid, and solid hydrocarbons that are
generally simpler in chemical structure, more easily handled, and free
of biological contamination.

Products other than carbon dioxide, water, and minerals can be obtained
from wastes by PC processes. Activated carbon, fuel, plastic, paper, and
solvents are examples of products produced from waste by commercial PC
processes.

A very large number of PC processes could be considered for treating
biomass, feces, and the other wastes of the various mission scenarios.
However, the main functions of the waste processing system for near term
space missions is likely to be stabilization or complete oxidation of
waste. Stabilization of waste is needed on missions with little food
production, and complete oxidation of biomass is needed for missions
where more than about 50% of the food is grown from plants.

A sampling of individual PC technologies was assessed at the workshop.
These technologies were: lyophilization, supercritical water oxidation
(SCWO), incineration, plasma (oxidation), carbon activation,
electrochemical (oxidation), hydrogen peroxide (oxidation), pyrolysis,
and gasification. The sampling was fairly representative of oxidation
technologies. Stabilization and alternative product formation
technologies were not as thoroughly represented. Lyophilization is an
example of a stabilization technology. Pyrolysis and activated carbon
formation are examples of alternative product producing technologies. A
list of the technologies and summaries of some of the key information
are shown below in Table 8. Following the table is a discussion of each
of the technologies.

Table 8. Summary Information on Physicochemical Technologies Assessed

+-----------+-------------+--------------+---------------+-----+------+
| **Tec     | **          | **Di         | *             | *   | **\$ |
| hnology** | Advantage** | sadvantage** | *Microgravity | *TR | to** |
|           |             |              | Concerns**    | L** |      |
|           |             |              |               |     | *    |
|           |             |              |               |     | *TRL |
|           |             |              |               |     | 5**  |
+-----------+-------------+--------------+---------------+-----+------+
| Lyoph     | -   Useful  | -   Low TRL  | -   Possible  | 2   | \$   |
| ilization |     on      |              |     water-gas |     | 600K |
|           |             | -   Does not |               |     |      |
|           |   near-term |              |    separation |     |      |
|           |             |    sterilize |               |     |      |
|           |    missions |              |               |     |      |
|           |             |              |               |     |      |
|           | -           |              |               |     |      |
|           |    Reclaims |              |               |     |      |
|           |     water   |              |               |     |      |
+-----------+-------------+--------------+---------------+-----+------+
| SCWO      | -   All     | -   High     | -   Liquid    | 4   | \    |
|           |     waste   |     Tem      |     and solid |     | $1-5 |
|           |             | perature (T) |               |     | M    |
|           | ```{=html}  |     and      |    separation |     |      |
|           | <!-- -->    |     Pressure |     issues    |     |      |
|           | ```         |     (P)      |               |     |      |
|           | -   Clean   |              |               |     |      |
|           |             | -   Solids   |               |     |      |
|           |    Products |     plugging |               |     |      |
+-----------+-------------+--------------+---------------+-----+------+
| Inc       | -   All     | -   Flue gas | -   Fluidized | Co  | Con  |
| ineration |     wastes  |              |     bed not   | nti | tin- |
|           |             | contaminants |               | n-u | uous |
|           | -   Hi      |              |  microgravity | ous | =\$0 |
|           |     process | -   High T   |               | = 4 |      |
|           |             |              | -             |     | Ba   |
|           |  conversion |              |    Gas-solids | Ba  | tch= |
|           |             |              |               | tch |      |
|           |             |              |   separations | =   | \$1  |
|           |             |              |               | 2-3 | M    |
+-----------+-------------+--------------+---------------+-----+------+
| Plasma    | -   All     | -   High     | -   Not       | 3-4 | \$   |
|           |     wastes  |     Power    |     suited    |     | 8-13 |
|           |             |     and      |     for       |     | M    |
|           | -   Fast    |     Temp.    |     Scenario  |     |      |
|           |             |              |     1         |     |      |
|           |    reaction | -            |               |     |      |
|           |             |    Scaledown | -   Heat      |     |      |
|           |             |              |     transfer  |     |      |
|           |             |    difficult |     affected  |     |      |
+-----------+-------------+--------------+---------------+-----+------+
| Carbon    | -   Useful  | -   Complex  | -   Solids    | 3   | \$5M |
| A         |     Product |              |     transfer  |     |      |
| ctivation |             | -   Product  |               |     |      |
|           | -           |     gas      | -   Avoid gas |     |      |
|           |    Produces |     requires |               |     |      |
|           |             |              |  condensation |     |      |
|           |             |   combustion |               |     |      |
+-----------+-------------+--------------+---------------+-----+------+
| Electr    | -   Low T & | -            | -             | 4   | \$5  |
| ochemical |     P       | Pretreatment |    Gas-liquid |     | M    |
|           |             |     reqrd.   |               |     |      |
|           | -   Scales  |              |    separation |     |      |
|           |     down    | -   Catalyst |               |     |      |
|           |     well    |     Regen.   |               |     |      |
+-----------+-------------+--------------+---------------+-----+------+
| H~2~O~2~  | -   Handles | -   Requires | -             | 1   | \    |
|           |     many    |              |    Gas-liquid |     | $2-3 |
|           |     wastes  |  preparation |               |     | M    |
|           |             |     or       |    separation |     |      |
|           | -   No      |     resupply |               |     |      |
|           |             |              | -   Injection |     |      |
|           |   catalyst, | -   Risk of  |     nozzle    |     |      |
|           |     no      |              |     redesign  |     |      |
|           |     heater  |   detonation |     for 0 G   |     |      |
+-----------+-------------+--------------+---------------+-----+------+
| Pyrolysis | -   Many    | -            | -   Solid,    | 3   | \    |
|           |     useful  |   Complexity |     liquid, & |     | $500 |
|           |             |              |     gas       |     | K    |
|           |    products | -   CO       |               |     |      |
|           |             |              |    separation |     |      |
|           | -   Treats  |   production |               |     |      |
|           |     many    |              |               |     |      |
|           |     wastes  |              |               |     |      |
+-----------+-------------+--------------+---------------+-----+------+
| Gas       | -   Many    | -   Low TRL  | -   Gas-solid | 1-2 | \$   |
| ification |     useful  |              |               |     | 600- |
|           |             | -   High     |    separation |     | 1000 |
|           |    products |     Temp.    |     issues    |     | K    |
|           |             |              |               |     |      |
|           | -   Minimum | -   Complex  |               |     |      |
|           |     NO~x~,  |              |               |     |      |
|           |     SO~2~   |              |               |     |      |
+-----------+-------------+--------------+---------------+-----+------+

2.  **[Physicochemical Technologies]{.underline}**

4.3.2.a Incineration

![](media/image6.wmf){width="10.0in" height="5.069444444444445in"}

# Figure 5. Incineration System

Process Description:

Incineration is a technology capable of completely converting all the
waste to carbon dioxide, water, and inorganic ash. Almost any waste can
be incinerated. Pretreatment is necessary to dry the waste and prepare
the waste for the feed system. The incineration system includes a
combustor and a contaminant cleanup system. The combustor does most of
the work of oxidation, but both thermodynamics and kinetic limitations
result in the formation of contaminants in the flue gas that typically
include carbon monoxide, trace hydrocarbons, hydrochloric acid, sulfur
dioxide, and nitrogen oxides. Catalytic systems and adsorption beds are
typically used to remove the contaminants in the flue gas cleanup
system. Figure 5 shows a diagram of the major components of an
incinerator.

Incinerators can function in batch or continuous mode. Continuous mode
means that the system holds temperature, pressure, and composition
constant while continuously feeding a constant flow rate of waste and
producing a continuous constant composition output. Batch operation
typically means injection of a batch of material into the system with no
output until some fixed period of time. During the batch cycle
temperatures, pressures, and compositions vary in the system. Feed to
batch systems is easier because a continuous and constant flow need not
be controlled. Ash collection is also easier and cleaner in batch
systems because the ash stays in the combustion chamber, does not pick
up contamination while moving through a system, and does not require
filtering or other special separation hardware such as a cyclone
separator. The disadvantage of batch processing is that the system must
be capable of handling the transient production of gases of varying
compositions, and the system can be large if batch cycle times are long
due to slow heating and cooling. Articles and books that discuss
incineration technology are references (28 and 29).

Advantages Identified for Incineration:

-   Extensive existing application and development of incineration on
    Earth

-   High conversion rates into end-products

-   Destruction of biological hazards in the waste stream

-   Potential for energy production

> **Disadvantages:**

-   Need to clean up the gas phase contaminants

-   Safety issues associated with high temperature

-   Requirement of preprocessing, and control issues related to rapid
    conversion of solid wastes to gases

Microgravity (and Hypogravity) Considerations for Incineration:

Fluidized bed designs are affected but can be designed to operate over a
wide range of partial gravity to microgravity. Designs other than
fluidized bed might be more appropriate for microgravity. There are
phase separations necessary \-- vapor/solid and vapor/liquid \-- that
are microgravity sensitive.

Technical Readiness Level of Incineration:

The current level of development is a TRL of 4 for a continuous gravity
dependent fluidized bed incinerator. Other types of batch and continuous
incinerators are at TRL 3-4.

**Research and Development Steps Needed to Fully Develop Incineration
Technology:**

-   Develop combustion techniques other than fluidized bed for
    microgravity operation

-   Develop improved catalysts for flue gas cleanup

-   Integrate biological and incineration technologies. For example,
    pretreatment of waste using biological approaches to remove a
    significant amount of alkali will simplify combustion systems and
    improve lifetime and reliability, while the difficulties of
    completely and quickly processing organic components of the waste
    with biological techniques are avoided.

-   Optimize the size, weight and power of the incinerator

#### 4.3.2.b Electrochemical Oxidation

**Process Description:**

Liquid organic material can undergo oxidative degradation at low
temperatures when treated in an electrochemical cell. Electrochemical
oxidation may be performed directly or indirectly. In direct oxidation,
the waste, usually in a soluble form, is oxidized when it comes into
direct contact with an anode (positive electrode). Common anode
materials include

![](media/image7.wmf){width="6.5in" height="5.104861111111111in"}

**Figure 6. Indirect Electrochemical Oxidation**

platinum, lead dioxide, or dimensionally stable anodes (DSAs). Organic
wastes are broken down at the interface between the anode surface and
the solution, i.e., the reaction is heterogeneous. Corresponding
reduction reactions take place at the cathode (negative electrode) where
hydrogen is usually formed. The process requires that the organic wastes
be placed in an electrolyte, typically an acid or alkaline solution. The
indirect process is an attempt to accelerate oxidative degradation. It
differs from the direct process in that redox mediators, e.g.,
Ce^3+^/^4+^, V^2+^/^3+^, Ag^+^/^2+^, Fe^2+^/^3+^, Co^2+^/^3+^, are added
to the electrolyte. The redox mediators carry out waste oxidation in the
bulk electrolyte, i.e., the organic waste oxidation reactions are
homogeneous. The reaction occurring at the anode is the regeneration of
the redox mediator. Indirect oxidation offers greater flexibility in the
types of waste slurry that can be treated. It should be noted that most
of the industrial pilot plants have been designed to use the indirect
oxidation method. The example given in the Figure 6 is of an indirect
process using cerium as the redox couple in a nitric acid electrolyte.

Electrochemical oxidation occurs at low temperature (\<100°C), producing
gaseous emissions that require reduced clean up compared to thermal
treatments (e.g., this method does not generate NO~x~, SO~x~ or CO).
However, emissions can include chlorine gas generated at the anode by
the oxidation of chloride ions that could be present in the waste.
Hydrogen generated at the cathode can be collected to provide a
feedstock for other processes (e.g generate electricity in a fuel cell,
etc.). The waste stream feed stock for indirect electrochemical
oxidation should be in a slurry form with maximum particle sizes not
exceeding 100 microns in diameter. It should be stressed, however, that
the exact extent of preprocessing has yet to be determined. The direct
oxidation method involves a two-step treatment, where a liquid biomass
suspension is first solubilized by a high temperature process in strong
alkali bath followed by electrochemical oxidation. Articles and books
that discuss electrochemical oxidation technology are references (30
--34).

**Advantages Identified for Electrochemical Oxidation:**

-   Operates at relatively low temperature and pressure

-   Production of oxides of C, N, and S is minimal/ negligible

-   Process is easily amenable to scale-down for a 4-6 person crew waste

**Disadvantages:**

-   Acid/alakali requirement (expendables)

-   Buildup of non-oxidizable inorganic materials

-   Gaseous emissions include Cl~2~

-   Requires consistent and very fine particle waste

**Microgravity (and Hypogravity) Considerations for Electrochemical
Oxidation:**

Microgravity and hypogravity concerns relate to the management of the
liquid electrolyte, separation of the gases formed at the anode and
cathode from the electrolyte, and gravity independent methods for
feeding and distributing the waste slurry into the electrolyte bath.

**Technical Readiness Level of Electrochemical Oxidation:**

The technology was assessed to be at TRL 4.

**Research and Development Steps Needed to Fully Develop Electrochemical
Oxidation Technology:**

-   Develop catalytic oxidation methods and effluent treatments for
    combustion gases

-   Optimize reactor materials, electrode materials, and membranes

**4.3.2.c Pyrolysis**

**Process Description:**

Pyrolysis is a process that breaks down wastes by heating them to high
temperatures without oxygen addition. By controlling the temperature,
the rate of heating, and the removal products, it is possible to obtain
a variety of products. The process is outlined in Figure 7.

Pyrolysis typically produces gas, liquid, and char. The amount of liquid
can be controlled from a maximum amount characteristic of the waste down
to zero. The char contains carbon, nitrogen, and inorganic ash. By
varying the method of pyrolysis the amounts and kinds of gaseous,
liquid, and char products can be selected from the wide variety of
potential products as shown in Figure 7. These products are char,
hydrocarbon liquid and hydrocarbon gas.

![](media/image8.wmf){width="9.375in" height="6.625in"}**Figure 7.
Pyrolysis Processing Schematic**

**Advantages Identified for Pyrolysis:**

-   Flexibility and adaptability with regard to feedstock

-   Simplicity, low mass, variety of potentially useful products

-   Reduction of waste volume

**Disadvantages:**

-   Complex product stream that may not have readily identifiable uses

-   Microgravity processing sensitivity

-   High temperature operation

-   Complex processing scheme

**Microgravity (and Hypogravity) Considerations for Pyrolysis:**

Solid, liquid, and gas separation steps are necessary.

Technical Readiness Level of Pyrolysis:

Currently the technology is at TRL 3. Cost is about \$500,000 to get to
TRL 5.

**Research and Development Steps Needed to Fully Develop Pyrolysis
Technology:**

-   Develop pyrolytic systems that are specific to biomass and feces

-   Develop microgravity phase separations that are specific to the
    pyrolysis process

-   Integrate the pyrolysis with other waste treatment technology, such
    as incineration if that is the appropriate overall system design

#### 4.3.2.d Gasification

**Figure 8. High Temperature Gasification**

Gasification is a process that converts any carbon-containing material
into a synthesis gas. Syngas is composed primarily of carbon monoxide
and hydrogen. The product gases can be used as a fuel to generate
electricity or steam or as a basic chemical feedstock for the
petrochemical and refining industries (see Figure 8). Typical raw
materials used in gasification are coal, petroleum-based materials, or
materials that would otherwise be disposed of as waste. The input
material is prepared and fed to the gasifier in either dry or slurried
form. The feedstock reacts in the gasifier with steam and oxygen at high
temperature and pressure in a reducing (oxygen starved) atmosphere. This
produces synthesis gas, or syngas, made up primarily of carbon monoxide
and hydrogen (more than 85% by volume) and smaller quantities of carbon
dioxide and methane. The high temperature in the gasifier converts the
inorganic materials in the feedstock (such as ash and metals) into a
vitrified slag that is usually very safe and stable for storage. Gas
treatment facilities refine the raw gas using proven commercial
technologies that are an integral part of the gasification plant. Trace
elements or other impurities are removed from the syngas and are either
recirculated to the gasifier or recovered. Sulfur is
![](media/image9.wmf){width="7.520138888888889in"
height="2.972916666666667in"}recovered either in its elemental form or
as sulfuric acid.

#  

# Figure 9. Magnetically Assisted Gasification 

A specific gasification reactor design (see Figure 9) was described that
addresses the needs of this system in microgravity environments and
offers a way of presenting concentrated solids to the reactor. A
magnetically assisted method was described which consists of three
steps: (1) filtration of the suspended particulate materials from an
aqueous slurry using a bed of granular ferromagnetic filtration media;
(2) destruction of the entrapped particulate matter by thermal
decomposition; and (3) removal and collection of the by product
inorganic ash from the ferromagnetic media by fluidization in the
reverse direction. A desirable feature of this design is that it enables
a high solids loading to be presented to the reactor even using low
solids loading streams as the input feed. This is because the filtration
step concentrates the solids. Zero-g stabilization of a fluidized bed
had been demonstrated in KC-135 flights. Reference (35) discusses
gasification processes.

**Advantages Identified for Gasification:**

-   Ability to treat all the waste constituents of the waste model with
    almost 100% conversion of waste to products

-   Little size reduction or preprocessing

-   Potential for the recovery of waste heat and valuable chemicals

-   Compact, reliable, and safe to operate

**Disadvantages:**

-   Although gasification is well developed commercially, it is at a low
    level of development for the specific NASA applications, which
    implies more expense to raise the TRL level.

```{=html}
<!-- -->
```
-   This is a high temperature process.

-   This is a complex process.

**Technical Readiness Level of Gasification:**

The method was rated at TRL 1-2. Cost to TRL 5 was estimated at the
workshop to be \$ 0.6-1 million. Considering the low level of TRL, the
cost is more likely to be on the higher end.

**Research and Development Steps Needed to Fully Develop Gasification
Technology:**

-   Gasification is a general area of technology. This technology needs
    to be developed to apply to a specific mission scenario.

-   Breadboard prototypes need to be fabricated and tested.

-   The system needs to be optimized.

-   The system needs to be prepared for integration into an overall life
    support system.

#### 4.3.2.d Supercritical Water Oxidation (SCWO)

Supercritical water oxidation (SCWO) is a method for oxidizing
substances in water at temperatures and pressures above the critical
point for water. At temperatures and pressures above the critical point,
pure water exists as a single fluid phase; there are no separate liquid
and vapor phases. Gases and most liquid organics (and some solid
organics) are completely miscible with water above water's critical
point. As a result the mass transfer limitations on reaction rates
caused by the need for oxygen to diffuse from a vapor phase to a liquid
water phase do not occur in supercritical water systems. This allows for
a high level of destruction of the wastes.

Figure 10 shows a diagram of a continuous SCWO processor that was built
for NASA. Dual piston pumps accomplish pumping of feed. Sticky solids
are handled via a two-stage reactor system. The first reactor is a
vessel reactor wherein sticky solids adhere to a reactor insert and
build up over time until sufficient accumulation has occurred to require
reactor shutdown and cleanout. The second reactor is a tubular reactor
to provide residence time for reaction completion. Energy efficiency is
achieved via two external recuperative heat exchangers.

Figure 11 shows a concept for a SCWO system with a single tubular
reactor. In this conceptual system accumulation of solids in the reactor
would be avoided by control of conditions and flow rates in the reactor.
The reactor would also be designed to achieve energy recovery via a tube
in tube countercurrent flow scheme.

![](media/image10.wmf){width="5.304166666666666in"
height="3.997916666666667in"}

**Figure 10. Diagram of Experimental NASA SCWO System**

![](media/image11.wmf){width="6.125in" height="4.617361111111111in"}

**Figure 11. Concept for an Energy Recuperative SCWO Tubular Reactor
System**

Not all materials are miscible with water above its critical point.
Solid organics such as biomass (plant/fecal material) tend to form solid
residual carbonaceous particles in supercritical water, and these
particles are more slowly oxidized than the dissolved organics. Pumping
slurries of biomass in water into a high-pressure reactor is also a
technological challenge. Inorganics such sodium chloride are not
dissolved in supercritical water. Sodium chloride tends to form sticky
particles that can clog tubular reactors. Pretreatment and pumping of
biomass and the handling of sticky inorganic salts are some of the
primary difficulties associated with SCWO. Articles and books that
discuss SCWO technology are references (36-41).

**Advantages Identified for Supercritical Water Oxidation:**

-   Complete oxidation of the carbonaceous material

-   Process temperature and pressure variation could potentially yield
    other useful intermediate products

**Disadvantages:**

-   High temperature and pressure of SCWO is a safety concern (the
    nominal operating conditions are about 870^O^K and 24,000 kPa)

-   The stored energy in the hot compressed gas can be hazardous in the
    case of a reactor failure

-   Precautions such as pressure relief, venting, monitoring, and
    shielding must be taken to avoid overly rapid reactions, high
    temperatures, and hardware corrosion

**Technical Readiness Level of Supercritical Water Oxidation:**

SCWO is at about a TRL 4 level of development. Development to TRL 5
would cost about \$1,000,000 to \$5,000,000.

**Microgravity Considerations of Supercritical Water Oxidation:**

There are liquid/gas and liquid/solid phase separation that will be
affected by microgravity.

**Research and Development Steps Needed to Fully Develop Supercritical
Water Oxidation Technology:**

-   Develop pretreatment systems to reliably deliver slurries to the
    SCWO system

-   Conduct long operation reliability testing

-   Develop improved methods of preventing and removing reactor scaling

-   Optimize the energy consumption and rejection

#### 4.3.2.e Lyophilization

Lyophilization (freeze drying) is a process for water recovery and
stabilization of waste. Typically the waste is frozen, a high vacuum is
pulled on the waste, heat energy is slowly supplied to the waste while
holding vacuum, and the water vapor produced is condensed and recovered.

Figure 12 shows a concept for a lyophilization process for water
recovery from feces. In this concept a tubular freeze dryer is inserted
into the feces collection device of the commode, the feces are frozen,
vacuum and heat are applied, and eventually the dry feces and collected
water are removed separately.

Although lyophilization is a well-developed technology for commercial
purposes (such as production of instant coffee), the technology has not
been applied to waste treatment*.* Articles and books that discuss
lyophylization technology are references (42-44).

![](media/image12.wmf){width="7.009722222222222in"
height="4.947222222222222in"}

**Figure 12. Lyophilization System for Freeze Drying**

**Advantages Identified for Lyophilization:**

-   Could be applied to near term missions in which the major objective
    of waste processing is to recover water and to stabilize waste
    (feces)

-   Recovers water

**Disadvantages:**

-   Dehydrated fecal material is not sterilized

-   Requires energy to recover the water as compared to wet storage of
    feces

**Microgravity Considerations for Lyophilization:**

The process includes water-gas separation that may be a microgravity
issue.

**Technical Readiness Level of Lyophilization:**

Current TRL is 2 and estimated cost to advance to TRL 5 is less than
\$1,000,000.

**Research and Development Steps Needed to Fully Develop Lyophilization
Technology:**

-   Develop a system that integrates with the BIO-Plex vacuum transfer
    of feces and centralized treatment

-   Optimize the systems with respect to energy usage

-   Develop a means for microgravity separation of water recovered by
    the system

#### 4.3.2.f Hydrogen Peroxide Oxidation

**Process Description:**

Hydrogen peroxide (H~2~O~2~) is a chemical oxidant that is a clear
liquid, slightly denser than water. It is infinitely soluble in water.
Typically, it is dissolved in water for the direct oxidation of soluble
organics in aqueous waste streams. Its oxidation efficiency can be
enhanced when it is used in combination with an iron salt to form
Fenton's reagent. It is also used as a concentrated oxygen source. The
H~2~O~2~ oxidation method discussed is unique because it involves
peroxide for decomposition of solid materials. The method relies on a
highly concentrated (i.e., 100%) H~2~O~2~ solution. The method depicted
in Figure 13 shows concentrated peroxide being supplied from a storage
tank. The concentrate is injected into a reactor vessel, where it reacts
spontaneously on contact with the waste material in what is described as
a "controlled burning process." Energy released during the reaction can
raise the temperatures inside the chamber to over 1300 °C. Provision is
made for controlling the rate of injection, through a feedback mechanism
from a pressure transducer, to prevent an overly violent reaction. The
wastes themselves act to catalyze the reaction, eliminating a
requirement for additional catalysts or fuels.

![](media/image13.wmf){width="6.504166666666666in"
height="3.9055555555555554in"}

**Figure 13. Hydrogen Peroxide Oxidation**

Expansion of the peroxide and gases being released during the reaction
provides excellent mixing so no agitator is required. A provision is
made to introduce supplemental air or oxygen into the chamber to sustain
combustion once it has been initiated by the peroxide injection step.

**Advantages Identified for Hydrogen Peroxide Oxidation:**

-   Complete oxidation of organics

-   Exothermic reaction (could potentially use the heat)

**Disadvantages:**

-   Requires supply of raw materials (H~2~O~2~)

-   Reactants are corrosive

**Technical Readiness Level of Hydrogen Peroxide Oxidation:**

The method was assessed as TRL 1. The basic mechanisms of controlled
injection, reactor mixing, and safe operation have yet to be established
in a 1 g environment. Little is known about the types of waste that
could be treated by the method. The emission composition from the NASA
waste feed has not been determined. Projected costs to reach a TRL of 5
are \$2-3 million, spread over two years.

**Research and Development Steps Needed to Fully Develop Hydrogen
Peroxide Oxidation Technology:**

-   Develop the basic mechanisms of controlled injection, reactor
    mixing, and safe operation

-   Design, build and test breadboard hardware for application to life
    support wastes

-   Optimize the breadboard systems

#### 4.3.2.g Plasma Arc Technology

**Process Description:**

Plasma arc incineration (Figure 14) uses extremely high temperatures in
an oxygen-starved environment to completely decompose waste material
into very simple molecules. The extreme heat and lack of oxygen results
in pyrolysis of the input waste material. The end result is a
combustible gas and an inert vitrified slag. The heat source is a plasma
arc torch, a device that produces a very high temperature (between 3,000
and 8,000 °C) plasma gas. The gasification process takes place in a
refractory-lined vessel, which is preheated before processing commences.
Within the vessel, an optimal, high-temperature processing zone is
created through which all the waste material is fed. The reactor vessel
operates at normal atmospheric pressure.

The chemical composition of different input waste materials will result
in different gas and slag characteristics. Waste materials such as
biomass, liquid wastes, and organic wastes will produce little slag
since virtually all of the waste can be gasified. Volume reduction and
destruction efficiency is a significant feature of this method. For
example, volume reduction in excess of 250:1 is typical for as-received
municipal waste. This destruction efficiency contrasts with
incineration, which can leave significant amounts of unprocessed
material in the ash. The resulting slag has a leachate toxicity several
orders of magnitude lower than those specified in current landfill
regulations. The residual solids have safe storage characteristics.

The method's potential to be configured for low environmental emission
characteristics was recognized. The method is a batch process. The team
devised an operating procedure where the waste is accumulated for two
weeks, followed by a 3-5 hour period of operation. During operation, the
method will be power intensive and there will be a sizeable heat load
that must be rejected. The method can be operated by one person and is
easy to start up and shut down. Articles and books that discuss plasma
arc technology are references (45-47).

![](media/image14.wmf){width="6.409722222222222in"
height="4.7444444444444445in"}

**Figure 14. Plasma Arc Incineration**

**Advantages Identified for Plasma Arc Technology:**

-   Accommodates virtually any input waste material, often in an
    as-received condition

-   Provides for virtually complete gasification of all volatiles in the
    source material

-   Non-combustible materials, including glass and metal, are reduced to
    an inert slag

-   Process is independent of input moisture content; therefore, there
    is no loss of destruction efficiency if the moisture content varies

-   Product gas is high in hydrogen and carbon monoxide, with traces of
    methane, acetylene, and ethylene; therefore, it can be combusted
    very efficiently resulting in carbon dioxide, nitrogen, and water
    vapor as the only gaseous exhaust

**Disadvantages:**

-   The method is untested in a space mission environment, and there is
    uncertainty regarding changes in heat transfer characteristics for
    the device

-   The mechanisms for feeding waste to the high temperature reaction
    zone may have to be modified for microgravity operations

-   Electromagnetic interference must be considered when operating the
    plasma

-   Scalability of the method was identified as a concern. Systems used
    presently are substantially larger than would be needed for space
    mission applications.

**Technical Readiness Level of Plasma Arc Technology:**

Mobile and transportable plasma systems are in use (reference) and may
be adaptable to this need. A TRL of 3-4 was assigned to this method.
Costs to advance to TRL 5 were estimated at \$8-13 million.

**Research and Development Steps Needed to Fully Develop Plasma Arc
Technology:**

-   Scalability of the system to handle the waste stream generated as
    mentioned in the different mission scenarios

-   Development of a Breadboard system specific to NASA requirements

-   Optimization of the breadboard system

-   Development and testing of an advanced system for integrated testing
    with other life support systems

#### 4.3.2.h Carbon Activation 

**Process Description:**

Waste materials do not always have to be converted to carbon dioxide and
water. Biomass waste can be converted to activated carbon. Activated
carbon can be used to remove contaminants from incinerator flue gas,
cabin air in the trace contaminant control system, and water in the
water treatment system. Although there are a number of alternative ways
of converting biomass to activated carbon, the process presented at the
workshop is a well-developed process.

MBR Research's proprietary thermal rapid activation (TRAC™)\* technology
processes cellulose-based char pellets into activated carbon. Typical
activation times are 10 minutes, compared to 6-8 hours in conventional
thermal activation, and the result is a pelletized product with BET
(Brunauer, Emmet, and Teller adsorption isotherm) surface area of
600 m^2^/g to 1,300 m^2^/g, with a relatively high proportion of
mesopores (pore diameters between 20 and 200 Angstrom). A U.S. Patent
was applied for in May 1999.

The complete processing cycle incorporates (1) feedstock pelletization,
(2) charring, (3) grinding of the char, (4) extrusion of the char with a
plasticizer/binder to form green pellets, (5) curing of these char
pellets, and, finally, (6) thermal activation under CO~2~. The process
elements are at near-atmospheric pressure and elevated temperatures.

Of the foregoing processes, pelletization, grinding, and extrusion
involve mechanical energy and are quite quantifiable. Pyrolysis, char
pellet curing, and activation all require heat input, yet produce
synthesis gas (of various composition and calorific content) with energy
beyond the thermal requirements of the system. Note that processing on
the order of 15 kg/day of waste by the crew, as described in NASA
publication, would entail an overall batch process where the mechanical
power requirements could be readily satisfied by crewmembers in exercise
mode.

Figure 15 shows a diagram of the system for producing activated carbon
from biomass. The diagram shows the steps, including pelletization,
pyrolysis, extrusion, carbonization, and activation. Articles and books
that discuss Carbon activation technology are references (48-50).

-   ![](media/image15.wmf){width="7.125in"
    height="4.794444444444444in"}Does not imply NASA endorsement.

# Figure 15. Production of Activated Carbon from Biomass

**Advantage Identified for Carbon Activation:**

-   Production of a useful product from the waste

**Disadvantages:**

-   High temperatures

-   Complex process

-   Production of by-product gases that require combustion

**Microgravity Considerations for Carbon Activation:**

Solids separation can be a microgravity problem. There is a need to
avoid gas condensation in order to avoid gas-liquid separations.

Technical Readiness Level of Carbon Activation:

Current TRL is 3 and cost to TRL5 is about \$5 million for the process
outlined above. However the process outlined above is designed to
produce commercial grade activated carbon. A useful but perhaps slightly
less active grade of activated carbon could be produced by a much
simpler process that would cost about \$1 million to develop to TRL 5.

Research and Development Steps Needed to Fully Develop Carbon Activation
Technology:

-   Develop a simpler process

-   Optimize process to produce good quality activated carbon

-   Integrate process with other life support hardware. The activated
    carbon can be used for incineration flue gas cleanup, trace
    contaminant control, and water cleanup.

### 4.4 Conclusions

Seven of the nine methods evaluated were thermal waste treatment
processes. A significant advantage of the thermal methods is that they
are very flexible in the types of input waste that they can treat.
Unfavorable heat rejection characteristics are a disadvantage of each of
these methods. Other than SCWO, all of the thermal methods require
cleanup of the gaseous combustion byproducts. The working group
recognized that considerable information on the cleanup of emissions
could be available from operators of the various treatment processes
both in Europe and in the United States. Many of the thermal processes
evaluated by the group are used commercially for hazardous and municipal
waste treatment and have had to implement techniques to meet stringent
air quality regulations prior to getting a permit to operate. This
database is a significant resource for future developments. The two
low-temperature processes (electrochemical oxidation and lyophilization)
have reduced heat rejection penalties but are limited in the types of
input feed they can accommodate. For all the technologies evaluated,
there was limited information available related to reliability and
maintenance of systems specific to NASA applications.

**5. SUMMARY ANALYSIS**

## 5.1 Feedstock Requirements and Process Characteristics

The first series of tables presents the feedstock requirements and
process characteristics for the various waste processing technologies.
Specifically, these tables list the process feed rate in terms of dry
waste mass per day, the process type, whether the process is batch or
continuous, any associated preprocessing requirements, necessary
catalysts or organisms, the composition of the waste stream, and the
percentage of the input waste stream converted to final products.

Pre- and post-processing technologies, as found in Table 9, generally
accept waste materials smaller than a certain size and of specified
composition. Any waste stream will likely require some form of size
reduction before passing to other waste processing technologies,
including other pre- and post-processing technologies. Thus, to
facilitate size reduction, hard and incompressible wastes, such as
glass, metals, and some composite materials, should be removed from the
process stream, possibly when such waste is generated. With the
exception of transport by aqueous slurries, pre- and post-processing
technologies require particle sizes on the order of a centimeter.

Biological processes are characterized in Table 10. Biological processes
address only biodegradable waste streams and require particles diameters
less than several centimeters down to less than a millimeter. All employ
microbes as a processing agent, but do not require a catalyst. Finally,
these microbial processes convert about a third to two-thirds of the
input waste stream to gaseous products in the short term (\<4 weeks)
with the remaining wastes being a stabilized organic material, which
biodegrades more slowly. This compost (humic material) can be recycled
within in plant growing medium.

Physicochemical processes, Table 11, generally convert nearly the entire
input waste stream to products. Physicochemical processes handle most
waste stream components except metals and can accommodate very high feed
rates. Specifically, while the biological processes will likely run
continuously, most physicochemical processes are most amenable to higher
feed rates with batch-mode operation for near-term missions. For larger
facilities, continuous-mode operation for physicochemical technologies
is likely. Finally, physicochemical technologies often use catalysts
within the primary process and to clean effluent streams.

Table 9. Feedstock Requirements and Process Characteristics for Pre- and
Post-Processing Waste Technologies

+-----------------+---+----+-----+--------------+-----+------+-----+
| Name            | [ | S  | P   | Pr           | Ca  | Wa   | P   |
|                 | ^ | ol | roc | eprocessing\ | tal | ste\ | erc |
|                 | 1 | id | ess | Issues       | yst | Str  | ent |
|                 | ] | W  | Ty  |              | /   | eam\ | age |
|                 | A | as | pe  |              | Org | Com  | of  |
|                 | p | te | ^3^ |              | ani | posi | Wa  |
|                 | p | Fe |     |              | sms | tion | ste |
|                 | . | ed |     |              |     |      | C   |
|                 |   | Ra |     |              |     |      | onv |
|                 | A | te |     |              |     |      | ert |
|                 | c | \[ |     |              |     |      | ed\ |
|                 | c | kg |     |              |     |      | \   |
|                 | . | /d |     |              |     |      | [Wt |
|                 | \ | \] |     |              |     |      | %\] |
|                 | N |    |     |              |     |      |     |
|                 | o |    |     |              |     |      |     |
|                 | . |    |     |              |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Collection,     | P | \  | Ba  | Particle     | n/a | H    | n/a |
| Transport,      | P | -- | tch | diameter \<  |     | uman |     |
| Vacuum          | P |    |     | 4 cm;\       |     | f    |     |
| W               | \ |    |     | Feed as      |     | ecal |     |
| aste Collection | 0 |    |     | slurry       |     | mate |     |
|                 | 1 |    |     |              |     | rial |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Bulk Compaction | P | 0  | Ba  | Particle     | n/a | Any  | n/a |
|                 | P | .1 | tch | diameter \<  |     |      |     |
|                 | P |  m |     | 15 cm;\      |     |      |     |
|                 | \ | ^3 |     | No           |     |      |     |
|                 | 0 | ^\ |     | in           |     |      |     |
|                 | 2 | p  |     | compressible |     |      |     |
|                 |   | er |     | materials    |     |      |     |
|                 |   | b  |     |              |     |      |     |
|                 |   | at |     |              |     |      |     |
|                 |   | ch |     |              |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Dry Size        | P | Va | Eit | Remove       | n/a | Any  | n/a |
| Reduction and   | P | ri | her | over-sized   |     | ex   |     |
| Partic          | P | ab |     | or stringy   |     | cept |     |
| le Size Control | \ | le |     | materials;   |     | g    |     |
|                 | 0 |    |     | Source       |     | lass |     |
|                 | 3 |    |     | separate     |     | and  |     |
|                 |   |    |     | hazardous    |     | me   |     |
|                 |   |    |     | materials    |     | tals |     |
|                 |   |    |     | and metals   |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Drying (Forced  | P | Va | De  | Particle     | n/a | Any  | n/a |
| Air Thermal     | P | ri | pen | size         |     |      |     |
| Convection,     | P | ab | ds; | reduction is |     |      |     |
| Forced Air,     | \ | le | Ba  | preferable   |     |      |     |
| Thermal Vacuum, | 0 |    | tch |              |     |      |     |
| and             | 4 |    | or  |              |     |      |     |
| Freeze Vacuum)  |   |    | C   |              |     |      |     |
|                 |   |    | ont |              |     |      |     |
|                 |   |    | inu |              |     |      |     |
|                 |   |    | ous |              |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Pneumatic       | P | \  | Eit | Particle     | n/a | Any  | n/a |
| Transport ‑ Dry | P | ~1 | her | diameter \<  |     |      |     |
| Material        | P | 1^ |     | 1 cm;\       |     |      |     |
|                 | \ | 2^ |     | Moisture     |     |      |     |
|                 | 0 |    |     | content      |     |      |     |
|                 | 5 |    |     | [\<]         |     |      |     |
|                 |   |    |     | {.underline} |     |      |     |
|                 |   |    |     | 60%          |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Screw Conveyor  | P | \  | Eit | Particle     | n/a | Any  | n/a |
|                 | P | ~1 | her | diameter \<  |     |      |     |
|                 | P | 1^ |     | 1 cm         |     |      |     |
|                 | \ | 2^ |     |              |     |      |     |
|                 | 0 |    |     |              |     |      |     |
|                 | 6 |    |     |              |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Slurry Pumping  | P | \  | Eit | Particle     | n/a | Any  | n/a |
|                 | P | ~1 | her | diameter \<  |     |      |     |
|                 | P | 1^ |     | 1 mm;\       |     |      |     |
|                 | \ | 2^ |     | Feed stream  |     |      |     |
|                 | 0 |    |     | \< 5 wt%     |     |      |     |
|                 | 7 |    |     | solids       |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Solid/Liquid    | P | Va | Eit | Size         | n/a | Any  | n/a |
| Blending;       | P | ri | her | reduction    |     | ex   |     |
| Slurrying       | P | ab |     |              |     | cept |     |
| (50‑95% Water)  | \ | le |     |              |     | g    |     |
|                 | 0 |    |     |              |     | lass |     |
|                 | 8 |    |     |              |     | and  |     |
|                 |   |    |     |              |     | me   |     |
|                 |   |    |     |              |     | tals |     |
+-----------------+---+----+-----+--------------+-----+------+-----+

Table 9 cont. Feedstock Requirements and Process Characteristics for
Pre- and Post-Processing Waste Technologies

+-----------------+---+----+-----+--------------+-----+------+-----+
| Name            | A | S  | P   | Pr           | Ca  | Wa   | P   |
|                 | p | ol | roc | eprocessing\ | tal | ste\ | erc |
|                 | p | id | ess | Issues       | yst | Str  | ent |
|                 | . | W  | Ty  |              | /   | eam\ | age |
|                 |   | as | pe  |              | Org | Com  | of  |
|                 | A | te | [   |              | ani | posi | Wa  |
|                 | c | Fe | ^2] |              | sms | tion | ste |
|                 | c | ed |     |              |     |      | C   |
|                 | . | Ra |     |              |     |      | onv |
|                 | \ | te |     |              |     |      | ert |
|                 | N | \[ |     |              |     |      | ed\ |
|                 | o | kg |     |              |     |      | \   |
|                 | . | /d |     |              |     |      | [Wt |
|                 |   | \] |     |              |     |      | %\] |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Solid/Solid     | P | Va | Eit | Size         | n/a | Any  | n/a |
| Blending        | P | ri | her | reduction    |     | ex   |     |
|                 | P | ab |     |              |     | cept |     |
|                 | \ | le |     |              |     | g    |     |
|                 | 0 |    |     |              |     | lass |     |
|                 | 9 |    |     |              |     | and  |     |
|                 |   |    |     |              |     | me   |     |
|                 |   |    |     |              |     | tals |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Storage[^3]     | P | \~ | Eit | Biological / | n/a | Any  | n/a |
|                 | P | 11 | her | chemical     |     |      |     |
|                 | P |  ^ |     | waste        |     |      |     |
|                 | \ | 2^ |     | s            |     |      |     |
|                 | 1 |    |     | tabilization |     |      |     |
|                 | 0 |    |     |              |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+
| Wet Size        | P | Va | Eit | Remove       | n/a | Any  | [   |
| Reduction and   | P | ri | her | over-sized   |     | ex   | ^4] |
| Partic          | P | ab |     | or stringy   |     | cept | n/a |
| le Size Control | \ | le |     | materials;   |     | g    |     |
|                 | 1 |    |     | Source       |     | lass |     |
|                 | 1 |    |     | separate     |     | and  |     |
|                 |   |    |     | hazardous    |     | me   |     |
|                 |   |    |     | materials    |     | tals |     |
|                 |   |    |     | and metals   |     |      |     |
+-----------------+---+----+-----+--------------+-----+------+-----+

Table 10. Feedstock Requirements and Process Characteristics for
Biological Waste Technologies

+-----------------+---+----+---+----------------+------+-------+-----+
| Name            | A | S  | P | Preprocessing\ | Cata | W     | P   |
|                 | p | ol | r | Issues         | lyst | aste\ | erc |
|                 | p | id | o |                | /    | St    | ent |
|                 | . | W  | c |                | O    | ream\ | age |
|                 |   | as | e |                | rgan | C     | of  |
|                 | A | te | s |                | isms | ompos | Wa  |
|                 | c | Fe | s |                |      | ition | ste |
|                 | c | ed | T |                |      |       | C   |
|                 | . | Ra | y |                |      |       | onv |
|                 | \ | te | p |                |      |       | ert |
|                 | N | \[ | e |                |      |       | ed\ |
|                 | o | kg |   |                |      |       | \   |
|                 | . | /d |   |                |      |       | [Wt |
|                 |   | \] |   |                |      |       | %\] |
+-----------------+---+----+---+----------------+------+-------+-----+
| Aerobic         | B | 8. | E | Feed 40 to 70% | None | Bio   | 25  |
| Completely      | 0 | 13 | i | moisture;\     |      | degra | -80 |
| Mixed (         | 1 |    | t | Particle       |      | dable |     |
| Slurry) Reactor |   |    | h | diameter       |      | w     |     |
|                 |   |    | e | [\             |      | astes |     |
|                 |   |    | r | <]{.underline} |      | only  |     |
|                 |   |    |   | 0.2 cm         |      |       |     |
+-----------------+---+----+---+----------------+------+-------+-----+
| Composting -    | B | 8  | E | Particle       | Sel  | Bio   | 35  |
| Plant Nutrient  | 0 | .4 | i | diameter 0.5   | f-su | degra |     |
| Extraction      | 2 | 9\ | t | to 5 cm;\      | stai | dable |     |
| Variant -- 7    |   | 4  | h | Feed moisture  | ning | w     |     |
| Day Residence   |   | 0. | e | content \~70%  | bi   | astes |     |
| Time (No Curing |   | 75 | r |                | olog | only  |     |
| S               |   |  ^ |   |                | ical |       |     |
| tage/Biofilter) |   | 5^ |   |                | cul  |       |     |
|                 |   |    |   |                | ture |       |     |
+-----------------+---+----+---+----------------+------+-------+-----+
| Composting -    | B | 8  | E | Particle       | Sel  | Bio   | 50  |
| Plant Nutrient  | 0 | .4 | i | diameter 0.5   | f-su | degra | -60 |
| Extraction      | 3 | 9\ | t | to 5 cm;\      | stai | dable |     |
| Variant         |   | 4  | h | Feed moisture  | ning | w     |     |
| ‑ 21 Day        |   | 0. | e | content \~70%  | bi   | astes |     |
|  Residence Time |   | 75 | r |                | olog | only  |     |
|                 |   |  ^ |   |                | ical |       |     |
|                 |   | 5^ |   |                | cul  |       |     |
|                 |   |    |   |                | ture |       |     |
+-----------------+---+----+---+----------------+------+-------+-----+
| Fixed-Film      | B | 6. | E | Dry            | Sel  | Bio   | 75  |
| Bioreactor      | 0 | 27 | i | feedstock;\    | f-su | degra |     |
|                 | 4 |    | t | Particle       | stai | dable |     |
|                 |   |    | h | diameter       | ning | so    |     |
|                 |   |    | e | [\             | bi   | luble |     |
|                 |   |    | r | <]{.underline} | olog | w     |     |
|                 |   |    |   | 0.2 cm;\       | ical | astes |     |
|                 |   |    |   | Leach          | cul  | only  |     |
|                 |   |    |   | biodegradable  | ture |       |     |
|                 |   |    |   | wastes         |      |       |     |
+-----------------+---+----+---+----------------+------+-------+-----+
| High-Solids     | B | 8  | B | Particle       | An   | Bio   | 60  |
| Leach Bed\      | 0 | .1 | a | diameter       | ini  | degra | -90 |
| Anaerobic       | 5 |    | t | \~2.5 cm\      | tial | dable |     |
| Digestion       |   |    | c | Feed moisture  | m    | w     |     |
|                 |   |    | h | content \~70%\ | icro | astes |     |
|                 |   |    |   | Remove human   | bial | only  |     |
|                 |   |    |   | urine          | cul  |       |     |
|                 |   |    |   |                | ture |       |     |
+-----------------+---+----+---+----------------+------+-------+-----+
| Paper and       | B | 6  | B | Particle       | 0.0  | Bio   | 40  |
| Biomass to      | 0 | .6 | a | diameter \<    | 01 g | degra |     |
| Products, e.g., | 6 |    | t | 1 cm;\         | of   | dable |     |
| ethanol         |   |    | c | Remove         | micr | w     |     |
|                 |   |    | h | biotoxins and  | obes | astes |     |
|                 |   |    |   | human waste    | per  | only  |     |
|                 |   |    |   | products       | kg   |       |     |
|                 |   |    |   |                | of   |       |     |
|                 |   |    |   |                | w    |       |     |
|                 |   |    |   |                | aste |       |     |
+-----------------+---+----+---+----------------+------+-------+-----+
| Single Cell     | B | 5  | [ | Feed particle  | 0.0  | Bio   | 33  |
| Protein         | 0 | .5 | ^ | size           | 01 g | degra |     |
| Production      | 7 |    | 5 | reduction;\    | of   | dable |     |
| and Crop Nu     |   |    | ] | Remove         | micr | w     |     |
| trient Recovery |   |    | \ | biotoxins;\    | obes | astes |     |
|                 |   |    | - | Nitrogen: Feed | per  | only  |     |
|                 |   |    | - | \< 0.05 Wt% N  | kg   |       |     |
|                 |   |    |   |                | of   |       |     |
|                 |   |    |   |                | w    |       |     |
|                 |   |    |   |                | aste |       |     |
+-----------------+---+----+---+----------------+------+-------+-----+

Table 11. Feedstock Requirements and Process Characteristics for
Physicochemical Waste Technologies

+------------------+---+---+-----+--------------+------+------+-----+
| Name             | A | S | P   | Pr           | Cata | Wa   | P   |
|                  | p | o | roc | eprocessing\ | lyst | ste\ | erc |
|                  | p | l | ess | Issues       | /    | Str  | ent |
|                  | . | i | Ty  |              | O    | eam\ | age |
|                  |   | d | pe  |              | rgan | Com  | of  |
|                  | A | W |     |              | isms | posi | Wa  |
|                  | c | a |     |              |      | tion | ste |
|                  | c | s |     |              |      |      | C   |
|                  | . | t |     |              |      |      | onv |
|                  | \ | e |     |              |      |      | ert |
|                  | N | F |     |              |      |      | ed\ |
|                  | o | e |     |              |      |      | \   |
|                  | . | e |     |              |      |      | [Wt |
|                  |   | d |     |              |      |      | %\] |
|                  |   | R |     |              |      |      |     |
|                  |   | a |     |              |      |      |     |
|                  |   | t |     |              |      |      |     |
|                  |   | e |     |              |      |      |     |
|                  |   | \ |     |              |      |      |     |
|                  |   | [ |     |              |      |      |     |
|                  |   | k |     |              |      |      |     |
|                  |   | g |     |              |      |      |     |
|                  |   | / |     |              |      |      |     |
|                  |   | d |     |              |      |      |     |
|                  |   | \ |     |              |      |      |     |
|                  |   | ] |     |              |      |      |     |
+------------------+---+---+-----+--------------+------+------+-----+
| Activated Carbon | P | 9 | Ba  | Particle     | Prop | Ce   | \-- |
| and Energy from  | C | . | tch | size         | riet | llul |     |
| Cellulosic Waste | 0 | 3 |     | reduction    | ary; | osic |     |
| By-Products      | 1 | 3 |     | and\         | Not  | wa   |     |
| using            |   |   |     | waste stream | cons | stes |     |
| t                |   | ^ |     | dewatering   | umed | only |     |
| he TRAC™ Process |   | 2 |     |              |      |      |     |
|                  |   | ^ |     |              |      |      |     |
+------------------+---+---+-----+--------------+------+------+-----+
| Batch            | P | \ | Ba  | Minimize     | For  | Any  | 99  |
| Incineration     | C | ~ | tch | chlorinated  | o    | ex   |     |
|                  | 0 | 1 |     | wastes       | xida | cept |     |
|                  | 2 | 1 |     |              | tion | vola |     |
|                  |   |   |     |              | &    | tile |     |
|                  |   | ^ |     |              | r    | me   |     |
|                  |   | 2 |     |              | educ | tals |     |
|                  |   | ^ |     |              | tion |      |     |
|                  |   |   |     |              |  ^6^ |      |     |
+------------------+---+---+-----+--------------+------+------+-----+
| Continuous       | P | \ | C   | Minimize     | For  | Any  | \   |
| Incineration     | C | ~ | ont | chlorinated  | o    | ex   | >99 |
|                  | 0 | 1 | inu | wastes;\     | xida | cept |     |
|                  | 3 | 1 | ous | Particle     | tion | vola |     |
|                  |   |   |     | diameter \<  | &    | tile |     |
|                  |   | ^ |     | 1 cm for     | re   | me   |     |
|                  |   | 2 |     | fluidized    | duct | tals |     |
|                  |   | ^ |     | bed          | ion  |      |     |
|                  |   |   |     | combustion   | [^6] |      |     |
+------------------+---+---+-----+--------------+------+------+-----+
| High Temperature | P | \ | Eit | Smaller      | None | Any  | \   |
| Gasification     | C | ~ | her | particles    |      |      | >99 |
|                  | 0 | 1 |     | are          |      |      |     |
|                  | 4 | 1 |     | preferred    |      |      |     |
|                  |   |   |     |              |      |      |     |
|                  |   | ^ |     |              |      |      |     |
|                  |   | 2 |     |              |      |      |     |
|                  |   | ^ |     |              |      |      |     |
+------------------+---+---+-----+--------------+------+------+-----+
| Indirect         | P | \ | Eit | Waste size   | A    | Any  | 60  |
| Electrochemical  | C | ~ | her | \< 10 µm     | r    |      | -95 |
| Oxidation        | 0 | 1 |     | (            | edox |      |     |
|                  | 5 | 1 |     | preferred);\ | co   |      |     |
|                  |   |   |     | Feedstock in | uple |      |     |
|                  |   | ^ |     | aqueous      |      |      |     |
|                  |   | 2 |     | slurry       |      |      |     |
|                  |   | ^ |     |              |      |      |     |
+------------------+---+---+-----+--------------+------+------+-----+
| Lyophilization   | P | 6 | Ba  | None         | None | Any  | 90  |
| (Freeze Drying)  | C | . | tch |              |      | m    | [   |
|                  | 0 | 0 |     |              |      | oist | ^7] |
|                  | 6 |   |     |              |      | sl   |     |
|                  |   |   |     |              |      | udge |     |
+------------------+---+---+-----+--------------+------+------+-----+
| Magnetically     | P | 1 | Eit | Feedstock in | \--  | Any  | \-- |
| Assisted         | C | 2 | her | aqueous      |      | ex   |     |
| Ga               | 0 | . |     | slurry;      |      | cept |     |
| sification (MAG) | 7 | 0 |     | C            |      | me   |     |
|                  |   |   |     | oncentration |      | tals |     |
|                  |   |   |     | may be       |      |      |     |
|                  |   |   |     | dilute       |      |      |     |
+------------------+---+---+-----+--------------+------+------+-----+

Table 11 cont. Feedstock Requirements and Process Characteristics for
Physicochemical Waste Technologies

+----------------+---+-----+-----+--------------+-------+------+-----+
| Name           | A | So  | P   | Pr           | Cata  | Wa   | P   |
|                | p | lid | roc | eprocessing\ | lyst/ | ste\ | erc |
|                | p | Wa  | ess | Issues       | Orga  | Str  | ent |
|                | . | ste | T   |              | nisms | eam\ | age |
|                |   | F   | ype |              |       | Com  | of  |
|                | A | eed |     |              |       | posi | Wa  |
|                | c | R   |     |              |       | tion | ste |
|                | c | ate |     |              |       |      | C   |
|                | . | \[  |     |              |       |      | onv |
|                | \ | kg/ |     |              |       |      | ert |
|                | N | d\] |     |              |       |      | ed\ |
|                | o |     |     |              |       |      | \   |
|                | . |     |     |              |       |      | [Wt |
|                |   |     |     |              |       |      | %\] |
+----------------+---+-----+-----+--------------+-------+------+-----+
| Plasma Arc     | P | \~  | Ba  | Dewatering   | None  | Any  | 84  |
| Thermal        | C | 11  | tch | of moist     |       | ex   | -98 |
| Destruction    | 0 | ^2^ |     | wastes\      |       | cept |     |
|                | 9 |     |     | is preferred |       | me   |     |
|                |   |     |     |              |       | tals |     |
+----------------+---+-----+-----+--------------+-------+------+-----+
| Pyrolysis in   | P | \~  | C   | Feed with    | None  | Unk  | 99  |
| Sub-Critical   | C | 11  | ont | 40% solid    |       | nown |     |
| Water          | 1 | ^2^ | inu | content      |       |      |     |
|                | 0 |     | ous |              |       |      |     |
+----------------+---+-----+-----+--------------+-------+------+-----+
| Pyrolysis      | P | 6   | Ba  | None         | SE    | Org  | 100 |
|                | C | -24 | tch |              | ROGEL | anic |     |
|                | 1 |     |     |              |       | w    |     |
|                | 1 |     |     |              |       | aste |     |
+----------------+---+-----+-----+--------------+-------+------+-----+
| Supercritical  | P | 1   | Eit | Particle     | Agent | Any  | 100 |
| Water          | C | 0.9 | her | diameter \<  | for   |      |     |
| Oxidation      | 1 |     |     | 100 µm;\     | N~2~O | (ex  |     |
| (SCWO)         | 2 |     |     | Feed stream  | dec   | cept |     |
|                |   |     |     | 4-15 wt%     | ompos | me   |     |
|                |   |     |     | solids;      | ition | tal) |     |
|                |   |     |     | Organic      |       |      |     |
|                |   |     |     | chlorides \< |       |      |     |
|                |   |     |     | 1.5 wt% dry  |       |      |     |
+----------------+---+-----+-----+--------------+-------+------+-----+

## 5.2 Process Parameters and Equipment Attributes

The second series of tables provides the ranges for the characteristic
process parameters and overall values for the physical requirements
associated with each technology. The temperature and pressure ranges
refer to the range of values normally associated within any of a
technology's processors. The residence time reflects the range within
the overall process as recorded on the workshop data form. Mass, power,
volume, cooling and logistics values define the physical dimensions and
required utilities for each technology.

Pre- and post-processing technologies, presented in Table 12, generally
operate at ambient conditions with residence times of less than an hour.
Generally, pre- and post-processing technologies require little power or
cooling and their primary cost is mass. Unfortunately, as noted above,
such technologies do not convert any waste products to useful life
support system commodities but simply alter the physical size or
moisture content.

Biological processes, given in Table 13, generally operate at
near-ambient temperatures and pressures, although residence times are
longer, often ranging from a half-week up to three weeks. Physically,
biological processes require little power or cooling per processor
volume. Unfortunately, biological processors are usually voluminous in
order to contain the associated process streams for extended residence
times. This loading in-turn, implies some unknown power consumption and
heat generation. Some individual biological technologies require higher
pressure and/or temperature with correspondingly greater power and
thermal requirements.

Physicochemical processes, Table 14, generally employ short residence
times but often operate at elevated temperatures and/or pressures.
Physically, physicochemical processes generally use higher power and,
correspondingly, generate higher cooling loads. Though not universal,
physicochemical processing equipment can often be compact and require
little mass. While the above comments are generally true, a closer
examination of Table 14 reveals many technologies that operate at
temperatures and pressures closer to ambient conditions.

Table 12. Process Parameters and Equipment Attributes for Pre- and
Post-Processing Waste Technologies

<table>
<colgroup>
<col style="width: 25%" />
<col style="width: 5%" />
<col style="width: 9%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Name</td>
<td><p>App.</p>
<p>Acc.<br />
No.</p></td>
<td>Temperature Range<br />
[K]</td>
<td>Pressure Range<br />
[kPa]</td>
<td>Residence Time<br />
[hr]</td>
<td>Total Mass<br />
[kg]</td>
<td>Total Power<br />
[kW]</td>
<td>Total Volume<br />
[m³]</td>
<td>Total Cooling<br />
[kW]</td>
<td>Logistics Mass<br />
[kg/yr]</td>
<td>Logistics Volume [m³/yr]</td>
</tr>
<tr class="even">
<td>Collection, Transport, Vacuum Waste Collection</td>
<td>PPP<br />
01</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>31.0</td>
<td>0.22</td>
<td>0.18</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Bulk Compaction</td>
<td>PPP<br />
02</td>
<td>n/a</td>
<td>n/a</td>
<td>n/a</td>
<td>15.1</td>
<td>0.1</td>
<td>0.35</td>
<td>--</td>
<td>1.8</td>
<td>1.8</td>
</tr>
<tr class="even">
<td>Dry Size Reduction and Particle Size Control</td>
<td>PPP<br />
03</td>
<td>248-348</td>
<td>76-126</td>
<td>&lt;&lt;&lt;1</td>
<td>100</td>
<td>2</td>
<td>3.5</td>
<td>--</td>
<td>32.5</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Drying (Forced Air Thermal Convection, Forced Air, Thermal Vacuum,
and Freeze Vacuum)</td>
<td>PPP<br />
04</td>
<td>&lt;273 to 363</td>
<td>&lt; 10<sup>-3</sup> to 101</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Pneumatic Transport ‑ Dry Material</td>
<td>PPP<br />
05</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>25</td>
<td>0.2</td>
<td>0.3</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Screw Conveyor</td>
<td>PPP<br />
06</td>
<td>Ambient</td>
<td>Ambient</td>
<td>--</td>
<td>22</td>
<td>0.2</td>
<td>0.40</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Slurry Pumping</td>
<td>PPP<br />
07</td>
<td>n/a</td>
<td>n/a</td>
<td>n/a</td>
<td>25</td>
<td>0.2</td>
<td>0.5</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Solid/Liquid Blending; Slurrying (50‑95% Water)</td>
<td>PPP<br />
08</td>
<td>Ambient</td>
<td>Ambient</td>
<td>&lt;1</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Solid/Solid Blending</td>
<td>PPP<br />
09</td>
<td>Ambient</td>
<td>Ambient</td>
<td>&lt;1</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Storage</td>
<td>PPP<br />
10</td>
<td>Ambient</td>
<td>Ambient</td>
<td>n/a</td>
<td>&lt;50</td>
<td>n/a</td>
<td>0.01-2.0</td>
<td>n/a</td>
<td>n/a</td>
<td>n/a</td>
</tr>
<tr class="even">
<td>Wet Size Reduction and Particle Size Control</td>
<td>PPP<br />
11</td>
<td>278-523</td>
<td>76-740</td>
<td>&lt;1-2</td>
<td>223.5</td>
<td>16</td>
<td>5.15</td>
<td>14.4</td>
<td>45.0</td>
<td>0.9</td>
</tr>
</tbody>
</table>

Table 13. Process Parameters and Equipment Attributes for Biological
Waste Technologies

<table style="width:100%;">
<colgroup>
<col style="width: 23%" />
<col style="width: 5%" />
<col style="width: 10%" />
<col style="width: 9%" />
<col style="width: 8%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Name</td>
<td><p>App.</p>
<p>Acc.<br />
No.</p></td>
<td>Temperature Range<br />
[K]</td>
<td>Pressure Range<br />
[kPa]</td>
<td>Residence Time<br />
[hr]</td>
<td>Total Mass<br />
[kg]</td>
<td>Total Power<br />
[kW]</td>
<td>Total Volume<br />
[m³]</td>
<td>Total Cooling<br />
[kW]</td>
<td>Logistics Mass<br />
[kg/yr]</td>
<td>Logistics Volume [m³/yr]</td>
</tr>
<tr class="even">
<td>Aerobic Completely Mixed (Slurry) Reactor</td>
<td>B01</td>
<td>293-313</td>
<td>20.3-1,013.3</td>
<td>24-1,152</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Composting - Plant Nutrient Extraction Variant ‑ 7 Day Residence
Time (No Curing Stage/Biofilter)</td>
<td>B02</td>
<td>293-333</td>
<td>50-110</td>
<td>120-216</td>
<td>346.3</td>
<td>Very Small</td>
<td>1.25</td>
<td>--</td>
<td>None</td>
<td>None</td>
</tr>
<tr class="even">
<td>Composting - Plant Nutrient Extraction Variant
‑ 21 Day Residence Time</td>
<td>B03</td>
<td>293-333</td>
<td>50-110</td>
<td>456-552</td>
<td>1,001.3</td>
<td>Very Small</td>
<td>3.46</td>
<td>--</td>
<td>None</td>
<td>None</td>
</tr>
<tr class="odd">
<td>Fixed-Film Bioreactor</td>
<td>B04</td>
<td>298-318</td>
<td>101</td>
<td>1-6</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>High-Solids Leach Bed<br />
Anaerobic Digestion</td>
<td>B05</td>
<td>290-356</td>
<td>85.6-104.7</td>
<td>605-740</td>
<td>--</td>
<td>--</td>
<td>2.6-4.2</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Paper and Biomass to Products, e.g., ethanol</td>
<td>B06</td>
<td>440-510</td>
<td>100-4,500</td>
<td>8-96</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Single Cell Protein Production and Crop Nutrient Recovery</td>
<td>B07</td>
<td>285-320</td>
<td>50-150</td>
<td>144-360</td>
<td>80</td>
<td>0</td>
<td>1.4</td>
<td>n/a</td>
<td>--</td>
<td>--</td>
</tr>
</tbody>
</table>

Table 14. Process Parameters and Equipment Attributes for
Physicochemical Waste Technologies

<table>
<colgroup>
<col style="width: 24%" />
<col style="width: 4%" />
<col style="width: 9%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 7%" />
<col style="width: 7%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Name</td>
<td><p>App.</p>
<p>Acc.<br />
No.</p></td>
<td>Temperature Range<br />
[K]</td>
<td>Pressure Range<br />
[kPa]</td>
<td>Residence Time<br />
[hr]</td>
<td>Total Mass<br />
[kg]</td>
<td>Total Power<br />
[kW]</td>
<td>Total Volume<br />
[m³]</td>
<td>Total Cooling<br />
[kW]</td>
<td>Logistics Mass<br />
[kg/yr]</td>
<td>Logistics Volume [m³/yr]</td>
</tr>
<tr class="even">
<td>Activated Carbon and Energy from Cellulosic Waste By-Products using
the TRAC™ Process</td>
<td><p>PC</p>
<p>01</p></td>
<td>300-1,200</td>
<td>100-105 <a href="#fn1" class="footnote-ref" id="fnref1"
role="doc-noteref"><sup>1</sup></a></td>
<td>1.4-3.6</td>
<td>26.7</td>
<td>31.0</td>
<td>0.116</td>
<td>110.7</td>
<td>54,728.1</td>
<td>223.2</td>
</tr>
<tr class="odd">
<td>Batch Incineration</td>
<td><p>PC</p>
<p>02</p></td>
<td>1,000-1,300</td>
<td>101</td>
<td>0-3</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Continuous Incineration</td>
<td><p>PC</p>
<p>03</p></td>
<td>1,000-1,250</td>
<td>113-121</td>
<td>&lt;&lt;1</td>
<td>303.0</td>
<td>6.6</td>
<td>4.53</td>
<td>7.1</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>High Temperature Gasification</td>
<td><p>PC</p>
<p>04</p></td>
<td>1,300-1,700</td>
<td>101</td>
<td>&lt;1</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Indirect Electrochemical Oxidation</td>
<td>PC05</td>
<td>320-370</td>
<td>101</td>
<td>--</td>
<td>3,310</td>
<td>20</td>
<td>5.1</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Lyophilization (Freeze Drying)</td>
<td><p>PC</p>
<p>06</p></td>
<td>230-298</td>
<td>0.01-101.3</td>
<td>10-40</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>7.3</td>
<td>0.004</td>
</tr>
<tr class="even">
<td>Magnetically Assisted Gasification (MAG)</td>
<td><p>PC</p>
<p>07</p></td>
<td>400-1,000</td>
<td>--</td>
<td>--</td>
<td>50?</td>
<td>1.0?</td>
<td>2?</td>
<td>?</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Peroxide Oxidation</td>
<td><p>PC</p>
<p>08</p></td>
<td>800-1,100</td>
<td>101-300</td>
<td>0.5-1.0</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Plasma Arc Thermal Destruction</td>
<td><p>PC</p>
<p>09</p></td>
<td>1,100-1,700 <a href="#fn2" class="footnote-ref" id="fnref2"
role="doc-noteref"><sup>2</sup></a></td>
<td>101-101.3</td>
<td>&lt;&lt;&lt;1</td>
<td>1,150</td>
<td>34.8</td>
<td>3.9</td>
<td>38.1</td>
<td>2.74</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Pyrolysis in Sub-Critical Water</td>
<td><p>PC</p>
<p>10</p></td>
<td>523-573</td>
<td>10,000</td>
<td>0.2</td>
<td>6</td>
<td>2</td>
<td>0.001</td>
<td>--</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="even">
<td>Pyrolysis</td>
<td><p>PC</p>
<p>11</p></td>
<td>900-1,300</td>
<td>500-2,000</td>
<td>0.5-2</td>
<td>25-60</td>
<td>0.6</td>
<td>0.002</td>
<td>0.4</td>
<td>--</td>
<td>--</td>
</tr>
<tr class="odd">
<td>Supercritical Water Oxidation (SCWO)</td>
<td><p>PC</p>
<p>12</p></td>
<td>775-973</td>
<td>23,500-26,000</td>
<td>0.01-0.03</td>
<td>613</td>
<td>0.65</td>
<td>0.289</td>
<td>1.4-3.4</td>
<td>--</td>
<td>--</td>
</tr>
</tbody>
</table>
<aside id="footnotes" class="footnotes footnotes-end-of-document"
role="doc-endnotes">
<hr />
<ol>
<li id="fn1"><p><sup>8</sup> The char pelletization step operates at
pressures between 2,000 and 12,000 kPa.<a href="#fnref1"
class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn2"><p><sup>9</sup> Torch temperatures are 3,000 to 7,000 K for
this operating temperature range.<a href="#fnref2" class="footnote-back"
role="doc-backlink">↩︎</a></p></li>
</ol>
</aside>

**5.3 Technology Readiness and Development Cost**

Table 15, Table 16, and Table 17, provide information on technology
readiness and anticipated costs associated with increasing the
technology readiness to develop test articles for integrated human test
scenarios. These tables provide the current technology readiness level
(TRL), the cost, in millions of dollars, \$M, to develop a technology to
a TRL of 5 so that it is ready for testing in an integrated human test.
The last two columns provide the estimated cost and time to fabricate a
test article once the technology is developed to a TRL of 5.

Overall, the data in these tables is scattered and incomplete. However,
from the data available, the development and fabrication costs
associated with the biological technologies appear to be less expensive
by a factor of two compared with the physicochemical technologies.

Table 15. Technology Readiness for Pre- and Post-Processing Waste
Technologies

+--------------------------+-------+-------+-------+-----------+------+
| Name                     | App.  | Cu    | Cost  | System    | Time |
|                          |       | rrent | to    | Cost at   | to   |
|                          | Acc.\ | TRL   | TRL   | TRL 5     | TRL  |
|                          | No.   |       | 5\    | \[\$M\]   | 5\   |
|                          |       |       | \[    |           | \[   |
|                          |       |       | \$M\] |           | yr\] |
|                          |       |       |  ^10^ |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Collection, Transport,   | ^11   | 4     | \--   | \--       | \--  |
| Vacuum Waste Collection  | ^PPP\ |       |       |           |      |
|                          | 01    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Bulk Compaction          | PPP\  | 4     | 0.20  | 0.06      | 1    |
|                          | 02    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Dry Size Reduction and   | PPP\  | 3     | 0.40  | 0.50      | 1    |
| Particle Size Control    | 03    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Drying (Forced Air       | PPP\  | 3-4   | \--   | \--       | \--  |
| Thermal Convection,      | 04    |       |       |           |      |
| Forced Air, Thermal      |       |       |       |           |      |
| Vacuum, and              |       |       |       |           |      |
| Freeze Vacuum)           |       |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Pneumatic Transport      | PPP\  | 4     | \--   | \--       | \--  |
| ‑ Dry Material           | 05    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Screw Conveyor           | PPP\  | 4     | \--   | \--       | \--  |
|                          | 06    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Slurry Pumping           | PPP\  | 4     | \--   | \--       | \--  |
|                          | 07    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Solid/Liquid Blending;   | PPP\  | 2-3   | 0.15  | \--       | 1-2  |
| Slurrying (50‑95% Water) | 08    |       | -0.25 |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Solid/Solid Blending     | PPP\  | 2-3   | 0.15  | \--       | 1-2  |
|                          | 09    |       | -0.25 |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Storage                  | PPP\  | 7     | \--   | \--       | \--  |
|                          | 10    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+
| Wet Size Reduction and   | PPP\  | 2-3   | 0.40  | 0.50      | 1    |
| Particle Size Control    | 11    |       |       |           |      |
+--------------------------+-------+-------+-------+-----------+------+

Table 16. Technology Readiness for Biological Waste Technologies

  ----------------------------- ------- --------- ---------- --------- --------
  Name                          App.\   Current   Cost to    System    Time to
                                Ref.    TRL       TRL 5\     Cost at   TRL 5\
                                                  \[\$M\]    TRL 5\    \[yr\]
                                                             \[\$M\]   

  Aerobic Completely            B01     4         \--        \--       \--
  Mixed (Slurry) Reactor                                               

  Composting - Plant Nutrient   B02     4         0.40       \--       2
  Extraction Variant                                                   
  ‑ 7 Day Residence Time                                               
  (No Curing Stage/Biofilter)                                          

  Composting - Plant Nutrient   B03     4         0.50       \--       2-3
  Extraction Variant                                                   
  ‑ 21 Day Residence Time                                              

  Fixed-Film Bioreactor         B04     2         \--        0.60      3-5

  High-Solids Leach Bed\        B05     4         0.50       \--       0.5-1
  Anaerobic Digestion                                                  

  Paper and Biomass to          B06     2-3       \--        \--       2-4
  Products, e.g., ethanol                                              

  Single Cell Protein           B07     3         \--        \--       3
  Production                                                           
  and Crop Nutrient Recovery                                           
  ----------------------------- ------- --------- ---------- --------- --------

Table 17. Technology Readiness for Physicochemical Waste Technologies

  ----------------------------- ------- --------- ----------- ----------- --------
  Name                          App.\   Current   Cost to TRL System Cost Time to
                                Ref.    TRL       5\          at TRL 5\   TRL 5\
                                                  \[\$M\]     \[\$M\]     \[yr\]

  Activated Carbon and Energy   PC01    3         0.60        0.35        0.5
  from Cellulosic Waste                                                   
  By-Products using                                                       
  the TRAC™ Process                                                       

  Batch Incineration            PC02    2-3       \--         \--         \--

  Continuous Incineration       PC03    4         0           0           n/a

  High Temperature Gasification PC04    2         \--         \--         \--

  Indirect Electrochemical      PC05    4         5.00        2.00        3
  Oxidation                                                               

  Lyophilization (Freeze        PC06    2         \--         \--         3
  Drying)                                                                 

  Magnetically Assisted         PC07    1-2       0.60        0.06-1.00   3-6
  Gasification (MAG)                                                      

  Peroxide Oxidation            PC08    1         \--         \--         \--

  Plasma Arc Thermal            PC09    3-4       \--         \--         \--
  Destruction                                                             

  Pyrolysis in Sub-Critical     PC10    \--       \--         \--         \--
  Water                                                                   

  Pyrolysis                     PC11    3         0.50        0.60        2

  Supercritical Water Oxidation PC12    3-4       1.00-5.00   1.00-2.00   1-2
  (SCWO)                                                                  
  ----------------------------- ------- --------- ----------- ----------- --------

# 

# 

# 6. FUTURE DIRECTIONS

The main objective of the workshop was to assess solid waste processing
technologies to develop the SWPRR strategy for NASA's Advanced Life
Support (ALS) program. The strategy will consist of a detailed
technology development implementation plan that describes how the best
technologies will be selected and how these technologies will be further
developed for use in future human missions beyond the International
Space Station. The workshop results (Volume II-Appendix) will be used
to 1) develop system-level models, 2) perform analyses for determination
of optimum solid waste processing systems and 3) identify research and
technology development (R&TD) gaps associated with these technologies.
As mentioned, the workshop results show that most of these technologies
(except storage) are lower than a technology readiness level of five.
The technical issues associated with bringing the SWPRR technologies to
a TRL of 5 for the various mission scenarios will be described,
prioritized and identified with a timeline for executing the development
process in a SWPRR Implementation Plan.

The next step is to outline the implementation plan for NASA's ALS
Project solid waste processing efforts. The plan will facilitate getting
from the present state of technology to determining, designing,
manufacturing, and testing the solid waste processing technology
necessary for future human missions. This plan will direct, focus, and
map efforts among the different participants (ALS, particularly SMAP and
R&TD, and test article developers).

Figure 16 outlines the priorities and development timeline over the next
twenty years. This assumes an initial human mission to Mars in 2018,
although this date is speculative. The integrated testing and validation
of solid waste processing technologies shown in the roadmap and timeline
are consistent with this date. Ground testing will be accomplished using
the BIO-Plex test bed.

![](media/image16.wmf){width="5.998611111111111in"
height="3.397222222222222in"}

**Figure 16. Timeline for Development of Life Support Technology**

The implementation plan should include the following:

1.) Definition of potential future human missions beyond Space Station,
emphasizing realistic missions and human-rated testing (e.g., BIO-Plex).
These missions need to be defined so that we can estimate the wastes
produced and the potential resources to be recovered and identify the
interfaces with other systems -- particularly water, air, and food.

> 2.) Identification of analyses to evaluate and identify the "best"
> technologies needed for the two major environments in which ALS
> systems must operate - microgravity and/or hypogravity.
>
> 3.) Map of ALS Project solid waste processing priorities and
> justification of these priorities based on analysis of data (e.g.,
> identification of technology "gaps" and integration issues associated
> with solid waste processing).
>
> 4.) Identify how to maintain solid waste R&TD balance across TRL
> levels, as shown in Figure 17. This will ensure that both the basic
> research needed for the development of new technologies and the
> development of "best" technologies are represented.
>
> 5.) A timeline of solid waste project events including major and minor
> milestones.
>
> 6.) Relevant quantitative/qualitative data or metrics SMAP will use to
> analyze different scenarios.

7.) Method for incorporating updates to the implementation plan on an
annual basis.

8.) Definition of the solid waste group's roles and responsibilities.

9.) Method for updating solid waste technology assessment document as
needed.

> ![](media/image17.wmf){width="5.997222222222222in"
> height="3.9854166666666666in"}

**Figure 17. The ALS Project Maintains a Balance of Activities Across
Technology Readiness Levels 1 Through 6.**

In conclusion, the implementation plan will provide the strategy for
guiding both the priorities and direction in ALS solid waste research
and development by specifically charting how technologies need to be
researched and developed. This plan will assist in determining the call
for proposals in the NASA Research Announcement (NRA), Small Business
Innovative Research (SBIR) , and Small Business Technology Transfer
(STTR) proposal process. Researchers and technology developers outside
of ALS will be able to determine whether their technology fits into the
overall scope of the solid waste processing implementation plan.

**7. ACRONYMS**

ALS Advanced Life Support

App. Acc. No. Appendix Accession Number

BET Brunauer, Emmet and Teller Isotherm

Bio Biological

CSTR Continuous Stirred Tank Reactor

DSA Dimensionally Stable Anode

FFB Fixed Film Bioreactor

HRT Hydraulic Retention Time

NRA NASA Research Announcement

PC Physicochemical

PPP Pre- and Post Processing

R&TD Research and Technology Development

SBIR Small Business Innovation Research

SCP Single Cell Protein

SCWO Supercritical Water Oxidation

SEBAC Sequential Batch Anaerobic Composting

SMAP Systems Analysis Modeling Project

STTR Small Business Technology Transfer

SWPRR Solid Waste Processing Resource Recovery

TRL Technology Readiness Level

VOCs Volatile Organic Compounds

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9.  **ACKNOWLEDGEMENT**

######### The Solid Waste Processing Resource Recovery Workshop would not have been possible without the hard work and diligence of all the workshop participants. These specialists in all areas for the handling and treatment of wastes provided the necessary expertise needed to perform the technology assessments. Special appreciation is extended to all the participants. A list of the participants is in the Appendix -- Volume II. Special appreciation is extended to the respective group leads that did a superb job in directing and executing the completion of the technology assessments in the allotted timeframe. They include Mr.George Savage (CalRecovery, Inc, Concord, CA), Dr. Harold Keener (Ohio Agricultural Research Development Center, Ohio State University) and Dr. Duncan Hitchens (Lynntech, Inc., College Station, TX). Thanks and recognition are given to Mr. John Keener and Anthony Hanford and Bruce Gertner (Lockheed-Martin) for their excellent work in developing the workshop assessment form and providing the technical information necessary for performing the technology assessments. The authors would like to extend their thanks and appreciation to the reviewers for all the improvements made to the preliminary draft report document. Many of the reviewers have been previously acknowledged with the exceptions of Dr. Alan Drysdale (Boeing), Dr. John Hogan (NJ-NSCORT) and Dr. Anthony Hanford (Lockheed-Martin). Finally, the authors would like to give special recognition and thanks to the following individuals for their fine support and participation at the workshop: Astronaut Shannon Lucid (JSC), Dr. Joan Vernikos (NASA Headquarters (HQ) Director of NASA Office of Life and Microgravity Science and Applications Division), Dr. Guy Fogelman (Human Support Technologies Lead at NASA HQ), Al Behrend (JSC -- ALS Program Manager), Dr. Don Henninger (New ALS Program Manger), Dr. Charlie Barnes (NASA Headquarters), Mark Kliss (Ames Research Center), Richard L. Sauer (JSC), Hubert Brasseaux (JSC), Trista Wagoner (NASA-HQ), Joy King (InDyne, Inc.), Crystal Rucker (InDyne, Inc.), Rachel Miller (InDyne, Inc.) and Chantel Whatley (JSC). 

[^1]: ^1^ These are the Technology Appendix Accession Numbers used as
    identifiers for each technology that is listed in the Appendix.

    ^2^ This feed rate is based on the waste model. If operated
    continuously, equipment employing this technology could process more
    waste per day.

[^2]: ^3^ Will this process be a batch or continuous process within a
    near-term life support system.

[^3]: ^4^ The information here assumes permanent storage of the waste
    for the duration of the mission. For temporary storage as a
    precursor to further processing, additional restrictions may apply
    as defined by the processing steps.

[^4]: ^3^

[^5]: ^5^ This technology accepts 8.49 kg/d of dry waste but the actual
    feed is 40.75 kg/d including moisture and recycled compost.

[^6]: ^6^ This process also requires catalysts and other agents to clean
    process effluent streams.

[^7]: ^7^ This is the percentage of water recovered from waste products
    but the waste itself is not coverted.