### An Envirogen Technologies Whitepaper August 2011

1 

# Treatment of Selenium

- Containing Coal Mining Wastewater with Fluidized Bed Reactor Technology

Proven Systems Provide Major Cost Advantages and “Best

- in

- Class” Performance

An Envirogen Technologies Whitepaper | August 2011Treatment of Selenium

- Containing Coal Mining Wastewaters 2



### Introduction

In the coal mining industry today, selenium
, in its many forms
, is gaining attention. New regulations covering selenium discharge are either in place or being developed

. It has been said that handling selenium wastes will increasingly become a limiting factor on the ability of the coal mining industry to grow. While a number of physical/chemical approaches show promise in selenium treatment, when considering optimal cost and treatment efficacy issues, biological treatment

– particularly fixed

- film biological
tr eatment

- is one of the most promising approaches to managing selenium

- containing wastewaters. Envirogen Technologies offers a patented fixed

- film fluidized bed reactor (FBR) biological treatment technology that has been proven as a „best in class‟ approac h for handling medium to high flow rates of
selenium

- containing wastewater. Envirogen FBR technology has several distinct features that make it ideally suited for the coal mining industry.

The noteworthy features of Envirogen FBR technology include its ab ility to consistently reduce
selenium levels to less than 5 μg/L , shorter required
residence times for treatment and a smaller overall footprint. Its flexibility in the choice of electron donor chemicals can translate into capital and operating cost savings with reduced solids generation. It also responds well to c hanges in feed flow and composition, consistently achieving discharge limit conditions. In addition, these systems can be modular, with all

- weather protection where desired. These features, combined with decades of experience by Envirogen‟s team, allow the design and installation of FBR systems with capital costs that are a fraction of the cost of competitive fixed

- film biological systems.



### The selenium dilemma
Waste rock is generally the primary source of selenium in coal mining operations. When exposed to water, various selenium species will leach or migrate from the rock and enter the environment. Selenium

occurs in various valence s tates from

- 2 to +6. The speciation of selenium plays a critical ro le in the effectiveness of any approach for removal, esp ecially to low levels. I n aqueous environments, selenium is most often fou nd as the oxygenated anions of selenite, Se(IV) and selenate, Se(VI)

. S elenium in mine
runoff most often occurs in the soluble form

. Selenium is commonly found in mining wastewaters in concentrations ranging from 3 to >12,000 μg/L. The US National Primary Drinking Water Standard MCL is 50 μg/L for selenium. The National Fresh Water Quality Standard is 5 μg/L for selenium. The U.S. FishTreatment of Selenium

- Containing Coal Mining Wastewaters 3

and Wildlife Se rvice has recommended that the N a tional F resh W ater Q uality S tandard be lowered to 2 μg/L to protect fish, waterfowl, and endangered aquatic species. Several states have followed with
enforcement actions at these same low levels. In Canada, permits may require stakeholders to monitor
leve ls in water or biota, or to comply with Canadian Water Quality Guidelines of 1 μg/L in surface waters. Province and local regulations may vary from these requirements.

Treatment of selenium in coal mining wastewaters presents a series of challenges. It ca n be present in relatively dilute concentrations and in streams with variable and often high flow rates. It is present in many soluble and particulate forms, which may affect process design and treatability.
The conditions of influent selenium

- containing

w astewaters can vary widely, with issues such as temperature, pH , total dissolved solids and other contaminants present
, affecting the ability to selectively and economically remove selenium. Treatment of selenium often results in the generation of a
concent rated by

- product requiring disposal, and re

- release from residuals can occur. Beyond these issues, the physical environment of coal mining operations offers challenges such as remoteness and harsh and/or cold weather. Currently available selenium treatment technology (Table 1) includes biological treatment and a number of physical

- chemical processes

– such as ion exchange, membrane filtration and adsorption

– that vary widely in eff iciency and cost. Most treatment options remain either too costly and/or unp roven for selenium

- containing waste streams for reasons that include removal levels
, variability in volume and composition of influents, system sizing and logistics considerations, as well as operating requirements.



### Table 1

Overview of Technologies for Re moval of Selenium in Water
Physical Chemical Biological
Reverse osmosis Iron co

- precipitation Algal

- bacterial Se removal
Nanofiltration Zero valent iron Algal volatilization Ion exchange Cupric co

- precipitation Heterotrophic microbial reduction
Ferrih ydrite adsorption Electrocoagulation Constructed wetlands Activated alumina adsorption Enhanced cementation Phytoremediation
Photoreduction
C arbohudrazideTreatment of Selenium

- Containing Coal Mining Wastewaters 4



### Biological Treatment of Selenium

- Containing Wastewaters

Biological treatment of selenium

- cont aining wastewaters has been an area of significant interest in the coal mining community recently. In general, biological treatment offers a low cost alternative to more expensive physical and chemical treatment methods and is effective in cold climates. Additionally, it has the proven ability to meet regulatory selenium limits.

Biological systems catalyze the reduction of selenium. Selenate can be reduced to selenite, and both
selenate and selenite can be reduced to elemental selenium.



### SeO 4 2

- 

### + organic carbon → SeO 3 2

- 

### + organic carbon → Se 0 

### + CO 2 

### + H 2 

### O

Th ese reaction s are desirable because elemental selenium is virtually insoluble and therefore can be removed from the environment through conventional liquid/ solids separation and disposal. In biological
treatme nt, the conversion of selenium anions to elemental selenium is accomplished via biologically catalyzed reduction. Selenium

- reducing bacteria (Figure 1) are considered heterotrophic. They utilize organic carbon as their electron donor and selenate/selenite as their electron acceptors. Commonly used electron donor materials include methanol, acetate, citric acid and molasses. New „designer‟ electron donors, generally composed of complex carbohydrates and organic process by

- products that have been proven effective for selenium reduction and precipitation
, are also available.

Figure 1: Selenium Reduction & Precipitation

One of the major issues in biological treatment of selenium is the presence of other anions in the influent streams. Both oxygen and nitrate are mo re favorable electron acceptors than oxidized forms of selenium. Figure 2 shows common anions and their order of biological reduction based on ORP. The order use of electron acceptors follows the more energetically favorable reactions first. Also, reductio n enzyme systems appear to have evolved such that reduction enzymes are generally inhibited by electron acceptors that are more energetically favorable, particularly if the microorganism contains more than one reduction system.Treatment of Selenium

- Containing Coal Mining Wastewaters 5

Fig ure 2: Redox Profile of B iological Reduction

From a practical standpoint, these relationships are critical. The presence of eith er oxygen or nitrate will
limit selenium reduction. Even in anoxic biological systems, the presence of nitrates is an important consideration in syst em design and the selection of microorganisms and electron donors. Many coal mining wastewaters contain high levels of nitrate that will be preferentially reduced before selenium
, and
must be removed before effective selenium reduction will occur. Sufficie nt electron donor material is required to reduce both nitrate and selenium. Th e FBR process offers the potential benefit of denitrification and selenium reduction in a single step.

Active, fixed

- film biological treatment systems have received significant a ttention from researchers and the coal mining community because of their potential to work with a broad range of selenium
concentrations in wastewaters

– including very dilute streams

– and for their ability to reduce selenium to very low levels . Th ese out comes are due to the fact that the heterotrophic bacteria are retained in the bioreactor for relatively long periods of time, improving the chance that they will come in contact with the
contaminants and the ability of these systems to control reaction conditions more precisely. Additionally, because of the tendency of the microbes to attach to the solid media and to form dense biomass films, these reactors can have high biomass concentrations. This is especially the case with the Envirogen FBR
technolo gy.Treatment of Selenium

- Containing Coal Mining Wastewaters 6

Today, there are two different types of active, fixed

- film systems that have received significant field testing
with selenium

- containing coal mining wastewaters

– the fixed

- film downflow filter (also known as a „packed bed reactor‟

– PBR) and the fluid ized bed reactor (FBR). In evaluating active, fixed

- film bioreactor technology, the following issues are salient in choosing one of these approaches:

 Treatment efficacy/efficiency

 Hydraulic residence times

 System footprint

 Flexibility in handling variab le & high flow rates

 Flexibility with electron donor material  Ability to handle solids & metals

 Recovery from upsets

 Track record of technology

 Cost of capital

 Cost of operation

 Ease of operation
The remainder of this paper will present information relate d to Envirogen Technologies‟ fluidized bed reactor technology

– and where applicable, compare and contrast technical and operating features with packed bed reactor technology.



### Envirogen Fluidized Bed Reactor Technology Proven technology with critical adva ntages for the coal industry

Envirogen‟s FBR is a n active, fixed

- film bioreactor that fosters the growth of microorganisms on a hydraulically f luidized bed of fine media. In this type of reactor, a fluid is passed through a granular solid material at
veloc ities sufficient to suspend or fluidize the solid media.

In Envirogen FBR systems, media types include sand and activated carbon media that are manufactured to exacting specifications for hardness, shape, size, uniformity, density and impurity levels. The small
fluidized media in the FBR provide a n extremely large active surface area upon whic h microorganisms can grow while treating co ntaminants. A large biomass inventory is produced while maintaining thin films, reducing

mass transfer limitations and offe ring high volumetric efficiency

.
Envirogen manufactures both aerobic and anoxic FBR systems. Aerobic systems utilize air or oxygen for removal of organics. Anoxic FBR syste ms are the technology of choice for inorganic contaminants such as perchlorate, nitr ate and selenium. Other distinguishing features of Envirogen FBRs include patented biomass control systems that are key to retaining media and steady

- state operation and plug flow; custom molded parts; proprietary design of internal vessel components and p roprietary and patented controls for chemical feed systems.Treatment of Selenium

- Containing Coal Mining Wastewaters 7



### Base System Design

Envirogen FBR installations typically feature one or more vessels in single

- or two

- stage configurations, depending on influent water characteristics and discharge limits (Figur e 3) . A range of materials can be used for vessel construction, including sta inless steel, fiberglass, lined

- carbon steel or concrete. Prefabricated FBR vessels from 2

- to 14

- feet diameter and up to 30

- feet in height are available

– offering very deep bed s in comparison to other fixed

- film technology. This vertical orientation is one of the factors that contribute to the FBR‟s smaller footprint compared to packed bed reactors or other biol ogical treatment systems. Field

- fabricated concrete or metal vessels are also available for very large applications. Overall system packages are outfitted with fluidization pump(s), piping, valves, chemical feed pumps and controls that may be field assembled or pre
- assembled based on client preferences

. Most Envirogen FBR systems are equipped with programmable logic control and may be provided with a SCADA package, telemetry and motor controls options.

Figure 3: Envirogen FBR for Perchlorate Removal



### System Operation

During start

- up, the FBR is seeded with heterotrophi c bacteria that are suited for nitrate and selenium
removal (Figure 4). Electron donor materials and nutrients are pumped into the FBR to promote microbial growth.Treatment of Selenium

- Containing Coal Mining Wastewaters 8

Figure 4: Start

- up of FBR system

Selenium

- containing wastewater is pumped from a feed t ank into the FBR in an upflow direction to suspend the media. As microorganisms grow on the media, the fluidized bed height expands (Figure 5).

Figu re 5: Fluidization of FBR mediaTreatment of Selenium

- Containing Coal Mining Wastewaters 9

With time, a biofilm develops on the media surface. Nitrate and selenium reduction occur on this biofilm. Treated water from the FBR system is discharged to a downstream liquid/solids separation system where the biological solids and elemental selenium are separated. Thickened or dewatered bio

- solids and
elemental selenium are disposed

.
One of the key features of operation is the technology used to fluidize the media bed and to uniformly distribute fluidization flow to the system. This is accomplished with the design and placement of the distribution nozzles and the sizing and arrangement of
the header

- lateral distributors. Uniformity of
flow is critical to establishing steady

- state plug flow conditions and the associated optimized performance.

Another key feature of these FBR systems is Envirogen‟s proprietary technology f or biomass control. In all properly functioning biological systems some of the energy that is derived from the consumption of electron donor is used by the microbes for biomass growth. This results in the production of excess biomass or “yield” that must b e removed from the bioreactor. In packed bed reactors this is accomplished with periodic backwash operations that remove large quantities of biomass using very high backwash rates

– creating turbulence and shea r to separate and wash out accumulated biomass

.
In Envirogen‟s FBR systems biomass is removed in a ste ady

- state manner with Envirogen‟ s patented biomass control devices. These systems allow the FBR to operate with an optimized and consistent ly high biomass concen tration, resulting in reliably high pe rformance.

Limitations inherent in packed bed reactors render them incapable of handling high feed nitrate, selenium and suspended solids concentrations. This is due to problems of rapid plugging, nitrogen gas binding, channeling and high backwash require ments. With Envirogen‟s patented biomass controls, FBRs effectively handle feed loads that are greater than an order of magnitude higher then packed bed
reactors.



### Design Flexibility

The design flexibility available through utilization of the FBR with resp ect to vessel heights and configuration, materials of construction, modularity, Envirogen‟s patented bed height control, biomassTreatment of Selenium

- Containing Coal Mining Wastewaters 10

control, proprietary chemical feed configurations and flexibility in electron donor selection all combine to produce improv ed performance, reduc ed capital and operating costs
, a n d minimi zed excess biomass production and associated processing and disposal costs. Furthermore, this allows for the use of alternate electron donors based on considerations of availability, cost and perf ormance.


### Advantages of the Envirogen FBR technology for the coal mining industry

Extensive testing of the Envirogen FBR technology ha s shown that it consistently offers highly efficient removal of selenium from coal mining wastewaters at dramatically lower cost levels tha n competitive technologies. Three aspects of Envirogen FBR systems support this success:

 The high performance nature of FBR treatment technology

 Proprietary & patented features of Envirogen‟s FBR systems

 Envirogen‟s decades of experience wi th FBR in treating inorganic contaminants

The following issues highlight the Envirogen FBR systems‟ performance advantages for the coal mining industry:

Optimization of microo rganism efficiency One of the key advantages of FBR technology over packed bed r eactors is the lack of „channeling‟ that occurs in FBR systems. Packed bed reactors tend to develop preferential pathways for flow due to solids
build

- up in the bed and nitrogen gas binding caused by conversion of nitrate to nitrogen gas. This can
cause pr essure drop in the typical fixed

- film system as well as short

- circuiting or partial flow by

- passing. These deviations from steady state plug flow conditions result in reduced performance. In the fluidized bed reactor, because of the even distribution of fl ow, a very high fraction of the biomass wi thin the
bioreactor is utilized

– meaning increased treatment efficiency. These issues directly affect the hydraulic residence time (HRT) required and explain why the footprints for Envirogen FBR systems are so muc h smaller than competitive packed bed bioreactors for the treatment of nitrate and selenium.

Steady

- s tate o peration Envirogen FBR systems are designed to be operated continuously

– meaning they do not require cyclical backwash operations. Packed bed reacto rs require periodic backwashing to slough off excess microbial growth, to eliminate channeling and to remove nitrogen gas pockets that have built up during the running part of the packed bed reactor operating cycle. Frequency of backwashing is related to t he loading of contaminants in the influent stream and requires large pumps and intermittent operation. In addition to increased energy costs, backwashing limits the flow of wastewater through the entire system since it is necessary to remove the backwashed unit from service, recover, clarify and recycle the dirty backwash suspension. Recycled backwash water adds to the feed loading and thereby limits net throughput.Treatment of Selenium

- Containing Coal Mining Wastewaters 11

Perhaps more importantly, the biomass in the system requires time to regrow following a back wash
, further increasing the required HRT . With higher loadings of feed nitrate, selenium and/or suspended solids, the backwashing requirements can become so excessive as to render the packed bed bioreactor ineffective or complet ely impractical.

Improved overall water quality
Besides selenium and nitrate
, another parameter that may be of concern is soluble biological oxygen demand ( BOD ) or chemical oxygen demand ( COD ) . Mine run

- off waters are generally very low in BOD and COD. Howev er, discharge from biological systems treating for these contaminants can contain

excess un
- reacted electron donor
, resulting in soluble BOD or COD in the bioreactor effluent. This will depend on the electron donor used and the quality of the biological co ntacting system, both of which
affect the complete ness of the reactions

.
For example, some grades of molasses contain a substantial fraction of non

- biodegradable or difficult to degrade compounds that will exit the bioreactor as soluble BOD and COD. Allowin g for flexibility in the choice of the electron donor(s) to be used, especially as this relates to two

- stage operation, can allow the system operator to control treated water BOD and COD. Additionally, the plug flow characteristics of the
FBR tend to resul t in more complete bio

- reactions and lower treated water concentrations.

Smaller overall footprint FBR systems have a smaller site footprint than other biological treatment systems. The key contributors
to this feature are the vertical orientation of the FBR vessels and the efficiency of treatment (lower HRTs). Treatment efficacy is affected by a high concentration of biomass and the tall beds. This smaller footprint
has a dramatic effect on construction and installation costs and schedules.

Dramatically l ower hydraulic residence times Despite having a smaller overall footprint, field studies have shown that FBR systems can achieve required performance with dramatically shorter HRTs than packed bed systems. This is due pr imarily to deep beds and steady

- stat e plug flow operation. HRTs for typical FBR systems used in selenium treatment for coal mining operations are 1/3 to 1/10 those required for packed bed reactors

.
Electron donor options Envirogen offers the ability to customize electron donor materials base d on decades of experience with the FBR technology. Key issues that are considered include treatment efficacy, overall water quality, operational ease of use, availability and cost. Table 3 shows a typical comparison of electron donor usage, costs and trea ted water quality as a function of alternate electron donors selection in a two

- stage FBR system treating selenium and nitrate.Treatment of Selenium

- Containing Coal Mining Wastewaters 12

Table 3: Electron Donors Comparative Evaluation

Molasses MicroCg 1 st stage Methanol 2 nd stage MicroCg 1 st stage Methanol 2 nd stage Molasses
Usage L/day 4260 3135 1362 (1 st stage) 627 (2 nd stage) 1362 (1 st stage) 852 (2 nd stage)
US$/L delivered 0.373 0.528 0.396 (methanol) 0.528 (molasses) 0.396 (methanol) 0.373 (molasses) US$/yr 580,000 604,000 317,700 312,900 FBR Effluent T SS mg/L 30 25 22.6 23.6 FBR Effluent filtered COD mg/L 100 50 20 30

Robustness of the system Envirogen FBR systems have a proven history over the past 30 years, operating effectively over a wide range of feed flow rates and influent types. The systems a re tolerant of high feed concentrations of total suspended solids (TSS) and metals. In addition, these systems have the ability to recover quickly from upsets such as power outages and loss of chemical feeds.

Modularity & extreme environment performance In many cases, Envirogen FBR systems can be pre

- fabricated for delivery to a coal mining treatment site. This contrasts with packed bed reactor systems which, because of their large size, are usually built

- in

place. FBR systems may be supplied as prefabric ated modules and associated equipment can be containerized in insulated and heated containers, per client requirements. This allows for ease of transportation and rapid installation

– even in bad weather conditions.

Generally speaking, it is expected that biological treatment systems suffer loss of efficiency when used in cold weather environments (> 15 o C). Recent tests by Envirogen on selenium

- containing wastewater at a coal mining site showed that the FBR system performed effectively at influent water te mperatures down to
4 o C.

Lower costs One of the major advantages of employing an FBR in a selenium treatment application is a considerable cost advantage in system design and installation compared with other comm ercially available technologies. This is pri marily due to smaller system footprints as well as the ability to manage issues such as suspended solids and waste disposal in a much more effective fashion
, over a broad range of
influent flow rates. A recent third

- party analysis performed for the North A merican Mining Council showed that initial capital costs for an FBR system can be 1/3 or less the cost of a packed bed reactor system designed for similar treatment requirements.Treatment of Selenium

- Containing Coal Mining Wastewaters 13

Technology track record Envirogen is an industry leader in the use of biorea ctor technology, with over 150 systems installed in the United States

. Envirogen FBR s ha ve been used in similar reductive applications for more than 10 years in applications such as perchlorate and nitrate , where low levels (<4 ppb) are consistently achiev ed at high flows (6,000 gpm) and in high TDS streams. The same anoxic operating regime is used for selenium
installations

.
Recently, Envirogen FBR technology demonstrated the ability to achieve <5 ppb selenium over a 10

- month period in treating mining leac hate at a U

. S

. - based coal mining site. Competitive trials run at the same site indicated that Envirogen FBR systems were the „technology of choice‟ for reliability and cost

effectiveness. Summary r esults for this trial are shown in Table 4



### .
Table 4: Operat ing results from 10

- month coal mining trial (USA)

A four

- month trial was also run at a Canadian coal mine

– examining Envirogen FBR technology in the presence of high nitrate levels and at colder influent water temperatures. Table 5 sh ows results of this
trial.Treatment of Selenium

- Containing Coal Mining Wastewaters 14

Table 5 : Operating results from 4

- month coal mining trial ( Canada)



### Envirogen Lifecycle Cost Assurance Programs

In any environmental installation the most important

– and often the most expensive

– contributors to a
treatment program are the performance and operating costs over its 10

- to 20

- year life. Developed to support all FBR installations
, Envirogen Lifecycle Cost Assurance Programs are designed to ensure performance, to deliver low lifecycle costs and to guarant ee the life of the asset s

. Elements of an Envirogen Lifecycle Cost Assurance Program range from basic O&M support services or the assignment
of Envirogen supervisory and management personnel to comprehensive operations programs wherein Envirogen becomes a single line item on the operating budget for the system in question. They can even include financing options for system design, construction and installation. Envirogen Lifecycle Cost Assurance Programs are typically 10 to 20 years or more, with the length generally following the anticipated life of the system in question. Guarantees are provided for system performance, operating cost components, asset life and overall lifecycle cost. In addition, Envirogen can also provide guarantees
for cost elements such as utility consumption and chemical usage for the life of the contract. Through the resources and experience that Envirogen Technologies brings to design, fabrication, installation, and long

- term operation, significant value can be realized via an Envirogen Li fecycle Cost Assurance Program. These include:

 Predictable a nd guaranteed costs for the lifetime of the asset

 Guaranteed performance , repair and maintenance costs, and regulatory compliance 

### in 2 stagesTreatment of Selenium

- Containing Coal Mining Wastewaters 15

 Opportunities for cost re duction through process improvements, capital improvement and energy/chemical savings

 Risk protection via performance a nd cost guarantees

 Improved budget management (avoid unbudgeted cost excursions)

 Cost

- effective access to industry specialists

 Continual pr ocess improvements

 Better utilization of capital

 A comprehensive EH&S Program



### Conclusions
With selenium regulations having an increasing presence in the coal mining industry landscape, efficie nt,
cost

- effective treatment is critical to the growth of the i ndustry. Envirogen FBR technology offers the industry‟s best, most broadly applicable solution to selenium treatment in systems that are field

- tested and ready for design and deployment. The design of Envirogen‟s FBR systems ensures that selenium
removal t argets can be consistently and reliably met

– at costs substantially below other commercially available competitive technology. The experience of the Envirogen team with FBR technology for decades ensures that the goals for a cost

- effective selenium treatm ent program can be met today and in
the future.