Internet: www.eere.energy.gov/femp/

No portion of this publication may be altered in any form without 

prior written consent from the U.S. Department of Energy, Energy 

Efficiency and Renewable Energy, and the authoring national laboratory.

Leading by example,

saving energy and 

taxpayer dollars in 

federal facilities

Technology Focus

A New Technology Demonstration Publication

Figure 1. Schematic 

of an RO system.

Pump Feed

water

Permeate

Semi-permeable

membrane

Concentrate

DOE/EE-0294

Saving Energy, Water, and Money with Efficient 

Water Treatment Technologies

New technologies for enhancing water purification processes

Introduction

Reverse osmosis (RO) is a method of purifying water for industrial processes and human 

consumption. RO can remove mineral salts and contaminants such as bacteria and pesticides. Advances in water treatment technologies have enhanced and complemented the 

conventional RO process, reducing energy and water consumption, lowering capital and 

operating costs, and producing purer water. This publication introduces RO, describes 

the benefits of High Efficiency Reverse Osmosis (HEROTM), and compares HERO with 

conventional RO/electrodeionization (EDI) technology.

Reverse Osmosis

Reverse osmosis is often used to treat saltwater or brackish 

water to create potable water. It is also used in a number 

of industrial processes to produce water with a high level 

of purity, reducing dissolved minerals and pollutants in the 

treated water. A stream of water, called the feed water, 

enters the RO system and is pressurized against a semipermeable membrane (Figure 1). 

Two streams exit the system, the concentrate and the permeate streams. The permeate 

is filtered, purified water. The concentrate is rejected water containing a high level of 

dissolved minerals. The concentrate is sent to drain, or a portion of it is recycled back to 

the feed stream to increase the system’s overall water recovery. The recovery rate (i.e., 

the ratio of the volume of permeate to the volume of the feed water) is typically about 

75% for a conventional RO system operating on a city water supply.

High Efficiency Reverse Osmosis

High Efficiency Reverse Osmosis is a proprietary system originally developed to provide 

ultrapure water to the microelectronics industry. HERO has several potential advantages 

over conventional RO: greater water recovery, higher quality permeate, higher operating flux (gallons per square foot of membrane per day), and generally lower costs. HERO 

systems are most advantageous for applications with challenging feed water (e.g., with 

a silica content greater than 20 ppm) or in areas with high water costs, limited available 

water, high water quality requirements, or zero liquid discharge requirements. HERO is 
Technology Focus

2 — FEDERAL ENERGY MANAGEMENT PROGRAM

typically used for industrial processes (Figure 2). It produces 

water that is higher in quality than 

necessary for potable use.

How It Works

The key to HERO is the chemical 

pretreatment that the feed water 

undergoes before undergoing RO. 

The pretreatment removes hardness from the feed water and raises 

its pH, which enables high efficiency RO. A schematic of the process 

is shown in Figure 3.

In the following discussion, the 

numbers in parentheses refer to 

the steps (circled numbers) in 

Figure 3. The number of steps in 

the process depends on the quality 

of the feed water; in some situations, some of the pretreatment 

steps might not be necessary.

Feed water entering the system (1) 

typically contains many dissolved 

and suspended impurities, including magnesium, calcium, silica, 

chlorine, and bacteria. Magnesium 

and calcium are the major constituents that make water “hard.” If left 

untreated, hard water leads to 

scaling on the RO membrane (i.e., 

calcium and magnesium compounds precipitate onto the membrane) at the high pH and high 

recoveries used in the RO phase of 

the HERO process. Scaling on the 

RO membrane shortens membrane 

life and increases maintenance 

costs. 

To remove hardness constituents 

such as calcium and magnesium, 

chemicals may be added to the 

feed water to raise the alkalinity to 

the same level as the hardness concentration. This hardness/alkalinity 

balance increases the efficiency of 

the subsequent weak acid cation 

(WAC) softening process (2). To 

produce soft water, hydrogen ions 

from the WAC resin are exchanged 

with hardness ions in the water. 

The addition of hydrogen ions 

(H+) reduces the pH of the feed 

water, which converts much of 

the feed alkalinity to carbonic acid 

and carbon dioxide. Additional 

acid may be added to this water 

to completely convert all the 

remaining alkalinity to free carbon 

dioxide gas, which then may be 

removed via degasification (3). 

This step improves the final water 

quality and reduces the amount of 

chemicals required to raise the pH 

in the next step. In the next step, 

Aquatech International Corporation/PIX13171

Figure 2. HERO system installed in a power station.

Carbon

dioxide

removal

Weak acid

cation

exchange

2 3 4

1

Feed water

Permeate

RO System

Concentrate

Acid Alkali

(if needed)

Alkali

(if needed)

Figure 3: Schematic of a HERO system.
Technology Focus

FEDERAL ENERGY MANAGEMENT PROGRAM — 3

the pH of the feed water is raised 

to pH 10.5 to increase the solubility of the silica and destroy biological organisms in the feed water. 

The feed water then enters the RO 

system (4).

Benefits and Costs

The HERO system provides several 

benefits. For example, it reduces 

scaling of the RO membrane. 

Dissolved silica is one of the major causes of membrane scaling. 

Increasing the pH of the water 

entering RO greatly increases the 

solubility of silica, thus eliminating 

its potential for scaling. Increasing 

the pH also destroys many bacteria and creates a slightly negative 

charge that repulses colloids; both 

reduce fouling of the membrane. 

The typical water recovery of 

the HERO process is 95%–99% 

(depending on site-specific characteristics) in comparison to a typical 

recovery rate for conventional RO 

of approximately 75%. In addition, 

HERO produces purer water than 

conventional RO processes do, 

and the operating flux for HERO is 

nearly double that of conventional 

RO.

Because the pretreatment process 

eliminates many of the causes of 

membrane fouling and scaling, 

HERO does not use antiscalant 

chemicals and requires less cleaning and maintenance than conventional RO does. HERO also has 

limited self-healing properties, so 

small problems tend not to cause 

major system disruptions. In addition, there are the environmental 

benefits of saving water and energy 

and the ability to use reject water 

from HERO (which is soft water at 

high pH) for acidic gas scrubber 

makeup or acid waste neutralization. 

Capital costs for HERO are generally higher than those of conventional RO for small (25–50 gallons per 

minute [gpm]) systems because 

of the pretreatment requirements. 

However, for systems larger than 

50 gpm, capital costs for HERO are 

generally about 15% lower because 

of the higher flux rate, which 

allows fewer RO membranes to 

be used. Because of higher water 

recovery rates and reduced fouling 

and scaling of the RO membranes, 

HERO operating and energy costs 

are also typically less than those 

of conventional RO. Case studies 

suggest that, depending on the 

characteristics of the feed water 

and water costs, operating a HERO 

system costs about 20%–40% less 

than operating a conventional RO 

system. 

Reverse Osmosis/

Electrodeionization

Reverse osmosis/EDI is another 

technique for purifying process 

water (Figure 4). Feed water is first 

treated by single- or double-pass 

RO. Then, the water undergoes 

EDI to deionize it.

Figure 4. Schematic of EDI.
Technology Focus

4 — FEDERAL ENERGY MANAGEMENT PROGRAM

During EDI, the RO-treated feed 

water is sent through an EDI cell. 

Voltage is applied across the cell, 

which forces the migration of ions 

(e.g., dissolved salts) out of the 

feed water, through the cell membranes, and into a concentrated 

reject stream. The current 

is the motive force to transport the 

ions, but it also splits the water 

molecules into hydrogen (H+) and 

hydroxyl (OH-) ions for complete 

regeneration of the ion exchange 

resin at the end of the EDI cell.

The high power requirements of 

EDI can be mitigated by designing 

a system with a longer path (more 

membrane), which requires less 

current per gallon produced. The 

trade-off is between a lower initial 

capital cost and lower operating 

and maintenance costs. In other 

words, a longer path requires more 

membrane (added capital cost) 

but results in less membrane 

maintenance and lower power 

requirements. 

Case Study: Sandia 

National Laboratories

Sandia National Laboratories in 

Albuquerque, New Mexico, recently decided to upgrade its water 

purification system. Ionics, a global 

separations technology company 

that can supply the HERO and 

RO/EDI systems, analyzed both 

for Sandia’s particular situation. 

The analysis suggested that HERO 

would consume less power and 

water and produce less wastewater than RO/EDI, whereas RO/EDI 

would consume fewer chemicals 

(Table 1). 

Comparison of HERO and RO/EDI

The annual cost for HERO was 

predicted to be 24% lower than 

for RO/EDI (Table 2). HERO was 

more cost-effective because of the 

high silica content (~60 ppm) of 

Sandia’s feed water. Sandia subsequently installed a HERO system 

with output of 160 gpm and a 93% 

recovery rate. The HERO-treated 

water is used to supply Sandia’s 

microelectronics development 

laboratory. 

Table 1. Comparison of RO/EDI and HERO*

Annual Statistics RO/EDI HERO

Power use (kWh) 2,838,667 1,849,760

Feed water use (1,000 gal) 160,421 116,817

Wastewater production (1,000 gal) 44,781 7,767

Chemicals (lb) (acid and caustic; does 56,871 198,272

not include cleaning chemicals or scale 

inhibitors)

*Analysis based on hypothetical 250-gpm systems.

Table 2. Annual costs of RO/EDI and HERO*

Annual Costs RO/EDI HERO

Utility $404,113 $251,918

Chemical $37,269 $57,716

Other consumables $454,353 $370,506

Total $895,735 $680,139

 * Analysis based on hypothetical 250-gpm systems.

** Component costs do not equal the total because of rounding.

Lessons Learned

Sandia learned several lessons during the installation and initial use 

of its HERO system: consider the 

chemistry, pay attention to commissioning, and know the quality 

of the water supply.

Consider the chemistry.

Hydrochloric acid (HCl) has been 

proven for use with HERO systems. 

However, Sandia decided to use 

sulfuric acid (H2SO4) to eliminate 

the need for a large outdoor HCl 

tank (using H2SO4 allows the use 

of a smaller tank but increases the 

complexity of the WAC regeneration). The use of H2SO4 combined 

with unanticipated variations in 

feed water quality required several 

**
Technology Focus

FEDERAL ENERGY MANAGEMENT PROGRAM — 5

Federal research laboratories use the ultrapure water produced by hyperfiltration technologies to develop advanced microelectronics like this 

thin-film solar cell. 

Warren Gretz, NREL/PIX10119

rounds of chemistry and adjustments of controls to fully automate 

the system and ensure reliable 

operation. Users must evaluate 

the benefits and drawbacks of 

different chemistries to make an 

informed decision about which 

chemical to use. 

Pay attention to commissioning. 

A thorough commissioning plan 

is essential to the successful 

implementation of a HERO system. 

Every control point—such as valve 

positions, pumps, and pressure 

set points—should be checked. 

Sandia’s commissioning plan covered typical construction checks 

(e.g., leak tests) and thorough testing of the entire system. First, the 

quality of the HERO-treated output 

water was checked to verify that 

contaminants were removed satisfactorily. Next, a 2-week test was 

conducted to verify that the entire 

system functioned correctly. This 

test was performed with the water 

treatment company that built and 

installed the system on site and 

was available for emergency support. Finally, a 30-day trial of the 

system was conducted without any 

outside support. 

Know the quality of the water 

supply. Knowing the quality of the 

water that will supply a HERO system is important when designing 

and operating the system. Sandia’s 

water supply was harder by 20%–

30% than that used in the design 

of its system, and this resulted in 
Technology Focus

6 — FEDERAL ENERGY MANAGEMENT PROGRAM

problems during commissioning. 

Sandia therefore recommends 

monitoring the water supply 

continuously for a period of time 

before the system is designed to 

provide an accurate characterization of water quality. 

Conclusions

Both HERO and RO/EDI may offer 

benefits over conventional RO 

alone. HERO is best for challenging feed waters and when system 

water efficiency or product quality 

is important. Because of higher 

water efficiency, HERO typically 

has lower capital costs than RO/

EDI. RO/EDI is best suited for 

environments in which a 

“chemical-free” system (i.e., 

minimal acid/caustic) is required. 

RO/EDI also may be more appropriate for situations in which the 

feed water cannot be efficiently 

softened (i.e., high hardness and 

low alkalinity) and it is not critically important to recover a high 

amount of water. 

Water Treatment System 

Suppliers

For more information, these two 

companies currently supply HERO 

and RO/EDI systems:

Aquatech International Corporation

One Four Coins Dr.

Canonsburg, PA 15317

Tel: 724-746-5300

Fax: 724-746-5359

E-mail: aquatech@aquatech.com

Web site: www.aquatech.com 

Ionics, Inc. 

65 Grove St.

Watertown, MA 02472

Contact: Tom Chiara, 

 Phoenix Office

Tel: 602-437-1355

Fax: 602-437-9540

E-mail: tchiara@ionics.com

Web site: www.ionics.com 

For information about additional 

manufacturers or suppliers of 

reverse osmosis or electrodeionizing treatment systems, please 

see the Thomas Register online: 

www.thomasregister.com
Technology Focus

FEDERAL ENERGY MANAGEMENT PROGRAM — 7

About FEMP’s New Technology Demonstrations

The Energy Policy Act of 1992 and 

subsequent Executive Orders mandate that energy consumption in 

federal buildings be reduced by 

35% from 1985 levels by the year 

2010. To achieve this goal, the U.S. 

Department of Energy’s Federal 

Energy Management Program (FEMP) 

sponsors a series of activities to reduce energy consumption at federal 

installations nationwide. FEMP uses 

new technology demonstrations to 

accelerate the introduction of energyefficient and renewable technologies 

into the federal sector and to improve 

the rate of technology transfer. 

As part of this effort, FEMP sponsors 

the following series of publications 

that are designed to disseminate 

information on new and emerging 

technologies:

Technology Focuses—brief information 

on new, energy-efficient, environmentally friendly technologies of potential 

interest to the federal sector.

Federal Technology Alerts—longer 

summary reports that provide details 

on energy-efficient, water-conserving, 

and renewable-energy technologies 

that have been selected for further 

study for possible implementation 

in the federal sector. 

Technology Installation Reviews—

concise reports describing a new 

technology and providing case study 

results, typically from another demonstration activity or pilot project. 

Other Publications—we also issue 

other publications on energy-saving 

technologies with potential use in the 

federal sector.

Federal Energy Management Program

The federal government is the largest energy consumer in the nation. Annually, the total primary energy consumed by the federal 

government is 1.4 quadrillion British thermal units (quads), costing $9.6 billion. This represents 1.4% of the primary energy consumption in the United States. The Federal Energy Management Program was established in 1974 to provide direction, guidance, 

and assistance to federal agencies in planning and implementing energy management programs that will improve the energy 

efficiency and fuel flexibility of the federal infrastructure. 

Over the years, several federal laws and Executive Orders have shaped FEMP’s mission. These include the Energy Policy 

and Conservation Act of 1975; the National Energy Conservation and Policy Act of 1978; the Federal Energy Management 

Improvement Act of 1988; the National Energy Policy Act of 1992; Executive Order 13123, signed in 1999; and, most recently, 

Executive Order 13221, signed in 2001, and the Presidential Directive of May 3, 2001.

FEMP is currently involved in a wide range of energy-assessment activities, including conducting new technology demonstrations, 

to hasten the penetration of energy-efficient technologies into the federal marketplace.
Disclaimer

This report was sponsored by the United States Department of Energy, Office of Energy 

Efficiency and Renewable Energy, Federal Energy Management Program. Neither the United 

States Government nor any agency or contractor thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility 

for the accuracy, completeness, or usefulness of any information, apparatus, product, or 

process disclosed, or represents that its use would not infringe privately owned rights. 

Reference herein to any specific commercial product, process, or service by trade name, 

mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, 

recommendation, or favoring by the United States Government or any agency or contractor 

thereof. The views and opinions of authors expressed herein do not necessarily state or 

reflect those of the United States Government or any agency or contractor thereof.

Printed with a renewable-source ink on paper containing

at least 50% wastepaper, including 10% postconsumer waste

A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner 

environment, and greater energy independence for America. Working with a wide array 

of state, community, industry, and university partners, the U.S. Department of Energy’s 

Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of 

energy technologies.

Produced for the U.S. Department 

of Energy, Energy Efficiency and 

Renewable Energy, by the National 

Renewable Energy Laboratory

DOE/EE-0294

June 2004

For More Information

EERE Information Center

1-877-EERE-INF or

1-877-337-3463

www.eere.energy/gov/femp

General Program Contacts

Ted Collins

Program Manager

New Technology Demonstrations

Federal Energy Management Program

U.S. Department of Energy

1000 Independence Ave., S.W.

Washington, D.C. 20585

Phone: (202) 586-8017

Fax: (202) 586-3000

theodore.collins@ee.doe.gov

Steven A. Parker

Pacific Northwest National Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-6366

Fax: (509) 375-3614

steven.parker@pnl.gov

Technical Contacts and Authors

Sheila Hayter

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401

Phone: (303) 384-7519

E-mail: sheila_hayter@nrel.gov

Stephanie Tanner and Eva Urbatsch

National Renewable Energy Laboratory

901 D Street, S.W., Suite 930

Washington, DC 20024

Phone: (202) 646-5218

E-mail: stephanie_tanner@nrel.gov

Jarett Zuboy

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401

Phone: (303) 275-4603

E-mail: jarett_zuboy@nrel.gov