Overview of Drinking Water Treatment Technologies

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Granular activated carbon

What is granular activated carbon?

Granular activated carbon (GAC) is a porous adsorption media with extremely high internal surface area. GACs are manufactured from a variety of raw materials with porous structures including:

  • bituminous coal
  • lignite coal
  • peat
  • wood
  • coconut shells

Physical and/or chemical manufacturing processes are applied to these raw materials to create and/or enlarge pores.  This results in a porous structure with a large surface area per unit mass.

Why is it useful?

GAC is useful for the removal of taste- and odor-producing compounds, natural organic matter, volatile organic compounds (VOCs), synthetic organic compounds and disinfection byproduct precursors. Organic compounds with high molecular weights are readily adsorbable.

Treatment capacities for different contaminants vary depending on the properties of the different GACs, which in turn vary widely depending on the raw materials and manufacturing processes used.

What are the advantages of using GAC?

GAC is a proven technology with high removal efficiencies (up to 99.9%) for many VOCs, including trichloroethylene (TCE) and tetrachloroethylene (PCE). In most cases, GAC can remove target contaminants to concentrations below 1 µg/l. Another advantage is that regenerative carbon beds allow for easy recovery of the adsorption media.

What are the disadvantages of using GAC?

The media has to be removed and replaced or regenerated when GAC capacity is exhausted. In some cases, disposal of the media may require a special hazardous waste handling permit. Other adsorbable contaminants in the water can reduce GAC capacity for a target contaminant.

How can the WBS model for GAC be used?

The work breakdown structure (WBS) model can estimate costs for two types of GAC systems where:

  • the GAC bed is contained in pressure vessels in a treatment configuration similar to that used for other adsorption media (for example, activated alumina), referred to as pressure GAC
  • the GAC bed is contained in open concrete basins in a treatment configuration similar to that used in the filtration step of conventional or direct filtration, referred to as gravity GAC

The WBS model for GAC includes standard designs to estimate costs for treatment of a number of different contaminants, including atrazine and various VOCs. The WBS model can also be used to estimate the cost of GAC treatment for removal of other contaminants.

To simulate the use of GAC for treatment of other contaminants, users will need to adjust default inputs (for example, bed volumes before breakthrough, bed depth) and, potentially, critical design assumptions (for example, minimum and maximum loading rates).

Where can I find more information on GAC?

The technical report Work Breakdown Structure-Based Cost Model for Granular Activated Carbon Drinking Water Treatment Technologies discusses GAC technology in detail.

Packed tower aeration

What is packed tower aeration?

Aeration processes, in general, transfer contaminants from water to air. Packed tower aeration (PTA) uses towers filled with a packing media designed to mechanically increase the area of water exposed to non-contaminated air. Water falls from the top of the tower through the packing media while a blower forces air upwards through the tower. In the process, volatile contaminants pass from the water into the air.

Why is it useful?

PTA is useful for removing volatile contaminants including:

  • Volatile organic compounds (VOCs)
  • Disinfection byproducts
  • Hydrogen sulfide
  • Carbon dioxide
  • Other taste- and odor-producing compounds

The more volatile the contaminant, the more easily PTA will remove it. PTA readily removes the most volatile contaminants, such as vinyl chloride. With sufficient tower height and air flow, PTA can even remove somewhat less volatile contaminants, such as 1,2-dichloroethane.

What are the advantages of using PTA?

PTA is a proven technology and can achieve high removal efficiencies (99 percent or greater) for most VOCs. PTA removal efficiency is independent of starting concentration. Therefore, it can remove most volatile contaminants to concentrations below 1 µg/L. PTA generates no liquid or solid waste residuals for disposal.

What are the disadvantages of using PTA?

Depending on the location and conditions, air quality regulations might require the use of air pollution control devices with PTA, increasing the technology cost. PTA uses tall towers that could be considered unsightly in some communities. Under certain water quality conditions, scaling or fouling of the packing media can occur if precautions are not taken.

How can the WBS model for PTA be used?

The work breakdown structure (WBS) model for PTA includes standard designs to estimate costs for treatment of a number of different contaminants, including methyl tertiary-butyl ether (MTBE) and various VOCs. However, the WBS model can be used to estimate the cost of PTA treatment for removal of other contaminants as well.

To simulate the use of PTA for treatment of other contaminants, users will need to adjust default inputs (for example, Henry’s coefficient, molecular weight) and, potentially, critical design assumptions (for example, minimum and maximum packing height).

Where can I find more information on PTA?

The technical report Work Breakdown Structure-Based Cost Model for Packed Tower Aeration Drinking Water Treatment Technologies discusses PTA technology in detail.

Multi-stage bubble aeration

What is multi-stage bubble aeration?

Aeration processes, in general, transfer contaminants from water to air. Multi-stage bubble aeration (MSBA) uses shallow basins that are divided into smaller compartments, or stages, using baffles.

Inside each stage, diffusers (consisting of perforated pipes or porous plates) release small air bubbles that rise through the water. The bubbles and their resulting turbulence cause volatile contaminants to pass from the water into the air.

Why is it useful?

MSBA is useful for removing volatile contaminants including:

  • Volatile organic compounds (VOCs)
  • Hydrogen sulfide
  • Carbon dioxide
  • Other taste- and odor-producing compounds

The more volatile the contaminant, the more easily MSBA will remove it. Vendors supply MSBA in skid-mounted, pre-packaged systems that can be particularly suitable for small systems.

What are the advantages of using MSBA?

MSBA is a proven technology. In recent EPA pilot tests, MSBA achieved high removal efficiencies (98 percent to greater than 99 percent) for most VOCs, removing them to concentrations below 1 µg/L. MSBA is a low-profile aeration technology that does not require tall, potentially unsightly towers. MSBA generates no liquid or solid waste residuals for disposal.

What are the disadvantages of using MSBA?

Depending on the location and conditions, air quality regulations might require the use of air pollution control devices with MSBA, increasing the technology cost.

MSBA is less efficient at removing contaminants than packed tower aeration, requiring high air flow rates to remove the most recalcitrant VOCs. Treating large water flows with MSBA can require a large number of basins. This might not be practical for large systems.

How can the WBS model for MSBA be used?

The work breakdown structure (WBS) model for MSBA includes standard designs for the treatment of a number of contaminants, including various VOCs. However, the WBS model can be used to estimate the cost of MSBA treatment for removal of other volatile contaminants as well.

To simulate the use of MSBA for treatment of other contaminants, users will need to adjust default inputs (for example, air-to-water ratio, number of stages) and, potentially, critical design assumptions (for example, maximum air surface intensity).

Where can I find more information on MSBA?

The technical report Work Breakdown Structure-Based Cost Model for Multi-stage Bubble Aeration Drinking Water Treatment Technologies discusses MSBA technology in detail.

Anion exchange

What is anion exchange?

In an anion exchange treatment process, water passes through a bed of synthetic resin. Negatively charged contaminants in the water are exchanged with more innocuous negatively charged ions, typically chloride, on the resin’s surface.

Why is it useful?

Anion exchange is useful for the removal of negatively charged contaminants including arsenic, chromium-6, cyanide, nitrate, perchlorate, per- and polyfluoroalkyl substances (PFAS), sulfate, and uranium.

Treatment capacities for different contaminants vary depending on the properties of the resin used and characteristics of the influent water. Several of vendors manufacture different resins, including those designed to selectively remove specific contaminant ions.​

What are the advantages of using anion exchange?

Anion exchange is a proven technology that can achieve high removal efficiencies (greater than 99 percent) for negatively charged contaminants. When the capacity of the resin is exhausted, it can be regenerated to restore it to its initial condition. The regeneration process uses a saturated solution, usually of sodium chloride (also known as brine). An alternative to regeneration is to dispose of the exhausted resin and replace it with fresh resin. This alternative is often employed when selective resins are used to remove perchlorate or PFAS.

What are the disadvantages of using anion exchange?

The spent regenerant brine is a concentrated solution of the removed contaminants and will be high in dissolved solids and excess regenerant ions (e.g., sodium, chloride). This waste stream will require disposal or discharge. Anion exchange treatment also can lower the pH of the treated water and, therefore, may require post-treatment corrosion control. When replacement with fresh resin is used as an alternative to regeneration, the spent resin, loaded with removed contaminants, will require disposal. In some cases, disposal of the resin may require a special hazardous waste handling permit.

How can the WBS model for anion exchange be used?

The primary work breakdown structure (WBS) model for anion exchange includes standard designs to estimate costs for treatment of arsenic and nitrate. EPA has developed separate WBS models, also available on this page, to estimate costs for treatment of perchlorate and PFAS. In addition, the WBS anion exchange models can be used to estimate the cost of anion exchange treatment for removal of other contaminants.

To simulate the use of anion exchange for treatment of other contaminants, users will need to adjust default inputs (for example, bed volumes before regeneration, bed depth) and, potentially, critical design assumptions (for example, minimum and maximum loading rates).

Where can I find more information on anion exchange?

The technical report Work Breakdown Structure-Based Cost Model for Anion Exchange Drinking Water Treatment discusses anion exchange technology in detail.

Cation exchange

What is cation exchange?

In a cation exchange treatment process, water passes through a bed of synthetic resin. Positively charged contaminants in the water are exchanged with more innocuous positively charged ions, typically sodium, on the resin’s surface.

Why is it useful?

Cation exchange is useful for water softening by removing hardness ions such as calcium and magnesium. It can also remove other positively charged contaminants including barium, radium and strontium.

Treatment capacities for different contaminants vary depending on the properties of the resin used and characteristics of the influent water. A number of vendors manufacture different resins, including those designed to selectively remove specific contaminant ions.​

What are the advantages of using cation exchange?

Cation exchange is a proven technology for water softening and removal of positively charged contaminants. It can achieve high removal efficiencies (greater than 99 percent) for positively charged contaminants. When the capacity of the resin is exhausted, it can be regenerated to restore it to its initial condition. The regeneration process uses a saturated solution, usually of sodium chloride (also known as brine).

What are the disadvantages of using cation exchange?

The spent regenerant brine is a concentrated solution of the removed contaminants and also will be high in dissolved solids and excess regenerant ions (e.g., sodium, chloride). This waste stream will require disposal or discharge.

How can the WBS model for cation exchange be used?

The work breakdown structure (WBS) model for cation exchange includes standard designs for water softening. The same designs may also be appropriate for radium removal. The WBS model can also be used to estimate the cost of cation exchange treatment for removal of other contaminants.

To simulate the use of cation exchange for treatment of other contaminants, users will need to adjust default inputs (for example, bed volumes before regeneration, bed depth) and, potentially, critical design assumptions (for example, minimum and maximum loading rates).

Where can I find more information on cation exchange?

The technical report Work Breakdown Structure-Based Cost Model for Cation Exchange Drinking Water Treatment discusses cation exchange technology in detail.

Biological treatment

What is biological treatment?

Biological treatment of drinking water uses indigenous bacteria to remove contaminants. The process has a vessel or basin called a bioreactor that contains the bacteria in a media bed. As contaminated water flows through the bed, the bacteria, in combination with an electron donor and nutrients, react with contaminants to produce biomass and other non-toxic by-products. In this way, the biological treatment chemically “reduces” the contaminant in the water.

Why is it useful?

Biological treatment is useful for the removal of contaminants including nitrate and perchlorate. Following a startup period, the bacterial population in the water will adapt to consume the target contaminants as long as favorable conditions, such as water temperature and electron donor and nutrient concentrations, are maintained.

What are the advantages of using biological treatment?

Biological treatment can achieve high removals (greater than 90 percent) of nitrate and perchlorate. The process destroys contaminants, as opposed to removing them, and, therefore, does not produce contaminant-laden waste streams. Biological treatment remains effective even in the presence of certain co-occurring contaminants.

What are the disadvantages of using biological treatment?

An active bioreactor will have a continuous growth of biomass that needs to be periodically removed. Although the excess biomass will not be contaminant-laden, it still requires disposal. Also, biological treatment adds soluble microbial organic products and can deplete the oxygen in treated water. Post-treatment processes are needed to control these effects.

How can the WBS model for biological treatment be used?

The work breakdown structure (WBS) model can estimate costs for anoxic biological treatment using three types of bioreactors:

  • pressure vessels with a fixed media bed
  • open concrete basins with a fixed media bed
  • pressure vessels with a fluidized media bed.

The WBS model for biological treatment includes standard designs for perchlorate and nitrate treatment. However, the model can also be used to estimate the cost of biological treatment for the removal of other contaminants.

To simulate the use of biological treatment for other contaminants, users will need to adjust default inputs (e.g., electron donor and nutrient doses) and critical design assumptions (e.g., minimum and maximum loading rates).

Where can I find more information on biological treatment?

The technical report Work Breakdown Structure-Based Cost Model for Biological Drinking Water Treatment discusses the technology in detail.

Reverse osmosis/nanofiltration

What are reverse osmosis and nanofiltration?

Reverse osmosis (RO) and nanofiltration (NF) are membrane separation processes that physically remove contaminants from water. These processes force water at high pressure through semi-permeable membranes that prevent the passage of various substances depending on their molecular weight. Treated water, also known as permeate or product water, is the portion of flow that passes through the membrane along with lower molecular weight substances. Water that does not pass through the membrane is known as concentrate or reject and retains the higher molecular weight substances, including many undesirable contaminants.

Why are they useful?

RO and NF are useful for the removal a wide range of contaminants. RO can remove contaminants including many   inorganics, dissolved solids, radionuclides and synthetic organic chemicals. RO can also be used for removing salts from brackish water or sea water. NF is useful for removal of hardness, color and odor compounds, synthetic organic chemicals and some disinfection byproduct precursors.

What are the advantages of using RO and NF?

RO and NF are proven technologies that can achieve high removals of a broad range contaminants at once. They do not selectively target individual contaminants and remain effective for water that contains mixtures of contaminants. The processes do not usually require adjustment based on the specific trace contaminants present.

What are the disadvantages of using RO and NF?

RO and NF reject part of the feed water (15 to 30 percent) that enters the process. This “loss” of water as concentrate can present a problem when water is scarce. Furthermore, this large volume concentrate stream is laden with removed contaminants, salts and dissolved solids and will require discharge or disposal. Also, the high pressures used in these treatment processes can result in significant energy consumption. Pre-treatment processes are frequently required to prevent membrane fouling or plugging. Finally, RO can lower the pH of treated water and, therefore, may require post-treatment corrosion control.

How can the WBS model for RO and NF be used?

The work breakdown structure (WBS) model can estimate costs for either RO or NF. It includes standard designs for feed waters of various quality in terms of gross chemical composition (e.g., salt concentrations). The design parameters typically do not require adjustment to target a specific trace contaminant, other than selecting the appropriate type of membrane (e.g., RO or NF) given the contaminant’s molecular weight and other characteristics.

Where can I find more information on RO and NF?

The technical report Work Breakdown Structure-Based Cost Model for Reverse Osmosis/Nanofiltration Drinking Water Treatment discusses these technologies in detail.

Adsorptive Media

What is adsorptive media?

Adsorptive water treatment technologies involve passing contaminated water through a media bed. The contaminants in the water adsorb to empty pore spaces on the surface of the adsorptive media as the water passes through. Granular activated carbon (GAC), described above, is one type of adsorptive media, but other types exist, including aluminum-based, iron-based, titanium-based, zirconium-based and other types of media.

Why is it useful?

Adsorptive media treatment is useful for removal of inorganic contaminants including antimony, arsenic, beryllium, fluoride, selenium, thallium, and uranium. The capacity of the media to adsorb different contaminants depends on the specific type of media used, the water chemistry (e.g., pH), and contaminant valence.

What are the advantages of using adsorptive media?

Adsorptive media is a proven technology with high removal efficiencies for certain inorganic contaminants (e.g., up to greater than 99% for arsenic, up to 99% or more for fluoride). When the appropriate media is used in combination with the appropriate water quality conditions (e.g., pH), the process can remove selected target contaminants to concentrations below relevant regulatory limits. Another advantage is that some types of adsorptive media can be regenerated in place after their capacity is exhausted. The regeneration process typically uses an acid wash, followed by a caustic wash.

What are the disadvantages of using adsorptive media?

The media has to be removed and replaced or regenerated when its adsorptive capacity is exhausted. When regeneration is employed, the spent regenerant is a concentrated solution of the removed contaminants and will require disposal or discharge. When replacement with fresh media is used as an alternative to regeneration, the spent media, loaded with removed contaminants, will require disposal. In some cases, disposal of the media may require a special hazardous waste handling permit.

How can the WBS model for adsorptive media be used?

The work breakdown structure (WBS) model can estimate costs for the following combinations of media and target contaminant:

  • Conventional activated alumina for removal of arsenic
  • Conventional activated alumina for removal of fluoride
  • Iron-modified activated alumina (also known as AAFS-50) for removal of arsenic
  • Granular ferric oxide (GFO) for removal of arsenic
  • Granulated ferric hydroxide (GFH) for removal of arsenic.

The WBS model can also estimate costs for treatment using alternative media and/or other contaminants, if the user provides appropriate assumptions about the media and adjusts default inputs (e.g., bed volumes before breakthrough, bed depth).

Where can I find more information on RO and NF?

The technical report Work Breakdown Structure-Based Cost Model for Adsorptive Media Drinking Water Treatment discusses the technology in detail.

Ultraviolet Photolysis and Advanced Oxidation Processes (UVAOP)

What is ultraviolet photolysis and advanced oxidation?

Ultraviolet (UV) light can be used on its own (in photolysis), or in combination with chemical addition (in UV advanced oxidation), to reduce the concentration of organic contaminants. In UVAOP drinking water treatment, water passes through a reactor vessel equipped with lamps that emit UV light. In photolysis, the contaminants are degraded by the photons emitted by the UV lamps. Advanced oxidation adds chemicals such as hydrogen peroxide (H2O2) or chlorine. These chemicals react with the UV light to generate radicals (such as hydroxyl) that in turn oxidize the contaminants.

Why is it useful?

UVAOP is useful to reduce the concentration of organic micropollutants that may be difficult to address with other technologies including 1,4-dioxane, N-nitrosodimethylamine (NDMA), and methyl tert-butyl ether (MTBE). The process can also be useful for treatment of taste and odor issues. The effectiveness of the process depends on the UV dose, chemical dose (in advanced oxidation), contact time, concentration of the target contaminants, and other water quality parameters (e.g., UV transmittance, presence of radical scavengers).

What are the advantages of using UVAOP?

UVAOP can achieve high removal efficiencies for 1,4-dioxane (up to greater than 99%) and MTBE (greater than 90%). The process destroys contaminants, as opposed to removing them, and therefore, does not produce contaminant-laden waste streams.

What are the disadvantages of using UVAOP?

UVAOP is non-selective and can oxidize non-target organic compounds present in the water. In some cases, this oxidation can increase the potential for formation of disinfection byproducts in the drinking water distribution system. Also, in advanced oxidation, the process will not completely consume the entire dosage of the chemical added. The presence of the excess chemical in the treated water may be of concern. Both of these disadvantages may require post-treatment using a process such as GAC. Finally, operating the UV lamps can consume significant electrical energy and the lamps themselves usually require periodic cleaning and replacement.

How can the WBS model for UVAOP be used?

The work breakdown structure (WBS) model can estimate costs for the following combinations of treatment processes and target contaminant:

  • Treatment of 1,4-dioxane using UV and H2O2 (UV/H2O2)
  • Treatment of 1,4-dioxane using UV and chlorine (UV/Cl)
  • Treatment of NDMA using direct photolysis.

The WBS model can also estimate costs for treatment of other contaminants by UV/ H2O2, UV/Cl, or direct photolysis, if the user adjusts default inputs (e.g., UV energy input, oxidant dose).

Where can I find more information on UVAOP?

The technical report Work Breakdown Structure-Based Cost Model for Drinking Water Treatment by Ultraviolet Photolysis and Advanced Oxidation Processes discusses the technology in detail.

Caustic Feed

What is caustic feed?

Caustic soda, also known as sodium hydroxide (NaOH), is sometimes added to drinking water to raise the water’s pH, making the water less acidic.

Why is it useful?

Caustic feed can be useful on its own to attain and maintain a desired pH and prevent downstream corrosion in a drinking water distribution system. It can also be useful following treatment processes that lower the pH of water to return the water to its original or more neutral pH. It may also be useful prior to certain treatment processes to optimize the pH of the water feeding those processes.

What are the advantages of using caustic feed?

Caustic soda is a liquid chemical that can rapidly change the pH of water without requiring extensive equipment for feeding and mixing.

What are the disadvantages of using caustic feed?

Concentrated caustic soda is harmful to human skin and therefore requires handling precautions and secondary containment. At higher concentrations, caustic soda will freeze at moderate temperatures (i.e., 50 percent solution freezes at 58 degrees Fahrenheit), so storage tanks may need to be indoors and/or equipped with special heating equipment. This disadvantage can be mitigated by using lower concentration caustic soda.

How can the WBS model for caustic feed be used?

The work breakdown structure (WBS) model can estimate costs for a process to add caustic soda into a water pipeline at an existing drinking water treatment plant. It includes several pre-defined scenarios of starting pH, target pH, and other water quality parameters. It can easily estimate costs for other scenarios if the user adjusts default inputs.

Where can I find more information on caustic feed?

The technical report Work Breakdown Structure-Based Cost Model for Caustic Feed Drinking Water Treatment discusses the technology in detail.

Phosphate Feed

What is phosphate feed?

Phosphate-based chemicals, such as phosphoric acid, zinc orthophosphate, or others, are sometimes added to drinking water to control corrosion in a distribution system.

Why is it useful?

Phosphate addition is among the treatment strategies for compliance with the federal Lead and Copper Rule.

What are the advantages and disadvantages of using phosphate feed?

Phosphate corrosion control chemicals containing orthophosphate are believed to combine with lead and copper in plumbing materials to form insoluble compounds, thus reducing lead and copper release at the tap. The effectiveness of this process depends on chemical dosage and pH. However, the addition of these chemicals does not permanently eliminate sources of lead and copper release (e.g., service lines). Changes in influent water quality can require re-optimization of corrosion control practices. In addition, different phosphate chemical formulations have different advantages and disadvantages. For example, phosphoric acid is potentially cheaper than zinc orthophosphate, but is a strong acid that can require safety precautions.

How can the WBS model for phosphate feed be used?

The work breakdown structure (WBS) model can estimate costs for a process to add phosphoric acid or zinc orthophosphate into a water pipeline at an existing drinking water treatment plant. It can estimate the cost of phosphate feed using different chemical formulations, if the user provides appropriate inputs for the alternative chemical (e.g., solution strength, density, price).

Where can I find more information on RO and NF?

The technical report Work Breakdown Structure-Based Cost Model for Phosphate Feed Drinking Water Treatment discusses the technology in detail.

Nontreatment options

What are nontreatment options?

Instead of treating a contaminated water source, nontreatment options replace the source with water that meets applicable drinking water standards. Examples include interconnection with another system and drilling a new well to replace a contaminated one.

Why are they useful?

Nontreatment can provide a route to compliance with drinking water standards for various contaminants, as long as an alternate water source is available.

What are the advantages of using nontreatment options?

Small water utilities, particularly those that lack financial and/or technical capacity, might be able to use nontreatment approaches to avoid the cost and labor associated with installing and operating new treatment processes.

What are the disadvantages of using nontreatment options?

Interconnection requires a neighboring utility with excess capacity that is willing to sell water to the affected utility. Installation of a new well requires the existence and accessibility of an uncontaminated aquifer.

How can the WBS model for nontreatment options be used?

The work breakdown structure (WBS) model can estimate costs for either of two nontreatment options:

  • interconnection with another system
  • drilling a new well to replace a contaminated one

Where can I find more information on nontreatment options?

The technical report Work Breakdown Structure-Based Cost Model for Nontreatment Options for Drinking Water Compliance discusses these options in detail.

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Last updated on April 5, 2024