Guidance for Treatment of Airport Stormwater Containing Deicers (2013)

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34 C H A P T E R 3 Identifying Deicer Treatment Technologies 3.1 Classification System for Deicer Treatment Many technologies are capable of removing deicers from stormwater. Classification of deicer treatment provides insight into the process of implementing deicer treatment systems. Figure 12 illustrates the classification system for deicer treatment technologies used in this guidebook. The classification system is also shown in Table 3 with examples of airports that have imple- mented the various treatment technologies. Appendix A provides a more detailed list of airports reviewed in the guidebook and the treatment technologies that they use. The classification system uses three categories to describe treatment: method, process, and technology. Characteristics associated with these categories are described in the following. Method is a broad classification that identifies the type of treatment and its typical location. The type of treatment is described as physical or biological. The location is described as on-site or off-site. On-site refers to a treatment system that is directly controlled by the airport operator in a facility typically on or close to the airport. Off-site refers to a treatment system that is con- trolled by an entity other than the airport operator at an off-airport location. On-site biological treatment is a biological treatment system operated by the airport. On-site physical treatment is typically a recycling system operated by the airport. Off-site biological treatment is typically discharge to the sanitary sewer with treatment at the POTW. Off-site physical treatment is typi- cally recycling at a privately operated facility. Process refers to subcategories of physical and biological treatment that describe the funda- mental elements of how the technology works, as summarized in the following. 1. On-site biological treatment processes. Biological processes have been used for over 100 years to treat contaminated water. All biological treatment systems are a combination of natural and engineered processes. Naturally occurring microorganisms, primarily bacteria, consume the organic contaminants in water as food. In all biological treatment systems, microorganisms (i.e., biomass) oxidize organic compounds contained in contaminated water, converting the compounds into simple end products and more biomass. End products can include carbon dioxide, methane, and water. While the essential treatment mechanism is natural for all biological treatment systems, various levels of engineering and control have been applied over the last century. The most prominent drivers for creating an engineered biological system are: • Reducing space requirements, • Improving treatment efficiency, • Providing better response to variations in influent characteristics and ambient conditions,

Identifying Deicer Treatment Technologies 35 • Providing a more predictable effluent quality, and • Providing more consistent costs and operations. All biological treatment systems are designed to create a contained environment that sup- ports contact between the bacteria and the organic pollutants, allowing the living organisms to flourish and resulting in reduction of the concentrations of the oxygen-demanding pollutant (measured as BOD, COD, etc.). This contact can occur in flowing streams, soils via overland flow and infiltration, wetlands, or man-made structures. Biological treatment systems are generally engineered to contain naturally occurring treatment processes in a smaller, confined area to allow optimization of treatment effectiveness and efficiency. Even biological treatment systems that are sold as “natural treatment systems” require some degree of engineering and control. Deciding on a type of biological treatment, therefore, is not a choice between natural and engineered. Instead it is largely an exercise of understanding the trade-offs between space requirements, extent of engineering, level of control and operational requirements, and cost. Today, biological treatment is the principal treatment method used by municipalities worldwide to treat discharges to sanitary sewers. It is also used in many varied types of industrial-facility wastewater treatment. TechnologyProcessMethod Off-site physical treatment Privately owned industrial recycling systems Evaporation Membrane filtration Off-site biological treatment POTW/municipal wastewater treatment plant Activated sludge (typical, but varies) Anaerobic sludge digestion On-site biological treatment Aerobic attached growth Aerated gravel beds Biofiltration Moving bed biofilm reactor Reciprocating gravel beds Activated sludge Aerated lagoon Aerobic suspended growth Anaerobic fluidized bed reactorAnaerobic attachedgrowth Passive facultative In-situ (soil-based) flow through Irrigation-based soil treatment Subsurface flow wetlands Reed bed wetlands On-site physical treatment Evaporation Distillation Mechanical vapor recompression Membrane filtration Reverse osmosis Figure 12. Deicer treatment classification system used in the guidebook.

36 Guidance for Treatment of Airport Stormwater Containing Deicers Advantages to biological technologies for treatment of deicer-affected stormwater include: • Compared to chemical oxidation and physical treatment technologies, biological treat- ment technologies generally have lower capital and operating costs, especially for storm- water with BOD5 concentrations of less than 10,000 mg/L. • They are better suited to treat mixtures of organic compounds (e.g., PG, EG, acetate, for- mate) in the stormwater than physical treatment technologies that isolate individual chem- icals or types of chemical compounds. Biological technologies are therefore well suited to runoff that contains significant amounts of both ADF and pavement deicers. • The primary deicer constituents in the stormwater are destroyed through conversion of the chemicals to cell mass and simpler chemicals, which is attractive for airports with PG and EG limits. • If sized and operated properly, they can achieve low effluent concentrations. • They are reasonably effective at treating waters with varying flow rates and mass loads. Disadvantages to biological technologies for treatment of deicer-affected stormwater com- pared to physical treatment technologies include: • Their effectiveness is dependent on keeping a population of microorganisms alive and healthy. With the variability in the deicing environment (flow rates, BOD loadings, tem- peratures), additional steps are frequently needed to control the influent loadings and create a consistent level of microorganism activity. • Low water temperatures slow biological activity significantly. Low temperatures will often require operating at less than design capacity to achieve desired effluent quality. • Deicer-impacted stormwater is generally devoid of the nutrients (forms of nitrogen, phos- phorus, and micronutrients) that bacteria need for their metabolism and growth. Nutrients Table 3. Proposed classification system deicer treatment as applied at airports. Method Process Technology Example Airport Using Technology* Off-site biological treatment Publicly owned treatment works/municipal wastewater treatment plant Activated sludge (typical, but varies) DTW Anaerobic sludge digestion MKE Off-site physical treatment Privately owned industrial recycling systems Evaporation and membrane filtration PIT On-site biological treatment Aerobic attached growth Moving bed biofilm reactor OSL Aerated gravel beds BUF Reciprocating gravel beds ILN Biofiltration CDG Aerobic suspended growth Activated sludge CVG Aerated lagoon BNA Anaerobic attached growth Anaerobic fluidized bed reactor PDX Passive facultative In-situ (soil-based) flow through FRA Irrigation-based soil treatment ZRH Subsurface flow wetlands CEF Reed bed wetlands LHR On-site physical treatment Evaporation Mechanical vapor recompression YYT Distillation DEN Membrane filtration Reverse osmosis BDL *See Acronyms and Abbreviations section for definition of airport codes.

Identifying Deicer Treatment Technologies 37 can be effectively added, but in practice the regularity and extent of nutrient addition in some deicer treatment systems has been less than optimal. • The health of the microorganisms is difficult to measure directly, so a variety of indirect measures are used. At times of unusual or upset conditions, relying on indirect measures can make troubleshooting more challenging. • Some biological treatment technologies produce significant volumes of biological solids composed of microorganisms that are no longer needed or viable. These wasted biological solids must be processed and disposed of. While the constituents in deicer-affected stormwater are generally highly biodegradable, the unique conditions of deicing have required that traditionally used biological wastewater treat- ment technologies be adapted for use in deicer treatment. For deicer-affected stormwater, four fundamental biological treatment processes have been used to date, as described in the following. The processes are defined by the biology type (aerobic and anaerobic) and the environment in which the bacteria grow (attached to inert media or suspended in water). a. Aerobic suspended-growth biological treatment. An aerobic treatment process is primarily characterized by the supplying of oxygen to the water to promote the growth of aerobic bacteria. By-products from aerobic deicer treatment systems include additional biomass and carbon dioxide. Suspended growth refers to the fact that the aerobic bacteria are sus- pended in a reactor by the action of water or air. These types of systems are actively con- trolled using human operators or computers. Two aerobic suspended-growth technologies have been used at airports: activated sludge (see Fact Sheet 101) and aerated lagoons (see Fact Sheet 103). Both technologies have been used since the early part of the 20th century for general wastewater treatment. b. Aerobic attached-growth biological treatment. An aerobic attached-growth process is char- acterized by aerobic bacteria growing on an inert media, such as gravel or plastic, con- tained in the treatment reactor that also receives an air supply. These types of systems are actively controlled using human operators or computers. By-products from aerobic deicer treatment systems include additional biomass and carbon dioxide. To date, the aerobic attached-growth technologies that have been used as a primary means to treat deicer from airports are the aerated gravel bed (see Fact Sheet 102) and the moving bed biofilm reactor (MBBR) (see Fact Sheet 107). c. Anaerobic attached-growth biological treatment. An anaerobic treatment process uses anaero- bic microorganisms living in the absence of oxygen to degrade the primary deicer constitu- ents in the stormwater discharges. By-products from anaerobic treatment include additional biomass, methane, and carbon dioxide. The anaerobic bacteria are attached to an inert media in the treatment reactor, such as activated carbon. These types of systems are actively con- trolled using human operators and computers. The one anaerobic attached-growth process that has been used to treat deicer-affected stormwater is the AFBR (see Fact Sheet 104). d. Passive facultative biological treatment. This category encompasses a wide variety of tech- nologies that share the elements of employing facultative bacteria and minimal process control. A facultative process, as defined here, is one that typically features a mixture of bacteria that are capable of degrading deicing constituents regardless of the oxygen level in the stormwater. The bacteria include aerobic bacteria that can obtain oxygen from the atmosphere, anaerobic bacteria that live in areas without oxygen, and facultative bacteria that can live in areas with or without oxygen. Passive refers to a reduced level of operator and computer control and a reduced use of mechanical equipment. Due to low biological reaction rates, these systems are typically large in size—a slower pollutant processing rate by the bacteria means a larger number of bacteria are required to accomplish the same level of treatment. The lack of process control, however, restricts the conditions in which the systems will function adequately and generally results in fewer options for responding

38 Guidance for Treatment of Airport Stormwater Containing Deicers Treatment Tips Anaerobic Aerobic Better effluent quality Fewer nutrient requirements Less reactor volume/footprint Faster response at start-up Less energy use Less sludge production Methane by-product may be used as fuel source Ability to treat at lower temperatures without heat addition Less complex operation Anaerobic Versus Aerobic Biological Deicer Treatment to changing deicing conditions. This is most significant in regard to cold-weather operation, when low water temperatures reduce the efficacy of facultative treatment processes. A number of specific technologies that can be classified as passive facultative processes have been tested and implemented for treatment of airport stormwater, including subsurface flow wetlands, soil-based (sometimes called in-situ) systems where stormwater passes through soil as fed from irrigation or overland flow means, and non-aerated technologies where water is passed through a bed of gravel or other media. Fact Sheet 108 further discusses passive facultative processes. 2. On-site physical treatment processes. Physical treatment includes processes where the removal of deicer from stormwater is carried out through physical phenomena. Unlike biological treatment, physical treatment is not designed to change the pollutants chemically. It is designed to segregate the stormwater into a high pollutant concentration fraction (typi- cally called a “concentrate stream”) and a low-concentration fraction (typically called a “dilute stream”). Most often, physical treatment processes are employed in deicer treatment to achieve the benefit of a recyclable end product (concentrated glycol) in the process of reducing concentrations in the dilute stormwater stream that will ultimately be discharged to the environment. Additional processes may be required to treat the dilute streams from physical treatment systems that may contain several hundred mg/L of BOD. If the concen- trated product is not recycled, it needs to be disposed of using an additional treatment pro- cess. To date, two primary physical treatment processes have been used for deicer-affected stormwater, as shown in the following. a. Evaporation processes. Evaporation processes use an applied energy source to heat the stormwater, evaporating the water and leaving behind a more concentrated fraction con- taining the bulk of the deicing chemicals. Two evaporation technologies have been used extensively in deicer treatment: mechanical vapor recompression (see Fact Sheet 106) and distillation (see Fact Sheet 105). b. Membrane filtration processes. Membrane filtration processes rely on a liquid being forced through a filter membrane with a high surface area. There are four basic pressure- driven membrane filtration processes for liquid separations. From smallest membrane openings to largest membrane openings, the four main technologies are reverse osmosis,

Identifying Deicer Treatment Technologies 39 nanofiltration, ultrafiltration, and microfiltration. Reverse osmosis is the only membrane filtration technology that can separate glycol molecules from water. Other membrane filtra- tion processes, especially ultrafiltration, may be used as a pretreatment step before reverse osmosis to remove larger particles. See Fact Sheet 111 for reverse osmosis. 3. Off-site treatment at a publicly owned treatment facility. In the United States and many other places, wastewater treatment plants operated by cities and other municipal entities are used to treat household sanitary sewage and polluted waters from commercial and industrial facili- ties. In the United States, these facilities are generally known as publicly owned treatment works. Elsewhere the facilities are more simply sewage treatment plants or municipal waste- water treatment plants. Most pollutant waters are conveyed to POTWs via sanitary sewer systems. Deicer-affected stormwater runoff that is discharged to the sanitary sewer is mixed with other wastewaters and passed through the entire treatment process. Some airports have arranged for treatment of a concentrated stream of deicer-affected stormwater directly in the anaerobic digesters that POTWs operate to break down the bio- logical solids generated from their treatment processes. This is beneficial to the POTWs because it provides an additional source for producing methane that the POTWs capture and use as a fuel source. A POTW could also use concentrated deicer as a carbon source for its denitrification process. Use of deicer in anaerobic digesters or the denitrification process requires a means for transporting, potentially storing, and metering the deicer into the pro- cess at the POTW. Treatment Tips Biological Treatment Physical Treatment Less pretreatment required Can produce saleable end product Wider range of pollutants treated Better response start-up and shutdown sequences Shorter start-up period Less energy use Fewer odors Less sludge production Potential for off-gas to be used as fuel source Ability to treat at lower temperatures without heat addition Ability to cost-effectively treat BOD <1% concentration Ability to cost-effectively treat BOD >1% concentration Ability to cost-effectively treat deicer use <300,000 gal/year Ability to cost-effectively treat deicer use >300,000 gal/year Ability to cost-effectively achieve low effluent concentrations Production of secondary waste stream requiring treatment Biological Treatment for Degrading Deicers Versus Physical Treatment for Recycling Deicers

40 Guidance for Treatment of Airport Stormwater Containing Deicers See Fact Sheet 109 for public wastewater treatment facilities. 4. Off-site treatment at a privately owned industrial recycling facility. Some airports are located close enough to a privately operated glycol recycling facility that it is economical to transport the concentrated segments of the deicer-affected stormwater runoff for off-site recycling. The off-site facility typically uses multiple recycling technologies that may include membranes, mechanical vapor recompression, thermal vapor recompression, other evaporation systems, or distillation. By separating and reclaiming the glycol from the deicer-affected stormwater, the recycling provider can generate revenue from the sales of glycol. This arrangement can reduce the treatment equipment that would otherwise be installed at the airport site and eliminate the corresponding operating expenses. 3.2 Features of Existing Individual Deicer Treatment Technologies In this section, the features of the 11 individual deicer treatment technologies defined in this guidebook are summarized. Guidebook users should reference the individual treatment technol- ogy fact sheets for more detailed information on the 11 technologies. Some specific variations of the technologies that have been implemented or tested are also discussed in this section in boxes entitled “Treatment Technology Example.” Applications of the 11 deicer treatment technologies in Table 4 are discussed in the airport deicer treatment system summaries in Appendix D. Treatment Tips On-Site Treatment Off-Site Treatment Storage needed Control of discharges potentially needed Lower risk in discharging collected water Lower operating cost Lower capital cost Fewer airport operational interferences during construction Fewer operators needed On-Site Versus Off-Site Deicer Treatment Fact Sheet No. Treatment Technology Sample of Airports Using the Technology (See Appendix D for Summaries)* 101 Activated sludge CVG 102 Aerated gravel beds BUF, LHR, YEG, ILN 103 Aerated lagoons BNA 104 Anaerobic fluidized bed reactors PDX, CAK, ALB 105 Distillation DEN, ZRH 106 Mechanical vapor recompression YHZ, DEN, CVG, BDL 107 Moving bed biofilm reactors OSL 108 Passive facultative treatment systems ZRH, CEF, YEG, LHR 109 Public wastewater treatment facilities DTW, DEN, PDX, BNA 110 Private recycling facilities DTW 111 Reverse osmosis BDL *See Acronyms and Abbreviations section for definition of airport codes. Table 4. Deicer treatment technologies featured in guidebook.

Identifying Deicer Treatment Technologies 41 3.2.1 Biological Treatment Technologies 3.2.1.1 Activated Sludge Activated sludge is one of the oldest and most widely used suspended-growth biological treat- ment technologies to treat wastewater. The activated sludge process, as used for deicer treatment, has two main components: an aerated basin where most of the BOD reduction occurs and a clarifier where biological solids are separated. The key element of an activated sludge process is the recycling of the sludge from the clarifier back to the aeration basin to obtain an elevated concentration of bacteria in the aeration basin, allowing more efficient treatment. Advantages of activated sludge compared to other treatment technologies include: • It can obtain very low effluent BOD concentrations, • It has a relatively small footprint, and • It can process large volumes. Disadvantages of activated sludge compared to other treatment technologies include: • It typically has an open-water surface, • It takes a high volume of biological solids (sludge) to process, and • It can be negatively affected by cold temperatures. The activated sludge technology is well suited to the following applications: • Treatment of more dilute concentrations (typically <5,000-mg/L COD ). • Airports requiring treatment of high flow volumes. • Airports in warmer climates. • Airports with low effluent limits (<40-mg/L COD ). The specific variations on the activated sludge technology that have been applied for deicer treatment are summarized in the following. • Extended aeration activated sludge. Extended aeration activated sludge is a slight variation on conventional activated sludge in which the activated sludge unit process is operated at a rela- tively long hydraulic retention time and increased biomass holding period. Advantages compared to other activated sludge variants include: – Lower sludge production, – Better ability to absorb shock loadings, and – Better ability to segregate BOD reduction and solids separation functions. Disadvantages compared to other activated sludge variants include: – Larger open-water surface and larger footprint, and – Challenges in maintaining healthy and sufficient biomass if deicer supply is variable. The extended aeration activated sludge technology is well suited for the following applications: – Airports with variation in influent stormwater characteristics. – Airports having a steady supply of deicer through the winter. – Airports needing to meet lower effluent limits for BOD. • Sequencing batch reactors (SBRs). Unlike other variants of activated sludge, which operate in a continuous flow-through mode, SBR technology is essentially a batch mode process adapted to continuous-flow operation. An SBR system typically consists of at least two identically equipped tanks with a common, switchable inlet. Each tank operates separately in a fill-and-draw mode,

42 Guidance for Treatment of Airport Stormwater Containing Deicers whereby the tank goes through successive filling, reacting (aeration), and solids-separating steps. The switchable inlet for the tanks allows the system to operate in a flow-through mode, with raw wastewater (influent) continuously flowing into at least one tank while treated efflu- ent can continuously flow out of at least one other tank. While one tank is in settle/decant mode, the other is aerating and filling. At the inlet is a section of the tank known as the bio- selector. This consists of a series of walls or baffles that direct the flow either from side to side in the tank or under and over consecutive baffles. This helps to mix the incoming influent and the returned activated sludge (RAS), beginning the biological digestion process before the wastewater enters the main part of the tank. Advantages of the SBR compared to other activated sludge variations include: – Small footprint—all operations contained in a single tank, and – Somewhat more resistant to cold temperatures because of less surface area for heat loss. Disadvantages of the SBR compared to other activated sludge variations include: – Higher degree of operator expertise required, and – More difficulty in optimized individual treatment and settling functions. The SBR activated sludge technology is well suited for the following applications: – Airports with limited space, and – Airports where low effluent concentrations are needed. The airport summary in Appendix D for Cincinnati/Northern Kentucky International Air- port features activated sludge treatment. 3.2.1.2 Aerated Gravel Beds The aerated gravel bed is a treatment technology that combines key facets of engineered wet- lands, trickling filters, and aerated lagoons. It achieves treatment using aerobic bacteria attached to gravel surfaces. The treatment capacity of an aerated gravel bed system is directly proportional to the surface area of the aerated gravel bed. Specific variations on the aerated gravel bed technology that have been applied at airports include: • Diffused air supply, and • Reciprocating gravel beds. Advantages of aerated gravel beds compared to other deicer treatment technologies include: • Minimal requirements for solids processing in treated effluent, • Less operationally complex than many other biological treatment systems, and • No need to reseed at the start of each deicing season. Disadvantages of aerated gravel beds compared to other deicer treatment technologies include: • Larger footprint, • Limited access to buried piping and equipment, and • Potential for long-term fouling and clogging if mass load targets are exceeded. The aerated gravel bed technology is well suited for the following applications: • Airports with runoff having glycol concentrations less than 0.5% (5,000 mg/L). • Airports with lower-concentration, higher flow rates to process, such as runoff from airfield areas. • Airports with available land that want a less-complex treatment operation.

Identifying Deicer Treatment Technologies 43 The following airport summaries in Appendix D feature some variation on aerated gravel beds: • Buffalo Niagara International Airport. • Wilmington Airpark. • London Heathrow International Airport. • Edmonton International Airport. 3.2.1.3 Aerated Lagoons Aerated lagoons are earthen basins that employ mechanical aeration systems to deliver oxygen to the lagoon water. Aerated lagoons are best suited for airports that typically have concentra- tions of less than 0.5% (5,000 mg/L) glycol. An aerated lagoon treatment system may provide both treatment and equalization storage. Specific variations of aerated lagoons that have been applied at airports include: • Mechanical surface aeration, • Facultative lagoons (without aeration), and • Algal treatment systems. Advantages of aerated lagoons compared to other deicer treatment technologies include: • Lower cost, and • Easier to operate than other biological treatment systems. Disadvantages of aerated lagoons compared to other deicer treatment technologies include: • Requires larger land area than activated sludge or similar technologies, • Requires management of nutrient and BOD loadings for optimal performance, • Loss of heat and performance in cold weather, and • Odors, especially in early summer, and open-water issues. The aerated lagoon technology is well suited for the following applications: • Airports with large land areas available. • Airports with less restrictive effluent limits. • Airports with runoff with BOD concentrations of less than 5,000 mg/L. The airport summary in Appendix D for Nashville International Airport features aerated lagoons. A discussion of the experiences of other airports with aerated lagoons is found in the Treat- ment Technology Example: Aerated Lagoons text box. 3.2.1.4 Anaerobic Fluidized Bed Reactors AFBR technology is an anaerobic biological process (i.e., does not require aeration or oxygen for the process) and is well suited for treatment of highly concentrated stormwater. In an AFBR, anaerobic bacteria grow on a media of activated carbon, sand, or other material housed in a reac- tor tank. This media bed is fluidized by forcing water into the bottom of the reactor. The AFBR system incorporates a process for separating and removing excess biological solids. The AFBR process is best suited to high-concentration water (~2,100-mg/L to 80,000-mg/L COD) and is also capable of achieving relatively low effluent concentrations (as low as 35 mg/L soluble COD after the biological solids removal in some systems). Advantages of the AFBR compared to other deicer treatment technologies include: • System is not subject to temperature fluctuations because the influent stormwater is heated using both heat reclaimed from the treated effluent and water heated by the burning of methane gas captured from the biological reactor and burned in a boiler,

44 Guidance for Treatment of Airport Stormwater Containing Deicers • Excess methane gas captured from the treatment reactors can provide energy savings by use for heating the treatment building and other processes in need of heat, • Resiliency to upsets caused by variation in stormwater characteristics, • Effluent COD concentrations in a predictable range when operated as required, • Low operating cost, • Can be shut down for the summer months and restarted without seeding, and • Because the anaerobic bacteria grow at a slower rate than aerobic bacteria in technologies like activated sludge and aerated lagoons, the quantities of biological solids generated in an AFBR are up to 10 times lower than the biological solids resulting from some aerobic treatment processes. Disadvantages of the AFBR compared to other deicer treatment technologies include: • More complex operation, with multiple support systems to manage together, • The maximum flow rates that can be treated are limited by process constraints, • Longer start-up periods due to the slower-growing bacteria, • Longer and more complex construction, • More equipment to maintain, and • More process data to collect and assess. The anaerobic fluidized bed reactor technology is well suited for the following applications: • Treating lower-flow, higher-concentration, and high-load deicer-affected stormwater, such as runoff from deicing pads or runoff segregated by concentration using online monitors. • Situations where low glycol concentrations in the effluent are required. • Operations that can take advantage of excess methane production for use in reducing energy costs. • Airports where the available space for treatment is limited. The following airport summaries in Appendix D feature anaerobic fluidized bed reactors: • Akron-Canton Airport. • Portland International Airport. Treatment Technology Example: Aerated Lagoons Aerated lagoons are some of oldest biological treatment systems, both for waste- water in general and for deicer. Frequently, however, airports discovered that treatment efficiencies were often limited by cold temperatures, lack of nutri- ents, variations in flow and BOD loading, and lack of oxygen. As a result, some airports focused on using the lagoons for winter runoff storage, with treatment only occurring when temperatures were adequate for biological treatment. For example, Rockford International Airport stores runoff collected during the deic- ing season until April when it begins treating the collected stormwater. Syracuse International Airport (SYR) also observed that treatment was not optimized until summer. SYR altered its operation so that the aerated lagoon collected and stored runoff until treatment began in the summer. After successful operation of the aerated lagoon during the summer months for several seasons, the local POTW made enhancements that now permit SYR to discharge to the local POTW without on-site treatment.

Identifying Deicer Treatment Technologies 45 3.2.1.5 Moving Bed Biofilm Reactors The MBBR technology incorporates both activated sludge (suspended bacteria) and attached bio- logical growth (fixed bacteria on media) in the treatment process. Aeration is provided to the tank to support activated sludge processes throughout the tank. The aeration also suspends media to pro- mote attached biological growth. An MBBR can achieve low effluent concentrations and is typically best suited for systems that have low influent BOD concentrations (<5,000 mg/L). It can typically accommodate higher flow rates than systems like AFBRs and recycling-based technologies. Advantages of MBBRs compared to other deicer treatment technologies include: • Is a well-understood process with a readily available operator pool, • Biogrowth is rapid, such that capacity increases quickly (relative to processes without media) from a seed, and • Is able to achieve very low effluent concentrations, in the range of less than 30-mg BOD/L, when sufficient detention time is available and water temperatures are sufficiently high. Disadvantages of MBBRs compared to other deicer treatment technologies include: • High operating costs, • Settling issues during biological upsets, and • Must reseed each season or keep a biological seed active over the summer. The moving bed biofilm reactor technology is well suited for the following applications: • Low-to-moderate BOD concentrations (<5,000 mg/L) where very low effluent concentrations are required. The airport summary in Appendix D for Oslo Gardermoen Airport (Norway) features MBBRs. 3.2.1.6 Passive Facultative Technologies Passive facultative treatment (PFT) systems are designed to employ chemical, physical, and biological treatment mechanisms, but with minimal man-made power or equipment. The PFT category encompasses lagoons, wetlands, sand filters, and similar approaches that provide pas- sive removal of glycols and other deicing compounds from contaminated stormwater. Some have labeled this broad category of technologies as “natural treatment systems.” However, that label does not sufficiently distinguish treatment technologies and is potentially misleading because (a) all biological treatment technologies are based on use of natural, living microorganisms, and (b) all treatment technologies require some degree of engineering and control with man-made equipment, instruments, and structures. PFT systems tend to have a lesser degree of engineer- ing and control. To successively function with less engineering and control, however, the PFT technologies require greater areas of land. The most successful PFT technology applications have required significant investments in testing, flow control, and monitoring. Specific variations of passive facultative technologies that have been applied at airports include: • Irrigation-fed soil (in-situ) treatment, • Infiltration basins, • Subsurface horizontal flow-through wetlands, • Vertical flow wetlands, and • Reed bed wetlands. Advantages of passive facultative technologies compared to other deicer treatment technolo- gies include: • Potentially less operator involvement needed, • Potentially lower cost,

46 Guidance for Treatment of Airport Stormwater Containing Deicers • Less maintenance, and • Can use land areas (such as infield areas for taxiways and runways) that are otherwise unusable for development. Disadvantages of passive facultative technologies compared to other deicer treatment tech- nologies include: • Require large land areas, • Performance of some systems can be uneven and subject to the effects of the variable storm- water influent, unless the influent loading to treatment is controlled, and • More difficult to get effluent monitoring data, so performance of the systems is difficult to document. Passive facultative technologies are well suited for the following applications: • Airports with large land areas available. • Airports with soil characteristics that allow the applied water to percolate in the soil while providing sufficient detention time for the bacteria in the soil/media to achieve treatment. • Dilute runoff from runways and taxiways. The following airport summaries in Appendix D feature passive facultative systems: • Edmonton International Airport (original technology, since upgraded). • London Heathrow International Airport (original technology, since upgraded). • Westover Air Force Reserve Base. • Zurich International Airport. Examples of the experiences of other airports with PFTs are found in the Treatment Technol- ogy Example: Passive Facultative Systems text box. 3.2.2 Physical Treatment Technologies 3.2.2.1 Mechanical Vapor Recompression Mechanical vapor recompression (MVR) is an evaporation process that uses compressors or blowers to increase the pressure of the vapors produced during evaporation, which allows for heat transfer back to the influent flow stream. MVR requires less energy input to achieve distillation than does thermal evaporation (distillation). The evaporation process allows the Treatment Technology Example: Passive Facultative Systems Washington Dulles International Airport (IAD) installed five non-aerated gravel bed biological treatment units as part of the construction of a new runway. The non-aerated gravel beds were designed to treat low-concentration fugitive deicing fluid in stormwater runoff from the new runway. Because the system is subsurface, it is less of a waterfowl attractant than a surface water treatment system. The non-aerated gravel bed at IAD does not use storage or nutrient addi- tion. Performance of the non-aerated gravel bed system at IAD is not monitored. Frankfurt Airport, Germany, uses a soil treatment system for low-concentration runoff from taxiways and runways. Runoff from the taxiways and runways is collected in slotted drains and treated by soil filters. This is a new system, and performance data should be available in the future.

Identifying Deicer Treatment Technologies 47 deicer-affected stormwater to be separated into two separate effluent streams. The two streams consist of a higher-concentration glycol concentrate stream and a lower-concentration glycol distillate stream. The MVR is best suited for recovering glycol from systems that have influent concentrations of greater than 1% (10,000 mg/L) glycol. Advantages of MVRs compared to other deicer treatment technologies include: • Can lead to reclaiming of a recyclable product (in combination with other technologies to raise glycol concentrations to sufficient levels), • Can be started and stopped quickly—no ramp-up time needed, and • Can be easily expanded. Disadvantages of MVRs compared to other deicer treatment technologies include: • The distillate stream may require additional processing to reduce BOD concentrations to levels acceptable for discharge (depending on effluent limits), • For airports with large collected volume, a large number of MVR units may be needed, and • MVR heat exchangers require more maintenance and cleaning when dealing with spent ADF with higher concentrations of thickened fluids (i.e., Type IV fluids). Mechanical vapor recompression technologies are well suited for the following applications: • Airports using deicing pads, and • Airports using glycol recovery vehicles. The following airport summaries in Appendix D feature mechanical vapor recompression: • Bradley International Airport. • Cincinnati/Northern Kentucky International Airport. • Denver International Airport. • Halifax International Airport. 3.2.2.2 Distillation Distillation is an evaporation process in which the influent is separated by vaporization and condensation into two streams. The two streams consist of a higher-concentration glycol con- centrate stream and a lower-concentration glycol distillate stream. The distillate stream typically requires further treatment. Distillation is best suited for recovering glycol from systems that have influent concentrations of greater than 15% (150,000 mg/L) glycol. Advantages of distillation compared to other deicer treatment technologies include: • Produces product with concentrations high enough for recycle market to offset processing costs, and • Reduces the costs of transportation of stormwater to off-site site facilities. Disadvantages of distillation compared to other deicer treatment technologies include: • Because of energy costs, distillation is only applicable to treatment of high-concentration streams. • The distillation process creates contaminated wash-down water and bottoms waste (sludge) from the columns that cannot be discharged and must be treated further. • The distillate or condensate water stream that distillation produces contains COD concentra- tions that are usually above acceptable levels to discharge to stormwater, which requires airports to discharge these residual streams to POTWs or other treatment systems for further treatment. • Distillation columns can be very large and tall. Height can be an issue at airports. • Large distillation systems can be expensive to build. A large volume of glycol needs to be reclaimed so that the glycol product can be sold to offset capital and operating expenses.

48 Guidance for Treatment of Airport Stormwater Containing Deicers There are few airports that spray and recover enough ADF to justify installation of an on-site distillation system. Distillation technologies applied at an airport are well suited for the following applications: • High-concentration fractions from deicing pads or systems that segregate water by concentration. • Treating concentrated discharges from MVRs or reverse osmosis systems. • Due to recent advances in distillation technology, the quality of the glycol produced is acceptable for reuse as a feedstock for on-site production of ADF at airports. This can provide substantial savings in logistics costs. However, distillation is energy-intensive; therefore, it is generally not cost-effective to distill and recycle waste glycol solutions at low concentrations. The following airport summaries in Appendix D feature distillation: • Denver International Airport. • Zurich International Airport. 3.2.2.3 Reverse Osmosis (Membrane Filtration) Reverse osmosis (RO) is a process where a semipermeable membrane is subjected to a pres- surized influent stream. In natural osmosis, when two different concentrations of solutes are separated by a semipermeable membrane, the solvent (typically water) diffuses through the mem- brane from the lower-concentration side to the higher-concentration side. In RO, a high pressure is applied to the high-concentration side and the solvent (water) passes through the membrane to the lower-concentration side. The RO membrane pores are sized extremely small, thereby pre- venting individual molecules of the targeted constituents to pass through. The RO process creates two streams. The permeate stream is produced by water that passes through the RO membrane and contains relatively low glycol concentrations, while the concentrate stream contains much higher concentrations than the original stormwater influent. RO typically works best for recover- ing glycol from systems that have influent concentrations of greater than 1% (10,000 mg/L) glycol. Advantages compared to other deicer treatment technologies include: • RO units can be used in conjunction with other complementary recycling technologies, such as MVR systems, to increase the amount of glycol that can be reclaimed, and • RO units can be designed to be modular, which means they can be installed on a relatively small footprint, and additional units can be added if increased capacity is required. Disadvantages compared to other deicer treatment technologies include: • Variability in influent deicer concentrations affects throughput. Generally, the higher the concentration of deicer in the stormwater, the slower the processing rate or the larger the RO pump required. • The production rate is highly affected by temperature, with lower temperatures decreasing throughput. • Desired effluent concentration of reject water affects influent processing rate and directly affects permeate quality for RO systems. • Reverse osmosis units applied to stormwater treatment require some type of pretreatment or filtration ahead of the RO system in an effort to protect the membranes. • To eliminate potential biological growth and scaling, membranes must be treated with biocide if the processing systems sit idle for extended periods. RO technologies are best suited for the following applications: • Situations where recycling is desired but collected concentrations are too low for MVR treatment to be economical.

Identifying Deicer Treatment Technologies 49 • Other situations where recycling is desirable. • Situations where it is desirable to create a more concentrated stream and a dilute stream for further processing. The airport summary in Appendix D for Hartford International Airport features reverse osmosis. 3.3 Features of Emerging Treatment Technologies Emerging deicer treatment technologies are considered those that have not been proven on a full-scale at an airport but merit potential consideration. If the history of deicer treatment is a guide, application of new technologies to deicer treatment will require a period of testing, trials, and adaptation that may evolve over several years. The following categories of emerging technologies are discussed later in this section: • Emerging biological technologies, and • Emerging chemical treatment technologies. In addition, enhancements to existing technologies are also discussed, including: • Biological technologies, • Physical treatment technologies, and • POTW discharges. 3.3.1 Emerging Biological Technologies 3.3.1.1 Treatment in Algal Ponds Biological treatment using micro-algae technology has been tested on deicer-affected storm- water. The technology uses elements of passive facultative lagoons and aerated lagoons, com- bined with the capability to harvest algae for sale on the market. Similar to other biological treatment technologies, the bacteria, not the algae, break down the deicer compounds. The tech- nology uses the carbon dioxide by-product of the bacterial treatment to intentionally promote the growth of algae. Through photosynthesis, the algae in turn produce dissolved oxygen that can be used by the bacteria. To meet the oxygen demand needs in the stormwater, additional oxygen can be supplied through methods such as the use of paddle wheels. The algae are harvested and can be sold for products such as biofuels, plastics, and fertilizer. Algal treatment has the following potential advantages for deicer treatment: • Potential reduction in oxygen supply required due to the oxygen produced by the algae, and • Potential development of an algae by-product that can be sold. Algal treatment has the following potential disadvantages for deicer treatment: • Treatment efficiency is not likely greater than other aerobic suspended-growth biological treatment systems, • Possible large land area required if large BOD design capacity is required, • Potential need to manipulate flows into treatment to optimize algae production, and • Potential cold temperature impacts on biological treatment and algae production. Most likely applications for algal treatment would be: • Airports in warmer climates, • Airports with available land, and • Airports interested in reducing deicer treatment costs through sale of a by-product.

50 Guidance for Treatment of Airport Stormwater Containing Deicers Space requirements and the need to further optimize the balance between deicer treatment and algal production are potential impediments to the use of algal technology for deicer treat- ment. It is recommended that any airport considering algal treatment perform a pilot-scale test prior to design. 3.3.1.2 Membrane Bioreactors A membrane bioreactor (MBR) is a variation of the suspended-growth activated sludge tech- nology that incorporates membrane filtration instead of gravity settling to separate solids. The earliest MBRs were used for municipal wastewater treatment in 1997. Like a conventional acti- vated sludge process, the MBR also uses an aeration basin with suspended biomass to treat the deicer. Unlike a conventional activated sludge process, the MBR uses membrane filter units to separate the biomass in the treated effluent from the water. The use of the membranes allows for better effluent quality and the ability to operate with higher concentrations of biomass in the aeration basin. The membranes can be internal or external to the aeration basin. Treatment Technology Example: Algal Treatment Pilot Test at Schiphol Amsterdam Airport (AMS) (Photo Courtesy of AMS) In 2009, AMS conducted a pilot-scale test of an algal treatment system. The pilot test was conducted in a raceway type of open, lined basin in which the water con- taining the deicer circulates around the basin to undergo treatment, and a paddle wheel is used to add oxygen. Treatment of deicer was provided by bacteria in the water. Algae are cultivated on top of the water. The objective at AMS was not only to break down the deicer but to produce an algae product that could be sold for use in other products. In the pilot testing, the airport was able to grow only the lowest-grade algae—suitable for bioenergy. The goal had been to produce algae that were suitable for sale as fertilizer. AMS tried a number of methods to improve the algae quality, especially in cold conditions, including use of waste building heat to warm the water and LED lighting. Although AMS considered the pilot test a success, they decided not to pursue a full-scale treatment system for a variety of reasons, including the amount of land needed to treat the full COD load that is collected. (Approximately 5 hectares would have been required.) AMS has subsequently moved toward design of an anaerobic-reactor–based technology.

Identifying Deicer Treatment Technologies 51 The MBR has the following potential advantages for deicer treatment: • Produces a higher-quality effluent for discharge. • The plant footprint is potentially 70% smaller than conventional aerated lagoons and acti- vated sludge systems because of reduced aeration basin size and elimination of the clarifier. This potentially makes the system small enough to fit into a building, which provides benefits from a heat loss and open-water surface perspective. • Better stability of biomass in the aeration basin and better removal efficiency because of the high biomass concentrations, which could provide improved response to variable stormwater characteristics. • Elimination of the challenging biomass settling process. • Lower biological solids production than conventional activated sludge. The MBR has the following disadvantages for deicer treatment: • Because of the effects of high water viscosity on the flow rate that can pass through the mem- branes and the fact that viscosity increases as temperature decreases, an MBR for treating cold deicer-affected stormwater will require a greater number of membranes. The costs of MBR systems are highly dependent on the number of membranes modules. • More intensive and costly maintenance associated with membrane cleaning and replacement. • The need for pretreatment to protect membranes. • Potential limitations associated with oxygen transfer in the aeration basin. The MBR technology has been considered by several airports, including PDX, CAK, and PIT, but based on the research survey results, it has not been installed on a full-scale or pilot-scale basis by an airport. Most likely applications would be: • Airports needing effluent with very low BOD concentrations, • Airports with space limitations, and • Airports in warmer climates. The airports in these instances would be willing to pay a somewhat higher cost to take advan- tage of the effluent quality and smaller space. It is recommended that any airport considering MBRs perform a pilot-scale test prior to design because of the lack of operating experience with MBRs treating deicer-containing stormwater. 3.3.1.3 Up-Flow Anaerobic Sludge Blanket Reactor The up-flow anaerobic sludge blanket (UASB) reactor is a variation of the AFBR. The process was developed in the Netherlands in the late 1970s. This process has been used to treat waste- water at food processing plants and paper mills, and occasionally at municipal wastewater plants. The process is essentially similar to the AFBR except that there is no inert media in the reactor. The anaerobic bacteria grow into granular shapes that stay fluidized in the reactor. If the granules shear and get too small or grow and get too large, the equilibrium keeping them suspended in the reactor is upset and they leave with the effluent. If the bed gets too large, some biological solids are wasted, as with a conventional wastewater treatment system. The UASB has the potential advantage for deicer treatment of having a simpler biological solids wasting process than an AFBR. The UASB has the following disadvantages for deicer treatment: • System upset causes sludge blanket to be lost, and • It is difficult to regrow sludge bed following process upset. The issue with regrowing a sludge bed and the instability of the sludge bed will make the UASB a challenge to operate as a deicer treatment system.

52 Guidance for Treatment of Airport Stormwater Containing Deicers UASBs have been used primarily in industries with high-strength wastewater such as brewer- ies and food production facilities. The UASB has many similarities to the AFBR in terms of ability to treat high-strength wastewater efficiently, isolation from weather, and production of methane that can be used as a fuel source. Lack of media in the reactor can lead to a more unstable opera- tion than an AFBR but may also offer more flexibility in design of the reactors than AFBRs. The most likely potential applications for a UASB are situations where they might offer an advantage over the AFBR, such as: • Airports that are interested in anaerobic treatment but have height restrictions, • Airports looking for a somewhat simpler biological solids wasting operation, and • Airports that plan on operating year-round with another organic load source. 3.3.2 Emerging Enhancements to Existing Biological Treatment Systems The evolution of biological treatment is more often about adaptations to existing technologies than use of new technologies. Operators of existing biological deicer treatment systems are continu- ing to make incremental improvements driven by their operating experience. Research is also being conducted on an academic level that may lead to improvements in existing technologies. Current research and incremental improvements for biological treatment systems relevant to deicer treat- ment include attempts to improve performance in the following areas relevant to deicer treatment: • Stability of operations through improved process control. • More efficient treatment with smaller footprints. • Energy efficiency. Potential enhancements to existing biological treatment systems that airports may consider include: • Online monitoring of TOC, COD, nutrients, and dissolved oxygen coupled with computer controls to create more stable biological populations and maximize the use of the treatment system’s capacity. • Improved systems for aeration, including: – Jet aeration in suspended-growth systems (provides both mixing and aeration, potentially independently). – Pure oxygen addition. • Activated carbon addition (provides physical adsorption of difficult-to-degrade compounds such as deicer additives). • Addition of media-aerated basins to create a joint attached-growth–suspended-growth sys- tem to improve stability and treatment efficiency. • Combining anaerobic systems that produce excess methane with aerobic systems that are heated by the methane to create a more efficient system. • Automatic pacing of nutrient feed systems either paced to the deicer load or to the effluent nutrient concentration. 3.3.3 Emerging Chemical Treatment Technologies Chemical treatment, where a chemical oxidant is used to break down the organic compounds in the stormwater, is a technology that has been successfully used to treat various types of waste- water. It is not necessarily an emerging technology for deicer treatment, but it could be an effec- tive technology under the right circumstances. Chemical treatment, however, may not be able to compete with biological and physical treatment on a cost basis. Chemicals could successfully be used to oxidize the organics in deicer-affected stormwater (like a large-scale version of COD analyses). However, it does not appear that chemical treatment

Identifying Deicer Treatment Technologies 53 is a good fit for deicer-affected stormwater because (a) the operating costs are greater than other technologies, and (b) it is difficult to correctly dose the chemical oxidant, resulting in either undertreating the stormwater or leaving a residual of the chemical oxidant in the stormwater. If chemical treatment were applied to deicer-affected stormwater, it would be most effective on high- concentration flows where the mass loadings were carefully controlled. 3.3.4 Emerging Enhancements to Physical Treatment Technologies Distillation technology has advanced, and systems have now been developed so that smaller modular distillation systems can be installed at airports to make this process more cost-effective. In addition, the airport that hosts the modular system can serve as a centralized distillation outlet for other airports in the region if it has appropriate permits to do so. 3.3.5 Emerging Enhancements to POTW Discharges The emerging opportunities associated with POTWs are situations where concentrated deicer could be trucked to the POTW plant and either injected into anaerobic sludge digesters or metered into the denitrification process as a carbon source. In both cases, the concentrated deicer could not be discharged to the sanitary sewer, but would need to be transported in batches from the air- port to the POTW. Some equipment may need to be added at the POTW to support the operation. Since the addition of deicer in these two circumstances is potentially beneficial to the POTW, sur- charge costs that would otherwise be applied for discharge into a sanitary sewer could be reduced. Currently, most POTWs probably are not candidates for either of these situations. For anaero- bic digestion of high-strength wastes (including concentrated deicer), the POTW would need to have the means of using the additional methane either to operate a generator to produce electric- ity for in-plant use or sale to the electric utility grid, or to clean and feed the excess methane into the natural gas utility distribution network. In the case of feed into denitrification, the POTW would have to include a separate denitrification process if the facility has NPDES permit limits for total nitrogen. At the current time, facilities with total nitrogen effluent limits are located with discharges into ocean or estuarine water bodies. Treatment Tips: Testing of Emerging Technologies Many of the deicer treatment technologies used at airports today were originally derived from technologies used to treat other types of contaminated water. The unique conditions of a deicer management environment, however, resulted in a period of adaptation. In particular, methods for managing the cold water tem- peratures, high degree of variability in constituent concentration and flow rate, high strength of the wastewater, and lack of nutrients needed to be developed, often on a trial-and-error basis. Experience with established deicer treatment technologies reveals the benefits of pilot testing wastewater technologies in a deicing environment before attempting on a full-scale basis. Some examples: • A multi-year assessment was conducted on lab and pilot scales with the anaero- bic fluidized bed treatment technology for the Albany International Airport. The testing allowed reactor heights, fluidization rates, treatment rates, solids production rates, and gas production rates to be established for design of a full-scale system.

54 Guidance for Treatment of Airport Stormwater Containing Deicers • A 3-year pilot study of the reciprocating gravel bed technology at the Wilm- ington Air Park was conducted to set design degradation rates. It was also determined from this testing that addition of wetland plants to the gravel beds yielded no additional treatment compared to a gravel bed without plants. • The Zurich International Airport conducted a 5-year testing program for their irrigation-based passive facultative treatment system. During that period, the parameters that needed to be controlled to achieve treatment goals were estab- lished, including monitoring and control based on groundwater levels, wind speed, water and air temperatures, and TOC concentrations. Based on these experiences with extensive testing of existing deicer treatment technologies, it is recommended that potential implementation of emerging technologies undergo similar testing prior to full-scale application.