May 20, 2008 | General

Making Water Reuse More Sustainable

BioCycle May 2008, Vol. 49, No. 5, p. 51
Key issues include treatment methods, municipal, industrial wastewater effluents, urban and agricultural runoff and new regulations for wide-scale reuse.
Robert Bastian, George O’Connor and Herschel Elliott

BY 2025, at least 3.5 billion people (48 percent of the world’s population) are projected to live in water-stressed conditions. Water scarcity is well known in the arid southwest U.S., but is even occurring in the normally water-plentiful southeast (e.g., Florida and Georgia). Today, conservation measures are increasingly viewed as long-range options – taking shorter showers, using low-flush toilets, reduced watering frequency, xeriscaping, etc. Currently in the U.S., public and domestic uses represent only about 12 percent of total water demand. In places like Florida, about 50 to 70 percent of potable water consumption is used outside, principally for irrigation.
Society no longer has the luxury of using water only once before it reenters the hydrologic cycle. Opportunities for the intentional reuse of various sources of degraded water include: Substitutes for fresh water applications that do not require high quality potable water; Augmenting water supplies and providing alternate sources; Providing flow to protect aquatic ecosystems; Reducing need for additional water control structures; and Complying with environmental responsibilities. While the potential for water reuse is enormous, significant barriers exist to widespread adoption. They include research questions, lack of national regulations and public acceptance concerns.
Degraded water – water that has suffered chemical, physical or microbiological degeneration – may be treated (sometimes to better than original quality) before reuse. Examples include municipal wastewater effluents and wastewater from animal operations, irrigation return flow/drainage, industrial (including food processing) wastewaters, storm water runoff and graywater. The WateReuse Association currently estimates that water reuse is growing at about 15 percent per year. The focus here is on methods involving water applications to soil systems. Attention is given to sustainability of reuse operations that include impacts on soils and on water supplies, where environmental health and safety are paramount.
Some degraded waters are reused as is, while others receive considerable treatment. Reuse can further degrade water quality (increase salinity, for example) or improve water quality through soil processes involved in the microbial degradation of organics, denitrification, retention of nutrients and trace constituents, etc. While the local volumes of degraded water vary widely on a local basis, nationally they are dominated by thermoelectric power generation and irrigation/livestock operations, which can account for 80 percent of recurring fresh water demands and dispositions.
Water use in thermoelectric power generation is primarily for cooling purposes resulting in water with increased temperature, higher salinity and biocide contamination. Irrigation/livestock operations require large amounts of fresh water, with return flows resulting from drainage water associated with irrigation in arid areas. Major water quality concerns include salinity, sodicity and specific ion toxicities (e.g., Zn, Cu, etc.) depending upon the water source.
Under most circumstances, secondary treatment – the minimum requirement for surface water discharge – is defined by the U.S. EPA as meeting a monthly average of 30mg/L for BOD5 and total suspended solids (TSS), and removing 85 percent of these parameters along with a pH between 6 and 9. More restrictive standards are applied to many surface water discharges, in some cases with requirements more restrictive than drinking water standards.
An area of growing interest deals with urban storm water runoff – from “megacenters” with populations of 10 million inhabitants. While interest in reuse of urban runoff as well as treated effluents is growing, it remains a relatively small component of the overall degraded water resources. High water use industries – food processors, pulp and paper mills – produce substantial quantities of wastewater with particular significance on a local basis. Industrial degraded waters often have unique qualities (i.e., pesticide residues, high nutrient loads) that challenge reuse applications.
Graywater is residential wastewater originating from clothes washers, bathtubs and sinks, distinguished from “black water” (wastewater from toilets, kitchen sinks and dishwashers). Of total residential usage, sources of graywater include baths and showers (about 18 percent), clothes washers (22 percent) and faucets (16 percent).
Use of graywater is gaining in popularity for irrigation and toilet flushing. The most common application is landscape irrigation – with minimal or no treatment. Some states like Arizona, California, New Mexico, Texas and Utah have comprehensive reuse regulations covering setback distances, filtration and runoff generation.
Major industrial users of water and potential users of effluents are power plants, oil refineries, concrete production and manufacturing facilities. Degraded water is principally used for cooling purposes. Other major industrial uses are in various production steps of some industries – pulp and paper, chemical, textile and petroleum. Environmental applications include wetland creation, enhancement and restoration to serve as wildlife habitat and refuges, and stream augmentation. Recreational uses range from landscape impoundments and water hazards on golf courses to full-scale development of water-based recreational impoundments involving incidental contact (e.g., fishing and boating) and direct body contact (swimming and wading).
Groundwater recharge can reverse declines of groundwater levels, protect underground freshwater and store surface water. Surface spreading operations and vadose zone injection wells directly involve soil processes (microbial degradation of water contaminants), retention of nutrients and physical filtration of suspended solids.
Indirect augmentation of potable water supplies with degraded water is a deliberate process, with major focus on health safeguards. It relies on treatment, mixing, dilution and assimilation that provide multiple barriers to protect potable water supplies. The use of surface waters that receive upstream discharges of effluents as sources of drinking water is in effect indirect potable reuse.
Restricted urban reuse includes irrigation of areas where public access can be controlled – such as golf courses, cemeteries and highway medians. Unrestricted reuse includes irrigation of such areas as parks and playgrounds, use for toilet flushing in commercial buildings, air conditioning, etc.
Florida currently leads the nation in the volume of wastewater effluent reused – dominated by such applications as irrigation of golf courses and housing development landscapes. Reuse programs in Florida enjoy wide public support; acceptance is influenced by reduced costs of reclaimed water and perceived safety.
California has comprehensive Title 22 water reuse regulations, which require an adequately oxidized, coagulated, clarified, filtered and disinfected effluent for unrestricted use. While irrigation of agricultural crops is the dominant form of water reuse in California, most of California’s urban reuse involves irrigating turf grasses in golf courses and lawns. Guidance aimed at overcoming the reluctance of some professional landscapers to use recycled water, due to concerns over salinity damage to landscape plants, was developed by Ken Tanji at University of California, Davis (see sidebar). The guidance should facilitate increased urban reuse in California.
Agricultural reuse can be divided into restricted and unrestricted applications, based on the crops grown and the expected human exposure. The distinction is especially pertinent for reuse of wastewater effluents in situations where significant human exposure to pathogens is expected, such as the production of food crops that are consumed raw.
Wide-scale reuse faces many technical, environmental and social challenges. Four major issues must be addressed: Meeting water quantity and quality requirements; Protection of health; Maintaining soil productivity; and Public acceptance. Some challenges are also faced when fresh water sources are applied to the soil via the major types of reuse. For example, ensuring that excessive salts do not impact plant growth or soil structure is a common challenge facing irrigation in arid regions. Protection of public health is a critical objective in all reuse applications.
Salinity has long been a concern with irrigation. Issues are related to impacts associated with dissolved compounds – such as sodicity, toxicity by specific ions and salinity. Guidelines need to be interpreted in the context of local climatic, agronomic and management characteristics.
Degraded waters contain a number of plant essential nutrients. There is often sufficient nitrogen and phosphorus to satisfy vegetation needs on the site. Potassium is also a major crop nutrient, but often needs to be supplemented for maximum yields when wastewater effluent is used for irrigation.
Humans and animals can potentially be exposed to disease-causing organisms (pathogens) through soil application of some degraded waters. Risk of exposure is greatest when the reuse water has been degraded through contact with human and animal wastes such as partially-treated domestic or CAFO (concentrated animal feeding operations) wastewaters.
Animal manures may receive little to no treatment to reduce pathogens loads, and frequently contain pathogenic viruses, bacteria (e.g., Escherichia coli O157:H7) and protozoa (e.g., Cryptosporidium) that pose a risk. There have been highly publicized outbreaks of food-borne illnesses and deaths, as well as major economic impacts associated with manure-contaminated water use on fresh produce.
Collectively, unregulated substances are referred to as emerging chemicals of concern (ECOCs), substances previously undetected or that had not been considered as a risk. A major source of ECOCs in the environment is the effluent from wastewater treatment plants that were not designed to eliminate these compounds. Some ECOCs are easily removed and degraded during sewage treatment, whereas others move through treatment plants largely unchanged. Animal wastes (manure, lagoon effluents) can also contain ECOCs (veterinary therapeutics, feed additives and natural hormones) and serve as sources to agricultural systems and the environment. Effects on aquatic organisms have attracted the most research attention, but a significant body of work exists on manure-borne ECOCs and their behavior in soil systems.
The bioactive properties of pharmaceuticals and other ECOCs introduced into surface and ground waters and soils can adversely affect humans and ecosystems. The risks remain inadequately quantified, but numerous effects have been documented or hypothesized. These include antibiotic resistance in bacteria (human, animal, soil microbes) exposed to even subtherapeutic concentrations of antibiotics and antimicrobials; and endocrine disrupting activity associated with synthetic or natural estrogens, or numerous other chemicals that mimic natural hormones or alter hormone production.
Level of pretreatment prior to degraded water reuse varies widely for different end uses. Processes can range from little to no treatment prior to reuse, to advanced biological wastewater treatment coupled with membrane technologies and high level disinfection. Where recharge of potable ground water aquifers is the objective, reuse water should not contain measurable levels of viable pathogens.
Conventional storm water harvesting normally involves simple collection and storage prior to use for urban irrigation. In many states, unrestricted urban reuse of wastewater requires secondary treatment, filtration and high-level disinfection. Advanced technologies – like membrane filtration, membrane bioreactors and reverse osmosis – are becoming common in reuse applications. Pollution prevention strategies can be used to reduce the introduction of contaminants of the reuse water during its initial degradation. For example, manipulation of animal diets may be a simple, cost effective way to greatly reduce contaminants in CAFO lagoon waters.
Storage is often needed to satisfy the variable demand for the reuse water regardless of the degraded water source. This is particularly evident in irrigation systems, where a reliable supply of water must be matched with diurnal and seasonal demands. Increased retention times may be needed to reduce suspended solids, or allow degradation or mineralization of contaminants. Regrowth or introduction of pathogens during storage may necessitate poststorage disinfection of treated wastewater effluents. For sites irrigated with wastewater effluent, regulations may prohibit or otherwise restrict discharge of runoff to surface waters.
Consideration of stakeholder issues must occur early on in the conceptualization of a reuse program planning. Public participation is essential. Endeavors to promote sustainability of reuse systems will largely be wasted if stakeholder concerns are not actively considered.
Prior to implementing degraded water reuse programs, legal and regulatory issues at several governmental levels need to be addressed. The US EPA has developed suggested guidelines for wastewater effluent reuse that serve as the basis for some state regulations. However, few states have specific regulations governing the reuse of other degraded waters (storm water, graywater) and often address proposed reuse programs on a time-consuming case-by-case basis. Some states have guidelines that are not directly enforceable but that are used in development of reuse programs. Lack of regulations or guidelines may restrict reuse applications where programs are permitted on a case-by-case basis.
Legislation such as the Clean Water and Safe Drinking Water Acts may constrain the use of wastewater effluents for indirect potable reuse. For irrigation systems using wastewater effluent, a National Pollutant Discharge Elimination System (NPDES) permit may be required for surface water discharge of runoff water. Many states have established buffer zones between the wetted area of effluent irrigation sites and residential areas, roadways and water supply wells.
Most state regulations for wastewater effluent reuse include monitoring requirements that reuse water be sampled for specific constituents at specified intervals. Although most states have a limited list of specified constituents (e.g., TSS, N, TOC, turbidity, total coliforms), the number of regulated constituents can be extensive. Groundwater monitoring also may be required for agricultural irrigation sites, depending on the quality of water and the site hydrogeology. Separate water quality requirements may exist for other reuse scenarios. Some states provide regulations specific to the use of wastewater effluent in creating or maintaining wetlands.
With water resource issues providing the impetus for greater water reuse, states are establishing and revising existing regulations and guidelines. Continued research is needed to ensure that such policies promote water reuse while protecting public health and the environment.
Intentional reuse of degraded waters (wastewater effluents, irrigation return flows, CAFO effluents, storm water and graywater) can be one solution to help meet the challenge of growing water demands. The future potential for wastewater effluent reuse, in particular, is enormous, while other degraded waters represent major reuse resources as well. Increased reuse of degraded waters can be feasible and sustainable if various barriers (e.g., public acceptance, stricter discharge limits or requirements, innovative technologies and better water management to ensure protection of health and the environment, political support) are effectively addressed. The absence of state guidelines or regulations likely fosters public perception that degraded water reuse is inadequately understood or not sufficiently protective of health to receive official endorsement. Federal reuse regulations, similar to the 40 CFR Part 503 biosolids rule could establish minimum standards and possibly foster public acceptance.
Many areas with limited water resources, such as the arid U.S. Southwest, already have well-established wastewater effluent reuse programs in place and years of experience utilizing irrigation return flows. As populations have increased, reuse of wastewater effluents has also grown rapidly even in normally wet areas (especially Florida, but also areas such as Georgia, North Carolina, Oregon and Washington).
Some of the issues likely to impact the sustainability of degraded water reuse are well studied (e.g., salinity, nutrients, trace inorganics, pathogens), but the application of principles developed from studies with fresh waters have not been fully evaluated in degraded water use scenarios. Examples include:
o Sustainable irrigation water management techniques developed for traditional field crops irrigated via furrow or overhead sprinkler systems may have to be adapted for ornamentals irrigated via drip systems with water containing excess Na+ contributed by home water-softeners.
o Guidance based on nutrient release from solid manures may not be appropriate for nutrient supply in liquid manure or wastewater effluents.
o Little attention has been given to the risk potential of effluent P land application (e.g., P-Index characterization).
o The soluble organic C concentration in some degraded waters (e.g., manure and food processing effluents) may alter the speciation and mobility of metals in soils and the potential for groundwater contamination.
oAvailable indicator organisms (used to determine wastewater treatment effectiveness) may not be accurate predictors of actual health threats posed to individuals coming in close contact with degraded waters in densely populated urban environments.
Other issues (notably emerging chemicals and pathogens of concern ECOCs) will require nontraditional research approaches and/or instrumentation. A host of chemicals are now being detected in degraded waters of all kinds (owing to greatly enhanced analytical capabilities). The list includes endocrine disruptors, pharmaceuticals, personal care products, fragrances, veterinary medications, etc. The behavior of these chemicals in the environment and the resulting risk to human health is largely unknown. Numerous models are available to predict chemical behavior, based on structural characteristics, chemical and physical properties, fugacity concepts and risk assessments, but reliable documentation (validated measurement of effects) is scarce. While some information is available for aquatic systems, the scarcity is especially obvious in soil systems. Describing the fate, transport and risk of ECOCs is an area requiring major research effort.
Similarly, little is known about “emerging pathogens” that could accompany waters contaminated by human or animal manures. The use of surrogate organisms (see above) to evaluate all pathogens behavior is in question and remains incompletely studied.
Ultimately, public (and political) acceptance is the major hurdle to degraded water reuse, especially in urban settings. Major educational programs, based on hard science, are needed to convince the public of the wisdom of reusing degraded waters. Water scarcity throughout the world demands effective research and educational programs to fully realize the potential for degraded water reuse and to address impending water shortages.
Robert Bastian is a Senior Environmental Scientist with the USEPA’s Office of Wastewater Management in Washington, D.C. George O’Connor is a Professor of Soil Chemistry in the Soil and Water Science Department at the University of Florida. Herschel Elliott is a Professor of Agricultural and Biological Engineering at Penn State University.
A MORE detailed article, “Degraded Water Reuse: An Overview” (by G.A. O’Connor, H.A. Elliott and R.K. Bastian), which this paper is based upon, was a part of a special collection of papers based on presentations on “Environmental Impact and Sustainability of Degraded Water Reuse” at the November 2007 Soil Science Society of America annual conference that will appear in the Journal of Environmental Quality between May and August 2008. To learn more about managing salinity when irrigating landscape plants with reclaimed water, see the new Salinity Management Guide CD on Managing Salinity of Recycled Water for Landscape Irrigation, by Ken Tanji, which was funded and is being distributed by the National WateReuse Foundation, National Water Research Institute, Southern California Salinity Coalition and others. For in-depth coverage of cutting edge water reclamation and reuse applications, see Water Reuse: Issues, Technologies, and Applications, a new Metcalf & Eddy text authored by Takashi Asano, Franklin L. Burton, Harold L. Leverenz, Ryujiro Tsuchihashi and George Tchobanoglous, published in 2007 by McGraw-Hill.

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