W3170: Beneficial Reuse of Residuals and Reclaimed Water: Impact on Soil Ecosystem and Human Health (formerly W2170)

(Multistate Research Project)

Status: Active



Millions of tons of residual by-products, such as urban wastes (biosolids, recycled water, food scraps and other municipal solid waste), agricultural waste (manure) and industrial sludges are produced in the U.S. On average, approximately 50% of biosolids, 98% of food scraps, and 45% of yard trimmings are currently disposed of in landfills or incinerated at substantial cost to the industry and public (King et al., 2011). Reuse of residuals as soil amendments offers the potential to substitute beneficial agronomic and environmental uses for disposal costs. Treated liquid wastes, such as wastewater effluent, recycled water and other non-potable waters, also present opportunities for beneficial reuse in lieu of surface water discharge or expensive treatment.

There have been many obstacles to optimized use of residuals. These include a lack of research to optimize residual based product development, conflicting regulations or the absence of regulations on residuals use, and lack of public outreach and communication. There is increasing evidence that land application of a variety of residuals may provide agronomic and environmental benefits that were either not previously well understood and/or that are critical to addressing emerging environmental issues associated with climate change (Brown et al., 2011). The W2170 workgroup propose to continue the investigation of biogeochemical cycling of plant nutrients, the movement of trace element and trace organic contaminants (TOrCs) into the food chain, the potential toxicity of trace elements and TOrCs in residuals to the soil and water ecosystems, and their long-term bioavailability in residual-amended soils to develop additional knowledge to help promote residuals recycling practices that are protective of human health and the environment. These results will provide data for continuing risk assessment required by the USEPA Part 503 Rule for land-application of biosolids as well as for developing regulations for land-based recycling of residuals and reclaimed water. Research will also focus on benefits of reuse including field and watershed scale effects on soil quality, plant drought response, soil carbon sequestration, water quality, greenhouse gas emissions, and climate change impacts associated with soil-based reuse of residuals and reclaimed water. We will also explore the potential for residual based products to be used in urban areas including urban agriculture, restoration, and green stormwater infrastructures. W2170 members are conducting research, on both short- and long-term application sites, whose results will enable the development of guidelines for maximizing the beneficial uses of a considerable variety and number of residual by-products.


The beneficial use of residuals requires both an understanding of potential hazards and value of the constituents in the by-products. Investigation of the fate and behavior of contaminants and nutrients in biosolids amended soils has been the historic focus of research of the W2170 (and its predecessors, W1170 and W170) multistate workgroup. Research conducted previously bu the workgroup formed the basis for the U.S. EPA Part 503 sludge rule, which is one of the few rules to include bioavailability assessments in the development of limits for critical contaminants (National Research Council, 2003). Two subsequent NAS reviews focused on the rule confirmed that scientific basis for this rule and risk assessment were valid (NRC, 2002). We are now faced with determining whether TOrCs merit regulation.

Human and ecological risk assessment (HERA) science continues to mature with bioavailability-based risk assessment frameworks being developed and/or considered for implementation in the U.S., Canada, the European Union, Australia and other countries. Research is needed to provide the scientific basis for risk-based methods to evaluate residuals and residual-treated soils for adoption by HERA frameworks. Research needed to evaluate contaminants in residuals includes (i) trace element speciation by advanced spectroscopic methods and wet chemical speciation methods, (ii) field studies to investigate potential plant uptake of frequently detected trace elements and TOrCs in residuals-amended soils, (iii) in vitro methods correlated with human and ecological endpoints, and (iv) novel in vivo methods.

Several members of the W2170 were extensively involved in the development of the Part 503 regulation and continue to be involved in the development of risk assessment for other residuals (e.g., the EPA risk assessment for land application of cement kiln dust and foundry sand) and for other pollutants not initially regulated or considered in Part 503 (e.g., barium, TOrCs). The scientific approach used in the development of Part 503 has been applied by this group to an expanded variety of residuals, contaminants and receptors. As the understanding of bioavailability is expanding, the group is broadening its focus to develop linkages between quantitative understanding of the contaminant forms and their bioavailability to a range of receptors.

In the past, our group has conducted cooperative projects involving laboratory incubations, greenhouse studies, and x-ray adsorption spectroscopy to elucidate the role of organic and inorganic components of biosolids in binding metals (Brown et al., 2003a; Hettiarachchi et al., 2003; Ryan et al., 2003, 2004a; Scheckel et al., 2004; Hettiarachchi et al., 2006). We have demonstrated that biosolids and other soil amendments can reduce the bioavailability of metals in contaminated systems (e.g., Hettiarachchi and Pierzynski, 2002; Brown et al 2003b; Brown et al., 2007; DeVolder et al., 2003; Basta et al., 2001), while developing various extractants to assess bioavailability of mineral and bioavailable fractions of inorganic contaminants (e.g., Rodriguez et al., 2003; Basta et al., 2003; Schroder et al., 2003; Brown et al., 2004; Ryan et al., 2004). As the potential for metals to affect a range of receptors is more fully understood, research has broadened to encompass a range of measurement endpoints. The goal of this research is to evaluate functions of the restored ecosystem utilizing tools such as in vivo and in vitro assays, toxicity assays, and measures of microbial community dynamics (Alexander et al., 2003; Basta et al., 2003; Schroder et al., 2003; Brown et al., 2004b). As a result of cooperative research conducted by members of W2170, alternative in situ remedial options have been included on a number of EPA Superfund National Priority List (NPL) sites. These include use of biosolids to rehabilitate metal-contaminated ecosystems. The tools developed for this research have also been applied to gain a fuller understanding of the functioning of biosolids-amended soils. The sustainability of biosolids application to agricultural lands has been demonstrated by evaluating the effect of biosolids application on soil function. Potential receptors have included earthworms and soil microorganisms. While important initial research has been done in this area and implications of this research are being recognized in the remediation of contaminated sites, this type of work is still at a developmental state. The multistate research group will continue research to improve our understanding of this field.

Another area of concern is the fate of residuals-borne trace organic chemicals (TOrCs) in soils. Classes of TOrCs include estrogenic compounds, personal care products, and pharmaceuticals (Topp and Clucci, 2004; Xia and Pillar, 2004). A wide range of TOrCs in streams in the vicinity of wastewater treatment plants and confined animal feeding operations has been frequently reported. The fate and persistence of these compounds during biosolids stabilization processes or following land application of residuals and non-potable water is not fully understood. Persistence in soils and potential for ecosystem effects as result of land application of residuals and non-potable water containing these micro-constituents is a critical area requiring additional research.

Impending water shortages are motivating renewed interest in the use of organic residuals and the intentional reuse of degraded waters (OConnor et al, 2008). Soil application of organic amendments for field crop production may have an ameliorative effect on drought-stressed crops. Heckman et al. (1987) found that field grown soybeans fertilized with biosolids had increased drought resistance and nitrogen fixation than the control treatment. Zhang et al. (2005) determined that biosolids subjected to various treatment processes enhanced endogenous antioxidant enzyme activity, photochemical efficiency, and drought resistance of tall fescue. Cogger et al. (2012) showed increased yields in dry land wheat fertilized with biosolids in comparison to synthetic fertilizer. This increase may be the result of increased soil water holding capacity in the biosolids amended soils (Brown et al., 2011).

Fresh water sources for irrigation are limited. While the application of treated or partially treated wastewater effluents to cropped and forested lands has long been practiced, other sources of degraded water (stormwater, irrigation return flow, gray water, and concentrated animal feeding operations [CAFO] effluents) are available to meet anticipated shortfalls. Since many of the major reuse opportunities involve water applications to soil systems (e.g., irrigation), addressing the benefits, risks, and sustainability of degraded water reuse logically fits within the scope of the proposed research project.

Some of the greatest challenges to expand the beneficial use of reclaimed water and treated wastewater effluent are concerns associated with TOrCs possessing endocrine disrupting activity (Miller, 2006). Many pharmaceuticals, personal care products, plastics, pesticides and industrial by-products possess such activity. The endocrine disrupting TOrCs are frequently detected in municipal, industrial, and agricultural wastewater but information on their environmental effects and fate in treated soils is limited. Endocrine disrupting compounds (EDCs) interfere with natural hormones causing reproductive and growth problems in animals, particularly aquatic organisms (Xia et al., 2005). A major concern is the ecological impacts at trace concentrations (~1 ng/L) of EDCs in surface waters from wastewater effluents or leachate from residuals-amended soils (Koplin et al., 2004). Soil organic matter increases with long-term irrigation using reclaimed wastewater (Quin and Mecham, 2005; Walker and Lin, 2008), so hydrophobic EDCs retention in soil should be enhanced (Wright et al., 2010). However, some EDCs are hydrophilic and have structures that resist enzymatic attack (Metcalf and Eddy, 2007), and their persistence and impact are less certain. Field research in a turfgrass system at the University of California, Riverside confirmed that these compounds have very limited mobility, even under heavy irrigation (Xu et al., 2009). Nevertheless, there are few published studies on the presence, mobility, and degradability of EDCs at effluent irrigation sites (see Pedersen et al., 2003; Kinney et al., 2006). The impact on groundwater beneath spray irrigation sites has received very limited attention.

In summary, research on contaminant bioavailability in both residuals amended soils and in contaminated soils restored with residuals is incomplete. New ecological endpoints must be investigated to improve risk assessment to ensure human health and environmental safety. Research is also needed to maximize yields with the the use of residuals and reclaimed wastewater. Both offer potential alternatives to current, sometimes environmentally degrading, agricultural and land restoration practices. The experience and expertise of W-2170 members in addressing these issues is widely recognized and is well positioned for continued success. The W-2170 membership offers the advantage of including institutions and entities (universities, USDA-ARS, USEPA, municipal government utilities) from across the entire United States. Such collaboration enables discoveries to account for widespread differences in climate, soils and types and sources of residuals, whose fate, transport, and impact will vary across these factors.
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