January 01, 2014

Sustainable Land Application of Sewer Sludge as a Biosolid

Christopher W. Smith

Sustainability is not a fad. Neither is the land application of biosolids. It is no coincidence, then, that the two go hand in hand, and that their combination is growing in public acceptance. Limiting waste and developing methods for reusing waste are two of the fundamental tenets of the continually growing environmental movement. Because the land application of biosolids is likely to become only more prevalent over the years and decades to come, such application must be done in a safe and sustainable fashion.

Historically, domestic sewer wastes have been treated in wastewater treatment facilities and disposed of by landfill or incineration. In the past forty years, however, the focus on managing such waste streams and products has shifted from treatment and disposal to finding beneficial uses through sustainability practices. As a result, one waste product that has seen increased attention is biosolids generated from the treatment of domestic sewer waste. This article explores the practice of land application of such biosolids, its regulations, and what to expect in the years to come—particularly in the management of domestic sewer sludge.

Biosolids are primarily organic material produced during wastewater treatment. Despite significant efforts by wastewater treatment facilities to investigate the beneficial uses of biosolids, only a few recognized applications exploit the beneficial characteristics of biosolids. This may be due in large part to the perceived risks or other complications that community stakeholders inaccurately associate with biosolids. Inaccurate perceptions aside, the recognized applications of biosolids include recycling as compost, mine-site rehabilitation, brick manufacture, silviculture, agriculture, and potting-mix production. Notwithstanding these varied recognized applications, the leading application is the direct application to land or soil in order to restore organic nutrients and to replenish organic soil matter.

The process of land application is nothing new. Farmers have been repurposing animal waste for millennia. But land application of human waste in a refined manner is a relatively new process. Part of the refinement that makes up this new process is due to federal, state, and local regulations on the practice. Under those regulations, biosolids have been approved for use on agricultural land, forests, rangelands, or disturbed land in need of reclamation. As a result of those regulations, approximately half of the biosolids produced in the United States are being used to improve soil conditions.


At the federal level, land application is regulated under the Clean Water Act (CWA) by the U.S. Environmental Protection Agency (EPA). See 40 C.F.R. § 503. At the state and local levels, the application is also regulated under solid-waste regulations. Such regulations, however, vary depending on the prevalence of the practice. See, e.g., California State Water Resources Control Board (State Board), Water Quality Order No. 2004-0012-DWQ (a general order requiring each land application site to be approved by the State Board before any biosolids are applied). Not surprisingly, federal, state, and local regulations mandate sustainable practices for land application.

Apart from regulations, sustainable land application practices also result from economic and environmental incentives. These incentives operate to benefit both sides of a biosolids transaction: the waste-treatment facility (the generator) and the operation applying the biosolids (the consumer).

In terms of economic incentives, generators conserve disposal costs, derive revenue from the sales of biosolids, and may be able to take advantage of waste-to-energy tax credits. Consumers observe economic incentives in the form of conserving purchasing costs for biosolids in lieu of more expensive commercial manufactured fertilizers. In terms of environmental incentives, generators conserve landfill space and reduce emissions from their facilities. Consumers see improved crop production, reduced levels of erosion, and greater protections for water quality. For their part, community stakeholders also stand to benefit. Economically, community stakeholders see the benefits of biosolids in the form of reduced taxes and lower utility bills from the generators. Environmentally, community stakeholders see the benefits of biosolids in the form of topsoil for recreational uses, land reclamation, and enriched forestland.

Despite the recognized benefits, the practice does have its detractors. For example, a large municipality in California attempted to engage in the practice in an adjacent county but was quickly challenged by that community through the enactment of local ordinances. See City of Los Angeles v. County of Kern, 581 F.3d 841 (9th Cir. 2009) (Kern III). In that example, the county of Kern enacted an ordinance that made it unlawful to apply biosolids to land within the county. The marketing campaign behind the ordinance was that the city of Los Angeles was simply shipping its waste off to the county of Kern to be disposed of there when it would not dispose of the waste in its own county. Community stakeholders balked at the idea of the city of Los Angeles’s sending its waste off to the county and decisively approved the ordinance. The city of Los Angeles filed suit to block the ordinance from going into effect, and the Ninth Circuit held that the ordinance was lawful. This case provides the quintessential example of misperception by community stakeholders and the momentum that such misconception can generate.

Proponents and detractors aside, the practice of land application of biosolids is here to stay. Bearing that in mind, the practice must be sustainable. And to make the practice sustainable, it is important not only to account for environmental interests and concerns but also to account for the interests and concerns of biosolids generators, biosolids consumers, and community stakeholders. By recognizing and accounting for all the interests and concerns involved, true sustainability can be achieved. This comprehensive accounting is what some scholars have come to define as the “triple bottom line” of sustainability, which accounts for economic prosperity, environmental stewardship, and corporate social responsibility. See Rick Mullin, Cracking the Sustainability Code, 4 Chemical & Engineering News 1 (2004).

Sewer Sludge as a Biosolid

Biosolids are solid, semisolid, or liquid materials resulting from treatment of waste, including most significantly domestic sewage sludge. The origins of the term can be traced back to the early 1990s when the wastewater treatment industry sought to change the connation historically associated with sewer sludge. Since that time, the EPA has begun to utilize the term and has created rules distinguishing the qualities of biosolids based on the presence of pollutants and pathogens.

Traditionally, biosolids were disposed of in landfills or through incineration. Both of these methods of disposal created their own environmental issues. As an alternative to these methods of disposal, wastewater treatment facilities began investigating the potential for use of biosolids as beneficial soil amendment. Their investigation revealed that the land application of biosolids was beneficial not only environmentally but also monetarily.

Misconceptions, mostly from community stakeholders, about biosolids abound. These misconceptions are due in large part to a lack of understanding by most as to what happens to human waste once it is flushed down the toilet. Without going through the process in detail, the domestic sewer sludge that comes out of the wastewater treatment plant is processed. That process typically involves thickening, digestion (anaerobic, aerobic, or both), alkaline stabilization, heat drying, conditioning, dewatering, and eventually compositing. The results of the processing then yield varying qualities of biosolids. These qualities dictate whether the biosolids are qualified for land application based on federal, state, and local regulations.

Regulating Land Application Practices

Land application is not without risks. For that reason, federal, state, and local regulations govern the practice. Most notable among the risks are those associated with pathogens and pollutants that are present in the biosolids when they are added to soil. Less notable risks include effects on soil quality, plant growth, and water quality. The applicable regulations seek to ensure that land application practice is undertaken in an environmentally sustainable manner.

Federal regulations on the generation, use, and disposal of biosolids begin under the 1987 Amendments of the CWA and 40 CFR Part 50, also commonly known as the “Part 503 Rule.” The goal of the Part 503 Rule is to protect public health and the environment from any reasonably anticipated adverse effects of pollutants and pathogens in biosolids. To that end, the Part 503 Rule establishes acceptable qualities of biosolids and the minimal requirements governing the application of biosolids to land as a conditioner of the soil and a fertilizer to crops or other vegetation grown in the soil.

In general, the Part 503 Rule considers biological, chemical, and physical properties. Some of the more specific properties are total solids, volatile solids, pH, nutrients, trace elements, organic chemicals, and pathogens. Total solids include suspended and dissolved solids the content of which depends on the type of wastewater process and biosolids’ treatment before land application. Volatile solids represent the readily decomposable organic matter and are an important determinant of the potential odor problems at land application sites. The pH provides the measure of the degree of acidity or alkalinity. Nutrients are the elements required for plant growth that provide biosolids with their real monetary value. Trace elements include all manner of elements but typically consider the presence of “heavy metals.” Organic chemicals include complex compounds that can comprise man-made chemicals from industrial wastes, household products, and pesticides. Finally, pathogens include disease-causing microorganisms that include bacteria, viruses, protozoa, and parasitic worms. Pathogens are particularly relevant to land application because they can present a public health hazard if they are transferred to food crops grown on land on which biosolids are applied, are transported away from the site by insects, rodents, or birds, or are contained in runoff from a site that is transferred to surface waters.

Additionally, the Part 503 Rule requires that any state regulations governing biosolids be at least as stringent as the rule. The Part 503 Rule prohibits land application of low-quality sewage sludge and encourages the application of biosolids that are of sufficient quality that they will not adversely affect human health or the environment. Ranking the quality of the biosolids for regulatory purposes involves measuring the levels of pollutants and pathogens in the sludge. As a separate measurement, the biosolids are also qualified based on their vector attraction: the attractiveness to insects, rodents, and other animals.

The Part 503 Rule restricts the levels of nine trace elements in sewer sludge: arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, scandium, and zinc. Only the faintest traces of these elements can be present in the biosolids for land application consideration because of their deleterious environmental impacts.

The 1987 Amendments to the CWA also impose pretreatment specifications that limit concentrations of certain pollutants, including the foregoing nine trace elements and other organic chemicals, in wastewater that industries discharge to a treatment facility. This mandate and the long-term impacts flowing from it are largely seen as one of the leading reasons why the quality of biosolids over the years has continued to improve. See Shimp, G., K. Hunt, S. McMillian, and G. Hunter, Pretreatment Raises Biosolids Quality, 5 Envtl. Protection 6 (1994).

Treatment Processes and Application Levels

Regardless of whether the regulations are established on the federal, state, or local level, they uniformly require a reduction in the presence of pollutants, the potential pathogens, and vector-attraction properties. In order to meet these reductions, chemical or biological processes, or both, are used. Those processes reduce the presence of pollutants, pathogens, and odor to land application standard.

As treatment for pollutants, the process typically involves dilution of the biosolids to reach acceptable levels under the pollutant concentration limits (PCLs). The PCLs are the most stringent pollutant limits included in the Part 503 Rule. The pollutants typically identified are heavy metals, including but not limited to arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc. The limits on pollutants are more stringent than for pathogens and vector attraction because the pollutants are seen as the most detrimental to human health and the environment.

As treatment for pathogens, the process typically involves application of high temperature, high pH with alkaline addition, drying, and composting. These treatment processes tend to yield two types of biosolids: Class A and Class B. See 40 C.F.R. § 503.32.

In order to achieve Class A, pathogens such as salmonella and bacteria must be reduced to below detectable levels. Once Class A is achieved, then the biosolids can be applied to land without any pathogen-related site restrictions. A yet higher-quality grade is Class A Exceptional Quality (EQ) biosolids. In these, the trace elements may be present in concentrations no greater than a specified level. EQ biosolids are not subject to the Part 503 Rule general requirements and management practices for land application. See EPA, Environmental Regulations and Technology, Control of Pathogens and Vector Attraction in Sewage Sludge (5 July 2003) (available as of Feb. 2013)); 40 C.F.R. § 503.13(b)(3), Table 3.

To achieve Class B, pathogens must be reduced to levels that are unlikely to cause a threat to public health and the environment under specific use conditions. The specific use conditions mandated for Class B biosolids are a result of varying detectable levels of pathogens. The thinking behind the approval of Class B for land application is that the specific use conditions will limit exposure to the biosolids until the processes applied to Class A can be achieved naturally. There are additional classes of biosolids beyond Class A and Class B, but those lower classes are not relevant to land application.

As treatment for vector attraction, the process typically involves the same methods employed to treat for pathogens (e.g., heat treatment and decomposition). Once the biosolids are treated, vector-attraction reduction operates to prevent disease vectors such as rodents, birds, and insects from transporting pathogens away from the site of the land application. While there are ten recognized options to demonstrate that land-applied biosolids meet vector-attraction requirements, the options can be broken down into two general approaches: (1) reducing the attractiveness of the biosolids to vectors with specified organic matter decomposition processes (e.g., drying and composting); and (2) preventing accessibility of the biosolids to vectors (e.g., incorporation of the biosolids below soil surface level or injection).

In evaluating the effectiveness of the treatment processes identified in the Part 503 Rule, the EPA, through the National Research Council (NRC), undertook a study to determine the effectiveness of the Part 503 Rule in protecting human health. See City of Los Angeles v. Cnty. of Kern, 509 F. Supp. 2d 865, 872 (C.D. Cal. 2007) (Kern II). In that study, the NRC found “no documented scientific evidence that the Part 503 [R]ule has failed to protect public health.” Id. The study did call for “‘additional scientific work [that] is needed to reduce persistent uncertainty’ arising from anecdotal allegations of disease, as well as to ensure that the regulation’s standards were supported by current data and methods, that the management practices called for by the regulations were effective, and that the regulations were being enforced.” City of Los Angeles v. Cnty. of Kern, 214 Cal. App. 4th 394, 402, 154 Cal. Rptr. 122 (2013) (quoting Kern II, 509 F. Supp. 2d at 872). Subsequent research has shown “nothing to undermine the conclusion that land application of biosolids in compliance with the Part 503 [Rule] presents minimal risk to human health.” Id.

Beyond the federal regulations in the Part 503 Rule, state and local regulations offer their own input in limiting the land application of biosolids. Many of those state and local regulations focus on the physical characteristics of the land subject to application. This focus makes sense when considering how state and local authorities are much more suited to consider such physical characteristics. Some of those physical characteristics taken into account are soil type, depth to groundwater, infiltration, drainage patterns, proximity to surface water, and permeability. Based on these physical characteristics, state and local authorities have almost uniformly found that a number of land types will never be suitable for the land application of biosolids: undesirable soil conditions (rocky, shallow); wetlands and marshes; areas bordered by ponds, lakes, rivers, and streams without appropriate buffer zones; areas of historical or archaeological significance; and other environmentally sensitive areas, such as floodplains.

Sustainable Land Application Practices

Environmental sustainability, as a concept, is rather amorphous. So in an attempt to define the concept, many have taken to using the “triple bottom line,” which focuses on three pillars—people, planet, and profit—to measure success. In the context of environmental sustainability, accounting for those three pillars means giving each pillar equal weight. And in the narrower context of environmental sustainability of the land application of biosolids, it means not only accounting for environmental and economic sustainability but also accounting for social sustainability. Science and economics are only part of what goes into developing environmentally sustainable land application projects; the other part involves people.

While social sustainability is often undervalued and overlooked, it is largely seen as the key to success. This is most certainly the case for the biosolids because social acceptance and political realities have a significant impact on the long-term success of land application. One need not look further than the litigation between the City of Los Angeles and the County of Kern as an example. See Kern III, 581 F.3d 841.

The importance of public involvement and the need to gain and maintain public acceptance in maintaining sustainable land application projects cannot be overstated. Ned Beecher, Ellen Harrison, Nora Goldstein, Mary McDaniel, Patrick Field, and Lawrence Susskind, Risk Perception, Risk Communication, and Stakeholder Involvement for Biosolids Management and Research, 34 J. Envtl. Quality 122 (2004). Frequently, the initial basis for community concern is related to misconceptions surrounding odor or nuisance conditions (e.g., noise, dust, flies, and truck traffic). Dispelling these misconceptions is a key to acceptance by communities. Without such efforts, sustainability of any land application project will be called into question. In addition to dispelling misconceptions, social sustainability can be achieved through voluntary partnerships with community stakeholders early in the development and implementation of land application practices. This should serve to avoid problems that might otherwise be overlooked until it is too late.

The second pillar, environmental sustainability, has been given more and more value as the environmental movement has continued to strengthen. For more than forty years, scientists, engineers, and other educated stakeholders have been researching, investigating, and evaluating the environmental impacts of land application practices. These efforts, in part, led to the Part 503 Rule. These efforts also led to numerous other discoveries about the sustainable benefits of land application.

For example, it was discovered that land application helps to improve, replenish, and maintain healthy soil by adding important nutrients, boosting soil water-holding capacity, and reducing topsoil runoff, all of which serve to increase crop yields. This discovery of improved crop production through land application has provided farmers with a viable alternative to reduce their dependency on chemical fertilizers. Further examples of discoveries: (1) the discovery that land application can reduce soil erosion and improve water quality overall and that the organic matter in biosolids assists with the binding of soil particles, the results of which offer improved soil properties, including texture and water-holding capacity, which in turn enhances root growth and increases drought resistance of vegetation; (2) the discovery that biosolids could provide topsoil for recreational uses, could be used to reclaim land and enrich forestland, and function to conserve landfill space (some of the approved recreational uses of land application are use at golf courses, sports fields, public parks, and other recreational areas); (3) the discovery that biosolids can be used to help reclaim disturbed land such as coal strip mines, gravel pits, quarries, construction sites, and landfills—these areas of disturbed land are often subjected to heavy equipment that strips away topsoil and that compacts underlying soils, exposing rock and subsoil and contributing to runoff and water pollution; (4) the discovery that biosolids can replace lost topsoil and in doing so have been shown to improve soil fertility and stability while also serving to decrease erosion; and (5) the discovery that use of biosolids conserve landfill space—this last discovery did not take years of research and investigation by scientists and engineers to recognize.

The third and final pillar, economic sustainability, is the underlying driver of the practice. It seems that no matter how much value is placed on social and environmental sustainability, economic sustainability will always be the leading driver. That said, the economics of the land application practice are quite remarkable. Whether the economics are considered from the perspective of the generators (wastewater treatment facilities), consumers (principally farmers), or the public at large, there are net economic benefits for all involved.

For generators, benefits include conservation of disposal costs, derived revenue from the sales of biosolids, and potential access to waste-to-energy tax credits. The conservation of disposal costs provides two forms of economic benefit. First, the generator does not have to bear the raw costs of disposal. Second, the generator conserves the space that it would be required to allot of disposal for other forms of waste. The revenue derived from biosolid sales also provides a benefit because the generator is deriving revenue from a source that was historically a cost. The generator may also be able to access waste-to-energy tax credits provided for under the federal tax code. See I.R.C. § 1603. Without getting into the details (of which there are many) of gaining access to such tax credits, suffice it to say that they operate as a significant incentive to generators to convert waste to various forms of energy, including biosolids.

For consumers, benefits come in the form of cost savings resulting from the purchase of biosolids for use as fertilizer in lieu of more expensive commercial manufactured fertilizer. Providing consumers (e.g., farmers) with an alternative to commercially manufactured fertilizers not only offers an opportunity for cost savings, but also drives the cost of commercial fertilizers down by adding competition to the marketplace where there previously was none.

For the public at large, benefits come in a similar form to that of consumers (i.e., cost savings). Members of the public at large pay to dispose of domestic sewage sludge in their utility bills. As the costs of disposing of such sludge continue to rise, so will those costs be passed on to the public at large. With the land application of biosolids, the costs of disposal decrease significantly, and as a result utility bills either remain at current levels or possibly even decrease as time goes on.

Looking Forward

Continued scientific research and study regarding land application is ongoing. The practice of land application and the generation of biosolids are not going to diminish; rather, they are likely to flourish in the decades to come. Recognizing this reality, researchers and scientists have been actively evaluating current practices to determine their sustainability and seeking to identify additional practices that will further promote sustainability. The current efforts being undertaken by these researchers and scientists include studying the ecosystem responses to biosolids, investigating biosolids for only recently identified constituents of concern, and applying new analytical techniques to investigation of biosolids. See, G.A. O’Connor, H.A. Elliott, N.T. Basta, R.K. Bastian, G.M. Pierzynski, R.C. Sims, J.E. Smith, Sustainable Land Application: An Overview, 34 J. Envtl. Quality 7 (2005). These efforts, and others like them, represent the continually growing interest that surrounds the land application of biosolids and ensuring sustainable practices.

Christopher W. Smith

Mr. Smith is a senior associate with Morris Polich & Purdy LLP in Los Angeles, California.