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SECTION I: INTRODUCTION

1.1 Biosolids Defined
1.2 Why Biosolids
1.3 Why a Biosolids White Paper?
1.4 Biosolids White Paper Organization
1.5 Background
1.6 Maine’s Regulations
1.7 Characterization of Biosolids in Maine.
1.8 How Do Biosolids Compare to Manures?
1.9 What Are The Trends In Maine?
1.10 What Are The Concerns?

1.1 Biosolids Defined
The treatment of municipal wastewater produces solids that have traditionally been called sludge. These solids may include portions directly removed from the wastewater and biological matter (i.e. biomass) generated by microorganisms during processes to remove organic matter and nutrients. Solids recovered from industrial processes are also called sludge and the term is often associated with potentially hazardous industrial wastes. Industrial sludges may have little or no agronomic value, so it is important to distinguish those solids produced from municipal wastewater that have value as a fertilizer or soil amendment. Hence the term biosolids is applied to specifically processed materials that contain plant nutrients or high amounts of organic matter. Biosolids may contain traces of potentially hazardous substances in concentrations that are considered to be below dangerous limits. The Maine and Federal regulations do not explicitly refer to treated sewage sludge as biosolids; however, the EPA (1995) defines biosolids as:
“The primarily organic solid product yielded by municipal wastewater treatment processes that can be beneficially recycled”.

The term biosolids has become an accepted term for the usable matter recovered from the processing and treatment of sewage sludge. This acceptance is reflected in Webster’s Collegiate Dictionary, 10th edition, which defines biosolids as:
“solid organic matter recovered from a sewage treatment process and used especially as fertilizer”.

It is important to distinguish the meanings of sewage sludge from biosolids. Biosolids have been treated to meet specific land-application criteria in accordance with the US EPA 503 rules (40 CFR 503 (c)) developed in 1993 to ensure safe agronomic use. In particular, sewage sludge contains pathogens, microorganisms that can cause illness or disease; biosolids have been processed to reduce pathogen content. Also, biosolids have been processed to reduce the attraction of disease carrying organisms, such as flies or rodents. These disease carriers are called vectors. Two types of biosolids are recognized based on their potential to contain pathogenic organisms. Class A biosolids have been treated to reduce pathogens to natural background concentrations and vector attractiveness to very low values; much lower than would be found in manures. Class B biosolids have been treated to reduce both pathogens and vector attractiveness, and uses are restricted by well-defined site suitability and access control regulations. These classes and uses of biosolids are clearly defined in the Maine regulations.

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1.2 Why Biosolids?
The land application of solids recovered from sewerage treatment process (biosolids) has benefits and risks. Rich in organic matter and containing nitrogen and phosphorous, these solids have value as a fertilizing soil amendment. Being derived from a waste product, biosolids contain traces of potentially hazardous metals, persistent organic compounds, and pathogenic organisms. The composition of the wastes generated by our society is a reflection of our consumption and disposal habits (Kroiss, 2004). Maine’s reuse regulations seek to balance the risks to public health while protecting the environment. The benefits and risks of land-applying biosolids is the theme of this document.

Overall, the general public lacks extensive knowledge of where their wastes go and how they are recycled. The beneficial re-use of wastewater treatment plant solids are not typically a major public concern. There have been exceptions where the public has felt that both the regulatory agencies and waste treatment plant operators have disregarded concerns about their health and the environment. This has led to the unfortunate situation of having communities divided by whether they support or object to the land application of biosolids. The social issues associated with waste management are beyond the scope of this review. The purpose of this paper is to summarize how the State of Maine regulates the beneficial utilization of biosolids through land application and to review relevant scientific research (210 recent publications). The intent is to provide a technical summary about how the use of sewage sludge (biosolids) is controlled to keep our waters clean and our environment safe.

The use of waste products, especially those that have strong odors, or come from an objectionable source, invariably causes public concerns. These concerns underlie a community’s desire to protect public health and safety, and so merit a serious public discourse. The gains and losses due to utilizing wastewater solids in Maine need to be examined using an analytical approach. The beneficial use of biosolids is not strictly an issue of right or wrong, or even good or bad, but an issue of balancing risks and benefits.

Human society cannot exist without a continuous process of determining acceptable risks. Just like driving a car, a reasonable adult will balance the benefits of getting to work on time with road conditions and the risks of having a traffic accident. In the case of wastewater treatment, there are the benefits of cleaner surface waters and an agronomic value derived from reusing biosolids balanced by the risks of metals in biosolids and the risks of public exposure to potentially hazardous substances. This paper will outline the benefits and risks of using biosolids as a fertilizer or soil amendment as derived from the scientific literature. A comparison of the risks of biosolids to manure or fertilizer will not be discussed in detail. Several comprehensive studies about the environmental effects of manure and fertilizer are available (see citations in Moss et al, 2002).

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1.3 Why A Biosolids White Paper?

Goal. The goal of this paper is to review research on the environmental benefits and liabilities of using biosolids for agronomic benefit as the basis for assessing how well Maine’s laws and regulations protect environmental quality. This effort includes a summary of the current status of biosolids utilization in Maine, with an emphasis on land application regulated under 06-096 CMR 419. The Maine land-application rules are compliant with existing federal rules (40 CFR Part 503). This work addresses two major themes:

1. Is the land application of biosolids, as regulated and practiced in Maine, sufficiently safe and protective of public health and the environment, particularly soil and water quality?
2. Maine public policy since 1988 favors beneficial use of biosolids over disposal options such as incineration or landfilling; is this beneficial use of biosolids supported by research?

Background: There is a perception in the wastewater treatment field that the general public misunderstands the environmental and human health effects of biosolids utilization in any form (Beecher et al., 2005; O’Connor et al., 2005). The existence of local opposition to utilization can be cited as the basis of this impression. This difference arises in part because opponents of biosolids use perceive a greater risk than the wastewater treatment plant operators. The perception of a greater risk, even if that perception is difficult to substantiate, is just as real in the minds of those opposed to biosolids reuse as any factual documentation of risks (Daughton, 2004; Beecher et al., 2005). This review provides a summary of research that can be used as a point of departure for discussions. Another aim of this paper is to help provide a broader background on the impact of biosolids utilization. As part of the continuing public debate, there is a need to have the arguments based on factual data that can help to define problems, answer questions, and aid in the interpretation of anecdotal information. The educational efforts of the wastewater industry and regulatory agencies, although technically complete and factual, made be viewed as agenda driven or unbalanced. Information sources that are considered biased often are rejected and ignored. If there is to be any progress made in determining how we balance the protection of public health with maintaining a clean environment, there must be effective and informed dialogue.

Needs: The wastewater treatment plant managers, concerned citizens, and others have requested a review of environmental and public health research relative to biosolids. The primary focus has been on the land application of biosolids because this is the area of greatest concern for potentially harmful impacts. The design of the analysis is based on the interpretation of more than 200 reports and peer-reviewed scientific papers. The peer-review process assures that the studies followed scientifically accepted methods of data collection and analysis. Using this protocol means that independent researchers should reach similar conclusions when analyzing the results of the same study. There is a wealth of research on how biosolids affect soil and water quality, as well as how pathogens from the waste treatment process are controlled or inhibited. The scientific studies are diverse and the results are not always accessible to the average citizen.

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1.4 Biosolids White Paper Organization
The paper is divided into five sections.

Section I provides a brief background on why we have the whole issue of utilizing biosolids, including an outline of how biosolids are regulated in Maine. The regulations should direct the management of biosolids based on the scientific research.

Section II addresses how biosolids affect soil quality by drawing from a substantial body of research.

Section III analyzes how biosolids affect water quality, both surface and ground, since a primary aim of the regulation is to protect water quality.

Section IV summarizes the current research on odors and pathogens in biosolids.

Section V takes the research studies and assesses whether the Maine regulations work to protect the environment and public health.

What occurs in Maine is important in the context of the whole country. The generation and management of biosolids has been the focus of national studies (NRC, 1996 and 2002) and efforts have been made to target key issues such as the Water Environment Research Foundation’s Biosolids Summit (Dixon and Field, 2004). This paper will help to relate national issues to Maine.

1.5 Background
The federal Clean Water Act (33 USC 1251 et seq.) was enacted in 1972 and it initiated a process to make our rivers, lakes, and streams cleaner. This process continues and many areas are once again enjoying the benefits of having water that has been restored to be swimable, fishable, and drinkable. As a society, we place a high value on our water resources, while at the same time we place high demands on these same resources (Bergstrom et al., 2001). These water quality gains come at a cost, and part of the cost has been removing sewage wastes from our waters.

Waterways have been used for waste disposal for centuries; even the ancient Romans had sophisticated systems of aqueducts and sewers to keep their urban areas healthy and clean. The Clean Water Act went beyond sewer systems to developing technologies to remove the chemical and biological burden that wastes place on water. This meant that cities and towns had to remove solids and soluble nutrients from the wastes in order to lower the burden. For areas without much industry, the wastes come predominantly from domestic sources such as toilets, sinks, showers, and washing machines. Industrial sources are strictly regulated under the National Pretreatment Program to prevent discharges that would adversely affect effluent quality and ultimately biosolids quality. This program has helped to reduce the metal content in biosolids over the last decade.

Through a series of treatment steps that screen and settle out the solids and use bacteria to consume the nutrients, sewage treatment plants discharge clear, practically potable, water. The solids produced at the treatment plant are an integral part of making the wastewater cleaner. Production of the solids is impossible to avoid. These solids contain the nutrients removed from the wastewater, along with other components that adhere to the solids. There are only a few acceptable methods for dealing with these materials: 1) disposal in a landfill; 2) incineration and disposal of the ash in a landfill; or 3) utilization of the solids as a fertilizer or soil-building material (Overcash, 2004; Overcash et al., 2005). Each of these sewage sludge disposal options is worthy of a detailed analysis and Krogmann et al. (1999) present a detailed summary of each. In this paper the third option, utilization, and particularly as Class B biosolids, will be assessed. Class A biosolids differ from Class B in terms of pathogen content and character of its organic matter, but the broader range of research on Class B biosolids allows for a more rigorous analysis.

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1.6 Maine’s Regulations
In Maine, sewage sludge used in land application is regulated as a solid-waste residual. The rules developed by the Maine Department of Environmental Protection (DEP) were authorized by the Legislature under statute 38 MRSA Sections 1304(1), (13), and (13-A). These statutes authorize the DEP to regulate solid wastes to minimize pollution of the environment. The innovative re-use of wastes, explicitly sludge land-application, is supported by statute. The statutes also state that the public must be notified of sludge utilization sites. Simplified, the Maine statutes direct the Maine DEP to support the highest value use for sewage sludge and direct the DEP to keep the public informed of utilization sites.

Under these legislative statutes, the Maine DEP has developed rules within its solid waste responsibilities for the Agronomic Utilization of Residuals (06-096 CMR, Chapter 419). Copies of the rules are available in most public libraries in Maine and all of the rules can be viewed online at the Maine DEP web page. The Maine rules conform to the US EPA rules for the land application of sewage sludge (40 CFR Part 503). Maine’s minimum quality standard for sewage sludge is equal to the EPA’s exceptional quality standard. The Maine DEP regulates the land application of sewage sludge (biosolids) using standards that meet or are more stringent than the US EPA requirements. This increases the level of protection to the environment and public health in Maine as compared to what is mandated by the federal government.

The Maine rules refer to sewage sludge that is acceptable for land application and the term “biosolids” is not used explicitly in the regulations. In the following discussion “biosolids” always refers to a sewage sludge that meets land application standards. In later sections of this report, research completed before the acceptance of the term “biosolids” uses the term “sewage sludge”. It is not usually clear if the sewage sludges applied before 1993 met today’s quality standards. The land application of septage wastes is not included in this summary.

The Maine rules for agronomic utilization of Class B residuals are comprised of several parts that cover:

• Licensing of generators and utilization sites,
• siting of utilization sites,
• operating standards including biosolids quality and composition,
• suspension of utilization sites,
• record keeping and reporting, and
• oversight.

First and foremost, the utilization of biosolids must be licensed by the Maine DEP (Chapter 419, Section 2). Program and site licenses are needed to store and apply biosolids. Public notice of license application is required and public comment regarding the application to the Maine DEP is invited (Chapter 419, Section 2(G), and Chapter 2). Typically notice is made as a legal notice in a local newspaper and at the town office, plus mailing to utilization-site abutters.

Siting. There are specific rules for the licensing of Class B biosolids land-spreading sites that include both material quality and site suitability (Chapter 419, Section 3(B)). The siting standard establishes quality guidelines for a maximum acceptable concentration of specific trace metals in the biosolids (Table I) and pathogen content. Any leachable residual, including biosolids, must be used with setback from wells, property lines, bedrock outcroppings, dwellings, and surface water features and be used over a soil of sufficient thickness to protect ground water (Chapter 419, Section 3(A)). Site suitability is defined to minimize erosion and loss of biosolids into surface and ground waters. Ideal locations are flat with a thick layer of fairly dense soils. Setbacks from surface water features (drainage ditches, streams, lakes, etc.) vary depending upon the land slope and vegetation type, such as wooded or open (Chapter 419, Section 3(B)(2)). These setbacks protect surface waters from direct transport of biosolids across the ground surface during a rainstorm. Neighboring properties are protected with setbacks from boundary lines. (Chapter 419, Section 3 (C)).

Agronomic Value. Biosolids must be used for a defined agronomic benefit (Chapter 419, Section 4(B)). This benefit may be from nutrients, such as nitrogen or phosphorous, or as a liming agent. The amount of biosolids utilized must be calculated based upon soil testing and crop requirements. This is a very important concept, because biosolids contain several nutrients and utilization must not exceed any crop or soil nutrient need.

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Environmental Protection. The Maine DEP is charged to protect the waters of the state, and utilization of Class B biosolids must not pollute any water by direct application, surface runoff, or leaching to ground water (Chapter 419, Section 4(E)). To protect water resources, biosolids may not be applied to frozen or snow covered ground, or during periods when the ground is saturated with water. Biosolids must be spread evenly at agronomic rates and utilization rates must account for crop harvest or fallowing. Vegetation must be maintained to minimize erosion losses. Buffer zones must be maintained to prevent the washing of biosolids into surface waters. Hydric soils are not suitable for land spreading and their use is prohibited. Hydric soils are defined to be saturated with water long enough during the growing season to favor the growth of wetland plants.

Class B biosolids in Maine typically have carbon to nitrogen ratios less than 25:1. This implies that excess nitrogen may be leached from the biosolids into groundwater. In addition to requiring agronomic application rates, the Maine DEP has additional standards to protect groundwater quality (Chapter 419, Section (4)(L)). These standards define suitable soils to minimize leaching, establish a separation distance to groundwater or bedrock, and limit the window for spreading (no spreading on frozen, snow-covered, or water-saturated soil).

Pathogen Control. Biosolids, because they contain human pathogens, have additional operational standards (Chapter 419, Section 4(I)). The Maine DEP classifies any residual that may contain human pathogens as a Type II residual. These residuals can be utilized only after they are treated to reduce the pathogen content and vector attraction potential. Two pathogen reduction standards are recognized: Class A and Class B. Class A biosolids have been processed to reduce pathogens to very low concentrations, equivalent to background values, based upon Salmonella and fecal coliform assays. Common methods used in Maine to make Class A biosolids are composting and advanced alkaline stabilization with supplemental drying. Processing sewage sludge to the Class B standard reduces pathogens, but not to as low a concentration as required for Class A. Common methods employed in Maine are lime stabilization, composting, and thermophilic aerobic digestion. Vector reduction techniques are employed to minimize biological contact with disease spreading organisms. Vector attraction reduction for Class B biosolids can also be attained by direct injection into the soil or tilling after application.

The potential risks of biosolids components entering the food chain through crops, livestock, or direct human contact is a public health concern. In order to minimize health risks, the Maine DEP places restrictions on the use of agricultural land that has received Class B biosolids, but not Class A (Chapter 419, Section (4) (I) (2)). These restrictions apply to when:

• crops can be grown and harvested;
• animals can be grazed;
• turf can be grown;
• topsoil harvested; and
• public access must be controlled.

Metals. There are heavy metals in biosolids that are characteristic of the region’s water supply and the diet of the source community. Heavy metals concentrations are monitored in biosolids and soils because some are plant or animal toxins (Chapter 419, Section (4)(J)). Additional setbacks are required when metals exceed the screening concentrations (Table I). Maine allows for certain maximum concentrations in biosolids that may be allowed is special one-time application (second column of Table I). Regardless of how much is applied, Maine has strict annual and cumulative metal loading limits (Chapter 419, Section (4)(J)(5)). All land utilization of biosolids must cease if metal loadings reach the cumulative limit in soil (fourth column of Table I) as determined from soil tests, regardless of agronomic requirements.

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TABLE I. Maine standards for metal content in sewage sludge, soil loading limits, and maximum acceptable metal content in soils at utilization site.

Hazardous Substances. The biosolids must be tested for the presence of numerous hazardous organic compounds (Chapters 405 and 418) including dioxins (Chapter 419, Section (4)(K)). Typically, biosolids contain few, if any, hazardous organic compounds or dioxins. The Maine DEP evaluates hazardous organic compounds on a case-by-case basis and has set a maximum acceptable concentration of 250 parts-per-trillion (ppt) limit for dioxins (expressed as the 1987 factors for toxic equivalents to 2,3,7,8 TCDD; tetra-chloro-dibenzo-dioxin).

Odors. Biosolids have the potential to generate nuisance odors. Under Chapter 400 (Section (4) (G) (1)), utilization must produce no unreasonable change in air quality. This is managed in Chapter 419 Section (4) (H) through three performance criteria. These criteria apply only to putrescible materials. All Class A biosolids and most Class B biosolids that meet the vector attractiveness reduction criteria should fall below the applicable threshold. The first performance criterion is requiring a 300 foot setback from occupied buildings; a greater setback may be needed if odors are unusually intense. The second is a site specific odor control plan to be implemented by the generator. The third standard is a requirement to notify the Department at least one day prior to site utilization.

Storage. The generation of biosolids occurs year-round, but spreading on agricultural land is limited by the cropping cycle. Typically, biosolids are spread in the late-spring during planting, after mid-summer croppings, or in the fall after harvest. In order to accommodate farm management, biosolids must be stored before application. The storage of biosolids is regulated because they can have a high moisture content and leachate can drain from stockpiles. The Maine DEP has extensive rules for stockpiling (Chapter 419, Sections (10) (11) (12)). The rules are different for covered storage and field stacking.

In general, biosolids storage must be sited away from dwellings, roads, water supplies, and floodplains (Chapter 419, Section (10)(A)). In particular, field storage sites must not contaminate the waters of the state. This mandate is met by limiting storage in a field to the agronomic amount needed and storing biosolids on flat ground. In addition, soils below the stockpile must be relatively dense with low permeabilities (< 2-inches per hour) in the C horizon (Chapter 419, Section (10)(C)). In order to protect surface and ground waters, soils must be 30 to 40 inches thick and the seasonal high-water table must be greater than 24 inches below the surface. Any leachate developed by the stockpile must be contained within the utilization area. Biosolids are not to be stockpiled within 250 feet of large water bodies such a great ponds, rivers, and perennial streams (Chapter 419, Section (10)(D)).

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1.7 Characterization of Biosolids in Maine

How Much is Produced? According to Maine DEP records there are 200 licensed wastewater treatment facilities in the state. These facilities vary in size from small towns to large cities; some of which may also receive industrial inputs. A smaller number of facilities (120) are listed as generating sewage sludge. The sewage sludge may not necessarily be treated to produce biosolids. Common management alternatives are land application, composting, or landfilling. In 2002, approximately 154,923 cubic yards of sewage sludge was generated in the state. Note that wastewater treatment plants record volumes in either cubic yards or gallons or pounds. To convert between these different units of measure the Maine DEP assumes that sewage sludge weighs 1700 pounds per cubic yard. The amount of sewage sludge generated each year varies by 10 to 20 per cent (Figure 1). This variability is due in part to lagoon storage facilities at some wastewater treatment plants and the plant operators’ ability to dewater the sludges.

FIGURE 1. Annual Sludge Production in Maine 1995-2002 (Figure modified from Maine DEP).

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How Much is Reused? Just as the amount of sewage sludge generated each year varies, the ultimate disposition of the sludges each year is also variable (Figure 2). A majority (>75%) of the sewage sludge is processed into Class A or Class B biosolids each year. Disposal in landfills accounts for 10 to 25 per cent of the sludge each year. The remainder of the annual production goes to different uses: landfills, storage, and transport out of state. In 2002, 35,738 cubic yards (23%) were processed to the Class B standard and reused in land applications. Another 46,581 cubic yards (30%) were processed to the Class A standard and 18,946 cubic yards (12%) were utilized in Maine; the remainder of the Class A biosolids were exported.

There are some important trends in sewage sludge disposition between 1995 and 2002 that reflect trends in management and utilization. The amount of Class A biosolids produced each year has been increasing consistently and now is the destination for more than half of all the sewage sludge produced. The land application of Class B biosolids has steadily declined over this period of eight years and in 2002 it accounted for less than 25 per cent of all the sewage sludge produced. It is important to note that both Class A and Class B biosolids can be applied to land. Class B biosolids use is restricted to agronomic applications while Class A biosolids, such as compost, have many more potential applications. Composted biosolids have been employed in diverse uses such as: road bank stabilization, landscaping around parking lots, playing fields, and land restoration projects.

The amount of sewage sludge sent to landfills varies each year. The landfilled amount varies due to sludge quality, economic incentives, or material designated for land application that could not be delivered because of weather conditions or limited storage. Landfilling is relatively expensive; the long-term outlook for landfills is a growing demand for the space and higher tipping fees.

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Not all sewage sludge generated in Maine is utilized in the state. Some is shipped out of state to other processing facilities, utilization sites, or landfills. The amount leaving the state is dependent upon demand by processors and disposal fees.

What is the Composition of Biosolids? Biosolids are produced from the solids collected at wastewater treatment plants and their composition depends upon what gets sent to the treatment plant. For many towns in Maine, the input is coming from homes and contains all the substances that we send down our drains. Large industries usually have their own dedicated wastewater treatment plants. Small industries will typically discharge wastes to municipal treatment systems after some amount of pre-treatment. The US EPA initiated pre-treatment of industrial wastes in 1978 under amendments to the Clean Water Act (40 CFR Part 403). Under the pre-treatment program industries must remove hazardous wastes from their sewage discharge. This program has helped to reduce the amount of hazardous chemicals that once ended up in sewage sludge (Krogmann and Chiang, 2002).

In Maine, the quality of the wastes, and ultimately the biosolids, are tested or monitored at multiple locations in the process. All testing is approved and reviewed by the DEP- the agency responsible for protecting the state’s water, air, and soil. Raw sewage is tested as it comes into the wastewater treatment plant. The biosolids product is tested on a routine and regular basis, semi-annually to monthly as determined by produced volumes. The characteristics of biosolids do not vary markedly over time and testing every few hundred cubic yards is considered to be sufficient. Any material can be selected by the Maine DEP for a spot test, anywhere, anytime. All testing must be performed using standard protocols, EPA analytical methods and in a timetable set by the regulators (06-096 CMR Chapter 405, Sampling and Analytical Plan Requirements). Manures and even commercial fertilizers are not subject to this amount of testing.

Biosolids have agronomic value because they contain measurable quantities of needed plant nutrients, especially: nitrogen, calcium, magnesium, potassium, sodium, phosphorous, and carbon. These nutrients may constitute up to several percent of the total mass. Micronutrients provided by biosolids are chloride and iron, plus some trace metals. Micronutrients usually are contained in the part-per-million (ppm) range. Some of these nutrients are readily available to plants while others are released more slowly. Each type of biosolids will have its own characteristic nutrient value.

FIGURE 2. Utilization of Sewage Sludge in Maine 1995-2002 (Data from Maine DEP).

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Biosolids are mostly water: Class B has 20% to 30% total solids; Class A has 40% to 50% total solids. The water in biosolids is slowly released. The high organic matter content of biosolids makes it a valuable amendment for improving water retention capacity in soils. Lime-stabilized biosolids have a high pH and can be used as liming materials as well as a fertilizer. Since soils in Maine are naturally acidic, crops grow better in soils that have been limed to reduce acidity. Some typical ranges for the nutrient content of Class B biosolids in Maine are presented in Table II. Some of the biosolids have had lime added prior to analysis and this contributes to the broad range of calcium concentrations.

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TABLE II. Typical Plant Nutrient Concentrations in Class B Biosolids in Maine.

Biosolids also contain metals in trace concentrations. Some metals are also plant nutrients when present in very low concentrations. However, in high concentrations some metals can impair plant growth (phytotoxicity) or degrade the quality of the crops. Maine has maximum ceiling concentrations for 16 different, and naturally occurring, metals in soils at utilization sites. Biosolids are required to be analyzed for the presence of 19 metals that have maximum acceptable concentrations in soils: aluminum, arsenic, barium, beryllium, cadmium, calcium, chromium, cobalt, copper, iron, lead, mercury, molybdenum, nickel, selenium, silver, sodium, vanadium, and zinc. The Maine screening standards for 10 metals are presented in Table I. The screening standards are equivalent to the US EPA’s Exceptional Quality standard for two metals and more restrictive for six others.

The actual concentrations of trace metals in biosolids in Maine vary considerably across the state. In general, nearly all of the sewage sludges produced in Maine have metal concentrations well below the screening limit. This implies that when sludges are applied at agronomic rates, the input of metals to the soil is small. The actual ranges of metals found in sewage sludge, including those processed into biosolids, are depicted in Figure 3. The data are plotted as cumulative frequency diagrams. Maine’s screening standard is shown as a vertical line in each plot. The curve depicts the portion of the data that fall below a certain value. For example, 100 per cent of the arsenic concentrations are less than 39 mg/kg and half of all concentrations are less than 6 mg/kg. The cumulative frequency plots show the variability of the concentrations better than a table of ranges. Steep curves imply that the concentrations have small variations and shallow curves have wide variations. This analysis is based on 182 samples reported from 51 sewage treatment plants in Maine during 2002.

Following is a summary of the trace metal concentrations detected in Maine sewage sludges that were processed into Class A or B biosolids during 2002. The concentrations are compared to the Maine screening standard which represents exceptional quality. The median is the value for the middle of the population (geometric mean); half of the samples are larger and half are smaller.

Although there are trace metals in sewage sludges generated in Maine, very few have concentrations that exceed the screening limits. The median concentrations for all metals are substantially below the screening limits, usually 50 per cent or less.

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FIGURE 3. Cumulative Frequencies of Trace Metals in Maine Sewage Sludge. Data from Maine DEP for 2002.

Figure 3-A: Arsenic
Arsenic. Arsenic occurs in concentrations up to 39 mg/kg in Maine sewage sludges. More than 90 per cent of all these sludges have concentrations below the Maine screening standard of 10 mg/kg. The median concentration is approximately 6 mg/kg, nearly half of the screening standard.

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Figure 3-B: Cadmium
Cadmium. Cadmium occurs in concentrations up to 16 mg/kg in Maine sewage sludges. More than 99 per cent of all these sludges have concentrations below the Maine screening standard of 10 mg/kg. The median concentration is approximately 3 mg/kg, nearly one-third of the screening standard.

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Figure 3-C: Chromium
Chromium. Chromium occurs in concentrations up to 240 mg/kg in Maine sewage sludges. All these sludges (100%) have concentrations below the Maine screening standard of 1000 mg/kg. The median concentration is approximately 17 mg/kg, less than 2 per cent of the screening standard.

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Figure 3-D: Copper
Copper. Copper occurs in concentrations up to 2429 mg/kg in Maine sewage sludges. More than 98 per cent of all these sludges have concentrations below the Maine screening standard of 1000 mg/kg. The median concentration is approximately 260 mg/kg, slightly less than one-third of the screening standard.

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Figure 3-E: Lead
Lead. Lead occurs in concentrations up to 523 mg/kg in Maine sewage sludges. More than 99 per cent of all these sludges have concentrations below the Maine screening standard of 300 mg/kg. The median concentration is approximately 40 mg/kg, nearly one-tenth of the screening standard.

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Figure 3-F: Mercury
Mercury. Mercury occurs in concentrations up to 10 mg/kg in Maine sewage sludges. More than 99 per cent of the sludges have concentrations below the Maine screening standard of 6 mg/kg. The median concentration is approximately 0.6 mg/kg, one-tenth of the screening standard.

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Figure 3-G: Molybdenum
Molybdenum. Molybdenum occurs in concentrations up to 72 mg/kg in Maine sewage sludges. All these sludges (100%) have concentrations below the Maine screening standard of 75 mg/kg. The median concentration is approximately 6 mg/kg, less than one-tenth of the screening standard.

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Figure 3-H: Nickel
Nickel. Nickel occurs in concentrations up to 290 mg/kg in Maine sewage sludges. More than 99 per cent of all these sludges have concentrations below the Maine screening standard of 200 mg/kg. The median concentration is approximately 17 mg/kg, less than one-tenth of the screening standard.

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Figure 3-I: Selenium
Selenium. Selenium occurs in concentrations up to 52 mg/kg in sewage sludges. All sludges (100%) have concentrations below the Maine screening standard of 100 mg/kg. The median concentration is approximately 1.5 mg/kg, nearly 2 per cent of the screening standard.

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Figure 3-J: Zinc
Zinc. Zinc occurs in concentrations up to 3422 mg/kg in sewage sludges. More than 98 per cent of all sludges have concentrations below the Maine screening standard of 2000 mg/kg. The median concentration is approximately 420 mg/kg, nearly one-fifth of the screening standard.

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Are There Hazardous Substances in Biosolids? The composition of biosolids depends upon the wastes sent to the wastewater treatment plant. Aggressive pollution-prevention programs that have targeted industries and household hazardous wastes have reduced the amount of hazardous substances entering the waste stream over the last decade. Since industries have reduced the amount of hazardous wastes that could end up in biosolids, Maine has been able to maintain its quality standards. The biosolids are screened for 148 different hazardous organic compounds. Some of the potentially hazardous organic compounds detected come from innocuous or unavoidable sources such as drinking water supplies, plastic pipes, or the action of bacteria during the waste treatment process. The presence of pesticides or poly-chlorinated biphenyls (PCBs) at concentrations above detection limits is almost nonexistent in biosolids. Concentrations of dioxins below the Maine limit of 250 ppt have been detected in some biosolids. Unfortunately, dioxins can be detected in almost everything from sewage sludge to soil. Much effort has been spent to identify and control sources of dioxin. Organic compounds that may be detected in some Maine biosolids are characterized below:

Acetone and 2-Butanone. These are common industrial chemicals and are found as solvents in paints, adhesives, and nail polish remover. A more likely source in biosolids is the formation of acetone or 2-butanone through bacterial fermentation of organic matter.

Bis (2-ethylhexyl) Phthalate. This compound is found anywhere plastic pipes are used. It is part of a family of compounds known as plasticizers; compounds that make plastics flexible. Similar compounds that may also be detected are butylbenzylphthalate and di-n-octylphthalate.

Chloroform. Chloroform is a disinfection by-product produced when drinking water is treated with chlorine to control pathogens. The chlorine reacts with natural organic matter in the source water to form chloroform. Chloroform is common to many public water supplies that use chlorine as a disinfectant.

Phenol. The occurrence of phenol in biosolids is due to several sources. Phenol can come from: its use as a sterilizing agent, chemical feedstock, plastics, or as a product of bacterial metabolism.

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1.8 How Do Biosolids Compare to Manures?

Manures are the raw wastes from farm animals; in Maine, sources can be cows, chickens, or pigs. There is a long tradition of using manure for a fertilizer. The nutrient value of biosolids tends to be comparable to manures for nitrogen and phosphorus, while the potassium content of biosolids is lower than manures. The trace metal content of biosolids is also comparable to biosolids. The trace metal concentration of biosolids is plotted in Figure 4 using the same data as shown in Figure 3. In Figure 4, the concentration ranges are depicted as boxes. The box itself shows the range of 75 percent of the samples, the line in the box is the mean value. The whiskers outside the box show the range of 90 percent of the samples and the dots are samples that lie outside of that 90 percent. The concentration scale is logarithmic in order to show all of the trace metals simultaneously.

FIGURE 4. Trace metals in biosolids.
Figure 4 shows the ranges in concentrations for 10 trace metals.

FIGURE 5. Trace metals in biosolids compared to manures.
Figure 5 shows the ranges in concentrations for 10 trace metals compared to manures. Concentration ranges are similar.

The trace metal concentrations for animal manures are compared to biosolids in Figure 5. The manure values are ranges only (solid vertical lines next to the boxes). Trace metals concentrations in manures are taken from several sources including Maine DEP (unpublished), national studies (Moss et al., 2002), and European studies (Eriksson, 2001; Moreno-Caselles et al., 2002). The ranges of trace metal concentrations in manures overlap the values for biosolids, with the exception of selenium. In terms of nutrients and trace metals, biosolids are very similar to common manures. In terms of pathogens, farm manures are not subject to any pathogen reduction or pathogen control processes.

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1.9 What Are The Trends In Maine?
In Maine, the relative disposition of biosolids has changed during the last few years. The uses have not changed and the overall end points continue to be: Class B land applied, Class A land applied, landfilling, export out-of-state, and Class B for other uses. These trends are visible in Figure 2. Land application of Class B biosolids is a declining part of the mix. These changes in how biosolids are managed underscore the challenges faced by the waste-water treatment plants. In particular, the treatment works must make sewage sludge in order to keep surface water clean and managing this sludge (biosolids) is an essential part of the overall process. When the wastewater treatment plant options are reduced to only landfills or Class A biosolids, costs increase. These costs are ultimately paid for by the community through higher fees or taxes. The future use of biosolids, as either Class A or B, will depend upon how current policy is implemented and how new policies are structured.

1.10 What Are The Concerns?
The improvement of surface water quality accomplished through wastewater treatment is highly valued by the public. The production of sewage sludge and biosolids are therefore necessary products of the treatment process. The agronomic use of biosolids represents a progression from treating the residuals as waste products to treating them as recyclable commodities. Reuse leads towards a sustainable system. Reusing biosolids is not a universally accepted practice (Tyson, 2002). In fact some would argue that the practice is not sustainable because of the eventual build-up of metals in soil (Orlando, 2001). There is the counter-argument that the practice is sustainable because sludge quality is continually being improved and biosolids utilization is an essential part of managing our society’s wastes (Krogman et al., 1999 and 2001; Kroiss, 2004). Groups, such as organic farmers, have expressed reservations about using a waste product to produce food crops. Animal manures are given a different type of acceptance even though manures pose similar potentials for adverse effects (Krogman et al., 2001; Tyson, 2002). In general, the concerns about biosolids have been grouped into two general categories: (1) Environment – soil and water quality; and (2) Human Health – risks of illness.

Environmental Effects –

• Groundwater or surface water contamination by metals, nutrients, or pathogens.
• Soil contamination by metals, persistent organic compounds, or pathogens.

Health Risks –

• Pathogens causing infection by direct exposure or bioaerosols.
• Metal accumulation into food crops or grazing animals.
• Potential exposure to trace organic compounds.

The following sections will summarize research centered on these concerns and will evaluate the effectiveness of Maine’s regulation of biosolids.

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