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Solids Management
Solids Management
The solids that enter the wastewater treatment plant are separated from the water portion of the wastewater so that these “biosolids” can be reused. This nutrient-rich, organic material is a valuable resource that just like any other fertilizer, can improve the condition of the of soil and contribute to better crop yields. Wastewater treatment plants that recycle biosolids must meet stringent regulatory requirements to assure the safe reuse of this material.
In January of 2014, the Racine Wastewater Utility entered into an agreement with Synagro...
Processes
During wastewater treatment, bacteria and other microorganisms break down components in wastewater into simpler and more stable forms of organic matter. Non-organic matter also settles into sludge. For instance, small amounts (parts per million) of heavy metals and other potentially toxic materials, including flame retardants (PBDEs) and persistent organic pollutants, are commonly found in sewage sludge in parts per million levels. What does not settle into sludge leaves the treatment facility as a treated wastewater effluent. Biosolids in their liquid form look like muddy water and contain 1-10% solids. Biosolids may be dewatered in a second step of the treatment process, which turns it into a “cake” with the texture of a wet sponge. In this stage it contains 20 to 25% solids. Racine dewaters their biosolids using belt filter presses to remove excess water from the product.
United States
According to the United States Environmental Protection Agency (EPA), biosolids that meet treatment and pollutant content criteria of Part 503.13 “can be safely recycled and applied as fertilizer to sustainably improve and maintain productive soils and stimulate plant growth.” After the 1991 Congressional ban on ocean dumping, the US EPA promulgated regulations – 40 CFR Part 503 – that continued to allow the use of biosolids on land as fertilizers and soil amendments which had been previously allowed under Part 257. The EPA promoted biosolids recycling throughout the 1990s. The EPA’s Part 503 regulations were developed with input from university, EPA, and USDA researchers from around the country and involved an extensive review of the scientific literature and the largest risk assessment the agency had conducted to that time. However, there was no risk assessment for pathogens or chemicals and heavy metals were not considered to be cancer causing agents. The Part 503 regulations became effective in 1993.
United States municipal wastewater treatment plants in 1997 produced about 7.7 million dry tons of biosolids, and about 6.8 million dry tons in 1998, according to sources relying on EPA estimates. As of 2002, about 60% of all biosolids were applied to land as a soil amendment and fertilizer for growing crops. Biosolids that meet the Class B pathogen treatment and pollutant criteria, in accordance with the EPA “Standards for the use or disposal of sewage sludge” (40 CFR Part 503), can be land applied with formal site restrictions and strict record keeping. Biosolids that meet Class A pathogen reduction requirements or equivalent treatment by a “Process to Further Reduce Pathogens” (PFRP) have the least restrictions on use. PFRPs include pasteurization, heat drying, thermophilic composting (aerobic digestion, most common method), and beta or gamma ray irradiation. Processes to reduce pathogens have no effect on heavy metals and may or may not have effects on the levels of other trace pollutants in biosolids. Treatment processes that involve significant amendments such as composting and alkaline stabilization may dilute total trace metals.
History of Bio-Solids
Historically, the problem of human waste disposal began when communities first formed. At that time, population densities were low enough that the surrounding land or waterways could handle human wastes. Wastes that were applied to land increased soil fertility. As populations grew, the nearby land could not handle all the wastes, so they were dumped into streams and rivers that carried the problem “away.”
Some early cultures put their human waste to good use. For thousands of years, Chinese society returned sewage, called “night soil,”...
Evolution of Residual Solids/Biosolids
Before the era of wastewater treatment, municipal wastewater was untreated and biosolids did not exist. Biosolids are an end product of municipal wastewater treatment and contain many of the constituents removed from the influent wastewater. Biosolids are a concentrated suspension of solids, largely composed of organic matter and nutrient-laden organic solids, and its consistency can range in form from slurry to dry solids, depending on the type of treatment.
Agricultural utilization of biosolids was practiced since residual solids were first produced. Given our experience with the use of human excrement, sewage, and animal manure on croplands, the application of biosolids to agricultural lands was a logical development. As an early example, municipal biosolids from Alliance, Ohio was used as a fertilizer as early as 1907. During the same period, Baltimore, Maryland used domestic septage in agricultural production.
Recent Advancements
Over the past 30 years, there has been an intense and concerted effort of scientific research worldwide to better understand the fate of potentially toxic and pathogenic constituents in biosolids when biosolids are applied to agricultural soils. The surge of technical information regarding agricultural application of biosolids led to the development of pollutant loading guidelines by the United States and western European countries.
Since the late 1970s and early 1980s source control and industrial wastewater pre-treatment programs were initiated to limit the discharge of industrial constituents into municipal sewers. These programs resulted in a dramatic reduction of trace elements in wastewater and biosolids. Municipal wastewater biosolids, particularly from industrialized cities, now contain significantly lower levels of trace elements than in earlier decades when much of the research on biosolids application to cropland was conducted. EPA first developed biosolids management regulations under the 1972 Federal Water Pollution Control Act to prevent biosolids-borne constituents from entering the nation’s navigable waters. In 1977 Congress amended the Act to add a new section, 405(d) that required EPA to develop regulations containing guidelines to identify alternatives for biosolids use and disposal and to specify what factors must be accounted for in determining the methods and practices applicable to each of these identified uses. Also to identify concentrations of pollutants that would interfere with each use.
In 1978, U.S. EPA established regulations limiting concentrations of cadmium, PCBs and pathogens. In 1987, Congress amended section 405 again and established a timetable for developing biosolids use and disposal guidelines. Through this amendment, Congress directed EPA to identify toxic pollutants that may be present in biosolids in concentrations that may affect the public health and the environment. and to promulgate regulations that specify acceptable management practices and numerical concentration limits for these pollutants in biosolids.
The intent of the 1987 amendment was to “adequately protect human health and the environment from any reasonably anticipated adverse effect of each pollutant.” This section also states that any permit issued to a POTW or other treatment works for wastewater discharge should specify technical standards for biosolids use or disposal.
Frequently Asked Questions
They are nutrient-rich organic materials resulting from the treatment of domestic sewage in a treatment facility. When treated and processed, these residuals can be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth.
Biosolids are treated sewage sludge. Biosolids are carefully treated and monitored and must be used in accordance with regulatory requirements.
We have biosolids as a result of the wastewater treatment process. Wastewater treatment technology has made our water safer for recreation and seafood harvesting. Thirty years ago, thousands of American cities dumped their raw sewage directly into the nation’s rivers, lakes, and bays. Through regulation of this dumping, local governments are now required to treat wastewater and to make the decision whether to recycle biosolids as fertilizer, incinerate it, or bury it in a landfill.
Biosolids are created through the treatment of domestic wastewater generated from sewage treatment facilities. The treatment of biosolids can actually begin before the wastewater reaches the sewage treatment plant. In many larger wastewater treatment systems, pre-treatment regulations require that industrial facilities pre-treat their wastewater to remove many hazardous contaminants before it is sent to a wastewater treatment plant. Wastewater treatment facilities monitor incoming wastewater streams to ensure their recyclability and compatibility with the treatment plant process.
Once the wastewater reaches the plant, the sewage goes through physical, chemical and biological processes which clean the wastewater and remove the solids. The wastewater treatment processes work to control pathogens (disease-causing organisms, such as certain bacteria, viruses and parasites) and other organisms capable of transporting disease.
After treatment and processing, biosolids can be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth. The controlled land application of biosolids completes a natural cycle in the environment. By treating sewage sludge, it becomes biosolids which can be used as valuable fertilizer, instead of taking up space in a landfill or other disposal facility.
The application of biosolids reduces the need for chemical fertilizers. As more wastewater plants become capable of producing high quality biosolids, there is an even greater opportunity to make use of this valuable resource.
The National Academy of Sciences has reviewed current practices, public health concerns and regulator standards, and has concluded that “the use of these materials in the production of crops for human consumption when practiced in accordance with existing federal guidelines and regulations, presents negligible risk to the consumer, to crop production and to the environment.”
Biosolids may have their own distinctive odor depending on the type of treatment it has been through. Some biosolids may have only a slight musty, ammonia odor. Others have a stronger odor that may be offensive to some people. Much of the odor is caused by compounds containing sulfur and ammonia, both of which are plant nutrients.
The federal biosolids rule is contained in 40 CFR Part 503. Biosolids that are to be land applied must meet these strict regulations and quality standards. The Part 503 rule governing the use and disposal of biosolids contain numerical limits, for metals in biosolids, pathogen reduction standards, site restriction, crop harvesting restrictions and monitoring, record keeping and reporting requirements for land applied biosolids as well as similar requirements for biosolids that are surface disposed or incinerated. Most recently, standards have been proposed to include requirements in the Part 503 Rule that limit the concentration of dioxin and dioxin like compounds in biosolids to ensure safe land application.
The biosolids rule is described in the EPA publication, A Plan English Guide to the EPA Part 503 Biolsolids Rule . This guide states and interprets the Part 503 rule for the general reader. This guide is also available in hard copy. In addition to the Plain English Guide, EPA has prepared A Guide to the Biosolids Risk Assessment for the EPA Part 503 Rule which shows the many steps followed to develop the scientifically defensible, safe set of rules (also available from EPA in hard copy.)
Biosolids are used to fertilize fields for raising crops. Agricultural uses of biosolids, that meet strict quality criteria and application rates, have been shown to produce significant improvements in crop growth and yield. Nutrients found in biosolids, such as nitrogen, phosphorus and potassium and trace elements such as calcium, copper, iron, magnesium, manganese, sulfur and zinc, are necessary for crop production and growth. The use of biosolids reduces the farmer’s production costs and replenishes the organic matter that has been depleted over time. The organic matter improves soil structure by increasing the soil’s ability to absorb and store moisture.
The organic nitrogen and phosphorous found in biosolids are used very efficiently by crops because these plant nutrients are released slowly throughout the growing season. This enables the crop to absorb these nutrients as the crop grows. This efficiency lessens the likelihood of groundwater pollution of nitrogen and phosphorous.
Biosolids have been used successfully at mine sites to establish sustainable vegetation. Not only does the organic matter, inorganic matrix and nutrients present in the biosolids reduce the bioavailability of toxic substances often found in highly disturbed mine soils, but also regenerate the soil layer. This regeneration is very important for reclaiming abandoned mine sites with little or no topsoil. The biosolids application rate for mine reclamation is generally higher than the agronomic rate which cannot be exceeded for use of agricultural soils.
Biosolids have been found to promote rapid timber growth, allowing quicker and more efficient harvest of an important natural resource.
Yes, biosolids may be composted and sold or distributed for use on lawns and home gardens. Most biosolids composts are highly desirable products that are easy to store, transport and use.
To determine whether biosolids can be applied to a particular farm site, an evaluation of the site’s suitability is generally performed by the land applier. The evaluation examines water supplies, soil characteristics, slopes, vegetation, crop needs and the distances to surface and groundwater.
There are different rules for different classes of biosolids. Class A biosolids contain no detectible levels of pathogens. Class A biosolids that meet strict vector attraction reduction requirements and low levels metals contents, only have to apply for permits to ensure that these very tough standards have been met. Class B biosolids are treated but still contain detectible levels of pathogens. There are buffer requirements, public access, and crop harvesting restrictions for virtually all forms of Class B biosolids.
Nutrient management planning ensures that the appropriate quantity and quality of biosolids are land applied to the farmland. The biosolids application is specifically calculated to match the nutrient uptake requirements of the particular crop. Nutrient management technicians work with the farm community to assure proper land application and nutrient control.
Anyone who wants to use biosolids for land application must comply with all relevant federal and state regulations. In some cases a permit may be required.
A voluntary EMS is now being developed for biosolids by the National Biosolids Partnership (NBP). The NBP consists of members from the Association of Metropolitan Sewerage Agency, the Water Environment Federation, the U.S. Environmental Protection Agency (EPA) and other stakeholders including the general public. Those facilities who pledge to follow the EMS are agreeing to follow community-friendly practices in addition to being in compliance with applicable state and Federal regulations. Community friendly practices refer to the control of odor, traffic, noise, and dust as well as the management of nutrients. Those who pledge to follow the EMS will be subjected to audit by impartial independent third parties.
