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Biosolids - Frequently Asked Questions

Everything You Need to Know

What are Biosolids?

Biosolids are the nutrient-rich organic materials resulting from the treatment of domestic wastewater in a specialized treatment facility. Biosolids are a beneficial resource, containing essential plant nutrient and energy producing organic matter, which can be recycled as a fertilizer and soil amendment or used to produce energy.

What is the difference between biosolids and sludge?

Biosolids are treated wastewater sludge. Biosolids are carefully treated and monitored and must be used in accordance with regulatory requirements.

Why do we have biosolids?

We have biosolids as a result of the wastewater treatment process. Water treatment technology has made our water safer for recreation and seafood harvesting. Thirty years ago, many American cities dumped their raw untreated wastewater directly into the nation's rivers, lakes, and bays. Through regulation of this dumping, local governments are now required to treat wastewater and to recycle biosolids as fertilizer, incinerate it, or bury it in a landfill. 

How are biosolids generated and processed?

Biosolids are created through the treatment of domestic wastewater generated from wastewater treatment facilities. The treatment of biosolids can actually begin before the wastewater reaches the wastewater treatment plant. In many 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, it goes through physical, chemical and biological processes that clean the wastewater and remove the solids. If necessary, the solids are then treated with lime to raise the pH level to eliminate objectionable odors. The wastewater treatment processes sanitize wastewater solids to control pathogens (disease-causing organisms, such as certain bacteria, viruses and parasites) and other organisms capable of transporting disease. 

How are biosolids used on land?

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.

Where are biosolids used?

Farmers and gardeners have been recycling biosolids for ages. Biosolids recycling is the process of beneficially using treated residuals from wastewater treatment to promote the growth of agricultural crops, fertilize gardens and parks and reclaim mining sites. Land application of biosolids takes place in all 50 states.

Why are biosolids used on farms?

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.

What percentage of biosolids is recycled and how many farms use biosolids?

EPA estimates that approximately 7 million tons of biosolids are generated by the 16,000 wastewater treatment facilities. About 60% of all biosolids are beneficially used as a fertilizer on farm land following treatment; 17% ends up buried in a landfill; 20% is incinerated; and about 3% is landfill or mine reclamation cover. Only a small percentage (much less than 1 percent) of the plant food supply has been fertilized with biosolids. Biosolids provide farmers with $60 to $160 per acre worth of fertilizer, including many essential nutrients that the farmer may not normally replenish in the soil. Biosolids also contain valuable organic matter that improves the health, quality and structure of the soil. 

Are biosolids safe?

Decades of studies have demonstrated that biosolids can be safely used on food crops. The National Academy of Sciences has reviewed current practices, public health concerns and regulatory 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." In addition, an epidemiological study of the health of farm families using biosolids showed that the use of biosolids was safe.

Do biosolids smell?

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. Most odors are caused by compounds that contain sulfur and ammonia, which are both plant nutrients. 

Are there regulations governing the handling and use of biosolids?

The federal biosolids rule is contained in 40 CFR Part 503. Biosolids that are to be land applied or incinerated 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 landfilled. Incinerated biosolids must meet metals standards and air emission requirements, including Clean Air Act provisions. 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. Biosolids are one of the most studied materials that have ever been regulated by EPA.

Where can I find out more about the regulations?

The biosolids rule is described in the EPA publication, A Plain English Guide to the EPA Part 503 Biosolids 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 prepare A Guide to the Biosolids Risk Assessments 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.)

How are biosolids used for agriculture?

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 by nitrogen and phosphorous.

Can biosolids be used for mine reclamation?

Severely disturbed soils can be reclaimed through the addition of biosolids to replace lost topsoil. Biosolids have been used successfully to reclaim surface strip mines, large construction sites, parks, wetlands and landfills. Biosolids improve soil fertility and stability, aiding revegetation and decreasing erosion. 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. 

How are biosolids used for forestry?

Biosolids improve forest productivity, increase growth of hybrid poplars and enhance the aesthetic value of Christmas trees. Where biosolids have been used, the trees grow faster than those living in unfertilized soils. Wildlife populations often increase in these areas because the under story vegetation is more abundant. Biosolids have been found to promote rapid timber growth, allowing quicker and more efficient harvest of an important natural resource.

Can biosolids be used for composting?

Yes, biosolids may be composted and sold or distributed for use on lawns and gardens. Biosolids composted with sawdust, wood chips, yard clippings, or crop residues make excellent mulches and top soils for horticultural and landscaping purposes. Many professional landscapers use composted biosolids for landscaping new homes and businesses. Home gardeners also find composted biosolids to be an excellent addition to planting beds and gardens. Most biosolids compost, are highly desirable products that are easy to store, transport and use.

Are there rules about where biosolids can be applied?

To determine whether biosolids can be applied to a particular 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.

Are there buffer requirements or restrictions on public access to sites with biosolids?

In general, Exceptional Quality (Class A) biosolids used in small quantities by the general public have no buffer requirements, crop type, crop harvesting or site access restrictions. Exceptional Quality biosolids is the name given to treated residuals that contain low levels of metals and do not attract vectors. When used in bulk, Class A biosolids are subject to buffer requirements, but not to crop harvesting restrictions. In general, there are buffer requirements, public access, and crop harvesting restrictions for virtually all forms of Class B biosolids (treated but still containing detectible levels of pathogens).

Can anyone apply biosolids to land?

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.

Did the federal government ban ocean dumping of sludge because of a threat to marine ecology?

There was little threat to the marine environment from the disposal of biosolids at the 106 Mile Ocean Dumping Site from pollutants in the biosolids. Years after this activity has ceased, monitoring surveys at that site have never demonstrated adverse effects on marine life there. The reason why Congress banned ocean dumping was not because biosolids were toxic to marine life. Congress recognized that the nutrients in biosolids could cause increased algae production, eventually leading to oxygen depletion at the site. Congress properly decided that it made much more sense and was better policy to get biosolids out of the ocean and use the nutrients in biosolids more productively to provide crop nutrients and to improve soil quality.

Is EPA pushing the use of biosolids as a fertilizer? Is the federal policy for biosolids driven by economics of disposal?

As a result of its decade-long assessment of biosolids, EPA concluded that recycling biosolids to land was an environmentally responsible solution, when used in accordance with the Part 503 rule. The Federal policies governing recycling of biosolids are based upon sound science that has demonstrated the benefits of such recycling. These policies are not driven by economics, and the choice of which option to select remains a local decision.

If land application of biosolids is so beneficial, why would any plant incinerate them?

Biosolids are incinerated for a variety of reasons. One of those reasons is that incineration is a safe and environmentally friendly utilization method. The two final products of incineration are sterile ash and clean air. Ash is completely free of pathogens and bacteria, and unlike occasionally odorous land applied biosolids, the Clean Air Act governs air emissions from incineration. Incinerated biosolids are also governed by the same 40 CFR Part 503 rule that pertains to land application. This means incineration is the most regulated of all biosolids utilization options. Another major reason biosolids are incinerated is that it is cost effective. With the higher transportation costs associated with land application, incineration can be economical. While biosolids have a nutritional value for plants, it also is a source of energy - call it a bio-fuel. Biosolids can be used to produce energy and in these energy dependent times, that can be an attractive benefit. Having an incineration option, together with a land application program, is also a benefit for wastewater utilities because a more diverse range of utilization options offers flexibility in the event that one option were to become temporarily unavailable.

Is recycling much cheaper than disposal?

In areas where disposal costs have increased due to shrinking landfill space and increased costs to maintain and monitor landfills, some cities and towns find that recycling biosolids is less expensive than landfilling. However, in most cases, landfilling is competitive or less expensive than land application. In such cases, many U.S. communities have made a decision to commit to recycling biosolids despite the additional cost. This is especially true where communities have committed to the additional costs of composting or heat drying biosolids prior to utilization.

Are biosolids that are land applied comprised of everything you flush down the toilet and everything industry puts down the drain?

This question implies that the biosolids that are being recycled to land are raw, untreated, and full of toxics. This is not the case. Biosolids that are land applied are carefully treated and used in accordance with the Part 503 rule and have their quality further assured by required industrial pretreatment. Many analytical studies by municipalities show that the quality of biosolids has continued to increase because of enhanced monitoring and pretreatment of industrial waste streams. 

Are Biosolids good for the environment?

Recycling biosolids is good for the environment. Organic matter has been recycled for centuries to improve soil fertility and productivity. When properly applied and managed, biosolids can: provide essential plant nutrients; improve soil structure and tillage; add organic matter; enhance moisture retention; and reduce soil erosion. Biosolids recycling is regulated by the U.S. Environmental Protection Agency and state and local authorities. Research and years of recycling experience have demonstrated that properly managed land application of biosolids is environmentally safe.

What is the consensus in the scientific community about the safety of using biosolids for food crop production?

Decades of research and actual application of biosolids have resulted in an overwhelming scientific agreement among qualified researchers that the use of biosolids, in accordance with existing Federal guidelines and regulations, presents negligible risk to the consumer, to crop production, and to the environment. In fact, the science-based approach used in developing the biosolids standards could serve as a model for policy and regulation in other areas of agricultural production and food safety.


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