What Are Biosolids?

Biosolids are, in effect, a slow release nitrogen fertilizer with low concentrations of other plant nutrients. In addition to significant amounts of nitrogen, biosolids also contain phosphorus, potassium, and essential micronutrients such as zinc and iron. Many western soils are deficient in micronutrients. Biosolids are rich in organic matter that can improve soil quality by improving water holding capacity, soil structure and air and water transport. Proper use of biosolids can ultimately decrease topsoil erosion.

When applied at agronomic rates (the rates at which plants require nitrogen during a defined growth period), biosolids provide an economic benefit in addition totheir environmental benefits. Colorado State University agronomists have shown continuous application of three dry tons per acre every other year to dryland wheat produces comparable yields, higher protein content, and larger economic returns compared with the use of 50-60 pounds per acre of commercial nitrogen fertilizer.

How Do Biosolids Differ From Sewage Sludge?

Most simply, biosolids is the new name for what had previously had been referred to as sewage sludge. Biosolids are primarily organic treated wastewater materials from municipal wastewater treatment plants -- with the emphasis on the word treated -- that are suitable for recycling as a soil amendment. Sewage sludge now refers to untreated primary and secondary organic solids. This differentiates biosolids which have received stabilization treatment at a municipal wastewater treatment plant from the many other types of sludge that exist (such as oil and gas field wastes) that cannot be beneficially recycled as soil amendments.

What Are The Reuse/Disposal Options?

The only options for reuse/disposal of biosolids are incineration, surface disposal, landfilling, or recycling as soil amendments. Incineration is very expensive. Landfilling and surface disposal are really temporary solutions to a permanent problem. Because biosolids are a valuable resource, recycling as soil amendments is the preferred disposal option.

Biosolids are the recyclable material resulting from treatment of wastewater. Approximately 40-50 percent of the 8-9 million tons of biosolids produced each year by municipal wastewater treatment facilities are recycled for beneficial use and reused in a variety of applications, including:

Biosolids are managed by a three-tier safety network. The Federal 40 CFR Part 503 regulations, in conjunction with Department of Ecology regulators as well as local health department officials. This system helps ensure that biosolids recycling stays a  safe and integral part of this country's water quality and waste management program.

Biosolids Recycling

Biosolids recycling returns a useful resource to the environment. Biosolids are rich in nutrients, containing nitrogen and phosphorus along with other supplementary nutrients in smaller doses, such as potassium, sulfur, magnesium, calcium, copper and zinc. Soil that is lacking in these substances can be reclaimed with biosolids use. The application of biosolids to land improves soil properties and plant productivity, and reduces dependence on inorganic fertilizers.

In the past, biosolids have been disposed of in landfills and even in the ocean and rivers. Now, as more and more treatment plants improve wastewater quality, treated biosolids are an even greater resource to be recycled and returned to the environment. Recycling reduces the volume of waste to be disposed of in limited capacity landfills. And the threat of pollution problems from disposal practices such as landfilling, ocean dumping or discharge to coastal waters is avoided.

Benefiting the Land

U.S. Environmental Protection Agency (EPA)statistics indicate that nearly 50 percent of biosolids are applied to the land. Land application of biosolids takes place in 46 of the 50 states. There are more than 500,000 acres that can receive biosolids under the approval programs in these states. Virtually all land uses are compatible with biosolids application if biosolids are properly treated and their application is well-managed.