What Are Biosolids

What Are Biosolids

During the water recycling process, bacteria and other tiny organisms feed on the solid material and break the wastewater down into harmless organic matter. The organic matter combined with bacterial cell masses settles out and is processed and treated to form biosolids. Biosolids, which are rich in nutrients and organic matter, have been approved by the U.S. Environmental Protection Agency (EPA) for land application as a fertilizer, soil amendment and for composted products. The EPA states that: (1) biosolids can be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth; (2) effective biosolids management options help ensure that useful materials are recycled on land and harmful materials are not released to water bodies.

Almost forty years ago, many American cities dumped their raw sewage directly into our nation’s oceans, rivers, lakes and bays. Today, because of improved treatment processes, our waterways are cleaner and safer for recreation and seafood harvest. As water recycling facilities have modernized with new technology, the amount of biosolids produced in Virginia and nationwide has increased.

Municipal wastewater recycling employs the same processes that nature uses to clean the environment. In streams and lakes, natural aeration helps purify the water, while bacteria and microorganisms break down solids. Wastewater recycling facilities (treatment plants) use settling basins, aeration tanks and digestion processes to reduce the pathogens (organisms that cause disease) and break down solids.

Wastewater recycling facilities also require businesses and industries to employ pretreatment measures that reduce contaminants from wastewater before it enters the sewer. Once wastewater is conveyed to a typical wastewater recycling facility, large debris “grit materials” (such as sticks, rags and sand) are removed. The wastewater is next allowed to sit in large settling basins, where some solids settle to the bottom and are collected. The solids that are collected from these primary and secondary treatment processes, called sludge, undergo additional biological treatment (digestion) to further decompose the material and destroy any potential disease causing organisms. During the digestion process natural bacterial and microorganisms (microbes) consume and break down the solid material. These microbes and other solid particles settle to the bottom of the digestion tanks where they are collected and removed for final processing, which typically involves removing excess water through a dewatering process.  Other solids treatment options are available to wastewater recycling facilities that do not offer digestion processes. At these facilities lime may be used as a treatment method to treat and stabilize the solids.

All solids treatment processes reduce odors and destroy most of the potentially harmful pathogens contained in the unprocessed solids. Once the solids have been completely treated and stabilized, they are called biosolids. The biosolids contain essential nutrients and organic matter and can then be recycled on farms and forests, or composted for home garden use. At newer wastewater recycling facilities, advanced treatment options may be employed to create exceptional quality biosolids that can be recycled with little or no restrictions on end use.

The wastewater separated from the solids during all of the processes mentioned is also cleaned. This water receives additional treatment before it is disinfected and safely returned to waterways or recycled back to land or to other beneficial end uses.

Biosolids will always bring with it some challenges; however it is imperative that strong scientific evidence continue to be the foundation for the beneficial use of biosolids. To this point, despite the continuing dialogue expressing concern regarding the ‘state of the science”, current science continues to support the beneficial use of biosolids in agriculture, forestland, and even home gardening where EQ biosolids are permitted.