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Biosolids are the treated, nutrient-rich, biologically produced, mostly organic material produced from the solids removed during the wastewater treatment process. Biosolids material is fairly homogeneous and has the consistency of thick cake batter. We package the biosolids that our plant produces into a product called METROGRO® Cake.


What Are Biosolids Made Of?

Our treatment process separates solids from water into a sewage sludge through aerobic, mechanical processes. These solids include

  • Human waste
  • Soap suds
  • Food particles
  • Toilet paper
  • Other materials that travel through sewers to our facility

The sludge is treated in a high temperature, biological process where microorganisms anaerobically ‘eat’ the wastes. This process kills the harmful pathogens and turns the sludge into biosolids.

How Are Biosolids Beneficial?

Research over the past 40 years shows that reusing biosolids for agriculture provides substantial benefit to our environment. Visit the Water Environment Research Foundation web site for information about current and future research projects related to the benefits of biosolids reuse.

  • Reduces the need for chemical pesticides by making plants less susceptible to insects & diseases
  • Reduces the need for chemical herbicides by inhibiting weed invasion
  • Provides nutrients necessary for microbial activity in soils
  • Improves soil structure by creating space for air and water
  • Reduces surface runoff on clay soils
  • Provides soil conditioning
  • Slows water percolation in sandy soils
  • Stabilizes soils prone to erosion
  • Enables better crop yields
  • Increases protein content in wheat
  • Saves valuable landfill space

Do Biosolids Have an Odor?

Yes. The decomposition of organic material releases sulfur and ammonia which are both plant nutrients. So, if biosolids are thoroughly digested at the wastewater plant, then the odor is usually that of a moist soil. We typically use an organic polymer additive in the process of dewatering biosolids which can also cause a salt water smell.

Are Biosolids Regulated?

Yes, prior to land application, biosolids must meet strict regulatory and quality standards established by federal, state and local governments. The rules that govern the use of land-applied biosolids contain numerical limits for metals, pathogen destruction and vector attraction reduction standards, site restrictions, crop planting and harvesting restrictions, monitoring, record keeping, and reporting requirements.

Where Can I Find More Information About Biosolids?

You can visit web sites for the National Biosolids Partnership (NBP), Water Environment Federation (WEF), Water Environment Research Foundation (WERF), National Association for Clean Water Agencies (NACWA), Environmental Protection Agency (EPA), National Research Council, National Sludge Alliance, and Cornell Waste Management Institute.

Contact Us

Have a question about biosolids or the treatment process? Submit an inquiry.