Composting.  This is an environmentally friendly way to recycle the nutrients and organic matter found in wastewater solids.  Composting systems turn wastewater biosolids, sawdust, yard waste and wood chips into high-quality compost.  As the material decomposes, oxygen filters through the compost site, releasing water, heat and carbon dioxide.  This process helps dry the organic material, while the generated heat increases the rate of decomposition and kills pathogens.

Heat Drying.  This process applies direct or indirect heat to reduce the moisture in biosolids.  It eliminates pathogens, reduces volume and results in a product that can be used as a fertilizer or soil amendment.  Because dryers produce a 90 percent dry material, additional VAR is not required.

Digestion.   In ATAD (autothermal thermophilic aerobic digestion) systems, biosolids are heated to 131°F to 140°F (55°C to 60°C) and aerated for about 10 days.  This autothermal process generates its own heat, and reduces volume.  The result is a high-quality Class A product acceptable for reuse as a liquid fertilizer.

Pasteurization.  Pasteurization produces a Class A material when the biosolids are heated to at least 158°F (70°C) for 30 minutes.  This extreme heat kills pathogens in the organic matter.  When followed by anaerobic digestion, the VAR is attained and the biosolids can be land applied with minimal restrictions.  The majority of the energy used in the pasteurization process is recovered with an innovative heat exchanger system and used to maintain the proper temperature in downstream anaerobic digesters.

Class B Technologies
Understanding 40 CFR Part 503
Class A & B Technologies from Siemens Water Technologies
Class A & B Biosolids