What are Biosolids?
Biosolids are organic fertilizer or soil amendments produced by the treatment of domestic wastewater which meet strict quality standards and scientific controls.
The Southwest Plant generates an average of 6000 dry tons of Biosolids per year (~16 dry tons per day). The biosolids are processed and utilized as a soil conditioner and fertilizer. The Northwest Clean Water Plant hauls approximately 1000 dry tons of biomass to the SW Clean Water Plant for full processing to become Biosolids. See the Biosolids page for more information.

What's in Biosolids?
*Nitrogen - plant essential nutrient.
*Phosphorus - plant essential nutrient.
*Organic Matter - indirect benefit that enhances the availability of trace elements for plant uptake and helps control soil erosion.
*Plant essential micro-nutrient (Cu, Fe, Mo, & Zn) - essential micro-nutrients important for plant growth and soil fertility.
Manure Expo 2014 Tour Handout
Biosolids Treatment Process
Aeration Basins (Biological Activity) & Clarification
The Aeration Basins are where the nutrients (Nitrogen & Phosphorus) are incorporated into the biomass.  It is the conversion of dissolved and suspended waste material into biomass by aerobic bacterial metabolism.  From there the process moves to the Clarifiers.  Clarification is the separation of treated waste and biomass by settling.
Biosolids Thickening
The biomass or excess microorganisms from the activated sludge biological treatment processes are 1st pumped to gravity belt thickeners (GBT). In this process, the waste biomass, which is about 1% solids, is conditioned with water-soluble polymers to flocculate the solids. The GBT process works by filtering free water from the flocculated biomass by gravity drainage through a porous belt. This produces biosmass with approximately 5% total solids.
Anaerobic Digestion
The next step is anaerobic digestion. This is accomplished by employing microorganisms in the absence of oxygen in one million gallon covered tanks called "anaerobic digesters."
Photo of the Anaerobic Digester, as seen from outside.
Anaerobic Activity
Conditions are carefully controlled in order to produce an environment where anaerobic biological activity can flourish. This breaks down solids, reducing their concentration by about 1/2. This process transforms the biomass into an inoffensive humus type of substance, called biosolids, which can be safely spread on land for soil conditioning and fertilization. Thus, the biosolids produced by the treatment processes are beneficially reused and recycled in an environmentally safe manner.

Anaerobic digestion results in the generation of methane gas, a valuable source of energy. This methane gas is used as a fuel for large engine driven plant equipment and to produce building heat, reducing the use of electricity and other fuels.
Biosolids Dewatering
The wastewater plants disposal option for biosolids recycling is to dewater the digested biosolids using high-speed centrifuges and then transport the material to area farms to be land applied as fertilizer. Again using polymers to aid in dewatering, the digested biosolids are taken from 3% solids to 23% solids. The biosolids material can be stockpiled at the SW Plant during occasions when it is too wet to land apply.  The City produces an average of 6000 dry tons of biosolids per year.
Biosolids Regulations
The biosolids produced by the treatment processes are beneficially reused and recycled in an environmentally safe manner according to the Environmental Protection Agency (EPA) Part 503 Biosolids Regulations.  Besides the EPA guidelines the SWCWP is a Bronze level member of the National Biosolids Partnership (NBP) following their guidelines for Best Management Practices as well as the University of Missouri Extension Center Water Quality guidelines for Biosolids.