What are Biosolids?
Biosolids are a nutrient-rich organic material that meets regulated standards for application to land as a fertilizer and soil conditioner. Biosolids are a byproduct of the wastewater treatment process. Because wastewater is collected from area industries as well as residences and businesses, the industries must meet discharge standards that protect the quality of the biosolids. Pathogen treatment and pollutant limitation requirements allow biosolids to be safely utilized as a resource.
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.
Collaboration with area farmers has allowed almost all of the biosolids produced to be land-applied and recycled back into the soil with the remaining amount uses as landfill cover or stored at the Southwest Facility until it can also be land-applied when weather permits.
What is in Biosolids?
- Nitrogen - a plant essential nutrient.
- Phosphorus - a plant essential nutrient.
- Organic Matter - indirect benefit that enhances the availability of trace elements for plant uptake and helps control soil erosion.
- Trace Metals - essential micro-nutrients important for plant growth and soil fertility (Cu, Fe, Mo, & Zn)
The City of Springfield recycles its Biosolids back by Land Application. This is a cost effective option and has beneficial properties for the farmer as well as the environment. A good best management practice program will also protect the water quality. The City produces a Class B Biosolid that meets or exceeds the EPA 40 CFR 503 strict regulations and quality standards for Land Application. The State of Missouri and City of Springfield go beyond the EPA regulations complying with the University of Missouri Extension Center Water Quality standards for Biosolids.
- Higher crop yields.
- Slow release of nutrients throughout the growing season.
- Approximately 3 years of life/application.
- Supplies essential nutrients to crops (Nitrogen, Phosphorus, Potash).
- Cost effective - saves farmer cost of buying commercial fertilizer.
- Average Nutrients applied pounds/dry ton (45 PAN, 68 Phosphorus, 4 potash).
- Helps prevent soil erosion through vigorous growth of vegetation.
- Protects water quality through best management practices.
- Saves diminishing landfill space.
- Strict buffer zones to protect surface and groundwater.
- Process produces a byproduct of methane gas that is captured for use to control plant process equipment that in turn reduces utility cost for plant operation.
How are Biosolids Produced?
The City produces a Class B Biosolid that meets or exceeds the EPA 40 CFR 503 strict regulations and quality standards for Land Application. Currently an average of 6000 dry tons of Biosolids are produced by the City of Springfield's Clean Water Plants. An average of 5500 dry tons is land applied on 3000 acres throughout the year following strict guideline from the Environmental Protection Agency (EPA) and Missouri Department of Natural Resources (MoDNR). The State of Missouri and City of Springfield go beyond the EPA regulations complying with the University of Missouri Extension Center Water Quality standards for Biosolids. The City also is a member of the WEF National Biosolids Partnership Best Management Practices program Bronze level.
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.
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.
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."
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.
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.
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.
Biosolids Land Application
Land application is the preferred method of disposal by the EPA for Biosolids.
- Adheres to strict regulatory requirements (buffer zones, reporting)
- Soil sample for application rate adjustments
- Laboratory sampling of Biosolids
- Farmer & neighbor assessment/notification of area prior to application
- ~3 year life out of application
- current 3 year average pounds/dry ton ( PAN 45.8, P 68.0, K 4.0)