Biosolids are nutrient rich, organic byproducts of wastewater treatment. They are produced by removing the organics from municipal sewage and are valued for their energy and agricultural properties.  

Monterey One Water’s biosolids are highly processed, regularly monitored, and tested to ensure that they meet or surpass the strict quality and safety standards established by the U.S. Environmental Protection Agency, State of California, and local governments to be recovered for reuse.

Biosolids Handling

  • Primary Clarifiers - During wastewater treatment, the flow of water is slowed so gravity can take over. Solids settle to the bottom (sludge) while fats, oils, and grease (FOG) float to the top. Both are skimmed, removed, and sent to the Anaerobic Digesters.
  • Anaerobic Digesters – Through heating and mixing, the majority of volatile solids are destroyed from the thickened primary and secondary waste sludge.
    • The product is methane gas, carbon dioxide, and Class B digested sludge.
  • Dewatering – The Class B digested sludge is then dewatered before it can be to use. Screw presses compact the sludge, squeezing out the water
    • When the sludge leaves the digesters, it’s about 2.5-3% total solids. After dewatering, the product is 17-20% total solids.
  • Drying beds - Dewatered sludge is then spread throughout drying beds to further remove water. After drying out for seven to fourteen days, the sludge is now ready to be used as a cover material. It is trucked to our neighbors, the Monterey Regional Waste Management District, where it is used to cover the waste piles in the landfill.

Monterey One Water is currently in the process of evaluating and implementing a Biosolids Management Plan.

Quick Facts:

  • M1W produces 70 tons of biosolids per day
  • Methane gas is used to generate power for the Regional Treatment Plant
  • 20,000 tons of Class B solids were produced in 2019
  • M1W has 38 usable drying beds