Sewage from homes, business, and industry arrives at the treatment plant by passing through large bar screens that remove wood, paper, and plastics from the water. Sand and gravel then settle out in the grit tank and are removed. Clarification tanks allow lighter materials to float to the surface and be skimmed off. Heavier material, called biosolids, falls to the bottom and is pumped to anaerobic digesters. Bacteria in the digesters break solids down, creating methane gas.
Methane powered generators serve as the source of energy for a sixth of the treatment process. Solids are digested for up to thirty days, reducing their volume by 50%. Following a dewatering process, biosolids are blended with greenwaste material to create compost, or they are applied directly to farmers’ fields as fertilizer. A small quantity is sent to the landfill.
After the majority of solids have been removed, water flows into aeration basins. The aeration basins are tanks injected with oxygen to stimulate the growth of microorganisms and their consumption of dissolved wastes. These microorganisms modify pollutants to reduce their impact on the environment.
As the water moves toward the next treatment phase, the microorganisms are removed in clarification tanks. As they settle to the bottom of the clarifiers, they are returned to the aeration basins to re-supply the self-sustaining population of microorganisms. Clean water
continues on to further treatment.
Tertiary Treatment and Disinfection
The water flows through a four-foot bed of coal. This small, black, granular coal (like the type used in some fish aquariums) acts as a filter to trap fine suspended solids and some potential pathogens, or disease causing organisms. Finally, ultraviolet light (UV) removes bacteria and viruses by destroying their DNA, the genetic material needed to reproduce. The reclaimed water then leaves the plant, and is clean enough for many approved reuse purposes.
Click here for a full size, printable schematic of the Recycled Water Treatment Process (pdf)