After sludge has settled via sedimentation, the sludge is withdrawn and treated. The aim of treating sludge is to:
- Stabilize the sludge
- Reduce odours
- Reduce sludge volume
- Decompose organic matter
- Kill disease causing organisms (disinfection)
Sludge treatment processes include:
Preliminary Operations
- Includes sludge grinding, degritting, blending, and storage necessary to provide a relatively constant, homogeneous feed to sludge-processing facilities.
Thickening
- Procedure used to increase the solids content of the sludge by removing a portion of the liquid fraction.
Stabilization
- Sludge is stabilized to reduce pathogens, eliminate offensive odors and inhibit, reduce, or eliminate the potential for putrefaction.
Conditioning
- Used to improve the sludge's dewatering characteristics.
Disinfection
- Sludge is disinfected by means of chemical addition, composting, heat treatment, long-term storage and pasteurization.
Dewatering
- Physical unit operation used to reduce the moisture content of the sludge.
Drying
- Process that involves reducing the water content by vaporization of water to the air.
Composting
- Composting is a cost effective and environmentally sound alternative for the stabilization and disposal of sludge.
Thermal Reduction
- Involves the total or partial conversion of organic solids to oxidized end products.
Ultimate Disposal
- Ultimate disposal of sludge from wastewater treatment plants can include:
- Disposal at landfills sites
- Accumulation at the plant via stockpiling or lagoons
- Beneficial uses (e.g. compost manufacturing)