Biosolids & Reuse in Compost

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Biosolids & Reuse in Compost

DIGESTION
 
The settled material that is removed from the primary tanks is further treated in anaerobic digesters. "Waste" activated sludge also is sent to these digesters. Through the digestion process there is a reduction in odors and pathogenic (harmful) bacteria levels, as well as a reduction of the overall sludge volume. During digestion the sludge is heated and mixed. Complex organic materials break down into simpler compounds, then acid-forming organisms convert these organic compounds into volatile organic acids. These acids are changed into methane and carbon dioxide by other bacteria. The production of these substances brings about a decrease in the amount of solids that need further processing. Depending on the volatility of the solids, this solids reduction can range from 30-40%. Biosolids leave the digester as a dark black liquid containing about 2% solids and 98%  water.
 
FILTERING
 
After digestion, the biosolids are mixed with a polymer, then put through belt filters for dewatering. Polymer makes it easier to separate the solids and water. The biosolids are spread in a thin layer on the belt filter where the water is pressed out and can drain away. Once through the filters, most of the water has been extracted, leaving biosolids the cnsistency of soft mud. This drier by-product (about 25 tons per day) is then trucked to the Compost Facility.