Heat Drying and Pelletization
Drying biosolids to a pelletized product creates a Class A product with very low moisture and broad marketability — at significant capital and energy cost.
Heat drying reduces biosolids to 90-95% solids, killing pathogens through high-temperature exposure — producing a Class A product.
Pelletized product has the lowest bulk density of any biosolids product and can be transported longer distances economically; market acceptance is highest because humidity, odor, and handling are minimal.
Energy cost is the largest operating cost and a major barrier at many plants — biogas from anaerobic digestion can offset a portion of the energy cost when both processes are on-site.
Fire safety in heat drying systems is a critical operational concern — dried biosolids are combustible, and several plant fires have occurred in dryers and product storage. Strict fire protection design and operating discipline are required.
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