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A biosolids dryer for municipal applications is designed to reduce the water content of sludge (biosolids) produced at wastewater treatment plants. By lowering the moisture content, the biosolids become lighter, easier to handle, safer to store, and often meet regulatory requirements for disposal or beneficial reuse (such as land application or as a fuel source). Here’s how it works step by step: 1. Feedstock: Dewatered Sludge After wastewater treatment, solids are thickened and dewatered (often using a filter press, centrifuge, or belt press). The output is a sludge that still contains 65–80% water. This “cake” is fed into the dryer. 2. Indirect Heat Transfer Most municipal biosolids dryers (like Met-Chem’s batch sludge dryer) use indirect heat rather than direct flame. Heat is applied to the walls of a stainless steel trough, and the sludge absorbs the heat through conduction. Heating media can be natural gas, steam, electricity, or hot water, depending on the system design.