Sewage source heat pump was integrated with internal circulation anaerobic digester (ICAD) to decrease the treatment cost of waste activated sludge. In the experiment, mesophilic digestion in ICAD was combined with thermal treatment at 60 °C with hydraulic retention time (HRT) of 1 day as pretreatment. The heat pump supplied heat recovering from the effluent of the wastewater treatment plant. The energy consumed by the heat pump was 39.2 and 48.6% less than the gas boiler and coal boiler respectively at a given amount of supplied heat. When the HRT of digestion was 10 days, the average total VSS removal and biogas yield rates of the system were 58.8% and 1.33 m3 · kgVSS−1 respectively. The integration of ICAD and sewage source heat pump offers a low-cost sludge treatment process with satisfactory organic removal.

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