Integrated system of greenhouse and solar heater for anaerobic digestion of excess activated sludge

Integrated system of greenhouse and solar heater (ISGSH) was used for heating and maintaining the required temperature for mesophilic digestion (in spring, autumn, and winter) and thermophilic digestion (in summer). Using excess activated sludge as influent, heat insulation effect of ISGSH, biogas production in the anaerobic digestion, and the energy output and consumption were investigated in four different seasons. The results indicated that relative to the reactor I operated under natural conditions, the temperatures in reactor II with the integrated system were increased by 13.0－28.5℃, 15.0－26.5℃, and 10.7－12.2℃，respectively, in spring, summer and autumn. Meanwhile, the biogas production, total solids(TS)and volatile solids (VS) removal rates were increased by 176.1%, 98.8%, and 109.9%, 6.8%－27.1%, and 7.5%－24.1%, respectively in spring, summer and autumn. Through the analysis of energy output and consumption in ISGSH, it was found that the energy conversion efficiencies in reactor II were enhanced by 21.8%, 38.5%, and 30.1% for spring, summer, and autumn, respectively. Although the energy consumption was higher than the energy output in winter, the ISGSH can realize the effective operation of anaerobic digestion.