Effects of moisture content on the performance of a two-stage thermophilic biofilter and choice of irrigation rate

Abstract

Abstract The stabilization, innocuity, and reutilization of sludge can be obtained via the co-combustion of sewage sludge in cement producing kilns. Off-gases containing odours and volatile organic compounds (VOCs) are generated during the process of sewage sludge drying. A two-stage thermophilic biofilter was constructed in a cement plant to remove SO2, NH3, and total VOCs (TVOCs) from the plant’s exhaust. The average concentrations of TVOCs, NH3, and SO2 in the inlet stream were 164.33, 38.46, and 51.12 mg/m3, and in the outlet stream were 44.54, 9.18, and 3.91 mg/m3, respectively. During biofilter operation, nutrient solution was circularly pumped onto the packing material to ensure the packing material remained moist. The moisture content of the packing material increased from 40 to 85% as the irrigation rate varied from 0.05 to 0.42 m3/h. The removal efficiencies of NH3 and TVOCs changed accordingly. When the irrigation rate was 0.3 m3/h, removal efficiencies were 88.71% for NH3 and 81.38% for TVOCs. More than 90% SO2 removal occurred throughout the operation. The polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method was used to assay the microbial population. Both microbial counts and diversity increased when the irrigation rate increased.