Effects of conductive carbon materials on dry anaerobic digestion of sewage sludge: Process and mechanism

Dry anaerobic digestion of sewage sludge (SS-DAD) is often inhibited by excessive acidification due to low water content and high organic loading. The effects of conducive carbon materials including powdered activated carbon (PAC) and powdered graphite (PG) on SS-DAD under mesophilic condition (35 degrees C) were investigated. The results demonstrated that the addition of PAC increased methane production of SS-DAD. The methane yield of PAC(50%) reactor (dosage of PAC is 50% of the volatile solids) amounted to 210 mL.gVS(added)(-1), which is 49% higher than that of control. PAC addition significantly enhanced the biodegradation process, as the reduction rate of total solids (TS) and volatile solids (VS) were increased by 36.4% and 34.1%, respectively, compared to the control. Inhibitory substrate adsorption experiments showed that PAC has significant adsorption (13.6 mg g(-1)) for VFAs, while PG showed almost no adsorption (0.81 mg g(-1)). Microbial community structure analysis showed hydrogenotrophic methanogens (Methanobrevibacter and Methanosphaera) were reduced in the PAC 50% reactor, while methanogens (Methanobacterium) which can also use formate as electron donor were increased. PAC amendment reshaped the microbial community in the SS-DAD system which may result in shifting of the major electron carrier from hydrogen to formate and increasing electron transfer efficiency of the SS-DAD system.