Semi-Continuous Mesophilic Anaerobic Co-Digestion of Thermally Pretreated solid wate

F. Lmomani
Qatar University,
Qatar

Keywords: fats oils and grease (FOG), anaerobic co-digestion, cell viability analysis

Summary:

The objective of this study is to investigate the mesophilic, anaerobic, co-digestion of agricultural solid wastes with thickened waste activated sludge (TWAS) and primary sludge (PS). Semi-continuous reactors were loaded at 1.7 kg VS/m3·d with hydraulic retention times (HRTs) of 12 and 18 days. A 22 factorial design was used to determine the effects of solid wasteloading at 0.40 and 0.72 kg VS/m3∙d by conventional thermal pretreatment of the solid waste at 50 and 70°C. Observations of the reactor waste show that higher pretreatment temperatures assist in solid waste integration and appear to limit coagulation and separation effects associated with digesting fats, oils and greases. The 0.40 kg VS/m3∙d solid waste loaded reactor with pretreatment at 70°C achieved the greatest improvement in biogas production over PS and TWAS co-digestion without solid waste addition; where a 24% and 16% improvement in biogas production was measured at 15 and 20 d HRT, respectively. Based on cell viability analysis of the reactor waste, solid waste containing reactors were shown to produce 48% and 39% more biogas per m3 of live cells; signifying that solid waste addition increased the activity of the microbial population embedded in the waste or caused a microbial shift in the waste towards more active communities.