PERFORMANCE OPTIMIZATION OF DOMESTIC FOOD WASTE DIGESTION UNDER MESOPHILIC CONDITIONS

Anaerobic digestion (AD) is a biological but engineered process in which micro-organisms break down the organic matter in wet biomass waste (sewage sludge, animal and food waste & slurry) in the absence of O2, to produce biogas (CH4, CO2, H2S & H2 ) and digestate (a nutrient-rich biofertilizer). The aim is to understand the dynamics of AD by determining how pH and nutrient characteristics affects AD for process optimization. To achieve this, an AD laboratory-scale semicontinuous continuously stirred tank reactor (CSTR) fed at OLR;1.5gVS/L.d with food waste of 18% total solids, (TS) and 16.5% volatile solid (VS) were subjected to Mesophilic (350C) conditions and Hydraulic residence times (HRTs) of 28days at pH values of 6.0, 6.6, 7.2 and 7.8. Based on bio-kinetics of 1st order degradation, a statistical non- regression tool (R2=0.95) was used to predict the biogas production (BGP). Results showed that at 350C and pH; 6, 6.6, 7.2 and 7.8, biogas production was 625.5ml/gVS, 696.5ml/gVS, 709ml /gVS and 685ml/gVS destroyed respectively indicating optimum performance at pH, 7.2. Again, to optimize the process, partial pressure of H2 was reduced below10.132Pa and pH maintained by buffering with KHCO3. CH4 production was 62.5% (350C) at pH 7.2 and 48.5% (350C) at pH 6. The system efficiency of removal at pH 7.2 was 60% VS at 350C indicating the most destroyed nutrient character determining BGP. The CH4 can be used to generate electricity by piping it to a combined-heat and power (CHP) engine while the heat produced can be used for space heating. Further research should be undertaken; for a different waste and in thermophilic condition and to develop an AD expert control system to enhance the process in future.