Bioenergy Potential and Kinetic of Biogas Production in Anaerobic Digestion of Slaughterhouse Effluent

Abstract

Many studies have investigated the technology of anaerobic digestion for waste treatment and its benefits. However, most of those studies have reported on solid waste. So, there are few articles on the anaerobic digestion of effluent, especially anaerobic digestion of slaughterhouse effluent and its bioenergy potential. The purpose of this study is to evaluate the bioenergy potential in slaughterhouse wastewater treatment. Then, anaerobic digestion (AD) was used in this study to assess the bio-energy potential and kinetics of biogas production during processing. The slaughterhouse wastewater collected was characterized before the experiments using french standard method “AFNOR”. pH, Temperature, turbidity, dissolved oxygen (O_2dis.), oxidation-reduction potential (ORP), Conductivity, Chemical Oxygen Demand (COD), biochemical oxygen demand in five days (BOD₅), total Kjeldahl nitrogen (TKN) and total phosphorus (P_tot) were analyzed and the ratio BOD₅/COD was calculated to evaluate the biodegradability of the biomass. Laboratory-scale anaerobic batch digesters consisting of a 1 L plastic container were used in all the experiments and the biogas produced in the digesters was measured daily by the water displacement method. The wastewater produced by slaughterhouses is biodegradable with a ratio between biological oxygen demand and chemical oxygen demand (BOD₅/COD) > 0.5. An effective AD design shows that over 90% of organic matter was removed when inoculation and the carbon/nitrogen (C/N) ratio were adjusted. The cumulative volume of biogas increased from 415 mL to 2,150 mL as the substrate/inoculum (S/I) ratio has decreased from 2.028 to 0.337 and increased from 1,140 mL to 5,250 mL as the C/N ratio increased from 6 to 22. The biogas produced has a high calorific value, as the methane content is 74%. Among the three kinetic models used to describe biogas production, a modified Gompertz model was found to be the best with R² between 0.983 and 0.993. This study points out energy potential of slaughterhouse wastewater and its benefit as it is managed efficiently.