Anaerobic co-digestion with industrial wastewater for biomethane production

Abstract

The increasing demand for energy has led to the utilization of fossil fuels more abundantly as a quick alternative for generation of energy. The use of these sources of energy however as led to the generation of greenhouse gases which tend to cause climate change, thus affecting the ecosystem at large. Thus, there have been the search for alternative sources which cannot be depleted but do generate minimal greenhouse gases. One of such alternate sources is industrial wastewater which have shown to have high concentration of nutrients in the form of organic contents which can be converted by micro-organisms into energy, usually known as biogas, comprising majorly of CH4, CO2 and H2. Another important factor is that industrial wastewaters are a renewable energy source which are continuously generated due to increasing urbanisation and population growth. In this study, the characteristics of three agro-industrial based wastewaters used shows their potential for application in anaerobic co-digestion”. Anaerobic co-digestion method was utilized to harness the synergetic effect of both sewage sludge and agro-industrial wastewater as co-substrate for the generation of biomethane. The result of the effect of varying mix-ratio of the substrates on biomethane production of sugar wastewater and dairy wastewater indicated that mix-ratio of 1:1 for sewage sludge to sugar wastewater operated at 35oC was suitable for optimum generation of biomethane of 1400.99 mL CH4/g COD added and COD reduction of 54%. The model generated using design expert was found to navigate the design space and could perfectly predict the yield of biomethane effectively for the sugar wastewater mix. The biomethane potential tests (BMP) experiment using varying inoculum-substrate ratio (ISR) showed that operating at mesophilic temperature of 25oC with ISR of 1:2 and 2:1 for sugar wastewater and dairy wastewater respectively does increase the methane production within the first three (3) weeks. The kinetic models that best fit the anaerobic co-digestion for sugar wastewater was the first order model while the simplified Gompertz model favoured the dairy wastewater perfectly. The biomethane potential tests indicate significant increase the biomethane production and as well reduction in the volatile solid and chemical oxygen demand (COD) content. In conclusion, both sugar and dairy wastewater can be recommended as co-substrates for anaerobic digestion of sewage sludge for increased and improved biomethane production while simultaneously reducing their COD content at the same time.