Assessment of various agitation speeds for Co digestion process

Abstract

In the present day context of environmental pollution, the continuous generation of organic wastes and its improper management has been playing a vital role. Current global Municipal Solid Wastes (MSW) generation levels are approximately 1.3 billion tonnes per year and are expected to increase to approximately 2.2 billion tonnes per year by 2025. These wastes have to be properly treated and should be safely disposed. Among the various processing technologies, the anaerobic digestion technology in the form of Co digestion process is the most valuable approach in the waste management sector as it provides a bio fuel and organic rich manure to the society. It requires a good operation technique like mixing in order to maintain the stability of the digester for biogas production. An attempt has been made by utilizing different types of wastes in a lab scale reactor for co digestion process with mixing technique. Kitchen wastes, Poultry Litter and slaughterhouse wastes were used as substrates and fresh cow dung as inoculum. Three Organic Loading rates of 2.5 g VS l/day, 2.68 g VS l/day and 2.83g VS l/day were taken with the hydraulic retention time of 35 days. The mixing was performed through the mixer at various speeds of 30 rpm, 45 rpm, 60rpm and 100 rpm during the co digestion process. When compared to other agitation speeds like 30rpm, 60 rpm and 100rpm, 45 rpm agitation speed performed its digestion upto 80th day with the minimum gas production of 0.1 l/day. The stability of the digester also maintained well with the VFA/Alkalinity ratio of 0.17 on the day of maximum yield and 0.12 at the end of digestion period. The percentage of Total Solids reduction and Volatile solids reduction for 45rpm agitation speed was 51.04% and 55.49% respectively. Hence, the agitation speed of 45rpm had been chosen as the optimum speed for lab scale co digestion process.