The Influence of Total Solid and Inoculum Ratio on Thermophilic Anaerobic Digestion of Waste Activated Sludge

Abstract

Compared to conventional mesophilic anaerobic digestion, thermophilic anaerobic digestion may offer attractive advantages such as higher volatile solid destruction efficiency, higher biogas generation, and higher disinfection effect and better dewater ability. In this study, two experiments of waste activated sludge were conducted to evaluate the influence of total solid and inoculums ratio on the biogas production and thermophilic (55±1°C) anaerobic process stability. In first experiment, the biogas production of 4 reactors with solid concentration of 6%, 8%, 10% and 12% respectively was observed. The biogas productions in 4 reactors were 4444 mL, 4891 mL, 5573 mL and 6327 mL respectively, the biogas productions per unit VS digested of each group were all above 360 mL/g and the methane content in biogas of each reactor was kept about 70%. During the operation, pH value in the reactor was kept between 6.5 and 8.4. In second experiment, the biogas production of 4 reactors with inoculums ratio of 20%, 30%, 40% and 50% respectively was observed. The biogas productions in 4 reactors were 4730 mL, 6630 mL, 6820 mL and 7175 mL respectively, the biogas productions per unit VS digested of each group were all above 340 mL/g and the methane content in biogas of each reactor was kept about 70%. During the operation, pH value in the reactor was kept between 6.4 and 8.6. Putting into consideration, the shortening of anaerobic digestion cycle, costs saving, and increasing economic benefits; choosing TS within the scope of 8-10%and inoculums ratio within the scope of 30-40% are more recommended. And the results showed that thermophilic anaerobic digestion process for waste activated sludge could be operated steadily.