Feasibility of annual dry anaerobic digestion temperature-controlled by solar energy in cold and arid areas.

Abstract

In cold and arid areas, variations of ambient temperature not only lead to a large amount of heat loss from anaerobic digestion reactors but also greater challenges in the stable production of biogas. Common temperature-controlled methods of biogas production, such as coal combustion, electric heating, biogas combustion and so on, are expensive and high energy-consuming. Openly, solar energy is economical and suitable for stable biogas production. However, no pilot studies have yet shown the feasibility of controlling the temperature of annual biogas production with solar energy in cold and arid areas. This paper first theoretically analyzed the energy balance between evacuated tube solar collectors and anaerobic reactors. Then a biogas production system was developed in Lanzhou City, China, consisting mainly of a 3m3 insulated anaerobic reactor and a solar collector with 30 sticks Φ58×L1800mm evacuated tubes. Annual batch experiments have been carried out to test the feasibility of stable biogas production at a temperature-controlled by solar energy in cold and arid areas. The results show that dry anaerobic digestion with 20% total solid (TS) can start and operate smoothly even under the condition of low solar irradiation for 3-4 consecutive days. The system can run stability by anaerobic digestion at 26±1°C in winter and spring, by mesophilic (37±1°C) and thermophilic (52±1°C) anaerobic digestion in summer and autumn, which implies a highly efficient operation strategy for agricultural and animal husbandry wastes treatment. These theoretical and experimental results provide a scientific basis and engineering reference for the application of biogas production temperature-controlled by solar energy and have important value for the efficient and low-cost anaerobic digestion treatment of agricultural and animal husbandry wastes in cold and arid areas.