Digestate recirculation to enhance biogas production from dry anaerobic digestion of cow manure and corn straw: Strategies and impacts

This study investigates the semi-continuous dry anaerobic digestion (AD) of cow manure and corn straw. While previous research on dry AD rarely explored digestate recirculation ratios (R) above 60 %, this study specifically examines R values of 60 %, 70 %, and 80 %, in conjunction with total solid (TS) contents of 20 % and 25 %. The research provides a comprehensive evaluation of material balance, microbial community dynamics, and the impact of TS variation on digestate recirculation efficiency. Results show that at R = 70 % and TS = 20 %, the maximum CH₄ production reaches 1.17 L/L/d, while the peak biogas production is 2.71 L/L/d. Increasing R leads to the accumulation of volatile fatty acids (VFAs), total ammonia nitrogen (TAN), and soluble chemical oxygen demand (SCOD). However, an excessively R of 80 % reduces biogas production by 58.97 %. A higher TS affects the material conversion efficiency during different AD stages, resulting in reduced biogas and CH₄ production, although it does not alter the overall trend of R's influence. Acetotrophic Methanosarcina and Methanosaeta play crucial roles in biogas production, As R increases, Methanosarcina becomes increasingly dominant.