The effects of micro-aeration on semi-continued anaerobic digestion of corn straw with increasing organic loading rates

Abstract

The benefits of micro-aeration on batch anaerobic digestion (AD) of organic wastes have been intensively studied. However, the effects of micro-aeration on the semi-continued AD under different organic loading rates (OLRs) were still lacking. This study investigated the effects of micro-aeration on semi-continued AD of corn straw with increasing OLRs from 1.1 to 2.1 volatile solid (VS)/(L·day). Results showed micro-aeration could benefit the AD process by increasing the median daily methane yields for 6%, 10% and 8% at OLRs of 1.1, 1.5 and 2.1 VS/(L·day), respectively. Moreover, micro-aeration stimulated the growth of facultative bacteria (Clostridia), which secreted more critical enzymes (e.g., cellulase and xylanase) and led faster degradation of corn straw as well as higher soluble humic acids (SHAs) concentration. The SHAs might act as electron shuttle to facilitate the direct interspecies electron transfer (DIET) among syntrophic bacteria (Cloacimonadia) and hydrogenotrophic methanogens (Methanobacterium), which led to a faster volatile fatty acids (VFAs) conversion into methane. This study confirmed the beneficial effects of micro-aeration on the semi-continued AD at different OLRs and unraveled the mechanisms behind.