(514af) Enhanced Anaerobic Digestion of Dairy Manure with Addition of Hay-Derived Biochar

Anaerobic digestion (AD) is considered as an effective method for the conversion of animal manures to biogas. However, the AD process often suffered from low digestion, fluctuation of pH, and accumulation of undesirable intermediates resulting in low methane production and process instability. In order to improve the AD performance, various additives have been applied for the AD process, such as activated carbon (AC), carbon nanotube, graphene, iron oxides, and carbon cloth. Recently, biochar (BC) has been considered as a low-cost and sustainable additive for improving the AD performance. BC can offer the benign environment for microbial growth, and act as a conductive medium for facilitating the direct interspecies electron transfer (DIET) between VFAs-oxidative bacteria and methanogens while buffering fluctuating pH. On the other hand, the grass alfalfa (AF), one of the most abundant hays in USA (about 56 million tons per year), could be a viable biomass feedstock for BC production. To overcome current limitations of AD of dairy manure, this study investigated the effects of alfalfa-derived BC (AF-BC) on biogas and methane production from the anaerobic digestion (AD) of dairy manure with four various loadings of AF-BC (0, 1, 5, and 10 g/L). Compared to the control without AF-BC addition, the addition of 1 and 5 g/L of AF-BC increased the biogas yield by 15.51% and 26.09%, and methane yield by 14.61% and 26.88%. The addition of AF-BC lowered the lag phase by 5.05-23.23% and the CO₂ content of biogas by 13.60-32.48% while increasing the COD removal efficiency by 19.19-35.94% in the AD of dairy manure. Moreover, the AF-BC also resulted in the decrease of total VFAs and acetic acid concentrations in the AD process. The increase of AD performance was mainly owing to the improvement of buffering ability of AD system and the DIET between AD microorganisms resulting from the AF-BC addition. In contrast, at 10 g/L of AF-BC, AF-BC did not show any clear improvement of biogas and methane yields possibly due to the inhibition of AD microorganisms and the imbalance of AD system by excessive AF-BC addition. Future works will focus on understanding effects of BC addition on microbial community changes, particularly shift of key bacteria associated with methane production, and mathematical modeling of the AD process.