Quick start of dry anaerobic digestion of kitchen waste using semi-continues horizontal plug-flow system

Dry anaerobic digestion (DAD) possesses advantages such as high volumetric gas production rate, low liquid effluent, and small floor space. However, it is prone to severe acidification during the startup phase, causing system collapse. Therefore, the successful startup and stable performance of dry anaerobic digestion merit further investigation. In this study, a horizontal plug-flow AD reactor (HPFRAD) was employed to investigate the optimum start-up conditions of dry anaerobic digestion of kitchen waste. As the organic load increased gradually from 0.78 kgVS·m−3·d−1 to 2.80 kgVS·m−3·d−1, the methane yield and production rate changed accordingly. The highest cumulative gas volume (3278 L) was achieved at an organic load of 2.80 kgVS·m−3·d−1, while the highest methane production rate (1059.14 L/kgVS) was attained at a lower organic load (1.90 kgVS·m−3·d−1). The relationship between organic load and gas production rate was nonlinear, necessitating the selection of the optimal organic load to achieve a balance between gas production efficiency and operational stability. Lower organic load with high methane production rate is therefore key for start-up of dry AD process. Microbial community analysis indicated that the abundance of microorganisms resistant to high VFAs and ammonia concentration was positively correlated with organic load. Methanosarcina emerged as the dominant methane-producing archaea with relative abundance of 0.11–0.79 under these conditions, highlighting the importance of resilient microbes in supporting start-up and maintaining good performance of HPFRAD system. However, excessively high organic loads (≥2.80 kgVS·m−3·d−1) still led to a decrease in microbial diversity. As the OLR increased from 1.90 kgVS·m−3·d−1 to 2.80 kgVS·m−3·d−1, the Chao index decreased by approximately 57 %.