Comparison of batch and fed-batch solid-state anaerobic digestion of on-farm organic residues: Reactor performance and economic evaluation

Abstract

Batch and fed-batch solid-state anaerobic digestion (SS-AD) of on-farm organic residues including cattle manure, cornstalk, and tomato residues (1:1:1.5, wet basis) were compared under mesophilic condition (35 ± 1 °C). Comparing to batch SS-AD, inoculum was needed in fed-batch was reduced by 60%, but increased cumulative methane yield by 45%. However, the overall daily methane yields in fed-batch SS-AD were 35% lower than that of batch SS-AD. The overall volatile solids (VS) reduction were obtained in fed-batch SS-AD was 12% higher than that in batch SS-AD. Furthermore, the effect of particle size of cornstalk on methane yield of fed-batch SS-AD was investigated. The highest cumulative methane yield of 283.3 L/kg VS feed was achieved in fed-batch SS-AD with cornstalk particle size of 40 mm. However, difference in cumulative methane yields caused by cornstalk particle size of 60 mm, 40 mm, and 10 mm in fed-batch SS-AD was not significant. Economic analysis was conducted to evaluate the economic performance of commercial-scale SS-AD (1,000 m 3 ) under batch, fed-batch, and combine fed-batch and batch system with the annual capacities of 6,400 metric tons (MT), 2,400 MT, and 4,800 MT, respectively. Batch SS-AD system has the highest net present value (NPV, 6.35 million US$) and internal rate of return (IRR, 24.7%) concerning economic analysis. However, batch SS-AD only achieved a slightly higher NPV and IRR compared to the combination of fed-batch and batch SS-AD system. Thus, it is more economical to start reactor with fed-batch SS-AD and later change to batch SS-AD under analysis conditions. • 60% less inoculum was needed in fed-batch solid state anaerobic digestion (FBSS-AD). • 45% higher methane yield was obtained in fed-batch SS-AD. • Effect of cornstalk particle size in FBSS-AD on cumulative CH 4 was not significant. • The highest NPV and IRR was achieved in scenario with batch SS-AD. • Combine fed-batch and batch system for SS-AD was financially attractive.