Examining a Hybrid plug-flow Pilot reactor for Anaerobic Digestion of Farm-Based Biodegradable Solids

Plug-flow digesters with periodic loading mechanism are more enthusiastic than fully mechanized digestion plants for the majority of small or medium scale farms according to the costs and operational complexities. A dual-compartment plug-flow reactor equipped with a passive heating system was designed and experimentally operated by purpose of demonstrating a simple and low cost technology for handling the biodegradable agricultural wastes. The reactor was successfully started up with pig feces as feedstock under a quasi-continuous loading and semi-dry condition with an average total solids content of 12.8% inside the digester and an average organic loading rate of 2.06kg-VS/(m3.d). The start-up phase was followed by co-digestion of pig feces and pre-treated cotton stalk. Even though the digester actually worked at a temperature range 12 to 30% below the optimal mesophilic level, acceptable rates of methane generation and VS destruction were observed. The biogas and methane yield were measured for single digestion stage as 0.332 and 0.202 m3/(kg-added VS) and for co-digestion stage as 0.482 and 0.325 m3/(kg-added VS) respectively. The cumulative biogas production data demonstrated a reasonable correlation (R2 over 0.99) with a simplified consecutive kinetic model.