Start-up of dry anaerobic digestion system for processing solid poultry litter using adapted liquid inoculum

• Treatment of poultry litter (PL) at higher solid content of above 15% is limited.
• Low-temperature treatment of solid PL with high nitrogen has been scarcely reported.
• Tested the adapted liquid inoculum to start the solid dry anaerobic digester (DAD).
• Higher total Kjeldahl nitrogen concentrations (>30 g/L) in PL inhibited the DAD.

The objective is to obtain the basic design criteria for starting up dry anaerobic-digestion (DAD) systems treating solid-poultry-litter (PL) with hay-bedding (TSmixture: 68.6%) using adapted liquid inoculum. Effect of organic loading rates (OLR) and mode of operation (particularly psychrophilic liquid inoculum recirculation-percolation mode) were evaluated in two phases; such that OLR of 5.4 and 21.6 gVS/kginoculumVS/d were maintained respectively for Phase-1 and-2; and top-down and down-up mode of liquid-inoculum recirculation into DAD-system were experimented. Digesters were operated at psychrophilic-temperature (@20 °C) with cycle length of 26 and 38 d for Phase-1 and -2, respectively. Results show that specific methane yield of 0.147–0.162 L/gVSfed was obtained for Phase-1 with a methane content of 35–39%; whereas Phase-2 had 61–70% lower yields compared to Phase-1. Though PL-digestion was possible at OLR <5.4 g VS/kginoculumVS/d, high nitrogen-content in PL inhibited the digestion process especially at higher OLR. However, adapted inoculum to TKN of >20 g/L could minimize the inhibition. Top-down-recirculation is recommended for simpler operation.