Anaerobic monodigestion of poultry manure: determination of operational parameters for CSTR

In this work the anaerobic monodigestion for the treatment of turkey manure was evaluated, without its codigestion with another substrate. The effect of the organic loading rate (OLR) and the substrate concentration (high total solids (TS) concentration) or product concentration (high volatile fatty acids (VFA) and/or ammonia (NH₃-N) concentrations) was studied. The results show that for a continuous stirred tank reactor (CSTR) operation, a maximum of 40 g/L of TS and 4.0 g/L of ammonium (NH₄⁺) was required. In addition, the maximum organic loading rate (OLR) will not exceed 1.5 kg VS/m³d. Higher TS and NH₄⁺ concentrations and OLR lead to a reduction on the methane productivity and volatile solids (VS) removal. During the CSTR operation, a high alkalinity concentration (above 10 g/L CaCO₃) was found; this situation allowed maintaining a constant and appropriate pH (close to 7.8), despite the VFA accumulation. In this sense, the alkalinity ratio (α) is a more appropriate control and monitoring parameter of the reactor operation compared to pH. Additionally, with this parameter a VS removal of 80% with a methane productivity of 0.50 m³_CH4/m³_Rd is achieved.