Prefermentation of liquid dairy manure to support biological nutrient removal

A continuously operated, intermittently fed reactor (fermenter) system with a 2-d solids retention time was proposed for supporting biological nutrient removal from liquid dairy manure. The first objective of this study was to select a material with high fermentation potential to be used as the fermenter feed. Primary sludge, liquid separated dairy manure, and flushed dairy manure were investigated for their fermentation potential. Liquid separated dairy manure had the highest fermentation potential, 0.73 mg volatile fatty acid as chemical oxygen demand/mg of initial volatile suspended solids (VSS). The second objective was to investigate the performance of a pilot-scale fermenter operated under an average organic loading rate (OLR) of 3 kg-VSS/m3/d. The reactor utilized 18% of the manure fermentation potential. Performance comparison of the pilot-scale fermenter and a lab-scale fermenter with an average OLR of 7 kg-VSS/m3/d highlighted the need to increase the OLR of the pilot-scale fermenter so that it can exploit a higher fraction of the manure fermentation potential. A continuously operated, intermittently fed fermenter with 2-d SRT can utilize the majority of the manure fermentation potential and support a downstream BNR reactor provided that it receives a sufficiently high OLR.