Effect of organic loading and retention time on dairy manure fermentation

The investigations presented and discussed herein establish an enhanced understanding on volatile fatty acid (VFA) production as a function of dairy manure fermenter organic loading (OL) and retention time (RT), first through a factorial of 64 fermentation potential (FP) batch tests, followed by analysis of a continuously operated pilot-scale fermenter. The maximum observed net FP - 0.103 mg VFA produced (as COD) (mg VS applied)(-1) - occurred at an OL of 40.7 g VS L(-1) and at a RT of 6 days. The pilot-scale fermenter exhibited an average yield of 0.09 mg VFA (as COD) synthesized (mg VS applied)(-1), with average effluent total VFA concentrations of 6398 mg VFA (as COD) L(-1). The research demonstrates that FP tests are an effective method to optimize continuously operated dairy manure fermenters, and that dairy manure fermentation can yield large quantities of organic acids at short RTs and high OL rates.