ANAEROBIC CO-DIGESTION OF DAIRY CATTLE MANURE AND WASTE OIL

This paper aimed at assessing the co-digestion of dairy cattle manure and waste oil, by quantifying specific biogas production, reduction of total (ST) and volatile (SV) solids, chemical oxygen demand (DQO) and neutral detergent fiber (FDN). Twenty-eight batch digesters were loaded with substrates composed of dairy cattle manure (4% ST), waste oil (0, 2, 4, 6, 8, 10 and 12% ST), inoculum, and water for dilution. We used prediction quadratic models for estimates on SV, DQO and FDN maximal reductions, as well as specific biogas production; therefore, we appraised the optimal rates of oil inclusion. By the results, we observed that the largest DQO, SV and NDF reductions were of 82.88, 47.53, 51.28 and 49.48%, being reached by waste oil rates of 5.74, 5.93, 4.77 and 6.45%, respectively. When adding 4.63% waste oil, biogas production reached 0.25 liters per g of added SV, which was 13% higher than the amount observed for substrates without oil inclusion. We also highlight that adding oil to dairy cattle manure substrates at rates between 4.4 and 6.5% increases biogas production and decreases solids contents.