| The aims of the dissertation were to quantify the impact co-digestion of dairy manure with food processing substrates has on AD performance and to develop new technologies aimed at economically digesting flush dairy manure. Co-digestion data was obtained at commercial-scale, providing new knowledge in regard to data quantity, scale, comparison to manure-only baseline, and application to economics and nutrient balance. Studies on flush manure digestion were conducted first at the laboratory-scale and then later at pilot-scale with the testing of a novel process: mechanical solids/liquid separation, yielding a liquid fraction for AD in a high-rate psychrophilic (27°C) hybrid reactor and a solids fraction for pathogen treatment in a hot-water (50°C) leaching-bed reactor.;Co-digestion (16.36% volumetric flow) produced reduction percentages of 40.61%, 55.28%, 67.72%, 99.87%, and 2 log10 for TS, VS, COD, and VFA, and fecal coliform, respectively. Compared to a manure-only baseline, the co-digestion scenario resulted in a 110% increase in biogas production, a tripling of gross receipts (67% directly due to substrate supplementation), an increase in methane productivities from 0.23 CH4/kg VSload to 0.37 CH 4/kg VSload, and 56.7%, 23.4% and 12.6% more TKN, TAN and TP loaded to the farm.;Microscopic and kinetic studies showed that >70% of microorganisms in flushed dairy manure were attached to the surface of manure fibrous solids due in theory to selection pressure driven bacterial immobilization originating in the cattle rumen. Further AD pilot-testing demonstrated no need for packing material in the reactor, instead using the fibrous solids present in the inflow for attachment, yielding high concentrations of methanosarcina capable of greater reactor stability when exposed to stresses.;The 8-hr hot-water fiber treatment reduced fecal coliforms by 99%, achieving a final concentration below100 cfu/g. AD of the liquid stream yielded a methane productivity of 0.12 m3 CH4/kg CODin at an HRT of 3-4 days and an OLR of 3-4 kg COD/m3 day. Reductions were 31.9, 40.9, 47.7, 60.2, and 93.4% for TS, VS, COD, SCOD, and VFA, respectively. Retained biomass was a loose sludge material not fixed to the media but instead to fibrous particles. Methanosarcina was the most widely present methanogen. |
