Anaerobic digestion of poultry processing wastes for bioenergy and nutrients recovery
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Anaerobic digestion (AD) is an attractive technology that can be used to recover energy (in form of methane in biogas) and nutrients from waste poultry blood. One challenge with treating high-strength high-protein wastes is the production of total ammonia nitrogen (TAN) during decomposition. The TAN severely inhibits methane producing bacteria and results in accumulation of fatty acids, which destabilizes the digester and causes AD process failure. This dissertation proposed and examined several ways to manage these drawbacks, namely, use of biocarriers, two-stage process, and struvite precipitation. Results show that a single-stage anaerobic digester filled with biochar has methane yield of 82 mL g-1 CODadded, and maximum volumetric biogas production of 0.64 L L-1d-1, when operated at 35oC and OLR of 4.7 g COD L-1 d-1. Two-stage anaerobic digesters (127-L) were tested for treating poultry blood wastes over a 400-d period. Digesters (operated at 26oC) had higher methane yield (189 mL g-1 CODadded, at OLR of 0.4 g COD L-1 d-1) than results from the literature on tests on similar feedstocks using single-stage digesters. The use of bamboo biocarriers improved the performance of two-stage digesters resulting in methane production of 361 mL g-1 CODadded, at OLR of 0.4 g COD L-1 d-1. Struvite precipitation (SP) removed more than 70% of TAN from effluents of the acidogenic digesters and showed an improved methane yield in subsequent biochemical methane potential (BMP) tests. The best performing reagent combination for SP was found to be Mg(OH)2 and H3PO4, which resulted in 74.1% nitrogen recovery and subsequently 29.4% increase in methane production (measured via a BMP). Results of this dissertation show that optimization methods reduce the impact of TAN inhibition of the AD process treating poultry blood wastes.