Methane production analysis of inhibited poultry digestion effluent after dilution and ammonia volatilization

Paul Foster Gamble

This study was conducted using manure waste from a concentrated animal feeding operation (CAFO) that consisted of 1.5 million chicken egg-laying at facility in Ohio in the Mid-West of the United States, which operated a mesophilic, plug flow anaerobic digester (AD) to handle its poultry litter waste. The AD had become sour (inhibited), most probably due to elevated levels of ammonia, and its gas production had dropped to 40% of its initial gas levels. Economic efficiencies in CAFOs are realized through integration of scale, mechanization, and technology in order to produce affordable animal products for consumption. However, as CAFOs continue to increase in size and concentrate geographically, animal feeds no longer comes from only the surrounding land but some have to be imported. The imported feeds have led to CAFOs being net nutrient positive (difference between imported nutrients and nutrients used within the CAFOs after nutrients are applied on available land at desired agronomic rates). Such scenarios heighten environmental concerns if these excess nutrients leach to groundwater or run-off to surface water masses, especially if they are not properly managed. Traditionally, poultry CAFOs dispose of their manure waste via either land application or export, but they have been exploring AD as an alternative option. The Ohio poultry manure anaerobic digester (AD) was built to handle its poultry litter in order to tap into AD's beneficial attributes including: stabilization and reduction of manure waste, production of a stable organic soil conditioner and/ or liquid fertilizer, and production of a combustible, renewable biogas. Yet the recycling of the digester's effluent back into the digester as influent led to the persistence of ammonia, a known inhibitor of digester microbial ecology at higher levels. The goal of this research was to investigate operation restoration of this sour AD via two treatments at various dilutions: 1) aeration of the digester's ammonia-inhibited contents, and 2) coupling aeration and heat treatment of the digester's ammonia-inhibited contents. The results of this study suggest that both aeration and dilution treatments are effective methods of conditioning inhibited digester's effluent and thus restoring normal operations of an inhibited digester.

Methane production analysis of inhibited poultry digestion effluent after dilution and ammonia volatilization

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