Sufficient wastewater (pre)treatment capacity is needed at poultry processing facilities to control effluent quality, e.g. biochemical oxygen demand, suspended solids, ammonia and phosphorus, according to Dr Spyros G. Pavlostathis and Malek G. Hajaya of the School of Civil and Environmental Engineering at the Georgia Institute of Technology in Atlanta in a report of their latest study sponsored by the US Poultry & Egg Association.

Although the combination of nitrification and denitrification leads to efficient nitrogen removal, poorly understood factors periodically lead to system upsets and incomplete nitrogen removal, they explain.

Ammonia is a poultry processing wastewater component that requires a high degree of removal before the final disposal of the treated wastewater. As discharge effluent limits are being established for total nitrogen, not just ammonia, nitrogen removal will become an even more pressing issue for poultry processing facilities, especially those with direct effluent discharge. The overall objective of this research project was to systematically assess the effect of conditions/parameters that can affect the efficiency of biological nitrogen removal (BNR) in poultry processing facilities by conducting targeted sampling in such facilities as well as long-term bench-scale testing.

Nitrification and denitrification tests conducted with mixed liquor samples collected at a poultry processing wastewater treatment plant during warm (fall) and cold (winter) seasons confirmed reports that low temperature conditions are more detrimental to nitrification than to denitrification.

A laboratory-scale, multi-stage BNR system maintained at room temperature (22-24°C) was continuously fed with poultry processing wastewater amended with a mixture of three benzalkonium chlorides (BAC), a class of quaternary ammonium compounds (QACs). The nitrogen removal efficiency initially deteriorated at a BAC feed concentration of 5mg per litre due to severe inhibition of nitrification in the unacclimated system. However, the system recovered after 27 days of operation, achieving high nitrogen removal efficiency, even after the feed BAC concentration was stepwise increased up to 120mg per litre. The same high nitrogen removal efficiency was retained when the system was operated at 10°C with BAC-amended poultry processing wastewater.

Microbial acclimation to and degradation of BAC was responsible for the successful operation of the BNR system with the BAC-amended poultry processing wastewater. Batch assays performed before, during, and post BAC exposure showed that the development of BAC biotransformation capacity and the acquisition of resistance to BAC, especially by the nitrifiers, contributed to the recovery of nitrification and led to a high nitrogen removal efficiency.

Simulations using a comprehensive mathematical BNR model developed for this research accurately described the fate and effect of BAC in the BNR system when the interactions between adsorption, inhibition, and resistance/biotransformation were considered within the conditions prevailing in each reactor of the BNR system. Adsorption determines the level of the inhibitory effect of BAC, while BAC biotransformation and resistance determine the extent of exposure of the microbial communities to BAC. Finally, the inhibitory effect of BAC is reduced, if not completely removed, by the development of BAC resistance and biotransformation capacity.

The Georgia researchers conclude that the results of their study will enable the rational design and operation of BNR systems for the efficient treatment of QAC-bearing wastewater. The outcome of this research provides information presently lacking, supporting the continuous use of QACs as antimicrobial agents in poultry processing facilities, when and where needed, while avoiding any negative impacts on biological treatment systems and the environment.

Pavlostathis and Hajaya add that, given the benefits of using QACs as effective sanitation chemicals in poultry processing facilities, the effectiveness of biological processes for the degradation of QACs in order to avoid process upsets, especially for the nitrification step, should be further evaluated using alternative process configurations (e.g. sequential batch reactors, fixed-film reactors) in order to capture process variability across the entire poultry processing industry.

August 2011