Fate and Effect of Peracetic Acid Solutions on Biological Wastewater Treatment Systems

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Chen, Jinchen
Pavlostathis, Spyros G.
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Peracetic acid (PAA), as a wide-spectrum effective disinfectant, has been extensively and increasingly used in many industries, especially in poultry processing to control food-borne pathogens. Upsets of biological wastewater treatment processes and failures of whole effluent toxicity (WET) tests have been reported as potentially caused by the excessive use of PAA solutions. However, information related to the fate and effect of PAA on biological wastewater treatment processes commonly used in poultry processing plants is extremely limited. This dissertation focused on the assessment of the fate of a PAA solution in poultry processing wastewater streams, factors contributing to PAA decomposition, and the evaluation of the effect of PAA on biological treatment processes, such as organic matter degradation, nitrification, and denitrification. On-site monitoring did not detect PAA in dissolved air flotation (DAF) influent and effluent samples collected at mid plant operation shifts; however, up to 25 mg/L PAA was detected in the DAF effluent at the end of the operation shift coinciding with emptying chiller tanks where PAA levels in excess of 1,000 mg/L are maintained. The PAA decomposition rate in poultry processing wastewater correlated positively with pH, temperature, wastewater strength and organic content, and negatively with initial PAA concentration. PAA decomposition resulted in equimolar concentrations of acetic acid. The inhibitory effect of the PAA solution on organic matter degradation, nitrification and denitrification was dose-dependent, with significant inhibition at PAA 40 mg/L; fast recovery was observed after direct PAA solution addition ended. Microbial acclimation to PAA did not take place under aerobic conditions, but a low degree of acclimation was observed under anoxic conditions over a long-term operation of semi-continuously fed bioreactors. The impact on nitrification was predominantly attributed to enzyme inhibition than to loss of nitrifiers, whereas the impact on denitrification was attributed to both enzyme inhibition and loss of culture viability. Intracellular reactive oxygen species (ROS) were not the cause of nitrification inhibition, but contributed to the decrease in denitrification activity. Nevertheless, the capacity of the microbial communities to manage PAA-induced cell oxidative stress increased in both aerobic and anoxic reactors over the long- term operation. Long-term evaluation of PAA on a continuously-fed, three-reactor biological nitrogen removal (BNR) system showed that continuous, direct addition of PAA at 80 to 200 mg/L in the first, anaerobic reactor did not affect the BNR system performance; however, organic matter degradation and nitrogen removal were severely affected by continuous feeding with wastewater carrying residual PAA at 80 and 200 mg/L. Direct addition of PAA at 3 mg/L to a highly enriched nitrifying culture resulted in severe nitrification inhibition not caused by loss of cell viability or cell oxidative stress, but rather by enzyme inhibition reflected in the culture transcriptional levels. The outcome of the study provides crucial information for the rational design and operation of biological treatment processes under the effect of PAA solutions. It also provides information for the poultry processing industry to develop a sound methodology that will ensure the continuous use of PAA solutions to achieve pathogen-free products, while avoiding upsets of biological processes treating PAA-bearing wastewater.
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