Investigation of Industrial Wastewater Discharge to a POTW

Two wastewater treatment plant operators employed at a Publicly Owned Treatment Works (POTW) sued the City, a dairy facility, and a petroleum refining company for exposure to elevated levels of hydrogen sulfide (H2S) and benzene. The plant operators claimed the City did not properly protect them from exposure to these contaminants, which entered the POTW from the two industrial dischargers. The refinery had an agreement with the City to discharge their wastewater to the treatment plant. Production wastewater from refining operations typically contains H2S and hydrocarbons. The dairy facility discharged to the POTW without a formal discharge agreement. The production wastewater from the dairy production represents one of the most heavily loaded wastewaters with extremely high organic content and is typically acidic with a pH of 3 to 4.Exponent was retained to evaluate wastewater quality and toxic exposure. Our site inspection revealed that the refinery transports wastewater to the treatment plant in a dedicated line, which does not mix with other wastewaters. In addition, an inspection of the refinery revealed that the production wastewater is always treated to remove contaminants such as H2S and benzene. Further, the water is tested daily/weekly for these contaminants. Samples taken from the refinery wastewater line revealed trace to non-detectable H2S levels. Refinery data were evaluated to quantify the amounts of the contaminants of concern that could be volatilized from the wastewater presenting a potential risk to workers exposed to the atmosphere in the wastewater line or in a manhole. Our analysis revealed the levels were significantly lower than applicable OSHA standards. Based upon our analysis, there was no adverse health risk posed to the plant operators.The cause of the problems stemmed from the discharge of untreated heavily loaded organic wastewater from the dairy facility. A review of records revealed that the plant operators spent a significant amount of time cleaning the sewer line that ran from the dairy facility to the POTW. It was during these cleaning operations that the plant operators claimed to have been immersed in wastewater. Heavy organic loading to a POTW introduced excessive electron donor with limited electron acceptor availability, resulting in ‘suffocation’ and death of bacteria. This leaded to the periodic development of septic conditions with the accompanying generation of noxious gases, such as H2S, from anaerobic decomposition of influent BOD. The food processing facilities' discharge to POTW was subsequently curtailed by the state environmental protection agency.