TROUBLESHOOTING PLANT PERFORMANCE UPSETS: A CASE STUDY OF THE HOPEWELL REGIONAL WASTEWATER TREATMENT FACILITY

Despite an established industrial pretreatment permit program, a publicly owned industrial treatment works (POITW) with high industrial loading treating approximately 27 million gallons per day (mgd) has periodically experienced significant upsets attributed to the presence of inhibitory compounds and slug loadings. On approximately December 26, 2005, the facility experienced a treatment upset that significantly affected biological treatment performance through early January 2006. The cause for the performance upset cannot be linked to a single influent constituent, industrial event, or operating event. However, several key findings were noted. First, the biological treatment system was experiencing stress prior to the onset of the performance upset. Second, the POITW had a daily influent BOD loading that exceeded the maximum month design capacity of the facility. Next, the measured percent of lower explosion limit suggested the presence of a highly volatile substance, such as turpentine, in the biological treatment tanks. However, the estimated turpentine waste stream concentration was not orders of magnitudes above typical concentrations, and the air emissions estimating model Toxchem did not indicate that a turpentine slug loading was present at the time of the air sampling event. Finally, review of organics data showed that several parameters were at elevated concentrations just prior to the on-set of or during the performance upset. However, based on results from a toxicity reference search, the measured concentrations of these compounds were below reported toxicity concentrations. Overall, this paper addresses some of the major challenges associated with treatment plant upset events, including identifying the onset of the upset condition and determining the cause and source of the upset. Although the cause for the December 2005 plant performance upset could not be determined, the method of analysis outlined here can be applied at any facility investigating a treatment upset event. Finally, this paper presents recommendations for additional monitoring to assist with identifying the onset of potential future upset conditions and sources.