The effects of shock loads of 1‐chloro‐2,4‐dinitrobenzene (CDNB); cadmium; 1‐octanol; 2,4‐dinitrophenol (DNP); weakly complexed cyanide; pH 5, 9, and 11; and high ammonia levels on activated sludge biomass growth, respiration rate, flocculation, chemical oxygen demand removal, dewaterability, and settleability were studied. For all chemical shocks, except ammonia and pH, concentrations that caused 15, 25, and 50% respiration inhibition were used to provide a single pulse shock to sequencing batch reactor systems containing a nitrifying or non‐nitrifying biomass. Cadmium and pH 11 shocks were most detrimental to all processes, followed by CDNB. The DNP and cyanide primarily affected respiration, while pH 5, pH 9, octanol, and ammonia did not affect the treatment process to a significant extent. A chemical source–process effect matrix is provided, which we believe will aid in the development of methods that prevent and/or attenuate the effects of toxic shock loads on activated sludge systems.

Upset events due to the inflow of toxic chemicals are a critical issue for wastewater treatment facilities. Understanding the source-effect relationship between toxic chemicals and treatment plants can lead to appropriate strategies for preventing future events and/or establishing corrective action plans for operator decision-making. Respirometry is among the tools that are used to identify toxic sources that can have an impact on process performance. Although it does not identify the chemical(s) in a wastewater that lead to process upset, respirometry can serve as a viable first step to identify wastewater streams that have the potential to disturb biomass metabolism in a wastewater bioreactor. A respirometric assay protocol was developed for this study to allow a regional wastewater treatment facility (RWTF) under the influence of several industries to screen industrial wastewaters for inhibitory properties based on two classifying criteria. All five industrial wastewaters tested revealed inhibitory properties, but one plant was routinely uninhibitory. Large day-to-day variations were found, illustrating the need for a large database of results for comparison over time.Additionally, a small volume contributor that was thought by the utility to be an unlikely source of problems contributed significantly to the wastewater oxygen demand and frequently demonstrated inhibitory properties. The modified respirometric procedure provided the RWTF with a protocol upon which it may be possible to identify industrial sources that cause process upset. A complimentary sample storage procedure and data analysis protocol were also suggested as part of the analytical procedure.

Wastewater treatment plants commonly experience upset events due to inflow of toxic chemicals resulting mainly from industrial sources. These events may have significant impacts on the biological treatment process, including loss of chemical oxygen demand (COD) removal efficiency, inhibition of nitrification or deflocculation with corresponding increased effluent solids. This work investigated the source-effect relationships of four categories of toxic chemicals on the activated sludge process, including heavy metal (cadmium, Cd), electrophilic chemical (chlorodinitrobenzene, CDNB), organic hydrophobic chemical (octanol) and ammonia. These studies were performed using lab scale sequencing batch reactors, operated at two solids retention times -2 and 10 days (non-nitrifying and nitrifying cultures) -and initially dosed with three different toxin concentrations, based upon respiratory inhibition of 15%, 25% and 50% of a non-shocked system. Ammonia was dosed at up to 10x the typical influent concentration. Process performance was monitored over time for effluent quality and mixed liquor stability. Results obtained for Cd showed increasing deflocculation, loss of soluble COD removal efficiency and loss of nitrification with increasing Cd concentrations. Results for octanol showed foaming, minor deflocculation and nitrification inhibition as the main effects. Ammonia shock was found to have no major effect on process performance, but minor nitrite buildup and minor deflocculation occurred. CDNB had effects similar to those seen for Cd on process performance, including deflocculation, loss of COD removal efficiency and loss of nitrification. It is hoped that these macroscopic effects will serve as a basis for the determination of molecular causal mechanisms for upset events and possibly lead to the development of mechanistically-based upset early warning devices.

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