Upset events due to the inflow of toxic chemicals are a critical issue for wastewater treatment facilities. Understanding the source-effect relationship of toxic chemicals can facilitate the prevention or improved reaction to upset events. Part one of this study was conducted to investigate the source of upset events at a regional industrial wastewater treatment plant (WWTP). Part two of this study determined the process performance effects of two chemical shocks, cyanide (zinc-cyanide complex) and pH, on nitrifying and non-nitrifying activated sludge. A modified respirometric assay protocol was developed to allow the industrial WWTP to screen industrial wastewaters for inhibitory properties. All five industrial wastewaters tested revealed inhibitory properties. 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 demonstrated inhibitory properties. The modified respirometric procedure enabled the WWTP to identify possible industrial sources that could cause an upset event. Lab-scale sequencing-batch reactors were used to determine the effects of cyanide and pH shock on activated sludge. Three reactors were shocked with increasing weak-acid complexed zinc cyanide or pHs of 5, 9, and 11. The resulting effects were compared to an un-shocked control reactor. It was found that respiration and nitrification were affected by the zinc cyanide complex, while COD removal, effluent TSS and dewaterability were not. Recovery was seen in less than 2 X solids residence time (SRT) for the nitrifying biomass and within 3 X SRT for the non-nitrifying biomass. The results of the pH experiment showed that the pH 11 shock affected the settleability, nitrification, COD removal, and effluent TSS levels of the reactors, while pH 5 and pH 9 shocks had no effect. Recovery was seen within 3 X SRT for both the nitrifying and non-nitrifying systems. / Master of Science

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

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Stream ecosystems are influenced by the surrounding landscape, and agriculture within their catchments has changed many characteristics of streams. Agriculture has been a prominent land use activity in the southern Appalachian Mountains of the eastern United States for over 500 years. However, recent socioeconomic changes in the region have caused many farmers to abandon agriculture leading to widespread reforestation of historical farmland. I investigated the influence of agriculture on the physical, chemical, and biological structure and ecosystem processes of streams in the southern Appalachians. In addition, I studied streams in watersheds previously agricultural but currently reforested to determine how historic agriculture generates long-term effects on streams. Stream draining agricultural catchments (i.e., agricultural streams) had higher temperatures, light inputs, nutrients, and suspended sediments than forested streams and contained smaller substrate, dominated by sand and silt. Temperature and light regimes recovered in streams of reforested catchments, but the other aspects of stream physicochemistry remained elevated or changed due to historical agriculture. I expected biological community structure and ecosystem processes to reflect these altered conditions in streams with current and historical agriculture. Higher chlorophyll, lower macroinvertebrate biodiversity, fewer shredder-detritivore invertebrates, and more pollution-tolerant organisms characterized agricultural streams compared to forested streams, but each of these biological features was similar in long-term forested streams and streams with reforested catchments but with agricultural histories. Agricultural streams had higher rates of gross primary production (GPP) and GPP to respiration (P/R) ratios than forested streams, indicating that agriculture enhances autotrophic metabolism in streams. Agriculture did not have a significant effect on wood breakdown or microbial biofilm development on wood substrates. Together, these data suggest that agriculture causes many different changes in stream physical and chemical properties and that many of these properties do not recover following reforestation of catchments over the past 50 years. However, biological community structure and ecosystem processes appear to respond to physical aspects of streams that do recover from historic agriculture including light, temperature, and organic matter supply and type. / Ph. D.