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UBC Theses and Dissertations

Aerobic granulation with low pH, low alkalinity municipal wastewater Leong, Jason


Aerobic granulation was successfully achieved using municipal wastewater with supplemental carbon addition, after a 166 day start-up period. During the start-up period, an increase in biomass particle size was noticed that correlated to a stepwise reduction in settling and decant time. During this time, the granular type formation had a fluffy structure with noticeable filamentous outgrowths. On the 82nd day of start-up, supplemental carbon, in the form of sugar, was added to the feed tank to increase the Organic Loading Rate (OLR) of the system. In addition to an increase in COD, a pH and alkalinity decrease in the feed occurred due to acetogenesis. Soon after the supplemental carbon addition, the biomass developed a denser morphology, with gelatinous, white-coloured, granules appearing on the 166th day. Although it was shown that aerobic granulation with low pH, low alkalinity municipal wastewater with supplemental carbon was possible, some issues were discovered. These issues include reduced nutrient removal, and lower granule density. The reduction in nutrient removal performance is potentially due to the lack of nitrification/denitrification, and shifting of the microbial ecology to favour Glycogen Accumulating Organisms (GAOs) or heterotrophs over Polyphosphate Accumulating Organisms (PAOs). It is hypothesized that the reduced pH of the influent was the main factor that caused the reduction in nutrient removal. The lower granule density is hypothesized to be a result of the absence of denitrification induced chemical phosphorus precipitation within the granule. As such, the lower granule density results in reduced granule settling velocities and increased Sludge Volume Index (SVI).

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