An Investigation of the Feasibility of Nitrification and Denitrification of a Complex Industrial Wastewater with High Seasonal Temperatures
Sabalowsky, Andrew R.
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The wastewater treated at the Hopewell Regional Wastewater Treatment Facility (HRWTF) is very unique both because it is comprised of effluents of seven different industries in the area in addition to the domestic wastewater in the area, and because it reaches high temperatures in the basins, often above 45oC during the summer. Four different bench scale systems consisting of continuously stirred tank reactors (CSTRs) in series were operated during the summer of 1997 to quickly assess the feasibility of nitrifying and denitrifying the total flow at HRWTF down to a final effluent total nitrogen concentration of 10 mg-N/L or less. The four main treatment strategies tested were: aerobic/anoxic treatment of the final effluent of HRWTF at moderate temperatures (approximately 30oC); anaerobic/anoxic/aerobic (A2/O) treatment of the primary effluent of HRWTF at moderate temperatures; treatment of the effluent of one of the industries which had a high ammonia wastewater and which was originally believed to contain nitrification inhibitors; and fully aerobic treatment of the primary effluent of HRWTF at high temperatures (of approximately 40 to 45oC) with an activated sludge gradually acclimated to such temperatures over the course of two months. At the end of the study, a two-week high temperature study was conducted on the system which had been treating the secondary effluent all summer with the same activated sludge which was acclimated only to temperatures around 30oC. The fully aerobic high temperature system which had been nitrifying the primary effluent all summer was converted to a modified Lutzack-Ettinger (MLE) process at the end of the study to test whether the primary effluent could be denitrified as well as nitrified at high temperatures with the sludge acclimated to high temperatures. All four of the main treatment strategies demonstrated that nitrification and denitrification of either the total flow or the high ammonia side stream could be achieved down to the desired total nitrogen concentrations. The high temperature study conducted on the system which had been treating the secondary effluent all summer indicated that the sudden increase from approximately 30oC to approximately 40oC over a twenty-four hour period, similar to the sudden temperature increase which occurs every spring at HRWTF, quickly ends nitrification in a system not acclimated to high temperatures, while denitrification and COD removal is hardly affected by such a temperature change. While the nitrification performance of the gradually acclimated system treating the primary effluent at high temperatures was adequate, problems maintaining a consistent MLVSS or ETSS concentration suggested that the high temperatures seen in the basins at HRWTF are likely to make consistent treatment difficult. As a result of considering both capital cost requirements and quality of treatment, the bench scale testing suggested that the most likely candidates for successful treatment of the total flow down to desired total nitrogen concentrations would involve either the A2/O treatment of the primary effluent of HRWTF, possibly with the addition of a cooling tower, or A2/O treatment of the high ammonia side stream, possibly involving the dilution of the wastewater with one of the other flows sent to HRWTF. It was concluded that pilot scale evaluation of the two options was required for a final design decision, and pilot scale evaluation was being performed when this thesis was completed.
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