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Evaluation of biological removal efficiency in a UCT process treating municipal wastewater during start-up stage.

This study reports the performance of University of Cape Town (UCT) municipal wastewater treatment plant, during the startup stage with the focus on the relationship between hydraulic retention time (HRT) and biological nutrient removal (BNR) efficiency. The entire experimental period was 144 days, divided into four periods. Results showed that the removal efficiency of TN, NH4+-N, and Kjeldahl nitrogen (KN) was closely related to the HRT. Furthermore, the biodegradation kinetics analysis was used to calculate the specific degradation rates of pollutants. The GPS-X modeling was also used to examine the effect of the UCT pilot plant on BNR. The UCT pilot plant used in this study achieved high BNR efficiency even during the startup stage. With HRT of 24 hr (Period 1, day 1-40, data set 1-10), the highest levels of TN, NH(4+)-N and KN removal efficiency were approximately 72, 76 and 78%, respectively. The COD showed consistent high removal efficiency, with the highest level of approximately 96% at HRT of 15 hr (Period 3, day 81-120, data set 21-30). The TP removal efficiency rose at first and subsequently decreased abruptly. The maximum removal efficiency was 85% with HRT of 19 hr (Period 2, day 41-80, data set 11-20). With the optimal HRT 19 hr, the average removal efficiency values of COD, TP, TN, NH(4+)-N and KN were 89, 80, 65, 67 and 68%, respectively. The GPS-X modeling results indicated that the UCT process was effective in COD, TP and TN removal.