Improving efficiency of nitrogen removal from municipal wastewater in modified A2O technological system – case study
Piotr Maciołek, Kazimierz Szymański, Beata Janowska, Maria Włodarczyk‐Makuła
Abstract
ABSTRACT Results of qualitative examination of municipal wastewater purified in a modernized A2O (Anaerobic/Anoxic/Oxic) treatment system have been presented in this paper. The tests were performed on the real system. Primary organic contamination indicators such as BOD 5 , COD Cr , and nitrogen compounds were analyzed. The test results were compared with those achieved before modernization. Thanks to the implementation of aerobic conditions modification in chambers and due to separation of the final denitrification stage, improvement of total nitrogen removal efficiency was achieved. Considering significant increase and fluctuations of total nitrogen concentration in wastewater supplied to the wastewater treatment plant (from 54 to 238 mg N tot /dm 3 ), the average concentration in treated wastewater did not exceed 6.7 mg/dm 3 , whereas the average annual final total nitrogen concentration before modernization was 9.0 mg/dm 3 . Efficiency of total nitrogen removal increased to 94% and efficiency of removal of organic compounds expressed by BOD 5 and COD Cr , as well as total phosphorus (98%–99%), was maintained at a similar level. The test results were subjected to statistical analysis and mutual correlations between particular pollutant elements, with particular consideration of nitrogen compounds, were determined. To evaluate these correlations the stepwise regression procedure was applied. Corrected coefficient of determination R 2 was used here to develop a model describing the process of total nitrogen removal from wastewater taking into account the variables that were strongly correlated with the dependent variable and, at the same time, the least correlated between themselves.