Investigating the efficiency of DO stressing on microbial culture as a strategy for removal of organic micropollutants from wastewater

Abstract

A lab-scale study was performed with the aim of testing the effects of Dissolved Oxygen (DO) perturbations on the removal of organic micropollutants and nutrients in an attached growth system. Trials were carried out to obtain six different DO patterns to be used for experimental runs. Sludge from municipal wastewater facility was used with white virgin reticulated polyester (WPS) cubes to cultivate biofilm. The DO patterns were used to investigate the oxidative stress produced on the microbial population and subsequently the production of oxidoreductases. The reactor operation was performed in batch mode and synthetic wastewater with acetate as the carbon source was used. Ten organic micropollutants were studied. pH, Acetate, Nitrate, Nitrite, Ammonium, Phosphate, Organic micropollutants and Enzyme Activity were parameters that were monitored and tested at three sampling points. Lignin Peroxidase and Cytochrome P450 were the two enzymes showing the highest activity while there was no or insignificant activity of Horseradish Peroxidase and beta-glucosidase. Intermittent high DO pattern showed the best overall efficiency in terms of removal. The highest organic micropollutant removal obtained across all treatments was only up to 64 % and Lincomycin proved to be easily removed across all treatments. Sucralose, Carbamazepine and Atrazine were found to be recalcitrant except in the intermittent high DO treatment. Ammonium removal were quite significant in most treatments and no nitrite accumulation was obtained which confirmed that nitrification was indeed happening. Only Constant DO treatments showed constant or increased nitrate concentrations showing denitrification was happening in all treatments except for the constant DO ones. The results obtained for phosphate were not quite clear as to the trend obtained as well as the fact that the autoclaved sludge treatment had a major release of phosphate. It can be inferred that the DO stressing did stimulate oxidoreductase production showing degradation of some organic micropollutants while the removal of some others seemed to be unaffected by the DO perturbations.