Investigation into the Removal of the By-product NDMA (N-Nitrosodimethylamine) from Ozonation Process in Wastewater Treatment

Abstract: In people’s modern life, daily usage of artificial compounds such as active pharmaceuticals ingredients (API) is usual. These compounds are likely to end up as micropollutants in the municipal wastewater. Municipal wastewater is the major source of pharmaceuticals in the aquatic environment. These chemicals can affect the health and behavior of wildlife and the local ecological system. Thus, it is necessary to remove these compounds through WWTPs. The main mechanics of micropollutants removal during treatment processes are sorption and biological degradation. The toxicity may increase after ozonation due to the formation of ozonation transformation products (OTPs) and oxidation by-products (OBPs). To eliminate possible negative ecotoxicological effects caused by biodegradable OTPs and OBPs generated during ozonation, an additional biological post-treatment is needed, such as sand filter, moving bed reactor and fixed bed reactor. This study aims to investigate the degradation of the ozonation by-product, NDMA, by different biomasses (suspended and attached growth) at different redox conditions (oxic and anaerobic). Together with NDMA, three other pharmaceuticals that are commonly detected in wastewater have been also investigated in order to make a comparison with NDMA. The work on the degradation of NDMA and three pharmaceuticals with suspended and attached growth under different redox conditions resulted in several interesting observations: ① NDMA could be completely degraded under oxic redox condition by the suspended biofilm carriers. ② Higher degradation rates of NDMA and the three pharmaceuticals were observed under oxic than anoxic conditions. ③ NDMA has shown similar characteristics of degradation as diclofenac, such as in what situation it is degradable, but NDMA has been considered to be degraded at a larger percentage than diclofenac. ④ Some pharmaceuticals turned out to be easier to be degraded by suspended biofilm carriers than by activated sludge under both redox conditions. ⑤ Ibuprofen and naproxen could be fully degraded under oxic condition by both activated sludge and suspended biofilm carriers.