Removal of organics in reverse osmosis concentrate by advanced treatment

Abstract

Due to its effective and reliable purification performance, reverse osmosis technology is one of the practical and affordable ways to produce high quality recycled water. However, a major drawback of reverse osmosis is the production of concentrate usually accounting for 15-20% of the input stream containing high levels of organic pollutants some of which could be toxic and bio-accumulative. Possessing a threat to the environment, reverse osmosis concentrate (ROC) must be treated to reduce or even eliminate the negative impact associated with the presence of organic pollutants. The main objective of this research was to investigate the applicability of homogeneous and heterogeneous advanced oxidation processes on municipal wastewater derived reverse osmosis concentrate treatment. For this purpose, reverse osmosis concentrate samples in the absence and presence of emerging contaminants were synthetically prepared with respect to physicochemical characteristics reported in the literature. Sulfamethoxazole and Carbamazepine were selected as target emerging contaminants owing to their common presence in wastewater sources. UVC/H2O2 and Fenton processes were selected as homogeneous advanced oxidation processes whereas solar photocatalysis by using commercially available photocatalysts as well as synthesized ones was considered as heterogeneous advanced oxidation process. Assessment of selected processes for their effectiveness on the removal of complex organic matter was presented in comparison to the sole photolytic oxidation conditions. Since molecular size distribution profiles of organic compounds in ROC plays an important role in order to assess the removal of different pollutants with respect to different molecular size fractions ROC samples were exposed to molecular size fractionation prior to and following photolytic and photocatalytic degradation processes. Expected potential risk was investigated through toxicity assessment prior to and following photodegradation and photocatalytic degradation processes. Organic fraction of reverse osmosis concentrate samples were monitored mainly by UV-vis and advanced fluorescence spectroscopic techniques in combination with PARAFAC modeling as well as organic carbon content.