Study On Removal Of Organic Pollutants From Reverse Osmosis Concentrate

The extensive application of dual-membrane process makes a rapid increase of reverse osmosis (RO) concentrate. Due to the biorefractory pollutants and high salt content, RO concentrate is difficult to reuse and harmlessly dispose, particularly organics cause a serious fouling to RO membrane, becoming the biggest obstacle for the further recovery of RO concentrate. Two different processes for the removal of organic pollutants from RO concentrate were studied in this paper, aimed to reduce the dissolved organic carbon (DOC) to less than 10 mg/L, which was required by the RO feeding. As a result, the RO system's recovery rate would be improved while discharge of RO concentrate could be reduced.Biochemical treatment as the most cost-effective and thorough method for organic matter degradation was firstly used to remove the organic pollutants from RO concentrate. The combination of ozonation and biological aerated filter was used in the study. Ozone with its strong oxidation was introduced to improve the biodegradability of RO concentrate and acclimated microorganism in high salinity wastewater system was intended to degrade organic pollutants. In the experiments, the dosage of ozone was 20 mg/L and contact time was 25 minutes for raw water. After ozonation, RO concentrate was stored for 12 hours in a storage tank, and then elevated into BAF with the hydraulic retention time of 2 hours. The result showed that the combined process had a little effect on degradation of organics, with only 11.8% of COD removal, which was difficult to reach the processing demands.Technical guarantee for industrial application was provided by the hybrid process with wide use of membrane technology. Powdered activated carbon (PAC) adsorption and microfiltration (MF) accumulative two-stage countercurrent adsorption process was put forward in this study. In the process, PAC was retained in the reactor by microfiltration, which could prolong the adsorption time of PAC, and play a great role in use of adsorption capacity. According to the theoretical calculation, accumulative two-stage countercurrent adsorption could save approximately 42.3% PAC than single-stage operation in the same adsorption. Moreover, the theoretical calculation was proved by jar test and bench-scale test, and DOC in the effluent could reach the target. In addition, it was favorable to control MF membrane fouling by adding PAC. MF membrane specific flux was recovered to 89.1% of the original one by physical cleaning after bench-scale test. Meanwhile, compared to other RO concentrate treatment technologies, hybrid process of PAC and MF as a promising treatment process was cost-effect and feasible.