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Treatment of reverse osmosis concentrate using an algal-based MBR combined with ozone pretreatment
Citation:
Woo, H., H. Yang, T. Timmes, C. Han, J. Nam, S. Byun, S. Kim, H. Ryu, AND H. Kim. Treatment of reverse osmosis concentrate using an algal-based MBR combined with ozone pretreatment. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 159:164-175, (2019). https://doi.org/10.1016/j.watres.2019.05.003
Impact/Purpose:
Reverse osmosis (RO) technology is increasingly adopted for the tertiary treatment and indirect reuse of secondary wastewater effluent. The concentrate, resulting from the filtration processes, remains a challenge to treat for the aquatic environment primarily due to the volume and the quality of the direct discharge. Reverse osmosis concentrates (ROC) typically contains high concentrations of inorganic salts and organic compounds. Due to their recalcitrance to microbial degradation, various integrated treatment strategies combined with complementary technologies for removing the compounds have been considered and investigated to minimalize the adverse impacts on the aquatic environment that are associated with the direct surface discharge of ROC. These strategies generally focused on reducing the organic pollutant loading into the environment from wastewater treatment facilities. The combination of bioremediation and physiochemical treatment is desirable for further removal of biodegradable fractions and inorganic nutrients prior to surface water discharge. To date, the authors have screened diverse algal species to determine their adaptability in the context of phycoremediation, selected the best candidate based on several criteria, and applied to the treatment of a wide range of refractory wastewaters. In the latest work, the authors have demonstrated that the treatment of synthetic ROC with Scenedesmus quadricauda is highly feasible to remove inorganic nutrients, reduce enteric bacteria, and degrade trace organic compounds (TOrCs). Various advanced analytical tools were employed to determine the viability of algal cells as bioagents during ROC treatment, to investigate the fate of organic compounds through the treatment of ROC, and to characterize the physicochemical properties of foulants retained on the surface of membranes. This study also investigated a novel alternative method to restore the permeability of organic-fouled membranes using an in-situ cleaning strategy forgoing the use of caustic chemicals. In addition to the concurrent removal of organic and inorganic components in a single biological process, this in-situ cleaning offers operational simplicity and adaptability to existing membrane facilities that currently perform periodic chemical cleaning.
Description:
Algal treatment was combined with pre-ozonation for the treatment of synthetic reverse osmosis concentrate (ROC) prior to microfiltration (MF). The research was mainly focused on minimizing the fouling of polyvinylidene fluoride (PVDF) membranes and maximizing the restoration of membrane permeability. The algal treatment alone was moderately effective for the mitigation of fouling in MF, while a better performance was achieved when the algal treatment followed ozonation. The combination of ozonation and algal treatment reduced membrane permeability decline and significantly increased the reversibility of fouling after hydraulic washing. A longitudinal evaluation was also performed with a goal of achieving a longer-term sustained removal of contaminants. Ozonation followed by algal treatment was very effective in attenuating fouling from both caffeine and carbamazepine, as well as removing polymeric organic matter and inorganic nutrients from ROC in a single bioreactor. In this study, an alkaline condition, produced by microalgae in the light without supplemental aeration was applied for in-situ cleaning of fouled membranes. The result showed that the algal-induced cleaning successfully restored the permeability of organic-fouled membranes during the filtration of both raw and algal-treated ROC. This in-situ strategy offers a novel option for periodic cleaning of fouled membranes while maintaining operational simplicity, especially for existing submerged membrane filtration facilities. While the feasibility of incorporating microalgae with membrane cleaning has been established, additional pilot-scale research and case studies using non-synthetic ROC, are recommended to better comparatively evaluate the performance of wastewater remediation with microalgae.
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DOI: Treatment of reverse osmosis concentrate using an algal-based MBR combined with ozone pretreatment
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