Biological treatment of reverse osmosis concentrate from low salinity water

With increasing water demand and growing scarcity of potable water, the reuse of water recovered from low salinity water like sewage or surface water is becoming an important issue from both technical and economic points of view. The reverse osmosis (RO) membrane processes widely used for water recovery inevitably produce RO concentrate having very high concentrations of salts and other materials of concern. Disposal to nature or feeding back into the recovery facility can be an option, but may have an impact on environment and raise legal problems. This study deals with the biological treatment of RO concentrate produced during water reclamation processes. The RO concentrate studied had low BOD₅ and T-P, but high T-N and COD concentrations. The sequencing batch reactor (SBR) process and the modified Ludzack-Ettinger (MLE) process were compared in controlled lab-scale experiments. The pilot-scale plant was operated to evaluate the performance of the SBR process under more realistic conditions. Kinetic parameters such as specific substrate utilization rate (SSUR), specific nitrification rate (SNR), and specific denitrification rate (SDNR) were obtained, and empirical equations were derived relating these parameters to the food-to-micro-organism (F/M) ratio. These parameters could prove useful tools for process design, operation, and improvement of anoxic and aeration tanks. Non-biodegradable COD components in the RO concentrate turned out to be hard to remove, which implies some physical or chemical process (e.g. flocculation, precipitation, or adsorption) may be needed in addition to the biological treatment process.