Importance of microbial adaptation for concentrate management in wastewater reuse process

Wastewater reuse has gained attention as an alternative and sustainable water resource. Reverse osmosis has been widely applied for wastewater reuse; however, generation of concentrate stream is the main drawback. Concentrate stream contains high concentrations of contaminants, and therefore, it should be properly treated prior to being discharged into a water body. Several technologies have been suggested for concentrate management, but the most common option is returning this stream to a wastewater treatment plant where a wastewater reuse plant is located. In this study, we investigated the feasibility of concentrate management by returning the concentrate to a wastewater treatment facility as a part of influent. The characteristics of the concentrate were extensively monitored, and it was verified that it contained high concentrations of salt and hardly biodegradable organics, which impede their application in biological wastewater treatment processes. The effect of seeding sludge was investigated using two different types of seeding sludge, adapted and unadapted. The adapted sludge taken at the wastewater treatment plant located at the wastewater reuse facility showed much better performance in terms of organic and nutrients removal. Moreover, the performance was recovered by a few days of additional adaptation time. However, the seeding sludge taken from another wastewater treatment plant (unadapted) showed poor performance due to different influent characteristics, especially salt concentration. Therefore, it could be concluded that the microbial adaptation step is very important for effective concentrate treatment when it is being returned to a wastewater plant as influent.