Biological denitrification of reverse osmosis brine concentrates: II. Fluidized bed adsorber reactor studies

This phase of the study (Part II) investigates the application of a high-rate fluidized bed adsorber reactor (FBAR) process for biological denitrification of reverse osmosis (RO) brine concentrate. The companion paper (Part I) reported the first phase of the project, describing the batch and chemostat biokinetic studies employed for evaluating the process feasibility, and for optimizing the reaction conditions including the carbon and energy source, pH, temperature, and the carbon-to-nitrogen ratio. This paper describes the next stage of the study involving FBAR experiments using granular activated carbon (GAC) for denitrification and sulfate reduction conducted at different hydraulic retention times, and nitrate concentrations. These experiments showed that nitrate removal efficiencies in excess of 99% were achieved. Similar FBAR experiments conducted with sand showed that initially less nitrate removal was experienced, but under steady-state conditions over 99% removal was achieved. Additionally, this study examined the simultaneous denitrification and sulfate removal in a similar FBAR process. A second FBAR, employed to remove the remaining sulfate from the first FBAR, achieved over 99% removal. A biofiltration process was designed and operated to effectively eliminate hydrogen sulfide in the sulfate-reducing FBAR process. The sulfate reduction FBAR was also responsible for the removal of toxic metals and metalloids present in the brine concentrate by a combination of sulfide precipitation and sorption onto iron sulfides.