A major technological concern with reverse osmosis in water purification, wastewater treatment, and water reclamation or recycling is the production of brine concentrates high in ammonia or nitrogen. This project addresses biological denitrification of reverse osmosis brine concentrates in a bioactive fluidized bed adsorber reactor (FBAR), accomplished in four stages. The first three stages are described in this paper, while the final stage is addressed in the companion paper (Ersever et al. 2007). The first stage optimized an FBAR to produce nitrified brine for subsequent denitrification studies. The second stage employed batch reactors to evaluate denitrification parameters such as temperature, pH, total dissolved solids, and carbon-to-nitrogen ratio. The specific denitrification rate was maximum at a temperature of 35 °C, pH of 8.0, and carbon-to-nitrogen ratio of 1.8. The third stage involved chemostats to determine Monod parameters under nitrate-, nitrite-, and carbon-limiting conditions. A biokinetic model was employed to simulate chemostat dynamics and to estimate the biological parameters. The final stage entailed FBAR denitrification experiments under different hydraulic retention times, nitrate concentrations, and packing media; simultaneous denitrification and sulfate reduction were addressed. A second FBAR used in series with the first achieved an overall sulfate reduction of 99%, and a biofilter effectively removed the hydrogen sulfide generated.

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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.Résumé : Cette phase de l'étude (Partie II) examine l'application d'un procédé avec réacteur adsorbeur à lit fluidisé (FBAR) de haut débit à la dénitrification d'un concentré de saumure obtenu par osmose inverse. L'article complémentaire (Partie I) examine la première phase du projet et décrit les études en discontinu et de biocinétique des chémostats utilisés pour évaluer la faisabilité du procédé et pour optimiser les conditions de réaction, dont la source de carbone et d'énergie, le pH, la température ainsi que le rapport carbone-azote. Le présent article décrit la prochaine étape de l'étude impliquant des expériences par FBAR utilisant du charbon actif granulaire pour la dénitrification et la sulfatoréduction réalisées à divers temps de rétention hydraulique et concentrations de nitrates. Ces expériences indiquent que l'efficacité de dénitrification dépassait 99 %. Des expériences similaires avec FBAR effectuées avec du sable indiquent qu'au début une dénitrification inférieure mais que, sous des conditions stables, une élimination supérieure à 99 % est atteinte. De plus, cette étude examine la dénitrification et l'élimination simultanées des sulfates dans un procédé FBAR similaire. Un deuxième FBAR utilisé pour éliminer les sulfates résiduaires du premier FBAR a atteint une élimination supérieure à 99 %. Un procédé de biofiltration a été conçu et exploité pour éliminer efficacement les sulfures d'hydrogène dans le procédé sulfatoréducteur du FBAR. Le FBAR de sulfatoréduction élimine aussi...