HYDROGENOTROPHIC WASTEWATER DENITRIFICATION USING HOLLOW FIBER MEMBRANE BIOREACTORS

Two membrane module configurations (Type I and Type II) were studied for denitrification of nitrate contaminated water using hydrogen (H2) as an electron donor. In both systems, hollow fiber membrane gas transfer modules were used to supply H2 to a denitrifying biofilm. In the Type I system, denitrification took place on the shell side and in Type II system denitrification took place on the lumen side of the fibers. Two bench scale hollow fiber membrane bioreactors (HFMBs) were constructed and investigated for treatment of nitrate contaminated water in a continuous process. Hydraulic retention time (HRT), influent oxygen concentration, and influent wastewater composition were varied during the experiments. Mass transfer models were developed for Type I and Type II systems and used to compare overall mass transfer coefficients for these systems. Acclimatized batch cultures from a wastewater treatment plant were used to inoculate the two HFMBs. A HRT of 8.7 hours was optimized for Type I system while a HRT of 10 hours was maintained in the Type II system. High nitrite concentrations were observed in both the systems during the initial acclimation phases, possibly due to organic carbon limitations. Nitrite accumulation was also observed during periods of pH stress, which were overcome by replacing periodic carbon dioxide sparging with bicarbonate addition to the feed water. Clogging problems were more frequent for the Type II system due to the accumulation of biomass in the narrow lumen of the membranes. Biomass clogging was rectified by periodically backwashing with the influent wastewater.