The objective of this research was to investigate the performance of a hollow fibre membrane bioreactor (HFMB) for hydrogenotrophic denitrification of contaminated drinking water. In the HFMB, H2 flows through the lumen of the hydrophobic hollow fibres and diffuses to an attached H2 oxidizing biofilm. Nitrate in the contaminated water serves as an electron acceptor. A hydrogenotrophic denitrifying culture was enriched from a wastewater seed. Batch culture experiments were conducted to compare heterotrophic (methanol as electron donor) and hydrogenotrophic denitrification rates and to investigate the conditions required for the HFMB studies. The batch cultures demonstrated mixotrophy, with denitrification rates of 30 g NO−3 -N m−3 d−1 for heterotrophic and 18 g NO−3 -N m−3 d−1 for hydrogenotrophic conditions. A laboratory-scale HFMB was constructed that utilized 2,400 polypropylene hollow fibres with an inner diameter of 200 m, an outer diameter of 250 m and a 0.05 m pore size. After a 70-day start-up period, the NO−3 loading rate was gradually increased over a three-month period. The NO−3 utilization rate reached a maximum of 770 g NO−3 -N m−3 d−1 at an influent NO−3 concentration of 145 mg NO−3 -N l−1 and a hydraulic residence time of 4.1 hours. Influent NO−3 concentrations of up to 200 mg NO−3 -N l−1 were almost completely denitrified. Tests with contaminated water from the Cape Cod aquifer resulted in an increase in product water turbidity and dissolved organic carbon (DOC) concentrations.
Keywords: biological denitrification, bioreactor, drinking water, hydrogen, membranes, nitrate