title: Small-scale, hydrogen-oxidizing-denitrifying bioreactor for treatment of nitrate-contaminated drinking water.
abstract: Nitrate removal by hydrogen-coupled denitrification was examined using flow-through, packed-bed bioreactors to develop a small-scale, cost effective system for treating nitrate-contaminated drinking-water supplies. Nitrate removal was accomplished using a Rhodocyclus sp., strain HOD 5, isolated from a sole-source drinking-water aquifer. The autotrophic capacity of the purple non-sulfur photosynthetic bacterium made it particularly adept for this purpose. Initial tests used a commercial bioreactor filled with glass beads and countercurrent, non-sterile flow of an autotrophic, air-saturated, growth medium and hydrogen gas. Complete removal of 2 mM nitrate was achieved for more than 300 days of operation at a 2-h retention time. A low-cost hydrogen generator/bioreactor system was then constructed from readily available materials as a water treatment approach using the Rhodocyclus strain. After initial tests with the growth medium, the constructed system was tested using nitrate-amended drinking water obtained from fractured granite and sandstone aquifers, with moderate and low TDS loads, respectively. Incomplete nitrate removal was evident in both water types, with high-nitrite concentrations in the bioreactor output, due to a pH increase, which inhibited nitrite reduction. This was rectified by including carbon dioxide in the hydrogen stream. Additionally, complete nitrate removal was accomplished with wastewater-impacted surface water, with a concurrent decrease in dissolved organic carbon. The results of this study using three chemically distinct water supplies demonstrate that hydrogen-coupled denitrification can serve as the basis for small-scale remediation and that pilot-scale testing might be the next logical step.
authors.affiliation: Department of the Interior, Water Resources Division, US Geological Survey, 3215 Marine Street, Boulder, CO 80303, USA. rlsmith@usgs.gov
authors.forename: Richard L
authors.initials: RL
authors.lastname: Smith
authors.forename: Seanne P
authors.initials: SP
authors.lastname: Buckwalter
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Repert
authors.forename: Daniel N
authors.initials: DN
authors.lastname: Miller
mesh_terms: D019149:Bioreactors; D002244:Carbon / Q000032:analysis / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D009930:Organic Chemicals / Q000032:analysis / Q000378:metabolism; D010084:Oxidation-Reduction; D043362:Rhodocyclaceae / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000378:metabolism; D018508:Water Purification / Q000295:instrumentation / Q000379:methods; D014881:Water Supply
chemical_list: D009566:Nitrates; D009573:Nitrites; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D002245:Carbon Dioxide; D002244:Carbon; D006859:Hydrogen