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ARS Home » Plains Area » Lincoln, Nebraska » Agroecosystem Management Research » Research » Publications at this Location » Publication #199493
Title: Small-scale, hydrogen-oxidizing-denitrifying bioreactor for treatment of nitrate-contaminated drinking water

Author
item SMITH, RICHARD - U.S. GEOLOGICAL SURV
item BUCKWALTER, SEANNE - U.S. GEOLOGICAL SURV
item REPERT, DEBORAH - U.S. GEOLOGICAL SURV
item Miller, Daniel

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2005
Publication Date: 8/1/2006
Citation: Smith, R.L., Buckwalter, S.P., Repert, D.A., Miller, D.N. 2006. Small-scale, hydrogen-oxidizing-denitrifying bioreactor for treatment of nitrate-contaminated drinking water. Water Research 39:2014-2023.

Interpretive Summary: The movement of nitrogen through aquifers in contaminated groundwaters is complex and hard to predict due to its potential to transform into a variety of compounds which interact to varying degrees with aquifer substrate. In this report, the movement of nitrate, ammonium, and nitrogen gas along with the abundance of natural N-isotopes and the results of an isotopic tracer test with ammonium are used to describe the long-term movement and fate of nitrogen in a sewage-contaminated aquifer. Ammonium within the core of the plume was unreactive and moved a quarter of the rate of groundwater flow. At the upper interface of the ammonium plume where oxygenated water was present, there was evidence for a slow conversion of ammonium to nitrate, which subsequently moved at the same rate as groundwater flow. Without intervention, the bulk of the ammonium would eventually discharge with little conversion to nitrate or nitrogen gas.

Technical 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.