Nitrate Removal from Groundwater Using a Denitrification Wall Amended with Sawdust: Field Trial
- Louis Schipper * and
- M. Vojvodić-Vuković
Nitrate (NO3) contamination of groundwater can cause pollution of receiving waters. We examined the mechanisms by which a “denitrification wall” removed NO3 from shallow groundwater. The denitrification wall was constructed by digging a trench (35 m long, 1.5 m deep, and 1.5 m wide) that intercepted groundwater. The excavated soil was mixed with sawdust (30% v/v) as a C source then returned to the trench. We assessed NO3 removal and denitrification in the wall for 1 yr. Incoming concentrations of NO3 in groundwater ranged from 5 to 16 mg of N L−1 but these decreased to <2 mg N L−1 in the denitrification wall. Total N in the wall declined during the year demonstrating that N immobilization was not a large sink for NO3. Denitrifying enzyme activity (DEA) reached a maximum of 906 ng of N g−1 h−1 after 6 mo of operation, indicating that denitrification was an important mechanism for NO3 removal. We calculated a maximum rate of NO3 removal by denitrification of 3.6 g N m−3 d−1. Substrate-amendment experiments showed that denitrification in the wall was primarily limited by NO3 concentration and not C. During the study there was no significant decrease (P < 0.05) in total C but the availability of the remaining C declined. Despite this decrease, the DEA and microbial biomass were stable during the last 6 mo. This study demonstrated that denitrification walls can effectively remove NO3 from groundwater thereby protecting receiving waters.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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