Nitrate management in a rural drinking water supply

Abstract

Bench-scale biological denitrification experiments were performed to evaluate efficiency of a local agricultural waste product, cornstalk, as a carbon feedstock, compared to a traditional feedstock, acetate, and to ion exchange. Additionally, a rural drinking water supply was monitored over a 16-month period to determine nitrate concentrations and establish baseline water quality conditions in wells and in the distribution system. Over the monitoring program, four groundwater wells remained consistently below the 10 mg/L MAC for nitrate, while levels in a fifth supply well were consistently near or above the MAC, with an average concentration of 8.36 ± 4.26 mg/L NO3−-N. Nitrate concentrations in a local private well were also regularly above the MAC, averaging 13.94 ± 9.71 mg/L NO3−-N. CSMR levels at all sampling points were well above the threshold that indicates potential lead corrosion – a factor to consider when evaluating nitrate treatments. Acetate columns were highly effective, achieving 95% nitrate removal in groundwater. Cornstalk columns achieved removal rates of 35% and 49% by single columns and two columns in series, respectively. Results were compared to ion exchange using a commercial nitrate-selective resin. Removal of approximately 10 mg/L of nitrate from an initial concentration of 20 mg/L were achieved near 300–400 bed volumes; however, CSMR would be expected to increase by 0.34 for every mg/L of NO3−-N removed.