Performance of a permeable reactive barrier for in situ removal of ammonium in groundwater

Nitrogen as ammonium (NH₄⁺-N) is one of the most common nitrogen contaminants in groundwater; this is particularly true in the industrial and agricultural regions of northern China, where rapid population growth and economic development have stressed public water supplies and reduced groundwater quality. In this study, we report the performance of a zeolite permeable reactive barrier (PRB) designed to remove ammonium from contaminated river water that infiltrates to a groundwater aquifer that serves as a drinking water supply for the city of Shenyang. Groundwater monitoring data obtained over 5 months of operation indicate that ammonium concentrations in the groundwater decreased from 2–10 mg/L to <0.5 mg/L after the PRB was installed in the vicinity. Data suggest that ammonium removal was mainly due to sorption and ion exchange, with NH₄⁺ exchanged with Na⁺ and K⁺ in the zeolite. After more than 1 year of continuous operation, there is no evidence of microbial ammonium oxidation. To our knowledge, this was the first field-scale demonstration of a PRB in China.