Assessment of the use of a zero-valent iron permeable reactive barrier for nitrate removal from groundwater in the alluvial plain of the Dagu River, China

Groundwater in a shallow aquifer used for potable supply in Qingdao, China, has been contaminated by nitrate by the excessive use of chemical fertilisers for vegetable production in the area. In this study, a representative site was selected to construct a non-continuous permeable reactive barrier (PRB) back-filled with a mixed reactive medium containing of zero-valent iron, activated carbon and medium- to coarse-grained sand. The PRB consists of alternate well and pillars and was constructed to provide a funnel and gate treatment system for two pumping wells. Groundwater monitoring during a trial of the system indicated that the concentrations of nitrate in monitoring wells within the treatment system rapidly declined (within a day) from about 120 mg/L to 20 mg/L. Reductions in nitrate concentrations were also observed in the pumping wells and downgradient monitoring wells, but changes in nitrate concentrations were moderated by mixing with contaminated groundwater. The PRB construction technique of using alternative wells and pillars combined with jet grouting was found to be effective for nitrate removal from groundwater at a small scale.