The innovative application of agriculture straw in in situ field permeable reactive barrier for remediating nitrate-contaminated groundwater in grain-production areas

Large amounts of straw produced each year are currently wasted. A potential use of this resource in permeable reactive barriers (PRBs) for the denitrification of polluted groundwater has not previously been reported. In this study, a field PRB filled with straw-based materials was installed to reduce nitrogen transport in the Huaihe River Basin. In initial laboratory-scale experiments, wheat straw, corn straw, corncobs, and woodchip substrates were investigated through elemental analysis, leaching experiments, and their functional gene abundance. The carbon and nitrogen contents of the substrates were 39.62-48.17% and 0.64-1.07%. Corn-straw (15.12 mg g(-1)) and wheat straw (8.04 mg g(-1)) exhibited higher leaching of total organic carbon (TOC), in the presence of denitrification functional genes. All agricultural waste released chromaticity (up to 750 degree) and nitrate, nitrite (< 0.05 mg g(-1)), and ammonium (< 0.30 mg g(-1)) ions. The field PRB filled with processed straw materials as substrates exhibited nitrate removal rates of 60-90% and minimal secondary pollution, due to biochemical coupling reactions. Hence, straw waste is a suitable alternative to woodchip for in situ PRB fillers.