Removing Atrazine from agricultural drainage water using woodchips bioreactors; effect of biochar amendment

Abstract. Cost effective in-situ techniques to remove contaminants from agricultural drain water are interesting engineering solutions to treat such waters. Denitrifying bioreactors are an edge-of-field bioremediation approach to remove Nitrate-N from agricultural drainage water. They facilitate denitrification by providing carbon substrates and an anaerobic environment and have been proven to lower nitrate concentrations in tile flow. With the carbon substrate, which usually is woodchips, biochar can be added to the bioreactors. Biochar, a product of thermal decomposition of biomass, has been shown to alter the nitrogen cycle in agricultural soils and to promote biological activities. In addition, biochar is an adsorbent for pesticides. This research examined the removal of atrazine in a woodchip substrate bioreactor and the effect of biochar amendment to the woodchips. Two types of laboratory bioreactors were employed. The first set was filled with wood chips only (W) and the second set with 50% biochar and 50% woodchips (WB). The effect of aerobic and anaerobic conditions and the presence and absence of nitrate – a competitor with atrazine as a nitrogen provider- on atrazine removal of the bioreactors was investigated. The results showed that the woodchips bioreactors removed 50% of the influent atrazine in 8 hours. The addition of biochar increased the removal of atrazine from 18% to 40%, compared to woodchips only. Addition of 10 mg L^-1 NO₃^--N decreased the atrazine removal by 5 to 15%. The aerobic condition had only a minor effect, possibly due to the existence of anaerobic packs in the porous W and WB bioreactors. Our laboratory findings that denitrifying bioreactors can remove both nitrate and pesticides from drain waters should be tested under field conditions and may prove to be an effective management option for decreasing the off-site impacts of agriculture on waterways.