Concurrent transport and removal of nitrate, phosphate and pesticides in low-cost metal- and carbon-based materials
D. Tong, J. Zhuang, J. Lee, J. R. Buchanan, and X. Chen.  2019.  Chemosphere, 84-91.

Low-cost Mg- and/or carbon-based materials have a great potential to remove soluble containments from surface- and ground water. This study examined mechanisms that control the removal of nitrate, phosphate and pesticides (tricyclazole, malathion and isoprothiolane) during their transport through calcined magnesia (MgO) and corn stalk biochar. Various miscible column breakthrough experiments were carried out and morphology and crystallographic structures of reactive materials were examined. Approximately 96% (17,827 mg-N kg-1) and 48% (6,200 mg-N kg-1) of nitrate were removed from biochar and MgO columns, respectively. Chemical adsorption dominated nitrate removal during early phase (i.e., <11 PVs for biochar and <100 PVs for MgO, respectively), and microbial denitrification dominated during the following phase. Abour 92% of the applied phosphate (2,014 mg-P kg-1) was removed in MgO column, while much less in biochar column (4%, 113 mg-P kg-1). Mineral surface analyses confirmed that electrostatic attraction, ligand exchange, and chemical precipitation were responsible for phosphate removal. For the three pesticides, biochar (1,260~2,778 mg/kg) exhibited larger removal capacity than MgO (28~2,193 mg/kg) due to the more functional groups on the surface of biochar. The removal of pesticides varied due to their physic-chemical properties. Malathion had highest removal rate (98~100%, 2,193~2,778 mg/kg), attributing to chemical sorption and bio-degradation, followed by isoprothiolane (47~79%, 950~1,260 mg/kg) and tricyclazole (28~1,962%).