Simultaneous arsenite and nitrate removal from simulated groundwater based on pyrrhotite autotrophic denitrification

In this study, pyrrhotite is applied to remove arsenite (As(III)) and NO₃^- from groundwater simultaneously. Batch experiments find that sulfur autotrophic denitrifiers are not inhibited by As(III) with concentration up to 70 mg·L^-1, and pyrrhotite autotrophic denitrification (PAD) can effectively remove As(III), NO₃^- and PO₄^3- simultaneously. Treating water with As(III) 874.50±32.76 µg·L^-1, NO₃^--N 30 mg·L^-1, and PO₄^3--P 0.5 mg·L^-1, the pyrrhotite-sulfur-limestone autotrophic denitrification (PSLAD) biofilter can achieve effluent with total Arsenic (As) 7.84±7.29 µg·L^-1, NO₃^--N 3.78±1.14 mg·L^-1, and PO₄^3--P below detection limit at hydraulic retention time 6 h. In the PSLAD biofilter, Thiobacillus is the most abundant bacterium, and it uses pyrrhotite and sulfur as electron donor to reduce NO₃^-, and basically Fe²⁺ and As(III) are oxidized to Fe³⁺ and arsenate, respectively. As and PO₄^3- were mainly removed through precipitates FeAsO₄ and FePO₄, respectively. Technology based on the PAD is a simple, cost-effective and efficient way for remediation of As(III) and NO₃^- co-contaminated groundwater, and avoiding contaminants transference between groundwater and surface water.