Successful Pilot Testing of Nanofiltration for Sulfate Removal from Mine-Influenced Water

A pilot study evaluates nanofiltration combined with gypsum precipitation for sulfate removal from mine-influenced water to achieve NPDES permit compliance. The UF-NF treatment train with chemical precipitation achieved 85% recovery in initial operations. Analysis of concentrate composition shows elevated sulfate (4,032 mg/L), calcium (463 mg/L), and magnesium (1,015 mg/L) requiring management through chemical precipitation. Pilot results indicate that calcite precipitation for secondary treatment is not necessary if higher recovery is not required, reducing system complexity. Key operational findings highlight high maintenance requirements for chemical precipitation and the importance of establishing optimal pH and sludge recirculation parameters for effective gypsum settling and residuals handling.