Comparison of ceramic and polymeric nanofiltration membranes for treatment of abandoned coal mine drainage

Performance of ceramic and polymeric nanofiltration membranes for treatment of abandoned mine drainage from a coal mine was investigated in this study. The increase in permeate recovery improved ionic rejection but reduced the permeability for both membranes. Arsenic was poorly rejected by both membranes with maximum rejection being 33% for the polymeric membrane. Fouling occurred at 75% permeate recovery and was dominated by gypsum scales. Chemical cleaning improved permeability but reduced ionic rejection indicating a slight increase in the effective membrane pore size for both membranes. When feed pH was adjusted to 4, ionic rejection increased for the ceramic membrane and decreased for the polymeric membrane due to impacts on the charge of the active layer. Addition of antiscalant improved ionic rejection for both membranes, especially for arsenic whose rejection improved by at least 141%, but resulted in about 40% decrease in permeability for both membranes and was attributed to the formation of a more complex and gel-like scale. A tighter polymeric nanofiltration membrane achieved >99% rejection of all multivalent ions to meet all drinking water standards except for arsenic, which has to be removed prior to nanofiltration step.