Microfiltration of a dental wastewater (DWW) for Hg removal

A tubular membrane (MWCO = 200 k, PVDF, negative surface charge) and a hollow-fiber (HF) membrane (MWCO = 500 k, PS, neutral surface charge) underwent testing to determine their effectiveness in treating a sterilized wastewater from a dental clinic. The tubular membrane, which had a lower MWCO, produced a higher permeate flux due to the increased turbulence at the membrane surface that was possible with the tubular configuration (Reynolds numbers for the tubular module were over five times greater than the HF module). Both membranes had similar Hg rejections (tubular - 97%, HF - 98%) and permeate Hg concentrations ( less than or equal to 10 mu g/L) due to particle size distribution of dental wastewater - the vast majority of the amalgam particles were larger than the pore size of either membrane. Permeate Hg was not a function of temperature, feed concentration, and intermittent operation. Because of their unique behavior and characteristics, both the HF and tubular modules will be tested at an actual dental clinic using nonsterilized dental wastewater.