Microfiltration of a Dental Wastewater for Hg Removal: Clinic Demonstration

Hollow fiber (HF) and tubular membranes were installed at a dental clinic and used to treat dental wastewater (DWW) over a six-month period. Both membranes rejected the vast majority of the Hg (Tubular: 99% rejection and permeate Hg=20.8 μg/L; HF: 97% rejection and permeate Hg=6.6 μg/L). Permeate Hg concentration and flux were not adversely affected by concentrating the DWW indicating that the system can be operated indefinitely. Biological growth blocked the openings of the HF lumens necessitating frequent maintenance. The tubular membrane with its large channel diameter (2.53 cm versus 1 mm for the HF) did not experience channel blockage. Given the small volume of DWW that is produced at a dental facility (≈3 L/d), the packing density and footprint of the membrane unit are not a major concern, thus, HF module offers no real advantage over the tubular module. Additionally, the increase maintenance that is required with the HF module is a distinct disadvantage making the tubular module better suited for dental facilities.