Arsenic removal using the membrane distillation process

Abstract

Arsenic is a carcinogenic element distributed in the earth's crust around the world. And arsenic poisoning has been frequently reported from the counties using the groundwater as a drinking water. In order to remediate the arsenic compounds from the water environment, the membrane distillation process is suggested in this study. Compared to the other conventional treatments (adsortion, coagulation, oxidation), the membrane distillation process has advantages to separate the toxic and highly mobile arsenite from the contaminated water sufficiently. A flat sheet type PTFE/PP composite membrane was studied in direct contact membrane distillation (DCMD) process to suggest the optimized remediation metheds for the arsenic and other contaminants from the contaminated water. Five different membranes were analyzed by characterizing membrane structure and material to suggest the optimized MD membrane and process. The PTFE/PP composite membrane showed the better flux compared to the other tested membranes. The heat and mass transfer modelling were conducted to calculate temperature variation across the membrane and the tortuosity to analyze the MD process. Using the external concentration polarization model, the arsenic and ion concentration on the membrane surface was estimated at the given conditions. By using the optimized MD system, the groundwater, the acid mine drainage (AMD), and the municipal waste water were remediated. The arsenite was dominant species in the groundwater due to low oxidation-reduction potential and treated successfully by the MD process. To simulate the field test, no pre-treatment process was carried out for the AMD and the municipal waste water. No flux reduction or the membrane fouling was observed during operation up to 420 min. The concentrations of arsenic, chromium, copper, lead, zinc, cadmium, and iron in the permeate was detected below the permissible level for the drinking water in Korea. The energy requirement (3.06 kWh/m3) of the MD system tested in this study was the huge. However, if the flux of the MD system is considered, the flux-energy ratio of the MD system tested in this study was 18 - 23 according to the feed ion concentration. This result shows that the MD process using the PTFE/PP composite membrane has a commercial potential.