Removal of arsenic from water using adsorption on alumina/membrane separation.

Abstract

A novel process has been developed to remove arsenic from wastewater and contaminated water effectively. The process consists of three major steps: adsorption of arsenic on finely dispersed activated alumina, separation of adsorbent particles from the liquid phase via membrane separation, and regeneration of the adsorbent. The effect of process parameters such as pH, residence time, adsorbent characteristics, presence of competing ions, and initial arsenic concentration were studied. A number of commercially available alumina samples were characterized and tested. Spent activated alumina was successfully regenerated at pH 12, using sodium hydroxide, and reused. Up to 70% of the adsorbed arsenic was desorbed during the regeneration of spent alumina. Arsenic concentrations of less than 50 $\mu$g/L were obtained within 10 minutes from initial arsenic levels of greater than 40 mg/L. The best samples of alumina were those with the smallest particle size (4 $\mu$m in diameter) and the largest surface area (880 m$\sp2$/g). The optimum pH for the arsenic removal was found to be in the range of 2 to 5. The effect of sulphate as a competing species on the overall rate of the adsorption process was not significant for sulphate concentrations of up to 100 mg/L. Two different membrane systems were tested for the separation of the alumina particles from treated water: (1) a hollow fibre membrane module with a pore size of 200,000 molecular cut-off and a surface area of 0.5 m$\sp2$ and (2) an ENKA polypropylene Tubular membrane with a nominal pore size of 0.2 $\mu$m and a surface area of 0.036 m$\sp2.$ Adsorbent concentrations of up to 60 g/L were easily handled by the membrane systems tested and a stable flux over a period of one day was observed. (Abstract shortened by UMI.)