A hybrid ultrafiltration membrane process using a low-cost laterite based adsorbent for efficient arsenic removal

Adsorption has proven to be most effective for arsenic removal. But standalone adsorption cannot cater to the need for large-scale treatment in centralized water supply systems. Combining adsorption with other low-pressure membrane processes may aid in scaling up and intensifying the overall arsenic removal. In the present pilot study, a low-cost laterite-derived adsorbent (LDA) has been used in combination with cross-flow ul-trafiltration (Ads-UF) to develop a strategy suitable for remediation of arsenic-contaminated water. Effect of adsorbent particles on permeate flux has been assessed at different transmembrane pressure (0.2-0.6 MPa). Two different hybrid configurations, with and without intermediate sand filtration (SF), i.e. Ads-SF-UF and Ads-UF, were considered. Resistance-in-series and combined complete pore block-cake layer models have been used to understand the flux profiles. In the case of arsenic-spiked groundwater, it was observed that flux decline, at 0.6 MPa, was 28% higher with Ads-UF during a 12 h run compared to Ads-SF-UF. Spent LDA retrieved from the sand column was found to retain the elemental composition as that of the unused LDA (as per FT-IR and EDX) and was considered safe for disposal based on Toxicity Characteristic Leaching Procedure (TCLP). Cost estimation for a facility with 200 m3/day treatment capacity has also been presented.

Automated summary

Adsorption is the most effective method for arsenic removal, but it cannot be applied in large-scale treatment in centralized water supply systems. In this study, a low-cost laterite-derived adsorbent (LDA) was combined with cross-flow ultrafiltration (Ads-UF) to develop a strategy for remediation of arsenic-contaminated water. The effect of adsorbent particles on permeate flux was assessed, and two different hybrid configurations were considered. The results showed that flux decline was higher with Ads-UF compared to Ads-SF-UF, and the spent LDA was found to be safe for disposal.