Polyelectrolyte-Enhanced Ultrafiltration (PEUF) Process for Low Level Arsenic Removal: Recovery of Polyelectrolyte from Retentate Stream

Abstract

Removal of low levels of arsenic from contaminated water using the polyelectrolyte-enhanced ultrafiltration or PEUF process technology has been studied. The cationic polyelectrolyte poly (diallyldimethyl ammonium chloride), PDADMAC, was utilized to bind arsenic (in the form of arsenate anion) in contaminated water and the polyelectrolyte-arsenate complex solution was then filtered off (as retentate) by ultrafiltration. The 99-99.9% arsenic removal from synthetic low level arsenic (100 ppb) contaminated water demonstrates that the technology can easily achieve the relatively new international arsenic maximum concentration level of 10 ppb. To make the PEUF process more economical and environmentally friendly, the PDADMAC in the retentate must be recovered. Precipitation of PDADMAC-arsenate solutions with divalent cations has been studied to separate out metal-arsenate compounds leaving free PDADMAC to reuse in the process. The metal-arsenate compound precipitation is strongly affected by divalent metal:As molar ratio, and pH of the solution. The precipitation results also suggest that polyelectrolyte retards formation of the metal-arsenate compounds and affects the size and morphology of the particles formed, thus directly affecting the sedimentation rate of the resulting precipitate.