Batch process of polymer-enhanced ultrafiltration to recover mercury (II) from wastewater

• Mercury (II) removal by polymer enhanced ultrafiltration (PEUF).
• Membrane fouling in PEUF was related to surface thermodynamics of the system.
• Modeling of batch PEUF process based on mass balance.

The removal of mercury (II) from water by polymer-enhanced ultrafiltration (PEUF) was carried out using polyethylenimine (PEI), polyvinylamine (PVAm) and poly(acrylic acid) (PAA) as the metal-binding polymers. All three water-soluble polymers had strong interactions with mercury (II) in aqueous solutions, and a high mercury rejection was achieved with PEUF. At a given polymer dosage, the permeate flux followed the order of PVAm > PEI > PAA, presumably due to different physiochemical properties (e.g., viscosity and interfacial property) of the solution systems. Membrane fouling by PVAm and PEI in cross-flow mode was insignificant, but the flux decline due to fouling by PAA was not negligible. The batch operation of PEUF was modeled based on mass balance, and the applicability of the model equations was validated with experimental data. For a given system, the mercury content in the concentrated retentate, the mercury retention rate, the batch time and membrane area needed to achieve a desired separation task could be predicted if prior knowledge of concentration dependences of permeate flux and solute rejection were known. The effects of the amount of feed solution to be treated per unit membrane area on the separation performance of batch PEUF was analyzed.