Membrane pretreatment and cleaning – mixed oxidants in practice
The prevalence of membrane filtration is rapidly growing in both the municipal and industrial water sectors. As membrane chemistries improve, so too do operational capacities and process requirements. Two main activities that contribute to membrane efficiency and lifetime are membrane pretreatment and membrane maintenance. Maintenance may be further differentiated into periodic backwashing and cleaning to remove particulates and biological/organic fouling. This article focuses on a technology – chlorine-based mixed-oxidant solution (MOS) – that assists in oxidizing and removing organics during membrane pretreatment and then acts as a disinfectant to remove biofoulants from membrane surfaces. Operational experience shows that pretreatment oxidation often eliminates the need for frequent backwashing while periodic or continuous mixed-oxidant feed prevents biofilm regrowth on ultrafiltration (UF) membranes. Studies indicate that mixed oxidants will remove biofilm from cellulose acetate and polyamide membranes as well.