Chemical cleaning of algae-fouled ultrafiltration (UF) membrane by sodium hypochlorite (NaClO): Characterization of membrane and formation of halogenated by-products

This paper presents an investigation of the variation in membrane characteristics and formation of halogenated by-products during the off-line chemical cleaning of algae-fouled ultrafiltration (UF) membrane by NaClO solution. The chemical treatment led to the recovery of membrane flux, decrease of membrane hydrophilicity and HA rejection. Proteins, amino acids, and polysaccharides contained in algal cells were easy to adsorb on the membrane surface and contributed to the formation of halogenated by-products during the NaClO cleaning process. The increase of NaClO concentration and temperature significantly promoted the formation of most selected halogenated by-products. With the increase of pH, trichloromethane (TCM), dichloroacetic acid (DCAA) and trichloronitromethane (TCNM) rose continuously; monochloroacetic acid (MCAA), trichloroacetic acid (TCAA) and trichloroacetonitrile (TCAN) followed an increasing and then decreasing trend. With the prolonged exposure time from 2 to 24 h, most halogenated by-products from the cleaning of algal cell-, extracellular organic matter (EOM)- and humic acid (HA)-fouled membranes monotonically increased, while the formation of 1,1-dichloro-2-propanone (DCP) and dichloroacetonitrile (DCAN) varied differently. NaClO cleaning of algal cell-fouled membrane generated much lower concentrations of selected carbonaceous halogenated by-products and TCNM, but caused higher yields of haloacetonitriles (HANs) than that of HA-fouled membrane.