A novel membrane-based integrated process for fractionation and reclamation of dairy wastewater

•An integrated process recycles water, caseins, whey proteins and lactose.•This process can mitigate the sludge/retentate disposal and membrane fouling.•IP-UF pretreatment greatly reduces fouling and concentration polarization of NF.•NF retentate with concentrated lactose is obtained with IP-UF pretreatment.•Fermentation fed by NF retentate with IP-UF pretreatment produces more LA.

An integrated isoelectric precipitation (IP) - ultrafiltration (UF) - nanofiltration (NF) - lactic acid (LA) fermentation process was established for recovering water, proteins, cells and LA from model dairy wastewater (MDW). This process could solve the problems of sludge/retentate disposal and membrane fouling during membrane-based wastewater treatment. The IP process greatly retarded concentration polarization and fouling of UF. However, PES membrane was still severely fouled by whey proteins. XPS results showed that carboxyl groups (CO) belonging to the proteins was on PES10 surface, but it was not found on Ultracel PLGC membrane. Proteins in MDW with IP were completely retained by Ultracel PLGC UF membrane and lactose almost passed through. After IP-UF pretreatment, the fouling of NF membrane was greatly retarded (irreversible fouling decreased from 44.4% to 11.1% in a pilot-plant test). Thus, the volume reduction ratio was highly increased to 37 and the retentate with high strength lactose of 44.2 g L−1 was obtained. With a model NF retentate (45.0 g L−1 of lactose) without proteins, 5.42 g L−1 of cell mass and 37.6 g L−1 of LA concentration were produced by the LA producer B. coagulans IPE22.

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