Fully recycling dairy wastewater by an integrated isoelectric precipitation-nanofiltration-anaerobic fermentation process

A novel integrated isoelectric precipitation-nanofiltration (NF)-anaerobic fermentation process was proposed for fully recycling model dairy wastewater (MDW). Isoelectric precipitation at pH 4.80 and subsequent centrifugation could remove most proteins. Acetic and butyric acids from anaerobic fermentation were available for acidic precipitation, and the performance was comparable to that of hydrochloric acid. The pretreatment of MDW by precipitation could greatly retard NF membrane fouling, especially at pH 7.09 owing to the electrostatic repulsion between solutes and membrane. NF270 membrane was preferred for MDW concentration due to its high antifouling performance, high permeability and acceptable permeate quality. Anaerobic fermentation fed with model NF retentate without caseins produced higher proportion of acetate, butyrate and hydrogen, and this effluent with shorter-chain volatile fatty acids (VFAs) and lower pH was more suitable for casein precipitation in dairy wastewater. (C) 2015 Elsevier B.V. All rights reserved