Treatment of silk production wastewaters by membrane processes for sericin recovery

Sericin protein, although a valuable resource for many industries including cosmetics, pharmaceutical and biomedical, has been discarded as a waste in silk industry, causing environmental pollution. This paper describes determination of a membrane-based process for sericin recovery from cocoon cooking wastewaters (CCW) that will enable value-added utilization of waste sericin. The iso-electric point (pI) of sericin was found as 5-6, whose MW was distributed as 180-200, 70-80, 30-40 and 10-25 kDa. Prior to membrane filtration. sericin was separated from other impurities via centrifugation (CFG) followed by microfiltration (MF) in the pre-treatment stage, which also helped minimize post membrane fouling. Ultrafiltration (UF) and nanofiltration (NF) were adopted at a pH equal to pI of sericin. UF achieved partial recovery of sericin polypeptides at 37-60%, which was attributed to increased transmission of uncharged sericin polypeptides at their pI. On the other hand, NF achieved sericin recovery as high as 94-95%, containing all MW fractions. Severe flux decline was the major problem due to protein-membrane interactions and high sericin concentrations, where concentration polarization mainly had a dominant effect. Although flux declines were as high as 58-88% in UF and 70-75% in NF, flux recovery by at least 83% was achieved by chemical cleaning using NaOH and free chlorine. (C) 2008 Elsevier B.V. All rights reserved.