The extraction of sericin protein from silk reeling wastewater by hollow fiber nanofiltration membrane integrated process

Sericin protein having high additional value in many industries such as textiles, pharmaceuticals and cosmetics is always discharged in silk reeling wastewater which causes serious environmental pollution. In this paper, different combined process of acidulation precipitation-ultrafiltration (UF)-nanofiltration (NF) was investigated and optimized to recover high-purity sericin protein from silk reeling wastewater. Inner-pressure hollow fiber polyamide NF composite membrane was prepared through the interfacial polymerization. The results showed that the recovery of sericin protein in the supernatant liquid after acidulation precipitation treatment could reach 72.1% when using the UF membrane (MWCO 6000)-NF membrane integrated process. When the mixture of sericin protein precipitation and concentrated liquid after UF and NF filtration was diluted four times, the better comprehensive results were achieved. The loss rate of sericin protein and the salt content of concentrated liquid was 34.1% and 29.1%, respectively while the conductivity after UF membrane treatment was lower than that of the local tap water. More than 86% sericin protein from cocoon cooking wastewater, refining wastewater and mixed wastewater could be recovered by the optimized UF-NF combination process. Using 0.2 mol L-1 hydrochloric acid as the cleaning agent could effectively recover the water flux of NF membrane. (C) 2015 Elsevier B.V. All rights reserved.