Large volumes of wastewaters containing proteins (mainly sericin), salts and tensioactives are produced in the degumming process (washing) of both yarn and tissues made from natural silk. These wastewaters bearing a COD above 6000 mg/l are generally treated in biological plants with increasing costs. Sericin represents, on the contrary, a valuable by-product that can be used in cosmetics and pharmaceutical production. To reduce treatment costs and at the same time to recover sericin and reuse process water, a hybrid membrane process is under study. Laboratory and field experiments show that ultrafiltration of the degumming waste solution with different membranes (with molecular weight cut-off in the 20-30,000 dalton range) allows recovery of more than 97% of the sericin but the permeate COD level exceeds 800 mg/l whose value is still too high for water reuse. A final reverse osmosis treatment on the ultrafiltration permeate allows reaching a low COD level (50 mg/l) and recovery of more than 70% of the wastewater for process reuse. Alternative process flow sheets for the silk degumming solution treatment are discussed on the basis of the obtained results.

Cited By (since 1996): 24Export Date: 21 January 2011Source: Scopus