SULFATE REMOVAL FROM INDIGO DYEING TEXTILE WASTEWATERS

Sulfate is an important parameter especially for discharges to sewer s ystems. The textile industry is a major source of sulfate. Some sulfat e sources in the industry have material replacement alternatives. Howe ver in some sources, sulfate or species convertible to sulfate are the main materials. The indigo dyeing process involves sulfur species as main materials. In this study, indigo dyeing wastewaters which contain significant concentrations of oxidized and non-oxidized sulfur compon ents are evaluated in terms of sulfate removal. The approach is a pret reatment at the source before being mixed with other wastewaters. The study is conducted in two steps. In the first step, conversion of spec ies to either sulfide or sulfate is experimentally evaluated. While re duction to sulfide poses problems, oxidation of all species to sulfate is found to be applicable. In the second step sulfate precipitation u sing calcium, barium and lead is practiced. Calcium precipitation prov ides up to 30% sulfate removal and these results are supported with ex isting literature data. Barium sulfate and lead sulfate precipitation provided practically complete removal. Economical evaluation of altern ative methods is also given. Copyright (C) IAWQ 1996. Published by Els evier Science Ltd.