Biotreatment, typically made up of an anaerobic bioreactor followed by an aerobic bioreactor, is a key unit operation in a treatment plant for industrial wastewater because of its low cost and effectiveness in pollutant degradation. Textile industry consumes huge amount of water. The unfixed dyes after dyeing should be removed before discharge. The dyes can be biodegraded through anaerobic-aerobic process. They are first decolorized in an anaerobic process; then the decolorized products are mineralized in an aerobic process. Seeding a superior strain, or in a form of consortium, as well as supplementing appropriate nutrient are found to enhance the decolorization in a single dye case. Numerous dyes and insufficient nutrient in the real dyeing wastewater may, however, limit the applicati...[ Read more ]

Biotreatment, typically made up of an anaerobic bioreactor followed by an aerobic bioreactor, is a key unit operation in a treatment plant for industrial wastewater because of its low cost and effectiveness in pollutant degradation. Textile industry consumes huge amount of water. The unfixed dyes after dyeing should be removed before discharge. The dyes can be biodegraded through anaerobic-aerobic process. They are first decolorized in an anaerobic process; then the decolorized products are mineralized in an aerobic process. Seeding a superior strain, or in a form of consortium, as well as supplementing appropriate nutrient are found to enhance the decolorization in a single dye case. Numerous dyes and insufficient nutrient in the real dyeing wastewater may, however, limit the application of the superior strains.

Illustrated with four projects, we focus on anaerobic decolorization of the textile dyes for discussing the construction of the bacterial consortia and the selection of the appropriate nutrient in the industrial point of view. Azo dyes contribute to 70% of the textile dyes consumption. Project 1 demonstrates a procedure to construct consortia for decolorizing one of the azo dyes, reactive blue 250 (RB250). Consortia were constructed by simply combining the bacteria showing different decolorization abilities, which were first obtained through enrichment-isolation procedure from a given sludge followed by a well plate test for evaluation of decolorization ability. The performance on decolorizing RB250 of the consortia and the individual decolorizing strains were compared. The construction procedure and the comparison results were rationalized on the possible interactions among the pollutants, nutrients and bacteria. Anthraquinone dyes, the second major textile dyes, also present in the dyeing wastewater. In Project 2, different consortia were constructed using azo and/or anthraquinone dyes as model dye(s). Approaches of consortia construction for decolorizing a dyeing wastewater are discussed.

Nutrient, as a co-substrate, is necessary for decolorization. The decolorization performance may vary with different dye-nutrient combinations. Project 3 suggests a screening test to select an industrially feasible nutrient for optimum decolorization. For economic reasons, a minimum amount of nutrient addition is preferable. Project 4 aims at discussing the industrial nutrient replenishment strategy which includes the determination of the minimum nutrient concentration for desired decolorization efficiency. A membrane bioreactor was used to mimic the real anaerobic reactor.