International Journal of Environmental Research and Public Health Article The Comparative Study on the Rapid Decolorization of Azo, Anthraquinone and Triphenylmethane Dyes by Anaerobic Sludge Daizong Cui †, Hao Zhang †, Rubao He and Min Zhao * College of Life Science, Northeast Forestry University, Harbin 150040, China; [email protected] (D.C.); [email protected] (H.Z.); [email protected] (R.H.) * Correspondence: [email protected]; Tel./Fax: +86-451-8219-1513 † These authors contribute equally to this work. Academic Editor: Miklas Scholz Received: 20 August 2016; Accepted: 21 October 2016; Published: 28 October 2016 Abstract: An anaerobic sludge (AS), capable of decolorizing a variety of synthetic dyes, was acclimated and is reported here. The sludge presented a much better dye decolorizing ability than that of different individual strains. A broad spectrum of dyes could be decolorized by the sludge. Continuous decolorization tests showed that the sludge exhibited the ability to decolorize repeated additions of dye. The chemical oxygen demand (COD) removal rate of the dye wastewater reached 52% after 12 h of incubation. Polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) profiles revealed that the microbial community changed as a result of varying initial concentrations of dyes. Phylogenetic analysis indicated that microbial populations in the sludge belonged to the phyla Acidobacteria, Firmicutes, Bacteroidetes, Chloroflexi and Proteobacteria. The degradation products of the three types of dye were identified. For azo dyes, the anaerobic sludge converted Methyl Orange to N,N-dimethylbenzene-1,4-diamine and 4-aminobenzenesulfonic acid; for triphenylmethane dyes, after Malachite Green was decolorized, the analyzed products were found to be a mixture of N,N-dimethylbenzenamine, 3-dimethyl-aminophenol and 4-dimethylaminobenzophenone; for anthraquinone dyes, two products (acetophenone and 2-methylbenzoic acid) were observed after Reactive Blue 19 decolorization. Together, these results suggest that the anaerobic sludge has promising potential for use in the treatment of industrial wastewater containing various types of dyes. Keywords: anaerobic sludge; synthetic dyes; decolorization; biodegradation; microbial community; intermediates 1. Introduction Synthetic dyes, classified on the basis of their chromophores as azo, anthraquinone, triphenylmethane and heterocyclic dyes, have been extensively used in the textile, printing, paper, cosmetics and food industries. Annually, approximately 2.8 × 105 t of textile wastewater with dyes is discharged into the environment worldwide [1]. These dyes are considered to be relatively persistent pollutants because they are extremely stable when exposed to light and aerobic conditions. Moreover, most dyes are toxic, and their transformation products are carcinogenic and mutagenic [2]. Thus, dye wastes must be treated before they are released into the environment. Decolorization of industrial dyes can be achieved through physico-chemical methods, such as adsorption, coagulation, precipitation and chemical oxidation. However, these methods have not been widely applied because of their low efficiency, high cost and intensive energy requirements. In recent years, many new processes for dye decolorization have been developed. One promising strategy is to use microbes to decolorize dyes. The biodegradation of dyes is considered to be an environmentally friendly and cost-effective option [3]. Int. J. Environ. Res. Public Health 2016, 13, 1053; doi:10.3390/ijerph13111053 www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2016, 13, 1053 2 of 18 Int. J. Environ. Res. Public 2016, 13, 1053 2 of 19 Int. J. Environ. Res. Public 2016, 13, 1053 2 of 19 Int. AtJ. Environ. present, Res. aPublic number 2016, 13 of, 1053 studies have focused on the utilization of bacteria to decolorize synthetic2 of 19 strategy is to use microbes to decolorize dyes. The biodegradation of dyes is considered to be an dyes.strategy Bacteria is to use are microbes capable to of decolorize reducing dyes. azo dyesThe biodegradation under both anaerobic of dyes is and considered aerobic to conditions; be an environmentallystrategy is to use friendly microbes and to cost-effective decolorize dyes. option The [3]. biodegradation of dyes is considered to be an suchenvironmentally bacteria, include friendly obligate and cost-effective anaerobes option such as [3].Clostridium sp. [4], facultative anaerobes such environmentallyAt present, friendlya number and of cost-effective studies have option focused [3]. on the utilization of bacteria to decolorize as EnterobacterAt present,sp. a and numberEscherichia of studiessp. [5 ,have6] and focused some aerobeson the utilization such as Pseudomonas of bacteria sp.to decolorize [7]. Similarly, syntheticAt present, dyes. Bacteriaa number are of capable studies ofhave reducing focused azo on dyes the utilizationunder both of anaerobicbacteria toand decolorize aerobic severalsynthetic phylogenetically dyes. Bacteria diverse are capable bacteria, of suchreducing as Shewanella azo dyessp., underCitrobacter both anaerobicsp. and Staphylococcus and aerobic sp., conditions;synthetic dyes. such Bacteria bacteria, are incl capableude obligate of reducing anaerobes azo dyessuch underas Clostridium both anaerobic sp. 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