Treatment Of High-salt Azo Dye Wastewater By Membrane Bioreactor (MBR) Bioaugmented With A Salt-tolerant Fungus

Synthetic azo dyes which belong to recalcitrant xenobiotic compounds are widely used in many industries,thus commonly exist in various industrial wastewaters and can cause serious damage to the environment.In addition,wastewater from related industries such as printing,dyeing and textiles industries often contains high concentrations of inorganic salts,which make them more difficult to be treated.Considering the above two problems,membrane bioreactors(MBRs)which were bioaugmented by salt-tolerant fungus were constructed and operated for the most efficient removal of dyes and total organics in wastewaters,basing on the works on isolation and study of salt-tolerant fungi.Azo dyes were used as target compounds in this study.A salt-tolerant yeast strain G1 which possess high biodegradability was isolated from the sea mud of the polluted area of a beach.The strain G1 was identified as Pichia occidentalis(KU358656)by morphological observation and 26 S rDNA sequence analysis methods.The characteristics of the strain was studied and the results showed that P.occidentalis G1 was an aerobic,mesophilic,salt-tolerant yeast which can adapt to weak acidic environment.In addition,a degradation pathway of azo dye Acid Red B(ARB)which consisted of reductive decolorization,deamination/desulfurization and TCA cycle was proposed.Results of key enzyme activity analysis showed that decolorization of ARB mainly depended on catalysis of NADH-DCIP reductase,which was detected both intracellularly and extracellularly.Additionally,further degradation of secondary byproducts mainly depended on lignin peroxidase(LiP),manganese peroxidase(MnP)and laccase(Lac),which only existed intracellularly.Among them,activity of LiP was the highest and that of Lac was the lowest.Three laboratory-scale MBRs which inoculated with activated sludge(1#),salt-tolerant yeast G1(2#)and both of them(3#,Strengthen the system)were constructed and operated to investigate the continuous treatment effectiveness of simulated high-salt ARB wastewater,basing on the inoculum size of strain G1 determined through pre-experiments.The whole process was divided into two stages with different influent ARB concentration(200 mg/L and 300 mg/L),meantime,shifts of ARB concentration and COD in influents and effluents,as well as sludge concentration in MBR(mixed liquid suspended solids,MLSS)were monitored throughout the whole operation processes.The results showed that the decolorization and COD removal efficiencies of 3# MBR which bioaugmented by the yeast G1 were higher than those of the other two.Meanwhile,the MLSS in 3#MBR was the highest among all the three sets with the least fluctuation range.In addition,the acute toxicity of the effluent at the end of the two-phase operation from 3# MBR was much lower than those from the other two,suggesting that the detoxification effectiveness was the best.Microbial community structures in three MBRs at different operation phases were analyzed through high-throughput sequencing technology.The results showed that microbial structures from different MBRs were obviously different.Some fungal and bacterial species which might effectively degrade ARB and its metabolic intermediates were enriched in the 3#MBR.Furthermore,Pichia was determined as a dominant genus in 3#MBR,which suggested that the fungus G1 might colonize in the microbial consortium.