Investigating degradation metabolites and underlying pathway of azo dye "Reactive Black 5" in bioaugmented floating treatment wetlands.

Muhammad Afzal,Fazal-e Habib,Samina Iqbal,Nain Tara,Mazhar Iqbal,Hans Brix,Qaiser Mahmood Khan

doi:10.1007/s11356-021-15130-8

Abstract

The direct discharge of azo dyes and/or their metabolites into the environment may exert toxic, mutagenic, and carcinogenic effects on exposed fauna and flora. In this study, we analyzed the metabolites produced during the degradation of an azo dye namely Reactive Black 5 (RB5) in the bacterial-augmented floating treatment wetlands (FTWs), followed by the investigation of their underlying toxicity. To this end, a FTWs system was developed by using a common wetland plant Phragmites australis in the presence of three dye-degrading bacteria (Acinetobacter junii strain NT-15, Pseudomonas indoloxydans strain NT-38, and Rhodococcus sp. strain NT-39). We found that the FTW system effectively degraded RB5 into at least 20 different metabolites with the successful removal of color (95.5%) from the water. The fish toxicity assay revealed the nontoxic characteristics of the metabolites produced after dye degradation. Our study suggests that bacterially aided FTWs could be a suitable option for the successful degradation of azo dyes, and the results presented in this study may help improve the overall textile effluent cleanup processes.

Highlights

Discharge of polluted water into the environment is a worldwide problem, in developing countries where the discharge of untreated wastewaters directly into water bodies is a common practice (Chandanshive et al 2016)
This study aims to identify metabolites produced during the biodegradation of Reactive Black 5 (RB5) in floating treatment wetlands (FTWs) inoculated with bacteria, and elucidate underlying biodegradation pathways of RB5 dye
P. australis at the dye concentration 200 mg L− 1 exhibited more development in root and shoot length, and root and shoot dry weight than the plants grown in the water having RB5 dye concentration 1000 mg L− 1

Summary

Introduction

Discharge of polluted water into the environment is a worldwide problem, in developing countries where the discharge of untreated wastewaters directly into water bodies is a common practice (Chandanshive et al 2016). Such a discharge of textile wastewater leads to water pollution in terms of elevated concentrations of noxious dyes These dyes are often detrimental to living organisms and cause depletion in the dissolved oxygen in the receiving water (Shehzadi et al 2014; Bilal et al 2017; Chatha et al 2017; Hussain et al 2018). This discharge of textile wastewaters is a big threat to aquatic life (Bilal et al 2016; Hussein and Scholz 2018; Hussain et al 2019). Even a small quantity of azo dyes can lead to unwanted consequences in the aquatic ecosystem (Shah and Patel 2014)

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