Abstract
The accumulation of recalcitrant azo dyes from untreated textile effluents has adversely impacted the ecosystem. The immense stability in their nature is conferred by the presence of azo bonds (N=N) in their structure. The reduction of this azo bond occurs exclusively under anaerobic conditions giving rise to colorless aromatic amines, which are carcinogenic. In the present study, a synthetic textile effluent containing mixed azo dyes such as Reactive Red, Reactive Black, and Reactive Brown, was treated using activated sludge under anaerobic conditions in a lab-scale anaerobic sequential batch reactor (An-SBR). At a concentration of 100 mg/L of mixed azo dyes, the An-SBR gave a maximum of 88% decolorization detected through UV-visible spectroscopy. Physicochemical analyses revealed 73% removal of BOD, 90% TDS removal, 69% COD removal, 4.05% TKN removal, 66% chloride removal, and 73% hardness removal. When the concentration of dyes was increased to 500 mg/L, the treatment showed a decrease in decolorization efficiency. This was then compared to a sequential anaerobic-aerobic treatment process performed in An-SBR and a laboratory-scale aerobic moving bed biofilm reactor (MBBR). The study revealed that the sequential process held more potential for commercial application than exclusively an anaerobic process. The metabolites formed during the treatment phase were extracted and analyzed by FT-IR and HPLC and identified through GC-MS analyses and were compared to those found in the untreated effluent. A phytotoxicity test was conducted on the remainder (secondary) sludge using Vigna unguiculata, and it was found to show a 50% reduction in germination and retardation in root and shoot length.
Highlights
E accumulation of recalcitrant azo dyes from untreated textile effluents has adversely impacted the ecosystem. e immense stability in their nature is conferred by the presence of azo bonds (N N) in their structure. e reduction of this azo bond occurs exclusively under anaerobic conditions giving rise to colorless aromatic amines, which are carcinogenic
When the concentration of dyes was increased to 500 mg/L, the treatment showed a decrease in decolorization efficiency. is was compared to a sequential anaerobic-aerobic treatment process performed in anaerobic sequential batch reactor (An-SBR) and a laboratory-scale aerobic moving bed biofilm reactor (MBBR). e study revealed that the sequential process held more potential for commercial application than exclusively an anaerobic process. e metabolites formed during the treatment phase were extracted and analyzed by FT-IR and high-performance liquid chromatography (HPLC) and identified through gas chromatography mass spectrometry (GC-MS) analyses and were compared to those found in the untreated effluent
Operational Setup. e synthetic textile effluent treatment was performed in a laboratory-scale anaerobic sequential batch reactor (An-SBR) and anaerobic moving bed biofilm reactor (MBBR). e An-SBR was constructed using acrylic having an inner diameter of 20 cm and a height of 50 cm. e reactor had a total volume of 15.7 l with a working volume of 8 l. e An-SBR was provided with an airtight lid to provide an anaerobic environment
Summary
Received 25 September 2020; Accepted 25 January 2021; Published 10 February 2021. e accumulation of recalcitrant azo dyes from untreated textile effluents has adversely impacted the ecosystem. e immense stability in their nature is conferred by the presence of azo bonds (N N) in their structure. e reduction of this azo bond occurs exclusively under anaerobic conditions giving rise to colorless aromatic amines, which are carcinogenic. A synthetic textile effluent containing mixed azo dyes such as Reactive Red, Reactive Black, and Reactive Brown, was treated using activated sludge under anaerobic conditions in a lab-scale anaerobic sequential batch reactor (An-SBR). The dye is extremely stable under natural conditions, spontaneous reduction of the azo bond under anaerobic conditions or International Journal of Chemical Engineering photocatalytic degradation may occur, leading to highly carcinogenic and mutagenic colorless aromatic amines [10]. A wide variety of biological methods have been in use to treat textile effluents containing azo dyes effectively. A laboratory-scale anaerobic sequential batch reactor (An-SBR) and an aerobic moving bed biofilm reactor (MBBR) were designed to treat a synthetic textile effluent containing 100 mg/L and 500 mg/L of mixed azo dyes—Reactive Red, Reactive Black, and Reactive Brown. A phytotoxicity assay was performed to study the secondary sludge’s effects on the germination and growth of cowpea Vigna unguiculata
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