Metabolization of by-products formed by ozonation of the azo dye Reactive Red 239 in moving-bed biofilm reactors in series

Natália C Dias,Tito L M Alves,Débora A Azevedo,Márcia Dezotti,João P Bassin

doi:10.1007/s43153-020-00046-6

Natália C Dias, Tito L M Alves + Show 3 more

Open Access

https://doi.org/10.1007/s43153-020-00046-6

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Abstract

In this work, the biodegradation of by-products formed by ozonation of the azo dye Reactive Red 239 was evaluated using two MBBRs in series. Two ozone dosages were applied and low carbon removals and increasing ozone consumption observed after discoloration show the formation of oxidation resistant by-products. Five by-products were identified by GC/MS. High COD removal (90%) was observed in the biological process. However, nitrification inhibition was observed with ammonium removal of only 40%. This inhibition was probably caused by 4-amino-6-chloro-1,3,5-triazine-2-ol, which passed unscathed in the MBBRs. The nitrifying activity of the biofilm was restored when the MBBRs in series were fed with synthetic effluent (without by-products), proving the inhibition of nitrifying bacteria by ozonation by-products. The association of ozonation with the biological process was efficient in RR 239 color removal and degradation of some by-products. Higher ozone dosages are required for triazine oxidation, which probably inhibited nitrification in the MBBRs in series. The importance of identifying by-products formed by ozonation and their metabolization or not in a biological process is clear. In addition to partially inhibiting nitrification, special attention should be paid to chemicals that pass undegraded through a biological process and can be released into receiving bodies.

Highlights

The synthetic dyes commonly found in the wastewater of the textile industry emerged in the eighteenth century
This study aimed to evaluate the association of azo dye Reactive Red 239 (RR 239) ozonation until complete color removal with subsequent aerobic biological treatment for the biodegradation of ozonation by-products
Increasing ozone consumption over time and Chemical oxygen demand (COD) removal (35%) after 20 min of ozonation suggest the formation of by-products of difficult oxidation

Summary

Introduction

The synthetic dyes commonly found in the wastewater of the textile industry emerged in the eighteenth century. 1000 to 3000 m3 of wastewater is generated per day for processing 10 to 20 tons of fibers (Ghaly et al 2014). Azo dyes present in effluents cause the reduction of photosynthesis and dissolved oxygen concentration in the receiver body. These dyes may be toxic to fish, may reduce the embryonic survival, cause morphological deformities and are genotoxic. Biological processes have been extensively used in the treatment of textile effluents (Adabju 2013). The degradation of an azo dye by biological process is impaired due to the azo group (–N=N–), linked to at least one but usually two aromatic groups, which makes these dyes resistant to biodegradation (Wang et al 2002; Solís et al 2012)

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