Optimization and enhancement of textile reactive Remazol black B decolorization and detoxification by environmentally isolated pH tolerant Pseudomonas aeruginosa KY284155
Hashem et al. AMB Expr
Optimization and enhancement of textile reactive Remazol black B decolorization and detoxification by environmentally isolated pH tolerant Pseudomonas aeruginosa KY284155
Rasha A. Hashem 0
Reham Samir 0
Tamer M. Essam 0
Amal E. Ali 0 1
Magdy A. Amin 0
0 Department of Microbiology and Immunology, Faculty of Pharmacy, Cairo University , Kasr El-Aini St., Cairo 11562 , Egypt
1 Department of Pharmaceutical Microbiology, Faculty of Pharmaceutical Sciences and Pharmaceutical Industries, Future University , Cairo 11787 , Egypt
Azo dyes are complex derivatives of diazene used in food and textile manufacture. They are highly recalcitrant compounds, and account for severe environmental and health problems. Different strains of Pseudomonas species were isolated from textile wastewater effluents. The bioconversion of Remazol black B (a commonly used water soluble dye) by Pseudomonas aeruginosa was observed in static conditions. The bio-decolorization process was optimized by a multi factorial Plackett-Burman experimental design. Decolorization of 200 mg L−1 reached 100% in 32 h. Interestingly, the presence of yeast extract, magnesium and iron in the culture media, highly accelerated the rate of decolorization. Moreover, one of our isolates, P. aeruginosa KY284155, was kept high degradation rates at high pH (pH = 9), which represents the pH of most textile wastewater effluents, and was able to tolerate high concentration of dye up to 500 mg L−1. In bacteria, azo-dye degradation is often initiated by reductive azo compound cleavage catalyzed by azo-reductases. Three genes encoding azo-reductases, paazoR1, paazoR2 and paazoR3, could be identified in the genome of the isolated P. aeruginosa stain (B1). Bioinformatics analyses of the paazoR1, paazoR2 and paazoR3 genes reveal their prevalence and conservation in other P. aeruginosa strains. Chemical oxygen demand dramatically decreased and phyto-detoxification of the azo dye was accomplished by photocatalytic post treatment of the biodegradation products. We suggest applying combined biological photocatalytic post treatment for azo dyes on large scale, for effective, cheap decolorization and detoxification of azo-dyes, rendering them safe enough to be discharged in the environment.
Bio-decolorization; Bioinformatics; Detoxification; Optimization; Remazol black B
Introduction
Textile wastewater usually contains a large variety of dyes
and chemicals additives used in the dyeing process, such
as heavy metals, soda ash, caustic soda and acetic acid.
Pollution with these dyes represents an important
environmental challengeto the textile industry
(Bansal and
Kanwar 2013)
. Azo dyes are the most commonly used
textile dyes, containing one or more azo groups attached
to aromatic groups. They are difficult to biodegrade
aerobically because of their chemical stability. Since
oxygen is a more efficient electron acceptor than azo dyes,
their aerobic bacterial treatment under shaking
conditions is less efficient than aerobic treatment under static
conditions or anaerobic ones
(Stolz 2001; Mantzavinos
and Psillakis 2004)
. More than 100,000 dyes are used in
the textile industry and more than 700,000 tons of
commercial dyes are produced annually (Lucas et al. 2007).
About 10–15% of these dyes is discharged into textile
wastewater effluent, which not only creates serious
environmental hazards, but also renders textile wastewater
aesthetically unacceptable. In addition, azo dyes
themselves are toxic and highly carcinogenic. Consequently, it
is important to treat textile wastewater before
discharging it to the environment
(Sudarjanto et al. 2006; Pratum
et al. 2011)
. Reactive azo dyes are highly recalcitrant to
conventional methods (biological methods) used in
wastewater treatment because of the presence of strong
electron-withdrawing groups that give them stability
against bacterial degradation
(Lucas et al. 2007;
Gregorio et al. 2010)
. Most azo dye degrading microorganisms
cleave the azo bond(s), which subsequently generates
colourless aromatic amines. These amines are toxic
products, but could be metabolized under aerobic conditions
to less toxic ones
(Mohanty et al. 2006)
.
Azo-reductases, found in bacteria, catalyse the
degradation of azo dyes through the reductive cleavage of azo
groups (–N=N–). In presence of an electron donor, azo
dyes are transformed into colourless aromatic amines
(Zimmermann et al. 1982)
. Azo-reductases are classified
into three main groups based on their structure: Group
I, the polymeric flavin-dependent NADH-preferred
azoreductases; Group II, the polymeric flavin-dependent
NADPH-preferred azo-reductases and Group III, the
monomeric flavin-free NAD(P)H-preferred
azo-reductases
(Nakanishi et al. 2001; Chen et al. 2010; Feng et al.
2012)
.
Since biological treatment alone does not always
provide satisfactory results for industrial wastewater, the
industry makes use of chemical treatment, such as an
advanced oxidation (...truncated)