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In this study, an attempt was made to examine the potential of two bacterial strains for decolourisation of Acid Orange 10. The strain, isolated from textile effluent treatment plant was characterised on the basis of morphological, biochemical and genotypic characteristics, and it was identified as Pseudomonas aeruginosa and Bacillus cereus. The effect of pH, temperature and initial concentration of dye was studied with an aim to determine the optimal conditions. Materials and methods The bacterial strains used in this study were P. aeruginosa ETL-1942 and B. cereus ETL-1949. Out of these two, P. aeruginosa ETL-1942 emerged as the most potent decolouriser, being selected for further studies. Results The selected bacterium shows higher decolourisation in the static condition compared to the shaking condition. The optimum pH was 7.0. It shows good decolourisation efficiency even in the alkaline region. The optimum temperature was 37°C. The strain could decolourise Acid Orange 10 (250 mg/l) by 94% within 24 hours under static conditions, pH 7.0, temperature of 37°C and initial dye concentration of 250 mg/l. Biodegradation and decolourisation was confirmed using UV-VIS spectrophotometry, thin layer chromatography and fourier transform infrared spectroscopy analysis. Conclusion The study confirmed the potential of P. aeruginosa ETL-1942 in the bioremediation of Acid Orange 10. Introduction Effluent discharged from the textile industries has variable characteristics in terms of pH, dissolved oxygen, organic and inorganic chemical content, etc. Together with industrialisation, awareness towards the environmental problems arising due to effluent discharge is of critical importance. Pollution caused by dye effluent is mainly due to durability of the dyes in wastewater1. Existing effluent treatment procedures utilise pH neutralisation, coagulation followed by biological treatment, but they are unable to remove recalcitrant dyes completely from effluents. This is because of the colour fastness, stability and resistance of dyes to degradation2. Dyes are difficult to biodegrade because of its synthetic origin and complex aromatic molecular structures which make them stable3. Bioremediation is the microbial clean-up approach, microbes can acclimatise themselves to toxic wastes and new resistant strains develop naturally, which can transform various toxic chemicals to less harmful forms. Several reports have suggested that the degradation of complex organic substances can be brought about by bacterial enzymes4–9. Different dyes used in the textile industry usually have a synthetic origin and complex aromatic molecular structures, which make them more stable and difficult to be biodegraded. Due to their ease of manufacturing methodology, azo dye accounts for almost 80% of annual production of commercial dyes all over the world. There are over 100 000 commercially available dyes with a production of over 7 × 105 tons per year3. Azo dyes, containing one or more azo bonds (-N=N-), account for 60%–70% of all textile dyestuffs used10. It is estimated that about 10%–15% of the total production of colourants is lost during their synthesis and dyeing processes11,12. Whereas, in the case of reactive dyes almost 50% of the initial dye load is found in the dye bath effluents. Coloured industrial effluent is the most obvious indicator of water pollution and the discharge of highly coloured synthetic dye effluents is aesthetically displeasing and causes considerable damage to the aquatic life. Although several physical–chemical methods have been used to eliminate the coloured effluents in wastewater, they are generally expensive and produce large amounts of sludge. Usually these conventional modes of treatment lead to the formation of some harmful side products. Interest is therefore now focused on the microbial biodegradation of dyes as a better alternative13. Some microorganisms, including bacteria, fungi and algae, can degrade or absorb a wide range of dyes14. The biological mode of treatment of dye bath effluents offers distinct advantages over the conventional modes of treatment. This method is more economical and leads to less accumulation *Corresponding author Email: shahmp@uniphos.com Applied & Environmental Microbiology Lab, Enviro Technology Limited (CETP), GIDC, Ankleshwar, Gujarat, India Research study Page 2 of 7 Licensee OA Publishing London 2013. Creative Commons Attribution License (CC-BY) Co m pe tin g in te re st s: n on e de cl ar ed . C on fli ct o f i nt er es ts : n on e de cl ar ed . Al l a ut ho rs c on tr ib ut ed to th e co nc ep tio n, d es ig n, a nd p re pa ra tio n of th e m an us cr ip t, as w el l a s r ea d an d ap pr ov ed th e fin al m an us cr ip t. Al l a ut ho rs a bi de b y th e As so ci ati on fo r M ed ic al E th ic s ( AM E) e th ic al ru le s o f d isc lo su re . For citation purposes: Shah MP, Patel KA, Nair SS, Darji AM. Exploring the strength of Pseudomonas aeruginosa ETL-1942 in decolourisation and degradation of acid orange dye to combat textile effluent: Applied aspects. OA Biotechnology 2013 Mar 01;2(2):12. of relatively harmless sludge. Most importantly, biological treatment of dye bath effluents is eco-friendly. It causes mineralisation of dyes to simpler inorganic compounds which are not lethal to life forms. The basic step in the decolourisation and degradation of azo dyes is the breakdown of azo bonds, leading to removal of colour. Azo dyes are known to undergo reductive cleavage whereas the resultant aromatic amines are metabolised under aerobic conditions15. So for complete mineralisation of azo dyes the microbial population forming a part of the treatment system should be able to work efficiently. In view of these problems, the most potent bacterial culture was selected in this study for maximum decolourisation of Acid Orange 10 (azo dye), being selected. The aim of this study was to explore the strength of Pseudomonas aeruginosa ETL-1942 in the decolourisation and degradation of acid orange dye to combat textile effluent. Material and methods The protocol of this study has been approved by the relevant ethical committee related to our institution in which it was performed. Sampling and analysis of effluent Ankleshwar Textile Industries in Gujarat, one of the most industrialised cities in India, was chosen for effluent sample collection. The effluent sample was collected from the middle point of the area. Standard procedures (Spot and Grab) were followed during sampling. The temperature and pH were determined at the sampling site. The pH was determined using a pH meter (Hanna digital pH meter) and temperature with a laboratory thermometer. The sample was transported to the laboratory at 4°C as in accordance with the standard methods16. The physicochemical parameters such as colour, biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids and total dissolved solids (TDS) were determined as soon as the sample was brought to the laboratory. Sample colour was analysed by spectrophotometer (Shimadzu UV 1800). BOD was determined by employing evaporation method by DO meter while COD was measured by COD instrument directly. Dyestuff and chemicals The textile dye, Acid Orange 10 was a generous gift from the local textile industry in Ankleshwar, Gujarat, India and used for this study without any further purification. All the other chemicals used were of the highest purity available and of analytical grade. Experimental methods The bacterial cultures were transferred to fresh nutrient medium containing Acid Orange 10 (250 mg/l) and were incubated at 37°C, under static conditions for three days. After day 3, aliquots (5 ml) of the culture media were withdrawn, centrifuged at 10 000 rpm for 10 minutes in a centrifuge at room temperature to separate the bacterial cell mass. The supernatant was used for analysis of decolourisation and all the experiments were repeated in triplicates. Absorbance of the supernatant withdrawn at different time intervals were measured at the absorbance maximum wavelength for the dye Acid Orange 10 (λ max = 480 nm) in the visible region on a Shimadzu UV-Visible spectrophotometer (UV 1800). The percentage of decolourisation was calculated from the difference between initial and final values using the following formula:

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Exploring the strength of Pseudomonas aeruginosa ETL-1942 in decolourisation and degradation of acid orange dye to combat textile effluent: applied aspects