Mustafa Işık

Effect of oxygen on decolorization of azo dyes by Escherichia coli and Pseudomonas sp. and fate of aromatic amines

The degradation of two azo dyes; Congo Red (CR) and Direct Black 38 (DB 38), in use in textile industries in Turkey, were investigated using two facultative microorganisms (Escherichia coli and Pseudomonas sp. ) under anaerobic, aerobic, and microaerophilic conditions. Hundred milligram per litre of dyes and 1000 mg glucose-COD/l containing basal medium were used and were incubated for 5 and 9 days. Simultaneous biomass activity and colour removal performance, was monitored during batch assays. The effects of two different microorganisms and aerobic/anaerobic conditions on decolorization were recorded with the monitoring of colour, pH, COD, dissolved oxygen, alkalinity, and volatile fatty acids concentrations. The aromatic amines (as benzidine) arising from the metabolites of anaerobic biodegradation of dyes and the recoveries of these aromatic amines were also monitored. High benzidine recoveries indicated the accumulation of aromatic amines under aerobic conditions. The colour of the CR and DB 38 dyes were removed up to 98 and 72%, respectively, by E. coli at the end of anaerobic incubation, while no decolorization occurred throughout the aerobic incubation. Under microaerophilic conditions, the azo dyes CR and DB 38 were decolorized up to 39 and 75% by E. coli, respectively. In studies with Pseudomonas sp., the colour of the CR and DB 38 dyes were removed up to 100 and 83%, respectively, after 5 days of anaerobic incubation, while 76 and 74% colour removal efficiencies were observed under microaerophilic conditions. # 2002 Elsevier Science Ltd. All rights reserved.

Decolorization of azo dyes under batch anaerobic and sequential anaerobic/aerobic conditions

Abstract Batch anaerobic and sequential anaerobic upflow anaerobic sludge blanket (UASB)/aerobic continuous stirred tank reactor (CSTR) were used to determine the color and COD removals under anaerobic/aerobic conditions. Two azo dyes namely “Reactive Black 5 (RB 5),” “Congo Red (CR),” and glucose as a carbon source were used for synthetic wastewater. The course of the decolorization process approximates to first order and zero order kinetics with respect to dye concentration for RB 5 and Congo Red azo dyes, respectively, in batch conditions. The decolorization kinetic constant (K 0) values increased from 3.6 to 11.8 mg (L h)−1 as increases in dye concentrations from 200 to 3200 mg L−1 for CR. Increases in dye concentrations from 0 to 3200 mg L−1 reduce the decolorization rate constant (k 1) values from 0.0141 to 0.0019 h−1 in batch studies performed with RB 5. Decolorization was achieved effectively under test conditions but ultimate decolorization of azo dyes was not observed at all dye concentrations in batch assay conditions. Dye concentrations of 100 mg L−1 and 3000 mg L−1 of glucose–COD containing basal medium were used for continuous studies. The effect of organic loadings and HRT, on the color removal efficiencies and methane gas productions were monitored. 94.1–45.4% COD and 79–73% color removal efficiencies were obtained at an organic system during decolorization of Reactive Black 5. 92.3–77.0% COD and 95.3–92.2% decolorization efficiencies were achieved at a organic loading rate of 1.03–6.65 kg (m3 day)−1 and a HRT of 3.54–0.49 for Congo Red treatment. The results of this study showed that, although decolorization continued, COD removal efficiencies and methane gas production were depressed at high organic loadings under anaerobic conditions. Furthermore, VFA accumulation, alkalinity consumption, and methane gas percentage were monitored at organic loading as high as 2.49–4.74 kg (m3 day)−1 and 24.60–30.62 kg (m3 day)−1, respectively, through the decolorization of RB 5 and CR dyes in the UASB reactor.

Aromatic Amine Degradation in a UASB/CSTR Sequential System Treating Congo Red Dye

Abstract In this study an anaerobic (upflow anaerobic sludge blanket reactor)/aerobic (completely stirred tank reactor) sequential system was used to treat a synthetic wastewater with minerals and co-substrate together with 100–4000 mg L−1 of Congo Red dye (Direct red 28) (CR), which is a banned azo dye in Turkey. The effect of hydraulic retention time (HRT) on the decolorization and the COD removal efficiency was investigated at constant 100 mg L−1 Congo Red concentration. 77% of COD and 95% of color was removed at a HRT of 0.486 days and a maximum organic loading rate of 6.656 kg COD m−3 day−1 in the anaerobic/aerobic stage. In the continuous operations, 88% of COD, 99% of color and 91% of total aromatic amine (TAA) were removed at a HRT of 3.60 days and at a CR concentration of 4000 mg L−1. This corresponds to an organic loading rate of 1.81 kg COD m−3 day−1, and a CR dye loading rate of 46.37 g dye m−3 h−1, respectively, in the whole system. The TAA produced under anaerobic conditions was ultimately removed in the aerobic stage, resulting in very low aromatic amine recoveries (5–18%) in the last one. Therefore the aerobic effluents exhibited higher IC50 and specific methanogenic activities (SMA) compared to anaerobic and dye containing samples, indicating the reduced toxicity.