Monoazo and diazo dye decolourisation studies in a methanogenic UASB reactor.

Mixed anaerobic bacterial consortia have been show to reduce azo dyes and batch decolourisation tests have also demonstrated that predominantly methanogenic cultures also perform azo bond cleavage. The anaerobic treatment of wool dyeing effluents, which contain acetic acid, could thus be improved with a better knowledge of methanogenic dye degradation. Therefore, the decolourisation of two azo textile dyes, a monoazo dye (Acid Orange 7, AO7) and a diazo dye (Direct Red 254, DR254), was investigated in a methanogenic laboratory-scale Upflow Anaerobic Sludge Blanket (UASB), fed with acetate as primary carbon source. As dye concentration was increased a decrease in total COD removal was observed, but the acetate load removal (90%) remained almost constant. A colour removal level higher than 88% was achieved for both dyes at a HRT of 24h. The identification by HPLC analysis of sulfanilic acid, a dye reduction metabolite, in the treated effluent, confirmed that the decolourisation process was due mainly to azo bond reduction. Although, HPLC chromatograms showed that 1-amino-2-naphthol, the other AO7 cleavage metabolite, was removed, aeration batch assays demonstrated that this could be due to auto-oxidation and not biological mineralization. At a HRT of 8h, a more extensive reductive biotransformation was observed for DR254 (82%) than for AO7 (56%). In order to explain this behaviour, the influence of the dye aggregation process and chemical structure of the dye molecules are discussed in the present work.

Batch tests for assessing decolourisation of azo dyes by methanogenic and mixed cultures.

Most of the published studies on azo dye colour removal involve anaerobic mixed cultures and there is some interest in the knowledge of how dye reduction occurs, if by facultative, strictly anaerobic or both bacterial trophic groups present in classic anaerobic digestors. This paper describes the behaviour of methanogenic and mixed bacteria cultures on the colour removal in batch systems, of a commercial azo dye, C.I. Acid Orange 7, used in paper and textile industries. The aim of this study is to demonstrate, by analysing dye decolourisation, that it occurs with mixed cultures as well as with strictly anaerobic (methanogenic) cultures. Tests were performed with a range of dye concentrations between 60 and 300 mg x l(-1). The influence of dye concentration on the carbon source removal and decolourisation processes was studied. The effect of carbon source concentration on colour removal was also analysed for both cultures. The degradation rates in mixed and methanogenic cultures were compared. The consumption of carbon source was monitored by COD analysis and dye degradation by ultraviolet-visible spectrophotometry and thin layer chromatography.

Calculation of single-ion activities in solutions simulating blood plasma.

While, in principle, flame photometry of sodium and potassium measures substance concentration, and ion-selective electrodes (ISEs) measure ion activity, the situation regarding the comparison of results from the two techniques when applied to blood plasma is complex. The problem can be approached experimentally from the point of view of calibration of ISEs with concentration standards, and similar procedures are adopted for commercial ISE-based clinical analysers. Nevertheless, there is interest in the evaluation of single ion activities in blood plasma and solutions simulating its ionic composition. The theory of mixed electrolyte solutions developed by Pitzer has been applied to some solutions currently proposed for calibrating ISEs, and the results compared with the Stokes-Robinson-Bates hydration approach. It is recommended that the values from the Pitzer treatment be adopted, because, although this has some empirical features, it has a sounder theoretical basis than the Stokes-Robinson-Bates hydration approach.