Decolorization and partial mineralization of a polyazo dye by Bacillus firmus immobilized within tubular polymeric gel

The degradation of C.I. Direct red 80, a polyazo dye, was investigated using Bacillus firmus immobilized by entrapment in tubular polymeric gel. This bacterial strain was able to completely decolorize 50 mg/L of C.I. Direct red 80 under anoxic conditions within 12 h and also degrade the reaction intermediates (aromatic amines) during the subsequent 12 h under aerobic conditions. The tubular gel harboring the immobilized cells consisted of anoxic and aerobic regions integrated in a single unit which was ideal for azo dye degradation studies. Results obtained show that effective dye decolorization (97.8%), chemical oxygen demand (COD) reduction (91.7%) and total aromatic amines removal were obtained in 15 h with the immobilized bacterial cell system whereas for the free cells, a hydraulic residence time of 24 h was required for an equivalent performance in a sequential anoxic and aerobic process. Repeated-batch experiments indicate the immobilized cells could decolorize C.I. Direct red 80 and reduce medium COD in five successive batch runs with enhanced activity obtained after each consecutive run, thus suggesting its stability and potential for repeated use in wastewater treatment. UV–visible spectrophotometry and HPLC analysis were used to confirm the partial mineralization of the dye. Data from this study could be used as a reference for the development of effective industrial scale biotechnological process for the removal of dyes and their metabolites in textile wastewater

Influence of chemical structures on biodegradation of azo dyes by Pseudomonas sp

No Abstract. Global Journal of Environmental Sciences Vol. 5(1) 2006: 19-2

Toxic Effect Of Azo Dyes On Nitrite-N Utilization By Nitrobacter

The toxicity of five azo dyes (toxicants) on Nitrobacter was investigated. The index for toxicity was inhibition of rate of nitrite-N utilization. The rate of nitrite-N utilization decreased with increase in concentration of each toxicant at specific exposure time. However, stimulation of utilization was obtained at low concentrations and short exposure time for two of the dyes. This was attributed to hyperactivity. The median effective concentration50 (EC50) values increased with increase in exposure time for each toxicant. This was attributed to acclimatization and/or detoxification. Inhibition was attributed to any/or all of the following factors: molecular size, impurities in the toxicants and dye content. KEY WORDS: Toxicity, Azo dyes, Nitrobacter, hyperactivity, acclimatization Global Journal of Environmental Sciences Vol.4(1) 2005: 47-5

Biodegradation of Azo dyes by immobilized and free cells of Pseudomonas sp.under fed-batch conditions

No Abstract. Global Journal of Environmental Sciences Vol. 5(1) 2006: 1-

Quantal Response Of Freshwater Shrimp (Desmocaris trispinosa) To Toxicity Of Azo Dyes

The quantal-response of freshwater shrimp (Desmocaris trispinosa) to the toxicity of five azo dyes was studied. Generally, increase in percentage mortality of the organisms was obtained with increases in concentration of the toxicants and exposure time. The median lethal concentration50 (LC50) and median lethal concentration50 (LC50) values were obtained from the concentration-mortality and time-mortality probit graphs, respectively. Based on the LC50 and LT50 values, the dyes were ranked in order of toxicity: Mordant Black 11>Acid Orange 10>Direct Red 28>Direct Orange 31>Direct Red 23. Differences in quantal effect of the toxicants was attributed to their molecular weight, dye content and/or impaired oxygen transfer through the respiratory apparatus of the organisms due to adsorption of the dye molecules on their gill surface. Evidence of bioaccumulation of the toxicants in guts and tissues of the shrimps was obtained and its implication to human health was discussed. KEY WORDS: Toxicity, azo dyes, Desmocaris trispinosa, quantal response, bioaccumulation Global Journal of Environmental Sciences Vol.4(1) 2005: 41-4

Effect of pH and nutrient starvation on biodegradation of azo dyes by Pseudomonas sp

The effect of pH and some nutrients starvation on biodegradation of azo dyes (Orange II and Direct Blue 71) by Pseudomonas sp. was investigated. Highest percentage decolourization values of 56.50% and 45.20% were obtained at pH 7.0 and 6.5 for Orange II and Direct Blue 71 respectively. Rate of decolourization decreased with increasing concentration of nitrate (sodium nitrate) or sulphate (magnesium sulphate heptahydrate). Highest percentage decolourization (79.29% for Orange II and 72.38% for Direct Blue 71) was obtained in positive controls (no nitrate added). Corresponding values for sulphate-limited conditions were 76.50% for Orange II and 78.24% for Direct Blue 71 in positive controls (no sulphate added). The nitrogen of the generated aromatic amines provided the sole source of nitrogen in positive controls. Desulphonation of the aromatic moiety provided the sole source of sulphur in the positive control medium. The study shows that detoxification of ecosystems contaminated with azo dyes are enhanced under nitrate and sulphate-limited conditions. @JASE

Biomordanting willow bark dye on cellulosic materials

A semi-quantitative study of willow bark dye adsorption on two different cellulose materials using biomordants was carried out. The studied celluloses were microcrystalline cellulose (MCC) AaltoCell and regenerated Ioncell-F (IC) fibres. The dye was a hot water extract of willow bark and the adsorption to cellulose was carried out using carboxylic acid-containing biomordants, namely, oxalic acid, citric acid and tannic acid. Alum was employed as the reference mordant. A semi-quantitative estimation of the dye uptake was conducted using high-performance liquid chromatography equipped with a diode array detector and also by visual inspection, as well as an evaluation of the coloration using CIELab parameters. The mechanism of the dye adsorption on the cellulose surfaces was studied via Fourier Transform–infrared spectroscopy. According to the results, MCC had a higher affinity for polyphenolic dye than the regenerated cellulose fibres. Dye uptake on MCC was 50%-80% and 44%-57% on IC. For MCC, the biomordants improved the dye uptake more effectively than the control mordant, alum, whereas for IC the biomordants were less effective than alum.Peer reviewe