Reduction of pigment dispersions by Shewanella strain J18 143

In order to develop a biotechnological solution to the disposal of waste pigment dispersions, the ability of azo dye-reducing Shewanella strain J18 143 cells to reduce model pigment dispersions was assessed. Resting cells were able to couple the oxidation of formate to the reduction of the azo/ketohydrazone chromophore in virtually insoluble pigmentary species. Pigments from the azoacetoacetanilide range and the azonaphthol range were used to investigate the effects of process parameters such as dispersion quality, addition of biocides, temperature and use of exogenous extracellular redox mediators. The physical impact of bioreduction on the pigment structure was also assessed. Pigments present in industrially manufactured dispersions were more readily reduced than those in powder form and the presence of a biocide in the dispersion did not affect the activity of cells of Shewanella strain J18 143. The initial pigment reduction rate increased with temperature up to 50 °C, but the higher temperatures had a detrimental effect on the long term activity of Shewanella strain J18 143. The reduction of the pigment dispersions was stimulated by the addition of the soluble electron shuttle anthraquinone-2,6-disulphonate. Particle sizing and environmental scanning electron microscopy showed that Shewanella strain J18 143 was able to degrade large pigment aggregates to produce individual pigment particles. GemSperse Orange EX5 was the pigment dispersion reduced to the corresponding amines most efficiently by Shewanella strain J18 143.