Abstract
When waste water of the dyeing industries are flowed into the sewarage, the lowering of the purificatory abilities in the activated sludge process are induced incidentally by the toxic properties of dyes for the microbes. In order to elucidate the toxic properties of the dyes, the respiratory inhibition of the microbes by various dyes were investigated by measuring the oxygen uptake rates. The inhibition by basic dye is stronger than that by acid dye when pH of the solution is above the isoelectric points of the microbes. The inhibition is reduced by mixing basic dye with acid dye to form the complex. Disperse dyes which have no charged groups show only weak inhibition at any pH. These facts indicate that the respiratory inhibition is influenced by the ionic interaction between the microbes and the dyes. The inhibition by direct dye is weaker than that by acid dye, suggesting that the permeation of direct dye into the microbe cell is difficult for such large molecule.
