Enhanced biodegradation of azo dyes using an integrated elemental iron-activated sludge system: II. Effects of physical-chemical parameters.

As part of a study to evaluate an integrated zero-valent iron (Fe(0))-biological oxidation process for treating azo dye wastewaters, we conducted batch and column experiments with the azo dye orange G to assess the effects of solution conditions on the performance of iron pretreatment. The influence of iron type and surface area, solution pH, dissolved inorganic salts, and phosphate ion on the reduction (decolorization) of orange G solution were examined. In batch experiments, increased iron surface area, decreased pH, and chloride and sulfate salts enhanced dye decolorization, whereas high pH (9.9) and phosphate concentrations (> 3 mg/L PO4-P) inhibited dye reduction. Results from batch experiments were confirmed in column experiments. An increase in temperature from 22 to 35 degrees C resulted in a near doubling of the reduction rate constant in a column study. The abiotic reduction results illustrate the feasibility and potential limitations of an integrated iron column, activated sludge treatment process for wastewaters containing azo dyes.