Continuous Treatment of Azo Acid Dyes by Photo-Dependent Denitrifying Treatment

Tests were implemented in a continuous-flow bench-scale reactor to evaluate the simultaneous removal of dye and nitrate by a photo-dependent denitrifying sludge (PDDS). Findings indicated that the best C/N ratio for the degradation of azo dyes using the proposed system was 1.5. Data indicated that the specific removal rate of azo dye AB92 was reduced with a reduction in hydraulic retention time, and increased with a reduction in solids retention time. The rate of TOC degradation declined with reductions in hydraulic retention time. The unique degradation pathway for AB92, which has nitro and hydroxyl substitutions in non-para positions, is described. Results from continuous flow experiments using the PDDS system suggested complete degradation of azo dyes AB92 (40 mg/L) and AO20 (30 mg/L) with a hydraulic retention time of 16 hours.