Physico-chemical evaluation and kinetic study of coloured printing wastewater prior and post-fenton treatment

Abstract

The paper reports removal of organic Black (Key) dye from real printing wastewater using nano zero valent iron particles as a catalyst in Fenton-like treatment. The degradation efficiency of Black diazo dye via Fenton-like treatment is reported to be 61% under established optimal process conditions: [Fe2+] = 0.75 mgL-1, pH = 2, [H2O2] = 1 mM, within a reaction time of 75 min. The absorption spectra of Black dye clearly indicate that dye degradation is a slow process with difficult decomposition of aromatic structures, due to the cleavage of diazo bonds by hydroxyl radicals. The physico-chemical characterizations (measurements of pH, electrical conductivity, temperature, turbidity, chemical oxygen demand, biochemical oxygen demand, total organic carbon, anionic surface-active substances and phosphorus content) as well as toxicity study (Vibrio fischeri bacteria) revealed the complex nature of printing effluent. Increased conductivity and biochemical oxygen demand content after Fenton treatment imply the formation of various byproducts and intermediates, formed in a solution during dye degradation. The mineralization percentage of Black dye of 58% is followed with 47% of chemical oxygen demand reduction. Results of toxicity test on Vibrio fischeri bacteria indicate that both untreated and treated printing effluents belong to moderate toxic samples with 58% and 67% of toxicity inhibition, respectively. Among three evaluated kinetic models (the first-order, the second-order, and Behnajady– Modirshahla–Ghanbary), experimental results fitted very well to the Behnajady - Modirshahla - Ghanbary model, indicating high initial rate of Black dye degradation.