H₂O₂/UV-C treatment of the economically important naphthalene sulfonate J-acid: Process optimization, kinetic evaluation and activated sludge inhibition

J-acid (2-amino-5-naphthol-7-sulfonic acid) is an economically important naphthalene sulfonate having a highly polar, aromatic structure that renders it a difficult-to-oxidize, coagulate or adsorb pollutant. In the present study, the treatability of aqueous J-acid employing H₂O₂/UV-C oxidation and the effect of H₂O₂ (0-150 mM) concentrations on J-acid and organic carbon (COD, TOC) abatement rates was investigated and modeled by employing competitive inhibition kinetics. Inhibition of oxygen uptake rate was evaluated as a tool for assessing the acute toxicity of J-acids photochemical degradation intermediates using heterotrophic biomass. Our results indicated that J-acid was difficult-to-oxidize via H₂O ₂/UV-C treatment and appreciably high H₂O₂ concentrations (≥ 60 mM) and UV-C doses (≥ 80 min; corresponding to 28 kWh/m³) were required to achieve significant (> 50%) removals in terms of the environmental sum parameters parameters COD and TOC. The calculated abatement rates by the use of kinetic model satisfactorily fitted the experimental data in terms of J-acid and COD. A positive correlation existed between the rate of activated sludge inhibition and the amount of photochemical degradation intermediates.