On the kinetics of organic pollutant degradation with Co²⁺/peroxymonosulfate process: When ammonium meets chloride

A large amount of chloride and ammonium ions were produced and released from industrial processes with non-biodegradable organic pollutants to affect efficiencies of advanced oxidation processes (AOPs). Here, the influences of chloride and ammonium ions on Co/peroxymonosulfate (Co/PMS) reaction system, a widely used AOPs to produce sulfate radicals, were investigated by examining the degradation efficiency of an azo dye (Acid Orange 7, AO7). The experimental results showed that a significant decrease in the degradation rate of AO7 was observed in the presence of NH₄⁺, while a dual effect of chloride on AO7 bleaching appeared. The presence of NH₄Cl was unfavorable for AO7 degradation at low concentration (<20 mM), whereas further addition of NH₄Cl (>20 mM) apparently accelerated AO7 discoloration rate. The apparent effects of the two co-existing inorganic ions were determined by roles of the dominating ions at varied molar ratio of [NH₄⁺]/[Cl⁻]. The present study may have technical implications for the treatment of industrial wastewater containing diverse ions in practice.