Performance of the solar/peroxymonosulfate process in (waste)water treatment: abatement of micropollutants, roles of reactive oxygen species, and formation of disinfection by-products

Abstract

This study investigated the effectiveness of peroxymonosulfate (PMS) as an oxidative agent in micro-contaminant removal with activation via simulated solar irradiation (Xe-lamp, emission spectrum ranging from 300 to 800 nm). During solar/PMS treatment, the abatement of nitrobenzene (NB), flunixin meglumine (FMME), aspirin (ASA), and benzoic acid (BA) followed pseudo-first order kinetics, with degradation at pH 8.5 faster (1.28–1.78 times) than that at pH 5.5. The removal of NB (1.22 mg L⁻¹), FMME (4.92 mg L⁻¹), ASA (1.80 mg L⁻¹), and BA (1.23 mg L⁻¹) reached 51.2%, 68.0%, 66.6%, and 90.7% in 15 min at pH 8.5, respectively, with corresponding pseudo-first order rate constants (k_obs) of 5.1 × 10⁻², 7.7 × 10⁻², 7.4 × 10⁻², and 1.6 × 10⁻¹ min⁻¹, respectively. Production of hydroxyl radicals, sulfate radicals (SO₄˙⁻), and other reactive oxygen species (ROS) was determined by using NB and BA as probe compounds in the solar/PMS system. At pH of 5.5–8.5, SO₄˙⁻ made a dominant contribution (45.7% and 52.0%, respectively) to the overall removal of ASA and FMME. Compared with treatment of chlorination alone, solar/PMS pretreatment followed by post-chlorination resulted in a significant increase in disinfection by-product (DBP) formation (by 176% for trihalomethanes and 273% for haloacetic acids) in the Yangtze River water samples, as well as inhibition of algae growth (by 35.6%) due to higher toxic effects of residual PMS or potential oxidation intermediates in the system. The lowest EE/O_total consumed in the solar/PMS system was estimated to be 72–110 kW h m⁻³ order⁻¹ with the optimal PMS dosages of 0.36–0.68 mM. This work identified ROS generated during solar/PMS treatment and evaluated their contributions to the efficient depletion of organic micro-pollutants. The potential risk of increased DBP production and bio-toxicity was also investigated when applying the system to actual water treatment.