Degradation of eight relevant micropollutants in different water matrices by neutral photo-Fenton process under UV254 and simulated solar light irradiation – A comparative study

• The photocatalytic stability of micropollutants in different matrices is presented.
• The ESR experiments point to a low efficiency of singlet oxygen formation.
• Gabapentin and metformin were the most persistent compounds.
• The degradation products are more toxic than the parent compounds themselves.

This is a comparative study of photolytic degradation under exposure to UV254 nm and solar-simulator irradiation of a mixture of eight equally concentrated micropollutants in the presence of H2O2 and Fe(II) in ultra-pure water, Lake Geneva water, and effluent from a wastewater treatment plant (WWTP).The electron spin resonance experiments point to a low singlet oxygen formation efficiency by the micropollutant mixture. This finding corroborates the micropollutants’ chemical stability under UVC irradiation (in decreasing order: gabapentin, metformin, metoprolol, atenolol, clarithromycin, primidone, methylbenzotriazole, and benzotriazole). The oxidation rate increased in the presence of low-concentration H2O2 and Fe(II), except for metformin and gabapentin. Gabapentin and metformin were the most persistent compounds, with less than 24% being removed after 60 min of UV254/H2O2/Fe(II) treatment. The low removal rates were observed in WWTP effluent and lake water, and using sunlight simulation.Guanylurea, phenol, oxalic acid, tartronic acid, glycolic acid, oxamic acid, and maleic acid, could also be detected as fragmental oxidation products. Furthermore, up to 300 μg/L of nitrate and ammonia were identified as final degradation products. Ecotoxicological tests showed that the degradation products are more toxic for algae Chlamydomonas reinhardtii than the parent compounds themselves.

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