Ecotoxicological assessment of wastewater treated by the novel solar chlor-photo-Fenton process for sustainable crop irrigation

Potential ecotoxicity of the solar chlor-photo-Fenton (SCPF) process as a novel approach for wastewater reclamation has been investigated in relation to reuse for crop irrigation. Several secondary effluents from wastewater treatment plants across different geolocations were treated by applying the process with low reagent concentrations of 0.1 mM of ferric nitrilotriacetate (Fe³⁺-NTA), 0.73 mM of hydrogen peroxide, at different chlorine doses ranging from 0.13 to 0.40 mM. Chlorination, using comparable chlorine concentrations, and the solar photo-Fenton process were evaluated in parallel to compare with SCPF. A UVB-LED system was also used to perform the SCPF treatment, demonstrating its adaptability to both solar and artificial light-driven applications. Potential environmental toxicity was assessed using a battery of bioassays, including bacterial toxicity and genotoxicity, phytotoxicity in algae and plants, and toxicity toward mixed microbial communities (microrespirometry). Water treated with SCPF exhibited minimal bacterial and algal toxicity (<13 %), low phytotoxicity as assessed by plant germination (35 % at high chlorine concentration) and shoot/root elongation (22 % and -30 %), low toxicity toward mixed microbial communities (<30 %), and low apparent levels of genotoxicity. In comparison, chlorination yielded higher ecotoxic responses across the bioassays, suggesting that SCPF may mitigate these adverse effects. Although Fe³⁺-NTA dissolution showed toxicity its ecotoxic impact was markedly reduced at the operational concentration of 0.1 mM used in SCPF. These results indicate that chlor-photo-Fenton can produce treated water with low apparent ecotoxicity, supporting its potential as an environmentally friendly and scalable solution for wastewater treatment and reuse.