Combined use of photocatalytic treatment and microalgal cultivation for glyphosate removal from contaminated waters

Glyphosate (N-(phosphonomethyl) glycine) is one of the most widely used compounds in herbicide products. Introduced by the Monsanto Company (USA), it was initially utilized in fruit trees cultivations, public parks in urban areas, and then in crops and for the elimination of some aquatic plants in water bodies (Maqueda et al., 2017). Although its indiscriminate usage, the potential effects of glyphosate-based herbicides on non-target organisms are mostly unknown and it is classified as probably carcinogenic compound to humans. For this reason, there is an urgent need to eliminate these compounds from wastewaters during their treatment. Several techniques were proposed for the removal of glyphosate from wastewaters, such as adsorption, chemical degradation, and microbial degradation (Feng et al., 2020). Amongst them, photocatalytic degradation is one of the most interesting technologies as it is considered environmentally friendly and versatile. It is realised in the presence of heterogeneous catalyst such as titanium dioxide (TiO2), which has demonstrated to be ideal for the photocatalytic degradation of many emerging pollutants and antibiotics, in the presence of an UV radiation (λ ≤ 380 nm) (Li et al., 2022). The photocatalytic degradation of glyphosate leads to the production of small, atoxic, compounds such as formic acid, nitrate, ammonium and phosphate. Microalgae are a class of photosynthetic microorganisms which may be well applied to the wastewater treatment because of their efficiency in the removal of inorganic and organic phosphorus (P) and nitrogen (N), but also of other compounds such as heavy metals. They are therefore able to use compounds such as nitrate, ammonium, phosphate and carbon compounds as nutrients. In this work, a combined treatment for the degradation of glyphosate was proposed, consisting in photocatalysis and microalgal treatment applied in series. TiO2 was used as heterogeneous photocatalysts, and the Chlorella microalga was inoculated in the pretreated solution after the photocatalytic treatment. Results showed that the biological treatment enhances the previous partial oxidation achieved with photocatalysis, achieving global removal efficiencies higher than single-separated processes. With this work, we demonstrated that photocatalysis and microalgae represent an effective and eco-friendly combined treatment for glyphosate-polluted wastewaters. This work was carried out under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.4 - Call for tender No. 3138 of 16 December 2021, rectified by Decree n.3175 of 18 December 2021 of Italian Ministry of University and Research funded by the European Union – NextGenerationEU; Award Number: Project code CN_00000033, Concession Decree No. 1034 of 17 June 2022 adopted by the Italian Ministry of University and Research, CUP UNIPA B73C22000790001, Project title “National Biodiversity Future Center - NBFC”