The global water crisis is hindering healthy human endurance and societal development. Water treatment is crucial for a sustainable balance between society and the environment. The industry must treat its wastewaters adequately as they are particularly rich in potentially hazardous compounds. The United Nations recognised the crisis and led to the establishment of the Sustainable Development Goals (SDGs) in 2015 [1]. A significant cause of water pollution is the inadequate release of organic contaminants to the environment. In particular, olive mill wastewaters (OMWW) are considered as hazard to environmental sustainability in the Mediterranean region.
Advanced oxidation processes (AOPs) represent an efficient, low cost and safe solution for the removal of recalcitrant compounds present in OMWW. In particular, heterogeneous photocatalysis with graphitic carbon nitride (GCN) activated by visible light using LEDs has been proven to be efficient in the degradation of several organic pollutants [2]. In this study, we investigated the use of GCN, prepared by a thermal treatment method, in the photocatalytic degradation of phenolic compounds often present in OMWW [3]. We explored the simultaneous in situ evolution of hydrogen peroxide (H2O2) as a mean to enhance pollutant degradation. Moreover, the improvement of the mineralisation process was sought with the addition of iron to mimic photo-Fenton-like conditions [4]. An impact superior than 20% in mineralisation was observed with relatively low dosages of iron ions (according to Portugal’s legislation) and under natural pH, which could enable a greater ease on the discharge of treated liquid effluents.

[1] Transforming Our World: The 2030 Agenda for Sustainable Development, UN General Assembly, 2015.
[2] Wee-Jun Ong, Lling-Lling Tan, Yun Hau Ng, Siek-Ting Yong, Siang-Piao Chai, Chem. Rev., 2016, 116, 12, 7159 7329, 10.1021/acs.chemrev.6b00075.
[3] André Torres-Pinto, Maria J. Sampaio, Cláudia G. Silva, Joaquim L. Faria, Adrián M.T. Silva, Appl. Catal. B Environ. , 2019, 252, 128-137, 10.1016/j.apcatb.2019.03.040.
[4] André Torres-Pinto, Maria J. Sampaio, Jessica Teixo, Cláudia G. Silva, Joaquim L. Faria, Adrián M.T. Silva, J. Water Process. Eng. , 2020, 37, 101467, 10.1016/j.jwpe.2020.101467.