The total volume of water on Earth is estimated at 1.4 x 109 km3, with 97.5% being salt water and 2.5% being fresh water (UNEP, 2003). Water use has been increasing worldwide by about 1% per year since the 1980s, driven by a combination of population growth, socio-economic development and changing consumption patterns. Global water demand is expected to continue increasing at a similar rate until 2050, accounting for an increase of 20 to 30% above the current level of water use, mainly due to rising demand in the industrial and domestic sectors.
(The United Nations world water development report 2019: leaving no one behind). However, the industrial, agricultural or other human activities (pesticides, solvents, pharmaceuticals, agrochemicals, petroleum refinery plants and landfill leachates, waste from septic systems), can significantly altered the biological, physical and chemical properties of water making it unsafe for the human health and the ecosystems balance (Dutta el al., 2014; S. Rahim Pouran et al., 2015).
Currently, one of the fundamental concerns is water pollution abatement via effective treatment of wastewaters containing refractory and toxic organic pollutants even at micro quantities.
(S. Rahim Pouran et al., 2015). The conventional separation and transformation technologies are inefficient and cannot produce effluents that meet water quality criteria and effluent limitation guidelines for recalcitrant compounds. For instance, biological methods can effectively treat wastewaters with high biodegradability ratio (BOD5/COD ? 0.4) (M. Umar et al., 2010). However, wastewaters containing these compounds are known to be high in chemical oxygen demand (COD) and low in biological oxygen demand (BOD). (The five-day biological oxygen demand (BOD5) is defined as the amount of oxygen that is consumed by aerobic heterotrophic bacteria during metabolization of organic water constituents over five days at 20 °C).
Advanced oxidation processes (AOPs), such as photochemical oxidation, catalytic wet oxidation, sonochemical oxidation, O3 oxidation, electrochemical oxidation, and Fenton oxidation, have been widely applied for direct mineralization of organic pollutants, hydrogen production by water splitting, or improvement of the biodegradability of organic pollutants through oxidation (Dutta et al., 2008; Hamd et al., 2012; Bokare el al., 2014; Sharma et al., 2018). Compared with other AOPs, the Fenton’s reagent is the most popular and interesting solution since it allows high depuration levels at room temperature and pressure conditions, wide application range, strong anti-interference ability, simple operation and rapid degradation and mineralization (Sagar Gawande et al., 2015; Chen et al., 2011; Wang et al., 2016). Nevertheless, the process has three obvious limitations: the narrow working pH range, the high costs and risks associated with handling, transportation and storage of reagents (H2O2 and iron catalyst), and the significant iron sludge related second pollution. In order to overcome these shortcomings and to improve the process, several strategies have been put in practice such as heterogeneous Fenton, photo-Fenton, electro-Fenton and the use of chelating agents.
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