Abstract
Heterogeneous Fenton processes with solid catalysts have gained much attention for water and wastewater treatment in recent years. In the field of solid catalysts, zero valent iron (ZVI) is among the most applicable due to its stability, activity, pollutant degradation properties and environmental friendliness. The main limitation in the use of ZVI in heterogeneous Fenton systems is due to its deactivation in neutral and alkaline conditions, and Fenton-like processes have been developed to overcome this difficulty. In this review, the effect of solution pH on the ZVI-Fenton performance is discussed. In addition, the pH trend of ZVI efficiency towards contaminants removal is also considered in oxic solutions (i.e., in the presence of dissolved O2 but without H2O2), as well as in magnetic-field assisted Fenton, sono-Fenton, photo-Fenton and microwave-Fenton processes at different pH values. The comparison of the effect of pH on ZVI performance, taking into account both heterogeneous Fenton and different Fenton-like processes, can guide future studies for developing ZVI applications in water and wastewater treatment.
Highlights
The Fenton reaction is widely accepted as a promising method for the degradation of organic and inorganic pollutants in water and wastewater [1,2,3]
The results indicated that Zero valent iron (ZVI)-K could effectively remove nitrobenzene from water (92% degradation under optimal experimental conditions) at pH values of up to 7.2
These results are in agreement with those of Harada et al [47], who studied the effect of the solution pH (3–7) on the performance of micro- and nano-sized ZVI in wastewater treatment
Summary
The Fenton reaction is widely accepted as a promising method for the degradation of organic and inorganic pollutants in water and wastewater [1,2,3]. The homogeneous Fenton reaction has disadvantages because of catalyst consumption and sludge disposal, due to the need to adjust pH after treatment that causes iron precipitation [8,9,10] To overcome these drawbacks, heterogeneous Fenton and Fenton-like processes have been developed by researchers over the past two decades. Porous materials (e.g., activated carbon, clay, zeolite, multi-walled carbon nanotubes and polymers) can be used as support for iron oxides [13,14] In this case, the overall performance of the Fenton reaction can be increased due to the extra cooperation of the catalyst’s support to adsorb pollutant molecules, and to initiate further pathways for radical generation and pollutants decomposition [13,14,15]. Conclusions and solutions are mentioned to manage the effect of pH on the heterogeneous ZVI-Fenton process aimed at pollutant degradation
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