## 1 Introduction
\[\text{RH}+\text{{}^{\bullet}OH}\rightarrow\text{H}_{2}\text{O}+\text{R}^{\bullet} \tag{9}\]  
\[\text{R}^{\bullet}+\text{H}_{2}\text{O}_{2}\rightarrow\text{ROH}+\text{{}^{ \bullet}OH} \tag{10}\]  
\[\text{Fe}^{2+}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}^{3+}+ \text{{}^{\bullet}OH}+\text{OH}^{-}\text{k}_{1}=70\text{ L/mol/s} \tag{2}\]0  
\[\text{Fe}^{2+}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}^{3+}+ \text{{}^{\bullet}OH}+\text{OH}^{-}\text{k}_{1}=70\text{ L/mol/s} \tag{2}\]1  
\[\text{Fe}^{2+}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}^{3+}+ \text{{}^{\bullet}OH}+\text{OH}^{-}\text{k}_{1}=70\text{ L/mol/s} \tag{2}\]2  
\[\text{Fe}^{2+}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}^{3+}+ \text{{}^{\bullet}OH}+\text{OH}^{-}\text{k}_{1}=70\text{ L/mol/s} \tag{2}\]3  
Although good oxidation efficiency is achieved by the Fenton oxidation, a large amount of sludge production limits its use in some cases.The ferrous ions react with hydroxide ions to form ferric hydroxo solid materials [24]. These reactions portray the coagulation ability of the Fenton's reagent by forming iron based precipitates and then generating sludges, which are consistently observed in the Fenton oxidation steps and need a long time to settle out [13]. However, the ferric hydroxo complexes are photo-active and can reproduce ferrous ions and hydroxyl radicals in photo-Fenton processes when Fe(0) is used as a catalyst in cooperation with the irridation via UV light (hv) [15], and the photo Fenton process exists in homogeneous and heterogeneous phases. In contrast to a ferrous iron, a zero-valent iron (Fe(0)) has been known to have an efficient catalytic effect and has been utilised for environmental remediation [25]. However, its application in the Fenton oxidation is yet to be fully developed. The Fe(0) is ionised or oxidised in the presence of water, dissolved oxygen or hydrogen peroxide to form ferrous ions and thereafter proceeds the conventional Fenton oxidation procedures under its reaction mechanism [26]. \[\text{Fe}^{2+}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}^{3+}+ \text{{}^{\bullet}OH}+\text{OH}^{-}\text{k}_{1}=70\text{ L/mol/s} \tag{2}\]4  
When designing experiments or reaction conditions, the Taguchi method has been used. It is to test the mean inner array and variation of each experimental run by evaluating the ratio of the signal-to-noise (SN). The signal corresponds to response or experimental yield and noise as an inevitable loss [27]. In contrast to the standard deviation, which directly depends on the mean value of response data and thus, the error is difficult to minimise, the SN ratio is used to replace the standard deviation to obtain robust optimum reaction conditions [27]. The Taguchi method performs two-steps optimisation at the parameter level combination, with minimum standard deviation and keeping the mean on the target [28]. The two steps can be described as:  
1. Set all factors that have a prominent contribution to SN ratios at the level to obtain maximum SN ratios. 2. Adjust the level of one or more factors that substantially affect the mean value but not SN ratios to put the response on the target. In real experimental conditions, the targets mean values can be changed during the process development. Therefore, SN ratios are used to calculate quadratic loss function and have three approaches. The SN ratios' condition is selected to minimise, maximise or to produce nominal results [28]. Choosing either of the below approaches for the analysis depends on the research demand:  
1. Smaller is better;
2. Nominal is better and;
3. Larger is better. The dissolved organic carbon is present in a vast variety of waters and its concentration increases with the rise in pollution level [29]. All water treatment technologies aim to completely transfer organic pollutants into carbon dioxide (mineralisation), but it is generally hard to achieve this.