## 3 Results and Discussions
### Physical-Chemical Monitoring
Those elevated pH values can trigger the conversion of ammonium (NH\({}_{4}\)\({}^{+}\)) into ammonia (NH\({}_{3}\)) [32] with the consequent release of greenhouse gasses [33]. Furthermore this could impact the agricultural yield for many crops removing NH\({}_{4}\)\({}^{+}\) from the soil and preventing plants from using it [34]. In CS batches Biochar showed a different trend from the other soil improvers and the Control, except for L/S = 10. In fact, for L/S = 1, L/S = 2, and L/S = 5, Biochar pH tended to increase during the monitoring period, while the other improvers showed equilibrium or a slight decrease. In SS Biochar batches showed two different trends. For L/S = 1 and L/S = 2 pH increased at the beginning of the monitoring period, while it decreased for the other L/S ratios. This was imputable to CaCO\({}_{3}\) precipitation, which is optimal in a pH range of 8.5-10 [35] and the following reaction can occur:  
\[\text{Ca}^{2+}+\text{HCO}_{3}^{-}\rightarrow\text{CaCO}_{3}+\text{H}^{+} \tag{1}\]  
with the consequent release of protons triggering the pH lowering [36]. For L/S = 1, L/S = 2, and L/S = 5 in CS batches and for L/S = 1 and L/S = 2 in SS batches, Biochar pH values were out of the optimal pH range for CaCO\({}_{3}\) precipitation. Biochar pH values were also affected by L/S ratios, indeed they tended to decrease with the increase of L/S ratios. Figure 4 shows the effect of different L/S ratios on pH. In the Control, pH increased starting from 8.5 for CS and 8.2 for SS, to reach an asymptotic value of 9.2. In Graphene and Zeolites batches no appreciable differences from the Control could be noted, with no statistically relevant differences among CS, SS, and Control. In the Compost batches a decrease of 0.2 pH points was induced by the acidic conditions of the Compost (Table 1), with statistically relevant differences respect to Control for all L/S ratios except for SS L/S = 1 and L/S = 10. In the Biochar batches, pH tended to converge towards the Control's pH at increasing L/S ratios, starting at pH near 12 in the CS batches, probably since Biochar induced carbonates dissolution, in agreement with [PERSON] et al. [12]. In both Biochar CS and SS statistically different means respect to Control were present, while for Zeolites no relevant differences were present, indicating that Zeolites addition did not influence pH. Figure 5 shows the results of ORP monitoring in the CS and SS batches for all L/S ratios. Zeolites revealed the highest values of ORP, while Biochar showed the lowest values for all L/S ratios and for both soils. Biochar did not show a clear trend with ORP values showing an initial decrease and a subsequent increase, in agreement with [PERSON] et al. [12]. This effect was imputable to the dissolution of organic compounds from Biochar thus providing electron donors that determined the ORP fluctuations [37]. In all treatments and for all L/S ratios ORP for Graphene and Compost batches were quite similar and close to those of the Control. The CS Graphene batches showed ORP values higher than the Control ones. Conversely, the SS Graphene batches showed ORP values slightly lower than the Control ones, apart from L/S = 10. For all L/S ratios, except for Biochar, the addition of the soil improvers stabilized ORP, which rapidly reached equilibrium values. Graphene, Compost, and Zeolites ORP values were not affected by the change of L/S ratios, with values close to 200-250 mV. Biochar ORP values were, instead, affected by the change of L/S ratios. The increase of L/S ratios increased ORP values that tended towards Control values. Figure 3: pH values variation in SSE batches experiments with CS (**left panels**) and SS (**right panels**) for different L/S ratios. Error bars denoted standard deviation calculated on three replicas. Different letters indicate statistically different means at 0.05 confidence. Figure 4: pH in SSE batches with CS (**left panels**) and SS (**right panels**) soils versus L/S ratios values at the end of the monitoring period.