## 3 Results and Discussion
### Bio-Mixture Effect on Leachates Chemical Characteristics
Likewise, sodium concentration followed a similar trend, since a decrease was noticed in all leachates of all three bio-mixtures, whilst when irrigation was completed, sodium concentrations in the leachates of the bio-mixtures and control soil were at the same levels (Figure 3b). Figure 4: Changes of: (**a**) SAR values and (**b**) Total Hardness (mg CaCO\({}_{3}\) L\({}^{-1}\)) values in the leachates of the 10 irrigation applications of the four treatments. Each value is the mean of three replicates. Figure 3: Changes of: (**a**) K (mg/L) concentrations, (**b**) Na (mg/L) concentrations, (**c**) Ca (mg/L) concentrations and (**d**) Mg (mg/L) concentrations in the leachates of the 10 irrigation applications of the four treatments. Each value is the mean of three replicates. Calcium and magnesium content was higher in the leachates of the second bio-mixture (biomix 2%) and the third bio-mixture (biomix 3%) compared to that of the first bio-mixture after the first irrigation, but they were still lower than that of the control soil, while at the end of the irrigation period concentrations were at the same levels, with slightly increased values in the leachates of the second bio-mixture (biomix 2%) (Figure 3c,d). Sodium absorption ratio (SAR) values in all leachates were also determined during the irrigation scheme in order to evaluate the potential impact of irrigation water on bio-mixtures and control soil. Compared to the control soil, slight reductions were observed in terms of sodium absorption ratio (SAR) values, which were all almost at the same levels (Figure 4a). As regards leachates' total hardness, values of all three bio-mixtures were lower than that of the control soil during the first irrigations while, at the end of all watering applications, all values decreased, in particular with a lower value observed in the first bio-mixture (biomix 1%) (Figure 4b). As far as the leachate copper contents were concerned, a decline was observed in all bio-mixtures in comparison to the copper content of the control soil leachate, whilst the lowest concentration was determined in the first bio-mixture (biomix 1%) at the end of irrigation (Figure 5a). Concerning iron, leachate concentration values fluctuated throughout the irrigation period (Figure 5b). Manganese showed a gradual increase in leachates of all three bio-mixtures during irrigation compared to its value in the control soil, recording a higher concentration in the second bio-mixture (biomix 2%) (Figure 5c). Regarding zinc concentration in the leachates, a reduction took place during the first water application in the first bio-mixture (biomix 1%) and the second bio-mixture (biomix 2%), though concentration values rise as irrigation continued; nevertheless, in the end, there were lower values in bio-mixture leachates than in the control soil leachate, with the lowest value being observed in the second bio-mixture (biomix 2%) (Figure 5d). Figure 5: Changes of: (**a**) Cu (mg L\({}^{-1}\)) concentrations, (**b**) Fe (mg L\({}^{-1}\)) concentrations, (**c**) Mn (mg L\({}^{-1}\)) concentrations and (**d**) Zn (mg L\({}^{-1}\)) concentrations in the leachates of the 10 irrigation applications of the four treatments. Each value is the mean of three replicates. Synopsizing, at the end of the irrigation scheme, leachate content deriving from soil supplementation with the bio-mixture used as a physical filter for OMWW degradation does not pose a threat to groundwater, since all values are within the limit concentrations [32].