## 3 Results and Discussion
### Results of Biodegradation  
#### 3.4.1 Degradation of DOC  
In consideration of the results obtained in the sterile control columns, the decrease of DOC concentration in the active column was only caused by the biodegradation process. Other processes such as sorption or chemical oxidation, potentially responsible for DOC removal, can be neglected in this study. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Soil Fraction**} & **Volumetric Soil** & **Volumetric Soil** & **Water Filled** & **Water Filled** & \multirow{2}{*}{**Water-Air-Ratio–Wet**} & \multirow{2}{*}{**Water-Air-Ratio–Dry**} \\  & **Moisture** & **Moisture** & **Pore** & **Pore** & & \\  & **Content-Wet** & **Content-Dry** & **Space-Wet** & **Space-Dry** & **Phase [-]** & **Phase [-]** \\  & **Phase (vol. \%)** & **Phase (vol. \%)** & **Phase (\%)** & **Phase (\%)** & & \\ \hline
125–200 μm & 0.39 & 0.38 & 89 & 86 & 7.9 & 6.1 \\
200–630 μm & 0.33 & 0.32 & 80 & 77 & 4.0 & 3.3 \\
630–1000 μm & 0.29 & 0.22 & 75 & 58 & 3.1 & 1.4 \\
1000–2000 μm & 0.24 & 0.16 & 65 & 44 & 1.9 & 0.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of water balance. After different lag phases (4 days for the fractions 630 \(\upmu\)m to 1000 \(\upmu\)m and 1000 \(\upmu\)m to 2000 \(\upmu\)m, and 12 days for the fractions 125 \(\upmu\)m to 200 \(\upmu\)m and 200 \(\upmu\)m to 630 \(\upmu\)m), the degradation in all soil fractions followed an exponential trend and continued with a stationary phase (Figure 3A). The highest microbial activity and consequently degradation rate of organic substances for this experimental condition (type of bacteria, temperature, infiltration cycle, water quality) was provided by the fraction 630 \(\upmu\)m to 1000 \(\upmu\)m (Figure 3B). The supply of oxygen and nutrients to bacteria as well as the soil moisture were optimal here due to the specific pore size distribution of these fraction (widest range of pore sizes defined by the PSD index), which corresponds to a WFPS of 58% in the dry phase. These results are consistent with data reported for other applications [19; 37; 38; 39; 40; 58; 59], where the biodegradation was most effective at WFPS 60%. Further, previous studies (Table 4) involving a wide range of soil types also indicate that the maximum microbial activity and consequently the highest biodegradation of organic substances can be expected between 50% and 70% of a soil's water holding capacity or field capacity. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Water** & **Water** & **Water** & **Static** & **Application** & **Source** \\
**Saturation** & **Saturation** & **Saturation** & **Potential (Pa)** & **Poil Type** & **(Biodegradation of)** & **Source** \\
**(\%)** & **(\%FC)** & **(\%WHO)** & & & & \\ \hline
28–95 & n.a. & 30–90 & 400–5000 & Loamy sand & Hydrocarbons & [60] \\
30–98 & n.a. & 25–85 & 300–4000 & n.a. & n.a. & [26] \\
53–71 & n.a. & 50–70 & 1000–2000 & n.a. & Pesticides & [61] \\
58–82 & n.a. & 58–82 & n.a. & Peat and sand & Pentachlorophenol & [62] \\
70–93 & n.a. & n.a. & n.a. & Sand/gravel & Hydrocarbons & [63] \\
26–47 & n.a. & n.a. & n.a. & Sandy loam & Pentachlorophenol & [64] \\
21–83 & n.a. & n.a. & n.a. & Sandy loam & Metolachlor & [65] \\
70–93 & 35–50 & n.a. & 500–1000 & n.a. & Fuel and solvent & [66] \\
53–70 & 50–70 & n.a. & 1000–2000 & Silty loam & Hydrocarbons & [67] \\ n.a. & n.a. & 50–80 & n.a. & Sandy loam & Polynucleararomatics & [68] \\
**(\(\mathrm{PNAs}\))** & **(\(\mathrm{PNAs}\))** & **(\(\mathrm{PNAs}\))** & **(\(\mathrm{PNAs}\))** & **(\(\mathrm{PNAs}\))** & **(\(\mathrm{PNAs}\))** \\ n.a. & n.a. & 66–100 & n.a. & n.a. & Constituents in waste fluid & [69] \\ n.a. & 60–80 & n.a. & n.a. & Silty sand & n.a. & [70] \\ n.a. & n.a. & 41–62 & n.a. & Sandy loam & n.a. & [71] \\ \hline \hline \end{tabular} Note: n.a.—not available.  
\end{table} 
Table 4: Water saturation and matric potential ranges for optimal biodegradation conditions.