## 2 Materials and Methods
The Germination Index is calculated with the Formula (1):  
\[\text{GI}\left(\%\right)=\text{(NG}_{\text{S}}\cdot\text{ARL}_{\text{S}} \cdot\text{NG}_{\text{C}}{}^{-1}\times\text{ARL}_{\text{C}}{}^{-1})\cdot\text{100} \tag{1}\]  
GI: germination index; NG: number of germinated seeds; ARL: average root length; S refers to the sample; and C refers to the control. **Analytical methods:** The Analytik Jena TOC analyzer multi N/C 3100 (Jena, Germany) was used to determine total organic carbon (TOC), dissolved organic carbon (DOC), and total nitrogen (TN). For DOC measurements, the sample was filtered with a [PERSON] 0.45 \(\upmu\)m membrane filter (Kent, UK). The chemical oxygen demand (COD) was measured \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & **1 Inoculum** & \multicolumn{2}{c}{**2 Raw**} & \multicolumn{2}{c}{**3 Depolyphenolized OMW**} & \multicolumn{2}{c}{**4 Co-Substrate**} & \multicolumn{2}{c}{**5 Retentate**} \\ \hline  & **Volume** & **VS** & **Volume** & **VS** & **Volume** & **VS** & **Volume** & **VS** & **Volume** & **VS** \\ \hline
**Sample Name** & **L** & **g** & **L** & **g** & **L** & **g** & **L** & **g** & **L** & **g** \\ \hline Inoculum & 0.35 & 6.11 & 0.35 & 6.11 & 0.35 & 6.11 & 0.35 & 6.11 & 0.35 & 6.11 \\ OMW & & & 0.10 & 6.11 & & & 0.07 & 4.28 & & \\ Depolyphenolized & & & & & 0.21 & 6.11 & & 0.10 & 3.06 \\ OMW & & & & & & & 0.02 & 1.83 & & \\ Co-Substrate & & & & & & & & 0.04 & 3.06 \\ Retentate & & & & & & & & 0.22 & 0.18 & \\ Water & 0.32 & & 0.22 & & 0.11 & & 0.22 & & 0.18 & \\ Total & 0.67 & 6.11 & 0.67 & 12.23 & 0.67 & 12.23 & 0.67 & 12.23 & 0.67 & 12.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition of the BMP samples (all OMW samples derive from OMW 1). based on the thermal disintegration of the samples at 1200 \({}^{\circ}\)C using the QuickCODlab-03D0318 analyzer and autosampler from LAR Process Analysers AG. The pH and conductivity were measured using an OHAUS Starter 2100 and a Consort C651 sensor. The Folin-Ciocalteau method was used to determine the polyphenol concentration in gallic acid equivalents. The following protocol, which was optimized at the Technical University of Berlin (TUB), was used to prepare 96-well plates: (1) add 90 \(\mu\)L ultrapure water; (2) add 20 \(\mu\)L of gallic acid standard or sample diluted to the calibrated concentration; (3) add 10 \(\mu\)L Folin-Ciocalteau reagent; and (4) add 100 \(\mu\)L Na\({}_{2}\)CO\({}_{3}\) (10.75%). The reaction time is 30 min in the dark (first 15 min shaking at 100 rpm). The light absorption at 620 nm is measured. The blank sample was subtracted, and gallic acid equivalents were calculated based on a linear calibration curve (gallic acid: 800, 400, 200, 100, 50, and 25 mg\(\cdot\)L\({}^{-1}\)). The dry matter (DM) was determined in accordance with DIN 12,880 by drying the sample for 24 h and weighing the mass difference. The dried samples were oxidized at 600 \({}^{\circ}\)C for 6 h to remove all organic components and re-weighted to determine the organic dry matter (VS). To quantify the methane content in the biogas, the sample vials are flushed for 5 min with nitrogen gas. The vial is then flushed with the produced biogas for at least 5 min and afterward analyzed in a gas chromatography system (Agilent Technologies 7890A GC System with a Bora bond q column and Agilent Technologies G188, Network Headspace Sampler). Based on the Nordmann method and a titration test adapted by the German Federal Agricultural Research Center (FAL), the ratio between the volatile fatty acids and the total alkalic carbonates (FOS/TAC) was measured. A total of 20 mL of sample is placed on a magnetic stirrer and homogenized consistently. Using the SCHOTT TitroLine Easy, 0.1 N H\({}_{2}\)SO\({}_{4}\) (=0.05 mol\(\cdot\)L\({}^{-1}\)) was titrated until the sample reached pH 5. The time and amount of acid needed are recorded. The titration is then continued until pH 4.4 is reached, and the needed time and amount of acid are recorded again.