## 2 Materials and Methods
### Analytical Methods  
The reducing sugars content was analyzed using the Miller method [16]. The method is based on the redox reaction between reducing sugars and sodium dinitrosalicylate which gives a reddish-brown derivative. Absorption was measured at a wavelength of 530 nm. Protein content was analyzed according to the Bradford method [17]. The method is based on the reaction of Coomassieie Brilliant Blue G-250 with proteins resulting in a shift in the dye color to blue with maximum absorption at 595 nm. Cellulose was determined by the spectrophotometric method [18]. Cellulose-containing materials are released from impurities such as lignin, hemicellulose, xylosans, and other low molecular weight compounds by extraction with an acetate-nitrite mixture. The purified cellulose was dissolved in 67% H\({}_{2}\)SO\({}_{4}\), followed by a color reaction with an anthrone reagent. The cellulose concentration was determined after measuring the absorbance at 620 nm. Determination of total solids (TS) and volatile solids (VS) was performed by a standard method by drying a certain volume of sample to constant weight at 105 \(\pm\) 3 \({}^{\circ}\)C (for determining TS) and subsequent annealing at 575 \(\pm\) 25 \({}^{\circ}\)C (for determining the ash content). The difference between TS and ash content shows the amount of vs. in the sample [19]. Because of the high organic content (and to avoid some losses during the annealing), the samples were heated slowly to ensure slow oxidation of organics and to prevent the sample from igniting. The heating, annealing, and cooling down to room temperature (in a desiccator) were repeated to reach a constant weight in two consistent measurements. The concentration of volatile fatty acids was determined by a Thermo Scientific gas chromatograph (Focus GC model) equipped with a Split/Splitless injector, column: TG-WAXMS A, (length 30 m, diameter 0.25 mm, film thickness 0.25 \(\upmu\)m), and flame ionization detector (FID). Prior to injection, the pH of the sample taken from the bioreactor was adjusted to pH 2.0 with 37% H\({}_{3}\)PO\({}_{4}\). After one hour, the sample was centrifuged at 15,000 rpm for 10 min and a liquor of the supernatant was mixed with an equal volume of 1% 2.2-dimethyl-butyric acid (as an internal standard). During each run of the chromatographic analysis, the temperature of the oven started from 110 \({}^{\circ}\)C and was set to increase to 210 \({}^{\circ}\)C and held for 2 min. The FID temperature was set at 210 \({}^{\circ}\)C. Biogas content of the gas produced from BR\({}_{1}\) (containing hydrogen) and gas produced from BR\({}_{2}\) (containing methane) was estimated as follows: with a device model \"Gasboard 3100P\" (Cubic Sensor and Instrument Co., Ltd., Wuhan, China), equipped with  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Lot** & **pH*** & **TS***, \%** & **VS***, \%** & **Proteins, g/L** & **Reducing** & **Cellulose,** \\  & & & & **g/L** & **Sugars, g/L** & **g/L** \\ \hline Amilum, 2010 & 4.2 & 50.5 & 91 & 10.2 \(\pm\) 0.5 & 282.4 \(\pm\) 10.1 & 2.46 \(\pm\) 0.1 \\ ADM, 2018 & 4.2 & 50.5 & 91 & 48.0 \(\pm\) 0.6 & 110.0 \(\pm\) 5.7 & N/A \\ \hline \hline \end{tabular}  
* The data are provided by ADM Razgrad EAD in the accompanying information sheet to the raw material.  
\end{table}
Table 1: Characteristics of CSL—104 (ADM Razgrad EAD).  
infrared sensors for measuring the relative content of CO2 and H2 (in % by volume); with the instrument model \"Drager, X-am7000\" (Germany), equipped with infrared sensors for measuring the relative content of CH4 and CO2 in percentage by volume and a catalytic sensor for H2S (in ppm).