## 4 Conclusions  
This study showed that both pretreatment of the lignocellulosic material with ultrasonic radiation and disintegration with a pulsed electric field increased methane production.  
The application of ultrasonic treatment in the UPB series increased the COD value from 5957 \(\pm\) 71 mg O\({}_{2}\)/L to 6991 \(\pm\) 86 mg O\({}_{2}\)/L. In the same series, the TOC concentration increased from 1922 \(\pm\) 76 mg/L to 2269 \(\pm\) 60 mg/L. Regarding the pulsed electric field treatment, the highest increase in the COD and TOC was obtained in the PEF5 series. The TOC concentration increased from 1922 \(\pm\) 48 mg/L to 2252, whereas the COD concentration increased from 5957 \(\pm\) 71 mg O\({}_{2}\)/L to 6973 \(\pm\) 85 mg/L. Regarding the UP, BMP increased from 210.42 \(\pm\) 7.92 mL/g VS to 250.06 \(\pm\) 8.68 mL/g VS. Biogas production coefficient increased from 307.29 \(\pm\) 13.65 mL/g VS to 365.07 \(\pm\) 11.71 mL/g VS. The application of pulsed electric field disintegration increased the BMP from 210.42 \(\pm\) 7.92 mL/g VS to 248.90 \(\pm\) 9.29 mL/g VS. Biogas productivity increased from 307.29 \(\pm\) 13.65 mL/g VS to 366.99 \(\pm\) 14.18 mL/g VS. Despite the slightly greater methane gain in the sample treated with ultrasounds, both the reaction rate and the methane production rate were more advantageous in the PEF-disintegrated sample.  
The data show that under the influence of PEF and UP, organic compounds were released into the dissolved phase, which caused an increase in BMP.  
This study demonstrated that disintegration using a pulsed electric field could find application in anaerobic digestion to improve BMP. Considering the energy balance carried out, it turned out that only in one series with PEF application was there an energy gain. Pretreatment with ultra-sound in all series showed energy losses.  
Conceptualisation, D.S.; funding acquisition, D.S. and M.Z.; investigation, D.S., A.N., and M.Z.; methodology, D.S., A.N., and M.Z.; supervision, D.S.; visualisation, D.S. and A.N.; writing--original draft, D.S., A.N., and M.Z.; writing--review and editing, D.S. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Series**} & \multirow{2}{*}{\(\mathbf{E_{in}}\) (**Wh/g TS**)} & \multicolumn{2}{c}{\(\mathbf{E_{out}}\)} & \multicolumn{2}{c}{\(\mathbf{E_{T}}\)} \\  & & \multicolumn{2}{c}{**(Wh/g TS)**} & \multicolumn{2}{c}{**(Wh/g TS)**} \\ \cline{3-6}  & & **PEF** & **UP** & **PEF** & **UP** \\ \hline
0 & - & - & - & - & - \\
1 & 0.05 & 0.03 & 0.00 & \(-\)0.02 & \(-\)0.05 \\
2 & 0.10 & 0.08 & 0.08 & \(-\)0.02 & \(-\)0.02 \\
3 & 0.15 & 0.19 & 0.11 & 0.04 & \(-\)0.04 \\
4 & 0.20 & 0.20 & 0.15 & 0.00 & \(-\)0.05 \\
5 & 0.26 & 0.22 & 0.17 & \(-\)0.04 & \(-\)0.09 \\
6 & 0.30 & 0.24 & 0.20 & \(-\)0.06 & \(-\)0.10 \\
7 & 0.36 & 0.24 & 0.22 & \(-\)0.13 & \(-\)0.14 \\
8 & 0.41 & 0.24 & 0.25 & \(-\)0.17 & \(-\)0.16 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Energy balance.  
**Funding:** The research was funded by the National Centre for Research and Development as part of the LIDER IX programme. The project is entitled \"Development of a lignocellulosic biomass disintegration technology using a pulsed electric field\" LIDER/8/0026/L-9/17/NCBR/2018. The subsidy amount was PLN 1,166,250.00. Project financially supported by the Minister of Education and Science under the program entitled \"Regional Initiative of Excellence\" for the years 2019-2023, Project No. 010/RID/2018/19, amount of funding 12,000,000 PLN.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.