## 4 Conclusions  
The use of ultrasound as a technique for the pretreatment of M-BGS biomass significantly influenced the efficiency of the AD process. The effects concerned both a higher solubilization of organic matter and a significant increase in the kinetics of the anaerobic processes.  
The ultrasonication of M-BGS resulted in an increase in the concentration of the dissolved COD and TOC fractions. In most of the variants, the COD and TOC concentrations increased by more than six times compared to the variant without UP. Strong positive correlations were found between the duration of UP and the COD and TOC concentrations in the dissolved phase, which allows for the use of simple linear models to predict the obtained technological effects.  
The study showed a positive effect of UP on the AD of M-BGS biomass. The highest efficiency of CH\({}_{4}\) production was found in the variants in which the ultrasonication lasted from 150 s to 200 s, and this was from 534 \(\pm\) 16 cm\({}^{3}\) CH\({}_{4}\)/g VS to 561 \(\pm\) 17 cm\({}^{3}\) CH\({}_{4}\)/g VS. These variants were also characterized by the fastest kinetics of the anaerobic process.  
An energy gain assessment of the anaerobic digestion of the M-BGS pretreated with ultrasound showed that the highest net energy output of 4.21 \(\pm\) 0.17 Wh/g VS was obtained with 150 s of sonication. Similarly, the estimation of the net energy gain indicated this variant of the experiment as the most effective. The data analysis confirmed the existence of strong correlations between the UP time, amount of biogas and methane production, and gross energy gain.  
It should be emphasized that the obtained results are only the basis for further development work. This type of innovative solution must reach the appropriate technical readiness level (TRL) before the development of implementation assumptions. This is performed in many stages throughout the concept, then small-scale tests, the design and construction of a prototype, a pilot-scale exploitation, and a fractional-scale operation can occur. Only then can the appropriate knowledge base be acquired to assess the ultimate performance and cost-effectiveness of the technology at scale. The research presented in the study is preliminary laboratory work at the initial TRL. This technology requires significant supplementation both with the results of the application of optimization techniques and a verification of the obtained technological efficiency and economic profitability in the operating conditions of a significantly larger installation.  
Conceptualization, M.D. and M.Z.; methodology, M.D. and M.Z. validation, M.D.; formal analysis, M.D. and M.Z.; investigation, M.D., M.K. and M.Z.; resources, M.D., M.K., M.Z. and J.K.; data curation, M.D., M.K., M.Z. and J.K.; writing--original draft preparation, M.D. and M.K.; writing--review and editing, M.D., M.K., M.Z. and J.K.; visualization, M.D. and M.K.; supervision, M.D.; project administration, M.D. and M.K.; funding acquisition, M.D. All authors have read and agreed to the published version of the manuscript.  
The manuscript was supported by Project financially supported by Minister of Education and Science in the range of 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, and the work WZ/WB-IIS/3/2022, funded by the Minister of Education and Science.  
Not applicable.