## 4 Discussion  
Literature analysis shows that most studies on the effect of overpressure on various parameters of the AD process were carried out in digesesters with a small volume: from 0.6 L [20] to 50 L [42]. Table 3 summarizes the results of such studies. The most similar substrate (simulated food waste) was subjected to anaerobic digestion in 3-L digesters by [PERSON] et al. [43]. At OLR of 2.67 kg COD/(m\({}^{3}\) \(\cdot\)day) and overpressure from 1 to 3 bars, the MPR and MY values were obtained in the range of 0.74-0.75 L/(L-day) and 280 mL/g COD, respectively; pH had near-neutral values (7.4-7.5). Interestingly, the methane content increased from 52.4% to 67% with an increase in excess pressure from 1 to 3 bar. The difference in AD performances can be explained by the extremely high OLR (5.49-16.38 kg VS/(m\({}^{3}\)-day) in the current work compared to [PERSON] et al. [43]. at an overpressure of 1-3 bars. The pH was in the range of 7.35-6.8 with a tendency to decrease with increasing overpressure, and the COD removal was 89.95%-95.28% with a tendency to increase with increasing overpressure [45]. The results obtained in [48] showed that an increase in pressure had a significant negative effect on the removal of COD, although the process proceeded at favorable OLR values. At an OLR of 20 kg COD/(m\({}^{3}\)-day), the pressure increase led to a decrease in COD removal from 88% at atmospheric pressure to 62% at 4 bar. In [48], despite the increase in methane content, MPR decreased with the increase in pressure. At the same time, MY also decreased: at an OLR of 20 kg COD/(m\({}^{3}\cdot\)day), the MY was around 330 mL/g COD\({}_{\text{removed}}\) at no overpressure and there was a consistent decrease in MY to 270 mL/g COD\({}_{\text{removed}}\) at an overpressure of 1 bar. At the same time, pH was in the range of 7.14-7.98 with a tendency to decrease with increasing overpressure. [PERSON] et al. [45] observed a decrease in the MY in the AD of grass/maize silage from 303.8 mL/g COD\({}_{\text{added}}\) to 258.0 mL/g COD\({}_{\text{added}}\), at increasing pressure from 1 bar to 9 bar. In current study, anaerobic codigestion of SS and OF-MSW at an overpressure in in digesesters of 150-200 kPa was possible at OLRs of 10.5-16.5 kg VS/(m\({}^{3}\cdot\)day), which is significantly higher than the OLR used at WWTP in the Russian Federation (3-6 kg VS/(m\({}^{3}\cdot\)day)) (information from personal communication with managers and operators of digesters of SelkhozBioGaz LLC and WWTPs (Lyuberetsky WWTP (Moscow, Russia), Kuryanovsky WWTP (Moscow, Russia), Nizhny Novgorod WWTP (Nizhny Novgorod, Russia))). Thus, the currents findings correlate well with data obtained by other authors using various substrates. High degrees of vs. removal in the current study were presumably associated with the use of pig feed containing a significant amount of easily biodegradable organic matter as a cosubstrate. The increase in the efficiency of the AD process at excess pressure in the digester is primarily associated with an increase in the concentration of dissolved carbon dioxide. Accepting electrons from hydrogen in hydrogenotrophic methanogenesis, it reduces its partial pressure and stimulates syntrophic interactions [16]. The second reason for AD process improvements can be in better buffering capacity due to higher bicarbonate ion concentration in the bulk liquid. Higher alkalinity helps to withstand shock loads of volatile fatty acids. Herein pressurized AD may well become an essential strategy to efficiently convert high-strength, easily degradable wastes such as OF-MSW or food waste into energy, thereby maximizing performance and process stability. Successful testing of semipilot overpressurized digesters makes it possible to further scale up the process in block-modular anaerobic bioreactors based on railway tanks, which are widely used as digesters in the Russian Federation and adapted to moderate pressurization.