## 3 Results and Discussion
The values of the potential methane production parameter, which for catering food waste are in the range of 216-1476 L/kg VS [33], enable the volume of methane that can be produced during this waste digestion to be established. For the potential methane production of 216 L/kg VS, these values are 43,170 m\({}^{3}\)/year, 70,970 m\({}^{3}\)/year, and 201,460 m\({}^{3}\)/year for towns A, C, and E, respectively. Considering the upper value of the parameter (1476 L/kg VS), the respective values would be 295,000, 484,980, and 1,376,650 m\({}^{3}\) methane/year, respectively (Table 6). The discharge of wastewater from food service (catering) facilities to the Sewerage system has certain consequences in terms of energy consumption. Organic pollutants contained in food waste must be neutralized in the process of aerobic biotereatment. The introduction of oxygen into the activated sludge chambers entails electricity consumption. The amount of energy used to this end was determined based on the value of the indicator showing the amount of energy consumption (kWh) per 1 kg of the BOD load removed (kWh/kgBOD\({}_{\text{rem.}}\)). According to literature data, the values of this indicator range from 0.533 to 4.34 kWh/kgBOD\({}_{\text{rem.}}\)[34,35]. In order to calculate the volume of load removed, the efficiency of BOD removal was assumed to be 95%. The results of the calculations are presented in Table 6.  
If the system for the collection of food waste from restaurants and other facilities for mass catering was in operation in town A, then the energy consumption recorded in its wastewater treatment plant in 2019 would be lower by 66,400 kWh (for a specific energy consumption of 0.533 kW/kg BOD\({}_{\text{rem. }}\)) or by 544,240 kWh (for a specific energy consumption of 4.34 kW/kg BOD\({}_{\text{rem.}}\)). In town C, these values would amount to 109,800 and 894,690 kWh/year, respectively. In turn, energy savings in town E would range from 311,700 to 2,539,770 kWh/year. The values presented above indicate a very strong need to introduce a system for collecting food waste from catering facilities and delivering it to sludge facilities at the wastewater treatment plants. On the one hand, implementation of this solution is expected to ensure a significant reduction in electricity consumption for the aerobic treatment of wastewater in treatment plants, a probable improvement in the quality of treated wastewater, a reduction in the amount of sewage sludge generated, and a reduction in the cost of its treatment. In addition, more biogas will be produced in sludge and waste fermentation facilities. On the expenditure side, there will be costs of implementing and maintaining a food waste collection system and increased costs of its processing in closed digesters. Taking into account the results of the calculations, it can be envisaged that the revenues and savings resulting from the implementation of the system will significantly exceed the expected costs. The implementation of a food waste collection system from catering facilities should underlie changes in the approach to food waste in entire towns. The next step should be to introduce a management system for this type of waste, including multi-family blocks of flats and single-family houses.