## 4 Description of the Experiment  
The experiment consists of five identical ADs, insulated metal cylinders (cylinders used for filling household gas) equipped with openings, as shown in Figure 1a. The five digesesters were thermally insulated with reflective foam rolls (Figure 1d) and equipped with electric heaters (12-volt LED strips) (Figure 1b), temperature control devices (thermostats) (Figure 1c), and a temperature sensor for each digester in the center of the substrate. The water displacement method was used to measure the volume of the produced biogas. The tube coming out of the digester is connected to the top of plastic gallons (25 L capacity), and a tube is connected to the bottom of the plastic tank to collect water in containers (Figure 1e). The weight of the water in kilograms represents the volume of the gas released in liters. The organic material used was kitchen food waste (leftover cooked rice and bulgur, potatoes, eggplant, and stale bread) at 6.5 kg, fresh human waste (toilet waste) at 1.5 kg, and fermentation inoculum (water from a previous digester with cow manure) at 2.5 kg. Each digester was filled with about 2 kg of the mixture, which consisted mainly of food waste (about 81%) and toilet waste (about 19%). The temperatures were set according to five values: 55, 50, 45, 40, and 35 \({}^{\circ}\)C. Temperature measurements for the five digesters were taken six times a day (every four hours) to achieve the best possible accuracy, and the average temperature for each digester was recorded. The results were as follows: 49.6, 45.9, 43.5, 37.5, and 33.2 \({}^{\circ}\)C. The daily amount of gas released was calculated based on the weight of the displaced water for each digester. The experiment was put into service on 12 September 2022 and ended on 10 November 2022. The data were recorded in a programmed Excel spreadsheet containing the modeling results from the Greenius 4.9.0.1 and steam calculations programs, and the mathematical equations used to obtain the results and the graphs. The results of the experiment are shown in Table 5.  
Figure 1: Experiment of biogas production from five batch digesters at different temperatures. Psychrophile bacteria, the temperature range is between 10 and 20 \({}^{\circ}\)C; Mesophiles bacteria, the temperature range is between 20 and 40 \({}^{\circ}\)C; Thermophiles bacteria, the temperature range is between 50 and 65 \({}^{\circ}\)C. Of course, these values are approximate and may vary from one reference to another. The most typical range is the second one, where mesophilic bacteria thrive. By reading the actual average temperatures while considering the thermal gradient occurring in the digester, where the sensor is placed in the middle of the liquid, the section close to the surface produces biogas at a higher temperature. In comparison, the surrounding section operates at a lower temperature due to the heat loss to the outer surroundings. By plotting the work points on the graph in Figure 2, we find that the first and second cases (points 1 and 2) fall within the range of moderate temperatures (20-40 \({}^{\circ}\)C) and below the ideal value for bacterial growth. The third point is the one that achieved the highest biogas production rate, representing the ideal value (37.5 \({}^{\circ}\)C) in this field. The fourth point, representing the fourth state, lies outside the average temperature range. The fifth point, which represents the fifth condition, is located at the beginning of the high-temperature range for bacterial growth and below the ideal value within this range. The decline in biogas production in cases 4 and 5 (points 4 and 5) compared to point 6 can represent a transitional area between the medium- and high-temperature ranges, as both have indicated; this is consistent with the results of [PERSON] et al. (2019) and [PERSON] (2019). Since the amount of its composite materials is constant, naturally switching from one operating temperature range to another does not increase the overall amount of biogas generated.