## 3 Results and Discussion
### Overall Operation of the IoT Anaerobic Bioreactor and Future Additions  
The cost for a preconfigured commercial bioreactor of 3 L according to an offer (July 2024) was EUR 46,500. The commercial reactor included a borosilicate glass vessel, stirrer, temperature control system, flow entry control system for two gases, pH, pO\({}_{2}\), and antifoam control, four peristaltic pumps with control, and an operating panel. However, incorporating a biogas analyzer module (measuring CH\({}_{4}\), CO\({}_{2}\), O\({}_{2}\), and H\({}_{2}\)S) would increase the cost of the commercial bioreactor by approximately EUR 8000 (offered October 2024). The 60 L pilot bioreactor was significantly lower than the commercial bioreactor. The total cost of the bioreactor without the IoT system was approximately EUR 20,000, including the materials (made of acrylic), four peristaltic pumps, labor, steel base for the bioreactor and peristaltic pumps, the stirring, and the heating system (Figure S1). The total cost of converting the bioreactor to an IoT-enabled device was under EUR 2000, excluding labor. The purchase of pH, REDOX, and ammonium electrodes was the highest expense, which accounted for 75% of the total. The remaining costs covered ESP32 boards, auxiliary circuit boards, temperature sensors, and other components. Moreover, the IoT system could be installed in existing bioreactors minimizing the cost only to the cost of the IoT system. Although the commercial bioreactor had more capabilities and probably better efficiency, the IoT bioreactor in this study was a more cost-effective solution for monitoring AD parameters. The high monitoring efficiency and low cost of these microcontrollers and IoT devices have been confirmed by other researchers [20; 30]. With proper maintenance, especially for the electrodes, all the equipment of the IoT system can be reused in other experimental setups. In contrast, most commercial bioreactors often feature custom sensors or ancillary equipment tailored to the device, limiting their use in other configurations. While the development time for a custom IoT bioreactor using microcontrollers such as the ESP32 may be longer, the resulting system offers greater customization options and long-term cost-effectiveness. The ability to program these microcontrollers provides researchers with a versatile tool for AD studies. It empowers researchers to tailor the system to specific research needs, enabling continuous data logging and remote monitoring. Additionally, since they are DC-powered, these devices can maintain data logging during power outages by switching to battery backup. Moreover, the required time to learn microcontroller programming has significantly decreased due to the rapid development of conversational AI, which can simplify complex code, explain functionality, suggest improvements, and even generate and execute code [56]. The IoT bioreactor has potential for future upgrades, such as the ability to monitor and adjust operational parameters, as well as adding new monitoring features. Operational adjustments could include controlling the runtime of substrate feed pumps for optimal sampling, automatic pH regulation using acid/base pumps, and electric valves for automated effluent bottle draining. Additional monitoring features could involve sensors for leak detection, both for liquids and biogas, enabling immediate response by the operator. Installing a web camera, integrated with other monitoring parameters, can improve site oversight through remote surveillance. Incorporating an in situ storage device, such as an SD card, can improve data security by safeguarding against potential data loss due to internet connectivity issues or cybersecurity breaches. Finally, the development of an AI-powered software solution could process bioreactor monitoring data. This AI system could be trained on historical data of the IoT bioreactor to optimize feedstock composition for obtaining the maximum CH\({}_{4}\) yield from the used substrates.