Improved control of anaerobic digestion A recent EU project has developed a system to give farmers improved control over anaerobic digestion of biological waste by monitoring fatty acid production. Digital Economy © Thinkstock Biogas can be produced in an anaerobic digestion plant, which employs bacteria to degrade organic matter in the absence of oxygen. Despite the positive environmental impacts of these plants, high investment costs and low profitability have limited their uptake in Europe. Better control and monitoring of biogas production would help increase profitability and stability. The EU-funded OPTI-VFA (Novel monitoring and process control system for efficient production of VFA and biogas in anaerobic digestion plant) initiative aimed to develop a prototype online monitoring and control system based on measuring volatile fatty acid (VFA) production in anaerobic digesters. OPTI-VFA began by surveying farmers and other anaerobic digester operators in Europe about their needs, which highlighted the importance of a VFA monitoring system. A vast model compound measurement study was made with commercial FTIR instrument in order to select suitable measurement technology and to develop calibration models to monitor VFAs in an anaerobic digester. A piezo actuated Fabry-Perot interferometer operating in Mid IR was chosen to be used in future prototypes. The next step was to model different aspects of the envisioned digester, and to design suitable measurement system which included a measurement prototype, optical probe and a control system. Once the prototype was designed, researchers built and tested it in the lab. Commercial partners also provided input on the device. OPTI-VFA's prototype uses infrared spectroscopy and developed calibration models to detect changes in VFA concentrations within the digester, and is controlled through a user-friendly software interface. Laboratory testing showed that the system is capable of measuring main VFA concentrations accurately in real time. A general simulation-based methodology has been developed to design and validate automatic controllers for conventional Anaerobic Digesters. A control strategy for a lab-scale 2-phase system was tested and demonstrated. The prototype is set to make a positive impact on the growing biogas and green chemicals industry. Keywords Anaerobic digestion, farmers, biogas, OPTI-VFA, monitoring and process control, volatile fatty acid, optical measurements, calibration, process simulation and modelling
