Anaerobic digestion is a biological process where the organic matter is degraded to form biogas and a digestate. Biogas can be fired in combined heat and power (CHP) engines or purified and injected into the gas grid. The total primary energy produced from biogas in Europe was 5.9 million toe in 2007, and there is still growing potential, since the white paper objective for 2010 is 15 million toe and there is a huge amount of organic waste available that is disposed without valorisation.
Control and optimisation of AD plants is a key issue and one of the main research topics of this field. AD plants operators usually have to drive the plant with the only information of pH and biogas composition. This often leads to a situation of underuse of the plant, if the operator prefers to drive the plant in a conservative way, or process malfunction, if the operator chooses to drive the plant near the load limit.
Out of all the parameters proposed to control the process, the more reliable is the volatile fatty acids profile (VFAP) that consists on the single VFA concentration (acetate, propionate, butyrate etc.). This parameter allows checking not only the process state but also predicting and avoiding process malfunction, what is not possible with other parameters (pH, biogas composition, etc.). With the information of VFAP, AD plants operators could optimise the plant, increase biogas production and avoid process stops. The currently available technique to measure VFAP is gas chromatography (GC): an off-line measurement that needs specific equipment and trained specialists, and takes 1-2 weeks between the sampling and the results, making the measurement no longer valuable for process optimisation.
AD-WISE aims to develop an on-line device able to get real time VFAP measurements based on optic techniques and to integrate these measurements in the control system of the AD plant in order to optimise the process (maximise biogas production while maintaining process stability).
Fields of science
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