The produced biogas was collected by acidified (pH = 3) saturated NaCl water solution displacement in a biogas collection unit. The gas meter consisted of a volumetric cell for gas–liquid displacement, a sensor device for liquid level detection, and an electronic control circuit for data processing and display. The methane content in the biogas was measured using a PerkinElmer Auto System Gas Chromatographer equipped with a Thermal Conductivity Detector (TCD) as described in Gianico et al. (2013).