Gravimetric measurements

Three reactor slides were used to characterise the thickness and density of biofilms in each of the three experiments at the end of the development process [48]. In brief, the slides were removed from the reactor, drained for 5 min at a vertical position and weighed for the determination of the wet mass. Then, the slides were dried for 24 h at 65 °C in an oven and weighed again. After that, the dried biofilm was washed off the slides with distilled water and laboratory tissues. The clean slides were dried again for 24 h at 65 °C and then weighed again. The dry mass was determined by the weight difference of the slides with and without the dried biofilm. After calculating the biofilm thickness and volumetric biofilm density, the areal biofilm density was calculated as the product of the biofilm thickness and the volumetric biofilm density. Finally, gravimetric measurements were conducted prior to the onset of each of the three experiments, in which all sterile slides were weighed to determine their weight without any biofilm attached to them. For these measurements the Fisherbrand™ Analytical Balance MH-214 was used (Fisher Scientific, England, UK) with 0.0001 g precision.