Comparative endoscopic and SEM analyses and imaging for biofilm, growth on porous quartz sand

The paper presents an endoscope technique to provide a non-destructive detection and imaging of biofilms on porous sand grains without disturbing the system. This in situ observation of biofilm growth was carried out by inserting an endoscope into the reactor after introducing the substrate into a water-saturated quartz sand-packed reactor. As the microbes grew on the media surface with time, an expansion was presented in biofilm area. In this way, the growth of biofilm on porous sand grains could be continuously captured. The expanding of the biofilm image was observed, and the biofilm on the sand grains was measured by image analysis of biofilm cross-sections. In order to further identify the biofilm growth, at the end of experiment the packed reactor was dismantled and biofilms along with the aquifer material were sampled for the biofilm growth observation by the scanning electron microscopy (SEM). The biofilm thickness was also measured by image analysis of biofilm cross-sections. The results demonstrated significant spatial variations in mean biofilm thickness (106.2 +/- 12.54 mum to 243.5 +/- 26.53 mum) and thickness variability (0.07-0.12) using image analysis of SEM. However, the mean biofilm thickness measurements done by image analysis of SEM were about 60-82% smaller compared with those by image analysis of endoscopy. This is because of the dehydration and alteration of the biofilm material after dismantling the reactor for SEM observations. In comparison, we found that the endoscope image could provide a first-hand observation of biofilm growth without disrupting the system, while the SEM image could give a better resolution.