This study uses confocal laser scanning microscopy to determine the coverage and thickness of biofilms on rock types commonly used in wetland sewage treatment systems in New Zealand. Samples of scoria, greywacke and slag - with glass used as a comparison - were submerged in subsurface flow wetlands and examined after six weeks.

An image analysis technique was used to quantitatively determine the coverage and thickness of each biofilm. The technique consisted of the biofilm quantification of each individual image obtained from the confocal optical sectioning. The results indicated that the biofilm coverage for the substrata types did not exceed 25%. However, there was a marked difference between the biofilm structures grown on the different substrata; that on glass formed thin spindly structures, and slag and scoria showed similar dense patches interspersed with open channel structures that followed the contours of the pocketed rock surface.