A novel methodology is proposed in this study to evaluate the tensile strength of biofilms by using a newly developed tensile test device. Three different types of biofilms were prepared for tensile test: Run 1 biofilm was aerobically cultivated on glucose, and Run 2 and Run 3 biofilms were denitrifying biofilms grown on glucose and on methanol, respectively, as a sole carbon source. Each of three biofilms was formed on the outer surfaces of tygon-made tubes (diameter 4.76 mm) submerged in a rectangular open-channel reactor.
The results demonstrated that the tensile strengths of three different biofilms had a tendency to increase with the biofilm development over a period of 50 days of reactor operation and eventually reached a similar range, approximately 500 to 1000 Pa, independent of biofilm types or cultivation conditions. An elastic coefficient of the biofilm was determined by assuming that a biofilm behaves as an elastic material during the tensile test. A strong positive correlation was found between the elastic coefficient and the tensile strength. However, the behavior of extracellular biopolymer (ECP) content and the biofilm density were not dependent on the tensile strength. Scanning electron microscope (SEM) observations also suggested that the biofilm structural properties such as elastic coefficient are more determinative factors for the tensile strength than are the biofilm physiological properties such as ECP content.