A novel method for evaluation of biofilm tensile strength resisting erosion

A novel methodology is proposed in this study to evaluate the tensile stren gth of biofilms by using a newly developed tensile test device. Three diffe rent types of biofilms were prepared for tensile test: Run 1 biofilm was ae robically cultivated on glucose, and Run 2 and Run 3 biofilms were denitrif ying biofilms grown on glucose and on methanol, respectively, as a sole car bon source. Each of three biofilms was formed on the outer surfaces of tygo n-made tubes (diameter 4.76 mm) submerged in a rectangular open-channel rea ctor. The results demonstrated that the tensile strengths of three different biof ilms had a tendency to increase with the biofilm development over a period of 50 days of reactor operation and eventually reached a similar range, app roximately 500 to 1000 Pa, independent of biofilm types or cultivation cond itions. An elastic coefficient of the biofilm was determined by assuming th at a biofilm behaves as an elastic material during the tensile test. A stro ng positive correlation was found between the elastic coefficient and the t ensile strength. However, the behavior of extracellular biopolymer (ECP) co ntent and the biofilm density were not dependent on the tensile strength. S canning electron microscope (SEM) observations also suggested that the biof ilm structural properties such as elastic coefficient are more determinativ e factors for the tensile strength than are the biofilm physiological prope rties such as ECP content. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.