In this study a novel methodology is proposed to estimate the adhesion strength of biofilm developed in an attached-growth reactor. The time variation of adhesion strength was quantified in the course of formation of a biofilm consisting of denitrifiers. The model biofilm was formed on the surfaces of polyvinyl-chloride plates placed in a rectangular open-channel reactor. The result indicates that the adhesion strength was not uniformly distributed throughout biofilm, but had a tendency to increase with biofilm depth and with the progression of biofilm formation. For example on the 32nd day from start-up the adhesion strength near the substratum interface attained a level in the order of 102 dyne·cm−2, whereas that in the vicinity of biofilm outer surface was only in the order of 100 dyne·cm−2. As well the biofilm dry density did not remain constant throughout biofilm, having a tendency similar to that of the adhesion strength. A strong correlation was observed between the dry density and the extracellular biopolymer content per unit biofilm volume. It was suggested that the adhesion strength was significantly affected by the dry density.

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