生物膜の剥離抵抗因子・付着と引張強度の新規試験機による評価

抄録

Biofilm mechanical strength could be categorized into two different concepts, tensile strength and adhesion strength. The former and the latter can be defined, respectively, as biofilm internal force that is resistant to erosion and as that resistant to sloughing at biofilm/substratum interface, when external force is imposed. In this study a novel methodology is proposed to evaluate separately these two different biofilm strengths by using a tensile test device. Test biofilms consisting of denitrifiers were formed on the outer surfaces of tygon-made tubes (diameter 4.76 mm, connected with each other by 2 cm length) submerged in a rectangular open-channel reactor.
The results demonstrated that biofilm tensile strength consistently increased up to about 1000 Pa as biofilm formation proceeded, accompanied with variations in biofilm thickness from 0.4 to 2.9 mm and in biofilm dry density from 2.0 to 8.5 mg SS/cm³ for a period of 50 days reactor operation. Whereas biofilm adhesion strength drastically dropped to below 50 Pa as the biofilm became aged. The live-cell ratio of the biofilm determined by INT method decreased to about 40% with biofilm maturation. This suggests that dead-cell is likely responsible for lessening the adhesion strength. For tensile test, biofilm body is assumed to behave as an elastic material. Elastic index of the biofilm was considerably related to the tensile strength and to the density. However, the behavior of extracellular biopolymer content (ECP) was not dependent on the tensile strength. SEM observations also suggested that rather than the biofilm physiological properties such as ECP content, the biofilm structural properties such as elastic index are more determinative factors for the tensile strength.