title: Micro-cantilever method for measuring the tensile strength of biofilms and microbial flocs.
abstract: Cohesive strength is an important factor in determining the structure and function of biofilm systems, and cohesive strength plays a key role in our ability to remove or control biofilms in engineered systems. A micro-mechanical device has been developed to directly measure the tensile strength of biofilms and other microbial aggregates. An important feature of this method is the combination of a direct measurement of force with particle separations that occur at a scale comparable to that observed for biofilm systems. The force required to separate an aggregate is determined directly from the deflection of cantilevered glass micropipettes with a 20-40-microm diameter. Combined with an estimate of the cross-sectional area of the aggregate at the point of separation this measurement indicates the cohesive strength of the aggregate. Samples of return activated sludge (RAS) and a Pseudomonas aeruginosa biofilm were tested using the device. The measured cohesive strengths of the RAS flocs ranged from 419 to 206,400 N/m(2), while many of the flocs exceeded the range of measurement of the device. Fragments of P. aeruginosa biofilm had cohesive strengths ranging from 395 to 15,640 N/m(2), with a median value of 3020 N/m(2). The median equivalent diameters of the particles detached from the aggregates were 32 microm for RAS and 30 microm for the P. aeruginosa biofilms.
authors: Department of Civil Engineering, University of Minnesota, 122 Civil Engineering Building, 500 Pillsbury Drive S.E., Minneapolis, MN 55455-0220, USA.
authors: Eric H
authors: EH
authors: Poppele
authors: Raymond M
authors: RM
authors: Hozalski
mesh_terms: D018441:Biofilms / Q000254:growth & development*; D001696:Biomechanical Phenomena / Q000295:instrumentation; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D012722:Sewage / Q000737:chemistry / Q000382:microbiology; D013718:Tensile Strength
chemical_list: D012722:Sewage