A quantitative and qualitative study of biofilm disinfection on glass, metal and PVC surfaces by chlorine, bromine and bromochloro-5,5 dimethylhydantoin (BCDMH)

The present study was conducted on artificial biofilm formed in a laborator y water system using three support surfaces: glass, galvanised iron and pol yvinyl chloride (PVC). Biofilm formation was followed by direct count on R2 A medium and by scanning electron microscope (SEM) examination. As describe d, the development of biofilm was not the same on the various surfaces. Bio film formed on various surfaces had different disinfection patterns as show n by the experimental data. Chlorine was the most efficient disinfectant ag ainst biofilm developed on glass and metal surfaces but less effective on P VC. Disinfection of glass and PVC biofilms with bromine was much less effec tive. Bromochloro-5,5 dimethylhydantoin (BCDMH) was very effective on galva nised iron, less effective on PVC and almost no effect was observed on glas s surfaces. Addition of EDTA (1 mM) to the biofilm system, prior to disinfe ction, was more effective in killing the biofilm bacteria, probably due to chelation of divalent ions (Ca2+, Mg2+) which open the matrix and allow the disinfectant to penetrate easily. Maintaining the system at certain BCDMH concentrations, following a disinfection shock with bromine and chlorine, a llowed the system to remain at a low level of bacteria. SEM inspection made it possible to follow the biofilm organisation on the various surfaces bef ore and after disinfection. Following disinfection, on all surfaces, the bi ofilm bacteria seemed to be "flat" and, after addition of EDTA, detachment of the extracellular polysaccharide polymer (EPS) from the surface was obse rved. It seems that the EPS perforation process allowed better penetration of the disinfectant into the biofilm barrier affecting bacterial viability. The various chemical and microbiological aspects of biofilm disinfection a nd future practices are discussed. (C) 1998 Published by Elsevier Science L td on behalf of the IAWQ. All rights reserved.