Autor(es):
Simões, M. 
; Pereira, M. O. ; Vieira, M. J.
Data: 2005
Identificador Persistente: http://hdl.handle.net/1822/3751
Origem: RepositóriUM - Universidade do Minho
Assunto(s): Biofilm behaviour; Biofilm control; Chemical treatment; Mechanical stability; Mechanical stress
Descrição
In this study a methodology was applied in order to ascertain the mechanical stability of biofilms, by using a stainlesssteel
(SS) rotating device immersed in a biological reactor where biofilms formed by Pseudomonas fluorescens were
allowed to grow for 7 days at a Reynolds number of agitation of 2400. The biofilms developed with this system were
characterised in terms of amount of total, extracellular and intracellular proteins and polysaccharides, amount of mass,
metabolic activity and mechanical stability, showing that the biofilms were active, had a high content of extracellular
constituents and an inherent mechanical stability. In order to assess the role of chemical agents on the mechanical
stability, the biofilms were exposed to chemical agents followed by mechanical treatments by submission to increase
Reynolds number of agitation. Seven different chemical agents were tested (two non-oxidising biocides, three
surfactants and two oxidising biocides) and their effects on the biofilm mechanical stability were evaluated. The increase
in the Reynolds number increased the biofilm removal, but total biofilm removal was not found for all the conditions
tested. For the experiment without chemical addition (only mechanical treatment), the biofilm remaining on the surface
was about 76%. The chemical treatment followed by the subsequent mechanical treatment did not remove all the
biofilms from the surface. The biofilm remaining on the SS cylinder ranged from 3% to 62%, depending on the
chemical treatment, showing that the chemical treatment is far from being a cause that induces massive biofilm
detachment and even the synergistic chemical and mechanical treatments did not promote biofilm removal. Some
chemical agents promoted an increase in the biofilm mechanical stability such as glutaraldehyde (GTA), benzalkonium
chloride (BC), except for the lower concentration tested, and sodium dodecyl sulphate (SDS), except for the higher
concentration tested. Treatments that promoted biofilm removal, to an extent similar to the control experiment
(without chemical treatment), were BC, for the lower and the higher concentration of SDS. Cetyltrimethyl ammonium
bromide (CTAB), ortho-phthalaldehyde (OPA), sodium hydroxide (NaOH) and sodium hypochlorite (SHC) promoted
the weakening of the biofilm mechanical stability.
