| Abstract: | The results of an evaluation of the effects of different factors on formation, growth and removal of biological films are reported. Experiments have been performed both on laboratory equipment and a test system located on a cooling-water system at an industrial site. The effects of temperature, nutrient availability and surface material of construction are discussed in relation to film formation. Experiments concerning continuous biocide treatment are assessed in relation to biofilm removal. A pure culture of Pseudomonas fluorescens was used to grow biological films in the laboratory under identical hydrodynamic conditions but at different temperatures. Drastic reductions in film thickness were noted at temperatures 5°C above and below the optimum temperature for growth of the organism. The effects of nutrient loading under similar hydrodynamic conditions have been studied in the laboratory. The maximum biofilm thickness was reduced by 55% when no air was present and by 80% when neither air nor nutrient were supplied. Biofilm growth at the industrial site was unexpectedly more pronounced on brass than mild steel. Examination of destruction of existing biofilms in the laboratory showed that at a concentration of 4 parts 10?-6 free chlorine (sodium hypochlorite) the initial rate of film removal was four-to-six times higher than that at 2.5 parts 10?-6 free chlorine. A higher velocity of sodium hypochlorite solution over the biofilm resulted in a higher rate of removal. The results are discussed in the light of published data in related tests. |
