Title: Evaluation of chemical and physical disinfection of process water and the treatment of biofilms in a pilot plant
Authors: Vankerckhoven, Eef
Dens, Jochen
Van Assche, Ado
Willems, Kris
Rediers, Hans
Issue Date: 2009
Publisher: Formatex Research Center
Host Document: Third international conference on environmental, industrial and applied microbiology: Book of abstracts pages:641-641
Conference: International Conference on Environmental, Industrial and Applied Microbiology (BioMicroWorld2009) edition:3 location:Lisbon, Portugal date:2-4 December 2009
Abstract: In several industrial and non-industrial applications, cooling water is reused and circulated in heat exchanger circuits. Cooling towers, heat exchangers, and humidifiers are just a few examples in which water is reused. However, continuous water reuse leads to a decreasing water quality due to the growth of microorganisms, biofouling, and corrosion. Microbial contamination of process water and formation of biofilms on the surface of piping and heat exchangers frequently result in operational problems and health risks. To avoid such problems, an effective, cost-efficient, and environmental-friendly water treatment is required. Nowadays, a variety of physical and chemical techniques are routinely used for water disinfection, including chlorination and ultraviolet light. However, these disinfection methods suffer from severe drawbacks. Moreover, the ecological aspects of the various disinfections techniques have rarely been taken into account in their evaluation.

In a recently started research project, different chemical and physical disinfection techniques (sodium hypochlorite, peracetic acid, hydrogen peroxide, chlorine dioxide, ultraviolet and ultrasound) are evaluated in their efficacy to inactivate free-living bacteria and treat biofilms. Many studies have already focused on disinfection using ultrasound, UV, or chlorination, but to study disinfection techniques in standardized conditions, mostly lab-scale experiments were carried out. In this study however, experiments are performed on a pilot plant system for a better simulation of conditions encountered in industrial environments.

The main focus of the project is to explore possible synergetic or additive effects between chemical disinfectants and other techniques. Such synergetic effects can ultimately result in a decrease of the amount of chemicals that are required for effective disinfection and treatment of biofilms. In a first set of experiments, the physicial disinfection techniques and different concentrations of chemical disinfectants were evaluated individually for their potential to inactivate free-living bacteria and treat biofilms.

When the inactivation of free-living bacteria is examined, treatment with UV, ultrasound and the chemical disinfectants resulted in a significant decrease in the number of free-living bacteria. Application of UV and ultrasound resulted in a 2-3 log reduction of the number of free-living bacteria. The effect of the chemical disinfectants on the number of free-living bacteria depended on the applied dose. Based on the concentration of the chemical disinfectants that is required to eliminate the free-living bacteria completely, hypochlorite was the most effective disinfectant, followed by chlorine dioxide. Peracetic acid was slightly more effective than hydrogen peroxide.

When biofilm-associated bacteria were assessed, it was observed that the efficacy of UV and ultrasound were comparable. Both physicial disinfection techniques caused approximately a 1.5 log reduction in the number of biofilm-associated bacteria, which is less effective than the efficacy to inactivate free-living bacteria. Regarding the chemical disinfectants, it was observed that the concentrations that enabled the complete inactivation of free-living bacteria, were not sufficient to completely remove the biofilm-associated bacteria. Consequenltly, higher doses of chemical disinfectant is required to effectively remove biofilms. Again, hypochlorite and chlorine dioxide appeared to be the most effective disinfectants.

However, it must be stated that chlorine-based disinfectants are also associated with problems such as the development of resistance to chlorination, discoloration and the production of unpleasant odors and flavors, or the production of toxic by-products. A reduction of the required hypochlorite concentration and hence a reduction of toxic by-products may be achieved by combining hypochlorite treatment with a physical disinfection technique.

In preliminary experiments it was already demonstrated that a combination of physical disnfection techniques and chemical disinfectants resulted in a synergetic effect in the efficacy to treat biofilms.

Keywords Disinfection; Biofilm; UV; ultrasound, chlorination; peracetic acid; hydrogen peroxide; pilot plant
Publication status: published
KU Leuven publication type: IMa
Appears in Collections:Microbial and Molecular Systems - miscellaneous
Bioengineering Technology TC, Technology Campus De Nayer Sint-Katelijne-Waver
Technologiecluster Bioengineering Technologie

Files in This Item:

There are no files associated with this item.


All items in Lirias are protected by copyright, with all rights reserved.