Disinfection of bacterial biofilms in pilot-scale cooling tower systems

Abstract

The impact of continuous chlorination and periodic glutaraldehyde treatment on planktonic and biofilm microbial communities was evaluated in pilot-scale cooling towers operated continuously for 3 months. The system was operated at a flow rate of 10,080 l day−1. Experiments were performed with a well-defined microbial consortium containing three heterotrophic bacteria: Pseudomonas aeruginosa, Klebsiella pneumoniae and Flavobacterium sp. The persistence of each species was monitored in the recirculating cooling water loop and in biofilms on steel and PVC coupons in the cooling tower basin. The observed bacterial colonization in cooling towers did not follow trends in growth rates observed under batch conditions and, instead, reflected differences in the ability of each organism to remain attached and form biofilms under the high-through flow conditions in cooling towers. Flavobacterium was the dominant organism in the community, while P. aeruginosa and K. pneumoniae did not attach well to either PVC or steel coupons in cooling towers and were not able to persist in biofilms. As a result, the much greater ability of Flavobacterium to adhere to surfaces protected it from disinfection, whereas P. aeruginosa and K. pneumoniae were subject to rapid disinfection in the planktonic state.

Effects of fluid flow conditions on interactions between species in biofilms

“…They are major sources of nosocomial pneumonias and bacteremia from hospital devices and water supply systems, and they have been found to be major contributors of biofilms associated with outbreaks of Legionellosis (Stamm et al ., ; Orrison et al ., ; Pearson et al ., ; Anaissie et al ., ). These two organisms have previously been used to form a well‐defined consortium with Klebsiella pneumoniae to examine the survival and growth of Legionella pneumophila in biofilms (Murga et al ., ) and to study biofilm colonization and disinfection in pilot‐scale cooling tower systems (Liu et al ., , ). Pseudomonas aeruginosa has been observed to dominate the community in closed batch systems, while Flavobacterium has been found to dominate in open (flow‐through) systems (Liu et al ., ).…”

Efficacy of dental unit disinfectants againstCandidaspp. andHartmannella vermiformis

“…At 360 h of incubation, yeasts were included into a mature biofilm and this status certainly explains the increased resistance of yeasts to chlorine. The greater efficacy of chlorine on planktonic compared to sessile microorganisms has been widely shown with other microbial species (Karpay et al ., ; Steed & Falkinham, ; Liu et al ., ). Only concentrations of 62 and 118 μg mL −1 of chlorine were shown to be completely effective against C. albicans whatever their age at the time of the treatment, preventing any growth of yeasts (Fig.…”

Reuse of refinery’s tertiary-treated wastewater in cooling towers: microbiological monitoring

“…This bacterium has been associated with early stages of biofilm formation in metallic material surfaces (Doğruöz et al 2009b;Liu et al 2009Liu et al , 2011; their primary role appears to be the establishment of an oxygen-free environment to harbor other potentially corrosive bacteria with diverse oxidative profiles (Pedersen et al 1988). They also produce exopolysaccharides, which protect cells from metallic ions and help to trap other species of microorganisms (Gubner and beech 2000;Ceyhan and Ozdemir 2008).…”

“…Besides total heterotrophic bacteria, Pseudomonas aeruginosa was chosen because it has been extensively studied and associated with biofilms and to compare the system in this study to those of other researchers who reported the efficacy of diverse biocides in the control of microbiota using P. aeruginosa biofilms (Costerton 1999;Moreno et al 1993;Ceyhan andOzdemir 2008, Blasco et al 2008;Liu et al 2009Liu et al , 2011. For monitoring sessile bacteria, glass surfaces were also used along with stainless and carbon steel coupons; also, corrosion coupons and linear polarization resistance (LPR) probes were used for monitoring corrosion in the two cooling towers.…”