Cooling Tower Water Research Articles

Legionella Pollution in Cooling Tower Water of Air Conditioning System in Shanghai, China

Background: Legionella disease (LD) is believed to be an environmentally acquired disease, inhaled as contaminated aerosolized water containing Legionella, and gains entry into the lungs. Cooling towers of air conditioning systems have been recognized as the primary source for Legionella Objective: to determine Legionella pollution prevalence, describe the amount of Legionella respect to temperature in CTWs of various type of public place. Methods: 321 cooling tower water (CTWs) from target sites were sampled, using probability proportion (around 1/500) to size (PPS) sampling Results: It was found that of the samples, 58.9% (189/321) samples were observed positive with Legionella, 19.9% were isolated as over 100 CFU/ml, and 0.9% even exceeding 1000 CFU/ml. Lp-1 was the most frequently isolated species (155/189, 82.0%), followed by L-mic that is at the second (44/189, 23.3%). In addition, the mean CFU/ml of Legionella in CTWs reached its peak in July, August and September (mean CFU/ml was 180, 170 and 170 respectively), and begins to drop gradually in October and November, down to 39.3 and 0.33 respectively. 15.4% of samples with exceeding 100 CFU/ml were observed in a hospital setting; 18.9%, 27.7%, 12.3%, and 22.7% of the samples exceeding 100 CFU/ml were from office buildings, subway stations, hotels, and stores respectively. Conclusion: The problem with Legionella pollution in CTWs, especially in subway stations and hospitals, is worrying. A significant correlation was found between the positive rate and CFU/ml of Legionella in CTWs and air temperature. To deal with the potential risk of LD, improved control and prevention strategies are urgently needed.

Effect of solution chemistry on water softening using charged nanofiltration membranes

The negatively charged polyamide thin-film-composite nanofiltration membranes have been used to possibly treat the sodium-enriched water, particularly cooling tower water, to separate hardness producing solute like MgSO 4 from univalent salts using ESNA and EDA nanofiltration membranes. The flux declines with increasing ionic strength of the feed solution. Rejection of objectionable hardness producing magnesium ions decreases with increasing ionic strength, a case hopefully not reported earlier, with hardly any change in the rejection of sodium chloride used to maintain the ionic strength of the solutions. The effect of pH has also been studied, which shows that flux decreases whereas rejection increases when the solution pH is either reasonably acidic or alkaline in nature. The rate of change in flux and rejection drops with increasing pH when the ionic strength was kept constant. The method is applied to the treatment of some tap waters, altering the ionic strength and pH, to show the validity of the findings. A good agreement in results confirms the phenomenon of variable rejection of hardness producing ions under different solution chemistry.

Distinct difference of flaA genotypes of Legionella pneumophila between isolates from bath water and cooling tower water

To investigate the genetic difference of Legionella pneumophila in human-made environments, we collected isolates of L. pneumophila from bath water (n = 167) and cooling tower water (n = 128) primarily in the Kanto region in 2001 and 2005. The environmental isolates were serogrouped and sequenced for a target region of flaA. A total of 14 types of flaA genotypes were found: 10 from cooling tower water and nine from bath water. The flaA genotypes of isolates from cooling tower water were quite different from those of bath water.

Extracellular polysaccharides produced by cooling water tower biofilm bacteria and their possible degradation

The extracellular polymers (EPS) of biofilm bacteria that can cause heat and mass transfer problems in cooling water towers in the petrochemical industry were investigated. In addition, these microorganisms were screened for their ability to grow and degrade their own EPS and the EPS of other species. Twelve bacteria producing the most EPS were isolated from cooling water towers and characterized biochemically by classic and commercial systems. These were species of Pseudomonas, Burkholderia, Aeromonas, Pasteurella, Pantoea, Alcaligenes and Sphingomonas. EPS of these species were obtained by propan-2-ol precipitation and centrifugation from bacterial cultures in media enriched with glucose, sucrose or galactose. EPS yields were of 1.68–4.95 g l−1. These EPS materials were characterized for total sugar and protein contents. Their total sugar content ranged from 24 to 56% (g sugar g−1 EPS), and their total protein content ranged from 10 to 28% (g protein g−1 EPS). The monosaccharide compositions of EPS were determined by HPLC. Generally, these compositions were enriched in galactose and glucose, with lesser amounts of mannose, rhamnose, fructose and arabinose. All bacteria were investigated in terms of EPS degradation. Eight of the bacteria were able to utilize EPS from Burkholderia cepacia, seven of the bacteria were able to utilize EPS from Pseudomonas sp. and Sphingomonas paucimobilis. The greatest viscosity reduction of B. cepacia was obtained with Pseudomonas sp. The results show that the bacteria in this study are able to degrade EPS from biofilms in cooling towers.

A survey of cooling tower water quality for condenser tube fouling potential

Fouling from cooling tower water is a serious problem in both power and refrigeration industries. The effect of fouling on enhanced tubes could be worse than that on smooth tubes because fouling may degrade the superior heat transfer performance by filling the gaps between the roughness elements with foulant. Condensers that use cooling tower water usually experience four different fouling mechanisms: corrosion, scaling, particulate, and biological fouling. Corrosion is prevented with chemical inhibitors, which pacify the piping and protect the metal surfaces. Cooling tower water can also be treated with biocide to prevent biological fouling. Therefore, the current paper addresses scaling and particulate fouling. The paper also establishes a database of water quality based on chemical analysis of samples collected from cooling towers across the country. The objective of the database is to determine water qualities that are typical of those found in actual cooling towers. From chemical analysis, three water qualities were determined: having an average fouling potential, a low fouling potential, and a severe fouling potential. These water qualities can be used in experimental determinations of fouling resistances in augmented tubes.

Quantitation of bacteria through adsorption of intracellular biomolecules on carbon paste and screen-printed carbon electrodes and voltammetry of redox-active probes

A new electrochemical method for the quantitation of bacteria that is rapid, inexpensive, and amenable to miniaturization is reported. Cyclic voltammetry was used to quantitate M. luteus, C. sporogenes, and E. coli JM105 in exponential and stationary phases, following exposure of screen-printed carbon working electrodes (SPCEs) to lysed culture samples. Ferricyanide was used as a probe. The detection limits (3s) were calculated and the dynamic ranges for E. coli (exponential and stationary phases), M. luteus (exponential and stationary phases), and C. sporogenes (exponential phase) lysed by lysozyme were 3 x 10(4) to 5 x 10(6) colony-forming units (CFU) mL(-1), 5 x 10(6) to 2 x 10(8) CFU mL(-1) and 3 x 10(3) to 3 x 10(5) CFU mL(-1), respectively. Good overlap was obtained between the calibration curves when the electrochemical signal was plotted against the dry bacterial weight, or between the protein concentration in the bacterial lysate. In contrast, unlysed bacteria did not change the electrochemical signal of ferricyanide. The results indicate that the reduction of the electrochemical signal in the presence of the lysate is mainly due to the fouling of the electrode by proteins. Similar results were obtained with carbon-paste electrodes although detection limits were better with SPCEs. The method described herein was applied to quantitation of bacteria in a cooling tower water sample.

Detection of Legionella pneumophila by PCR-ELISA Method in Industrial Cooling Tower Water

Water supply and Cooling Tower Water (CTW) are among the most common sources of Legionella pneumophila (LP) contamination. A nonradio active method is described to detect LP in industrial CTW samples. DNA was purified and amplified by nested -PCR with amplimers specific for the 16s rRNA gene of LP. The 5' end biotinylated oligomer probe was immobilized on sterptavidin B coated microtiter plates. The nested-PCR product was labeled with digoxigenin and then hybridized with 5'-biotinylated probes. The amplification products were detected by using proxidase-labled anti dioxygenin antibody in a colorimetric reaction. The assay detected LP present in 1 L of 5 CTW samples examined. All of the samples were Legionella positive in both culture and PCR-ELISA methods. The PCR-ELISA assay appears to exhibit high specificity and is a more rapid technique in comparison with bacterial culture method. Thus could prove suitable for use in the routine examination of industrial CTW contamination.

Hospital-acquired legionellosis originating from a cooling tower during a period of thermal inversion

A case of hospital-acquired legionellosis occurred in a 75-year-old male patient who underwent surgery due to malignant melanoma. Legionellosis was proven by culture of Legionella pneumophila serogroup 1 from bronchoalveolar lavage (BAL) fluid. Being a chronic smoker the patient used to visit the sickroom balcony that was located about 90 m to the west of a hospital cooling tower. Routine cooling tower water samples drawn during the presumed incubation period revealed 1.0x10(4) CFU/100 ml (L. pneumophila serogroup 1). One of three isolates from the cooling tower water matched the patient's isolate by monoclonal antibody (mab)- and genotyping (sequence-based typing). Horizontal transport of cooling tower aerosols probably was favoured by meteorological conditions with thermal inversion. The case report stresses the importance of routine maintenance and microbiological control of hospital cooling towers.

A literature survey of water-side fouling applicable to cooling tower condensers

Because of the complexity of fouling, it has been primarily studied as individual mechanisms. However, in actual field conditions, multiple mechanisms may be present. Little is understood about how different mechanisms interact. In cooling tower applications, water is treated with corrosion inhibitors and biocides to eliminate biological and corrosion fouling mechanisms. The fouling in cooling towers is, therefore, typically a combination of precipitation and particulate fouling. This paper presents a literature survey of research in the area of particulate, precipitation, and combined fouling modes in heat exchangers that use cooling tower water. Several experiments, models, and correlations are briefly described. The article concludes with a review section on long-term fouling data.

Granulation Process for Producing Spherical Particles of a Rubber Antioxidant in a Water Cooling Tower

A new granulation technology for producing spherical particles of a rubber antioxidant and its key factors were studied. The granulation is based on the interfacial tension and immiscibility of the rubber antioxidant in water. Melted antioxidant was ejected from nozzles to form drops in air that fell into a water tower where they were cooled and solidified into spherical particles as they fell. After dewatering and air drying, spherical particles with a uniform size were obtained. Experiments performed on the granulation of antioxidant 4020 are described and the key factors, including falling height, drop temperature and surfactant concentration in water were studied. The mechanism of drop entrancement in water was analyzed and the stable operating conditions were investigated. The technology produces spherical particles with a uniform size using smaller equipment and is also suitable for producing spherical particles from other melted materials with similar physical properties.

Detection and quantification ofLegionella pneumophilain water samples using competitive PCR

The presence of high levels of Legionella pneumophila in man-made aquatic systems correlates with the incidence of nosocomial Legionnaires' disease. This requires a rapid, reliable, and sensitive quantification of L. pneumophila concentrations in suspected water systems. In this research, a homologous competitor was developed and evaluated in a L. pneumophila competitive polymerase chain reaction (cPCR) to quantify this human pathogen in a quick, cost-effective, and reliable way. Accuracy of cPCR was evaluated by analyzing cooling tower and tap water samples spiked with known concentrations of L. pneumophila bacteria, in parallel with the standard culture method. Legionella pneumophila amounts detected and calculated from cPCR and culture correlated very well: r = 0.998, P = 0.002 for tap water and r = 0.990, P = 0.009 for cooling tower water. Nevertheless, for both kinds of water samples, mean numbers of L. pneumophila calculated from cPCR results were always higher than those obtained by culture. This study makes it clear that the rapid, sensitive, and cost-effective L. pneumophila cPCR is a promising alternative to the standard time-consuming culture method and expensive real-time PCR to enumerate L. pneumophila bacteria in environmental water samples.

Development of an improved PCR–ICT hybrid assay for direct detection of Legionellae and Legionella pneumophila from cooling tower water specimens

A novelly improved polymerase chian reaction and immunochromatography test (PCR–ICT) hybrid assay comprising traditional multiplex-nested PCR and ICT, (a lateral-flow device) was developed for direct detection of Legionella bacteria from environmental cooling tower samples. The partial 16S rDNA (specific for Legionella spp.) and dnaJ (specific for Legionella pneumophila) genes from Legionella chromosome were first specifically amplified by multiplex-nested PCR, respectively, followed by detection using ICT strip. Reading of results was based on presence or absence of the two test lines on the strips. Presence of test line 1 indicated existence of Legionella spp. specific 16S rDNA and identified Legionella spp. Presence of test line 2 further indicated existence of dnaJ and thus specifically identified L. pneumophila. In contrast, for non-Legionellae bacteria no test line formation was observed. Results of direct detection of Legionella bacteria and L. pneumophila from water tower specimens by this assay showed 100% sensitivity, and 96.6% and 100% specificity, respectively compared with traditional culture, biochemical and serological identification methods. The PCR–ICT hybrid assay does not require sophisticated equipment and was proved to be practically useful in rapid and direct Legionellae detection from environmental water samples.

Fouling Mitigation in a Heat Exchanger: High Cycles of Concentration for a Cooling-Tower Application

The purpose of the present study is to investigate the effect of a physical water treatment (PWT) technology on fouling mitigation in a simulated cooling tower operating at high cycles of concentration. Hard water was produced by evaporating pure water in a circulating open cooling tower, where dissolved calcium carbonate ions became concentrated with time. Heat transfer tests were conducted in a rectangular channel by varying the cycle of concentration (COC) from 5 to 10, and fouling resistances were measured over 270 hrs for each case with and without the PWT treatment. Another test was conducted with no blowdown case with and without the PWT treatment. The fouling resistance at 5 cycles with the PWT treatment was about 70% less than that in the case without the PWT treatment at the end of 270-hr tests. Even at 10 cycles, the PWT treatment reduced the fouling resistance by 60% from the value for the no treatment case. Thus, one can conclude that the PWT technology can help circulating cooling-tower water at relatively high COC for significant freshwater conservation, while keeping fouling resistances below industry standards.

The natural fluid nitrous oxide—an option as substitute for low temperature synthetic refrigerants

A theoretical investigation was performed concerning the coefficient of performance (COP) of cascade refrigerating systems using N 2O as refrigerant for the low temperature cascade stage and various natural refrigerants like ammonia, propane, propene, carbon dioxide and nitrous oxide itself for the high temperature stage. The basis of the comparison was a conventional R23/R134a-cascade refrigerating system for heat rejection temperatures of +55, +35 and +25 °C for air cooling, cooling tower water cooling and city water cooling, respectively. It can be stated that such an application of N 2O at the primary stage and ammonia or hydrocarbons as refrigerants at the secondary stage in refrigerating systems achieves similar COP-values compared to the R23/R134a-cascade refrigerating system, whereas CO 2 and N 2O in a transcritical cycle in general perform worse. An application of N 2O in a two-stage compression cycle with interstage injection and city water cooling at low and high interstage temperatures has a nearly equal COP as a conventional R23/R134a-cascade refrigerating system and is an interesting alternative for small laboratory refrigerating systems.

A study of Legionella pneumophilia in Tianjin, China

Legionella is a bacterium identified as the causative agent of Legionnaires' disease commonly found in water and soil in natural environments and human habitats. While most studies are focused on cooling tower water as the source of infection, few studies have compared Legionella from cooling-tower water and water in man-made environments. This cross-sectional study with a randomized cluster sampling design aims to provide information on Legionella found in cooling-tower water and water in man-made environments. Legionella was identified using a dual analytical approach: the serological and the 16SrRNA semi-nest PCR methods. Nine different types of Legionella were identified with the Lp7 type detected in China for the first time. Results indicated slight but insignificantly increased odds (OR=1.64, 95%CI=0.54-4.98) of Legionella detection in cooling tower water as compared to water obtained from fountains and parks, suggesting that the mechanism of exposure plays an important role in the causal pathway of outbreaks of Legionnaires' disease.

Enhanced Antifungal Effect of the Selective Medium for the Detection of Legionella Species by a Combination of Cycloheximide, Amphotericin B and Thiabendazole

The accurate detection of Legionella from environmental water samples using conventional plate culture methods is often made difficult by the overgrowth of non-target microorganisms on the selective agar plates. Acid pretreatment is a very effective pretreatment to decrease the overgrowth of heterotrophic bacteria. However, acid pretreatment would not be expected to eliminate molds. We evaluated the effects of four kinds of antifungal agents, individually and in combination, on the growth of Legionella strains and molds. Consequently, it was demonstrated that the combination of cycloheximide, amphotericin B and thiabendazole was very effective in eliminating molds on agar plates, and resulted in the improved detection of Legionella. Examination of 214 cooling tower water samples using the enhanced antifungal selective medium (CAT alpha) instead of GVPC alpha selective medium demonstrated a decrease in contamination by molds from 13.6% to 1.9% without affecting the growth of Legionella.

Soil as a source of Legionella pneumophila serogroup 1 (Lp1)

Objective: To investigate the potential source of a case of Legionnaires' disease caused by an unusual serotype of Legionella pneumophila serogroup 1 (Lp1) in regional Victoria in May 2001.Method: Epidemiological and environmental investigation of the source of infection of a case of Legionnaires' disease in regional Victoria in May 2001.Results: Extensive environmental investigations did not reveal any cooling water tower systems close to the residence or the shopping centre that the case visited prior to illness. The sputum culture and a soil sample from the field at the plant nursery where the case worked prior to illness were both positive for Legionella pneumophilia serogroup 1, MDU pulsovar 97: 103.Conclusion: Legionella pneumophila has been found in soil and was further found to be associated with a case of Legionella pneumophila.Implications: Public health authorities should consider exposures to soil and potting mixes when investigating cases of Legionella pneumophila where the case has no apparent association with cooling towers. Safe gardening practices should be promoted among the community.

Quantitative Detection ofLegionella pneumophilain Water Samples by Immunomagnetic Purification and Real-Time PCR Amplification of thedotAGene

A new real-time PCR assay was developed and validated in combination with an immunomagnetic separation system for the quantitative determination of Legionella pneumophila in water samples. Primers that amplify simultaneously an 80-bp fragment of the dotA gene from L. pneumophila and a recombinant fragment including a specific sequence of the gyrB gene from Aeromonas hydrophila, added as an internal positive control, were used. The specificity, limit of detection, limit of quantification, repetitivity, reproducibility, and accuracy of the method were calculated, and the values obtained confirmed the applicability of the method for the quantitative detection of L. pneumophila. Moreover, the efficiency of immunomagnetic separation in the recovery of L. pneumophila from different kinds of water was evaluated. The recovery rates decreased as the water contamination increased (ranging from 59.9% for distilled water to 36% for cooling tower water), and the reproducibility also decreased in parallel to water complexity. The feasibility of the method was evaluated by cell culture and real-time PCR analysis of 60 samples in parallel. All the samples found to be positive by cell culture were also positive by real-time PCR, while only eight samples were found to be positive only by PCR. Finally, the correlation of both methods showed that the number of cells calculated by PCR was 20-fold higher than the culture values. In conclusion, the real-time PCR method combined with immunomagnetic separation provides a sensitive, specific, and accurate method for the rapid quantification of L. pneumophila in water samples. However, the recovery efficiency of immunomagnetic separation should be considered in complex samples.

Cooling and Solidification of Melted Drops in an Immiscible Cooling Medium

The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water-cooling tower and during urea granulation in an air-cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters.

Enumeration of Legionella pneumophila in cooling tower water systems

Legionella pneumophila, the causative agent of Legionnaires' disease, is known to colonise and frequently grow in cooling tower waters. Disease is acquired by inhaling aerosol contaminated by legionellae. Determination of the count of Legionella pneumophila in cooling tower waters may, therefore, be useful for risk assessment. In our survey, 103 water samples from 50 cooling towers were examined over a five-year period to indicate the seasonal distribution and the ecology of L. pneumophila, as regards temperature and pH. L. pneumophila serogroup 1 was found in 44% of the isolated strains, which is primarily responsible for the majority of Legionnaires' disease. The large majority of examined towers had levels of L. pneumophila in the high-risk category. These cooling towers have been linked to many outbreaks of Legionnaires' disease.