Effect of CaCO<Subscript>3</Subscript> particles and suspended bacteria on biofilm components and activity in the model recirculating cooling water system

Biofilms are a serious problem in industrial recirculating cooling water systems. Biofilm formation and properties are affected by many factors, such as inorganic particles and suspended bacteria. In this research a laboratory model recirculating cooling water system was applied to investigate the effects of CaCO₃ concentration and suspended bacterial count on extracellular polymeric substances (EPS) content and dehydrogenase activity (DHA) in the attached biofilms. In addition, nutrient level was also the key factor when investigating the effect of suspended bacterial count. The results showed that EPS content and DHA first increased and then decreased with the increase of CaCO₃ concentration from 0 to 200 mg/l. At the low nutrient level, with the increase of suspended bacterial count from 4.04 to 5.78 log₁₀ c.f.u./ml, biofilm EPS content decreased firstly and then increased. However, biofilm DHA always gradually increased. At the medium nutrient level, biofilm EPS content increased firstly and then decreased and DHA always gradually decreased when suspended bacterial count ranged from 4.04 to 5.78 log₁₀ c.f.u./ml. At the high nutrient level, biofilm EPS content and DHA both showed the increasing trend with the increase of suspended bacterial count. This work provides the basis and reference for management strategies in actual recirculating cooling water systems.     

炼油厂循环冷却水系统中有害微生物的研究

调查了我国十六个主要炼油厂循环冷却水系统中主要引起污损、腐蚀的有害微生物——形成粘液异养菌、硫酸盐还原菌、铁细菌、真菌的数量及类型;探讨了菌数量和污损危害的相关性,从而提出了炼油厂循环冷却水有害菌控制指标：粘液异养菌<105／ml,硫酸盐还原菌<102／ml,铁细菌<103／ml,真菌相似文献   

Effect of different salinities of a dynamic water system on biofilm formation

AISI-1020 carbon steel coupons were fixed onto a water circulation loop in order to study the effect of varying NaCl concentrations on formation of biofilms by natural populations of microorganisms. Overall, we observed a reduction in the number of bacteria attached to the metal surfaces as NaCl levels increased. At 12.85 and 80 g/l NaCl, the respective bacterial counts were: 1.7×10⁹ CFU/cm² and 7.5×10² CFU/cm² for aerobic species; 1.3×10⁴ CFU/cm² and 2.1×10 CFU/cm² for anaerobic species; and 1.8×10³ CFU/cm² and 4.6×10 CFU/cm² for sulfate-reducing species. However, the opposite trend was observed for the numbers of iron-reducing bacteria: 4.1×10⁶ CFU/cm² at 12.85 g/l NaCl and 7.5 10⁸ CFU/cm² at 80 g/l NaCl, respectively. Fungal counts remained constant throughout the experimental period. The salt concentration at which the maximum corrosion rate was observed was 35 g/l. In view of the marked loss of metal mass recorded at this salinity, AISI-1020 carbon steel proved to belong to the group of alloys less resistant to corrosion. Journal of Industrial Microbiology & Biotechnology (2000) 25, 45–48. Received 07 December 1999/ Accepted in revised form 25 April 2000     

Fouling and corrosion in an open recirculating cooling system

The paper discusses the problem of fouling and corrosion in the Service Water System of a nuclear reactor employing an open recirculating cooling system. Field and laboratory experiments were carried out using carbon steel as test material. The studies included corrosion rate measurements, corrosion product characterisation (using XRD, EDAX and IRAS), and the effects of addition of biocide (chlorine) and corrosion inhibitor (polyphosphates) on the bacterial population of the cooling water. The fouling films which developed on metal and glass coupons as well as debris collected from within the cooling system were chemically characterised. The results indicated the prevalence of microbiologically induced corrosion (MIC) within the system. The findings are discussed in the light of the information available on MIC of cooling water systems.     

Comparative assessment of different biocides in swimming pool water

For disinfection of swimming pool water chlorine of chlorine-based products are normally used. In practice, these products have proven their worth regarding killing of pathogenic micro-organisms. Detailed values of their biocidal activity in swimming pool water were not found in literature. In the given study the efficacy of sodium hypochlorite (NaOCl) versus five micro-organisms was investigated.It is known that chlorination of swimming pool water may lead to formation of specific unwanted products like haloform. Nowadays, the concentration of those by-products in swimming pool water is limited and specific measures exist to minimize their formation. Nevertheless, there is increasing interest in alternative methods without by-product formation like e.g. hydrogen peroxide (H₂O₂) treatment.In the given study the antimicrobial activity of sodium hypochlorite was compared with that of different hydrogen peroxide-based products. The test procedure used was specifically designed to simulate practical conditions in a swimming pool but at the same time to lead to adequate reproducibility. Five test organisms were selected being relevant for the swimming pool area: Pseudomonas aeruginosa, Escherichia coli, Legionella pneumophila, Staphylococcus aureus and Candida albicans.The swimming pool water for the test was artificially prepared. Water hardness, temperature and pH value were adjusted to a defined level. Regarding simulation of organic load it was found that a mixture of urea, creatinine and several amino acids was most appropriate.Addition of the test organisms was done in three portions: one big in the beginning and two smaller after 10 and 20 min to simulate recontamination by bathers. Total test period was 30 min. The number of surviving cells was determined after 30 s as well as after 10, 20 and 30 min.Sodium hypochlorite was tested at a concentration of 1 ppm active chlorine. Compared to that three products based on hydrogen peroxide were investigated: pure hydrogen peroxide, hydrogen peroxide + silver nitrate and a trade product based on hydrogen peroxide.Sodium hypochlorite resulted in total kill of the inoculated organisms after 10, 20 and 30 min corresponding to a log 4 reduction. In contrast to that the biocidal effect achieved by the hydrogen peroxide-based products was significantly lower than one log cycle notwithstanding a very high concentration of up to 150 ppm.The test results confirm the very good killing activity of sodium hypochlorite versus micro-organisms relevant for the swimming pool area. Products based on hydrogen peroxide, with or without silver ions, are from a microbiological point of view no real alternative to chlorine disinfection in swimming pools.     

应用噬菌体控制工业循环冷却水中有害微生物的研究

利用噬菌体控制工业循环冷却水系统中有害微生物的研究表明,分离出的９株噬菌体在冷却水培养液中,其杀菌率为８５．４％,而在动态模拟培养液中和挂片上,其杀菌率分别为８３．３％和７０％．     

Effect of phosphate availability on biofilm formation in cooling towers

Abstract

Phosphate limitation has been suggested as a preventive method against biofilms. P-limited feed water was studied as a preventive strategy against biofouling in cooling towers (CTs). Three pilot-scale open recirculating CTs were operated in parallel for five weeks. RO permeate was fed to the CTs (1) without supplementation (reference), (2) with supplementation by biodegradable carbon (P-limited) and (3) with supplementation of all nutrients (non-P-limited). The P-limited water contained ≤10?µg PO₄ l^?1. Investigating the CT-basins and coupons showed that P-limited water (1) did not prevent biofilm formation and (2) resulted in a higher volume of organic matter per unit of active biomass compared with the other CTs. Exposure to external conditions and cycle of concentration were likely factors that allowed a P concentration sufficient to cause extensive biofouling despite being the limiting compound. In conclusion, phosphate limitation in cooling water is not a suitable strategy for CT biofouling control.     

The efficacy of biocides and other chemical additives in cooling water systems in the control of amoebae

Aims:  In vitro experiments were undertaken to evaluate biocide formulations commonly used in cooling water systems against protozoa previously isolated from cooling towers. The investigations evaluated the efficacy of these formulations against amoebic cysts and trophozoites.
Methods and Results:  Laboratory challenges against protozoa isolated from cooling towers using chlorine, bromine and isothiazolinone biocides showed that all were effective after 4 h. The presence of molybdate and organic phosphates resulted in longer kill times for bromine and isothiazolinones. All treatments resulted in no detectable viable protozoa after 4 h of exposure.
Conclusions:  The chemical disinfection of planktonic protozoa in cooling water systems is strongly influenced by the residence time of the formulation and less so by its active constituent. Bromine and isothiazolinone formulations may require higher dosage of concentrations than currently practiced if used in conjunction with molybdate- and phosphate-based scale/corrosion inhibitors.
Significance and Impact of the Study:  Cooling water systems are complex microbial ecosystems in which predator–prey relationships play a key role in the dissemination of Legionella . This study demonstrated that at recommended dosing concentrations, biocides had species-specific effects on environmental isolates of amoebae that may act as reservoirs for Legionella multiplication in cooling water systems.     

The effect of material choice on biofilm formation in a model warm water distribution system

Water distribution systems (WDS) are composed of a variety of materials and may harbour potential pathogens within surface-attached microbial biofilms. Biofilm formation on four plumbing materials, viz. copper, stainless steel 316 (SS316), ethylene propylene diene monomer (EPDM) and cross-linked polyethylene (PEX), was investigated using scanning electron microscope (SEM)/confocal microscopy, ATP-/culture-based analysis, and molecular analysis. Material ‘inserts’ were incorporated into a mains water fed, model WDS. All materials supported biofilm growth to various degrees. After 84 days, copper and SS316 showed no significant overall differences in terms of the level of biofilm formation observed, whilst PEX supported a significantly higher level ofbiofilm. EPDM exhibited gross contamination by a complex, multispecies biofilm, at a level significantly higherthan was observed on the other materials, regardless of the analytical method used. PCR-DGGE analysis showed clear differences in the composition of the biofilm community on all materials after 84 days. The primary conclusion of this study has been to identify EPDM as a potentially unsuitable material for use as a major component in WDS.     

Effect of water velocity on the early development of manganese-depositing biofilm in a drinking-water distribution system

Abstract A study of the development of biofilm colonizing the surfaces of pipes in a drinking-water distribution system has shown that water velocity significantly influenced the nature and physiological activity of the biofilm. Biofilm developed at a velocity of 0.5 m s⁻¹ actively oxidized and deposited manganese, but at 0.01 m s⁻¹ no manganese was deposited. Budding bacteria were the dominant microorganisms depositing manganese but a variety of other organisms were also present in the biofilms. The budding bacteria oxidizing manganese were Pedomicrobium manganicum and Metallogenium .     

The effect of material choice on biofilm formation in a model warm water distribution system

Water distribution systems (WDS) are composed of a variety of materials and may harbour potential pathogens within surface-attached microbial biofilms. Biofilm formation on four plumbing materials, viz. copper, stainless steel 316 (SS316), ethylene propylene diene monomer (EPDM) and cross-linked polyethylene (PEX), was investigated using scanning electron microscope (SEM)/confocal microscopy, ATP-/culture-based analysis, and molecular analysis. Material 'inserts' were incorporated into a mains water fed, model WDS. All materials supported biofilm growth to various degrees. After 84 days, copper and SS316 showed no significant overall differences in terms of the level of biofilm formation observed, whilst PEX supported a significantly higher level of biofilm. EPDM exhibited gross contamination by a complex, multispecies biofilm, at a level significantly higher than was observed on the other materials, regardless of the analytical method used. PCR-DGGE analysis showed clear differences in the composition of the biofilm community on all materials after 84 days. The primary conclusion of this study has been to identify EPDM as a potentially unsuitable material for use as a major component in WDS.     

Diversity and dynamics of bacterial species in a biofilm at the end of the Seoul water distribution system

To investigate changes in the bacterial species and hygienic safety of the biofilm at the end of the drinking water distribution system in Seoul (Korea), denaturing gradient gel electrophoresis (DGGE) and DNA sequencing were used to analyse the bacterial population in the biofilm of a semi-pilot galvanized iron pipe model. The presence of sequences from aerobic Sphingomonas sp., anaerobic Rhodobacter sp., and unculturable bacteria indicated that these organisms coexisted after 1 day of model operation, demonstrating the ease of biofilm formation on galvanized iron pipes in the end region of the water distribution system studied. Sequences similar to those of unculturable bacteria, E. coli, and anaerobic bacteria were detected during the course of succession on the biofilm. More complicated band patterns were observed after 70 days of operation. PCR-DGGE illustrated changes in the biofilm during succession as well as the possibilities of anaerobic conditions and faecal contamination of the drinking water system. PCR-DGGE and culture-dependent fatty acid methyl ester (FAME) analysis showed different patterns for the same samples (Lee & Kim 2003); however, PCR-DGGE showed less diversity than did FAME analysis. This study compared the culture-dependent FAME and culture-independent PCR-DGGE methods directly, and their use in promoting the hygienic safety of drinking water.     

Observations on cohorts of Tubifex tubifex cultured at different food levels,using cellulose substrate

In order to clarify the relationship between food availability and population dynamics in aquatic oligochaetes, short term cultures and cohort cultures of Tubifex tubifex were reared using substrates with different food concentrations, obtained by mixing sand with different amounts of cellulose powder.In short term experiments, T. tubifex seemed capable of utilizing cellulose substrates for growth or egg production. Yet, in the cohort experiment, newly hatched worms could not grow on cellulose substrates. Survivorship, however, appears to be influenced by cellulose concentration giving an indication that this material, although inadequate, is somehow utilized.     

Effect of different levels of positive end-expiratory pressure on lung water content

To compare the effects of 2-, 5-, and 10-cmH2O positive end-expiratory pressure (PEEP) on pulmonary extravascular water volume (PEWV), pulmonary blood volume (PBV), pulmonary dry weight (PDW), and distensibility, we separately ventilated perfused dogs' lungs in situ and produced pulmonary edema with oleic acid (0.06 ml/kg). Three groups were studied: I, PEEP, 5 cmH2O in both lung; II, PEEP, 2 cmH2O in one lung and 10 cmH2O in the other; and III, PEEP, same as II, but the chest was rotated to compensate for differences in heights. The PEWV and distensibility were less (P less than 0.05) in lungs exposed to 10-cmH2O than to either 2- or 5-cmH2O PEEP. After chest rotation, the difference between 10- and 2-cmH2O PEEP on PEWV was eliminated but that on distensibility was not. We conclude that 10-cmH2O PEEP 1) decreased water content because of lung volume-induced effects on intravascular hydrostatic pressure and 2) improved distensibility by recruitment of alveoli, irrespective of PEWV.     

Effect of flow regimes on the presence of Legionella within the biofilm of a model plumbing system

AIMS: Stagnation is widely believed to predispose water systems to colonization by Legionella. A model plumbing system was constructed to determine the effect of flow regimes on the presence of Legionella within microbial biofilms. METHODS AND RESULTS: The plumbing model contained three parallel pipes where turbulent, laminar and stagnant flow regimes were established. Four sets of experiments were carried out with Reynolds number from 10,000 to 40,000 and from 355 to 2,000 in turbulent and laminar pipes, respectively. Legionella counts recovered from biofilm and planktonic water samples of the three sampling pipes were compared with to determine the effect of flow regime on the presence of Legionella. Significantly higher colony counts of Legionella were recovered from the biofilm of the pipe with turbulent flow compared with the pipe with laminar flow. The lowest counts were in the pipe with stagnant flow. CONCLUSIONS: We were unable to demonstrate that stagnant conditions promoted Legionella colonization. SIGNIFICANCE AND IMPACT OF THE STUDY: Plumbing modifications to remove areas of stagnation including deadlegs are widely recommended, but these modifications are tedious and expensive to perform. Controlled studies in large buildings are needed to validate this unproved hypothesis.