• Journal of Korean Society of Environmental Engineers
• /
• v.27 no.3
• /
• pp.309-315
• /
• 2005

In this study, the bacterial regrowth characteristics in drinking water were investigated for various nutrient concentrations and forms using improved BRP method as a traditional approach and specific regrowth rate as a new index. The results of bacterial regrowth potential for glucose and $NH_4^+-N$, which was evaluated by BRP method as a traditional index, appeared to be higher relative to that of acetate or humic acids as carbon source and $NO_2^--N\;or\;NO_3^--N$ as nitrogen sources, respectively. The results obtained by specific regrowth rate as a new index were similar to that of BRP method with respect to the nutrient conditions examined in this study; i.e., the specific regrowth rate for glucose(ranged from 0.005 to $0.082\;hr^{-1}$) was feater than that acetate and humic acids(ranged from 0.005 to $0.068\;hr^{-1}$ and from 0.005 to $0.008\;hr^{-1}$, respectively). And specific regrowth rate for $NH_4^+-N$ (ranged from 0.008 to $0.072\;hr^{-1}$) was feater than that $NO_2^--N\;and\;NO_3^--N$ (ranged from 0.008 to $0.055\;hr^{-1}$ and from 0.008 to $0.059\;hr^{-1}$, respectively). Therefore, specific regrowth rate can be applied in order to evaluate the bacterial regrowth potential in drinking water.

• KSBB Journal
• /
• v.19 no.2
• /
• pp.104-109
• /
• 2004

Activated carbon has been used in water treatment, because they strongly adsorb organic material including contaminant. Water purifier usually use activated carbon, and bacterial regrowth on that could induce many problems. Model columns, packed with coal- and plant-based granular activated carbon (GAC), were operated with rechlorinated tap water to compare the degree of bacterial regrowth on different GACs. GAC columns decreased the concentration of total organic carbon and chlorine, while they are not good for the decrease of ions. Breakthrough of bacteria were occurred after eight days of operation, and reached 1.1 ${\times}$ 10$^3$ CFU/mL on coal based GAC and 6.2 ${\times}$ 10$^2$ CFU/mL on coconut based one. Bacterial activities on GAC were between 15.35 ∼ 29.06 $\mu\textrm{g}$ INT-formazan/g-GAC/h. Bacterial concentration and activities were higher in coal based GAC than coconut based one. Bacterial regrowth on GAC was clarified and regrowth effect of coal-based GAC was higher than that of coconut-based one.

• Journal of Korean Society of Environmental Engineers
• /
• v.27 no.4
• /
• pp.431-437
• /
• 2005

In this study, the profiles of the bacterial regrowth of indigenous bacteria in tap water and Pseudomonas fluorescence P17 were investigated for cases when carbon (glucose), and/or nitrogen ($NO_3^-$-N), and/or phosphorus ($PO_4^{3-}$-P) were added below sufficient nutrient concentration (SNC) and when carbon sources (glucose and acetate) and nitrogen sources ($NH_4^+$-N and $NO_3^-$-N) were added together. The bacterial regrowth was decreased with limitation of nutrients, and were lowered relatively in the sample, which plural nutrients were limited. In addition, phosphate might be the effective nutrient to control the bacterial regrowth in drinking water because the bacterial regrowth was significantly decreased by the limitation of phosphate. In contrast, the bacterial regrowth was retarded with increasing the concentration of $NO_3^-$-N. For simultaneously adding carbon(glucose or acetate) and nitrogen sources ($NH_4^+$-N and $NO_3^-$-N), the regrowth counts appeared highly in the condition, for both glucose and acetate. And, the regrowth was increased with increasing $NH_4^+$-N concentration as a nitrogen source.

• Journal of Korean Society of Water and Wastewater
• /
• v.22 no.2
• /
• pp.205-212
• /
• 2008

This study aimed to investigate the biofilm formation, bacterial regrowth, and bacterial community structure in the granular-activated carbon (GAC) filter adsorbers (FAs) used in water treatment plants. In 2005 and 2006, raw water, settled water, GAC FA by depth, and filtered water were collected twice a year from water treatment plants (WTPs) B and S. The number of heterotrophic bacteria, including mesophilic and psychrophilic bacteria, in such collected waters was investigated along with the total number of coliforms therein. Heterotrophic bacteria were detected in most samples, mainly at the surface layers of the GAC FAs, and fewer such bacteria were found in the lower and bottom layers. An increase in the bacterial number, however, was observed in the samples from various depths of the GAC FAs in WTPs B and S compared with the surface layers. An increase in the bacterial number was also detected in the filtered water. This may indicate that there is a regrowth of the bacteria in the GAC FA. Considering, however, that heterotrophic bacteria were not found in the filtered water, it can be deduced that most bacteria are removed in the chlorination process. Coliforms were detected at the surface layer of the GAC FAs, but their regrowth was not observed. MicroLog systems were used to identify the bacteria community distribution. Eight genera and 14 species, including Pseudomonas spp., were detected in WTP B, and 8 genera and 9 species, including Aeromonas spp., in WTP S. Further studies are required to elucidate their role in the biofilms in water treatment processes.

• Journal of Environmental Science International
• /
• v.16 no.1
• /
• pp.121-128
• /
• 2007

This study performed in order to evaluate the effects of pipe materials on corrosion and bacteria regrowth using a laboratory scale batch test. Two varieties of feed water with different microbial conditions were selected: tap water, surface river water (Han River water), and five pipe materials; carbon steel, copper, galvanized iron, stainless steel, and PVC, Carbon steel and galvanized iron pipes showed higher corrosion rates than other materials. In terms of attached bacterial growth, pipes with PVC and stainless steel showed higher bacteria concentration compared to other materials. Pseudomonas vesicularis was the predominant bacteria found on biofilm. The behavior of bacterial growth in the pipes was observed using a scanning electron microscope.

• Journal of Environmental Health Sciences
• /
• v.32 no.4 s.91
• /
• pp.282-291
• /
• 2006

This study investigated the inactivation of the total coliform, an indicator organism in chlorine and chlorine in order to control microbial regrowth for water distribution systems and select an appropriate disinfection strategy for drinking water systems. The disinfection effects of chlorine and chlorine dioxide with regard to the dosage of disinfectant, contact time and DOC was investigated experimentally. In spite of the consistency of chlorine residuals at approximately 0.2 mg/l, bacteria regrowth was detected in the distribution system and it was confirmed by the scanning electron microscope results. The influence of organic carbon change on the killing effect of chlorine dioxide was strong.

• Journal of Environmental Health Sciences
• /
• v.32 no.5 s.92
• /
• pp.431-439
• /
• 2006

This research was conducted using a model home plumbing system composed of copper, stainless steel, galvanized iron, carbon steel, and PVC (polyvinyl chloride) pipe. The number of bacteria present in stainless steel pipe and PVC was higher than other pipes. High turbidity and zinc release were found in galvanized iron pipe material and detected during the first 6 months. Conversely, there was a decrease in turbidity and zinc release after 6 months resulting in levels similar to other pipes. Copper concentration decreased as operation times increased. In this experiment, the number of bacteria detected in biofilm for a copper pipe continued to increase. Pipe material influenced bacterial numbers in biofilm and water. This showed that elevated chlorine could not control bacterial growth in biofilm for galvanized iron and stainless steel systems. It also suggested that the dosing of chlorine might not be available for all kinds of pipes. Therefore, another complementary method should be introduced to manage biofilm effectively in water distribution systems.

• Korean Journal of Microbiology
• /
• v.31 no.3
• /
• pp.255-260
• /
• 1993

The Enterobacter cloacae biofilms developed on slide glasses and galvanized-iron coupons were applied to test the attached bacterial resistance to chlorination. The chlorine resistances of biofilm bacteria grown on the slide glasses and galvanized-iron coupons were 14 and 480 times that of the suspended bacteria, respectively. The chlorine resistance of particleattached bacterial populations was 48 times that of suspended bacterial populations. The biofilm bacterial densities developed on the slide glasses and galvanized-iron coupons which were immersed in the flowing tap water for 75 days were $4.75 {\times} 10^{4}$ and $1.12 {\times} 10^5 cfu/cm^{2}$ It is concluded that main mechanisms of enteric or HPC bacterial resistance to chlorination in tap waters are bacterial attachment or . adsorption to particles or bacterial aggregations and formation of biofilms on the inner wall of distribution systems by escaped bacteria from chlorination in water treatment processes, which results in bacterial regrowth in water distribution systems.

• Journal of Veterinary Clinics
• /
• v.14 no.2
• /
• pp.215-222
• /
• 1997

Enrofloxacin-colistin combination, widely used in Gram negative infections in veterinary sector, was investigated in terms of MIC and initial killing rate using E coli k 88ab, Salmonella typhimurium, Pasteurella multocida type A, Bordetella bronchiseptica and Staphylococcus aureus as test organisms. On the basis of MICs of enrofloxacin-colistin combination against the above bacteria, killing rates of the combination of enrofloxacin and colistin at the ratio of 5:0, 4:1, 3:2, 1:1, 2:3, 1:4 and 0:5, indicated high and rapid antibacterial acitivities against all but Staphylococcus aureus R-209, with the number of bacteria reducing to less than one percent within two hours. At the MIC of enrofloxacin or colistin, both antibacterials showed the highest killing rates during 2-4 hours against Gram negatives such as E coli K88ab,Pasteurella multocida type A and Bodetella bronchiseptica but allowed the regrowth of the same pathogens thereafter. On the while, the combination of two antibacterials at a fourth MIC resulted in high killing rate without bacterial regrowth during 24 hours, suggesting the synergistic antivacterial effects. The combination, however, did not show favourable activity against Gram negatime S typhimurium and Gram positive S aureus ergistic antibacterial activity against Gram negatime pathogens but also colistin showed LPS-neutraization, we could suggest the combination should provide clinically positive therapeutic armarium in Gram negative infections.

• Korean Journal of Microbiology
• /
• v.31 no.3
• /
• pp.245-254
• /
• 1993

Distribution and variation of bacterial densities of heterotrophic plate count (HPC) and Enterobacteriaceae in the water supply systems comprising raw, treated, and three tap water samples of a water treatment plant in Seoul were studied 23 times from 1991 to 1992. HPC bacteria of raw. treated, and tap waters on $R_{2}A$ agar media were at a density of $1.22{\times}10^{3} to 3.05{\times}10^{5}$, $1.50{\times}10^{1} to 4.29{\times}10^{3}$ and 2 to $5.41{\times}10^{3}$ cfu/ml, respectively. Densities of Enterobacteriaceae in raw, treated, and tap waters on mENDO-LES agar media ranged from 0.] to 8200 cfu/ml, 0 to 17.5 cfu/JOO mI. and 0 to 47.5 cfu/IOO ml, respectively. Injured Enterobacteriaceae of treated and tap waters on m-T7 agar media were at a density of o to 27 and 0 to 35 cfu/100 mI. These results showed that the density of bacteria in the treated water outflowing from the water plant significantly increased as the water flowed along the distribution sytems, which is so-called bacterial regrowth. The predominant bacteria] types in the water supply system were Pw'udomonas and Acinerobacter. In raw water, the ratio of Pseudomonas was higher than that of Acinetobaeter, but in treated and tap waters. both ratios were reversed. The most predominant species of Enterobacteriaceae was Enterobacter agglomerans. Some species such as Citrobacter freundii. Escherichia coli. Klebsiella pneumoniae. and Shigella dysenteriae which are opportunistic pathogens or pathogens were not found in the treated water but additionally detected in tap waters.