Polycarbonate Coupons Research Articles

Effects of chlorine and pipe material on biofilm development and structure in a reclaimed water distribution system

The effects of chlorine and pipe material on biofilm development and structure were studied in a model reclaimed water distribution system using annular reactors (ARs). The initial chlorine dose of influents in ARs with polycarbonate pipes and cast iron pipes was 3.59 and 10.15 mg/L, respectively, which could maintain the reclaimed water quality (HPC 102–103 CFU/mL). The chlorine and pipe material influenced the bacterial community. Biofilms formed faster and to a greater extent in ARs with cast iron coupons (HPC 107 CFU/cm2) compared to those with polycarbonate coupons (HPC 105 CFU/cm2). Using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) analysis, it was found that Gammaproteobacteria were prevalent in all cases with polycarbonate pipes, whereas with cast iron pipes microbial populations were affiliated with the phylum Proteobacteria, including the classes Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Deltaproteobacteria, followed by the phyla Bacteroidetes and uncultured bacterium.

Mechanisms Involved in Microbially Enhanced Oil Recovery

Microbial enhanced oil recovery (MEOR) represents a possible cost-effective tertiary oil recovery method. Although the idea of MEOR has been around for more than 75 years, even now little is known of the mechanisms involved. In this study, Draugen and Ekofisk enrichment cultures, along with Pseudomonas spp. were utilized to study the selected MEOR mechanisms. Substrates which could potentially stimulate the microorganisms were examined, and l-fructose, d-galacturonic acid, turnose, pyruvic acid and pyruvic acid methyl ester were found to be the best utilized by the Ekofisk fermentative enrichment culture. Modelling results indicated that a mechanism likely to be important for enhanced oil recovery is biofilm formation, as it required a lower in situ cell concentration compared with some of the other MEOR mechanisms. The bacterial cells themselves were found to play an important role in the formation of emulsions. Bulk coreflood and flow cell experiments were performed to examine MEOR mechanisms, and microbial growth was found to lead to possible alterations in wettability. This was observed as a change in wettability from oil wet (contact angle 154°) to water wet (0°) due to the formation of biofilms on the polycarbonate coupons.

Maturation and survival of Cronobacter biofilms on silicone, polycarbonate, and stainless steel after UV light and ethanol immersion treatments.

Cronobacter sakazakii cells in biofilms formed on silicone, polycarbonate, and stainless steel coupons immersed in reconstituted powdered infant milk formula were treated with ethanol (10 to 70%) and UV light (12 to 2,160 mW.s/cm(2)) as antibacterial treatments. Biofilm maturation curves were determined after immersion at 25 degrees C for up to 144 h. Populations increased after subsequent immersion at 25 degrees C for 24 h in reconstituted powdered infant milk formula to the respective maximum levels of 7.96, 7.91, and 6.99 log CFU per coupon. Populations attached to silicone and polycarbonate surfaces to a greater extent than to stainless steel (P < 0.05). Treatment with 10% ethanol did not cause a significant decrease in the level of C. sakazakii, but treatment with 30, 40, and 50% ethanol reduced the levels to approximately 1.73, 3.02, and 4.17 log CFU per coupon, respectively. C. sakazakii was not detected on any coupon after treatment with 70% ethanol or 2,160 mW.s/cm(2) UV light. A synergistic effect of sequential ethanol and UV treatments was not observed.

A field study evaluation for mitigating biofouling with chlorine dioxide or chlorine integrated with UV disinfection

The drinking water industry is continually seeking innovative disinfection strategies to control biofouling in transmission systems. This research, conducted in collaboration with the East Bay Municipal Utility District (EBMUD) in California, compared the efficacy of chlorine dioxide (ClO 2) to free chlorine (Cl 2) with and without pre-treatment with low-pressure ultraviolet (UV) light for biofilm control. An additional goal was to determine disinfection by-product (DBP) formation with each disinfection strategy. Annular reactors (ARs) containing polycarbonate coupons were used to simulate EBMUD's 90-mile aqueduct that transports surface water from a source reservoir to treatment facilities. ARs were dosed with chemical disinfectants to achieve a residual of 0.2 mg/L, which is a typical value mid-way in the aqueduct. The experiment matrix included four strategies of disinfection including UV/ClO 2, ClO 2, UV/Cl 2 and Cl 2. Two ARs acted as controls and received raw water (RW) or UV-treated water. The data presented show that the UV/ClO 2 combination was most effective against suspended and attached heterotrophic (heterotrophic plate count, HPC) bacteria with 3.93 log and 2.05 log reductions, respectively. ClO 2 was more effective than Cl 2 at removing suspended HPC bacteria and similarly effective in biofilm bacterial removal. UV light alone was not effective in controlling suspended or biofilm bacteria compared to treatment with ClO 2 or Cl 2. Pre-treatment with UV was more effective overall for removal of HPC bacteria than treating with corresponding chemical disinfectants only; however, it did not lower required chemical dosages. Therefore, no significant differences were observed in DBP concentrations between ARs pre-treated with UV light and ARs not pre-treated. Disinfection with ClO 2 produced fewer total trihalomethanes (TTHMs) and haloacetic acids (HAAs) than chlorination but did produce low levels of chlorite. These data indicate that replacing Cl 2 with ClO 2 would further control microbiological re-growth and minimize TTHM and HAA formation, but may introduce other DBPs.

Mycobacterium marinumbiofilm formation reveals cording morphology

Abstract The emergence of the nontuberculosis mycobacteria (NTM) as clinically relevant pathogens has warranted the study of these ubiquitous organisms in the context of their likely environmental niche, the biofilm. We assayed the NTM bacterium Mycobacterium marinum strain 1218R, a fish outbreak isolate, for biofilm formation on different surfaces over time using three different methods. Using the MBEC system, biofilm development occurred continually over the 14-day culture period reaching a mature or stable biofilm state after 7 days postinoculation. Quantification of M. marinum biofilm formation on high-density polyethylene (HDPE), polycarbonate (PC) and silicon (Si) coupons over a 14-day period was evaluated using a continuous flow reactor system. M. marinum developed biofilms on all of the surfaces tested. However, substantially more biofilm accumulated on the silicon than on the other substrates (Si>HDPE>PC) under the same growth conditions indicating that silicon was the most effective substratum studied for the generation of M. marinum biofilms and suggesting a correlation between surface hydrophobicity and attachment. Finally, confocal laser scanning microscopy was used to visualize M. marinum biofilm development in situ over time and revealed an unusual biofilm ultrastructure. Large cell clusters attached to the surface grew in parallel sinuous arrays of cells that formed large cords.

Disinfectant efficacy of chlorite and chlorine dioxide in drinking water biofilms

The drinking water industry is closely examining options to maintain disinfection in distribution systems. In particular this research compared the relative efficiency of the chlorite ion (ClO 2 −) to chlorine dioxide (ClO 2) for biofilm control. Chlorite levels were selected for monitoring since they are typically observed in the distribution system as a by-product whenever chlorine dioxide is applied for primary or secondary disinfection. Previous research has reported the chlorite ion to be effective in mitigating nitrification in distribution systems. Annular reactors (ARs) containing polycarbonate and cast iron coupons were used to simulate water quality conditions in a distribution system. Following a 4 week acclimation period, individual ARs operated in parallel were dosed with high (0.25 mg/l) and low (0.1 mg/l) chlorite concentrations and with high (0.5 mg/l) and low (0.25 mg/l) chlorine dioxide concentrations, as measured in the effluent of the AR. Another set of ARs that contained cast iron and polycarbonate coupons served as controls and did not receive any disinfection. The data presented herein show that the presence of chlorite at low concentration levels was not effective at reducing heterotrophic bacteria. Log reductions of attached heterotrophic bacteria for low and high chlorite ranged between 0.20 and 0.34. Chlorine dioxide had greater log reductions for attached heterotrophic bacteria ranging from 0.52 to 1.36 at the higher dose. The greatest log reduction in suspended heterotrophic bacteria was for high dose of ClO 2 on either cast iron or polycarbonate coupons (1.77 and 1.55). These data indicate that it would be necessary to maintain a chlorine dioxide residual concentration in distribution systems for control of microbiological regrowth.

An efficient biofilm removal method for bacterial cells exposed to drinking water

Reliable quantification of microbial growth in a drinking water environment has typically been difficult, primarily due to the development of thin, patchy biofilms. Therefore, initial sampling and resuspension procedures become critical to the subsequent biomass determination. Biofilm cells attached to polycarbonate coupons of an annular reactor (AR) have typically been removed by aseptically scraping the coupon surface with a sterile utility knife. The advantage of this method is its simplicity, however, scraping often compromises sterility and is highly subject to individual variation. The purpose of this research was to develop a method that could remove and resuspend biofilm cells efficiently, consistently and with a good recovery rate. This paper presents a comparison of removal and resuspension methods. Three methods used to remove cells from the polycarbonate coupons include: scraping with a utility knife, swabbing and stomaching. In addition, four methods were selected for cell resuspension and involved the use of a tissue blender, vortex, stomacher and a sonicator. Of the removal methods examined, stomaching consistently yielded the highest number of culturable and total bacterial cells, ranging from two to four times more cells than scraping procedures. For one experimental set, the number of colonies enumerated by heterotrophic plate count (HPC) from the stomacher ranged from 1.0–1.7×10 6 CFU/cm 2, whereas numbers obtained using the scraping method were 4.6–4.9×10 5 CFU/cm 2. It was found that the number of HPCs recovered with stomaching was significantly greater at the 5% level than that obtained using the scraping method. Similarly, for cell resuspension, stomaching provided the highest enumeration. Once removal was achieved, sonication also provided good resuspension. An analysis of variance showed that, compared to the resuspension step, the removal step is more significant at the 5% level to the recovery of biofilm cells. The stomacher has the unique advantage of combining cellular removal and resuspension into a single step. This method was, therefore, selected as an ideal method for recovery of biofilm cells. Subsequent optimization measures using the stomacher showed that sterile deionized water was a suitable diluent for recovering cells from a drinking water environment. At normal speed (i.e., 230 rpm±5%), the optimal stomacher run length for maximum cell removal was 2 min.