Peracetic acid disinfection: a feasible alternative to wastewater chlorination.

The paper summarizes the results of a bench-scale study to evaluate the feasibility of using peracetic acid (PAA) as a substitute for sodium hypochlorite both for discharge into surface water and for agricultural reuse. Trials were carried out with increasing doses (1, 2, 3, 5, 10, and 15 mg/L) and contact times (6, 12, 18, 36, 42, and 54 minutes) to study disinfectant decay and bacterial removal and regrowth, using fecal coliform and Escherichia coli (E. coli) as process efficiency indicators. Peracetic acid decay kinetics was evaluated in tap water and wastewater; in both cases, PAA decays according to first-order kinetics with respect to time, and a correlation was found between PAA oxidative initial consumption and wastewater characteristics. The PAA disinfection efficiency was correlated with operating parameters (active concentration and contact time), testing different kinetic models. Two data groups displaying a different behavior on the basis of initial active concentration ranges (1 to 2 mg/L and 5 to 15 mg/L, respectively) can be outlined. Both groups had a "tailing-off" inactivation curve with respect to time, but the second one showed a greater inactivation rate. Moreover, the effect of contact time was greater at the lower doses. Hom's model, used separately for the two data groups, was found to best fit experimental data, and the disinfectant active concentration appears to be the main factor affecting log-survival ratios. Moreover, the S-model better explains the initial resistance of E. coli, especially at low active concentrations (< 2 mg/L) and short contact times (< 12 minutes). Microbial counts, performed by both traditional methods and flow cytometry, immediately and 5 hours after sample collection (both with or without residual PAA inactivation), showed that no appreciable regrowth took place after 5 hours, neither for coliform group bacteria, nor for total heterotrophic bacteria.     

Disinfection of an advanced primary effluent with peracetic acid and ultraviolet combined treatment: a continuous-flow pilot plant study

Disinfection of an advanced primary effluent using a continuous-flow combined peracetic acid/ultraviolet (PAA/UV) radiation system was evaluated. The purpose was to determine whether the maximum microbial content, established under Mexican standards for treated wastewaters meant for reuse--less than 240 most probable number fecal coliforms (FC)/100 mL--could be feasibly accomplished using either disinfectant individually, or the combined PAA/UV system. This meant achieving reduction of up to 5 logs, considering initial concentrations of 6.4 x 10(+6) to 5.8 x 10(+7) colony forming units/100 mL. During the tests performed under these experiments, total coliforms (TC) were counted because FC, at the most, will be equal to TC. Peracetic acid disinfection achieved less than 1.5 logs TC reduction when the C(t) x t product was less than 2.26 mg x minimum (min)/L; 3.8 logs for C(t) x t 4.40 mg x min/L; and 5.9 logs for C(t) x t 24.2 mg x min/L. In continuous-flow UV irradiation tests, at a low-operating flow (21 L/min; conditions which produced an average UV fluence of 13.0 mJ/cm2), the highest TC reduction was close to 2.5 logs. The only condition that produced a disinfection efficiency of approximately 5 logs, when both disinfection agents were used together, was the combined process dosing 30 mg PAA/L at a pilot plant flow of 21 L/min and contact time of 10 minutes to attain an average C(t) x t product of 24.2 mg x min/L and an average UV fluence of 13 mJ/cm2. There was no conclusive evidence of a synergistic effect when both disinfectants were employed in combination as compared to the individual effects achieved when used separately, but this does not take into account the nonlinearity (tailing-off) of the dose-response curve.     

炼化企业中水紫外线消毒及其影响因素简

研究水质对254 nm紫外线透射率的影响，通过动态实验考察了照射时间、254 nm紫外线透射率以及紫外线剂量对炼化企业中水消毒效果的影响并同时考察异养菌、硫酸盐还原菌和铁细菌的光复活及暗修复现象。结果表明，有机物是影响炼化企业中水紫外线消毒的重要因素；紫外线对炼化企业中水中的异养菌具有良好的灭活作用；增加照射时间对消毒效果的提升作用受254 nm紫外线透射率的影响；紫外线透射率在较低的范围内时对消毒效果的影响相对较大，在较高的范围内时影响较小；紫外线剂量-响应曲线受254 nm紫外线透射率的影响；剂量的“成分”，即照射时间和透射率的不同组合，也会对消毒效果产生影响；在80 mJ/cm²的剂量下，20 h内异养菌出现了较强烈的光复活和暗修复现象，铁细菌仅出现了明显的光复活现象，硫酸盐还原菌没有表现出明显的复活。     

Treatment of Arctic wastewater by chemical coagulation,UV and peracetic acid disinfection

Conventional wastewater treatment is challenging in the Arctic region due to the cold climate and scattered population. Thus, no wastewater treatment plant exists in Greenland, and raw wastewater is discharged directly to nearby waterbodies without treatment. We investigated the efficiency of physicochemical wastewater treatment, in Kangerlussuaq, Greenland. Raw wastewater from Kangerlussuaq was treated by chemical coagulation and UV disinfection. By applying 7.5 mg Al/L polyaluminium chloride (PAX XL100), 73% of turbidity and 28% phosphate was removed from raw wastewater. E. coli and Enterococcus were removed by 4 and 2.5 log, respectively, when UV irradiation of 0.70 kWh/m³ was applied to coagulated wastewater. Furthermore, coagulated raw wastewater in Denmark, which has a chemical quality similar to Greenlandic wastewater, was disinfected by peracetic acid or UV irradiation. Removal of heterotrophic bacteria by applying 6 and 12 mg/L peracetic acid was 2.8 and 3.1 log, respectively. Similarly, removal of heterotrophic bacteria by applying 0.21 and 2.10 kWh/m³ for UV irradiation was 2.1 and greater than 4 log, respectively. Physicochemical treatment of raw wastewater followed by UV irradiation and/or peracetic acid disinfection showed the potential for treatment of arctic wastewater.     

Effects of temperature on bacterial transport and destruction in bioretention media: field and laboratory evaluations

Microbial activities are significantly influenced by temperature. This study investigated the effects of temperature on the capture and destruction of bacteria from urban stormwater runoff in bioretention media using 2-year field evaluations coupled with controlled laboratory column studies. Field data from two bioretention cells show that the concentration of indicator bacteria (fecal coliforms and Escherichia coli) was reduced during most storm events, and that the probability of meeting specific water quality criteria in the discharge was increased. Indicator bacteria concentration in the input flow typically increased with higher daily temperature. Although bacterial removal efficiency was independent of temperature in the field and laboratory, column tests showed that bacterial decay coefficients in conventional bioretention media (CBM) increase exponentially with elevated temperature. Increases in levels of protozoa and heterotrophic bacteria associated with increasing temperature appear to contribute to faster die-off of trapped E. coli in CBM via predation and competition.     

Disinfection and dewatering of wastewater solids by interstitial vapor generation.

Disinfection of wastewater solids (waste activated solids [WAS]) by interstitial vapor generation was investigated. In addition to the magnitude of disinfection, the amount of water removed and cost relative to traditional residuals disinfection processes was also examined. The process of interstitial vapor generation occurs as a result of the rapid heating of liquid in the interstices of the solid-liquid array. Intense heating causes boiling of the slurry liquid, resulting in an expanding vapor front that simultaneously dewaters the wastewater solids and contributes to the destruction of viable pathogenic microorganisms. Objectives of the study were threefold: (1) to validate disinfection of WAS using the interstitial vapor technique; (2) establish the degree of possible drying of the residuals using the techniques; and (3) establish the key operating variables for the process. Results showed a significant reduction in the most probable number of total coliforms and Escherichia coli (E. coli). Specifically, greater than four-log unit reductions were produced for both total coliform and E. coli bacteria. In addition to quantifying the reduction in bacteria, the percent solids were increased from an initial amount of 7.6% (mass basis) to a final solids content greater than 90% using optimal processing conditions. Cost comparisons were also conducted and shown to be quite favorable when compared with traditional disinfection methods such as lime addition. Because of the high level of E. coli reduction achieved, the process of interstitial vapor generation is shown to be capable of converting a class B biosolids into a class A pathogen reduced product. For example, an initial most probable number (MPN) of 1.2 x 10(6) E. coli bacteria were reduced to 19 at the extreme conditions of the process, well below the requirement of an MPN of 1000 for fecal coliform bacteria. Given its ability to disinfect and dewater wastewater solids, the interstitial vapor generation process was found to be a robust and beneficial technique to produce an environmental and publicly acceptable recyclable biosolids resource.     

Escherichia coli and total coliforms in water and sediments at lake marinas

Escherichia coli, a fecal coliform, and total coliforms were monitored between September 1999 and October 2001 in five marinas at Lake Texoma, located on the Oklahoma and Texas border. The general trend was that densities of E. coli were lower in the summer season due to the lower loading of fecal material into Lake Texoma and the ecological conditions of the lake, such as more vigorous grazing by protozoa and less viability of E. coli at an elevated temperature. The densities of total coliforms greatly increased in the summer. E. coli levels increased with depth, and the bottom water samples had higher densities of E. coli mainly due to their association with particles. There was a direct relationship between amount of gasoline sold, which was related to recreational boating activity, and the resuspension of E. coli. This indicated that recreational boating activity in lake marinas may have resuspended bottom sediments with bound E. coli, and the presence of E. coli in marinas was not an indication of recent fecal contamination. E. coli were detected in the largest densities at the boat dock points, followed by the gasoline filling station, and marina entrance. In addition, enumeration of bacteria in bottom sediment showed that the densities of E. coli and total coliforms in sediment were much higher compared to those in lake water.     

Point-of-use water disinfection using UV light-emitting diodes to reduce bacterial contamination

The treatment process described in this research explores the impact of exposing water samples containing fecal coliforms to the radiation produced by single ultraviolet (UV) light-emitting diodes (LEDs) operating at 265 nm. UV LEDs are long lasting, compact in size and produce more efficient light output than traditional mercury-vapour bulbs, making them ideal for application in point-of-use disinfection systems, such as in remote areas. In this study, contaminated water samples containing either a pure culture of Escherichia coli or tertiary effluent from the City of Regina Wastewater Treatment Plant were used to study the application and efficiency of using UV LEDs for water disinfection. The results indicate that bacterial inactivation was achieved in a time-dependent manner, with 1- and 2.5-log E. coli reductions in water following 20 and 50 min of UV LED exposure, respectively. Ultraviolet radiation was less effective in reducing coliform bacteria in wastewater samples due to the elevated turbidity levels. Further work remains to be completed to optimize the application of UV LEDs for point-of-use disinfection systems; however, the results from this study support that bacterial inactivation using UV LEDs is possible, meriting further future technological development of the LEDs.     

Effects of freezing on the survival of Escherichia coli and Bacillus and response to UV and chlorine after freezing.

Escherichia coli (E. coli) and Bacillus megaterium bacteria were frozen at -15 degrees C using a freezer and a spray freezing method. The frozen Bacillus spores were also exposed to UV and free chlorine. An average of 4.7-log inactivation was obtained from the spray ice with 2-day storage time, while the freezer freezing only caused 0.84-log reduction with the same storage time. Significantly higher inactivation levels were observed for the E. coli cells with 2-day storage compared with those without storage. The spray freezing was found more effective in killing the E. coli cells, while more cells were sublethally injured by the freezer freezing. Freezing did not kill the Bacillus megaterium spores, but affected their response to UV and chlorine. Greater inactivation levels were observed at higher free chlorine doses or longer contact time, and the UV fluence-response curve showed initial rapid kill followed by tailing for the frozen spores.     

Evaluation of disinfection techniques in the treatment of advanced primary treated wastewater for Ciudad Juárez, México.

The purpose of this study was to develop and evaluate the effectiveness of alternative disinfection techniques at the bench-scale level using wastewater from Ciudad Juarez, Mexico, as model feed. This paper presents findings on the effectiveness of UV radiation, peracetic acid (PAA), chlorine dioxide (ClO2), and hypochlorous acid (HOCl) as disinfectants for advanced primary treatment (APT) plant effluent. Wastewater samples for bench-scale testing were collected from an agua negra ("black water") ditch that is part of the combined sewer system in Ciudad Juarez. Bench-scale simulations of the APT process used in Ciudad Juarez were run using a jar test apparatus and aluminum sulfate [Al2(SO4)3] as the coagulant. Jar test effluent from the bench system was used for disinfection testing. The Mexican discharge quality standard for total coliforms is 10 000/100 mL. Ultraviolet radiation met this standard at a dose of 47.5 mW-s/cm2. Ultraviolet disinfection proved reliable and effective despite the presence of suspended solids, and UV dose effectiveness expressed as a total coliforms survival ratio was best explained by a linear regression model. The ClO2 dose ranged from 10 to 20 mg/L and was only effective under ambient temperature conditions found during the winter months; PAA disinfection never met Mexican standards. Chlorine disinfection was effective at a dose range of 8 to 10 mg/L on samples collected at low temperature conditions. Since the completion of this research, Ciudad Juarez has discontinued the use of chlorine disinfection because of its high cost and ineffectiveness.     

Do alternate bacterial indicators and pathogens increase after centrifuge dewatering of anaerobically digested biosolids?

The objectives of this research were to evaluate the potential for sudden increase and/or regrowth of alternative bacteria as either indicators or pathogens after dewatering of thermophilic and mesophilically digested biosolids. The results showed that, in general, for thermophilic processes, even when a statistically significant (p < 0.05) sudden increase and regrowth occurred for fecal coliforms, Escherichia coli, and Enterococci, it did not occur for Salmonella or Aeromonas. For the mesophilic process evaluated, sudden increase did not occur, but regrowth occurred for fecal coliforms, E. coli, Enterococci, and Salmonella. The results have implications for Class A and B biosolids regulations, as both fecal coliform and Salmonella are part of the regulatory limits. The results also suggest that the public health risks are minimal, as a result of the potential sudden increase and regrowth that may occur.     

Reduction of photoreactivation with the combined UV/peracetic acid process or by delayed exposure to visible light.

Photoreactivation of microorganisms following UV inactivation is a well-known, but complex, phenomenon. It is affected by several factors, including UV fluence, wavelength, light intensity, and exposure time to photoreactivating light. The effect on photoreactivation of a combined peracetic acid (PAA)/UV process has not been investigated. Accordingly, this study compared the degree of photoreactivation, under both sunlight and artificial lights, following UV and combined PAA/UV inactivation of fecal coliforms. Effluent samples from the Montreal Wastewater Treatment Plant (MWTP) (Quebec, Canada) were exposed, for 3 hours, to both low- and high-intensity artificial lights and sunlight. All resulted in similar photoreactivation levels. However, average photoreactivation for UV-treated wastewater samples was 1.2 logs, compared with 0.1 log for the combined PAA/UV treatment. Hence, the use of PAA in combination with UV can significantly reduce the potential for photoreactivation. To simulate the photoreactivation conditions of the MWTP effluent (which passes through a 4-km outfall tunnel with approximately 3 hours detention time), UV-treated samples were kept in the dark for 3 hours before photoreactivating light exposure. After this period, photoreactivation levels were close to zero. Hence, the effects of photoreactivation may be diminished by use of a combined disinfection scheme and/or by delaying exposure of the disinfected wastewater to light.     

Effects of feed-supplementation and hide-spray application of two sources of tannins on enteric and hide bacteria of feedlot cattle

Pathogenic bacteria attached to the hide or shed in the feces of cattle at slaughter can contaminate carcasses intended to be processed for human consumption. Therefore, new pre-harvest interventions are needed to prevent the carriage and excretion of foodborne pathogens in cattle presented to the processing plant. The objectives of this study were to examine the antimicrobial effects of hydrolysable tannin-rich chestnut and condensed tannin-rich mimosa extracts on bacterial indicators of foodborne pathogens when applied as a hide-intervention and as a feed additive to feedlot cattle. Water (control) or solutions (3 % wt/vol) of chestnut- and mimosa-extract treatments were sprayed (25 mL) at the left costal side of each animal to a 1000 cm2 area, divided in four equal quadrants. Hide-swabs samples obtained at pre-, 2-min, 8-h, and 24-h post-spray application were cultured to enumerate Escherichia coli/total coliforms and total aerobic plate counts. In a second experiment, diets supplemented without (controls) or with (1.5 % of diet dry matter) chestnut- or mimosa-extracts were fed during a 42-day experimental feeding period. Weekly fecal samples starting on day 0, and rumen fluid obtained on days 0, 7, 21 or 42 were cultured to enumerate E.coli/total coliforms and Campylobacter. Tannin spray application showed no effect of treatment or post-application-time (P > 0.05) on measured bacterial populations, averaging 1.7/1.8, 1.5/1.6 and 1.5/1.7 (log??CFU/cm2) for E. coli/total coliforms, and 4.0, 3.4 and 4.2 (log??CFU/cm2) in total aerobes for control, chestnut and mimosa treatments, respectively. Mean (± SEM) ruminal E. coli and total coliform concentrations (log(10) CFU/mL) were reduced (P < 0.01) in steers fed chestnut-tannins (3.6 and 3.8 ± 0.1) in comparison with the controls (4.1 and 4.2 ± 0.1). Fecal E. coli concentrations were affected by treatment (P< 0.01), showing the highest values (log?? CFU/g) in fecal contents from mimosa-fed steers compared to controls (5.9 versus 5.6 ± 0.1 SEM, respectively). Total coliforms (log CFU/g) showed the highest values (P < 0.01) in feces from chestnut- and mimosa-fed steers (6.0 and 6.1 ± 0.1 respectively) in comparison with controls (5.7 ± 0.1). Fecal Campylobacter concentrations (log??CFU/g) were affected by treatment (P < 0.05), day (P < 0.001) and their interaction (P < 0.01) with the controls having lower concentrations than chestnut- and mimosa-fed steers (0.4, 1.0, and 0.8 ± 0.3, respectively). It was concluded that under our research conditions, tannins were not effective in decreasing measured bacterial populations on beef cattle hides. Additionally, chestnut tannin reduced E. coli and total coliforms within the rumen but the antimicrobial effect was not maintained in the lower gastrointestinal tract. Further research is necessary to elucidate the possible antimicrobial effects of tannins at site-specific locations of the gastrointestinal tract in beef cattle fed high-grain and high-forage diets.     

Survival and activity of Streptococcus faecalis and Escherichia coli in petroleum-contaminated tropical marine waters

The in situ survival and activity of Streptococcus faecalis and Escherichia coli were studied using membrane diffusion chambers in tropical marine waters receiving oil refinery effluents. Protein synthesis, DNA synthesis, respiration or fermentation, INT reduced per cell, and ATP per cell were used to measure physiological activity. Cell densities decreased significantly over time at both sites for both S. faecalis and E. coli; however, no significant differences in survival pattern were observed between S. faecalis and E. coli. Differences in protein synthesis between the two were only observed at a study site which was not heavily oiled. E. coli was more active in protein synthesis and respiration than S. faecalis at both oiled and unoiled sites, and the percentage of the E. coli population that was respiring was significantly higher than S. faecalis fermenting cells at both sites. However, S. faecalis cells were more active in DNA synthesis and higher in ATP content than E. coli cells at both sites. Although fecal streptococci have been suggested as a better indicator of fecal contamination than fecal coliforms in marine waters, in this study both E. coli and S. faecalis survived and remained physiologically active for extended periods of time. These results suggest that the fecal streptococci group is not a better indicator of fecal contamination in tropical marine waters than the fecal coliform group, especially when that environment is high in long-chained hydrocarbons.     

Application of photocatalysis as a post treatment method of a heterotrophic-autotrophic denitrification reactor effluent

The aim of this study is the application of photocatalysis as an effective post treatment scheme for the removal of the organic matter and bacteria released by an innovative biological denitrification process referred to as heterotrophic-autotrophic denitrification, which combines heterotrophic and autotrophic denitrification processes. Photocatalytic treatment was applied using TiO2 as a photocatalyst in the loading range of 0.25-2.00 g l(-1) for irradiation periods up to 60 min using a black light fluorescent lamp with an intensity of I(0)=1309 microW cm(-2). The photocatalytic inactivation data were modelled to pseudo first order kinetics as well as by the areal rates to evaluate the photocatalyst loading effect. Chlorination was used as a final disinfection step to attain an overall inactivation of total coliforms as well as to the formation of very low level of trihalomethanes.     

Effects of wastewater disinfection on waterborne bacteria and viruses.

Wastewater disinfection is practiced with the goal of reducing risks of human exposure to pathogenic microorganisms. In most circumstances, the efficacy of a wastewater disinfection process is regulated and monitored based on measurements of the responses of indicator bacteria. However, inactivation of indicator bacteria does not guarantee an acceptable degree of inactivation among other waterborne microorganisms (e.g., microbial pathogens). Undisinfected effluent samples from several municipal wastewater treatment facilities were collected for analysis. Facilities were selected to provide a broad spectrum of effluent quality, particularly as related to nitrogenous compounds. Samples were subjected to bench-scale chlorination and dechlorination and UV irradiation under conditions that allowed compliance with relevant discharge regulations and such that disinfectant exposures could be accurately quantified. Disinfected samples were subjected to a battery of assays to assess the immediate and long-term effects of wastewater disinfection on waterborne bacteria and viruses. In general, (viable) bacterial populations showed an immediate decline as a result of disinfectant exposure; however, incubation of disinfected samples under conditions that were designed to mimic the conditions in a receiving stream resulted in substantial recovery of the total bacterial community. The bacterial groups that are commonly used as indicators do not provide an accurate representation of the response of the bacterial community to disinfectant exposure and subsequent recovery in the environment. UV irradiation and chlorination/dechlorination both accomplished measurable inactivation of indigenous phage; however, the extent of inactivation was fairly modest under the conditions of disinfection used in this study. UV irradiation was consistently more effective as a virucide than chlorination/dechlorination under the conditions of application, based on measurements of virus (phage) diversity and concentration. Taken together, and when considered in conjunction with previously published research, the results of these experiments illustrate several important limitations of common disinfection processes as applied in the treatment of municipal wastewaters. In general, it is not clear that conventional disinfection processes, as commonly implemented, are effective for control of the risks of disease transmission, particularly those associated with viral pathogens. Microbial quality in receiving streams may not be substantially improved by the application of these disinfection processes; under some circumstances, an argument can be made that disinfection may actually yield a decrease in effluent and receiving water quality. Decisions regarding the need for effluent disinfection must account for site-specific characteristics, but it is not clear that disinfection of municipal wastewater effluents is necessary or beneficial for all facilities. When direct human contact or ingestion of municipal wastewater effluents is likely, disinfection may be necessary. Under these circumstances, UV irradiation appears to be superior to chlorination in terms of microbial quality and chemistry and toxicology. This advantage is particularly evident in effluents that contain appreciable quantities of ammonia-nitrogen or organic nitrogen.     

The exploration of potassium ferrate(VI) as a disinfectant/coagulant in water and wastewater treatment

This paper aims to explore potassium ferrate(VI) (K2FeO4) as an alternative water treatment chemical for both drinking water and wastewater treatment. The performance of potassium ferrate(VI) was evaluated in comparison with that of sodium hypochlorite (NaOCl) and that of NaOCl plus ferric sulphate (FS) or alum (AS). The dosages of ferrate(VI), NaOCl and FS/AS and sample pH values were varied in order to investigate the effects of these factors on the treatment performance. The study demonstrates that in drinking water treatment, ferrate(VI) can remove 10-20% more UV(254)-abs and DOC than FS for the same dose compared for natural pH range (6 and 8). The THMFP was reduced to less than 100 microg l(-1) by ferrate(VI) at a low dose. In addition to this, ferrate(VI) can achieve the disinfection targets (>6 log10 inactivation of Escherichia coliform (E. coli)) at a very low dose (6 mg l(-1) as Fe) and over wide working pH in comparison with chlorination (10 mg l(-1) as Cl2) plus coagulation (FS, 4 mg l(-1) as Fe). In wastewater treatment, ferrate(VI) can reduce 30% more COD, and kill 3log10 more bacteria compared to AS and FS at a similar or even smaller dose. Also, potassium ferrate(VI) can produce less sludge volume and remove more pollutants, which could make sludge treatment easier.     

西安地区旅游景点水体卫生细菌学调查及保护对策

以粪大肠菌和异养细菌总数做指标，对西安地区旅游景点水体的卫生细菌学状况进行了调查。结果表明，西安市区内旅游景点的人工湖、天然湖等大都受到不同程度的污染，而离市区较远、海拔较高的旅游景点则污染较轻。     

Effect of chlorination and ultraviolet disinfection on tetA-mediated tetracycline resistance of Escherichia coli

Antibiotic-resistant bacteria are an emerging threat to public health during drinking water consumption and reclaimed water reuse. Several studies have shown that the proportions of antibiotic-resistant bacteria in waters may increase when exposed to low doses of UV light or chlorine. In this study, inactivation of tetracycline-resistant Escherichia coli and antibiotic-sensitive E. coli by UV disinfection and chlorination was compared to determine the tolerance of tetracycline-resistant E. coli to UV light and chlorine, and tetracycline resistance of a tetracycline-resistant E. coli population was studied under different doses of the disinfectants. Our results showed that relative to antibiotic-sensitive E. coli, tetracycline-resistant E. coli had the same tolerance to UV light and a potentially higher tolerance to chlorination. The mortality frequency distributions of tetracycline-resistant E. coli exposed to tetracycline were shifted by both chlorination and UV disinfection. When compared to the hemi-inhibitory concentrations (IC₅₀) of tetracycline-resistant E. coli with no exposure to UV or chlorination, the IC₅₀ of tetracycline-resistant E. coli treated with tetracycline was 40% lower when inactivation by UV light or chlorination reached 3-log but was 1.18 times greater when inactivation by chlorination reached 4.3-log. Chlorination applied to drinking water or reclaimed water treatment may increase the risk of selection for highly tetracycline-resistant E. coli.     

Use of hydrophilic and hydrophobic microfiltration membranes to remove microorganisms and organic pollutants from primary effluents.

Primary-effluent wastewater from the Allegheny County Sanitary Authority (Pennsylvania) was used as a surrogate for combined-sewer-overflow waters contained in the sewershed. Pathogens contained in combined-primary-effluent wastewaters or combined-sewer overflows (CSOs) may pose a human-health threat to those coming in contact with such receiving waters. Polymeric ultra- and nano-membranes can be used to capture these microorganisms from CSOs. This research investigates the ability of polymeric hydrophobic and hydrophilic membranes, ranging in pore size from 0.2 to 0.8 microm, to remove pathogen-indicator organisms (Escherichia coli, enterococcus, and fecal coliforms). Membranes, with pore size 0.45 microm and smaller, were able to reduce the bacteria levels to nondetectable levels, with the sole exception of one membrane with pore size 0.3 microm.