Occurrence of diarrheagenic Escherichia coli genes in raw water of water treatment plants

Purpose

The high incidences of waterborne diseases are frequently associated with diarrheagenic Escherichia coli (DEC). DEC may pose a health risk to people who contact surface water for recreation or domestic use. However, there is no published report on the monitoring of DEC in drinking water sources in Taiwan. In this study, the occurrence of DEC genes in raw water for water treatment plants in Taiwan was investigated.

Method

Raw water samples were taken from water treatment plants adjacent to the Kaoping River in southern Taiwan. Each water sample was treated with membrane filtration followed by DNA extraction from the concentrate and concentrate enrichment, respectively. The target genes for various DEC strains of genes were identified, including enteroaggregative E. coli (EAEC), enterohemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), and enterotoxigenic E. coli (ETEC).

Results

Among 55 water samples analyzed, DEC genes were detected in 16 (29.1%) samples. Strain-specific genes for EAEC, EHEC, EIEC, and EPEC were found in the percentages of 3.6%, 10.9%, 9.1%, and 9.1%, respectively. The specific gene for ETEC is not detected in the study. By looking at the presence/absence of specific genes and water sample characteristics, water temperature was found to differ significantly between samples with and without EHEC gene. In addition, pH levels differed significantly for EHEC and EPEC presence/absence genes, and turbidity was significantly different for water with and without EPEC genes.

Conclusion

DEC genes were detected in 29.1% of the raw water samples in the study location. The potential health threat may be increased if the treatment efficiencies are not properly maintained. Routine monitoring of DEC in drinking water sources should be considered.     

Motility of Pseudomonas aeruginosa in saturated granular media as affected by chemoattractant

To examine and quantify the effects of glass beads and chemoattractant on bacterial motility in granular media, we examined the motile behavior of P. aeruginosa in a saturated granular medium and quantified the effects of glass beads and the presence of a chemoattractant. By recording individual cell trajectories in microfluidic channels under a high-speed confocal microscope, we directly measured the cell's run direction and corresponding run-length, speed and turn angle. Bacterial run speed increased in the presence of chemoattractant in both aqueous and granular media. But it decreased in glass-beads compared to in aqueous media due to the restricted pore geometry and interactions between bacteria and grain surfaces. Notably, the relatively higher frequency distribution at turn angles of 170° decreased dramatically, while the smaller peak at 70° increased and became dominant on a bimodal distribution, showing more bacteria changed directions at smaller turn angles rather than reverse their swimming directions. Additionally, the presence of glass beads also decreased the chemotactic velocity and random motility by similar proportions due to the restrictive geometry and the interactions between bacteria and glass beads surface. Our study indicates that the swimming parameters measured from aqueous media cannot be directly adopted in models for predicting bacteria travel in granular media.     

Predicting the bioavailability of sediment-associated polybrominated diphenyl ethers using a 45-d sequential Tenax extraction

A 45-d Tenax extraction was used to evaluate the bioavailability of polybrominated diphenyl ethers (PBDEs) in three spiked sediments. The effect of aging on desorption kinetics of PBDEs was investigated by incubating one of the sediments for 7, 14, 30 and 60 d at room temperature. Desorption kinetics were well described by a three-compartment model. The fraction of very slow desorption (Fvs) contributed the most of the desorbed PBDEs from sediments. The total desorption amount of PBDEs decreased with the increase of total organic carbon in the sediments, suggesting that organic matter is an important factor controlling the partition of PBDEs in sediments. The total desorption amount of PBDEs decreased while log [(Fslow+Fvs)/Frap] increased with logKow of PBDE congeners, indicating that the bioavailability of PBDEs in sediment decreases with logKow of the congeners. As the residential time of PBDEs in the sediment increased from 7 to 60 d, Frap of individual PBDE congeners decreased gradually with simultaneous increase of Fvs. There was a good positive correlation between Frap and F6/F24, indicating that either 6 h or 24 h Tenax extraction could be a proxy for Frap and bioavailability. In general, the results in present study suggest that the bioavailability of nona- and deca-BDEs in sediment is very low due to their strong hydrophobicity and large molecular size.     

Biodegradation of nicotine by a novel Strain Shinella sp. HZN1 isolated from activated sludge

The nicotine-degrading bacterium HZN1 was isolated from activated sludge and identified as Shinella sp. based on its physiological characteristics and analysis of 16S rDNA gene. Strain HZN1 is capable of using nicotine as the sole carbon source in the mineral salts medium. The optimum temperature and pH for strain HZN1 growth and nicotine degradation were 30°C and 7.0, respectively. It could degrade approximately 100 % of 0.5 g L(-1) of nicotine within 9 h. Three intermediate metabolites were produced by the strain HZN1 and identified as cotinine, myosmine and nicotyrine using gas chromatography-mass spectrometry. This is the first report of nicotine-degrading strain from the genus of Shinella. The results showed that strain HZN1 could be potentially employed in bioremediation of nicotine. Our findings would provide a new insight into the biodegradation of nicotine.     

Effects of pH and ionic strength on sulfamethoxazole and ciprofloxacin transport in saturated porous media

Many antibiotics regarded as emerging contaminants have been frequently detected in soils and groundwater; however, their transport behaviors in soils remain largely unknown. This study examined the transport of two antibiotics, sulfamethoxazole (SMZ) and ciprofloxacin (CIP), in saturated porous media. Laboratory columns packed with quartz sand was used to test the effects of solution pH and ionic strength (IS) on their retention and transport. The results showed that these two antibiotics behaved differently in the saturated sand columns. In general, SMZ manifested a much higher mobility than CIP for all experimental conditions tested. Almost all SMZ transported through the columns within one pore volume in deionized water (i.e., pH=5.6, IS=0), but no CIP was detected in the effluents under the same condition after extended column flushing. Perturbations in solution pH (5.6 and 9.5) and IS (0 and 0.1M) showed no effect on SMZ transport in the saturated columns. When pH increased to 9.5, however, ~93% of CIP was eluted from the sand columns. Increase of IS from 0 to 0.1M also slightly changed the distribution of adsorbed CIP within the sand column at pH 5.6, but still no CIP was detected in the effluents. A mathematical model based on advection-dispersion equation coupled with equilibrium and kinetic reactions successfully simulated the transport of the antibiotics in water-saturated porous media with R(2)=0.99.     

Spatio-temporal variations of nitrogen in an agricultural watershed in eastern China: catchment export, stream attenuation and discharge

Using the monthly hydrogeochemical data of ChangLe River system from 2004 to 2008, total nitrogen (TN) export load (S(n)) from nonpoint sources (NPS) to stream and in-stream attenuation load (A(L)) was estimated by the inverse and forward format of an existing in-stream nutrient transport equation, respectively. Estimated S(n) contributed 96 ± 2% of TN entering the river system, while A(L) reduced the input TN by 23 ± 14% in average. In-stream TN attenuation efficiency in high flow periods (10 ± 5% in average for the entire river system) was much lower than that in low flow periods (39 ± 17%). TN attenuation efficiency in tributaries (28 ± 16% in average) was much higher than that in mainstream (11 ± 8%). Hydrological conditions are important in determining the spatio-temporal distributions of NPS TN export, stream attenuation and discharge. Increasing the water residence time might be a practical method for mitigating stream TN.     

V/Ce共掺杂TiO2光催化降解甲醛的实验研究

采用溶胶凝胶法制备了不掺杂、V 掺杂、Ce掺杂、V/Ce共掺杂纳米TiO₂光催化剂,并将其分别负载于瓷砖上,利用X射线衍射分析（XRD）和扫描电镜分析（SEM）技术对薄膜样品的结构和形貌进行了表征。通过对甲醛的降解实验评价光催化剂的光催化活性。实验结果表明,光催化剂的负载量、共掺杂离子的掺杂量、掺杂配比、煅烧温度影响纳米TiO₂的光催化活性。V/Ce共掺杂TiO₂光催化剂产生了协同效应,其光催化活性优于纯TiO₂和单掺杂TiO₂样品。     

初始pH值对磷酸盐还原除磷的影响研究

以超高盐（盐度7％,以NaCI计）高磷榨菜废水为研究对象,考察了初始pH值对磷酸盐还原进程的影响。实验结果表明,初始pH值对磷酸盐还原除磷效能影响显著。初始pH为8时,磷酸盐还原除磷率达到最高,平均值为65．45％。同时,初始pH值还会影响污泥中活性磷的形成以及基体对磷化氢的吸附。此外,偏碱性有利于磷形态转化,且BD-P（主要是一些可溶性的、还原性强的、带有Fe-P化合物的集合）含量的高低调控着生物膜内间隙水中溶解态可反应性磷（DRP）和可还原水溶态磷（RSP）含量,最终决定着磷酸盐还原进程。随着初始pH值的升高,污泥对磷化氢的吸附能力降低导致污泥中结合态磷化氢（MBP）含量不断减少。     

甲醛降解菌的筛选及降解特性研究

从采集活性污泥中筛选得到1株具有高效降解甲醛能力的菌株并命名为JQ-1,根据其形态特征,初步判断菌株JQ-1属假单胞菌属。同时对菌株JQ-1的生长特性及降解特性进行了初步研究。实验结果表明,该菌株降解甲醛的最适条件为：甲醛废水浓度为50mg／L,pH值为6,培养温度为25℃,摇床转速为150r／min。在最适条件下,菌株JQ-1具有较强的降解甲醛能力,当甲醛废水浓度为50mg／L时,在24h内甲醛降解率可达87％以上。     

膜生物反应器(MBR)-反渗透(RO)工艺深度处理印染废水的实验研究

采用膜生物反应器（MBR）-反渗透（RO）工艺对印染废水进行了深度处理实验。原水经MBR系统处理后,COD去除率、ss去除率和色度去除率分别达89．9％、100％和87．5％。MBR系统处理出水进入反渗透（RO）系统进行处理,硬度去除率和除盐率分别达99．62％和99．64％,同时可进一步除去剩余的COD、色度。系统出水水质满足生产回用的要求。