复合地层中双护盾TBM与围岩相互作用机制三维数值模拟研究

 为研究复合地层中双护盾TBM与围岩之间的相互作用机制,采用FLAC3D建立完整的TBM模型,研究复合地层中以下几种情况对TBM掘进时围岩变形及护盾所受接触力和摩擦阻力的影响：地层(1)为断面内上软下硬、上硬下软;地层(2)为沿洞线方向具有不同软岩长度;地层(3)为沿洞线方向具有不同软硬交替厚度。同时,将不均匀间隙作为函数引入护盾压力计算式中。得出地层(1)条件下受不均匀间隙的影响,围岩纵轴向剖面位移(LDP)曲线自下而上先后与护盾接触,接触部位主要位于隧道腰部及以下区域,接触压力主要集中在前、后盾中后方,且前盾尾部压力值最大;地层(2)条件下,护盾所受摩阻力随软岩长度的增加逐渐增大并最终趋于稳定;地层(3)条件下TBM前后护盾所受摩阻力呈周期性波动,其变化规律与围岩位移曲线变化频率基本对应。而且不论地层(2)或地层(3)中,围岩LDP曲线形态都不同于均匀地层。这些认识对于进一步研究复合地层中TBM与围岩的相互作用及预测卡机有重要意义。     

EnergyPlus vs. DOE-2.1e: The effect of ground-coupling on energy use of a code house with basement in a hot-humid climate

For low-rise buildings, the heat losses or gains through the ground coupled building envelope can be a significant load component. Studies have shown that current simulation tools give dissimilar results for the ground coupled heat transfer (GCHT) with basements. This paper quantifies and explains the differences between EnergyPlus and DOE-2.1e (DOE-2) basement GCHTs based on their results for an all electric code house in a hot and humid climate zone. The code house was modeled with two basement configurations i.e. a conditioned basement and an unconditioned crawlspace. DOE-2 was used with Winkelmann's basement model and EnergyPlus was used with its GCHT calculator utility, Basement. The results revealed that the ground isolated EnergyPlus houses used 3-23% more cooling, 12-29% less heating and 3-7% lower overall HVAC electricity use when compared to the ground isolated DOE-2 houses. Ground coupling added up to three times more heat loss in EnergyPlus than in DOE-2. This increased the overall energy use difference between these two programs from 3-7% (ground isolated) to 14-25% (ground coupled). These results showed that a truth standard is required for basement heat transfer calculations of low-rise buildings.     

Occurrence and formation potential of N-nitrosodimethylamine in ground water and river water in Tokyo

N-nitrosodimethylamine (NDMA), a disinfection byproduct of water and wastewater treatment processes, is a potent carcinogen. We investigated its occurrence and the potential for its formation by chlorination (NDMA-FP_2Cl) and by chloramination (NDMA-FP_2NHCl) in ground water and river water in Tokyo. To characterize NDMA precursors, we revealed their molecular weight distributions in ground water and river water. We collected 23 ground water and 18 river water samples and analyzed NDMA by liquid chromatography-tandem mass spectrometry. NDMA-FP_2Cl was evaluated by chlorinating water samples with free chlorine for 24 h at pH 7.0 while residual free chlorine was kept at 1.0-2.0 mgCl₂/L. NDMA-FP_2NHCl was evaluated by dosing water samples with monochloramine at 140 mgCl₂/L for 10 days at pH 6.8. NDMA precursors and dissolved organic carbon (DOC) were fractionated by filtration through 30-, 3-, and 0.5 kDa membranes. NDMA concentrations were <0.5-5.2 ng/L (median: 0.9 ng/L) in ground water and <0.5-3.4 ng/L (2.2 ng/L) in river water. NDMA concentrations in ground water were slightly lower than or comparable to those in river water. Concentrations of NDMA-FP_2Cl were not much higher than concentrations of NDMA except in samples containing high concentrations of NH₃ and NDMA precursors. The increased NDMA was possibly caused by reactions between NDMA precursors and monochloramine unintentionally formed by the reaction between free chlorine and NH₃ in the samples. NDMA precursors ranged from 4 to 84 ng-NDMA eq./L in ground water and from 11 to 185 ng-NDMA eq./L in river water. Those in ground water were significantly lower than those in river water, suggesting that NDMA precursors were biodegraded, adsorbed, or volatilized during infiltration. The molecular weight of NDMA precursors in river water was dominant in the <0.5 kDa fraction, followed by 0.5-3 kDa. However, their distribution was inconsistent in ground water: one was dominant in the <0.5 kDa fraction, and the other in 0.5-3 kDa. Molecular weight distributions of NDMA precursors were very different from those of DOC. This is the first study to reveal the widespread occurrence and characterization of NDMA precursors in ground water.     

Bacteria from drinking water supply and their fate in gastrointestinal tracts of germ-free mice: A phylogenetic comparison study

Microorganisms in drinking water sources may colonize in gastrointestinal (GI) tracts and this phenomenon may pose a potential health risk especially to immunocompromised population. The microbial community diversity of the drinking water was compared with the GI tracts of the mice using phylogenetic and statistical analyses of 16S rRNA gene sequences. A group of germ-free mice were fed with drinking water from public water supply that passed through an automated watering system with documented biofilm accumulation. From drinking water and GI tracts of the germ-free mice, 179 bacteria were isolated and 75 unique 16S rRNA gene phylotypes were sequenced as operational taxonomic unit (OTU, >97% similarity). Three major groups of the genus Acidovorax (21%), Variovorax (42%) and Sphingopyxis (15%) were found in drinking water. Three major groups of the genus Ralstonia (24%), Staphylococcus (20%) and Bosea (22%) were found in GI tracts. Ralstonia (6%, 24%), Sphingopyxis (15%, 2%), Bacillus (3%, 5%), Escherichia coli (3%, 2%) and Mesorhizobium (3%, 5%) were found in both sources - drinking water and GI tract. A lineage-per-time plot shows that the both bacterial communities have convex shape lines, suggesting an excess of closely related ecotypes. A significant F_ST test (0.00000-0.00901) coupled with an insignificant P test (0.07-0.46) implies that the tree contained several clades of closely related bacteria. Both phylogenetic and statistical results suggest a correlation between the bacterial communities originating in the drinking water and those associated with the GI tracts. The GI tract showed a higher genetic diversity than the drinking water, but a similar lineage-per-time plot was obtained overall. It means a sudden evolutionary transformation and colonization occurred with high selective forces.     

Distribution of Asellus aquaticus and microinvertebrates in a non-chlorinated drinking water supply system--effects of pipe material and sedimentation

Danish drinking water supplies based on ground water without chlorination were investigated for the presence of the water louse, Asellus aquaticus, microinvertebrates (<2 mm) and annelida. In total, 52 water samples were collected from fire hydrants at 31 locations, and two elevated tanks (6000 and 36,000 m³) as well as one clean water tank at a waterworks (700 m³) were inspected. Several types of invertebrates from the phyla: arthropoda, annelida (worms), plathyhelminthes (flatworms) and mollusca (snails) were found. Invertebrates were found at 94% of the sampling sites in the piped system with A. aquaticus present at 55% of the sampling sites. Populations of A. aquaticus were present in the two investigated elevated tanks but not in the clean water tank at a waterworks. Both adult and juvenile A. aquaticus (length of 2-10 mm) were found in tanks as well as in pipes. A. aquaticus was found only in samples collected from two of seven investigated distribution zones (zone 1 and 2), each supplied directly by one of the two investigated elevated tanks containing A. aquaticus. Microinvertebrates were distributed throughout all zones. The distribution pattern of A. aquaticus had not changed considerably over 20 years when compared to data from samples collected in 1988-89. Centrifugal pumps have separated the distribution zones during the whole period and may have functioned as physical barriers in the distribution systems, preventing large invertebrates such as A. aquaticus to pass alive. Another factor characterising zone 1 and 2 was the presence of cast iron pipes. The frequency of A. aquaticus was significantly higher in cast iron pipes than in plastic pipes. A. aquaticus caught from plastic pipes were mainly single living specimens or dead specimens, which may have been transported passively trough by the water flow, while cast iron pipes provided an environment suitable for relatively large populations of A. aquaticus. Sediment volume for each sample was measured and our study described for the first time a clear connection between sediment volume and living A. aquaticus since living A. aquaticus were nearly only found in samples with sediment contents higher than 100 ml/m³ sample. Presence of A. aquaticus was not correlated to turbidity of the water. Measurements by ATP, heterotrophic plate counting and Colilert^® showed that the microbial quality of the water was high at all locations with or without animals. Four other large Danish drinking water supplies were additionally sampled (nine pipe samples and one elevated tank), and invertebrates were found in all systems, three of four containing A. aquaticus, indicating a nationwide occurrence.     

高地温隧道地温特征及预测研究

尼格隧道属长大深埋隧道,兼有高水温与高岩温,最高水温达63.4 ℃,最高岩温达88.8 ℃,最高气温达56.4 ℃。为了研究隧道地温特征并进行地温预测,针对性地设计了一系列地温测量方案,研究成果表明:灰岩段表现为高水温,水温＞气温＞岩温,水温与气温随着隧道进深及埋深呈现上升趋势,出水量及水温在接触带附近达到高值,洞内气温受水温、隧道出水量、积水量影响大;花岗岩段表现为高岩温,无水,岩温与气温随隧道进深及埋深呈现上升趋势,两者差值约为25~30 ℃;超前钻孔在孔深＞2 m时岩温达到稳定;一个完整施工循环的施工环境气温呈现4个阶段:气温下降阶段(打钻施工环节),气温骤升阶段(爆破施工环节),气温快速上升阶段(新爆围岩散热),气温缓降阶段(出渣施工环节),出渣环节由于车辆及挖机等机械作业影响,气温出现多处异常高值;施作二衬后,二衬内外壁温差约3.4 ℃;利用热量传递理论、地热成因理论预测的最高地温值与实测值较为吻合。该工程案例颇为典型,本文研究对西南高地热区隧道工程建设具有指导意义。     

A year long study of the presence of free living amoeba in Spain

Free-living amoeba such as Acanthamoeba and Balamuthia mandrillaris can act as opportunistic parasites on a wide range of vertebrates and they are becoming a serious threat to human health due to the resistance of their cysts to harsh environmental conditions, disinfectants, some water treatment practices and their ubiquitous distribution. This work was carried out in order to study the presence of these free-living amoebae (FLA) and their possible seasonality in a continental-Mediterranean climate in different types of water. For this purpose, a total of 223 water samples were collected during one year from four drinking water treatment plants (DWTP), seven wastewater treatment plants (WWTP) and six locations of influence (LI) on four river basins from Spain. Water samples were concentrated using the IDEXX Filta-Max^® system and analyzed by a triplex real time PCR that detects Acanthamoeba, B. mandrillaris and Naegleria fowleri. Agar plates were also seeded for Acanthamoeba culture. From the three FLA studied, N. fowleri was not detected in any sample while B. mandrillaris was found at the entrance of a DWTP; this being, to our knowledge, the first report of these protozoa in water worldwide. On the other hand, the presence of Acanthamoeba observed was higher, 94.6% of the studied points were positive by real time PCR and 85.2% by culture, resulting in 99.1% positive for Acanthamoeba with both methods. All genetically analyzed Acanthamoeba were genotype T4 but nine different T4/DF3 sequences were observed, three of them being described for the first time, assigning new codes. No seasonal distribution of Acanthamoeba was found. These facts should serve as a warning to contact lens wearers of the risk of a poor hygiene when handling their contact lenses. It should also serve as a signal to physicians to consider FLA as a possible causative agent of nervous system infections as well as Acanthamoeba keratitis due to their high environmental presence shown in this study.     

Interface transmissivity of conventional and multicomponent GCLs for three permeants

A laboratory investigation of the interface transmissivity is reported for five different geosynthetic clay liners (GCLs) and a range of different geomembranes (GMBs) for a range of stresses from 10 to 150?kPa. The GCLs were prehydrated under normal stress before permeation. The GCLs examined comprised three multicomponent (a smooth coated, a smooth laminated, and textured coated) and two conventional (one with granular and one with powdered sodium bentonite) GCLs. The effect of a 4?mm circular defect in the coating of a multicomponent GCL directly below the 10?mm diameter hole in the GMB is investigated. The effect of GMB stiffness and texture is examined. Additionally, the effect of hydration and permeation of smooth coated GCL with highly saline solution and synthetic landfill leachate (SL3) is presented. It is shown that the 2-week interface transmissivity (θ_2-week) can be one to two orders of magnitude higher than steady-state interface transmissivity (θ _steady-state) at low stresses (10?kPa–50?kPa), whereas at high stresses (150?kPa) the variation is substantially less. For a smooth coated GCL hydrated and permeated with reverse osmosis (RO) water, GMB stiffness and texture has a limited effect on interface transmissivity when the coating is placed in contact with GMB at normal stresses of 10?kPa–150?kPa, whereas coating indentations result in much high interface transmissivity when placed in contact with GMB. GCL prehydration and permeation with highly saline solutions leads to higher interface transmissivity compared to RO water. With a 4.0?mm defect in the coating, the interface transmissivity between the coating and woven geotextile is higher than that between the coating and GMB for the stress levels and GCL examined.     

Prevalence and occurrence of zoonotic bacterial pathogens in surface waters determined by quantitative PCR

The prevalence and concentrations of Campylobacter jejuni, Salmonella spp. and enterohaemorrhagic Escherichia coli (EHEC) were investigated in surface waters in Brisbane, Australia using quantitative PCR (qPCR) based methodologies. Water samples were collected from Brisbane City Botanic Gardens (CBG) Pond, and two urban tidal creeks (i.e., Oxley Creek and Blunder Creek). Of the 32 water samples collected, 8 (25%), 1 (3%), 9 (28%), 14 (44%), and 15 (47%) were positive for C. jejuni mapA, Salmonella invA, EHEC O157 LPS, EHEC VT1, and EHEC VT2 genes, respectively. The presence/absence of the potential pathogens did not correlate with either E. coli or enterococci concentrations as determined by binary logistic regression. In conclusion, the high prevalence, and concentrations of potential zoonotic pathogens along with the concentrations of one or more fecal indicators in surface water samples indicate a poor level of microbial quality of surface water, and could represent a significant health risk to users. The results from the current study would provide valuable information to the water quality managers in terms of minimizing the risk from pathogens in surface waters.     

地下水对软土盾构隧道施工的影响规律分析

潜水和承压水是地铁软土区间盾构隧道施工过程中的主要危险源,为研究潜水水位变化和承压水水压变化对区间隧道施工的影响,采用FLAC3D软件,选用修正剑桥模型,对不同潜水水位和承压水头作用下盾构隧道的地表沉降、衬砌内力等进行分析。研究结果表明,当隧道洞身全部位于地下水中时:(1)潜水条件下,考虑渗流时地表最大沉降量比不考虑渗流时增大约50%;盾构隧道最大地表沉降与潜水水位呈线性关系;(2)承压水条件下,考虑渗流时地表最大沉降量比不考虑渗流时增大约10%,盾构隧道最大地表沉降与承压水头不成线性关系,随着承压水头的增大,地表最大沉降的增长速率越来越大;(3)潜水水位从-6.8 m变化到-2.8 m及承压水头从8 m变化到12 m的过程中,隧道衬砌管片弯矩和轴力随着潜水水位的升高或承压水头的增大而逐渐减小。     

Development of the Soft Ground Abrasion Tester (SGAT) to predict TBM tool wear,torque and thrust

The Norwegian University of Science and Technology (NTNU), SINTEF Rock Engineering and BASF Construction Chemicals have jointly developed a new test device called the Soft Ground Abrasion Tester (SGAT). The ambition and purpose of the design of the test and the applied test procedure is to replicate an in situ soil – TBM excavation tool contact, in a small and simplified scale. The current development is attempting to bridge a gap when it comes to estimating soft ground and soil abrasivity, as earlier research on e.g. the NTNU/SINTEF Soil Abrasion Test™ (SAT) shows that it does not catch up all driving factors for soft ground and soil abrasivity directly. The paper summarizes the development of the SGAT apparatus, and shows its capabilities to evaluate, quantify and compare how the soil mineralogy, water content, pressure, compaction, and the use of soil conditioning additives influences the wear rate on the SGAT excavation tool. During testing the required torque and thrust are monitored and logged, making it possible to measure various soil–soil conditioning matrixes requirement for operational parameters.     

Utilization of bagasse ash as a pozzolanic material in concrete

The physical properties of concrete containing ground bagasse ash (BA) including compressive strength, water permeability, and heat evolution, were investigated. Bagasse ash from a sugar factory was ground using a ball mill until the particles retained on a No. 325 sieve were less than 5wt%. They were then used as a replacement for Type I Portland cement at 10, 20, and 30wt% of binder. The water to binder (W/B) ratio and binder content of the concrete were held constant at 0.50 and 350 kg/m³, respectively.The results showed that, at the age of 28 days, the concrete samples containing 10–30% ground bagasse ash by weight of binder had greater compressive strengths than the control concrete (concrete without ground bagasse ash), while the water permeability was lower than the control concrete. Concrete containing 20% ground bagasse ash had the highest compressive strength at 113% of the control concrete. The water permeability of concrete decreased as the fractional replacement of ground bagasse ash was increased. For the heat evolution, the maximum temperature rise of concrete containing ground bagasse ash was lower than the control concrete. It was also found that the maximum temperature rise of the concrete was reduced 13, 23, and 33% as compared with the control concrete when the cement was replaced by ground bagasse ash at 10, 20, and 30wt% of binder, respectively. The results indicate that ground bagasse ash can be used as a pozzolanic material in concrete with an acceptable strength, lower heat evolution, and reduced water permeability with respect to the control concrete.     

Effects of LOI of ground bagasse ash on the compressive strength and sulfate resistance of mortars

Raw bagasse ash collected from the Thai sugar industry has a high loss on ignition (LOI) of ～20%. When ground and ignited at 550 °C for 45 min, the LOI was reduced to ～5%. These high and low LOI of ground bagasse ashes were blended in the ratios of 1:2 and 2:1 by weight to give ground bagasse ashes with LOIs of 10% and 15%, respectively. Each of these ground bagasse ashes was used to replace Portland cement type I at 10%, 20%, 30%, and 40% by weight of binder to cast mortar.The results showed that the development of compressive strengths of mortars containing ground bagasse ash with high LOI was slower than that of mortar containing ground bagasse ash with low LOI. However, at the later age, both types of ground ash mortars displayed similar compressive strengths. Mortars containing high LOI (～20%) of ground bagasse ash at 20% and 30% by weight of binder could produce higher compressive strengths than a control mortar after 28 and 90 days, respectively. Mortar bars containing ground bagasse ash at 10% showed a greater potential sulfate resistance and displayed a reduce expansion compared to a control mortar. However, mortar bars containing high LOI (larger than 10%) of ground bagasse ashes showed greater deterioration from sulfate attack than the mortar bars containing low LOI (less than 10%) of ground bagasse ashes, especially at high replacement levels (30–40%).     

Chemistry, Mineralogy and maturity status of Obhor Sabkha, Saudi Arabia

The mineralogy and pore water chemistry of subsoil of the relatively stronger crustal layer above the watertable and the ground water chemistry at two locations in the coastal clayey sabkha areas of Obhor, Saudi Arabia confirm the predominance of evaporites like halite, gypsum, aragonite and calcite and the trend of progressive sabkhaization from top downwards. Of the two locations studied, Station 1 with higher soluble salts contents (TSS up to 28%) in soil and interstitial water salinity (up to 384,200 mg/l) is in a well developed sabkha and Station 2 with lower TSS and salinity is in a slightly developed sabkha as per the classification of Bahafzallanet al. (1993). Clay mineral montmorillonite was identified as a trace (in bulk powder sample) at 45 cm depth at Station 1 and illite at same depth at Station 2 and further work for clay mineral identification is suggested.     

Dynamic properties and liquefaction behaviour of cohesive soil in northeast India under staged cyclic loading

Estimation of strain-dependent dynamic soil properties, e.g. the shear modulus and damping ratio, along with the liquefaction potential parameters, is extremely important for the assessment and analysis of almost all geotechnical problems involving dynamic loading. This paper presents the dynamic properties and liquefaction behaviour of cohesive soil subjected to staged cyclic loading, which may be caused by main shocks of earthquakes preceded or followed by minor foreshocks or aftershocks, respectively. Cyclic triaxial tests were conducted on the specimens prepared at different dry densities (1.5 g/cm³ and 1.75 g/cm³) and different water contents ranging from 8% to 25%. The results indicated that the shear modulus reduction (G/G_max) and damping ratio of the specimen remain unaffected due to the changes in the initial dry density and water content. Damping ratio is significantly affected by confining pressure, whereas G/G_max is affected marginally. It was seen that the liquefaction criterion of cohesive soils based on single-amplitude shear strain (3.75% or the strain at which excess pore water pressure ratio becomes equal to 1, whichever is lower) depends on the initial state of soils and applied stresses. The dynamic model of the regional soil, obtained as an outcome of the cyclic triaxial tests, can be successfully used for ground response analysis of the region.     

The effects of long term uniform corrosion on the buckling of ground based steel tanks under seismic loading

Material degradation due to corrosion significantly alters the seismic response of ground-based cylindrical steel storage tanks. A numerical study is conducted to investigate the effects of internal shell corrosion on the dynamic buckling of three cone roof ground-based, steel cylindrical tanks with height to diameter ratios (H/D) of 0.40, 0.63 and 0.95, subjected to horizontal seismic base excitations. Internal corrosion is considered as a time dependent uniform thinning of the wall at the upper and the lower parts of the tank being in contact with, respectively, atmospheric oxygen and acid gases and residual water. Detailed numerical models of the tank–liquid systems at different stages of corrosion degradation are subjected to two representing accelerograms and for each model the critical peak ground acceleration (PGA) for dynamic buckling of the shell and its associated mode of failure are evaluated. It is found that in all three tanks, the critical PGA is markedly reduced with thinning of the shell, irrespective of the type of ground input. The buckling mode of failure of the tanks also changed from an elastic diamond-shaped failure at the top of the shell to an elasto-plastic elephant foot type failure near the base, after 10 years for the shorter tanks (H/D=0.4 and 0.63) and after 15 years for the tallest tank. The effects of uniform corrosion degradation on the critical buckling load of the tanks were found to be such that after 20 years of thinning due to corrosion, the static loading alone was responsible for the elephant foot buckling of the shell.     

Occurrence of Mycobacterium avium subsp. paratuberculosis in raw water and water treatment operations for the production of potable water

Mycobacterium avium subsp. paratuberculosis (Map) causes Johne’s disease of cattle and is implicated as a cause of Crohn’s disease in humans. The organism is excreted in animal faeces and can contaminate water catchment areas. This coupled with Map’s survival in the environment means that water destined for domestic use may be a source of exposure. This work was designed to determine the occurrence of Map in Lough Neagh (the largest freshwater lake in the British Isles), used as a reservoir, and in two water treatment works (WTW1 and WTW2) which abstract from the lough and which have slow sand filtration (SSF) and dissolved air flotation respectively as their principal treatment regimes. The organism was not detected in lough water samples by culture (n = 70) but 29% (20/70) were positive by PCR. In the raw water to WTW1 and WTW2 no culture positives were detected but 54% (13/24) and 58% (14/24) respectively were PCR positive. In WTW1 there were no culture positives at the SSF or final water but 31% (8/26) and 45% (9/20) respectively were PCR positive. In WTW2 similar results were obtained with 26% (6/23) and 48% (11/23) in the floccules and final water respectively. At WTW2 however one culture positive was detected in the final water. This latter finding is of concern. The inability to reach definitive conclusions indicates the need for further research, particularly in the detection methods for viable Map.     

Adhesion of Campylobacter jejuni and Mycobacterium avium onto polyethylene terephtalate (PET) used for bottled waters

Adhesion of the bacteria Campylobacter jejuni and Mycobacterium avium onto polyethylene terephtalate (PET), a polymer widely used within the bottled water industry was measured in two different groundwater solutions. From this, it was found that whilst the percentage cell adhesion for a given strain did not change between groundwater types, substantial variation was obtained between the two bacterial species tested: M. avium (10-30% adhered cells) and C. jejuni (1-2%) and no major variations were measured as a function of groundwater composition for a given strain. To explain this, the interfacial electro-hydrodynamic properties of the bacteria were investigated by microelectrophoresis, with the resultant data analysed on the basis of electrokinetic theory for soft biocolloidal particles. The results obtained showed that M. avium carries a significant volume charge density and that its peripheral layer exhibits limited hydrodynamic flow permeation compared to that of C. jejuni. It was also demonstrated that steric hindrance to flow penetration and the degree of hydrophobicity within/of the outer bacterial interface are larger for M. avium cells. In line with this, the larger amount of M. avium cells deposited onto PET substrates as compared to that of C. jejuni can be explained by hydrophobic attraction and chemical binding between hydrophobic PET and outer soft surface layer of the bacteria. Hydrophobicity of PET was addressed by combining contact angle analyses and force spectroscopy using CH₃-terminated AFM tip.     

Adenovirus-associated health risks for recreational activities in a multi-use coastal watershed based on site-specific quantitative microbial risk assessment

We used site-specific quantitative microbial risk assessment (QMRA) to assess the probability of adenovirus illness for three groups of swimmers: adults with primary contact, children with primary contact, and secondary contact regardless of age. Human enteroviruses and adenoviruses were monitored by qPCR in a multi-use watershed and Adenovirus type 40/41 was detected in 11% of 73 samples, ranging from 147 to 4117 genomes per liter. Enterovirus was detected only once (32 genomes per liter). Seven of eight virus detections occurred when E. coli concentrations were below the single sample maximum water quality criterion for contact recreation, and five of eight virus detections occurred when fecal coliforms were below the corresponding criterion. We employed dose-harmonization to convert viral genome measurements to TCID₅₀ values needed for dose–response curves. The three scenarios considered different amounts of water ingestion and Monte Carlo simulation was used to account for the variability associated with the doses. The mean illness risk in children based on adenovirus measurements obtained over 11 months was estimated to be 3.5%, which is below the 3.6% risk considered tolerable by the current United States EPA recreational criteria for gastrointestinal illnesses (GI). The mean risks of GI illness for adults and secondary contact were 1.9% and 1.0%, respectively. These risks changed appreciably when different distributions were fitted to the data as determined by Monte Carlo simulations. In general, risk was at a maximum for the log-logistic distribution and lowest for the hockey stick distribution in all three selected scenarios. Also, under default assumptions, the risk was lowered considerably when assuming that only a small proportion of Adenovirus 40/41 (3%) was as infectious as Adenovirus type 4, compared to the assumption that all genomes were Adenovirus 4. In conclusion, site-specific QMRA on water-borne adenoviruses in this watershed provided a similar level of protection against public health risks as would be obtained by enumeration of fecal indicator bacteria under the new U.S. EPA guidelines.     

Batch-Mixed Iron Treatment of High Arsenic Waters

This paper develops batch-mixed treatment with zero-valent iron as a point-of-use technology, appropriate for arsenic removal from water stored within rural homes in Bangladesh and West Bengal, India, where arsenic poisoning has affected an estimated 20 million people. Batch tests with iron yielded the following results: (1) High arsenic removal (>93%) was achieved from highly arsenated waters (2000 μg/L) over short contact times (0.5–3 h) with iron filings added at doses ranging from 2500 to 625 mg/L; (2) Most rapid arsenic removal was observed in head-space free systems with sulphates present in solution, while phosphate buffers were observed to inhibit arsenic removal by iron; (3) The arsenic removed from water was found to be strongly bound to the elemental iron filings, such that the treated water could be decanted and iron could be reused at least 100 times; (4) Some iron dissolved into water over the contact period, at concentrations ranging from 100 to 300 μg/L, which are within safe drinking water limits. These results indicate that, with appropriate assessment of water chemistry in the affected region, treatment with metallic iron followed by simple decantation can be used as a practical, in-home, point-of-use technique for reducing human exposure to arsenic in drinking water.