Assessing the effects of bacterial predation on membrane biofouling

Membrane biofouling is one of the major obstacles limiting membrane applications in water treatment. In this study, Bdellovibrio bacteriovorus HD 100, a Gram-negative predatory bacterium, was evaluated as a novel way to mitigate membrane biofouling and its subsequent performance decline. Dead-end microfiltration (MF) tests were carried out on Escherichia coli DH5α and B. bacteriovorus HD 100 co-culture feed solutions. Predation of E. coli was performed at either a low or high multiplicity of infection (MOI), which is defined as the predator to prey cell ratio. The MOIs tested were 2 and 200, and the viability of both the E. coli prey and the predator was monitored over 48 h. The higher MOI (high predator, HP) culture showed a nearly 6-log loss in E. coli number after 24 h when compared to both the control and low MOI (low predator, LP) cultures, whereas the E. coli population within both predated cultures (HP and LP) became nearly identical at 48 h and 4-log lower than that of the control. The unpredated cultures led to significant loss in water flux at 12, 24, and 48 h of culture, but the HP and LP membranes showed less loss of flux by comparison. Analysis of the total membrane resistance showed a similar trend as the flux decline pattern; however, irreversible resistance of the membrane was much higher for the 48 h LP culture compared to the unpredated and HP cultures at 48 h. This increase in irreversible resistance was attributed mainly to E. coli debris, which accumulated in the medium after the predator lysed the prey cells. These results show that pretreatment of wastewater using a suitable concentration of predatory bacteria such as B. bacteriovorus can enhance membrane performance.     

基于核磁共振实时成像技术的裂隙砂岩渗流特性研究

地下工程岩体内部存在着大量不规则、多尺度的孔(裂)隙,使得其渗流问题十分复杂,研究裂隙岩体的渗流特性及流场分布对岩体工程安全和深部资源开发利用具有重要的工程实际意义.利用核磁共振岩石渗流过程实时在线分析与成像系统对含不同裂隙性状的砂岩试样开展裂隙岩石渗流试验,对渗流过程中试样的体积含水率、T2谱曲线和渗透系数等参数的演...     

Effects of ozonation on the permeate flux of nanocrystalline ceramic membranes

Titania membranes, with a molecular weight cut-off of 15 kD were used in an ozonation/membrane system that was fed with water from Lake Lansing, which had been pre-filtered through a 0.45 microm glass fiber filter. The application of ozone gas prior to filtration resulted in significant decreases in membrane fouling. The effects of ozonation could not be explained by physical scouring of the filter cake. Decrease in the pH resulted in a concomitant increase in the dissolved ozone concentration in the feed water and in an improvement in permeate flux recovery. Increasing the ozone concentration beyond a threshold value had no beneficial effect on permeate flux recovery. Ozone decomposition, resulting in the formation of OH or other radicals at the membrane surface, is thought to result in the decomposition of organic foulants at the membrane surface and reduce the extent of membrane fouling.     

基于核磁共振下的冻土-结构正融过程界面特性研究

升温解冻导致冻土-结构相互作用发生劣化,为探究正融过程中冻土-结构相互作用,基于NMR分层测试技术对正融过程中界面未冻水含量进行测试,得到界面温度-未冻水含量变化规律;同时开展不同法向压力下界面剪切试验,得到界面温度-抗剪强度相关关系,从而进一步探究界面温度-未冻水含量-抗剪强度之间的内在联系。结果表明：NMR分层测试T2曲线可从微观尺度对界面融化过程进行表征,即正融过程界面小孔隙冰晶体融化开始,随着融化程度的加深大孔隙的冰也开始融化,最后直至界面处冰完全融化。根据界面温度-未冻水含量-抗剪强度的变化特征可将整个正融过程划分为冻结阶段、相变阶段、融化阶段3个阶段。依据莫尔-库仑破坏准则分析可知,正融过程中界面内摩擦角、黏聚力呈“此消彼长”的变化特征,其中随着解冻程度加深界面内摩擦角呈先减小后增大,而界面黏聚力呈现先增大后相对减小。     

Dampness in buildings and health. Nordic interdisciplinary review of the scientific evidence on associations between exposure to "dampness" in buildings and health effects (NORDDAMP)

Several epidemiological investigations concerning indoor environments have indicated that "dampness" in buildings is associated to health effects such as respiratory symptoms, asthma and allergy. The aim of the present interdisciplinary review is to evaluate this association as shown in the epidemiological literature. A literature search identified 590 peer-reviewed articles of which 61 have been the foundation for this review. The review shows that "dampness" in buildings appears to increase the risk for health effects in the airways, such as cough, wheeze and asthma. Relative risks are in the range of OR 1.4-2.2. There also seems to be an association between "dampness" and other symptoms such as tiredness, headache and airways infections. It is concluded that the evidence for a causal association between "dampness" and health effects is strong. However, the mechanisms are unknown. Several definitions of dampness have been used in the studies, but all seems to be associated with health problems. Sensitisation to mites may be one but obviously not the only mechanism. Even if the mechanisms are unknown, there is sufficient evidence to take preventive measures against dampness in buildings.     

Assessing the technical efficiency of container ports based on a non-monotonic inefficiency effects model

This study aims to assess the technical efficiency of container ports in the Mediterranean and the Black Sea for the 2017–2019 period. A non-monotonic inefficiency effects model is used since it can reveal non-monotonic relationships and capture observation-specific marginal effects. Findings imply that while increasing physical size has non-monotonic effects on efficiency, increasing connectivity has monotonic positive effects on efficiency. Decision-makers should avoid large-scale infrastructure investments triggered by only the fierce competition to control underutilization. Making decisions focused on higher connectivity about marketing and operational structure could positively impact the performance of container ports.     

Prediction of residential radon exposure of the whole Swiss population: comparison of model‐based predictions with measurement‐based predictions

Radon plays an important role for human exposure to natural sources of ionizing radiation. The aim of this article is to compare two approaches to estimate mean radon exposure in the Swiss population: model‐based predictions at individual level and measurement‐based predictions based on measurements aggregated at municipality level. A nationwide model was used to predict radon levels in each household and for each individual based on the corresponding tectonic unit, building age, building type, soil texture, degree of urbanization, and floor. Measurement‐based predictions were carried out within a health impact assessment on residential radon and lung cancer. Mean measured radon levels were corrected for the average floor distribution and weighted with population size of each municipality. Model‐based predictions yielded a mean radon exposure of the Swiss population of 84.1 Bq/m³. Measurement‐based predictions yielded an average exposure of 78 Bq/m³. This study demonstrates that the model‐ and the measurement‐based predictions provided similar results. The advantage of the measurement‐based approach is its simplicity, which is sufficient for assessing exposure distribution in a population. The model‐based approach allows predicting radon levels at specific sites, which is needed in an epidemiological study, and the results do not depend on how the measurement sites have been selected.     

Quantitative study of the effect of electromagnetic field on scale deposition on nanofiltration membranes via UTDR

Ultrasonic time-domain reflectometry (UTDR) as an in situ, non-invasive real-time technique has been successfully utilized to quantify membrane fouling and cleaning. This study describes an existing ultrasonic technique for quantitative study of the effect of magnetic fields on CaCO₃ scale deposition on the membrane surface during crossflow nanofiltration (NF). The fouling experiments were conducted with CaCO₃ solution containing Ca²⁺ of 1.8 and 3 mmol/L. The experimental electromagnetic field (EMF) was 0.02 T. A commercial NF membrane and a highly sensitive ultrasonic sensor were used in all the experiments. Results show a good relationship between the ultrasonic measurements and the development of CaCO₃ scale on the NF membrane surface. An increase in the amplitude of differential signal with operation time results from the deposition of the CaCO₃ scale layer. In addition, the movement of the differential signal in the time domain observed is associated with an increase in the thickness of the fouling layer. The UTDR technique is capable of measuring the rate of fouling layer formation under different treatment conditions, i.e. with non-magnetic field (NMF) and EMF. Scale layer of deposited CaCO₃ obtained in the experiment with NMF is denser and thicker than that with EMF. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses imply that the magnetic treatment suppresses the formation of calcite crystals and prefers vaterite and aragonite. Furthermore, the ultrasonic technique is sensitive to the different fouling rate between experiments carried out with 1.8 and 3 mmol/L CaCO₃ solutions. The thickness of the fouling layer measured by weight measurement is consistent with that obtained by UTDR in real time. The thinner and less dense scale layer is the main reason for the slower flux decline. Overall, independent measurements such as the flux-decline data, SEM analysis and weight measurement corroborate the ultrasonic measurements.     

高掺量粉煤灰混凝土强度特性的试验研究

利用裂区试验设计方法分析了两种外加剂粉煤灰混凝土的强度特性，得出水胶比、粉煤灰掺量、外加剂种类是影响粉煤灰混凝土强度的显著因素，试验证明，I型外加剂更适宜于高掺量粉煤灰混凝土。     

Assessing the effects of flood resilience technologies on building scale

The impacts of floods on housing are increasing due to more frequent and severe weather events as well as the ongoing development of settlements in flood-prone areas together with the rising vulnerability of assets at risk. Therefore, the improvement of the resilience properties of buildings to better cope with flooding has become a key issue towards more flood resilient cities in European research in recent years. The implementation of flood resilience technologies (FReT) on the individual property scale provides a previously untapped potential to reduce flood damage to buildings due to insufficient transparency of their effects. To overcome this obstacle, the paper presents a four-step extension of a synthetic approach for flood vulnerability analysis to provide evidence on the potential effects of FReT uptake concerning flood damage mitigation. The proposed approach has been integrated in the GIS-based flood damage simulation model HOWAD to support the assessment of FReT alternatives. The simulation of flood damage to buildings in the case study Heywood, Greater Manchester (United Kingdom) revealed the potential of the extended approach to determine the consequences of FReT implementation on building scale.     

Effect of mechanical cleaning with granular material on the permeability of submerged membranes in the MBR process

The research on fouling reduction and permeability loss in membrane bioreactors (MBRs) was carried out at two MBR pilot plants with synthetic and real wastewater. On the one hand, the effect of mechanical cleaning with an abrasive granular material on the performance of a submerged MBR process was tested. Additionally, scanning electron microscopy (SEM) measurements and integrity tests were conducted to check whether the membrane material was damaged by the granulate.The results indicate that the fouling layer formation was significantly reduced by abrasion using the granular material. This technique allowed a long-term operation of more than 600 days at a flux up to 40 L/(m² h) without chemical cleaning of the membranes. Moreover, it was demonstrated that the membrane bioreactor (MBR) with granulate could be operated with more than 20% higher flux compared to a conventional MBR operation. SEM images and integrity tests showed that in consequence of abrasive cleaning, the granular material left brush marks on the membrane surface, however, the membrane function was not affected.In a parallel experimental set up, the impact of the operationally defined “truly soluble fraction” <0.04 μm from wastewater and activated sludge on the ultrafiltration membrane fouling characteristics was investigated. It was shown that the permeability loss was caused predominantly by the colloidal fraction >0.04 μm rather than by the dissolved fraction of wastewater and activated sludge.     

Influence of exposure sites on trace element enrichment in moss-bags and characterization of particles deposited on the biomonitor surface

The hypothesis that exposure environment and land use influence element accumulation and particulate size composition in transplants of Hypnum cupressiforme has been tested using moss-bags containing oven-devitalized material. The samples were exposed for three months in ten green sites and ten roadsides in two areas with different land use (A, residential; B, residential/industrial) in the Trieste conurbation (NE Italy). Observations by SEM and EDX-ray microanalysis revealed that particle density was smaller in samples exposed in A than in B, with prevalence of particles containing Al, Ca, Fe and Si, and in good accordance with the element contents measured by acid digestion and ICP-MS. Moss-bags were generally less contaminated in green sites than in roadsides, apparently due to the different enrichment in coarse particles. In both environments, however, the majority of entrapped particles (up to 98.2%) belongs in the inhalable, small size classes (≤ PM₁₀). The need for careful selection of the exposure sites during the phase of biomonitoring planning is discussed.     

Manufacturing effects on the hydraulic properties of needlepunched nonwoven geotextiles

Needlepunched nonwoven geotextiles are entangled to form a complex three-dimensional structure by random fibers, accounting for its bulky nature, wide range of pore size distribution, and good drainage. With needlepunched nonwoven geotextiles, water can move in both the vertical and horizontal directions. This paper examines two types of needlepunched nonwovens: one produced from polyester staple fiber and the other made from polyester spunbond continuous filaments. Experimental results indicate that the permittivity of staple needlepunched nonwoven geotextiles varies from 1.77-4.51 s⁻¹; the permeability coefficient varies from 0.63-2.87 × 10⁻² m/s. The permittivity of spunbond needlepunched nonwoven geotextiles varies from 1.13-1.97 s⁻¹; the permeability coefficient varies from 0.48-1.09 × 10⁻² m/s. In addition, the transmissivity of needlepunched nonwoven geotextiles decrease to an essentially constant value as the normal stress is increases. The transmissivity of needlepunched nonwoven geotextiles examined varies from 155-2.75 × 10⁻⁶ m²/s over the normal stress range examined (5-200 kN/m²). The AOS value of 3 denier staple fiber needlepunched nonwovens is less than 0.074 mm, the AOS value of spunbonded 7 denier and, 15 d and 20 d needlepunched nonwovens are 0.21 mm, 0.25 mm and 0.30 mm, respectively.     

'EUROPART'. Airborne particles in the indoor environment. A European interdisciplinary review of scientific evidence on associations between exposure to particles in buildings and health effects

The relevance of particle mass, surface area or number concentration as risk indicators for health effects in non-industrial buildings has been assessed by a European interdisciplinary group of researchers (called EUROPART) by reviewing papers identified in Medline, Toxline, and OSH. Studies dealing with dermal effects or cancer or specifically addressing environmental tobacco smoke, house dust-mite, cockroach or animal allergens, microorganisms and pesticides were excluded. A total of 70 papers were reviewed, and eight were identified for the final review: Five experimental studies involving mainly healthy subjects, two cross-sectional office studies and one longitudinal study among elderly on cardiovascular effects. From most studies, no definite conclusions could be drawn. Overall, the group concluded that there is inadequate scientific evidence that airborne, indoor particulate mass or number concentrations can be used as generally applicable risk indicators of health effects in non-industrial buildings and consequently that there is inadequate scientific evidence for establishing limit values or guidelines for particulate mass or number concentrations.     

Consequences of mass transfer effects on the inetics of nitrifiers

The influence of membrane separation and mass transfer effects on the kinetics of nitrifiers was evaluated by running a membrane bioreactor (MBR) and a conventional activated sludge (CAS) plant in parallel. Both pilot plants were operated at the same sludge age and treated the same domestic wastewater. The half-saturation constants for the substrate were low in both MBR and CAS and did not differ significantly between the two processes (K(NH(4))) and 0.14+/-0.10 g(N)m(-3) and (K(NO(2))) and 0.28+/-0.20 g(N)m(-3) for the MBR and CAS, respectively). However, the half-saturation constants for oxygen exhibited a major difference between the two processes for both the ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacteria. The experiments yielded K(O,AOB)=0.18+/-0.04 and 0.79+/-0.08 g(O2) as well as K(O,NOB)=0.13+/-0.06 and 0.47+/-0.04 g(O2) m(-3) (substrate only NO(2)) for the MBR and CAS, respectively. The higher K(0) values of the CAS were attributed to mass transfer effects within the large flocs prevailing in the conventional system. In contrast, the sludge from the MBR consisted of very small flocs for which the diffusion resistance can be neglected. On the basis of these results, the implementation of mass transfer effects in activated sludge models is discussed and consequences for the operation of MBRs are highlighted.     

A numerical investigation of the impact of low boundary walls on pedestrian exposure to air pollutants in urban street canyons

A previous investigation into methods of exposure reduction for the pedestrian in the urban commuter environment highlighted the impact of a low boundary wall on the dispersion of air pollutants from adjacent traffic sources. The impact of low boundary walls on the dispersion of air pollutants in street canyons has been brought forward in this investigation to examine them, in more generic terms, with a view to highlighting exposure reduction strategies for pedestrians. 3D Computational Fluid Dynamics (CFD) models were used to examine this effect for varying wind speeds and directions in different street canyon geometries. The results of this investigation show that a low boundary wall located at the central median of the street canyon creates a significant reduction in pedestrian exposure on the footpath. Reductions of up to 40% were found for perpendicular wind directions and up to 75% for parallel wind directions, relative to the same canyon with no wall. The magnitude of the exposure reduction was also found to vary according to street canyon geometry and wind speed.     

The effects of long-term corrosion on the dynamic characteristics of ground based cylindrical liquid storage tanks

Results of numerical investigations on the effects of material degradation due to corrosion on the dynamic characteristics of ground-based, anchored, steel liquid storage tanks are presented. Internal corrosion is considered as a time-dependent constant thinning of the wall, at locations in contact with residual water, water condensate, atmospheric oxygen and acid gases. Dynamic analyses are performed on numerical tank-liquid models, having different aspect ratios and wall thicknesses at different stages of wall thinning at the specified locations. The aim of the analyses is to determine the corrosion effects on the natural periods and mode shapes of vibration. Steady-state, harmonic base excitation analyses are also carried out to determine the corrosion effects on the hydrodynamic pressures produced in the liquid. It is found that progressive corrosion has significant effects on the tank fundamental period and its associated mode shape of vibration as well as the magnitude and location of the maximum hydrodynamic pressure and that as design provisions should cover the service life of the tank, the errors associated with the current code provisions for design of such tanks cannot be ignored.     

Influence of the characteristics of natural organic matter on the fouling of microfiltration membranes

Natural organic matter (NOM) plays a significant role in fouling microfiltration membranes in drinking water treatment processes even though the NOM is retained only to a small extent. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and microfiltration membranes. Filtration experiments were performed using 0.22 μm hydrophobic and hydrophilic polyvinylidene fluoride (PVDF) membranes in a stirred-cell system on the NOM isolated from three Australian surface waters. As expected, the fouling rate for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Focusing on the hydrophobic membrane, it was shown that the high molecular weight fraction of NOM (>30 kDa) was responsible for the major flux decline. Filtration tests on the four fractions of NOM isolated on the basis of hydrophobicity and charge using non-functionalised and anionic resins revealed that the fouling potential for the three waters was hydrophilic neutral>hydrophobic acids>transphilic acids>hydrophilic charged. The low-aromatic hydrophilic neutral compounds were the main determinant of the rate and extent of flux decline. This was linked to the colloidal size fraction (>30 kDa) and to the selective concentration of calcium in the fraction leading to organics-Ca²⁺ bridging. It was also shown that the higher the aromaticity of the NOM the greater the flux decline, and the aromatics mainly resided in the hydrophobic acids fraction. Overall, the fouling mechanism controlling the flux decline involved the combined effects of adsorptive and colloidal fouling by the hydrophilic neutral fraction in the internal pore structure of the membrane.