Determination of nutrients limiting biofilm formation and the subsequent impact on disinfectant decay.

Understanding the contribution of both organic and inorganic nutrients to biofilm development and the subsequent impact of developed biofilms on disinfectant decay are important requirements for distribution system management strategies. Nutrient limitation may be one way to control biofilm development without increasing disinfectant dosing. Little is known, however, of the nutrient requirements of biofilms in distribution systems. Indeed, the effects on biofilm development due to the addition of nutrients to distribution systems and what impact biofilm development may have on disinfectant decay is still poorly understood. This study used annular reactors to determine the nutrients limiting for biofilm development in drinking water from two different Sydney sources and the subsequent effects of biofilm development on disinfectant decay. It was found that biofilm development in Sydney water was limited by organic carbon and that biofilm development promoted chloramine decay. Moreover, biofilm development occurred in the presence of chloramine. The ability of biofilms to respond to increases in disinfectant concentrations was dependent on the biomass of the biofilms. In a comparative study using chlorinated drinking water containing very low levels of organic carbon, biofilm development was not detected. Removal of organic carbon resulted in greater persistence of chlorine, which led to greater biofilm control. It was also shown that biofilms could contribute cells to the aqueous phase. The results of the study indicate that treatment and system management strategies should incorporate organic carbon removal to limit biofilm development through a combination of retarding bacterial growth and enhancing disinfectant persistence.     

Remise en etat des carrieres et stabilite des fronts

Rehabilitation of massive rock quarries first depends on the object in view. Rehabilitation takes into account all the elements: first of all, safety must be considered. In this view, the existence of working face and the risk of long term instability has to be taken into account. The risk may be defined by a direct observation of the altered rocks, of the diaclases, dip and of every element of the rock structure. So the rehabilitation may lead to modify or accept various working faces and even in some cases to direct the project. The investigation of proper treatments for the working faces requires all the techniques concerning the modification, protection, prevention, that have to be adapted to every particular case. In all quarries it is the long term stability which is under consideration.     

Occurrence and persistence of enteroviruses, noroviruses and F-specific RNA phages in natural wastewater biofilms

Enteroviruses and noroviruses are pathogenic viruses excreted by infected individuals. Discharged in wastewaters, some of these viruses can be captured by biofilms. In the present study, we assessed the occurrence and persistence of these viruses in wastewaters and in corresponding biofilms. Natural wastewaters and biofilms were analyzed monthly from January to July using real-time RT-PCR. Enterovirus RNA was detected in wastewater in June while norovirus RNA was detected from January to March. In contrast, biofilm analysis revealed the presence of both enterovirus and norovirus genomes throughout the study period. For instance, enterovirus and norovirus genogroups (GG) I and II were detected in 50, 46 and 37% of the biofilm samples, respectively (n = 24). In a laboratory experiment, persistence of norovirus GGI RNA (quantified using molecular techniques) and F-specific bacteriophages (quantified using both culture and molecular techniques) was assessed in wastewater and corresponding naturally-contaminated biofilms at both 4 and 20 °C. The concentrations of viral genomes (norovirus GGI and F-specific RNA phage) were very stable in biofilms. Indeed, no significant decrease was observed during the persistence experiment that lasted 49 days. Furthermore, regardless of our experimental conditions, viral genome and infectious F-specific bacteriophages persisted longer in biofilm than in wastewater. According to our results, wastewater biofilms may contribute to the persistence and dispersal of pathogenic viruses outside of epidemic periods.     

邻近建筑工程深基坑施工技术应用研究

在对建筑工程进行深基坑施工时,对其邻近建筑都有着很深的影响。对于这些影响,必须要针对深基坑施工技术的应用进行全面的分析。从而保证即使施工地区有邻近建筑,深基坑施工技术也可以很好的应用。     

Investigation of natural biofilms formed during the production of drinking water from surface water embankment filtration

Populations of bacteria in biofilms from different sites of a drinking water production system were analysed. Polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) analyses revealed changing DNA band patterns, suggesting a population shift during bank filtration and processing at the waterworks. In addition, common DNA bands that were attributed to ubiquitous bacteria were found. Biofilms even developed directly after UV disinfection (1-2m distance). Their DNA band patterns only partly agreed with those of the biofilms from the downstream distribution system. Opportunistic pathogenic bacteria in biofilms were analysed using PCR and Southern blot hybridisation (SBH). Surface water appeared to have a direct influence on the composition of biofilms in the drinking water distribution system. In spite of preceding filtration and UV disinfection, opportunistic pathogens such as atypical mycobacteria and Legionella spp. were found in biofilms of drinking water, and Pseudomonas aeruginosa was detected sporadically. Enterococci were not found in any biofilm. Bacterial cell counts in the biofilms from surface water to drinking water dropped significantly, and esterase and alanine-aminopeptidase activity decreased. beta-glucosidase activity was not found in the biofilms. Contrary to the results for planktonic bacteria, inhibitory effects were not observed in biofilms. This suggested an increased tolerance of biofilm bacteria against toxic compounds.     

Consistency Evaluation of Landscape Design by a Decision Support System

The planning of road structures must take into consideration both structural design and aesthetic design. Road planners and designers must keep in mind aesthetic design in the planning stages. In Japan, various design techniques have been established, and many design guidelines and design manuals have been compiled. However, most design techniques are derived from empirical knowledge, and their explanations are often subjective. We have developed a decision support system in landscape planning to simplify complicated processes and avoid fuzziness in decision making. We have collected a large amount of empirical knowledge and have created a database for use in developing design techniques. The main system supports designers and allows planners to select suitable design techniques considering environmental conditions and design policy based on a knowledge-based system. The introduction of three concepts—visual importance, visual suitability, and four kinds of design consistency—allows solution of certain design problems.     

Environment and the transport planner

The transport planner sees the problem of the conflict between the motor car and the environment in today's conditions and foresees how the problems are going to grow in the future. He strives to provide the means to satisfy the growing demand for road space but he is conscious that his solutions can be, in themselves, damaging to some aspects of the quality of life. He faces the dilemma of deciding where to strike the balance between these conflicting considerations. The planner has to suggest this point of balance; in order to do so, he must be able to make logical and credible forecasts of the results of different kinds of transport policy and he must be able to present these clearly to the politicians and the public. So that he can produce such forecasts, he has constantly to improve and refine his techniques; the paper indicates some of the ways in which this is being done in Great Britain today.     

Degradation of polymers in a biofilm airlift suspension reactor

The effect of degradation of polymeric substrates (starch and soy proteins mixture) on the structure of biofilms has been studied. The characteristics of the obtained biofilms were compared to those obtained on corresponding monomeric substrates (glucose and aspartic acid). Based on literature suggestions it was hypothesized that the polymeric substrates, which have a low diffusion rate in the biofilm matrix, would affect the biofilm structure if hydrolytic activity occurs in the biofilm. The obtained biofilm could be expected to present properties like low density and rough surface, facilitating transport and conversion of large polymeric molecules. From the present study it was concluded that the structure of the formed biofilms was influenced by the substrate degraded, however no unequivocal effect of degradation of a polymer on the biofilm structure could be observed. The hydrolytic activity with soy protein and starch as substrate was under stable conditions found to be mainly associated to the biofilm (more than 95% of the total activity). During unstable conditions or start-up significant hydrolytic activity occurred outside the biofilm.     

Effect of salinity and inorganic nitrogen concentrations on nitrification and denitrification rates in intertidal sediments and rocky biofilms of the Douro River estuary, Portugal

The regulatory effects of salinity and inorganic nitrogen compounds on nitrification and denitrification were studied in intertidal sandy sediments and rocky biofilms in the Douro River estuary, Portugal, over a 12-month period. Nitrification and denitrification rates were measured in slurries of field samples and enrichment experiments using the difluoromethane and the acetylene inhibition techniques, respectively. Salinity did not regulate denitrification in either environment, suggesting that halotolerant bacteria dominated the denitrifier communities. However, nitrification rates were stimulated when salinity increased from 0 to 15 practical salinity units. NO3- addition experiments revealed that NO3- availability stimulates denitrification rates in sandy sediments, but not in rocky biofilms; however, in rocky biofilms a positive and linear relationship was observed between denitrification rates and water column NO3- concentrations (r=0.92) during the monthly surveys. The N2O:N2 ratios increased rapidly when NO3- increased from 63 to 363 microM; however, results from monthly surveys showed that environmental parameters other than NO3- availability may be important in controlling the variation in N2O production via denitrification. Ammonium additions to sandy sediments stimulated nitrification rates by 35% for the 20 microM NH4+ addition, but NH4+ appeared to inhibit nitrification at high concentration addition (200 microM NH4+). In contrast, rocky biofilm nitrification was stimulated by 65% when 200 microM NH4+ was added.     

An effective approach to prediction of the collapse mode in automotive seat structure

Safety is an important issue in automobile design, in which the seat structure plays a crucial part. Engineering of the seat structure has a wide range of benefits for the manufacturer in the areas of cost savings and better design techniques. The seat in an automobile must not only be comfortable for the passenger, but must also be designed to protect the occupant from a wide range of impact situations. The seat structure in our advancing automotive world must also have a simple, lightweight design to keep down material and manufacturing costs. Despite the importance of seat structure design, many manufacturers do not have the time or money to perform an in-depth analysis of multiple different designs. The nonlinear behaviour of the seat structure forces engineers to use virtual prototyping and numerical analysis in its design. Use of a complex model and the long computation time of a numerical model drive up the cost and limit the turn around time in the production and design of an automobile seat structure.This paper proposes a cost-effective analysis of a seat system to ensure the safety of the occupants in the case of a frontal impact. In order to predict the major collapse mode of a seat structure in this scenario, the strength effectiveness of each component in the seat system is examined using a self-developed experimental procedure. To be sure of shear deformation of the inner track section of the seat structure, a detailed FE simulation is carried out, leading to an effective 2-D finite element method with plastic hinge to represent the major collapse mode. The simulation results are then compared with corresponding tests in order to verify their validity.     

Dynamics of lead immobilization in sulfate reducing biofilms

We have evaluated the effects of selected minerals present in subsoil environment on the efficiency of lead removal from contaminated groundwaters using biofilms composed of sulfate-reducing microorganisms, and examined the stability of metal deposits after the biofilms had been temporarily exposed to the air. To quantify the studied effects, lead was immobilized in biofilms of Desulfovibrio desulfuricans grown anaerobically in two flat-plate flow reactors, one filled with hematite and the other with quartz. While the biofilms in both reactors were heterogeneous and consisted of voids and channels, the biofilms grown on hematite were denser, thicker, and more porous than those grown on quartz. The average H₂S concentrations, measured using microelectrodes, were higher in the biofilms grown on quartz than those measured in the biofilms grown on hematite. During 18 weeks of operation, iron was continuously released from the hematite. Lead was immobilized more efficiently in the biofilms grown on quartz than it was in the biofilms grown on hematite. Lead deposits were partially reoxidized, especially in biofilms grown on hematite, and the biofilms in both reactors responded to the presence of oxygen by lowering their density and increasing the H₂S production rate.     

Survival of Mycobacterium avium in a model distribution system

A pilot study was designed to examine the impact of nutrient levels, pipe materials, and disinfection on the survival of M. avium in model drinking water distribution system biofilms. Studies showed that the survival of the organism was dependant upon a complex interaction between pipe surface, nutrient levels, and disinfectants. The findings showed that when no disinfection was applied, M. avium could be recovered from biofilms at nutrient levels of 50microg/L assimilable organic carbon. M. avium concentrations were lower on copper pipe surfaces following disinfection with free chlorine as compared to monochloramine. However, due to the interference of corrosion products, chloramination of iron pipe surfaces controlled M. avium levels better than free chlorine. These data demonstrate the significance of pipe materials on the survival of M. avium complex in biofilms. Elimination of competitive heterotrophic bacteria on copper pipe surfaces by the application of disinfection resulted in a population of nearly 100% M. avium. Heat treatment of M. avium biofilms was affected by the pipe composition and organic content of the water. Effluent temperatures >53 degrees C were required to control the occurrence of M. avium in the pipeline system. Although additional studies are required using improved detection methods, the results of this investigation suggest that reducing the biodegradable organic material in drinking water, control of corrosion, maintenance of an effective disinfectant residual, and management of hot water temperatures can help limit the occurrence of M. avium complex in drinking water biofilms.     

Visualisation of transient processes in biofilms by optical coherence tomography

Biofilms occur in natural and engineered water systems. In technical processes, biofouling lowers the water quality and increases the frictional resistance in tubes. In wastewater treatment plants, biofilms are used for the removal of organic and inorganic pollutants. For improvement of antifouling strategies and for process optimisation in wastewater treatment plants, analytical techniques for online monitoring of biofilms are needed. Optical coherence tomography (OCT) is a non-invasive optical tomography technique, which is increasingly applied in medical diagnostics. It reveals photon-reflecting structures in tissue with lateral and axial resolution in the range of 10 microm. In this paper, we demonstrate the capabilities of OCT for the monitoring of biofilm structures and their detachment. OCT is able to reveal spatially resolved structural information on biofilm without staining. A main focus of this work is set on the ability of OCT to monitor transient processes with temporal resolution in a second to minute scale. These key features of OCT allow online monitoring of biofilm growth and detachment in a flow channel. Three-dimensional (3D) imaging quality, spatial resolution, and temporally resolved profiling of biofilms are demonstrated. The results give rise to the hope that OCT may evolve to a standard tool for monitoring of biofilm density.     

杂散参数对冲击电流波形影响的数学分析

在冲击电流试验回路中,输出波形必须满足IEC标准规定的要求。已有研究表明,杂散参数对陡波冲击电流发生回路的影响尤为严重,而且避雷器等试品具有非线性U-I特性,在冲击电流发生回路的设计中必须考虑。针对此问题,首先研究了回路的剩余电感对输出波形的影响。对于波前时间小于1μs的陡波冲击电流发生器,回路需要的总电感在1μH左右,所以要尽量减小回路的剩余电感,否则会使波前时间增大,超出IEC标准要求。然后在线性回路情况下推导了考虑杂散电容时回路输出电流的表达式,进而研究杂散电容对输出波形的影响。研究表明,随着杂散电容的增大,波前时间和波尾时间增大,回路效率降低。但只要杂散电容小于0.1μF,其对冲击电流波形参数引起的误差都在IEC标准规定的误差容限之内。实际回路杂散电容以pF计,因此可以忽略不计。最后,同时考虑试品的非线性特性和杂散电容,分析了杂散电容对输出波形的影响,结论与在线性回路情况下一致。另外避雷器试品有助于提高波头陡度,这是陡波冲击试验中的有利因素。     

近距巷道平行开挖合理错距研究

矿井下运输巷道是矿业生产的重要通道。文中针对极松软地层近距双水平巷道掘进问题,以内蒙古上海庙矿区为工程背景,依据工程区地应力场的实测结果及岩石力学实验参数,运用FLAC^3D三维数值分析计算软件对开拓巷道的合理错距进行了数值模拟研究。通过分析巷道周边应力分布、塑性区变化、位移速率矢量场方向变化以及监测位移数据变化,研究了巷道在分步开挖过程中,不同的开挖错距对已开拓巷道监测端面的影响。结果表明在极松软地质条件下,巷道围岩周边高应力区分布范围较大,新开拓的巷道会对相邻已开拓巷道周边的应力、塑性破坏区及位移速率矢量场产生影响,双近距水平巷道合理开拓错距宜保持在50 m以上。     

黄土中的构造斜节理及其对黄土隧道稳定性的影响

本文根据野外调查与隧道施工的资料,论证了在老黄土中存在构造斜节理,它们是构造地应力造成的,与岩石中的构造节理相似。文中对黄土某些构造斜节理的产状及其形成原因进行了力学分析,并对这些构造斜节理的节理面和因开挖洞室导致局部应力集中而产生的土体中破裂面的特征作了总结与对比。文中通过实例说明黄土中的这些构造斜节理构成了黄土中的软弱结构面,这些软弱结构面与地下洞室开挖的临空面可能将土体切割成不稳定结构体。这就成了坍方或影响洞室稳定性的主要原因。因此,在黄土地下工程设计及其施工中,不仅要应用土力学的基本原理与方法,而且还有必要应用岩体力学的基本原理与方法。     

Geogrid connections

Connections can have a significant impact on the performance of geosynthetic systems whether their intended function is separation or reinforcement. When reinforcement is the function, the connection must be considered as a limiting strength factor and evaluated by the same performance standards as the reinforcement material alone. If used in critical structures with design lives of more than 1 or 2 years, the geosynthetic and its connections must be evaluated for durability limitations such as creep, site damage and chemical degradation. Geogrid connections typically fall into this category.

Geogrid connections are accomplished by either overlapping or mechanical connections. Overlap connections must be designed and constructed to assure proper overlap lengths. Overlap length is governed by soil interaction behavior. Geogrid-soil interaction is measured by pull-out testing and pull-out performance is a function of geogrid dimensional stability. Overlaps can be secured by a variety of tyiing techniques but these ties are not efficient for load transfer. Geogrid Bodkin Joints are the preferred mechanical connection for assuring full load transfer between adjacent layers of some geogrids.

This paper discusses geogrid connections, the techniques used, and the factors that affect their performance.     

Stratification in the cohesion of biofilms grown under various environmental conditions

The objective of this study was to use indirect methods to assess the biofilm cohesion and its vertical stratification. Biofilms were grown under low hydrodynamic strengths in two reactors, a low shear stress reactor (LSSR) or under a defined shear stress in a Couette-Taylor Reactor (CTR), using different electron donors and acceptors. The stratification of biofilm cohesion was characterized from a gradual increase of the hydrodynamic strengths in terms of shear stress (erosion) and abrasion (collisions of particles). Whatever the nature of the biofilms, erosion tests demonstrated a gradual impact of a wall shear stress increase on the biofilms remaining on the substratum surface. These observations demonstrated that the biofilm cohesion was heterogeneous and increased with the biofilm depth. Both erosion and abrasion tests highlighted a basal zone of high cohesion. Investigations based on PCR-SCCP and oxygen uptake rate showed the presence of active microorganisms in this zone.     

Effect of turbulence on nitrifying biofilms at non-limiting substrate conditions

The effect of turbulence on nitrifying biofilms was studied in five cylindrical PVC (polyvinyl chloride) reactors, each having ten biofilm sampling taps, over a period of 196 days. Bulk water in the reactors was stirred by paddles at 32, 92, 140, 278 and 500 rpm and the turbulent intensities measured at 10 mm from the wall were 0.6, 1.5, 2.6, 4.4 and 8.9 cm/s. Biofilms appeared as isolated colonies and continued to grow as filament-type biofilms. Higher turbulence resulted in higher NH₄-N flux and higher areal biomass density. Turbulent diffusion of substrates and by-products in the vicinity of filament-type biofilms must have resulted in the above phenomena. Photographic observation of the biofilm surfaces on sampling taps showed uniform biofilm filaments at higher turbulent intensities and large variation in the height of filaments at low turbulent intensities. Substrate flux and biofilm structure (areal density, filament height and cross-sectional area of filament) are inter-related parameters and are strongly affected by turbulence near the biofilm. Substrate flux is expressed as a power function of turbulent intensity, volumetric density and substrate concentration for filament-type biofilm when substrates are non-limiting.     

Contagion externalities and the conversion of low-intensity land uses on the urban fringe

The last decade has been characterized by a growing concern over the conversion of important farmlands and unique natural environments to developed uses. Preservation of agricultural, recreation, and/or open space uses of land around expanding urban areas faces unique problems. This paper examines the impact of spatial considerations on preservation policy. In particular, the allocative significance of contagion externalities is explored for both short-run and long-run policy formation, and empirical evidence for two U.S. cities is presented. It is concluded that failure to account for the external effects generated from urban development will lead to inefficient preservation strategies based on fiscal incentives and misspecified preservation goals.