A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model...A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers （ADCPs） and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code （EFDC）, was developed based on a terrain-following vertical （sigma） coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models with different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tideand wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.展开更多
The recently developed elasto-viscoplastic Creep-SCLAY1S model has been used in conjunction with PLAXIS 2D to investigate the effectiveness of vibro-replacement in a creep-prone clay. The Creep-SCLAY1S model accounts ...The recently developed elasto-viscoplastic Creep-SCLAY1S model has been used in conjunction with PLAXIS 2D to investigate the effectiveness of vibro-replacement in a creep-prone clay. The Creep-SCLAY1S model accounts for anisotropy, bonding, and destructuration, and uses the concept of a constant rate of viscoplastic multiplier to calculate creep strain rate. A comparison of settlement improvement factors with and without creep indicates that ‘total’ settlement improvement factors （primary plus creep） are lower than their ‘primary’ counterparts （primary settlement only）. The lowest settlement improvement factors arise for analyses incorporating the effect of bonding and destructuration. Examination of the variations of vertical stress with time and depth has indicated that vertical stress is transferred from the soil to the column as the soil creeps. This results in additional column yielding. In addition, the radial and hoop stresses in the soil are lower for the ‘creep’ case. The reduced radial stresses lead to additional column bulging and hence more settlement, whereas the hoop stress reductions appear to be a secondary effect, caused by additional plastic deformation for the ‘creep’ case.展开更多
Roxarsone （3-nitro-4-hydroxyphenylarsonic acid, ROX） has been widely used for decades as an organoarsenic feed additive to control intestinal parasites and improve feed efficiency in animal production. However, most...Roxarsone （3-nitro-4-hydroxyphenylarsonic acid, ROX） has been widely used for decades as an organoarsenic feed additive to control intestinal parasites and improve feed efficiency in animal production. However, most of the ROX is excreted into the manure, causing arsenic contamination in wastewater. The arsenic compounds are toxic to microorganisms, but the influence of continuous ROX loading on upflow anaerobic sludge blanket （UASB） reactor is still unknown. In this study, the impact of ROX and its degradation products on the performance of the UASB reactor and the degradation and speciation of ROX in the reactor were investigated. The UASB reactor （hydraulic retention time： 1.75 d） was operated using synthetic wastewater supplemented with ROX for a period of 260 days. With continuous ROX addition at 25.0 mg.L-1, severe inhibition to methanogenic activity occurred after 87 days operation accompanied with an accumulation of volatile fatty acids （VFAs） and a decline in pH. The decrease of added ROX concentration to 13.2 mg.L-1 did not mediate the inhibition. As（III）, As （V）, MMA（V）, DMA（V）, HAPA and an unknown arsenic compound were detected in the reactor, and a possible biotransformation pathway of ROX was proposed. Mass balance analysis of arsenic indicated that 60%-70% of the arsenic was discharged into the effluent, and 30%-40% was precipitated in the reactor. The results from this study suggest that we need to pay attention to the stability in the UASB reactors treating organoarsenic-contaminated manure and wastewater, and the effluent and sludge from the reactor tO avoid diffusion of arsenic contamination.展开更多
In recent years,there has been an increased resort to microtunnelling/pipe-jacking as a means of constructing underground conduits(for water,sewage,gas,and other utilities)to avoid on-street disruption in urban areas....In recent years,there has been an increased resort to microtunnelling/pipe-jacking as a means of constructing underground conduits(for water,sewage,gas,and other utilities)to avoid on-street disruption in urban areas.In this paper,technical details of two 1200 mm internal diameter microtunnels in silty sand totalling over 550 m in length are discussed.While average skin friction values are extremely low for both drives suggesting effective lubrication practice,differences in normalised bentonite volumes appear to be responsible for differences in skin friction.Full or near full buoyancy of the pipeline has been demonstrated for the majority of the drive.The frictional stress increase after a stoppage is shown to depend on not only the stoppage duration but also on the normalised lubrication volume.Interpretation of data in the manner presented in the paper is an important means of assimilating experience of microtunnelling in different ground conditions.展开更多
This study assessed the effects of reducing hydraulic retention times （HRTs） from 21 days to 10.5 days when anaerobically co-digesting pig manure and food waste. Continuously stirred tank reactors of 3.75 L working ...This study assessed the effects of reducing hydraulic retention times （HRTs） from 21 days to 10.5 days when anaerobically co-digesting pig manure and food waste. Continuously stirred tank reactors of 3.75 L working volume were operated in triplicate at 42℃. Digester HRT was progressively decreased from 21 to 15 days to 10.5 days, with an associated increase in organic loading rate （OLR） from 3.1 kg volatile solids （VS）·m^-3.day^-1 to 5.1 kg VS·m^3.day-1 to 7.25 kg VS.m^-3·day^-1. Reducing HRT from 21 days to 15 days caused a decrease in specific methane yields and VS removal rates. Operation at a HRT of 10.5 days initially resulted in the accumulation of isobutyric acid in each reactor. High throughput 16S rRNA gene sequencing revealed that this increase coincided with a shift in acidogenic bacterial populations, which most likely resulted in the increased isobutyric acid concentrations. This may in turn have caused the increase in relative abundance of Clocamonaceae bacteria, which syntrophically degrade non-acetate volatile fatty acids （VFAs） into H2 and CO2. This, along with the increase in abundance of other syntrophic VFA oxidizers, such as Spiorchatetes, suggests that VFA oxidation plays a role in digester operation at low HRTs. Reducing the HRT to below 21 days compromised the ability of the anaerobic digestion system to reduce enteric indicator organism counts below regulatory limits.展开更多
Globally, more than 55 billion tonnes of manure are generated every year from the livestock sector. However, livestock manure management systems, consisting of storage, processing, transportation, and disposal, are of...Globally, more than 55 billion tonnes of manure are generated every year from the livestock sector. However, livestock manure management systems, consisting of storage, processing, transportation, and disposal, are often inadequate, both in developed and developing countries.展开更多
基金supported by the China Scholarship Council(Grant No.2011671057)the European Regional Development Fund(ERDF)through the Atlantic Area Transnational Programme(INTERREG IV)the National University of Ireland
文摘A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers （ADCPs） and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code （EFDC）, was developed based on a terrain-following vertical （sigma） coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models with different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tideand wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.
基金the funding provided by the Irish Research Council(IRC) for the research into stone column behaviour in creep-prone soilspart of CREEP(Creep of Geomaterials,PIAP-GA-2011-286397) project supported by the European Community through the programme Marie Curie Industry-Academia Partnerships and Pathways(IAPP) under the 7th Framework ProgrammeThe support from the BIG(Better Interaction in Geotechnics) project from the Swedish Transport Administration
文摘The recently developed elasto-viscoplastic Creep-SCLAY1S model has been used in conjunction with PLAXIS 2D to investigate the effectiveness of vibro-replacement in a creep-prone clay. The Creep-SCLAY1S model accounts for anisotropy, bonding, and destructuration, and uses the concept of a constant rate of viscoplastic multiplier to calculate creep strain rate. A comparison of settlement improvement factors with and without creep indicates that ‘total’ settlement improvement factors （primary plus creep） are lower than their ‘primary’ counterparts （primary settlement only）. The lowest settlement improvement factors arise for analyses incorporating the effect of bonding and destructuration. Examination of the variations of vertical stress with time and depth has indicated that vertical stress is transferred from the soil to the column as the soil creeps. This results in additional column yielding. In addition, the radial and hoop stresses in the soil are lower for the ‘creep’ case. The reduced radial stresses lead to additional column bulging and hence more settlement, whereas the hoop stress reductions appear to be a secondary effect, caused by additional plastic deformation for the ‘creep’ case.
基金Acknowledgements This research was partially supported by the National Science Foundation of China （Grant Nos.51578205 and 51538012）, the Fundamental Research Funds for the Central Universities （No. JZ2016HGTB0722）, and the Program for Cultivating Excellent Talents in Beijing （No. 2013D002020000001）.
文摘Roxarsone （3-nitro-4-hydroxyphenylarsonic acid, ROX） has been widely used for decades as an organoarsenic feed additive to control intestinal parasites and improve feed efficiency in animal production. However, most of the ROX is excreted into the manure, causing arsenic contamination in wastewater. The arsenic compounds are toxic to microorganisms, but the influence of continuous ROX loading on upflow anaerobic sludge blanket （UASB） reactor is still unknown. In this study, the impact of ROX and its degradation products on the performance of the UASB reactor and the degradation and speciation of ROX in the reactor were investigated. The UASB reactor （hydraulic retention time： 1.75 d） was operated using synthetic wastewater supplemented with ROX for a period of 260 days. With continuous ROX addition at 25.0 mg.L-1, severe inhibition to methanogenic activity occurred after 87 days operation accompanied with an accumulation of volatile fatty acids （VFAs） and a decline in pH. The decrease of added ROX concentration to 13.2 mg.L-1 did not mediate the inhibition. As（III）, As （V）, MMA（V）, DMA（V）, HAPA and an unknown arsenic compound were detected in the reactor, and a possible biotransformation pathway of ROX was proposed. Mass balance analysis of arsenic indicated that 60%-70% of the arsenic was discharged into the effluent, and 30%-40% was precipitated in the reactor. The results from this study suggest that we need to pay attention to the stability in the UASB reactors treating organoarsenic-contaminated manure and wastewater, and the effluent and sludge from the reactor tO avoid diffusion of arsenic contamination.
基金The first author is funded by an Irish Research Council Enterprise Partnership Scheme(IRC-EPS)Postgraduate Scholarship,with Ward and Burke Construction Limited as the industry partner.The third author is supported by the Royal Academy of Engineering(U.K.)under the Research Fellowship Scheme.
文摘In recent years,there has been an increased resort to microtunnelling/pipe-jacking as a means of constructing underground conduits(for water,sewage,gas,and other utilities)to avoid on-street disruption in urban areas.In this paper,technical details of two 1200 mm internal diameter microtunnels in silty sand totalling over 550 m in length are discussed.While average skin friction values are extremely low for both drives suggesting effective lubrication practice,differences in normalised bentonite volumes appear to be responsible for differences in skin friction.Full or near full buoyancy of the pipeline has been demonstrated for the majority of the drive.The frictional stress increase after a stoppage is shown to depend on not only the stoppage duration but also on the normalised lubrication volume.Interpretation of data in the manner presented in the paper is an important means of assimilating experience of microtunnelling in different ground conditions.
文摘This study assessed the effects of reducing hydraulic retention times （HRTs） from 21 days to 10.5 days when anaerobically co-digesting pig manure and food waste. Continuously stirred tank reactors of 3.75 L working volume were operated in triplicate at 42℃. Digester HRT was progressively decreased from 21 to 15 days to 10.5 days, with an associated increase in organic loading rate （OLR） from 3.1 kg volatile solids （VS）·m^-3.day^-1 to 5.1 kg VS·m^3.day-1 to 7.25 kg VS.m^-3·day^-1. Reducing HRT from 21 days to 15 days caused a decrease in specific methane yields and VS removal rates. Operation at a HRT of 10.5 days initially resulted in the accumulation of isobutyric acid in each reactor. High throughput 16S rRNA gene sequencing revealed that this increase coincided with a shift in acidogenic bacterial populations, which most likely resulted in the increased isobutyric acid concentrations. This may in turn have caused the increase in relative abundance of Clocamonaceae bacteria, which syntrophically degrade non-acetate volatile fatty acids （VFAs） into H2 and CO2. This, along with the increase in abundance of other syntrophic VFA oxidizers, such as Spiorchatetes, suggests that VFA oxidation plays a role in digester operation at low HRTs. Reducing the HRT to below 21 days compromised the ability of the anaerobic digestion system to reduce enteric indicator organism counts below regulatory limits.
文摘Globally, more than 55 billion tonnes of manure are generated every year from the livestock sector. However, livestock manure management systems, consisting of storage, processing, transportation, and disposal, are often inadequate, both in developed and developing countries.
