Abstract:The partial nitrification, denitrifying phosphorus removal and anammox (PNDPR-A) was proposed, which is a new type of efficient energy-saving coupling process. To further reduce the energy consumption of sewage treatment, the PNDPR-A process was adopted for the treatment of actual domestic sewage. The proportion of domestic sewage was gradually increased in three stages (25%, 50%, and 100%) to adapt to actual domestic sewage. Affected by the complex water quality of the sewage in the early stage, the NH+₄-N oxidation rate of PNDPR unit decreased and the NO-₂-N accumulation was reduced, which directly affected the subsequent denitrification effect of Anammox unit. To tackle this problem, the aeration intensity in aerobic 1 period was increased by 10% for PNDPR unit, so as to achieve NH+₄-N oxidation rate and NO-₂-N accumulation effect comparable to those of simulated sewage. In phase Ⅲ, 10-20 mg/L of NO-₂-N were added to Anammox unit, aiming at alleviating the problem of non-ideal influent nitrogen content of Anammox unit due to the low NH+₄-N oxidation rate of PNDPR unit in the early stage. After 40 d of cultivation and domestication, the PNPDR-A process was realized for actual domestic sewage treatment. The average effluent COD, NH+₄-N, NO-₂-N, and NO-₃-N concentrations of the subsequent system were 6,3.4,5.2, and 1.1 mg/L, respectively, indicating the high-efficient treatment of actual domestic sewage.

Abstract:To explore the stability of the completely autotrophic nitrogen removal over nitrite (CANON) process in the treatment of actual domestic sewage, sequencing batch reactor (SBR) was used to inoculate the CANON sludge that is stably operated in the laboratory, and actual domestic sewage was used as the influent. Actual domestic sewage has complex water quality, contains organic carbon sources, and has low ammonia nitrogen content, which brings about the problem of proliferation of nitrite-oxidizing bacteria (NOB) and heterotrophic bacteria (such as denitrifying bacteria). It is necessary to improve the operating parameters in response to this problem. In this work, the CANON reactor was operated in a hydraulic screening and alternate oxic/anoxic intermittent starvation mode. In continuous dynamic experiment, the reactors ran in a cycle of 3 d starvation and 3 d recovery. During intermittent starvation, two alternate oxic/anoxic ratios (1∶1 and 2∶1) were adopted for the flocculent sludge discharged by R1 and R2 for oxic/anoxic intermittent starvation. The contribution rate of autotrophic denitrification of both reactors exceeded 80%, while that of the denitrification pathway was less than 1% on the 50th day. The alternate oxygen intensification of intermittent starvation effectively inhibited NOB and denitrifying bacteria in the system. The final ammonia nitrogen removal rate was stabilized at 87.78% and 94.14%, and the total nitrogen removal rate reached 75.59% and 82.07% respectively, which can realize the stable operation of CANON process for domestic sewage treatment with low ammonia nitrogen. The CANON sludge cultured by domestic sewage had a darker color. On the 50th day, the volume average particle size of the R1 and R2 reactors reached 673 and 659 μm respectively. The mass fraction of extracellular polymeric substance (EPS) was affected by multiple factors such as total nitrogen concentration and organic carbon source, and maintained a trend of slow growth.

Abstract:Substrate layer is the key factor determining the purification efficiency of road runoff by dry grass swales. Six dry grass swale columns with different substrate components were constructed for simulation, and the artificial runoff containing representative polycyclic aromatic hydrocarbons (PAHs) was used as influent water. The performance of different simulation columns for the removal of PAHs was analyzed, and the mass balance was performed, in order to evaluate the effects of the presence and types of exogenous organic matters in substrates on the removal efficiency of PAHs and their fate. Results show that the average removal rates of NaP, PhA, and FlA were 69.0%-87.5%, 33.7%-72.9%, and 90.8%-96.8%, respectively. The dry grass swale with a shallow substrate layer was less conducive to the removal of low molecular weight (LMW) PAHs. The addition of exogenous organic matters in substrates was beneficial to improve the removal efficiencies of influent PAHs. During the five-month operation period, with the increase in the molecular weight of PAHs, the accumulation of PAHs in substrates increased and the degree of biodegradation was correspondingly decreased. Under the operation conditions close to the actual situations, the microbial degradation rates of NaP, PhA, and FlA were 62.1%-76.6%, 32.2%-42.9%, and 17.1%-36.6%, respectively. Biochar and woodchips could effectively improve the degradation rates of PAHs, and both of them can be used as exogenous organic materials in practical application of low impact development (LID) facilities, while woodchips are more economical.

Abstract:To further explore the safety assurance technology for reclaimed water, a pilot ozone oxidation-biological activated coke filtration system (O₃-BACK) was built and its effects on the removal of organic pollutants and pathogenic bacteria from secondary effluents of municipal wastewater treatment plants, as well as on the comprehensive biotoxicity of luminescent bacteria were investigated. Results showed that the development of activated coke filtration column from adsorption saturation to biological activated coke could be divided into three stages. With the introduction of O₃ pretreatment unit, the average removal amount and removal rate of COD_Cr by subsequent BACK columns in the stabilization period increased by 20.81% and 28.35% respectively, compared with BACK filtration alone. The effluent COD_Cr, UV₂₅₄, chromaticity, and turbidity of BACK column maintained at 12.74 mg/L, 0.04 cm^-1, 2 degree, and 0.75 NTU. O₃ oxidation was effective in the removal of humic substances, aromatic protein fluorescent fractions, and trace organic pollutants. Except for perfluorooctanoic acid, the concentrations of 11 trace organics such as sulfamethoxazole in BACK effluent were reduced to less than 10 ng/L. O₃ inactivated fecal coliform (FC) by nearly 2log, and the FC concentration in BACK effluent was 31-504 MPN/L, meeting the requirement of “reclaimed water for aesthetic environment use” with FC < 1 000 L^-1 (GB/T 18921—2019). The luminous intensity inhibition rate (IR) of O₃ oxidized effluent increased, with an average value of 11%, while the IR value of the final effluent after the BACK column was always negative, with no biotoxicity. The O₃-BACK can effectively reduce pollutants while ensuring the water safety of reclaimed water, providing a reliable technical option for wastewater reclamation and reuse.

Abstract:High energy consumption, complex operation, large amount of operation and maintenance, and high cost restrict the development and extensive application of drinking water treatment technology in rural areas. In this study, the ultra-low pressure gravity-driven membrane (GDM) filtration technology was specifically developed, which has the advantages of simple operation, low maintenance, low energy consumption, and chemical free. To further improve the removal efficiency of pollutants, we constructed a hybrid process of granular activated carbon (GAC) slow filter and GDM (GAC/GDM). Results show that pretreatment by GAC slow filter could significantly improve the removal efficiency of UV₂₅₄, dissolved organic carbon (DOC), and ammonia nitrogen, with the average removal efficiency of 75%, 86%, and 90%, respectively. Meanwhile, the membrane flux was improved by 32% compared with GDM control. The regulation effect of either water cycle (CGAC/GDM) or weak aeration (AGAC/GDM) on the performance of the hybrid process was investigated. During long-term filtration, compared with GDM control, the stable flux of CGAC/GDM and AGAC/GDM was increased by 36% and 49%, respectively. However, the removal efficiency of DOC and UV₂₅₄ in CGAC/GDM and AGAC/GDM declined slightly compared with GAC/GDM, since water cycle and weak aeration increased the concentration of dissolved oxygen in the feed water before GDM filtration, which promoted the hydrolysis of organic pollutants retained within the bio-cake layer on the membrane surface by the microorganisms. Therefore, the proposed GAC/GDM hybrid process can simultaneously improve the stable flux level and pollutant removal, which will provide theoretical and technical support for the development and application of membrane filtration technology in the rural areas.

Abstract:Water demand forecasting is the key to allocating water resources, saving energy, and reducing water age of water distribution network. Existing research focuses on the forecasting models but ignores the pre-processing steps such as abnormal detection, which restricts the accuracy of the models. A local outlier factor (LOF) model based on density was proposed to identify abnormal values of water demand data. The LOF was then combined with light gradient boosting machine (LightGBM) to form a hybrid water demand forecasting model LOF+LightGBM. The model was tested through actual cases. Results show that the root-mean-square error of the forecasting model based on data processed by LOF reduced by about 10% on average, compared with the forecasting model based on raw data. The mean absolute error of LightGBM on different datasets was 24.7% lower than artificial neural network (ANN) and support vector machine (SVR) on average. Overall, LOF+LightGBM showed the best prediction performance and the Nash-Sutcliffe model efficiency coefficients for three district metered areas (DMAs) were 0.6,0.951, and 0.942, respectively. The training and computational time of all the models was less than 0.7 s. In conclusion, LOF model, LightGBM model, and LOF+LightGBM model are conducive to improving the accuracy of the water demand forecasting model.

Abstract:Setting up a series of water quality monitoring points at important locations of water supply networks is an effective way for monitoring water quality in real time. Most existing layout optimization methods for water quality monitoring points focus on small-scale networks and are difficult to be applied to complex large-scale networks due to inefficient iterations and inferior solutions. Considering the large number of nodes and the high similarity of neighboring nodes in a large-scale water supply network, an optimization solution framework for water quality monitoring point layouts was established to minimize the monitoring time and maximize the coverage ratio of pollution events. The solution framework adopted water quality monitoring point selection models based on node importance indexes of complex networks and comprehensive evaluations of node hydraulic characteristics to simulate pollution events on important nodes of large-scale networks. Meanwhile, an evolutionary strategy of the genetic algorithm was upgraded to improve qualities of solution sets based on node spatial similarity. Simulation experiments on a large-scale network show that the proposed method could solve the problems of low iteration efficiency and low solution quality when the scale of a water supply network was large, so as to obtain an effective layout of water quality monitoring points.

Abstract:The stress-strain characteristics and saturation response of cavity expansion under constant suction in unsaturated soil were investigated. The semi-analytical drained solutions were derived for cylindrical cavity expansion in unsaturated soil based on the unsaturated critical state model (UCSM), the soil-water characteristic curve (SWCC) considering hydraulic hysteresis, and the nonlinear model of saturation varying with void ratio under constant suction. According to the equilibrium differential equations of soil elements around the cylindrical cavity, an auxiliary coordinate was introduced considering boundary conditions, and the problem was solved by first-order differential equations with three principal stress components, void ratio, and saturation as basic unknowns. The solutions fully considered the influence of matric suction and over-consolidation ratio on the expansion response, and explored the stress distribution and volume change in soil around the cylindrical cavity, as well as the saturation evolution law during the expansion process. Results show that the soil exhibited the characteristics of suction hardening during the cylindrical expansion under constant suction and the suction hardening phenomenon tended to be stable with the increase in suction. The saturation of soil at and around the cavity wall changed significantly during the expansion process and was greatly affected by suction. For soil with lower suction, the saturation was mainly affected by the water content change. While for soil with higher suction, the saturation was mainly affected by the void ratio change. This solution can well capture the saturation response of unsaturated soil under different stress histories and hydraulic states, which can provide guidance for the interpretation of in-situ tests such as cone penetration tests in unsaturated soil.

Abstract:The dynamic response of low height reinforced embankment under load with variable velocity was investigated. The load was assumed to be a uniform load, and the horizontal stress caused by the variable velocity of the load was taken into consideration. The low height reinforced embankment was considered as a layered isotropic elastic layer, and the Goodman model was employed to represent the interlayer contact conditions. The governing equations of the dynamic response of low height reinforced embankment in the Fourier transform domain were derived using the Garlerkin method. The generalized numerical solutions were obtained using a combination method of modal superposition method, Duhamel integral, and Fourier inverse transform. Two examples were used to verify the correctness of the method. The influences of the interlayer state, acceleration, embankment height, and reinforcement modulus on the dynamic response of the low height reinforced embankment were investigated. Results show that the interlayer contact state had a significant effect on the deflection at the bottom of the pavement structure, especially on the longitudinal deflection, and the effect was greater when the load moved with variable velocity. Thus, the upper and lower surfaces should be in full contact in practical engineering. With the increase in the initial velocity and acceleration, the dynamic deflection and stress increased significantly, and the dynamic stress path on the foundation became larger and rotated clockwise. Acceleration had an effect on reducing the stress in low reinforced embankment. Increasing the stiffness of the reinforced material could effectively reduce shear stress ratio by 47.9% and normal stress by 29%.

Abstract:To obtain the influence characteristics of cyclic impact loading on coal-rock damage under local static load constraints, we studied the damage factors and crack evolution of coal-rock samples during constant impulse cyclic impact and incremental impulse cyclic impact under local static load constraints by using the self-developed constrained pendulum-impact dynamic loading device. Experimental results show that when the constrained zone was in an elastic state, the partition with larger static load restraint area had stronger impact resistance; when the constrained zone was in a plastic state, the partition with larger static load restraint area had weaker impact resistance. The incremental impulse cyclic impact had higher damage efficiency to coal-rock than the constant impulse cyclic impact. The difference in rock breaking efficiency between the two cyclic impact methods was mainly reflected in the static load constrained zone, and the greater the static load value was, the higher the sensitivity of the damage factor to the impact method was. The crack propagation on the coal-rock surface was consistent with the zoning characteristics of the damage factor. When the static load constrained zone was in an elastic state, the static load had an inhibitory effect on the crack growth, and the cracks mainly expanded and derived along the partitions that were less constrained. When the static load constrained zone was in a plastic state, the cracks mainly propagated in the partitions that were more constrained, and tensile cracks in vertical direction were dominant in the constrained zone, while the cracks in the non-constrained zone mostly grew in an oblique direction. As the static load value increased, the fractal dimension of the surface cracks on the sample decreased first and then increased. The local static load constraints improved the impact resistance of coal-rock, and the damage factor of coal-rock showed obvious zoning characteristics.

Abstract:To study the synergistic flexural damage resistance characteristics of the surrounding rock-shotcrete lining structure of water transportation tunnel, two granite-shotcrete composite beams were prepared for four-point bending tests with different loading rates. The four-point bending tests of the granite-shotcrete composite beams were monitored by two nondestructive monitoring techniques: digital image correlation (DIC) and acoustic emission (AE). Results show that when the crack extended from the shotcrete to the granite surface, the load-strain curve showed an obvious inflection point in the post-peak descending section, which can be a sign of granite crack initiation. Through identifying the damage types in shotcrete by AE technology, we found that the proportion of shear damage increased with the increase in strain rate. For the visual analysis of the internal damage of the composite beam, the spatial b-value was calculated using the acoustic emission damage localization data. Then, a new Rb-value was constructed by attaching coefficients to the spatial b-value in combination with the density distribution law of damage localization in space. Compared with the spatial b-value, the cloud map of Rb-value had a higher differentiation of different damage degrees, which improved the visualization of damage. Finally, the damage clouds localized by Rb-values were compared with the crack clouds monitored by DIC, which verified the effectiveness of the proposed method for damage visualization using AE technology.

Abstract:A discrete element particle flow procedure was adopted to investigate the mechanical behaviour of rock under true triaxial conditions. The deformation and damage processes, the intrinsic connection between microcrack growth and evolution, and the intermediate principal stress effects in marble specimens were analyzed under different stress paths. Results show that the parallel bond model could accurately reflect the mechanical properties and damage modes of marble under true triaxial compression. The effects of intermediate principal stress on the peak strength, elastic modulus, failure angle, and failure mode evolution were significant. The octahedral theory could well fit the failure stress of the marble under true triaxial compression, and the obtained failure strength envelope had obvious linear characteristics. On the basis of the stress-strain curve, the crack expansion during the compression was divided into four stages: linear elastic stage, crack stable expansion stage, crack unstable expansion stage, and post-peak damage stage. With the increase in the intermediate principal stress, the brittle failure characteristics of the post-peak section of the stress-strain curve became stronger. The failure modes of the rock specimen changed from tensile failure to mixed tensile-shear failure, and the intermediate principal strain changed from tensile to compression. The evolution of rock damage showed a spoon-shaped trend as the intermediate principal stress changed.

Abstract:The paper aims to analyze the distribution of skin friction along piles caused by soil consolidation in newly formed dredger fill sites. Based on the continuous drainage boundary conditions and the ideal elastoplastic load transfer model, a theoretical model for the deformation analysis of pile foundations at newly filled sites was established considering the effect of soil consolidation. With the introduction of the continuous drainage boundary, the consolidation settlement of the double-layer foundation was acquired. The ideal elastoplastic load transfer method was used to simulate the pile shaft displacement-stress relationship, and the analytical solutions of skin friction and pile head settlement were obtained. Compared with experimental results, the proposed model was verified. The effects of time factor, thickness ratio of double-layer foundation, pile head load, and mechanics of pile foundation on axial force and skin friction were analyzed. Results show that as time increased, the negative skin friction increased and the neutral point of the skin friction moved downwards. When the thickness ratio of in-situ soil layer to new dredger fill layer increased, the negative skin friction decreased and the neutral point of the skin friction moved upwards. With the increase in the pile head load, the negative skin friction decreased and the neutral point moved upwards.

Abstract:Based on the soil-water two-phase mixing theory and the operator separation technology, a decoupled Arbitrary Lagrangian Eulerian method (ALE method) was developed, aiming to overcome the analysis interruption caused by mesh distortion in large deformation analysis of traditional updated Lagrangian (UL )method. The ALE method was applied to the seismic liquefaction analysis of caisson wharf on loose sand foundation. Results show that the ALE method could complete the seismic response analysis of caisson wharf under strong earthquake when the UL method failed, and provide numerical solutions with higher accuracy while maintaining the mesh quality. In addition, the ALE method was applied to the assessment of liquefaction mitigation measures of caisson wharf, providing a method for the optimal design of caisson wharf on loose sand foundation. Results show that the displacement response of caisson structure and the uplift of the front of the caisson toe could be significantly reduced by soil densification in replacement region. Soil densification in backfill region could reduce the displacement response of caisson structure under the condition of soil non-densification in replacement region, but it had little effect on the displacement of caisson structure under soil densification in replacement region. Both the replacement region and the backfill region had critical densification ranges, and there was no obvious change in the displacement response of the caisson structure while exceeding the critical densification ranges. The combination of gravel piles with densification in replacement region and backfill region could further decrease the displacement response of the caisson structure and increase the anti-liquefaction potential of the caisson structure.

Abstract:Reliable estimation of the uplift bearing capacity of plate anchor in sand is significant for predicting the mooring stability of floating renewable energy devices on the sea. On the basis of two-dimensional finite element method, a modified Mohr-Coulomb (MMC) constitutive model was employed to simulate the strain softening behavior of medium dense and dense sand, and the corresponding user subroutine was developed to examine the uplift bearing capacity of strip plate anchor foundation in sand. The rationality of the finite element model was verified by comparison of theoretical solutions and other centrifuge tests results. Through a series of parametric studies, results show that the embedded depth of plate anchor had great influence on the uplift bearing capacity of the plate, and the bearing capacity factor at H/B=10 was 273% higher than that at H/B=1. The larger the relative density of sand was, the larger the uplift bearing capacity was. Compared with loose sand (D_r<33%), the bearing capacity factor of plate in dense sand (D_r=100%) increased by 25%. The frictional factor of plate anchor had little effect on the uplift bearing capacity factor. On the basis of the numerical simulation results, a corrected formula of uplift bearing capacity factor of plate anchor at different depths in medium dense and dense sand was proposed, which provides a theoretical basis for the application of plate anchor foundations in medium dense and dense sand.

Abstract:In view of the relationship between the soil-structure interaction (shaft tower and well bore) and the seismic analysis of shaft tower in Ⅱ and Ⅲ sites, the influence on the seismic response of shaft tower with or without considering the soil-structure interaction in Ⅱ and Ⅲ sites was systematically studied by means of theoretical analysis and numerical analysis. The theoretical equation of motion in time domain was proposed and established, and the solution was presented with Runge-Kutta method and programmed using MATLAB language. Combined with finite element software, the numerical analysis model of the system was established. Taking the shaft tower of a reinforced concrete shear wall structure as an example, the influence on the seismic response of the shaft tower was obtained considering the system interaction under the conditions of Ⅱ and Ⅲ sites. Results show that the theoretical analysis model was in good agreement with the numerical analysis model, and the maximum difference between the theoretical solution and the numerical solution was 9.8%, which verifies the accuracy of the two models. The average amplification factors of the seismic response of three seismic waves under the conditions of Ⅱ and Ⅲ sites were 1.8 and 2.4 times respectively. In engineering design, the influence of soil-structure interaction on the seismic analysis of shaft towers should be considered under the conditions of Ⅱ and Ⅲ sites; the softer the soil is, the greater the influence of soil-structure interaction on the seismic analysis of the shaft tower is.

Abstract:Loess is a kind of special soil, whose mechanical characteristics are easily affected by hydro-thermal effect. In this study, a typical type of loess (Lanzhou loess) in western China was selected as the research object to investigate the effects of temperature, degree of compaction, and water content on the shear strength of seasonal frozen loess through low temperature triaxial test. Results showed that the cohesion and internal friction angle of the frozen Lanzhou loess increased with the decrease in temperature. The cohesion was greatly affected by temperature, while the internal friction angle was relatively less affected by temperature. In addition, the cohesion and internal friction angle of the frozen Lanzhou loess increased with the increase in the degree of soil compaction. In terms of water content, ice crystal and unfrozen water in the soil changed the strength of soil skeleton and the bonding force between soil particles and ice. Taking the optimal water content of the soil as the boundary point, the shear strength of the frozen Lanzhou loess on both sides of the boundary point showed opposite changing trends. It can be concluded that temperature, compaction degree, and water content have great influence on the shear strength of the frozen loess in Lanzhou, which should be fully considered in the engineering construction of the seasonal frozen soil region covered by loess.