Abstract:In order to assess the impact of different carbon/nitrogen (C/N) on anoxic/aerobic sequencing batch reactor (SBR) nitrosation system, the C/N was adjusted to 0,2/3,1, 4/3,2, 3,6 at room temperature (18-20 ℃). The results showed that the activated sludge system with the influent chemical oxygen demand (COD) loading and ammonia loading of 0.2 and 0.3 kg/(m³·d) successfully achieved nitritation only after 24 d. It needed more time to achieve nitritation with no COD in influent. When the C/N was less than 6, the system maintained good nitritation performance with the nitrosation rate of over 90%. When the C/N was 6, the nitrosation rate dropped to 70%. When the C/N was 4/3, the heterotrophic bacteria used the influent COD for denitrification adequately, the total nitrogen removal efficiency reached 49.8%, and the COD removal efficiency remained above 80%. Because the sludge system lacked the carbon source, the total nitrogen removal efficiency increased with the increase of the C/N when it was less than 4/3. When the C/N was 4/3 to 2, the COD and total nitrogen removal efficiencies almost remained unchanged. When the C/N was 2 to 6, due to the reduction of influent ammonia loading, the removal efficiencies of COD and total nitrogen showed a downward trend. At the end of operation (154 d), COD and total nitrogen removal efficiencies were 64.8% and 18%, respectively. When the C/N increased due to an increase in COD, the proteins (PN) tended to increase gradually, and polysaccharides (PS) almost did not change, while the decrease in ammonia caused an increase in the C/N, PN and PS decreased, but the value of PN/PS increased.

Abstract:To explore the feasibility of the green water purification process of ultrafiltration with short process and low chemical dosage, continuous filtration was used as the pretreatment process, and a pilot study of continuous filtration-ultrafiltration process for Songhua River water treatment was performed in terms of treatment efficiency and membrane fouling. In addition, a comparison experiment with direct ultrafiltration was performed to investigate the role of continuous filtration in the combination process. The results showed that the continuous filtration-ultrafiltration process had excellent removal efficiency for turbidity and ammonia nitrogen. The removal rates were 99.75% and 70.77%, respectively. But the removal of organic matter was inefficient. The removal rates of COD_Mn and UV₂₅₄ were 32.21% and 17.12%, respectively. In the early stage, the rate of membrane fouling was slow, and it became faster after the 15th day. The transmembrane pressure increased to the superior limit of 50.3 kPa on the 50th day. Continuous filtration showed a good removal effect on tryptophan protein, and ultrafiltration showed different degrees of removal of soluble biometabolites, tryptophan proteins, fulvic acid organics, and humic acids. Humic acids and tryptophan proteins were the main irreversible contaminants of ultrafiltration membranes. The removal rate of COD_Mn, UV₂₅₄, and ammonia nitrogen by the combination process were 9.97%, 7.02%, and 33.84% higher than that of direct filtration, respectively. Moreover, the membrane fouling rate of the combination process was much less than that of direct ultrafiltration. Continuous filtration pretreatment cannot only improve the removal efficiency of organic matter and ammonia nitrogen, but also alleviate ultrafiltration membrane fouling effectively.

Abstract:Three agricultural biomasses, wheat stalk powder (WSP), corn stalk powder (CSP), and rice husk powder (RHP) were used to enhance sludge dewaterability at different pH values. Capillary suction time (t_CS), filtration resistance (SRF, F_SR), etc. were used to characterize sludge dewatering performance. Sludge particle size and Zeta potential were investigated to reflect the changes of sludge properties. Turbidity, extracellular polymeric substance (EPS), bound water, and sludge cake structure were used to explain the mechanism of synergistic effect. The results showed that the optimum sludge dewatering performance was achieved when the pH value was 3 with a dewatered sludge cake moisture content of 61.5% under 2 MPa pressure. When WSP, CSP, and RHP were dosed separately, F_SR decreased to 7.32×10⁸, 7.41×10⁸, and 8.29×10⁸ s²/g, respectively. Sludge t_CS and F_SR increased remarkably with pH values lower than 2 or ranging from 8 to 11, and 0.75 g/g DS biomass could not improve sludge dewaterability, especially under strong alkali conditions. Strong acidity and alkali made sludge release more turbidity and organic matter which would block sludge cake and filter medium. The mechanism of acid and biomass improving the sludge dewatering performance of sludge is that acid (pH=3) promotes sludge extracellular polymerization (EPS) decomposition, while biomass provides water pore channels for dewatering as skeleton builder.

Abstract:Membrane fouling has always been an urgent issue to be tackled in membrane filtration field. The development of new characterization technology of membrane fouling is beneficial for understanding its process and provides reference for its control. This research tried to characterize organic membrane foulants directly through the front-face fluorescence excitation-emission matrix (FF-EEM). Bovine Serum Albumin (BSA), as the standard foulant, was used with Polyvinylidene fluoride (PVDF) membrane for this ultrafiltration experiment. The FF-EEM coupled with parallel factor analysis (PARAFAC) quantified the foulants accumulated on the surface of the membrane during the experiment. The research confirmed the validity of the application of FF-EEM on membrane foulants characterization. The result showed that the BSA deposition rate was relatively slow at the initial stage of the experiment, while as the filtration went on, a filter cake layer was formed on the surface of the membrane and the BSA deposition rate got faster, which led to more filtration resistance. It proved that FF-EEM is accurate and convenient in the characterization of the membrane foulants, and is expected to provide technical support for further research studies and online detection of organic membrane fouling.

Abstract:To determine the influence factors of biocathode bioelectrochemical system(bioc-BES) used for p-nitrophenol (PNP) degradation in actual production, the effects of applied voltage, PBS concentrations, and external resistance on the PNP removal were studied. The results showed that when external resistance was 10 Ω, with the increase of applied voltage from 0.2 V to 0.6 V, the PNP degradation rate constant increased from (0.024±0.005) h^-1to (0.098±0.001) h^-1,and 0.5 V was the best applied voltage for PNP removal. With the phosphate buffer solution concentration increasing from 10 mmol/L to 200 mmol/L, the PNP degradation rate constant increased from (0.039±0.004) h^-1 to (0.071±0.011) h^-1, and 50 mmol/L was optimal for PNP removal. The external resistance, which increased from 1 Ω to 100 Ω, had no obvious difference on PNP removal. These results indicated that the biocathode BES is well adaptable for environment and able to provide a theoretical basis for efficient PNP removal in practical wastewater treatment.

Abstract:Anaerobic ammonium oxidation (ANAMMOX) is known as the most effective process for nitrogen removal from organic wastewater with low ratio of carbon to nitrogen. But ANAMMOX population is difficult to enrich and sensitive to environment change, which results in a long start-up process. Thus, the tardy start-up of ANAMMOX process is a major issue for engineering application. In preliminary research, an upflow oxygen limitation biofilm reactor (UOLBR) was constructed to treat piggery wastewater with high ammonium (NH⁺₄-N) and low C/N ratio. After the 180-day start-up process, an excellent synchronous removal of chemical oxygen demand (COD) and total nitrogen (TN) was achieved with ANAMMOX as the dominant nitrogen removal pathway. Idled for 2 months, the UOLBR was restarted at 25 ℃ with a hydraulic retention time of 10 h and an effluent reflux ratio of 25∶1. Fed with manure-free piggery wastewater with the COD/TN ratio of 0.6-1.0, performance of the UOLBR during the restart-up process was evaluated. Operation process of the reactor was divided into 2 stages with a dissolved oxygen of 2.5-3.0 and 0.2-0.5 mg/L, respectively. The results showed that the UOLBR could recover from the idle state and a new steady state was reached within 53 days. Within the steady phase, the removal rates of COD, NH⁺₄-N, and TN in the reactor averaged 63.96%, 96.5% and 91.7%, with residues of about 1,7.0 and 16.4 mg/L in the effluent, respectively. Analysis of microbial community along with mass balance indicated that the recovered UOLBR was again characterized by ANAMMOX as the dominant approach for nitrogen removal from the wastewater. This work would be helpful for the start-up and management of ANAMMOX processes.

Abstract:The combined use of preoxidation treatment and organic polymer flocculant can increase the concentration of nitroso-dimethylamine (NDMA), a nitrogen-containing disinfection by-product. The concentration of NDMA is about 60-100 ng/L under typical water treatment process. In order to understand the influence of different factors and the reaction mechanism, the amounts of NDMA produced after the polyamine reacted with sodium hypochlorite or potassium permanganate under different conditions and chloramine disinfection were studied. The results showed that with the increase of the amount of preoxidant, pH, polyamine, and Br^- concentration, NDMA production increased correspondingly. Low concentration of NH+₄ could lead to an increase of up to 17.5% in NDMA production, but it gradually decreased to initial level with increased concentration. With the increase of NO-₂ concentration, NDMA production decreased significantly. When the concentration of NO-₂ reached 10 mg/L, the amount of NDMA production was about 15% of the initial level. The preoxidation process of chlorination conforms to the UDMH mechanism, while the preoxidation process of potassium permanganate involves the UDMH mechanism and hydroxyl radical mechanism.

Abstract:A novel oxidation way of electrically protected and enhanced activated carbon fibers (ACF) activating peroxodisulfate (PDS) was adopted in this work for the degradation of aqueous Carbamazepine, a sort of typical persistent medical pollutant. The removal rate by PDS system, ACF adsorption system, ACF activating PDS system, electrolysis system, protected ACF electrolysis system, and electrically protected and enhanced ACF activating PDS system was studied. The influences of PDS initial concentration, voltage, and initial pH value on the degradation of carbamazepine were also researched. Besides, characteristics detection of activated carbon fibers and radical quenching were conducted to reveal the oxidation mechanism in electrically protected and enhanced ACF activating PDS system. The results showed that the removal rate of carbamazepine in electrically protected and enhanced ACF activating PDS system was much higher than that in other processes. The excessive high initial PDS concentration could not promote the removal rate of carbamazepine. The removal rate of carbamazepine increased with the increase of voltage and the decrease of initial pH value. Activated carbon fibers could be protected from oxidation damaging with free electron implantation in cathode in electrically protected and enhanced ACF activating PDS process, which greatly prolonged its service life and significantly improved the utilization rate of PDS.

Abstract:Effective disinfection measures are in urgent need due to the serious biosafety issues in domestic hot water supply system. In this study, biofilms annular reactor was applied to simulate the domestic hot water pipeline system. The effects of chlorine and chlorine dioxide on microbial inactivation in biofilm were investigated. The changes of microbial community and the surface structure of biofilm were further explored using Illumina MiSeq sequencing and scanning electron microscopy (SEM). The results show that by increasing disinfectant concentration, the microbial inactivation rate could be notably improved while the inactivation effect remained stable. 1.5 mg/L chlorine or chlorine dioxide did not achieve a good microbial inactivation effect. However, the complete inactivation of Escherichia coli, total number of bacteria and heterotrophic bacteria (HPC) were observed in the presence of 3-5 mg/L chlorine and chlorine dioxide. 3-5 mg/L chlorine and chlorine dioxide can effectively control the biofilm of hot water pipeline. The results suggest that adequate concentration of disinfectant and disinfection time are important for keeping high inactivation effect. The pipeline biofilm was high in bio-diversity. Different from those in municipal water supply system and the secondary water supply system, the predominant phyla of pipeline biofilm were Deinococcus-Thermus and Proteobacteria, as well as some detected pathogenic bacteria. The shock disinfection of chlorine or chlorine dioxide showed a different inactivation effect on each phylum. Specifically, compared with chlorine, chlorine dioxide had a better inactivation effect on pathogenic bacteria, Proteobacteria, and Chlamydiae. The results of SEM indicate that the surface structure of biofilm was effectively destroyed by chlorine and chlorine dioxide, resulting in the larger gaps, shrinkage, and shedding of biofilm. Moreover, the effect of chlorine dioxide on biofilm surface structure was higher than chlorine. Overall, the results are important for the biosafety in hot water system.

Abstract:To improve the forecast period of real-time urban flooding warning, a real time warning simulation method based on radar technology was proposed. The base reflectivity of feature time was predicted and the optimized Z-R relationship was used to compute rainfall. Then the rainfall in the future was obtained and taken as an input in the hydraulic model. By real time simulation, the urban flooding in the feature was obtained and the urban flooding real time warning was realized. The result shows that urban flooding distribution can be obtained through the urban flooding real time warning based on radar technique, and more than 50 minutes’ forecast period can be saved. Compared with rain gage-based real time simulation, the length of forecast period can be reduced by 5-25 minutes, thus more time was provided for flood prevention department. The rainfall spatial distribution was taken as input in this method. Compared with rain gage input, rainfall spatial distribution was taken into full consideration.

Abstract:Post-ozonation is an important step during advanced water treatment by ozone-biological activated carbon. Post-ozone dosing control in waterworks is directly related to the operation efficiency of post-ozonation and the treated water quality of advanced water treatment. Source water quality is highly affected by the upstream water quality, climate, and weather conditions, as well as sudden pollution accidents. The influential factors of each link in water treatment plant are complicated. Thus, the influent water quality and water flow of post-ozonation change frequently. When the influent water quality and water flow change, how to adjust the ozone dosage in time to ensure ozonation efficiency and restrict bromate formation is a challenge in operation optimization of post-ozonation. A composite control method consisting of disturbance observer (DOB) and model predictive control (MPC) was proposed based on the control objective of CT value (i.e., product of C and T, Cis the concentration of ozone residual in water, T is the contact time of ozone and water) and proportional control of water flow. MPC was employed for the feedback control of ozone dosing. DOB was adopted to estimate the model mismatch and external disturbance of ozonation caused by the change of influent water quality and water flow. The estimated values were applied for the feed-forward control of ozone dosing. Both simulations and experimental results show that compared with MPC feedback control, the proposed DOB-MPC composite control of post-ozone dosing has better control performance and disturbance rejection effect, which can effectively improve the operation efficiency of post-ozonation and the stability of treated water quality of advanced water treatment.

Abstract:Currently, UV photolysis technology is seen as an effective method to deal with refractory organic matter or other pollutants because of its mild reaction conditions, strong oxidizing capacity, and other advantages. The shortcomings of the traditional mercury lamps, such as short lifetime, single wavelength, and low luminous efficiency, have limited their application in practical engineering. Microwave electrodeless lamp is a new type of high efficiency light source. It has the characteristics of high photooxidation activity, large spectral range selectivity, and simple device. At the same time, microwave and ultraviolet radiation are combined to greatly enhance the degradation of pollutants. Besides, microwave has the advantages of fast heating, small space occupation, no variation in light intensity, no heat medium and thermal inertia. Firstly, the principle of microwave and microwave-assisted photooxidation were introduced. Secondly, the principle of luminescence of microwave electrodeless lamp was also introduced. The application of electrodeless lamp in the treatment of water and gas and its regeneration of adsorbent were explored. At the same time, its influence factors were summarized, including electrodeless lamp, microwave power, temperature, and dielectric properties. Moreover, suggestions for further studies were also put forward.

Abstract:In the soft soil areas, such as Shanghai, artificial freezing method is adopted for constructing 98% underground engineering of metro side channel, pumping stations, and cross-river tunnels, but the method also causes notable problems of frost heaving and thaw collapsing on subway tunnel and surrounding geology environment. Although physical and mechanical properties of frozen soils have been studied, it is hardly sufficient for the research on the dynamic plastic deformation of freezing-thawing saturated silty sand. A remold-striping equipment was designed, and a method of saturating and freezing-thawing was proposed. The dynamic cumulated axial strain characteristics of freezing-thawing saturated Shanghai silty sand was studied using triaxial testing system. The experimental results reveal that compared with traditional compaction method, the remold-stripping equipment and proposed test methods provide an effect way for remolding, saturating, and freezing-thawing silty sand. The height and volume frost heaving ratio of intact saturated silty sand sample showed less influence with freezing temperature, but remolded silty sand frost heaving ratio increased as freezing temperature decreased. The axial permanent axial strain was closely related to the dynamic pore water pressure and less influenced by freezing temperature. Reducing vibration frequency resulted in smaller cumulated plastic strain. Increasing effect cell pressure and dynamic stress amplitude can significantly reduce the dynamic cumulated axial plastic strain of remolded freeing-thawing saturated sandy silt. Improved semi-logarithmic mode of cumulated permanent axial strain on freeing-thawing saturated silty sand was proposed and verified by experimental data, which could exactly forecast development trend of dynamic permanent axial strain.

Abstract:Soft coal seams with coal and gas outburst tendency do not have impulsion tendency, but rock burst disasters occur in soft coal seams under mining in the deep stope, and the existence of this dynamic disaster is confirmed by literature research and cases analysis. The unconfined unidirectional compression test and bursting liability identification indicated that coal samples were not prone to burst, and the monotonic strain strength softened after ultimate load. To study the mechanism of bursting disasters in soft coal seams, the boundary constraints and loading conditions of the excavating face and the mining face under the engineering background were simulated, and the pressure test under the single-degree-of-freedom border was carried out to investigate the stress, strain, and acoustic characteristics of the whole disaster process. The results showed that when coal samples loaded under the boundary condition of single-degree-of-freedom, the strain strength of all the three coal samples appeared as the process of softening-hardening-bursting, and the softening-hardening process even arose repeatedly. The strain strength hardening degree before bursting was remarkable, and the hardening coefficients of the three coal samples were 1.6,1.53, and 2.25, respectively. After strain strength hardening, the compression strength of coal samples before bursting disaster exceeded the threshold value of bursting tendency. Under the pressure with the constraint of single-degree-of-freedom, the bursting disaster, similar to that happens in hard coal seams, occurred when the strain hardening met the strength requirement of bursting, which reasonably explains the cause of rock burst in soft coal seams. When excavating and mining in soft coal seams with coal and gas outburst tendency under the condition of high stress in the deep mines, it is necessary to pay attention to rock burst caused by strain strength hardening. The intensity of such impulsion is generally not high in engineering, but it can induce highly harmful coal and gas outburst or unusual gas emission.

Abstract:In load-structure model for tunnel design, the rock mass resistant coefficient (k) is an important parameter which affects the behavior of the tunnel structure prominently. The anisotropy of k appears due to the presence of joints. However, no adequate efforts have been made to research the anisotropic distribution of k in jointed rock masses. Ten influencing factors including the elastic modulus of rock, Poisson’s ratio, and the properties of two sets of joints were analyzed for evaluating the anisotropic distribution of k, by using orthogonal array testing strategy (OATS) and distinct element method (DEM), with Xinggongjie Station Tunnel Project on No. 2 Line of Dalian Metro as an example. The results show that the distribution curves of k were oval-shaped. The maximum value was along the direction of the two joints angle bisector. Using the variance analysis of OATS, the significant influencing factors at the level of five percent were the elastic modulus of the rock, the normal stiffness of the joints, the spacing of the joints, and the intersection angle of two sets of joints. With the increase of the ratio of tunnel diameter to joint spacing, the anisotropy coefficient of k increased first and then started to drop, which converged to one when the ratio was equal to zero or infinite. Based on the above analysis results, the elliptic function of k was derived and was verified. The engineering example shows that the resistant coefficient of jointed rock mass is obviously anisotropic, which has little influence on the axial force of lining and remarkable influence on bending moment.

Abstract:For the frozen thawing rock mass in the engineering practice, taking the initial damage state of rock as the baseline state, the damage caused by freezing thawing and loading is considered as meso damage, and the damage caused by joints is regarded as macroscopic damage. According to the hypothesis of Lemaitre strain equivalence, a composite damage model of jointed rock mass considering macro and micro defects was derived. The effect of the penetration rate and the number of freezing and thawing on the deterioration of mechanical properties of rock mass was analyzed by this model. The results show that when the penetration rate was constant, the damage evolution curve increased with the increase of freeze-thaw times, and the experimental and theoretical peak strength (or modulus of elasticity) curves decreased with the increase of freeze-thaw times. When the freeze-thaw times were constant, the damage evolution curve was positively correlated with the penetration rate, and the experimental and theoretical peak strength (or modulus of elasticity) were negatively correlated with the penetration rate. It indicates that the penetration rate and the freezing thawing times have a certain effect on the deterioration of the rock mass, and the freezing thawing effect of the saturated test group is worse than the natural test group. The calculated results of the model were compared with the experimental values, and the theoretical curves are in good agreement with the experimental curves, which verified the rationality and validity of the model.

Abstract:Based on the assumptions of uniformity and one-dimensional stress wave theory, the splitting tests of C75 concrete were conducted using a large-diameter Hopkinson pressure bar to study its dynamic tensile strength property and strain-rate effect, and the dynamic stress equilibrium was carefully checked. At the same time, the stress contours were visualized with MATLAB, and the theoretical basis for the center cracking of Brazil disc was provided based on the modified Griffith theory. The failure processes of specimens in the dynamic splitting were simulated using LS-DYNA software. The results show that the dynamic tensile strength and the logarithmic strain rate were almost linearly dependent when the strain rate ranged from 10⁰ to 10¹/s. The specimen broke diametrically at low projectile velocity. Triangular crushed zones appeared at the two ends of the specimen with the increase of projectile velocity, and they became more serious in incident end. Under the 2D condition, the contours of the ratio of the maximum to minimum principal stress of the Brazil disc specimen (σ₁/σ₃) resembled a closed diamond, and the ratio of compressive strength to tensile strength at the center of the disc specimen had a maximum value of -3.0. The dynamic behaviors of the C75 concrete can be well described using the viscoplastic Cowper-Symonds constitutive mode considering strain rate effect. The simulation of the fracture process showed good agreement with the results observed by using the high-speed photography. The tensile strength of the C75 concrete is much better than that of the C35 concrete with the same water-cement ratio, but its strain rate sensitivity is lower than that of the C30 geopolymer concrete.

Abstract:In order to study the effect of dissolution on the seepage property of broken rock, an experimental system for testing the seepage property of broken rock under the condition of mass loss was designed. The halite was added in the broken mudstone to simulate the dissolution phenomena in nature, which can accelerate the dissolution process. The evolution law of seepage property of broken mudstone under dissolution was discussed. The effects of seepage pressure, halite content, and particle size of mudstone on the permeability of broken mudstone under dissolution were analyzed. The results show that dissolution caused loss of soluble matters and fine particles in broken rock to damage the pore structure and framework structure inside that specimen easily, thereby resulting in the expansion of underground watercourse in structure and the sharp increase of permeability parameters. The permeability parameters were positively related to the seepage pressure, halite content, and particle size of mudstone. For the rock specimen with greater seepage pressure, higher halite content, and larger particle size of mudstone, the more obvious expansion of underground watercourse tended to occur due to dissolution. In addition, in the seepage process of rock specimens, the watercourse blockage caused by the particles migrations also occurred, which results in the gradual decrease of permeability parameters.

Abstract:To study the dynamic properties and failure characteristics of karst cave roof under combined action of pile load and earthquake, supported by the pile foundation project of the Zhoujiawan Bridge of the Chongqing-Guizhou Railway, the main control parameters of rock materials, model piles, and seismic waves were determined based on the separation similarity method. Through 19 groups of mixture ratio tests, the index of the similar material ratios of rock masses used in shaking table tests were obtained, and the small-scale shaking table model tests of karst pile foundation were conducted considering the influence of different thicknesses of the roof and diameters of the cave. The results showed that the existence of caves changed the local fundamental frequency and dynamic characteristics of the model, and it hindered the transmission of seismic waves and dissipated energy. The frequency spectrum of the wave had no direct relation with the size of the upper load. The cracks in the pile-end caused by the combined action of the pile-end load and the earthquake gave rise to the overall amplitude decrease of the seismic waves, which caused the change of the fundamental frequency of the model. The internal cracks in the model increased with the enhancement of the acceleration of the seismic waves, resulting in a progressive increase in the damping ratio, which caused the main frequency of the vibration to decrease. Variation of the same kind of seismic wave only altered the wave amplitude, while different kinds of seismic waves led to the distribution changes of the fundamental frequency. The strain of the monitoring point increased with the increment of the peak of the seismic waves. Shearing failure of the karst roof occurred when the diameter of the cave was small, but punching-shearing failure happened when the diameter was larger.

Abstract:To investigate the effect of construction disturbance on vertical vibration characteristics of pipe pile, a simplified mechanical model of vertical vibration for pipe pile embedded in radially inhomogeneous soil was proposed by employing the viscous damping model and considering pipe pile as uniform cross-section and elasticity based on the plane stain model of annular complex stiffness transfer. Firstly, based on Laplace and complex stiffness transfer method, the composite stiffness of pile-soil interface was derived. Secondly, the frequency domain analytical solution of pile head dynamic impedance was obtained by using the compatibility condition. Finally, effects of the slenderness ratio of pile, the inner and outer diameters of pile, the elastic modulus of pile, the viscous coefficient of soil, and the construction disturbance intensity and range on the complex impedance at the pile head were analyzed. The results showed that the amplitude and resonance frequency of complex impedance at the pile head decreased with the increase of slenderness ratio of pile; the inner soil attenuated vertical vibration of pipe pile to a certain extent; the more the softening (hardening) intensity of the surrounding soil was, the lower (higher) the amplitude of complex impedance became; the amplitude of complex impedance at the pile head increased (decreased) with the enlargement of softening (hardening) range due to construction disturbance. It is suggested that the radial inhomogeneity should be considered in the analysis of vertical vibration for pipe pile when the construction disturbance is distinct.

Abstract:The study of pile-soil interface under cyclic loading is an important research direction of pile-soil interaction. The degenerate effects of pile-soil interface under cyclic loading consist of degenerate shear stress, degenerate normal stress, and the breakage mechanism of sand particles, which interact with each other and control the bearing capacity of pile-soil interface. Interfacial roughness has important influence on pile-soil mechanical mechanism. Macroscopic and microscopic mechanism of cyclic degradation behavior on pile-sand interface under different interface roughness was researched by utilizing self-developed visual constant normal stiffness (CNS) interface shear apparatus combined with digital image correlation (DIC) measurement technology. The experimental results showed that the relation curves of shear stress and normal stress developed as “hysteretic loop” and “disk” shapes, respectively. Under the same roughness, the interfacial shear stress and the normal stress both degraded logarithmically with the increase of the numbers of the cycles, while this degradation rate increased with the increase of interfacial roughness. The stress path curve developed as a “butterfly ring” shape, and the friction angle increased with the increase of interfacial relative roughness. The interfacial shear band was gradually thickened with the increase of shear cycles and interface roughness, and this thickness reached about (4-5) D₅₀ after 30 cycles. In addition, the particles in the shear band were significantly broken and the relative crushing rate was 1.86%-10.25%, which increased with the increase of interfacial roughness.

Abstract:Traditional pumps cannot have both high pressure and high flow performance at the same time. In order to solve this problem, a rotary eccentric extrusive pump was designed which has the characteristics of high flow rate of the centrifugal pump and high pressure of the reciprocating pump. In this study, the principle and design method of the rotary eccentric extrusive pump were put forward. The expressions of the inner envelope line of the cylinder and rotor profile were deduced. The size and position of the inlet and outlet, the material and force of the crankshaft, and the sealing system of the rotor underwent rationality analysis. A test of the rotary eccentric extrusive pump was carried out, and the curve of flow-time and pressure-time, the variation of volumetric efficiency, mechanical efficiency, hydraulic efficiency, and total efficiency with the change of outlet diameters and motor rate were analyzed. The results show that when the input power was 17.6 kW and the motor RPM（Revolutions Per Minute）was 800 r/min, the flow of the test pump reached 32.17 m³/h and the pressure reached 1.7 MPa. The hydraulic efficiency increased with the increase of RPM and reached a inflection point when the RPM reached 800 r/min. When the RPM was within 800 r/min, the non-uniform coefficient of flow was less than 2.4%, the volume efficiency was above 85%, the maximum of mechanical efficiency was 90.23%, and the overall efficiency reached a maximum of 60.75%. The rotary eccentric extrusive pump is characterized by high pressure and high flow performance at the same time, and is worthy of promotion and application.

Abstract:In marine environment, chloride-ion (Cl^-) penetration and alkali aggregate reaction are important factors affecting the durability of concrete. In this paper, an appropriate amount of nano-SiO₂ or nano-Al₂O₃ was added to ordinary marine concrete to study the durability of concrete with nano-particles under the combined influence of Cl^- penetration and alkali aggregate reaction. The experimental results showed that Cl^- penetration and alkali aggregate reaction promoted the durability of the concrete mutually. Nano-SiO₂ or nano-Al₂O₃ of different amounts could inhibit the Cl^- penetration and alkali aggregate reaction of concrete to different degrees so that the durability of the concrete under the interaction of the two factors was improved. The optimum amount of nano-SiO₂ and nano-Al₂O₃ in concrete was both 2.0%. When the total content of Cl^- in concrete was basically stable, the total amount of Cl^- in concrete with nano-SiO₂ or nano-Al₂O₃ was decreased by 18.04% and 11.60%, respectively. In the 39th week, the expansion rate of concrete with nano-SiO₂ or nano-Al₂O₃ was reduced by 28.75% and 16.87%, respectively. The addition of nano-particles could improve the pore structure of concrete, enhance the Cl^- penetration resistance of concrete, inhibit the generation of Friedel’s salt, thereby mitigating the expansion of concrete. Additionally, nano-particles can promote secondary hydration of cement, reduce the aggregation degree of Ca(OH)₂ crystal in the transition zone, and restrain the formation of CaCl₂ complex compound and alkaline environment required for alkali aggregate reaction.

Abstract:To improve the structural safety of LNG plate-fin heat exchanger, the analysis model on stress of plate-fin structures was established based on thermal-elastic theory. The stress characteristics of plate-fin structures at different brazed joints were analyzed by thermal-stress coupling method. Results showed that the maximum equivalent stress reached the peak value at the brazed joint near fin and plate side when the curvature radius of the brazing angle was 0.5 mm and the fusion distance was 0.137 5 mm, which was mainly induced by the maximum normal stress. The equivalent stress, the maximum normal stress, and the maximum shear stress changed steadily at the brazing seam. The equivalent stress of the brazed joints near fin and plate side increased with the increment of curvature radius on brazing arc. The stress concentration at brazed joints was reduced with the decrease of the curvature radius. The equivalent stress at the brazed joints near plate side decreased when the fusion distance on brazing arc increased, while it was opposite at the brazed joints near fin side. The equivalent stress of the brazed joints near plate side was larger than that near the fin side when the fusion distance on brazing arc was less than 0.08 mm. The above research results provide theoretical basis for the design, manufacture, and operation of LNG plate-fin heat exchangers in large LNG plants.

Abstract:To study the safety management of the sudden large passenger flow in metro stations, this paper focuses on the metro station evacuation and its strategy improvement under high imbalance between demand and supply. To relieve the stress of the sudden large passenger flow during metro system’s operation, a multi-station coordination control method is proposed. The reasons for large passenger flow mainly include holiday period, large-scale events, severe weather, and metro facilities faults. Based on the formation mechanism of large passenger flow, a coordinated current limiting control model was established to minimize the passenger loss delays and maximize the interval load rate, which can provide quantized basis for flow-control management. Finally, through the example analysis, the controlled flow rate and the number of stranded passengers before and after control were compared, and the effectiveness and reliability of the model were verified.

Abstract:In order to improve the perceived status of passengers and enhance the appeal of conventional public traffic, 9 different types of stops and 1024 passengers’ behavior and perception at these stops were surveyed and analyzed. The Pearson correlation analysis was used to explore the relationship between passenger waiting behavior and waiting environment, waiting behavior and perception time deviation, waiting environment and perception time deviation. The influence factors model of perceived time deviation was also established. The results show that the facilities of benches, ceiling, real-time information, and Wi-Fi were significantly related to passenger waiting behaviors including surfing, stroll, as well as no behavior. Any facility can increase the number of surfing users. If Wi-Fi was available, the number of passengers selecting stroll and no behavior would drop. Stroll passengers decreased if there were benches on the platform. These stop facilities can reduce passengers’ perception deviation of waiting time. Passengers’ behaviors such as calling, surfing, and reading newspapers and magazines can also reduce their perceived deviation, while smoking, strolling, and no behavior can lead to the increase of perception deviation.

Abstract:The activated sludge or microbial biofilm are the main habitats of microbial consortia in processes of biological wastewater treatment. The transformation and degradation of pollutants in wastewater can be realized through different metabolic pathways of microorganisms. The microbial community structure directly affects the rate of biotransformation of pollutants and the types of end products, while a comprehensive understanding of the microbial community structure and function can provide a microbiological basis for directional regulation of biological wastewater treatment. Since most of microorganisms are still uncultivable, it becomes a major challenge to reveal microbial dark matter in biological treatment systems. The rapid development of nucleic acid sequencing technique and bioinformatics has promoted the study of environmental microbiology and microbial ecology. In recent years, various meta-omics techniques based on high-throughput sequencing have served as an important tool for studying uncultured microorganisms and unknown genetic resources. Metagenomics and metatranscriptomics can systematically investigate the physiological and metabolic characteristics of microorganisms in specific environments, and provide a better understanding of microbial response and metabolic regulation to environmental variations. Currently, the meta-omics research on microbial dark matter has obtained some novel mechanisms in circulation of substances that break through the traditional understanding. This paper reviews the development of nucleic acid sequencing technique and discusses the recent advances in microbiological researches of biological nitrogen removal, enhanced biological phosphorus removal, and microbial electrochemical techniques based on metagenomics and metatranscriptomics. Finally, we provide an outlook on the prospective development and major challenge for meta-omics researches on biological wastewater treatment.