Abstract:Humanity has inhabited and proliferated on the earth, constructing countless habitats. From rudimentary shelters used by ancient civilizations to today's skyscrapers and high-speed railways, civil engineering has undergone technological changes across multiple epochs. With the increasingly challenges posed by global climate change and ecological issues, the characteristics associated with traditional engineering construction such as, high energy consumption, emissions, pollution, and non-degradable solid waste, are gradually becoming incompatible with the demands for today's construction. These include carbon neutrality, sustainability and recyclable. A transformation of civil engineering is inevitable. This article proposes the concept of “biogenic construction”. It is a system comprising four areas: microbial construction, plant construction, animal construction, and bioinspired construction. Each of the four areas is explained in terms of biogenic construction theory, technology, materials, equipment, processes, inspection, and testing. Some specific cases are also used to explain the concepts and applications. The perspectives of biogenic construction are also discussed.

Abstract:The post-grouting technique can effectively improve the soil performance against disturbance and break the mud crust around the bored pile. Most of the researches on post-grouting focused on pile tip, while the pile side grouting is rarely involved, which affects its further application. To study the influence of pile side grouting volume on the compressive load behavior, an model test was carried out on the basis of the post-grouting technique of the field pile test. The test results show that, when the load is at a high level, the bearing capacity of the pile with 2 L and 3 L grouting volumes are 18.2% and 66.0% greater than that of the pile with volumes of 1 L, respectively. The increased rate is positively correlated with grouting volume, and the settlement of pile top can be greatly reduced. The axial force of the post-grouting pile decreases rapidly near the position of grouting, and the axial force near the tip of post-grouting pile is relatively low in the whole loading process. The post-grouting pile demonstrates the characteristics of the friction piles. The cement grout diffuses upward and downward from the grouting position, and the diffusion heights are both about 14 times the pile diameter for this model test. The pile side resistance of the post-grouting pile increases significantly in the range of the grout diffusion stage, and the increasing trend is more obvious the closer to the grouting point.

Abstract:Based on pullout tests, the effect of normal stress, compaction degree as well as water content of backfills on interaction mechanism of reinforcement-soil interface and reinforcement displacement were investigated and the evolving pattem of reinforcement displacement was analyzed. The results showed that geogrid displacements along the full-length obviously lagged behind the displacement at loading end, and with increase of distance away from loading end, the geogrids displacements tended to decrease nonlinearly. An increase in normal stress, compaction degree or water content caused to the decrease in geogrid displacement for the identical pullout force and the same measured points. Moreover, the farther the location of measured points is, the weaker the effect of above-mentioned factors on geogrids displacements. During the pullout tests, the main failure modes included the geogrid pulled out fully and breakup failure of geogrid, and the peak pullout forces were approximately linear with the displacement at loading end. The peak pullout forces were closely related with the normal stress, compaction degree, water content or pullout rate. To increase compaction degree or water content of backfills, which caused to enhance interface interaction of reinforcement and soil, contributed somewhat the increase of friction angle of reinforcement-soil interface made the apparent cohesion of interface to increase remarkably, and the apparent cohesion of reinforcement-soil interface reached the greater value when the water content of backfills equals to the optimum water content. The test results showed that it is necessary to strictly control the water content of the backfill soil, and allowing the reinforced structure to deform properly is conducive to playing the role of reinforcement.

Abstract:The impact of back edge tensile cracks on soil slope stability evaluation is explored in this study. This paper mainly summarized the influence of trailing edge tensile cracks on the instability mode, providing a theoretical basis for establishment of slope tensile-shear coupling failure stability evaluation system and identification of instability modes such as collapse and stepped landslide. Moreover, the influence mechanism was preliminarily explored from the results of indoor model testing result, and it was found that the slope height, slope angle and mechanical parameters of soil slope would directly affect the tensile crack initiation position, occurrence and depth of the trailing edge, which would have a significant impact on the slope stability. Finally, the main problems in the current research on soil slope stability evaluation and trailing edge tensile cracks were summarized and reviewed.

Abstract:Fluid flow in fractures is one of the important factors affecting rock mass stability. The fluid in the fracture not only produce external pressure but also weaken the fracture strength. Therefore, engineering accidents including slope instability and tunnel collapse frequently occur. In order to explore the mechanism of seepage on the block stability of fractured rock masses, this study proposes a stability analysis method considering both seepage force and effect of fracture strength weakening by water, based on the Key Block Theory (KBT). In this method, the fluid pressures in fractures are simulated by Unified Pipe-network Method (UPM), and the relationship between fracture strength,s weakening and fluid pressures is determined by an empirical formula. This method is adopted to study the influence of seepage on the stability of a fractured rock slope. Results show that the action modes of seepage pressure and fracture water weakening on slope stability of fractured rock masses are different. The seepage force affects both the anti-sliding force and sliding force of the block. Therefore, the influence of seepage force on the block stability is more complicated, including changes of the block stability states, sliding surface, and the instability pattern. Fracture water weakening only reduces the anti-sliding force of blocks, and then reduces the stability of block, while not change the instability pattern of unstable block. Moreover, there is generally a critical pressure which is the most dangerous for rock slope engineering.

Abstract:In current slope reliability analysis, the failure probability might be wrongly calculated because of the inadequate consideration of anisotropic spatial variability of soil parameters. Therefore, a random finite difference method (RFDM) framework considering anisotropic spatial variability is established. Taking the general anisotropic spatial variability slope as a reference slope, the influence of anisotropic spatial variability on slope reliability is systematically studied from the aspects of fluctuation range direction structure, cross-correlation coefficient, variation coefficient and fluctuation range. The results show that the coordinate-transformation-based anisotropic random field simulation method can effectively characterize anisotropic spatial variability of soil parameters. Strain-clustering-based slope critical slip surface searching algorithm can accurately determine the complex critical sliding surface of slope. Compared with the general anisotropic spatial variability, the slope failure probability is overestimated and greatly underestimated when considering rotational anisotropy and transverse anisotropy, respectively. In addition, considering isotropic random fields can overestimate and underestimate the slope failure probability in case of greater and smaller scale of fluctuation, respectively.

Abstract:Due to insufficient research on interaction mechanism between freeze-thaw soil and anchor, the influence of freeze-thaw of soil on the internal force of anchor cannot be fully considered in engineering practice. Therefore, development of an empirical relationship of collapsible loess cohesion considering the influence of freeze-thaw cycles based on the triaxial shear test on collapsible loess in Xining City is essential. Based on the deformation coordination relationship between the anchor body and the surrounding soil layer, the analytical formula of the axial force and shear stress of the anchorage section of the frame prestressed anchor under freeze-thaw conditions is deduced, and the results of the theoretical calculation are compared with field tests, and the influence is analyzed. Results show that the cohesion of the soil decreases exponentially with increase of freeze-thaw cycles, and the axial force and shear stress of the anchorage section increase sharply in the first 3 cycles, and then become stable after 7 cycles. The axial force at the anchorage front section is more influenced by freeze-thaw cycles than the back end. However, the variation pattem of shear stress along the anchorage with freeze-thaw cycles is same. Results of the field tests proved the rationality of the calculation method, which can provide a reference for design and calculation of frame supporting structure in such areas.

Abstract:For comparison and selection of groundwater control scenarios for subway deep foundation pits in deep and high permeable aquifers, this paper presents the qualitative and quantitative comparison and selection framework by using analytic hierarchy process, fuzzy comprehensive evaluation and numerical calculation methods. Comprehensive comparison of various scenarios to groundwater control for a deep metro excavation in highly-permeable aquifers is established. Taking Shuibu metro station in Fuzhou as an example, five different groundwater control scenarios (i.e. open dewatering, fully penetrating curtains, deep horizontal bottom sealing curtain, partially penetrating curtains with dewatering, underwater excavation) are evaluated and analyzed using the proposed method. The results show that the scenario of both partially penetrating curtains and dewatering is the best for groundwater control. Then, the numerical simulation is used to analyze the surrounding surface settlement caused by dewatering. The results show that the surface settlement is in the range of 12-23 mm, which shows that the partially penetrating curtains with 42 m length can effectively control the surface settlement caused by dewatering. This method provides a solution for comparison and design of groundwater control scenarios for subway foundation pits in deep and high permeable aquifers.

Abstract:It is of great significance to assess the risk of building damage along the line that may be caused by metro tunnel construction. How to balance efficiency and accuracy is a challenge for risk assessment of tunnel underpass buildings. An improved three-stage building damage assessment method is proposed, in which the risk of tunnel underpass buildings is initially screened in the first two stages simultaneously from the perspective of both the hazard of tunnel excavation to the building and the vulnerability of the building itself, and a detailed multi-indicator assessment of the risk of tunnel underpass buildings is performed in the third stage. In the initial risk screening, Peck empirical formula and the ultimate tensile strain method are used to assess the hazard of tunnel excavation to the building, and the building integrity and the building, physical characteristics are used as the basis for building vulnerability assessment. In the detailed assessment of buildings damage risk, a three-dimensional finite element numerical model is established and multiple control indicators are selected to comprehensively assess the building damage risk caused by tunnel underpass. A shield tunnel underpass masonry building project is taken as an example to verify the rationality of the proposed method, and the results show that the introduction of vulnerability assessment as another basis for initial risk screening can effectively avoid underestimation of risk. The comparison of the assessment results with the measured shows that the improved three-stage method can accurately assess the risk of tunnel underpass buildings.

Abstract:Micro steel pipe pile is widely used in the reconstruction, reinforcement and rectifying of existing buildings considering that it is of high construction efficiency and environmentally friendly. The construction sequence would influence the effect of reinforcement or rectification and even the safety of the building. However, the research about influence of the construction sequence on displacement of the existing foundation reinforced by micro steel pipe piles is still relatively insufficient. Based on transparent soil material and particle image velocimetry (PIV) technology, this study performed the visual model test of reinforcing existing foundation via micro piles in different sinking orders (counterclockwise type, combined clockwise and counterclockwise type, Z type and symmetrical type), analyzed the displacement field of soil caused and the influence of different sinking orders on the cushion cap, pointed out the optimal strengthening scheme. The results indicate that under the test conditions, the pile under the cushion cap had a compacting effect on the surrounding soil. When the pile sanked around the cushion cap, the soil displacement around was less significant, and the soil disturbance zone was reduced by 42%, and the maximum displacement was reduced by 36% compared with the case of no cushion cap. The symmetrical reinforcement sequence was optimal, considering that the lifting displacement was only reduced by half.

Abstract:In order to study the variation pattern of dynamic tensile properties of phyllite under the coupling effect of water temperature, three groups of samples were subjected to 0, 1, 3, 5, 7, 8 and 11 times of temperature cycle natural cooling, temperature cycle cold water cooling and dry-wet cycle respectively. The dynamic Brazilian splitting test samples was carried out by Hopkinson bar test device. The dynamic tensile properties of phyllite under water and temperature deterioration were studied from five aspects: dynamic tensile strain curve, dynamic peak tensile strength, dynamic elastic modulus, energy analysis and macroscopic failure. It is found that the stress-strain curve includes extremely fast elastic deformation stage, yield deformation stage and failure stage. With the increase of the number of water temperature cycles, the extreme elastic deformation stage of stress-strain curve gradually decreases, and the strain growth rate in the yield deformation stage increases continuously. The dynamic peak tensile strength of phyllite shows a negative exponential function distribution, and the dissipation energy ratio decreases continuously. Under the condition of water temperature coupling, the peak tensile strength and dissipation energy ratio of phyllite are generally smaller than those of temperature cycle natural cooling. Under the dynamic impact, the phyllite occurs tensile failure throughout the bedding, mainly broken into 2 pieces. With increase of the number of water temperature cycles, the main phyllite fragments undergo tensile failure along the bedding plane and shear failure across the bedding plane, and the average size of the phyllite fragments decreases continuously. Under the condition of temperature circulating cold water cooling, the average size fragment is smaller and the decrease is the most significant.

Abstract:Incineration method has remarkable reduction effect and has become the main treatment method for municipal solid waste. However, incineration would produce a large amount of slag, for reuse of municipal solid waste incineration bottom ash, this paper investigated the bottom ash from a Wuhan incineration plant, and comprehensively analyzed the physical, chemical and engineering characteristics of the bottom ash by experiments and testing. Then the characteristics of bottom ash in different areas were summarized and compared with the present study. Furthermore, the feasibility of using the bottom ash as subgrade material in road engineering was discussed. The results show that, the bottom ash particles are various and randomly arranged, and the surface is smooth and distributed with obvious fine pores. The bottom ash is classified as a poorly graded coarse-grained sandy soil with low plasticity and high specific gravity. The leaching concentration of heavy metals from this bottom ash does not exceed the threshold value specified in the relevant national standards. The compaction characteristics of this bottom ash are similar with those of sand or gravel, it has relatively low compressibility, and its consolidation characteristics are not obvious. The permeability coefficient of the bottom ash is slightly greater than that of fine sand, and it can be considered as a landfill impermeable layer after being mixed with bentonite. The internal friction angle of bottom ash is close to that of gravel and has certain cohesion. In terms of the bearing capacity, the relatively high CBR reveals that the bearing capacity of this bottom ash meets the requirement of subgrade materials in road engineering.

Abstract:In order to amend the defects of vacuum preloading method, PHD-PVD vacuum preloading combined with electroosmosis to treat engineering waste slurry was proposed. Through six groups of large-scale model tests, the drainage, current intensity and settlement value during consolidation process of engineering waste slurry are monitored, After the test, the soil water content and vane shear strength were measured and combined with mercury intrusion test (MIT) to analyze the soil consolidation effect. The effect of intermittent disconnection of vacuum pump and power supply on the proposed method to strengthen the waste slurry of the project was studied. The test results show that the combination of electroosmosis method can effectively improve the drainage efficiency of PHD-PVD vacuum preloading method in the following stage, and the far end soil has a high degree of consolidation; Intermittent disconnection treatment of vacuum pump and power supply creates new drainage channels in the soil, which to some extent alleviates the siltation near the drainage board, maintains a fast drainage rate in the late test period, and improves the total drainage. MIT results show that the engineering waste slurry treated by intermittent PHD-PVD vacuum preloading combined with electroosmosis method has smaller peak pore diameter and denser soil microstructure.

Abstract:In order to explore the aerodynamic force of vehicles at the transition section of embankment and bridge, a 1：50 large-scale embankment-bridge transition section and vehicle experimental model are established in this paper. Two kinds of wind barriers are arranged in the bridge and embankment sections, and multiple pressure measuring points are arranged on the surface of the vehicle model to study the aerodynamic force of vehicles at the embankment-bridge transition section at different wind directions under different windproof measures. The experiment results show that compared with no wind-proof measures, the most unfavorable wind direction angle will change from -15° to 0° after the arrangement of the bridge wind barrier, and the three-component force of the vehicle at the transition section under this wind direction is the largest. After further arrangement of embankment wind barrier, the most unfavorable wind direction angle remains unchanged, but the lateral coefficient and torque coefficient of the vehicle at 0° wind direction angle are greatly reduced. The arrangement of embankment wind barrier can effectively reduce the three-component force of vehicles. The influence of changing the parameters of land wind barrier is not the same in different wind directions. The direction of the incoming flow should be fully considered in the arrangement of windbreak measures for the embankment-bridge transition section to achieve the optimal effect.

Abstract:When the turbulence flows through a rectangular blunt body, due to the stretching and rotating motion of the vortex, the downstream fluctuating pressure has obvious unsteadiness and spatial three-dimensionality, which mainly depends on the ratio of the turbulence integral scale to structural characteristic size. In order to further study the mechanism of turbulence scale effect, the unsteady aerodynamic characteristics of fluctuating pressure rectangular downstream direction on stationary rectangular cylinder with side ratio B/D=4 were investigated by the three-dimensional spectrum tensor theory and synchronically surface pressure measurement. The results show that when the turbulence moves from the stagnation point of the rectangular section to the separation point, the spectral energy of the fluctuating pressure shifts from low frequency to high frequency, and this phenomenon becomes more obvious with the decrease of L_u/D (L_u is the longitudinal integral scale of turbulence, D is the windward height). In contrast, the three-dimensional effect of turbulence and the distortion effect decrease with the increase of L_u/D. During this process, the energy of the fluctuating pressure is significantly attenuated only at low frequencies due to the blocking effect, and there is no significant change at high frequencies. Finally, the introduction of three-dimensional pressure admittance reveals the unsteady effect mechanism of the fluctuating pressure on the windward side of the rectangular section under the action of turbulence. For the pressure at the stagnation point, the greater the L_u/D, the closer the pressure admittance is to the quasi-steady theory; for the non-stagnation point pressure, the farther it is from the stagnation point, the more obvious the blocking effect of turbulence will weaken the low-frequency energy and the weaker the three-dimensional effect of turbulence. The distortion effect is controlled only by L_u/D.

Abstract:In order to promote the application of composite materials in building structures, a study was conducted on the flexural performance and overall comfort of prefabricated steel-concrete composite stair treads. Six stair tread specimens were tested using a four-point bending test, focusing on the influence of the shear reinforcement and the connection method between the tread and the stringer on the load-bearing performance of the stair treads. The test results showed that compared to angle steel and bolt shear reinforcement, channel steel shear reinforcement significantly improved the load-bearing capacity of the stair treads. Moreover, the load-bearing capacity of the welded specimens was less affected by the shear reinforcement and higher than that of the simply supported specimens. This indicates that welding can be considered as the primary connection method between the steel-concrete composite stair treads and stringers in future engineering applications. To accurately study the mechanical behavior of the stair treads, ABAQUS software was used to model the stair treads. The finite element model accurately simulated the mechanical behavior of the stair treads. Based on the validation of the model accuracy, a comfort analysis was conducted on the overall stairs. The natural frequency of the stairs and the acceleration response under human-induced excitation were within the specified limits, satisfying the comfort requirements for walking. The stairs will not cause any noticeable discomfort during use, meeting the requirements of ergonomics. The test and modeling analysis have proved that channel steel shear reinforcement provided a significant improvement in the load-bearing capacity of the stair treads Welding can be considered as the primary connection method between the stair treads and stringers, and the comfort analysis showed that the stairs met the specified requirements.

Abstract:In order to reveal the influence of salt erosion and freeze-thaw cycle coupling effect of steel fiber on concrete damage evolution, four groups of concrete specimens with different mass fractions of steel fiber were tested under salt freeze-thaw test. The damage of concrete after salt freeze-thaw cycles was analyzed by ultrasonic method and laser scanning method. The damage degree D of concrete after salt freeze-thaw cycles was obtained by analyzing the change of ultrasonic wave velocity. The Weibull distribution model between D and freeze-thaw cycles n was established. The surface roughness was used to characterize the surface damage of the concrete. The change rate of roughness ΔR of concrete with different steel fiber dosage was studied as a function of freeze-thaw cycles. The results indicate that the damage of concrete decreases with the increase of steel fiber dosage. The relationship between D and n established by ultrasonic method satisfied the two-parameter Weibull distribution model, and the determination coefficient is higher than 0.95. It has an exponential relationship between D and ΔR due to its determination coefficient higher than 0.80.

Abstract:With the increase of service life, the concrete strength of existing RC building structure degradates. To study the change law of the time-dependent compressive strength of concrete under freeze-thaw environment, the compressive strength of concrete of existing RC buildings in Harbin, Jilin and its surrounding areas was tested on the spot by combining ultrasonic-rebound stress test with core-drilling method. By normalizing and merging 924 groups of concrete compressive strength data, nonparametric test method was adopted to determine the probability distribution function of the normalized concrete strength, and the relationship between relevant parameters and service age was analyzed by regression analysis. The test results show that under freeze-thaw environment, the modified time-varying model of ultrasonic-rebound stress test satisfies the linear variation law, the time-dependent concrete compressive strength obeys normal distribution, the variation of mean value and standard deviation of concrete relative compressive strength with service age can be fitted by quadratic polynomial model and linear model respectively.

Abstract:In order to study the damage evolution of recycled concrete under high temperature of carbonation, the experiments were conducted on C30 recycled concrete (0%, 50% and 100% mass fraction replacement) under different temperature gradients (room temperature 20 ℃, medium and low temperature 200 ℃, and medium and high temperature 400 ℃) after carbonation with axial compression tests and simultaneous acquisition of acoustic emission (AE) signals, and the damage model of recycled concrete was established based on the analysis of acoustic emission characteristic parameters. The test results show that, analyzed AE damage location, cumulative impact count and energy count, dynamic monitoring of recycled concrete (RC) axial compression failure was realized from initial damage to micro fracture evolution, then to macro fracture propagation and finally to specimen failure; for RC specimens with different replacement ratio of coarse aggregate for comparison, the dense and concentrated location of damage points was the same as the failure position during loading process. Furthermore, RC with three different replacement ratios of coarse aggregate have the initial damage increases, the AE parameters increase and the stress decreases with the increase of temperature gradient. As a result, the concrete damage model based on AE cumulative impact count can be used to analyze the damage evolution law of RC after carbonization at high temperature under axial compression.

Abstract:Electrochemical chloride extraction can effectively eliminate harmful chloride ions of concrete structures and reduce the failure risk of concrete structures. The electrochemical dechlorination of concrete structure was carried out by means of strong electric field, and the strong electric field action of 40 min, 80 min and 120 min was involved in different early ages. The change and distribution characteristics of internal chloride content were tested, and the springback strength test was carried out on the specimens cured for 28 days after electrification. The results show that the chlorine removal efficiency can be significantly improved by the intervention of strong electric field at an early age, and the working time is about 1/300 of the traditional electrochemical methods when reaching the same chlorine removal effect. The distribution characteristics of chloride ions show that the distribution of free chloride ions is more uniform than that of traditional electrochemical parameters, and the bound chloride ions still have the phenomenon of accumulation in the middle of the protective layer. The standard curing is carried out after the action of strong electric field, and the rebound test results show that the strong electric field has no obvious effect on the macroscopic strength of the concrete protective layer.

Abstract:Due to the large amount of dredged sand produced by dredging in the lower reaches of the Yangtze River, the resource utilization of dredged sand has been given attention. The mortar was prepared by partially replacing manufactured sand with dredged sand, and the influence of different static stop time on the characteristics of dredged sand mortar was studied, the compressive strength at different ages was tested, through X-ray diffraction, scanning electron microscopy, and mercury pressing technology, the micro characteristics of different static stop time different dredged sand replacement rate mortar. The results show that with the increase of static stop time, the 90 d compressive strength increases gradually, and the impermeability is also significantly improved; The compressive strength of mortar increases with the addition of dredged sand, and increases first and then decreases with the increase of replacement rate of dredged sand; The compressive strength of dredged sand mortar has a great relationship with the replacement rate of dredged sand, and its influence degree is related to the static stop time. The dredged sand has a prominent strengthening effect on the low static stop time; dredged sand can effectively improve the problems of pore structure coarsening and pore enlargement caused by steam curing. Appropriate replacement rate of dredged sand has obvious improvement effect on the performance of steam curing mortar.

Abstract:The environmental effect of solidified contaminated soil is an engineering issue that needs to be studied in the process of waste soil reapplication. Taking cadmium, lead and nickel contaminated soil as the research object, through the initial screening of the curing rate index, the suitable curing material ratio, simulating wetting and drying cycles, long-term water immersion, high temperature, freeze-thaw cycles environment, and evaluate the environmental effects of soil after cement, cement+fly ash and lime solidification by the leaching toxicity index, combined with microscopic and heavy metal morphology analysis, evaluate the instability mechanism. The result shows that inorganic materials can increase the solidification rate of heavy metals to more than 90%, 8% lime is suitable for the solidification of cadmium contaminated soil, and 32%+8% cement+fly ash is suitable for lead and nickel contaminated soil. Solidification of contaminated soil under water environment (wetting and drying , water immersion) has no environmental risk, and its leaching toxicity is lower than the limit in the Identification standard for hazardous wastes: Identification for extraction toxicity (GB 5085.3—2007); but solidification contaminated soil is sensitive to temperature (high temperature, freeze-thaw), especially cement, cement+fly ash solidified contaminated soil, when the temperature exceeds 70 ℃, the leaching toxicity exceeds the standard limit, and it is close to the freeze-thaw cycles 5-7 times the standard limit. High temperature will promote the transformation of the occurrence of heavy metals from a stable state to an unsteady state. The freeze-thaw cycles will destroy the structure of the heavy metal-solidified product system. The application of inorganic materials to solidify heavy metal contaminated soil needs to consider the influence of environmental temperature.

Abstract:Ecological floating beds are widely used as an economical and environmentally friendly technology for the treatment of black smelly water bodies, while their treatment capacity is limited by the plant root area and the depth of plants reaching the water body. In this study, the enhancement effects and microbial mechanism of different fillers on the treatment capacity of ecological floating beds were investigated by constructing ecological floating beds with interspecies of Myriophyllum aquaticum and Iris sibirica plants through suspension balls, biological ropes, elastic and combined fillers respectively. Furthermore, the optimal addition of selected filter and its kinetic model of pollutant removal from the floating bed was investigated. The results showed that the best removal rates of COD, ammonia nitrogen and total phosphorus were >99%, 43.85% and 14.03%, respectively. The highest microbial abundance, the most uniform species composition distribution and the highest microbial diversity on the surface of the bio-rope filler have been observed, and the bio-rope filler can enrich nitrogen and phosphorus removal functional bacteria such as Flavobacterium, Exiguobacterium, Chryseobacterium, Microbacterium and Caulobacter. 12.5 m/m³ is the best amount of bio-rope filler for the remediation of mild black smelly water bodies, and the corresponding removal rates of COD, ammonia nitrogen, and total phosphorus are respectively 96.4%, 38.5% and 56.6%. The kinetic model fitting revealed that the primary kinetic model could better fit the ammonia nitrogen and COD degradation patterns of bio-rope-enhanced ecological floating bed.

Abstract:A ligand-to-metal charge-transfer synergistic and Fenton-like gathered reaction (LFGR) was developed to effectively decompose Ni-EDTA, a typical strong complex in near-neutral wastewater. Based on the removal efficiency of Ni(Ⅱ) and other systems, the complex broken characteristics of Ni-EDTA under near-neutral conditions were analyzed. The effects of Fe(Ⅲ) and H₂O₂ dosage, pH, turbidity, common organic acids and conventional inorganic salts on the complex broken characteristics of LFGR were investigated. The main reactive oxygen species in the LFGR system were identified in combination with the observation of H₂O₂ consumption, free radical quenching experiment, free radical signal detection and degradation product analysis, and the complex broken process and dominant mechanism of Ni-EDTA were further analyzed. The removal properties of heavy metal EDTA complexes (M-EDTA) by LFGR and other UV activated oxidation technologies were quantitatively compared, and the operating cost advantages of LFGR were further clarified. For the near-neutral simulated wastewater with 1.0 mmol/L complex concentration, the optimal reaction conditions of LFGR are as follows: Fe(Ⅲ) salt dosage = 0.1 mmol/L, H₂O₂ dosage = 50 mmol/L, and UV illumination time is 20 min. Under the above reaction conditions, the EDTA can be completely transformed and the Ni(Ⅱ) removal rate of Ni-EDTA can reach 99.40% after alkali precipitation; LFGR shows good anti-interference to common organic acids and conventional inorganic salts in water. H₂O₂ is consumed by Fenton-like reaction with Fe(Ⅱ) produced by ligand-to-metal charge-transfer. The main process of LFGR is that Fe(Ⅲ) replaces Ni(Ⅱ), stimulates the ligand-to-metal charge-transfer reaction and promotes the photolysis of EDTA, UV further drives Fe(Ⅲ) reduction and accelerates Fe species cycling, and further coordinates with Fenton-like reactive oxygen species (mainly ·OH and ·O₂^-) to enhance the complex decomposition. LFGR can achieve a variety of M-EDTA good breaking effect under near-neutral conditions, the total cost of treatment of each ton of water is 4.21 Yuan, with good technical economy.

Abstract:In order to achieve the purpose of non-membrane advanced treatment of landfill leachate secondary effluent, a powerful electrochemical reaction unit is constructed with a composite cathode and a dimensionally stable anode (DSA) as the core. The composite cathode is synthesized from carbon felt and iron powder by magnetic adsorption. The composite cathode would precipitate iron-based coagulants and reduce nitrate nitrogen in the leachate. The anode is a Ti/RuO₂-IrO₂ electrode, which can activate Cl^- in the leachate to generate active chlorine and oxidize and remove ammonia nitrogen in the leachate. The powerful electrochemical reaction and ozone oxidation are applied in the same unit, and a powerful electrochemical-ozone coupling process is constructed to strengthen the removal of organic matter and total nitrogen in the secondary effluent of the leachate. The results show that when the current intensity is 1.5 A, the initial pH is 7, the adsorption density of iron powder is 0.42 g/cm², and the ozone dosage is 4.58 mg/min, the removal rate of COD is 46.46%, and the removal rate of TN is 81.70%. Through infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR), and cyclic voltammetry (CV), the reaction mechanism of the process for the removal of organics was explored. The results showed that ·OH and ·Cl were generated in the coupled process system. The organic compounds such as aliphatic compounds, esters, ethers, and phenols in the leachate were effectively removed, and the biodegradability of the leachate was improved. After the coupling process is combined with the small SBR biochemical system, the effluent meets the requirements of the Standards for Pollution Control of Domestic Waste Landfills (GB 16889—2008).