Abstract:As an important technology for drinking water safety guarantee, membrane separation has its promising application prospects in drinking water treatment. Due to relatively low fabrication cost, polymeric membrane has been widely studied and used in membrane separation technology for drinking water treatment. However, some disadvantages limit its further application, including poor physical, chemical and thermodynamic stability and short lifespan. Therefore the study of ceramic membrane with prominent material advantages becomes especially important. In this review, the classification and characteristics of ceramic membrane were introduced firstly; then the mechanisms of filtration and membrane fouling were analyzed, and the research progress of ceramic membrane technology, combined process of pretreatments and ceramic membrane, and surface modification technology for ceramic membrane in drinking water treatment were discussed; further the prospect of ceramic membrane technology in drinking water treatment was presented. The optimization of preparation technology, enhancement of the study of mechanisms for membrane fouling and pretreatments, and the optimization of hybrid processes are becoming important research directions of ceramic membrane technology for drinking water treatment.

Abstract:To compare the effect of two different operational modes on partial nitrification (PN), two-stage continuous stirred-tank reactors (CSTR) 1# (anoxic-oxic) and 2# (controlling DO and HRT) were constructed and operated at room temperature (18-22℃). Start-up time, stability, aeration consumption, sludge settling ability, as well as the adaptability to the decreasing of ammonia nitrogen concentration were investigated. PN in 1# and 2# were accomplished in 26 d and 41 d, respectively. When the effluent of an anaerobic/oxic (A/O) process for phosphorous removing (containing ammonia nitrogen 35-43 mg/L) was used as influent, PN was stable both under 1# and 2# condition, however, aeration consumption could be reduced by about 20% in 2#. When the ammonia nitrogen decreasing from 43 to 27 mg/L, PN in 1# would be unstable and the rates of PN decreased to 67.39%. For comparison, PN in 2# could be maintained stable with an ammonia removal rate of >88%. Settleability of sludge was good both in 1# and 2#. Rapid start-up could be achieved through controlling DO and HRT, and a stable and efficient PN could be maintained through anoxic-oxic.

Abstract:In order to assess the impact of the inorganic carbon on the recovery and stability of SNAD process, excessive inorganic carbon was added to the SNAD reactor, which has collapsed due to the nitrate accumulation. The reactor was operated for 36 d under the conditions with a 370%-430% of theoretical inorganic carbon additive, and the effluent nitrate decreased from 12.1 mg/L to 3.47 mg/L under steady-state operation, simultaneously the feature ratio increased from 2.31 to 20.77. Then reduced the inorganic carbon additive to 260%-320% of the theoretical inorganic carbon concentration, the total nitrogen removal load increased from 0.176 g/(L·d) to 0.299 g/(L·d) after 42 d operation, the aerobic ammonia oxidation activity (AOR) and anaerobic ammonia oxidation activity (ANR) also increased from 0.061 4 g/(g·d) to 0.081 1 g/(g·d), and 0.040 6 g/(g·d) to 0.065 9 g/(g·d), respectively. Thus, sufficient inorganic carbon source not only released the problem of nitrate build-up, but also enhanced the activity of AOB and AnAOB.

Abstract:To improve the safety of distributing raw water, a BAR(Biofilm Annular Reactor)was constructed to simulate the distribution system and the effect of dissolved oxygen (DO) concentration on the effluent water quality and biofilm was studied. The 454-pyrosequencing technology was employed to analyze the diversity of biofilm in the reactor. Experimental results showed that the turbidity and the concentration of total iron, ammonia nitrogen decreased obviously with DO concentration increasing, while the concentrations of total nitrogen and COD_Mn changed slightly. The numbers of iron bacteria and sulfate-reducing bacteria reduced significantly, while the richness and diversity of the biofilm related bacteria (such as nitrifying bacteria) improved. So, increasing DO concentration can alleviate the pipeline corrosion and develop biofilm purifying water role.

Abstract:To investigate the operational efficiency of the combined process of contact oxidation and ultrafiltration for the pollutants removal of groundwater, which contained high concentration of Mn(II), Fe(II) and ammonia, a pilot-scale system was conducted and operated in Harbin. Moreover, membrane fouling potential was also investigated under different fluxes. The concentrations of total iron, Fe²⁺, Mn²⁺ and NH₄⁺-N in the feed water were approximately 14.67, 11.23, 0.83, and 2.22 mg/L, respectively. Experimental results showed that the effluent water quality of the combined process met Chinese Drinking Water Standard (GB5749—2006), with an average concentration of iron, manganese and ammonia in the effluent of 0.06, 0.04 and 0.44 mg/L, respectively. Furthermore, the turbidity of UF effluent was lower than 0.10 NTU, and with a bacteria removal efficiency of approximately 100%. SEM-EDS results demonstrated a low flux would be beneficial to alleviate the membrane fouling.

Abstract:To enhance the production efficiency of short chain fatty acids (SCFAs) in anaerobic sludge fermentation reactor, sludge from another stabilized fermentation reactor (over 90 days) under pH 10 was seeded into the reactors to examine its effect on SCFAs production. Two sets of experiment were designed to investigate the SCFAs production with/without seeding sludge under pH=7.4±0.2 and pH=10±0.2, respectively. Experimental results showed that (1) under same pH condition, the maximum SCFAs accumulation with seeding sludge additive increased by 4.9 mg COD/g VSS (pH=7.4±0.2) and 16.4 mg COD/g VSS (pH=10±0.2) respectively, in comparison with the control reactors; (2) with two reactors with seeding sludge, the maximum SCFAs accumulation at pH 10±0.2 increased by 146.2 mg COD/g VSS as compared with the condition of pH=7.4±0.2; (3) the maximum SCFAs accumulation at pH 10±0.2 without seeding sludge was 129.8 mg COD/g VSS higher than that of pH 7.4±0.2 with seeding sludge. Overall, seeding sludge improved SCFAs production efficiency, meanwhile, seeding sludge under alkaline pH could play synergetic role in enhancing the SCFAs accumulation.

Abstract:To investigate the effect of magnesium ion on the bulk performance of microbial fuel cell anode microorganism, analytical methods such as electrochemical measurement and high-throughput sequencing were applied to determine the potential promotion of magnesium on anode potential, electrochemical activity and anode microbial community structure under different ion concentrations were evaluated. With the magnesium ion concentration increased from 0.5 (M1) to 2.0 (M2) and further to 5.0 mmol/L (M3), the anode potential of microbial fuel cell was declined from-0.443(M1) (CK, vs. Ag/AgCl) to-0.469(M2) to-0.477 V (M3), respectively, in comparison with that of-0.417 V in control test. Accordingly, power density was enhanced from 36.65 mW/m² (CK) to 40.19 mW/m² (M1), 44.21 mW/m² (M2) and 45.48 mW/m² (M3). Furthermore, electrochemical activity and electricigen biomass were increased notably, indicating magnesium could enhance the power output of microbial fuel cell and played an important role in extracellular electron transfer.

Abstract:In order to enhance the sludge organics degradation rate in sludge wetland treatment system, this paper for the first time combining the bioelectrohenesis with STW system to improve the performance of STW and recovery biomass energy simultaneously. The degradation rate of sludge and power output under different organic loading of the MFC-STW system, using Canna as wetland plants, were investigated. Experimental results showed that both of the output voltage and power density of MFC-STW system increased significantly with the increasing of sludge loads. The maximum output voltage and power density of the MFC-STW system under steady-state operation were 0.794 V and 0.268 W/m³, respectively. During the charged circulation period, moisture content of the bottom layer sludge in MFC-STW system reached 84%, which was 7% lower than that in the with a STW system with no electricity production. Moreover, the average TCOD degradation rate of MFC-STW system was 74%, was 11% higher than the blank test. Bioelectrogenesis could improve the performance of sludge dehydration and degradation during sludge wetland treatment.

Abstract:To investigate the effects of direct continuous recycling of waste streams generated from drinking water treatment plant on effluent water quality, polite-scale experimental models was constructed and the changing rule of water quality was studied for 14 days both in summer and winter in the northeast China. The optimal recycle ratios of sedimentation sludge and filter backwash water were found to be 4% and 6% in summer, respectively, and was 2% and 6% in winter. Under the optimal recycle ratios, the continuous direct recycling waste streams could reduced the coagulant dosage by 33.3% in summer and 18.2% in winter compared to control trials based on reaching the sedimentation effluent standard (< 2.5 NTU). Water quality parameters such as turbidity, color, UV₂₅₄, TOC in settled and filtrated water were monitored periodically. Results indicated that contaminants could be removed more effectively in the recycling process compared to the control trials. Moreover, relative higher temperature could improve removal efficiencies. Over the entire operation period, there was no significant contaminants accumulation. Recycling waste steams was a feasible approach for enhancing coagulation process.

Abstract:A three-electrode cell has been developed to investigate corrosion characteristics of cast iron pipe and impact of the corrosion on water quality. The cast iron pipe corrosion parameters were measured by electrochemical workstation with microbe as controlled variable. The water quality was analysed in the corrosion system meanwhile. The results indicated that the average free-corrosion potential of the cast iron pipe was-0.515 V in non-sterile group during 66 days and the free-corrosion current was 7.61×10^-4 mA/cm², while the parameters for the reference group were-0.471 V and 5.26×10^-4 mA/cm², respectively. The water in non-sterile group deteriorated quickly with total iron exceeding 0.3 mg/L 3 days later. And chroma and turbidity of the water were 70 and 115 NTU. Corrosion rate of reference group was lower compared to non-sterile group, while the water became "red water" finally. Cast iron pipelines are prone to comprehensive corrosion characterized by electrochemical corrosion when there is little anti-corrosive coating on internal wall, leading to water quality deterioration.

Abstract:The water supply pipe network pressure management area (PMA) partition, which is pressure-control oriented and regional metrology considered, effectively controls the leakage rate of urban water supply network. PMA partition with graph theory is proposed in this study. First of all, to initially partition the water supply network and set the partition number with adaptive AP clustering algorithm and economic calculation. Secondly, Dijkstra algorithm is adopted to calculate the shortest path of each cluster center point to the source of the water and determine the position of each division of the water supply pipe, and then establish a partition boundary optimization model and apply simulated annealing algorithm to solve the model. Finally, combine some partitions properly with artificial expertise and form the final plan. This partition, computer algorithm oriented and combined with artificial expertise, embraces larger search space than the traditional artificial partition of trial and error and can guide the actual water supply network PMA partition.

Abstract:The corrosion and blockage in pipes has influenced on pipe wall thickness variation. This paper proposes frequency domain response function to evaluate the pipe wall thickness. System field matrix by continuous and momentum equations is derived, and the evaluation model of the pipe wall thickness is based on frequency response function. The position of pipe wall thickness change and length of wall thickness varying are evaluated by pressure response function in frequency domain (h) and the number of peak (m). The theoretical equation is verified by the field experiment, and estimation error is less than 4%. Meanwhile, the degree of wall thickness change directly affects the resonant peak shift, and frequency response model can be used to evaluate current pipeline status

Abstract:To further unravel dynamic adsorption behavior of bovine serum albumin on the PVDF ultrafiltration membranes modified with three different additives (PVP, PVA or PEG), the membranes were fixed upon clean crystal by spin-coating, and the adsorption and cleaning of protein on different membrane surface were measured using quartz crystal microbalance with dissipation monitoring. It was found that the adsorption amount of BSA on PVDF/PEG membrane was relatively low, and the adsorbed layer structure was dense and difficult to remove by DI water cleaning. While for PVDF/PVP and PVDF/PVA membrane surfaces (especially PVDF/PVA), the conformation of the layers varied on later stage obviously, |-ΔD/Δf| values increased seriously, and the adsorption layers become looser. The results show that the absorbed mass of BSA is related to the hydrophilicity of membrane surfaces using the same additives, and the membranes modified with different additives show the different adsorption behaviors. Specific additives (—OH, —O—and—CON—) play a major role in determining the viscoelastic of absorption layer.

Abstract:In order to reveal the influences of fouling layers formed by different organic matters on gypsum scaling behaviors on the surface of nanofiltration membranes, bovine serum albumin (BSA), humic acid (HA) and alginate (SA) were chosen as typical organic foulants to contaminate the composite polyamide nanofiltration membrane, respectively. After that, the gypsum scaling experiment was conducted. The gypsum crystal morphologies of different fouling conditions were observed by scanning electron microscopy (SEM). The interaction forces of membrane-gypsum and gypsum-gypsum in different membrane fouling conditions were investigated by atomic force microscope (AFM) combined with self-made gypsum probe. The results indicated that, compared with the virgin membrane condition, the adsorption of organic foulants on nanofiltration membrane had changed the membrane surface properties and influenced gypsum crystal nucleation mechanism. The degree of gypsum scaling in three organic fouling conditions decreased in the order of SA>HA>BSA. These phenomena were likely due to the interactions between SA and Ca²⁺ which could shorten the nucleation time of gypsum crystals, enlarge the crystals size and result in the fastest membrane flux decrease. The complexation between HA and Ca²⁺ increased the thickness and compaction of scaling layer, leading to a relatively serious membrane flux decline. Besides, the weak Ca²⁺ combination ability and particular heart-shape molecular structure of BSA led to a less degree of gypsum scaling compared to the other two kinds of organic conditions.

Abstract:To solve the problem of backwashing interval shortness of water plants, several film peeling solvents including HCl, Na₂SO₃ and H₂O₂ were examined to peel off the overgrown filter film from filter sands surface. An optimized dosage and time were determined by batch tests. Subsequently, the optimized conditions were tested in the pilot-scale columns. The filter sands before and after treatment were characterized by scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). The results demonstrated that the optimized dosage and time by HCl peeling were found to be 14.6 mg/g film and 40 min, and they were 11.7 mg/g film and 40 min for both Na₂SO₃ and H₂O₂. After treatment by the film peeling solvents, the backwashing interval could be efficiently recovered. Especially for HCl, the bed voidage increased from 27.7% to 39.1%, and the backwashing interval increased from 33.7 h to 61.6 h. At the same time, the catalytic oxidation activity was not affected by the peeling, and the water quality of effluent was still lower than the permitted limit. From the results of SEM and XRF, the morphologies and elements of some films were rarely changed. Considering the recovery of the backwashing interval and economic factors, HCl is a suitable choice for peeling off the filter film.

Abstract:To solve the deficiency of organic micro-pollutants removal in traditional technologies, the degradation study of chlortetracycline (CTC) in aqueous solution using UV activated persulfate technology (UV/PS combined process) was carried out. The removal effectiveness of CTC with UV process, PS process and UV/PS process was compared. Then the effects of initial CTC concentration, persulfate dose, as well as pH on the degradation rate of CTC were discussed. The active free radical in the reaction system was identified, and the reaction rate between the radical and CTC was determined. The results showed that CTC degradation with these three processes followed pseudo-first-order kinetic, and CTC removal efficiency can be significantly improved through the combination of UV process with PS process. The CTC degradation rate increased considerably as the persulfate dose increased, but decreased as the initial CTC concentration increased. The observed oxidation kinetic constant was influenced by pH values, and reached its highest and lowest level at pH 3 and 7 respectively．The active radical in the UV/PS process was SO₄^-·, and the reaction rate between CTC and SO₄^-·was 8.8×10⁸ L·mol^-1·s^-1.

Abstract:To enhance the adsorption capacity of activated carbon fibers (ACF) towards heavy metals, the surface modification of ACF was conducted and the physical and chemical characteristics were analyzed. Additionally, the competitive adsorption of Pb(Ⅱ), Cu(Ⅱ) and Co(Ⅱ) from liquid solution on the modified ACF were evaluated. It was found that both the modified and unmodified ACF had large specific surface areas and pore volumes. Compared with the unmodified ACF, the crystallinity of Fe and HNO₃ modified ACF showed a trend of decrease, and the Fe modified ACF appeared on obvious Fe characteristic diffraction peak. The rate of heavy metal ions adsorption onto ACF were so fast that the adsorption equilibrium achieved at about 60 minutes, and the adsorption equilibrium time increased after the Fe and HNO₃ modification. The removal of Pb(Ⅱ), Cu(Ⅱ) and Co(Ⅱ) were influenced significantly by the initial pH. The adsorption affinity to the three heavy metals was in the order of Pb > Cu > Co for all types of ACF. With the increase of initial concentration, the adsorption amount of Pb(Ⅱ) and Cu(Ⅱ) increased, while the adsorption amount of Co (Ⅱ) increased firstly and then decreased. The Langmuir and Freundlich models could well describe the competitive adsorption process of Pb (Ⅱ) and Cu (Ⅱ), but not effectively simulate the adsorption process of Co (Ⅱ).

Abstract:With the improvement of urban planning, surface processing industrial parks are continuous built in China.Due to its complex water quality and abundant existence of heavy metals, the traditional biological treatment unit exposed serious threaten from the existed heavy metals.Thus, the most common cation in electroplating wastewater, Cu²⁺, was chosen as object and the tolerant bacteria were isolated for enhancing its bulk removal.Two bacteria strains that have strong tolerance ability to Cu²⁺ were isolated and named as L2 and L3, and the effect of adsorption time, pH, temperature and initial concentration on Cu²⁺ removal were investigated. Results showed L2 and L3 have a high Cu²⁺ activity both in LB medium and wastewater medium, and the adsorption of Cu²⁺ could be achieved in a short time, with an optimal pH of 6.0 and temperature of 28℃, respectively.Under the optimal condition, the maximum adsorption ability was 34.15 mg/g Cu²⁺ for L2 and 45.68 mg/g for L3. A fast and efficient removal of Cu²⁺ can be realized, which is anticipated to be used in the actual electroplating wastewater treatment.

Abstract:To clarify the performance of functional microorganisms involved in biological citric acid wastewater treatment systems, bacterial community structure of anaerobic granular sludge was investigated in an internal circulation (IC) anaerobic reactor treating citric acid industry wastewater. Microstructure observation was carried out by environmental scanning electron microscope (ESEM), and the microbial diversity and microfloras were analyzed by high-throughput sequencing. Particle size distribution results showed that the most particles' diameters ranged from 1.0 mm to 4.0 mm (accounted for 74.4%). ESEM results showed that spherical bacteria were the dominant microorganisms in granular sludge. The total dataset comprised 8 397 high quality sequences, which could be subdivided into 873 operational taxonomic units. A library coverage of 0.936 implied that the granular sludge exhibited a high microbial diversity and abundance. The Shannon index, ACE index and Chao1 index were 4.376, 3 415.51 and 2 246.51, respectively. Genus classification revealed that there were four typical bacterial groups: hydrolytic fermentative bacteria for organic matter degradation were closely related to Paludibacter, Parabacteroides, Erysipelotrichaceae, Clostridium, Phascolarctobacterium, Aminobacterium, Saccharofermentans and Alkaliflexus, which accounted 24.93% of the bulk bacterial; H₂-producing and acetogenic bacteria were correlated with Petrimonas and Syntrophomonas, which accounted for 34.89%; methanogens of Methanosaeta accounted 3.44%; and the microflora groups of Levilinea, Longilinea and Thermovirga could be capable of tolerating toxic industrial wastewater, accounting for 14.62% instead.

Abstract:Benzophenone (BP) type ultraviolet (UV) filters are widely used in paints, coating materials and colorants. In order to investigate the occurrence of BP-type UV filters in painters, 10 urine samples from painters and other 10 urine samples from general population were collected in Harbin City. Urinary concentrations of five BP-type UV filters including 2-hydroxy-4-methoxy benzophenone (BP-3), 4-hydroxy benzophenone (4-HBP), 2, 4-dihydroxy benzophenone (BP-1), 2, 2′, 4, 4′-tetrahydroxy benzophenone (BP-2) and 2, 2′-dihydroxy-4-methoxy benzophenone (BP-8) were analyzed. The results indicated that the painters in Harbin were widely exposed to BP-3, 4-HBP, BP-2 and BP-8. BP-2 and BP-8 were the major BP-type UV filters. For all BP-type UV filters in painters, BP-3, 4-HBP and BP-2 shared the same origin, and 4-HBP and BP-8 shared the same origin.However, the BP-2 and BP-8 originated differently. The excretion doses of BP-type UV filters in painters were higher than that in general population, which indicated a possoble relationship between the exposure doses of BP-type UV filters and the working environment for painters. Long term exposure to paint or coating materials can increase the burden of BP-type UV filters in human.

Abstract:A zebrafish (Danio rerio) model was applied to evaluate the developmental toxicity of short-chain chlorinated paraffins (SCCPs). Death rates, hatching rates, malformation rates and body length were observed after the zebrafish embryos were exposed to different concentrations of C₁₀ (50.2% Cl) separately for 24, 48, 72 and 96 h. The results indicated that C₁₀ (50.2% Cl) could exert lethal and sub-lethal effects on the early life stage of zebrafish. Higher concentrations of C₁₀ (50.2% Cl) (1 000 and 10 000μg/L) could not only cause significant death rates increase to 100% after 96 h exposure and hating delay after 48 h exposure, but also induce a series of malformations, including spinal curvature, yolk deformity, pericardial edema, malformation of tail and uninflated swim bladder. Since the growth inhibition of juvenile zebrafish caused by C₁₀ (50.2% Cl) on the exposure concentrations no matter high or low, SCCPs might be a risk to the aquatic ecology and fish development.

Abstract:In order to investigate the removal mechanism of ammonia by biochar three-dimensional electrode, a lab-scale innovative three-dimensional electrode reactor using biochar as reactive media was established, and the removal trend and mechanism of ammonia (in non-chlorine water) during the reactor operation were investigated. Experimental results indicated that the biochar three-dimensional electrode reactor could achieve a high ammonia reduction in a short time (ρ₀=100 mg/L, t=3 h, η=45.72%). The ammonia transform process is a hydroxyl consumption reaction, which fitted well with the first-order kinetic model well, and biochar adsorption contributed insignificantly on bulk ammonia removal, while the direct and indirect oxidation within the reactor would convert the ammonia nitrogen to gaseous nitrogen and nitrate nitrogen instead.

Abstract:To optimize the heat transfer performance of the thermal-system heater, based on the particle swarm optimization algorithm and entransy dissipation theory, in this paper, a minimum entransy dissipation approach for optimization design was developed, taking entransy dissipation number as the objective function. The optimum size of the heat exchanger was determined without the pre-set structure of the heat exchanger and the phase change of working fluid of the heat exchanger was considered in the optimization design progress, which is different from the traditional design calculation. The convection heat transfer coefficient of steam condensation on the shell side was corrected by the latent heat value. For a specific thermal-system heater, the optimized design results showed that the exchanger effectiveness was increased by about 7.8%, while the pumping power reduced by about 19.6%, indicating that it achieved minimum power consumption when the thermal performance of thermal-system heater was optimized.

Abstract:The objective of this study is to analyze the cavitation characteristics in liquid hydrogen and nitrogen. The aim was realized by implanting the Schnerr-Sauer cavitation model and the physical properties of liquid hydrogen and liquid nitrogen at different temperatures into the CFX solver code, and coupling the energy equation considering the latent heat. Then the three-dimensional numerical simulation of cavitating flows was conducted around a hydrofoil in liquid hydrogen and nitrogen, and the experimental results of the pressure and temperature were utilized to validate the numerical strategy. The results show that the thermodynamic effects have more pronounced impact on the pressure and temperature in the cavitation region of liquid hydrogen. The liquid phase volume fraction in liquid nitrogen is smaller in the core cavitation region than that of liquid hydrogen, and the rate of phase transition from vapor to liquid is large in the closure region. The mass transfer rate between liquid and vapor can be used to evaluate the temperature, pressure and phase volume fraction inside the cavity effectively.

Abstract:In order to study the dynamics modeling and stability control design of supercavitating vehicle at the acceleration stage, the shape of natural cavity and the deviation of its axis were investigated according to the principle of cavity expansion independence. The influences of the cavity memory effect, gravity, cavitator orientation effect and attack angle were considered. The hydrodynamic force on each region of the supercavitating vehicle was calculated by means of the theory of slender bodies. Then a mathematical model for the acceleration stage of the supercavitating vehicle was presented for the longitudinal plane. Based on the precision linearization method, a depth tracking controller was designed. The simulation results show that this controller has better tracking performance; the planing force goes to zero in a short time, so the stability of the vehicle is improved and the friction drag of the partially wetted region is decreased.

Abstract:One of the key technique problems of reconstructing underground gas storage (UGS) using low permeability depleted gas reservoir is the stability of gas-water interface (GWC). To analyze the stable migration of GWC in gas storage reconstructed from low permeability gas reservoir using CO₂ as part of the cushion gas during capacity expansion by gas injection and seasonal peak shaving of UGS, a dual-porosity numerical model was established based on the characteristics of low permeability micro fractured reservoir. Taking the reservoirs of Wen-23 gas storage reconstructed, the Zhongyuan Oilfield, as research objects, the effects of CO₂ injection method on capacity expansion of UGS and migration behavior of GWC when peak shaving were simulated and discussed. The results showed that the method of continuously CO₂ injection increased capacity expansion speed but reduced the stability of GWC and reservoir pressure field during capacity expansion. The method of CO₂ injection at intervals reduced the rate of capacity expansion by 4.8% after 4 cycles, but could ensure stable migration of GWC and the stable of reservoir pressure field. Besides, the stability of GWC and reservoir pressure field were better ensured by the transformation between dissolved state and supercritical CO₂ during seasonal peak shaving of USG, and the utilization of reservoir space were increased, simultaneously.

Abstract:In order to explore the positive material with excellent cycling ability and good safety, the effects of co-mixed ratios(10∶0、8∶2、7∶3、6∶4、5∶5、0∶10) of LiNi_0.4Co_0.2Mn_0.4O₂ with LiMn₂O₄ as the positive material of lithium ion battery on the first discharging properties, cycling abilities, rate capabilities, impedance spectroscopy and cyclic voltammetry were investigated. The co-mixed electrode materials were also characterized by SEM. The results indicated that the co-mixed ratio affected the electrochemical performances of the co-mixed materials. The materials with the ratios of 8∶2, 7∶3 and 6∶4 showed higher specific volumetric capacity, better cyclic and rate performances than that of LiNi_0.4Co_0.2Mn_0.4O₂ and LiMn₂O₄ materials. The co-mixed material with the ratio of 8∶2 is the best.

Abstract:To figure out kinetic performance of LiMn_1.5Ni_0.5O₄ positive-electrode material, spinel LiMn_1.5Ni_0.5O₄ positive-electrode materials were prepared by a hydrothermal-assisted coprecipitation method. The structure and lithium ion insertion-extraction kinetic of the material were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The results showed that LiMn_1.5Ni_0.5O₄ material powders prepared by coprecipitation method had a spherical morphology, a small particle size and narrow particle size distribution. During cycling of LiNi_0.5Mn_1.5O₄, the transfer resistance increased the diffusion coefficient of lithium-ion decreased, and then the electronic conductivity and ionic conductivity reduced. After the temperature rose, the solution resistance for LiNi_0.5Mn_1.5O₄ material changed a little, but the transfer resistance gradually increased and the diffusion coefficient of lithium-ion gradually decreased. In addition, the dissolution rate of LiNi_0.5Mn_1.5O₄ material was accelerated, and the thickness of solid electrolyte interphase (SEI) layer extended. The insertion-extraction kinetic of LiMn_1.5Ni_0.5O₄ material had a close relationship with temperature and cycle times.

Abstract:In terms of the importance of SRGM (Software Reliability Growth Model) in evaluating and ensuring reliability, in order to grasp the modeling and working mechanism of SRGM, the typical process of SRGM modeling and the differences of performance in different models are studied in this article. First, the fundamental assumptions and the meaning of SRGM modeling are illustrated, and the development of SRGM is summarized. Second, the modeling processes and the relationship of two basic types of SRGM are analyzed. For the tendency of considering more real testing factors into SRGM, the SRGM modeling process relative to the imperfect debugging and TE (Testing-Effort) are discussed. Finally, the performances of 8 typical models selected are compared using 4 published failure data sets, and analyses on the differences are illustrated. The results indicate that the objective differences in different failure data sets and subjective differences in cognition of testing process by different researchers are the main causes that account for the different performances of SRGMs. Further establishing a more accurate and comprehensive SRGM and selecting excellent ones on finite failure data sets are the problems that must be solved in the future.

Abstract:In order to examine the impaction of different initial phase angles on the hydrodynamic performance of vertical axis tidal twin-turbine with different densities, this paper used CFD numerical simulation method to obtain the variation law of efficiency curves, and then explained the change mechanism through the detail analysis of the pressure diagram and vorticity graph of different density vertical axis tidal turbine with different phase angles. The results show that the influences of the phase angle on different density twin-turbine are similar. With the increase of phase angle, the efficiency of unit 1 with middle and high ratios is reduced gradually, unit 2 is the exact opposite of unit 1; When different density tidal turbine works at the respective middle phase angle, the efficiency of unit 1 and unit 2 of almost the same, which benefits the power delivery. Moreover, middle phase angles minimize the pressure of units. So the respective middle phase angle should be chosen as the optimal phase angle for different density tidal twin-turbines.

Abstract:To increase accuracy of estimating permeability coefficient of saturated soils using piezocone penetration tests (CPTU), taking account that the permeability coefficient of saturated soils estimated by the existing flow model to the spherical or the hemispherical surface is generally lower than the measured value, a modified approach was proposed, in which the initial excess pore water pressure, the location of filter element and seepage model were studied after the researches on evaluation of permeability coefficient of saturated soils were briefly reviewed. Based on the existing results, the initial excess pore water pressure around the shoulder of the cone was regarded as negative exponential attenuation distribution. Combined with the radial flow model to a cylindrical surface, the expression of horizontal permeability coefficient of saturated soils was derived. The comparison between the predicted and measured values demonstrates that the modified approach is reasonable and effective. The results show that the horizontal permeability coefficient determined by the modified approach is larger than that of previous approaches and more close to the corresponding measured value in laboratory tests. The horizontal permeability coefficient of saturated soils can be continuously and rapidly determined by CPTU.