Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.

The adsorption properties of NaY zeolite for separation of ethylene glycol and 1,2-butanediol: Experiment and molecular modelling

The separation of ethylene glycol(EG)and 1,2-butanediol(1,2-BDO)azeotrope in the synthesis process of EG via coal and biomass is becoming of increasing commercial and environmental importance.Selective adsorption is deemed as the most promising methods because of energy saving and environment favorable.In this paper,NaY zeolite was used to separate 1,2-BDO from EG,and its adsorption properties was then investigated.The isotherms of EG and 1,2-BDO in vapor and liquid phases from 298 to 328 K indicated that they fitted Langmuir model quite well,and the NaY zeolite absorbent favored EG more than 1,2-BDO.The Grand Canonical Monte Carlo(GCMC)and molecular dynamics(MD)simulation techniques were conducted to investigate the competition adsorption and diffusion characteristics in different adsorption regions.It was observed that EG and 1,2-BDO molecules all have the most probable locations of the center of the 12-membered ring near the Na cations.The diffusivities of EG are lower than those of 1,2-BDO at the same adsorption concentration.At last,the breakthrough curves of the binary mixture regressed from the empirical Dose–Response model in fixed-bed column showed that the adsorption selectivity of EG could reach to as high as 2.43,verified that the NaY zeolite could effectively separate EG from 1,2-BDO.This work is also helpful for further separation of other dihydric alcohol mixtures from coal and biomass fermentation.

Dynamic shear modulus of undisturbed soil under different consolidation ratios and its effects on surface ground motion

The dynamic shear modulus for three types of undisturbed soil under different consolidation ratios is presented by using the resonant column test method. Its effects on surface ground motion is illustrated by calculation. The test results indicate that the power function is a suitable form for describing the relationship between the ratio of the maximum dynamic shear modulus due to anisotropic and isotropic consolidations and the increment of the consolidation ratio. When compared to sand, the increment of the maximum dynamic shear modulus for undisturbed soil due to anisotropic consolidation is much larger. Using a one-dimensional equivalent linearization method, the earthquake influence factor and the characteristic period of the surface acceleration are calculated for two soil layers subjected to several typical earthquake waves. The calculated results show that the difference in nonlinear properties due to different consolidation ratios is generally not very notable, but the degree of its influence on the surface acceleration spectrum is remarkable for the occurrence of strong earthquakes. When compared to isotropic consolidation, the consideration of actual anisotropic consolidation causes the characteristic period to decrease and the earthquake influence factor to increase.

Phosphorus removal by adsorbent based on poly-aluminum chloride sludge

Phosphorus adsorption tests were carried out using poly-aluminum chloride sludge(PACS),which was collected from a water treatment plant in Nanjing.The amount of phosphorus adsorbed by PACS increased quickly within the first hour and reached equilibrium after about 48 h.The adsorption behavior of PACS for phosphorus is consistent with the Langmuir adsorption isotherm equation(R2>0.99)and parallel first-order kinetic equation(R2>0.98).With the increase of the PACS concentration,the adsorption capacity of PACS for phosphorus decreased,and the removal rate increased.The results of batch tests showed that the adsorption capacities of PACS for phosphorus ranged from 1.64 to 1.13 mg/g when the pH value varied from 4 to 10.However,the adsorption capacity of PACS was not evidently influenced by temperature.In comparison with the ion exchange resin,the adsorption capacity of PACS was barely inhibited by competitive ions,such as SO2
4,NO
3,and Cl
.The PACS surface after adsorption became smooth,and the vibration peaks of AleO and AleOH shifted.Both HCl and NaOH have a strong desorption effect on PACS after adsorption saturation,and with higher concentrations of HCl and NaOH,the desorption effect was stronger.Results of column adsorption experiments showed that with lower phosphorus and hydraulic loads,the adsorption column took longer to reach saturation.This indicated that PACS could be used as an efficient material for removal of phosphorus from water.This study provides a new treatment method with PACS.

Migration of Biodegradable Organic Matter in Underlying Soils of Household Waste Dumpsites: A Case Study in Abomey-Calavi, Benin

This paper presented the first part of the studies about the development of a tool for groundwater contamination prediction, conducted by the Laboratory of Sciences and Technology of Water (UAC/Benin). The investigation made consisted in estimating the combined effect of retardation factor and biodegradation on migration processes of leachate, in the underlying soils of household waste dumpsites, without active safety barrier. Leachate infiltration tests for different initial conditions were made on soil columns and the breakthrough curves were traced for electrical conductivity, the 5 day biochemical oxygen demand (BOD5) and total kjeldahl nitrogen TKN. A mathematical migration model was developed and solved numerically by finite difference method and implemented with Matlab R2013a. Thus, the calibration of the model was made with electric conductivity data by determining the dispersion coefficient of the studied soils (D = 0.96 cm2/min). Simulations for model verification showed that the established model can perfectly predict the migration of biodegradable organic pollution (BOD5) but did not give conclusive results for the monitoring of nitrogenous organic matter (TKN). The influence of the retardation factor on the migration of biodegradable organic pollutants in soils was linear, while the biodegradation rate of the organic material on migration showed an exponential pattern.

Interactions between H_(2)O_(2)and dissolved organic matter during granular activated carbon-based residual H_(2)O_(2)quenching from the upstream UV/H_(2)O_(2)process

Granular activated carbon(GAC)filtration can be employed to synchronously quench residual H_(2)O_(2)from the upstream UV/H_(2)O_(2)process and further degrade dissolved organicmatter(DOM).In this study,rapid small-scale column tests(RSSCTs)were performed to clarify the mechanisms underlying the interactions between H_(2)O_(2)and DOM during the GAC-based H_(2)O_(2)quenching process.It was observed that GAC can catalytically decompose H_(2)O_(2),with a long-lasting high efficiency(>80%for approximately 50,000 empty-bed volumes).DOM inhibited GAC-based H_(2)O_(2)quenching via a pore-blocking effect,especially at high concentrations(10 mg/L),with the adsorbed DOM molecules being oxidized by the continuously generated·OH;this further deteriorated the H_(2)O_(2)quenching efficiency.In batch experiments,H_(2)O_(2)could enhance DOM adsorption by GAC;however,in RSSCTs,it deteriorated DOM removal.This observation could be attributed to the different·OH exposure in these two systems.It was also observed that aging with H_(2)O_(2)and DOM altered the morphology,specific surface area,pore volume,and the surface functional groups of GAC,owing to the oxidation effect of H_(2)O_(2)and·OH on the GAC surface as well as the effect of DOM.Addi-tionally,the changes in the content of persistent free radicals in the GAC samples were insignificant following different aging processes.This work contributes to enhancing understanding regarding the UV/H_(2)O_(2)-GAC filtration scheme,and promoting the application in drinking water treatment.

Leaching Behavior of Trace Elements in Coal Spoils from Yangquan Coal Mine, Northern China

The long-term dumping of coal waste piles has caused serious environmental problems. Release of trace elements（including rare earth elements, REEs） from coal spoils gobs was investigated at Yangquan coal mine, Shanxi Province, China. X-ray diffraction（XRD） was used to analyze the mineral composition of the coal spoils. The minerals of the coal-spoil samples are mainly kaolinite and quartz, with a minor proportion of pyrite. The batch and column tests were employed to simulate the leaching behavior of trace elements from coal spoils. Elements V, Cr, Zn, As, Pb, and Cd are highly enriched in all coal spoils. The coal spoils also have elevated levels of Ga, Ge, Se, Sn, Hf, and Th. The leachate of coal spoils, fried coal spoils and CSFGM（coal spoils fire gas mineral） samples are acidic, with the p H values ranging between 3.0 and 6.6. The released elements with high concentrations（over 100 μg/L） include Fe, Mn, Co, Ni and Zn, while moderately-released elements are Cu, Se, Mo and As. A high content of heavy metals in batch-test leachate with CSFGM indicates an increased mobility of heavy metals in coal spoil combustion byproduct. Within the first hour washing with the electrolyte solution, a rapid rise of common cations, trace elements, and REEs content, as well as a drop of p H value, in effluent was observed. An increased leaching velocity favors the release of trace elements from coal spoils. In addition, the pulse input of precipitation led to more elements to be released than continuous leaching.

Hydrous cerium oxides coated glass fiber for efficient and long-lasting arsenic removal from drinking water

A novel arsenic adsorbent with hydrous cerium oxides coated on glass fiber cloth(HCO/GFC)was synthesized.The HCO/GFC adsorbents were rolled into a cartridge for arsenic removal test.Due to the large pores between the glass fibers,the arsenic polluted water can flow through easily.The arsenic removal performance was evaluated by testing the equilibrium adsorption isotherm,adsorption kinetics,and packed-bed operation.The pH effects on arsenic removal were conducted.The test results show that HCO/GFC filter has high As(Ⅴ)and As(Ⅲ)removal capacity even at low equilibrium concentration.The more toxic As(Ⅲ)in water can be easily removed within a wide range of solution p H without pre-treatment.Arsenic contaminated ground-water from Yangzong Lake(China)was used in the column test.At typical breakthrough conditions(the empty bed contact time,EBCT=2 min),arsenic researched breakthrough at over 24,000 bed volumes(World Health Organization(WHO)suggested that the maximum contaminant level(MCL)for arsenic in drinking water is 10 mg/L).The Ce content in the treated water was lower than 5 ppb during the column test,which showed that cerium did not leach from the HCO/GFC material into the treated water.The relationship between dosage of adsorbents and the adsorption kinetic model was also clarified,which suggested that the pseudo second order model could fit the kinetic experimental data better when the adsorbent loading was relatively low,and the pseudo first order model could fit the kinetic experimental data better when the adsorbent loading amount was relatively high.

Development of natural treatment system consisting of black soil and Kentucky bluegrass for the post-treatment of anaerobically digested strong wastewater

To develop a sound post-treatment process for anaerobically-digested strong wastewater,a novel natural treatment system comprising two units is put forward.The first unit,a trickling filter,provides for further reduction of biochemical oxygen demand and adjustable nitrification.The subsequent soil–plant unit aims at removing and recovering the nutrients nitrogen（N）,phosphorus（P）and potassium（K）.As a lab-scale feasibility study,a soil column test was conducted,in which black soil and valuable Kentucky bluegrass were integrated to treat artificial nutrient-enriched wastewater.After a long-term operation,the nitrification function was well established in the top layers,despite the need for an improved denitrification process prior to discharge.P and K were retained by the soil through distinct mechanisms.Since they either partially or totally remained in plant-available forms in the soil,indirect nutrient reuse could be achieved.As for Kentucky bluegrass,it displayed better growth status when receiving wastewater,with direct recovery of 8%,6% and 14% of input N,P and K,respectively.Furthermore,the indispensable role of Kentucky bluegrass for better treatment performance was proved,as it enhanced the cell-specific nitrification potential of the soil nitrifying microorganisms inhabiting the rhizosphere.After further upgrade,the proposed system is expected to become a new solution for strong wastewater pollution.