Influence of Multi-Layered Structure of Vadose Zone on Ecological Effect of Groundwater in Arid Area: A Case Study of Shiyang River Basin, Northwest China

The natural vegetation in arid areas of northwest China is strongly dependent on the availability of groundwater. Significantly, capillary water plays an essential role in regulating the ecological groundwater level in the multilayered structure of the vadose zone. The soil-column test and field survey in the lower reaches of the Shiyang River Basin were conducted to investigate the influence of the multi-layered structure of the vadose zone on maintaining the ecological effect of groundwater. Based on the field survey, the results show that the depth of groundwater is 3.0 m, and the rising height of capillary water is 140 cm. In the soil-column test, the height of the wetting front of the column was 125 cm. During the water releasing test, the water held by the vadose zone was 182.54 mm, which would have maintained Haloxylon’s survival in a growing season. Therefore, the multi-layered structure of the vadose zone extends the ecological groundwater depth and consequently enhances the ecological function of groundwater. Importantly, with a lower groundwater level, the clay soil layer within the rising height range of the original capillary water would hold more water and maintain a higher water content for a certain period to supply surface vegetation.

Design of a column test bench for the evaluation of alternative absorbent materials in wastewater treatment

One of the most used processes for wastewater treatment is filtration, still having unknowns related to the new possible absorbent materials which can provide better pollutant removal. This project proposes a column test bench capable of working with different materials, particle diameters (> 0.35mm) and densities and densities with three columns of 1.5 m length and 4 inches of diameter.. To perform this project, the type of reactive material for the filter medium was identified, considering the nominal and critical size of the fine sand (0.35m), as a basis for determining the design of the length, diameter of the and thickness column. The design conditions were taken so that the hydraulic system can function as a slow and rapid filter. The most critical operating conditions were selected, Qmax: 16.72 lpm and Filtration Rate: 19.80 m / h. Under these operating conditions, a hydraulic head loss of 2.77 m was obtained within the sand column. The result of this research is the design of a column test system that can work under different hydraulics conditions and absorbent materials with sizes greater than 0.35 mm, intended for the investigation of wastewater treatment from car washers and the removal of heavy metals. The final cost of building the column test is about 25% of the commercial price system.

Evaluation of Long-Term Leaching of Arsenic from Arsenic Contaminated and Stabilized Soil Using the Percolation Column Test

Arsenic in the soil can leach into groundwater and contaminate drinking water, posing a serious risk to human health. The stabilization of arsenic in contaminated soil is one of the immobilization technologies used to remediate contaminated lands. However, few studies have evaluated the long-term release of As and pH changes in stabilized soils. We compared different stabilization techniques in the field by mixing contaminated soil with 5% of either acid mine drainage sludge (AMDS), coal mine drainage sludge (CMDS), steel slag, or cement. We evaluated the results using an up-flow percolation column test to observe any pH changes and As releases from the stabilized soils up to a liquid–solid (L/S) ratio of 50 (approximately representing a 50 year period). At the initial stage of percolation (at an L/S ratio of 0.2 or 0.2 of a year of exposure), some alkaline components and any incompletely bound As in the soils washed out with the eluent. The pH of the cement-stabilized soil was approximately 12 throughout the experiment (up to 50 L/S). Adding stabilizers to the soil reduced As leaching by 54–81% (overall efficiency) compared to the control (contaminated soil only). The order of stabilization efficiency was: steel slag (55.0%) < AMDS (74.3%) < cement (78.1%) < CMDS (81.5%). This study suggests that the groundwater of the stabilized soil should be carefully monitored for the initial five years because the soluble ionic species can leach over this period.

Source water quality requirements for artificial groundwater recharge

This study was an investigation of the need for pre-treatment of a new raw water source for artificial groundwater recharge. The study was done through a column test, well sampling and survey data relating to 11 artificial recharge plants in Sweden. The column test showed that only 30% of the natural organic matter (NOM) was removed from the new raw water source during infiltration. The survey revealed that the new water source's quality was within the range requiring pre-treatment prior to infiltration. The well sampling results showed a significant correlation between the NOM-content in the raw and treated waters for WTPs without pre-treatment (r = 0.78 and ρ = 0.04), indicating one of the short-term limitations of artificial recharge. The study results indicate that the new raw water source is unsuitable for direct use in artificial recharge and that treatment is required prior to infiltration.

Evaluation of Dynamic Properties of Sodium-Alginate-Reinforced Soil Using A Resonant-Column Test

Ground reinforcement is a method used to reduce the damage caused by earthquakes. Usually, cement-based reinforcement methods are used because they are inexpensive and show excellent performance. Recently, however, reinforcement methods using eco-friendly materials have been proposed due to environmental issues. In this study, the cement reinforcement method and the biopolymer reinforcement method using sodium alginate were compared. The dynamic properties of the reinforced ground, including shear modulus and damping ratio, were measured through a resonant-column test. Also, the viscosity of sodium alginate solution, which is a non-Newtonian fluid, was also explored and found to increase with concentration. The maximum shear modulus and minimum damping ratio increased, and the linear range of the shear modulus curve decreased, when cement and sodium alginate solution were mixed. Addition of biopolymer showed similar reinforcing effect in a lesser amount of additive compared to the cement-reinforced ground, but the effect decreased above a certain viscosity because the biopolymer solution was not homogeneously distributed. This was examined through a shear-failure-mode test.

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 pH 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.

Determination of water retention curves for one residual soil and two distinct non-woven geotextiles

The water retention curves (WRC) presented in this study were determined for materials constituting prototypes of evapotranspirative capillary barrier coverage, which used gneissic residual soil and non-woven geotextile. The determination of the WRC was made possible by the hanging column test for the two distinct non-woven geotextiles and the hanging column and filter paper tests for the residual soil. Both tests were executed with both the drying and wetting trajectories. The curves were adjusted and the hydraulic conductivity functions were estimated, thus enabling a greater understanding of the hydraulic behavior of the materials involved. The non-woven geotextiles and residual soil presented WRC, as expected, similar to the WRC presented in the literature for similar materials.