Relative Saturated Hydraulic Conductivity Research Articles

Applying lysozyme, alkaline protease, and sodium hypochlorite to reduce bioclogging during managed aquifer recharge: A laboratory study

Alleviating bacterial-induced clogging is of great importance to improve the efficiency of managed aquifer recharge (MAR). Enzymes (lysozyme and alkaline protease) and sodium hypochlorite (NaClO) are common biological and chemical reagents for inhibiting bacterial growth and activity. To investigate the applicability of these reagents to reduce bioclogging, percolation experiments were performed to simulate a weak alkaline recharge water infiltration through laboratory-scale sand columns, with adding 10 mg/L lysozyme, alkaline protease, and NaClO, respectively. The results showed that, with the addition of lysozyme, alkaline protease, and NaClO, the average clogging rates (the reduced percentages of relative saturated hydraulic conductivity of the sand columns per hour during the percolation experiments) were 0.53%/h, 0.32%/h and 0.06%/h, respectively, which were much lower than that in the control group (0.99%/h). This implied that bioclogging could be alleviated to some extent following the treatments. For further analyzing the mechanisms of the regents on alleviating bioclogging, the bacterial cell amount and extracellular polymeric substances (EPS) concentration were also measured to study the effects of lysozyme, alkaline protease, and NaClO on bacterial growth and EPS secretion. Lysozyme and alkaline protease could disintegrate bacterial EPS by hydrolyzing polysaccharides and proteins, respectively, while they had little effect on the bacterial cell amount. The addition of NaClO significantly decreased the bacterial cell amount (P < 0.05) and thus greatly alleviated bioclogging. Although the lowest average clogging rate was achieved in the NaClO group, it can generate disinfection by-products that are potentially harmful to the environment and human health. Therefore, the biological-based method, i.e., enzyme treatment, could be a promising option for bioclogging control. Our results provide insights for understanding the mechanisms of lysozyme, alkaline protease, and NaClO to alleviate bioclogging, which is of great importance for addressing the clogging problem during MAR activities and achieving groundwater resources sustainable utilization.

Influence of electrolyte concentration, sodium adsorption ratio and cation combinations on relative saturated hydraulic conductivity of saline soil

Influence of electrolyte concentration, sodium adsorption ratio and cation combinations on relative saturated hydraulic conductivity of saline soil

Analysis of pedotransfer functions to predict the effects of salinity and sodicity on saturated hydraulic conductivity of soils

Soil sodicity and salinity are global issues associated with irrigated and non-irrigated land management. The combination of high sodium adsorption ratio (SAR) and low electrical conductivity (EC) of the soil solution decreases the saturated hydraulic conductivity of soils. Unfortunately, there have been few attempts to model the changes in saturated hydraulic conductivity in response to EC and SAR. The objectives of this study was to analyze previously developed functions to predict changes in saturated hydraulic conductivity (Ksat) with EC and SAR and to develop new simple functions to predict changes in Ksat with EC and SAR. The performance of previously developed functions were analyzed on 10 different soils. New pedotransfer functions (PTFs) were developed to predict the effects of EC and SAR on relative saturated hydraulic conductivity. The developed PTFs were able to predict the changes in relative Ksat with a geometric root mean squared error (GMRMSE) of 1.80 compared to 3.38 cm day−1 from the semiempirical function used as a module implemented by the Hydrus hydrological modeling application. A PTF was developed to predict the change in relative saturated hydraulic conductivity in soils with swelling clay minerals that does not require X-ray diffraction to quantify clay mineralogy and has the same prediction parameters used for every soil. The developed PTF can easily be used by agricultural and irrigation managers to predict the effects of irrigation water chemistry on relative saturated hydraulic conductivity.

Variations in bacterial community during bioclogging in Managed Aquifer Recharge (MAR): A laboratory study

Understanding evolution of bacterial community diversity, composition, and structure is of great importance for targeted prophylaxis and treatment of bioclogging of reclaimed water after Managed Aquifer Recharge (MAR). Based on laboratory percolation experiments, temporal variations in bacterial 16S rRNA gene copy number and community diversity, composition, and structure were investigated using real-time quantitative polymerase chain reaction (qPCR) and high-throughput sequencing in this study. During the percolation experiments, the relative saturated hydraulic conductivity (Ks') decreased from 1.0 to 0.011 at 588.3 h, indicating that a complete clogging occurred in the sand columns. Correspondingly, the bacterial 16S rRNA gene copy numbers reached a maximum of 3.9 × 109 copies per gram of sand at 180.5 h, and then decreased to 6.2 × 108 copies per gram of sand at the end of the test. Four microbial samples were collected in situ from the reclaimed water (SRW), and the clogged sand columns, namely SK0.52, SK0.08 and SK0.011, of which the Ks’ values decreased to 0.52, 0.08 and 0.011, respectively. The Chao richness index values of the bacterial community were 352, 207, 205, and 197 for SRW, SK0.52, SK0.08, and SK0.011, respectively, revealing lower species richness in the sand columns. The Shannon index values were 3.27, 2.84, 3.51, and 3.21 for SRW, SK0.52, SK0.08, and SK0.011, respectively. Meanwhile, the Evenness index values were 0.56, 0.54, 0.67, and 0.61 for the four samples in turn. This result implied that the changes in bacterial diversity and evenness were not obvious. The principal coordinate analysis (PCoA) results showed major differences in bacterial community composition between the four samples. A variety of bacterial phyla were found, among which Proteobacteria were predominant. For the non-Proteobacterial phyla, Parcubacteria, Acidobacteria, Chlamydiae, Gracilibacteria, Chloroflexi, and Saccharibacteria disappeared when moving from the raw reclaimed water to the solid porous media. Instead, Bacteroidetes and Actinobacteria were detected in the sand samples. Although some differences existed, a core group of bacteria persisted and might play a critical role during MAR bioclogging.

Effects of biological crust coverage on soil hydraulic properties for the Loess Plateau of China

AbstractBiological soil crusts (BSCs) are ubiquitous living covers that have been allowed to grow on abandoned farmlands over the Loess Plateau because the “Grain for Green” project was implemented in 1999 to control serious soil erosion. However, few studies have been conducted to quantify the effects of BSC coverage on soil hydraulic properties. This study was performed to assess the effects of BSC coverage on soil hydraulic properties, which are reflected by the soil sorptivity under an applied pressure of 0 (S0) and −3 (S3) cm, saturated hydraulic conductivity (Ks), wetting front depth (WFD), and mean pore radius (λm), for the Loess Plateau of China. Five classes of BSC coverage (i.e., 1–20%, 20–40%, 40–60%, 60–80%, and 80–100%) and a bare control were selected at both cyanobacteria‐ and moss‐covered sites to measure soil hydraulic properties using a disc infiltrometer under 2 consecutive pressure heads of 0 and −3 cm, allowing the direct calculation of S0, S3, Ks, and λm. The WFD was measured onsite using a ruler immediately after the experiments of infiltration. The results indicated that both cyanobacteria and moss crusts were effective in changing the soil properties and impeding soil infiltration. The effects of moss were greater than those of cyanobacteria. Compared to those of the control, the S0, S3, Ks, WFD, and λm values of cyanobacteria‐covered soils were reduced by 13.7%, 11.0%, 13.3%, 10.6%, and 12.6% on average, and those of moss‐covered soils were reduced by 27.6%, 22.1%, 29.5%, 22.2%, and 25.9%, respectively. The relative soil sorptivity under pressures of 0 (RS0) and −3 (RS3) cm, the relative saturated hydraulic conductivity (RKs), the relative wetting front depth (RWFD), and the relative mean pore radius (Rλm) decreased exponentially with coverage for both cyanobacteria‐ and moss‐covered soils. The rates of decrease in RS0, RS3, RKs, RWFD, and Rλm of cyanobacteria were significantly slower than those of moss, especially for the coverage of 0–40%, with smaller ranges. The variations of soil hydraulic properties with BSC coverage were closely related to the change in soil clay content driven by the BSC coverage on the Loess Plateau. The results are useful for simulating the hydraulic parameters of BSC‐covered soils in arid and semiarid areas.

En

Multilayer Artificial Neural Networks (ANNs) with the backpropagation algorithm were used to estimate the decrease in relative saturated conductivity due to an increase in sodicity and salinity. Data from the literature on the relative saturated hydraulic conductivity measured using water having levels of sodicity and salinity in different types of semiarid soils were used. The clay content of these soils is predominantly montmorillonite. The input data consisted of clay percentage, cation exchange capacity, electrolyte concentration, and estimated soil exchangeable sodium percentage at equilibrium stage with the solution applied. The data was divided into three groups randomly to meet the three phases required for developing the ANNs model (i. e. training, evaluation, and testing).The activation function selected was the TANSIG layer in the middle, while the exit function was the PURELIN layer. The comparisons between the experimental and predicted data on relative saturated hydraulic conductivity during training and testing phases showed good agreement. This was evident from the statistical indicators used for the evaluation process. For the training phase, the values of mean absolute error (MAE), root mean square error (RMSE), the correlation coefficient (r) and the determination coefficient (R2) were 0.08, 0.13, 0.91, and 0.83, respectively. The performance of the ANNs model was evaluated against a part of the data selected randomly form the whole set of data collected (i. e. data not used during the model testing phase). The resultant values for MAE and RMSE, r and R2 were 0.12, 0.16, 0.82 and 0.68, respectively. It should be noted that many factors were not considered, such as soil pH, type of clay, and organic matter, due to the limitations of the data available. Using these factors as input in ANNs might improve model predictions. However, the results suggested that the ANNs model performs well in soils with very low levels of organic matter.

Effects of a bentonite–water mixture on soil-saturated hydraulic conductivity

To reduce water loss in light-textured soils, hydraulic conductivity should be reduced by mixing the soils with some soil conditioners, e.g. sodium-bentonite. The objectives of this study were to investigate the effects of irrigation water with different bentonite concentrations (0, 0.05, 0.1, 0.15 and 0.2%) on hydraulic gradient (i) and relative saturated hydraulic conductivity (K rs) in a laboratory soil column with a loamy sand soil. Addition of sodium-bentonite to the soil increased i throughout each experiment. Furthermore, addition of bentonite reduced K rs, and a 0.2% bentonite–water concentration after infiltration of 48 mm of bentonite–water mixture (BWM), reduced the K rs value to 56% of K s. K rs was reduced as the concentrations of bentonite increased and its value reached ∼0.5 to 0.6 as the infiltration of BWM increased. The lowest value of K rs and the greatest reduction rate occurred at a bentonite concentration of 0.2%. It is concluded that BWM can be used as a channel liner. Using a 0.2% bentonite concentration resulted in a reduction in the seepage ratio from 1.0 to 0.08.

Determining the influence of stones on hydraulic conductivity of saturated soils using numerical method

Mountainous soils usually contain a large number of rock fragments (particle diameter > 2 mm), which influence soil hydraulic and retention properties. Data characterizing the properties of these soils usually describe only the fine earth (particle diameter < 2 mm). To quantitatively describe soil water movement in stony soils, their most important characteristic, i.e., the effective saturated hydraulic conductivity ( K se ), must be known. The objective of this study was to use a numerical method for estimating the saturated soil hydraulic conductivity that depends on relative stone content (stoniness), and sizes and shapes of stony parts. The method is based on a numerical version of the classical experiment of Darcy. The steady-state water flow under a unit hydraulic gradient through hypothetical soils containing stones was simulated using the two-dimensional simulation model HYDRUS-2D. Four soil textural types were considered. Special attention was paid to the moraine soil from the FIRE site in High Tatras. A relationship between the relative saturated hydraulic conductivity, K r , and the relative stone content, R v , was derived. K r ( R v ) function is decreasing slower for larger stones. Numerical results were used to propose an empirical equation to estimate K r of soils containing rock fragments of a spherical shape of various diameters.

Decrease in hydraulic conductivity and particle release associated with self-filtration in saturated soil columns

The dynamics of the process of self-filtration in soil columns have been evaluated for two soils with different structural cohesion (Balkuling agricultural soil and a mining residue) by carrying out experiments focusing on microscopic particle behaviour during filtration. Soil column experiments were set up to simultaneously measure changes in hydraulic gradients (Δ H/Δ L) along the columns and outflow particle sizes and concentrations during pressure leaching with solutions of 100, 10 and 1 mmol/L NaCl and deionised water. The lowest ionic strength has resulted in more reduced hydraulic conductivity and relatively more release of colloids associated with hydrodynamic shear and dispersion. Steady increases in hydraulic gradient (Δ H/Δ L) and corresponding decreases in relative saturated hydraulic conductivity ( K/ K o) with time were observed for both soils and follow similar trends at all column depths. The most severe increases in Δ H/Δ L and decreases in K/ K o always occurred near the inlet to the columns and the decline gradually decreased along the column. The decrease in K/ K o and increase in Δ H/Δ L were clearly influenced by the size as well as the concentration of migrating particles in the porous medium. The finer mobile particles in the mining residue were clearly more readily self-filtered at the lower concentration than the larger Balkuling soil particles producing more rapid increases in Δ H/Δ L and decreases in K/ K o. This was attributable to more effective self-filtration and more pore clogging probably due to increased development of the diffuse double layer, swelling and dispersion within the soil matrix at these concentrations.

Influence of sodium adsorption ratio on sodium and calcium breakthrough curves and hydraulic conductivity in soil columns

The paper examines the effects of electrolyte concentration and sodium adsorption ratio (SAR) on the relative saturated hydraulic conductivity (RHC) and the ionic behaviour of calcium (Ca) and sodium (Na) ions in the Na–Ca exchange complex. Batch binary exchange and saturated column transport experiments were carried out to quantify these effects using an agricultural Balkuling soil and a mining residue. Generally, RHC has been found to decrease with time, with increasing SAR, and with decreasing electrolyte concentration. The more rapid decrease in RHC in the mining residue, particularly at the lowest concentration (1 mmol/L), was consistent at all SAR values. The decreases in RHC were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching. Significant differences in RHC were observed in the passage of fronts of decreasing electrolyte concentrations for CaCl2 and SAR 15 solutions through the soil columns. These differences were attributable to structural alterations (slaking) of the media and the nature of the particles released and mobilised within the porous structure at any given point in the column. Measurements at the critical threshold concentration and turbidity concentration at SAR 15 revealed structural breakdown of the pore matrix system as evidenced by decreased RHC. The increase in SAR to 15 is initially accompanied by erratic RHC, presumably due to the break up of soil aggregates under the increased swelling forces. The less coherent mining residue soil was substantially more vulnerable to blockage of pores than the Balkuling soil in which clay particles are likely to be more readily mobilised, and hence available to re-deposit and occlude the matrix pores.

Chemical and physical behavior of two kentucky soils: III. Saturated hydraulic conductivity ‐imhoff cone test relationships

Abstract Clay dispersion is considered to be one of the most pronounced causes for reduction in soil hydraulic conductivity. The purpose of this study was to establish the dispersion potential of two Kentucky soils (Pembroke and Uniontown) as a function of solution ionic strength, solution composition (sodium absorption ratio, SAR) and pH through the quantification of a dispersion index (DI) and related the latter to soil relative saturated hydraulic conductivity (RSHC). The study demonstrated that DI increased as the electrolyte concentration decreased and the sodium adsorption ratio (SAR) and pH increased. Furthermore, the DI of the Uniontown soil was more dependent on electrolyte concentration, and SAR changes, but less dependent on pH changes than that of the Pembroke soil. The relationship between RSHC and DI also appeared to be dependent on electrolyte concentration SAR and pH. These components were shown to regulate saturated hydraulic conductivity via two mechanisms: (1) clay dispersion and (2) clay swelling. Clay dispersion was associated more with the Pembroke soil while clay swelling was associated more with the Uniontown soil. These observations were consistent with the thermodynamic exchange parameters of these two soils.