Reduction In Hydraulic Conductivity Research Articles

Seawater exposure causes hydraulic damage in dying Sitka-spruce trees.

Sea-level rise is one of the most critical challenges facing coastal ecosystems under climate change. Observations of elevated tree mortality in global coastal forests are increasing, but important knowledge gaps persist concerning the mechanism of salinity stress-induced nonhalophytic tree mortality. We monitored progressive mortality and associated gas exchange and hydraulic shifts in Sitka-spruce (Picea sitchensis) trees located within a salinity gradient under an ecosystem-scale change of seawater exposure in Washington State, USA. Percentage of live foliated crown (PLFC) decreased and tree mortality increased with increasing soil salinity during the study period. A strong reduction in gas exchange and xylem hydraulic conductivity (Ks) occurred during tree death, with an increase in the percentage loss of conductivity (PLC) and turgor loss point (πtlp). Hydraulic and osmotic shifts reflected that hydraulic function declined from seawater exposure, and dying trees were unable to support osmotic adjustment. Constrained gas exchange was strongly related to hydraulic damage at both stem and leaf levels. Significant correlations between foliar sodium (Na+) concentration and gas exchange and key hydraulic parameters (Ks, PLC, and πtlp) suggest that cellular injury related to the toxic effects of ion accumulation impacted the physiology of these dying trees. This study provides evidence of toxic effects on the cellular function that manifests in all aspects of plant functioning, leading to unfavourable osmotic and hydraulic conditions.

The impact of clay dispersion and migration on soil hydraulic conductivity and pore networks

Using saline and sodic waters for irrigating agricultural lands has increased worldwide, which may cause adverse effects on soil porosity, structural stability and permeability. However, few studies have investigated the effect of clay swelling, dispersion and migration on the reduction of saturated hydraulic conductivity (Ksat) by analysing the total porosity and pore size change through the profile. In this study, two soils with contrasting mineralogy was used and packed at two different bulk densities (1.0 and 1.2 g cm−3). Soil columns were leached with three types of sodium adsorption ratio (SAR) solutions, i.e. good quality water (GQW), SAR 10 and SAR 50 solutions, before distilled water (low ionic strength) was leached through. The results indicated that the application of distilled water decreased Ksat for all soils, particularly in the initially sodic water treated columns. The Ksat of leaching with distilled water in low density columns were generally higher, but showed more degree of reduction than more compacted columns, mainly related to the high initial porosity and macropores that enabled dispersed clay to move through the soil column and out in the leachate. The application of distilled water significantly reduced the proportion of macro and mesopores, whereas increased the proportion of micropores in both soils, particularly for soil columns initially treated high SAR solutions. When the dispersed clay was trapped within the column, the depth of clay accumulation was affected by a combined effect of packing density, soil type and water quality.

Hydraulic consequences of enzymatic breakdown of grapevine pit membranes.

Xylella fastidiosa (Xf) is the xylem-dwelling bacterial agent associated with Pierce's disease (PD), which leads to significant declines in productivity in agriculturally important species like grapevine (Vitis vinifera). Xf spreads through the xylem network by digesting the pit membranes (PMs) between adjacent vessels, thereby potentially changing the hydraulic properties of the stem. However, the effects of Xf on water transport vary depending on the plant host and the infection stage, presenting diverse outcomes. Here, we investigated the effects of polygalacturonase, an enzyme known to be secreted by Xf when it produces biofilm on the PM surface, on stem hydraulic conductivity, and PM integrity. Experiments were performed on six grapevine genotypes with varying levels of PD resistance, with the expectation that PM resistance to degradation by polygalacturonase may play a role in PD resistance. Our objective was to study a single component of this pathosystem in isolation to better understand the mechanisms behind reported changes in hydraulics, thereby excluding the biological response of the plant to the presence of Xf in the vascular system. PM damage only occurred in stems perfused with polygalacturonase. Although the damaged PM area was small (2%-9% of the total pit aperture area), membrane digestion led to significant changes in the median air-seeding thresholds, and most importantly, shifted frequency distribution. Finally, enzyme perfusion also resulted in a universal reduction in stem hydraulic conductivity, suggesting the development of tyloses may not be the only contributing factor to reduced hydraulic conductivity in infected grapevine.

Entrapment of clay particles enhances durability of bacterial biofilm-associated bioclogging in sand

Utilization of bacterial biofilms and extracellular polymeric substances (EPS) for engineered bioclogging has recently garnered increasing attention in various geotechnical practices, such as leakage sealing in water-front structures, soil erosion protection, earthquake-induced liquefaction mitigation, and hydraulic barrier installation. However, the long-term durability is still questioned as to how long the biofilm-associated bioclogging would last as the biofilms readily degrade in nutrient-poor conditions. Therefore, we explore the feasibility of using fine clay particles to enhance the durability of biofilm-induced bioclogging. A series of column experiments were performed to compare the clogging durability of bentonite-associated biofilms against that of biofilms only. The results confirmed that a continuous feed of nutrients to the model bacteria, Bacillus subtilis, stimulated biofilm formation and caused a ~ 99% reduction in hydraulic conductivity of sands. However, nutrient-poor fluid flow caused instantaneous sloughing of biofilms and removal of bioclogging. By contrast, bioclogging associated with bentonite–biofilm aggregates demonstrated enhanced durability against shear detachment by fluid flows in a starved condition. EPS analysis and SEM imaging revealed that bentonite particles in the introduced suspension formed aggregates with biofilms by coating and being embedded within biofilms. This study suggests that the exploitation of bentonite–biofilm aggregations can remarkably enhance bioclogging durability in nutrient-poor conditions. This coupled clay–biofilm clogging approach is expected to provide benefits in developing a strategy for engineered bioclogging in geotechnical practices.

Retraction: Reduction in hydraulic conductivity and organic contaminants through biofilm formation on porous media (IOP Conf. Ser.: Mater. Sci. Eng. 1145 012002)

This article (and all articles in the proceedings volume relating to the same conference) has been retracted by IOP Publishing following an extensive investigation in line with the COPE guidelines. This investigation has uncovered evidence of systematic manipulation of the publication process and considerable citation manipulation.IOP Publishing respectfully requests that readers consider all work within this volume potentially unreliable, as the volume has not been through a credible peer review process.IOP Publishing regrets that our usual quality checks did not identify these issues before publication, and have since put additional measures in place to try to prevent these issues from reoccurring. IOP Publishing wishes to credit anonymous whistleblowers and the Problematic Paper Screener [1] for bringing some of the above issues to our attention, prompting us to investigate further.[1] Cabanac G, Labbé C and Magazinov A 2021 arXiv:2107.06751v1 Retraction published: 23 February 2022

Reduction in hydraulic conductivity and organic contaminants through biofilm formation on porous media

The creation of municipal solid waste produces serious ecological and community health problem throughout the world, particularly in emerging countries. Undeveloped scrapyards are the eldest and most communal method of solid waste disposal. If this is not properly managed, the migration of leachate from dump yards or landfills and the discharge of pollutants creates subsurface water pollution. Among different pollution measures, biofilm accumulation is the major choice. These studies indicate that biological barriers may be a promising technology to suppress pollutant plumes in the field. The present research focused on, the theory of biofilm aggregation in sand columns has been further to estimate the hydraulic conductivity of synthetic leachate and changes in organic pollutant concentration. Two different column research combinations were completed by using synthetic leachate as substrate solution. One column is used as a blank, and the other column is corrected with a mixed microbial culture separated from the leachate. The layered experimental mode using two different sizes of sand (0.3 mm and 0.6 mm) is used for column packing. The tower continuously supplies synthetic leachate for 50 days. Compared with the layered sand column, the hydraulic conductivity of the layered sand microbial column has the largest decrease, which is 88.42%. The analysis of organic pollutants in wastewater leachate also clearly shows that, compared with natural and synthetic liners used to control the migration of leachate in the underground environment, layered sand modified with microorganisms has appropriate remedial measures.

Pump it up! How xylem sap pH controls water transport in leaves.

Pump it up! How xylem sap pH controls water transport in leaves.

Effects of bacterial activity on the saturated hydraulic conductivity of remolded loess

Loess is widely used as a construction material in engineering projects on the Loess Plateau of China but is regarded as one of the most problematic soils due to water sensitivity. Hydraulic conductivity ( K ) is an essential parameter in assessment of water transfer in porous media. However, the influence of bacterial activity on the saturated permeability of remolded loess is still unclear and rarely being studied. We systematically studied the effects of Gram-negative bacterial activity (a common bacteria in the loess region) on the hydraulic properties of remolded loess, with the aim to better understand water flow through loess. A series of laboratory experiments were conducted to identify the variation in hydraulic conductivity under various bacterial inoculation and carbon constraint conditions. The results indicated that the K was relatively stable (0.14–0.16 m/d) at the initial phase and decreased by 81–93% reaching 0.01–0.05 m/d at the end of the experiments. The variation of hydraulic conductivity can be divided into the unaffected stage, linear reduction stage and stable stage. The growth of bacteria and the accumulation of extracellular polymeric substances occupied the pores between soil particles in the sample, which reduced the porosity and lead to the decrease of K . Higher available carbon contents and greater initial inoculum sizes speeded up the process of hydraulic conductivity reduction. The delayed effect was observed between rapid decline of hydraulic conductivity and exponential growth of bacteria. It should be highlighted that the reduction of hydraulic conductivity in the soil columns was mainly dependent on clogging in the inlet layer. Our findings provide a better insight into the change of hydraulic conductivity related to bacterial activities, and promote the reorganization of water cycle uncertainty and the prevention of engineering geological disasters in loess areas. • Saturated hydraulic conductivity decreased by 81–93% due to bacterial activities. • Delayed effect between linear reduction of hydraulic conductivity and exponential growth of bacteria. • Reduction of hydraulic conductivity is mainly due to bacterial growth in inlet layer.

Use of digital image technique to study leachate penetration in biocemented residual soil

Recently, biocementation has become a trend of soil improvement. Nevertheless, few studies were conducted in its application to improve engineering properties of fine-grained soil. In this study, digital image technique (DIT) was employed to determine the effect of biocementation via enzymatic induced calcium carbonate precipitation (EICP) technique on the leachate penetration pattern and medium-term hydraulic conductivity of the compacted residual soil made from fine-grained soil. The findings have shown that the of leachate penetration pattern and hydraulic conductivities of the EICP treated soils were considerably affected by the formation of biocementation or CaCO3 precipitation. It was found that the rate of leachate penetration was faster within the first 14 days of the test. It was also determined that at the end of 28 days, the amount of leachate penetrated the untreated soil, 0.50 M, and 1.0 M EICP treated soils were 14.16 mm, 10.08 mm, and 6.03 mm, respectively. The results have shown that EICP treatment resulted in the reduction of hydraulic conductivity by 28. 28.83% and 41.33% in 0.50 M and 1.00 M treated soils, respectively.

60-year record of stem xylem anatomy and related hydraulic modification under increased summer drought in ring- and diffuse-porous temperate broad-leaved tree species

Key messageBy combining dendrochronological time-series analysis with radial vessel features, we show that the reconstruction of hydraulic properties improves our understanding of tree species’ acclimation potential to climate change.The vascular architecture plays a crucial role in the productivity and drought tolerance of broadleaf trees, but it is not yet fully understood how the hydraulic system is acclimating to a warmer and drier climate. Because vessel features may record temporal and spatial variability in climatic signals of the past better than tree-ring width, we combined dendrochronological time-series analysis with the calculation of stem hydraulic properties derived from radial vessel features. We aimed to reconstruct the development and sensitivity of the hydraulic system over six decades and to identify climatic control of xylem anatomy for five co-existing broad-leaved diffuse- and ring-porous tree species (genera Acer, Fagus, Fraxinus and Quercus) across three sites covering a precipitation gradient from 548 to 793 mm. We observed a significant influence of the climatic water balance (CWB) on the vessel features of all species, but the time lag, magnitude and direction of the response was highly species-specific. All diffuse-porous species suffered a decline in vessel diameter in dry years, and increase in vessel density in dry years and the year following. However, F. sylvatica was the only species with a significant long-term change in anatomical traits and a significant reduction in potential hydraulic conductivity (Kp) after dry winters and in dry summers, accompanied with the largest long-term decline in tree-ring width and the largest growth reduction in and after years with a more negative CWB. In contrast, the comparison across the precipitation gradient did not reveal any significant vessel-climate relationships. Our results revealed considerable plasticity in the hydraulic system especially of F. sylvatica, but also evidence of the drought-sensitivity of this species in accordance with earlier dendroecological and physiological studies. We conclude that the long-term reconstruction of hydraulic properties can add substantially to the understanding of the acclimation potential of different tree species to climate change.

The feedback interaction between biomass accumulation and heterogeneous flow in porous media: Effect of shear stresses

Bioclogging, resulting from excess biomass growth in porous media, can influence flow, solute transport, and biogeochemical reactions in natural and remedial subsurface systems. In this study, we investigated bioclogging in heterogeneous porous media using a reactive-transport model, with a focus on the effect of shear stresses on the spatial changes of biomass accumulation and hydraulic properties. The results show that, when the shearing-induced detachment was negligible, the accumulation of biomass was mainly controlled by substrate transport. Newly generated biomass was then accumulated in the regions with high hydraulic conductivity due to the fast substrate supply, resulting in a homogenization of hydraulic conductivity. When the shearing-induced detachment was significant, newly generated biomass was less accumulated in the flow paths with higher hydraulic conductivity, and more in the pore regions with relatively low hydraulic conductivity, resulting in the increase of heterogeneity in hydraulic conductivity. The results were then used to establish a macroscopic correlation between the reduction of porosity and the reduction of hydraulic conductivity as a result of biomass growth, and to identify factors controlling such a correlation. A correlation was established and was found to be significantly affected by flow velocity and shearing-induced biomass detachment. Overall, this study indicated that flow-induced shearing is important in understanding bioclogging and its effect on hydraulic conductivity and water flow in porous media.

Impact of powdered and liquid laundry detergent greywater on soil degradation

Pressure on freshwater resources has resulted in greater greywater reuse for irrigation. Laundry greywater is one of the largest yet potentially soil damaging streams of domestic greywater. There is limited research on the susceptibility of soils with various properties to degradation by laundry greywater. Thus the aim of this laboratory study was to investigate the effect of typical liquid and powdered laundry detergent greywater application on humus removal and hydraulic conductivity on a range of urban soils from the Cape Town region, South Africa. Powdered detergent (PD) greywater was significantly more detrimental in terms of soil humus removal and decreasing hydraulic conductivity compared to the liquid detergent (LD) greywater attributed to its alkaline pH (pH 9.95) and 30-fold higher Na content. Sandy soils were the most susceptible to humus losses due to PD greywater application (7.5% soil C lost) while Fe oxide-rich chromic soils were the least (1.5% soil C lost). Granite-derived, kaolinitic soils were most susceptible to reduction in hydraulic conductivity (81% reduction) due to PD greywater application, while Fe-rich chromic soils were the least (47% reduction). PD greywater should not be used for irrigating soils due to its aggressive soil degrading qualities while LD greywater should be used cautiously.

Effect of freeze-thaw cycles on engineering properties of biocemented sand under different treatment conditions

The recently developed microbially induced calcite precipitation (MICP) method is a potentially effective and environmentally friendly technique to improve the unfavorable soil conditions. However, the durability of biotreated sand under freeze-thaw cycles has not been investigated. This study investigates the effects of freeze-thaw (FT) cycles on shear strength and shear modulus of Narmada river sand (a poorly graded liquefiable sand) treated with MICP under different conditions. The bacterial growth and biotreatment were conducted under non-sterile and environmentally uncontrolled conditions that are typically encountered in the field conditions. First, the effects of main control variables involved in the MICP treatment, specifically two bacteria strains i.e., Sporosarcina pasteurii ( S. pasteurii ) and Bacillus sphaericus ( B. sphaericus ), two treatment cycles viz. 12 h and 24 h, and different pore volumes (1 PV, 0.75 PV, and 0.5 PV) of cementation solution injection, were investigated. After 18 days of continuous treatment, the biocemented specimens were tested for unconfined compressive strength (UCS), split tensile strength (STS), hydraulic conductivity, ultrasonic pulse velocity (UPV), and shear modulus after 0, 5, 10, 15 and 20 freeze-thaw (FT) cycles. The calcite content distribution in all of the biotreated samples was also analyzed. The results demonstrated that the maximum UCS, STS, UPV, shear modulus, and reduction in hydraulic conductivity were 2333.2 kPa, 437.7 kPa, 2670 m/s, 13 GPa, and 96.6%, respectively, at 12% calcite content using S. pasteurii , 12 h treatment cycle, and injection of 1 PV cementation solution in every cycle up to 18 days. The biocemented specimens maintained almost 90% shear strength and 77% shear modulus after 10 FT cycles in 9–12% calcite precipitated samples augmented with S. pasteurii. The similar biocemented samples resulted in 14–17% and 31–35% decrease in shear strength, and 41–44% and 54–57% decrease in shear modulus after 15 and 20 FT cycles, respectively. • Non-sterile cultivation of bacteria was explored to optimize time, energy, and cost. • Bioaugmentation with two bacteria was investigated in uncontrolled environment. • Strength and shear modulus increase with the increase in calcite content. • Ultrasonic pulse velocity results showed rock-like behavior of biocemented sand. • Biocemented sand was found durable even after 20 freeze-thaw cycles.

Hydraulic conductivity and calcium carbonate content of biocemented heavy-metal contaminated mine waste soil

It is not uncommon for mining activity to generate wastes associated with negative engineering impacts include susceptibility to runoff due to the absence of vegetation, erosion, and sinkhole. Due to their high degree of permeability, movement of heavy metal contaminants in waste soils and aquifers occurs actively along with the hydrogeological parameters, and research on using biocementation methods such as enzyme induced calcite precipitation (EICP) to reduce the hydraulic conductivity is therefore beneficial. Mine waste soil collected from a copper mine in Lohan Dam, Sabah is characterized physically, morphologically, and chemically then treated with EICP under different operational parameters include curing duration (1,3,7 days), curing temperatures (5, 10, and 25 oC ), and relative density (70 and 80 %). The hydraulic conductivity was then tested using a constant head permeability test and the calcium carbonate content (%) is determined using the HCL washing method. Properties of the Lohan Dam wastes are found to be predominantly coarse grain soil of low plasticity, high specific gravity, high permeability, acidic in nature, and low organic content. Morphologically, they are composed of powdered and hardened particles with dark brown color with high amount of irregular-shaped particles. Mineralogical, Lohan Dam soil wastes contain a high level of heavy metals beyond the safety level of the Department of Environmental Malaysia. EICP treatment had to change the degree of permeability from ‘high and medium’ to ‘low’ with a 94-97% reduction in hydraulic conductivity corresponding to the amount of calcium carbonate content produced ranging 6.94-9.63%. In conclusion, relative density shows the marginal effect, curing duration, and temperature shows a more significant impact on the treatment effectiveness.

Evaluation of Injection capabilities of a biopolymer-based grout material

Injection grouting is one of the most common ground improvement practice to increase the strength and reduce the hydraulic conductivity of soils. Owing to the environmental concerns of conventional grout materials, such as cement-based or silicate-based materials, bio-inspired biogeotechnical approaches are considered to be new sustainable and environmentally friendly ground improvement methods. Biopolymers, which are excretory products from living organisms, have been shown to significantly reduce the hydraulic conductivity via pore-clogging and increase the strength of soils. To study the practical application of biopolymers for seepage and ground water control, in this study, we explored the injection capabilities of biopolymer-based grout materials in both linear aperture and particulate media (i.e., sand and glassbeads) considering different injection pressures, biopolymer concentrations, and flow channel geometries. The hydraulic conductivity control of a biopolymer-based grout material was evaluated after injection into sandy soil under confined boundary conditions. The results showed that the performance of xanthan gum injection was mainly affected by the injection pressure and pore geometry (e.g., porosity) inside the soil. Additionally, with an increase in the xanthan gum concentration, the injection efficiency diminished while the hydraulic conductivity reduction efficiency enhanced significantly. The results of this study provide the potential capabilities of injection grouting to be performed with biopolymer-based materials for field application.

Rock-like behavior of biocemented sand treated under non-sterile environment and various treatment conditions

Microbially induced calcite precipitation (MICP) is a recently developed technique for microbiological ground improvement that has been applied for mitigating various geotechnical challenges. However, the major challenges, such as calcite precipitation uniformity, presence of different bacteria, cementation solution optimization for cost reduction, and implementation under non-sterile and uncontrolled field environment are still not fully explored and require detailed investigation before field application. This study aims to address these challenges of MICP to improve the geotechnical properties of sandy soils. Several series of experiments were conducted using poorly graded Narmada River (India) sand, which were subjected to various biotreatment schemes and tested for unconfined compressive strength (UCS), split tensile strength (STS), ultrasonic pulse velocity (UPV), hydraulic conductivity (after 6 d, 12 d, and 18 d of treatment), and calcite content. The microstructure of sand was examined through a scanning electron microscope (SEM). Initially, the sand was individually augmented with two non-pathogenic bacterial strains, i.e. Sporosarcina (S.) pasteurii and Bacillus (B.) sphaericus. The stopped-flow injection method was adopted to provide cementation solutions at three different durations (treatment cycle) of 12 h, 24 h, and 48 h and three different pore volumes (PVs) of 1, 0.75, and 0.5. The pore volume here refers to the porosity which is expressed as a ratio, i.e. a porosity of 50% was used as 0.5. The results showed rock-like behaviors of biocemented sand with the UCS, STS, and UPV enhancement up to 2333 kPa, 437 kPa, and 2670 m/s, respectively. The hydraulic conductivity reduction of 96.6% was achieved by 12% of calcite formation after 18 d of treatment using Sporosarcina pasteurii, 12-h treatment cycle, and one pore volume of cementation media in each cycle. Overall, a 24-h treatment cycle and 0.5-pore volume cementation solution were found to be the optimal treatment which was effective and economical to achieve heavily cemented, rock-type biocemented sand using both bacteria.

Interfacial Shearing Behavior along Xanthan Gum Biopolymer-Treated Sand and Solid Interfaces and Its Meaning in Geotechnical Engineering Aspects

Recently, environment-friendly microbial biopolymer has been widely applied as a new construction material in geotechnical engineering practices including soil stabilization, slope protection, and ground injection. Biopolymer is known to exhibit substantial improvements in geotechnical properties, such as shear strength enhancement and hydraulic conductivity reduction, through the formation of direct ionic bonds with soil particles, especially clay particles. Moreover, the rheological characteristics (e.g., pseudoplasticity, shear-rate dependent thixotropy) of biopolymers render distinctive behaviors such as shear thinning and lubrication effect under a high strain condition, while recovering their viscosities and shear stiffnesses when they are at rest. To ensure the practical applicability of biopolymer-based soil treatment, it is important to understand the interfacial interaction (i.e., friction) between biopolymer-treated soil and adjoining structural members which can be constructed in a biopolymer-treated ground. Thus, in this paper, interfacial shearing behavior of biopolymer-treated soil along solid surfaces as well as internal shearing on biopolymer-soil matrix were explored via direct and interface shear test. Experimental results show a predominant effect of the soil moisture content on the interfacial shear behavior of biopolymer-treated soil which attributes to the rheology transition of biopolymer hydrogels. At low moisture content, condensed biopolymer biofilm mobilizes strong intergranular bonding, where the interfacial shear mainly depends on the physical condition along the surface including the asperity angle. In contrast, the biopolymer induced intergranular bonding weakens as moisture content increases, where most interfacial failures occur in biopolymer-treated soil itself, regardless of the interface condition. In short, this study provides an overall trend of the interfacial friction angle and adhesion variations of xanthan gum biopolymer-treated sand which could be referred when considering a subsequent structural member construction after a biopolymer-based ground improvement practice in field.

Empirical evaluation of sand filters to evolve practical designs for artificial recharge through dry wells

• Agricultural runoff can be filtered for groundwater recharge through dry wells. • Hydraulic conductivity of filters reduced exponentially with cumulative filtration. • Provision of sedimentation tank or raised filter helped maintain high conductivity. • The top deposition and entrapment in 5 cm accounted for 87.5% of the total sediment. • Removal of top 3–4 cm of layer resulted in 70–80% recovery of hydraulic conductivity. A laboratory based empirical assessment of hydraulics of sand filters was carried out under the compelling practical condition of exposure to alternate cycles (wet and dry spell) of filtration. The lab-scale simulations purportedly attempted to mimic the field scale condition of sediment loading in runoff as suspended sediment. The sand filters having a layer thickness of 50 cm and 30 cm with a particle size of <2 mm and 0.2–0.5 mm on the gravel-pebble base were tested for the progressive change in hydraulic conductivity and sediment removal during the filtration event under a combination of treatments using different sediment concentrations (1.5 g l −1 , 2 g l −1 , and 2.5 g l −1 ) and water heads (20 cm and 40 cm). A sharp reduction in filter hydraulic conductivity was observed in the case of higher sediment concentration. A filtration hiatus of 2 days between tests resulted in significant improvement in the hydraulic conductivity of the filter matrix. The provisions of pre-entry sedimentation trap before filtration could maintain a scaled-up hydraulic conductivities for a longer duration. A layer of additional reinforcement of an agro-net above the filter matrix, though facilitated easy cleaning after a filtration event, but resulted in a scaled-down hydraulic efficiency. Removal of the top 3 to 4 cm of the filter top could recover about 70 to 80% of the initial hydraulic conductivity. After filtration of sediment equivalent to 16.1 and 17.0 kg m −2 , the top deposition accounted for 72.07 and 73.12%, respectively, which along with the sediment entrapped in the top 5 cm accounted for more than 87% of the total sediment. A steady state concentration of sediment in the filtrate in all the above combinations was found to converge asymptotically below 0.10 g l −1 which, in a limited means used as a basis to custom designed field scale recharge filter using the sand as matrix filter.

Effect of biochar particle size on water retention and availability in a sandy loam soil

The ability of biochar to enhance the physical and hydrological properties of light textured soils is highly dependent on the characteristics of biochar including its particle size. To investigate the effect of biochar particle size on water characteristics and soil structure of a sandy loam soil, date palm biochar prepared at a pyrolysis temperature of 450–500 °C was fractioned by dry sieving into four sizes: 2–1, 1–0.5, 0.5–0.1, and <0.1 mm, and mixed in soil pots with a sandy loam soil at an application rate of 4%. The soil pots were incubated in a greenhouse for 120 days, and water content was kept at field capacity throughout the experiment. Water retention, hydraulic conductivity, and soil structure parameters were measured. Results showed that the largest increase in both water content at field capacity and available water content was observed with the smallest biochar particle size due to increased microporosity as a result to the larger internal surfaces and the porous structure of the biochar particles. Condense particle packing and increased tortuosity due to increased microporosity resulted in a reduction in saturated hydraulic conductivity and bulk density of the soil and biochar mixtures. Soil structure was improved in the soil and biochar mixtures at all biochar particle sizes, nevertheless, no significant increase in soil structures was observed among biochar particle sizes < 1 mm. The application of biochar with particle sizes < 1 mm can enhance the physical and hydrological properties of light textured soils and increase water conservation in the soil, which will help to reduce the amount of water required for irrigation. However, assessment under field conditions is required to assess the long-term effect of biochar on water characteristics and soil structure.

Hydraulic conductance of dentin after treatment with fluoride toothpaste containing sodium trimetaphosphate microparticles or nanoparticles.

To evaluate the hydraulic conductance of dentin after treatment with fluoride toothpastes containing sodium trimetaphosphate microparticles (TMPmicro) or nanoparticles (TMPnano). The dentinal tubules of bovine dentin blocks (4 × 4 × 1 mm) were unobstructed for determination of the maximum hydraulic conductance of the dentin. The dentin blocks were randomized into four groups (n = 15/group) of toothpastes (placebo, 1100 ppm F, and 1100 with 3% TMPmicro or 3% TMPnano) which were applied for 7 days (2×/day) using a brushing machine. The dentin surface (5/group) was analyzed by scanning electron microscopy. The hydraulic conductance post-treatment was measured in the other ten blocks. Thereafter, the same blocks were immersed in citric acid (pH 3.2) for 1 min, and the conductance was determined again. The data were submitted to 2-way ANOVA repeated measures, followed by the Student-Newman-Keuls test (p < 0.05). The percentage conductance reduction post-treatment for the groups were placebo = 1100 ppm F < 1100 TMPnano < 1100 TMPmicro (p < 0.001). After acid attack, the percentage reduction was placebo < 1100 ppm F < 1100 TMPnano < 1100 TMPmicro (p < 0.001). The toothpastes containing TMP showed the highest obliteration of dentinal tubules. The addition of TMPmicro to fluoride toothpaste produced a greater reduction in hydraulic conductance when compared with 1100 ppm F toothpaste. The increased capacity of toothpastes containing TMP to reduce hydraulic conductance indicates their potential to reduce symptoms of dentinal hypersensitivity.