Soil Clogging Research Articles

Experimental Study on the Migration and Clogging of Fine Particles in Coarse-Grained Soil with Seepage

The migration and clogging of fine particles in the pores of coarse-grained soil with seepage is of great significance to reduce the leakage of soil at the dam base and lower the permeability of soil. Therefore, the homemade infiltration test device was used to test the infiltration and clogging of soil samples with different particle size ratios D15/d85 (D15 represents the particle size corresponding to the cumulative percentage content of soil particles smaller than a certain particle size in the coarse particles which is 15%, and d85 represents the particle size corresponding to the cumulative percentage content of soil particles smaller than a certain particle size in the fine particles group which is 85%). The factors affecting the deposition of fine particles in coarse-grained soil and the characteristics of fine particle migration and penetration were analyzed. The clogging of coarse-grained soil, hydraulic gradient and pore changes characteristics before and after clogging were studied. The results show that: 1) The main factor affecting the retention of fine particles in coarse-grained soil is the particle size ratio, and the retention rules conforms to the Peak-Gauss function relationship. The penetration law of fine particles satisfies the Logistic function relationship, which can directly predict the internal clogging of coarse-grained soil. 2) The particle size ratio is the main factor affecting the blockage in each mode, followed by the influence of the water head, When the particle size ratio is less than 13.10, the clogging ratio decreases with the increase of particle size ratio, and the hydraulic gradient increases with the increase of particle size ratio. When is greater than 13.10, the clogging ratio increases with the increase of particle size ratio, and the hydraulic gradient decreases with the increase of particle size ratio. 3) The degree of clogging in coarsegrained soil is closely related to the change in porosityand and can be judged according to the change of porosity in coarse-grained soil. The research results deepen the understanding of fine particle migration on the rules of coarse-grained soil clogging and can provide a theoretical basis for related engineering applications.

Effect of salinity on the fate of pesticides in irrigated systems: a first overview.

This review investigates the impact of salinity on the fate of the active compounds of pesticides in a cultivated environment. Due to the over-exploitation of water resources and intensification of agriculture, salinity outbreaks are being observed more often in cultivated fields under pesticide treatments. Nevertheless, there is a poor understanding of the incidence of varying water salt loads on the behavior of pesticides' active ingredients in soil and water bodies. The present review established that water salinity can affect the diffusion of pesticides' active ingredients through numerous processes. Firstly, by increasing the vapor pressure and decreasing the solubility of the compounds, which is known as the salting-out effect, salinity can change the colligative properties of water towards molecules and the modification of exchange capacity and sorption onto the chemicals. It has also been established that the osmotic stress induced by salinity could inhibit the biodegradation process by reducing the activity of sensitive microorganisms. Moreover, soil properties like dissolved organic matter, organic carbon, clay content, and soil texture control the fate and availability of chemicals in different processes of persistence in water and soil matrix. In the same line, salinity promotes the formation of different complexes, such as between humic acid and the studied active compounds. Furthermore, salinity can modify the water flux due to soil clogging because of the coagulation and dispersion of clay particle cycles, especially when the change in salinity ranges is severe.

Building Information Modelling for Application in Geotechnical Engineering

BIM (Building Information Modelling) is used to create and manage data during design, construction, and operation. It helps to effectively manage resources and optimize processes in the construction industry. Geotechnical engineering is one of the complex disciplines that may require BIM integration. Various data types must be provided in a timely manner and require real-time feedback, fast processing, and construction guidance. The first problem presented in the paper is the use of the traditional 2D-based method used by engineers for a particular task. It seems to be impractical when some adjustments are included. Another issue is the lack of communication between the workers. It poses the problem of information exchange and misunderstanding during the interpretation of technical data. This paper aims to find different integration techniques and steps for integrating geotechnical data into the BIM process. Methods used to examine the topic are qualitative research, literature review, and case studies. These methods were useful for studying the problems and introducing the soil information into the BIM application. Firstly, a case study with I-BIM was considered, and the BIM–FEM–BIM interaction was applied to introduce geotechnical information with Plaxis 3D. The results have shown that further development of BIM in infrastructure is needed. Another case study explored the present state of the geotechnical design in BIM and potential solutions. The new frameworks were recreated: many boreholes were imported to the BIM, and a 3D geometric model of the entire hill was created for the hill fortification structure with soil clogging. The last two studies in Malaysia modeled a 3D subsurface and used two geotechnical formats, AGS and CVS. The first includes more information than the second; however, the second can be used for a more generalized model. Overall, BIM–FEM interaction can be used as a geometric model for data transfer. However, the open data format of the Industry Foundation Class (IFC) or geotechnical data format of the AGS and CVS were suggested to be used for greater flexibility. It was also found that excessive information makes the model loaded and complex. Therefore, it was recommended that big data be summarized properly with minimal loss of necessary data. Further research is needed to understand data transmission schemes of geotechnical information better. Moreover, it is recommended to put all the strategies directly into practice to create a geotechnical design.

On the critical particle size of soil with clogging potential in shield tunneling

Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles. However, soil clogging rarely occurs in strata with coarse-grained soils. Theoretically, a critical particle size of soils should exist, below which there is a high risk of soil clogging in shield tunneling. To determine the critical particle size, a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents. It was found that the tangential adhesion strength at the soil–steel interface gradually increased linearly with applied normal pressure. When the particle size of the soil specimen was less than 0.15 mm, the interfacial adhesion force first increased and then decreased as the water content gradually increased; otherwise, the soil specimens did not manifest any interfacial adhesion force. The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force, thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling. The critical particle size of soils causing clogging was determined to be 0.15 mm. Finally, the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.

Experimental study and field validation on soil clogging of EPB shields in completely decomposed granite

Clogging may occur inside the shield machine during earth pressure balance (EPB) tunnelling in cohesive soils. Soil conditioning can be used to reduce clogging potential and ensure the efficiency of the shield tunnelling. The current methods used to assess the clogging potential mainly focus on pure clayey soils or artificial mixed soils, the clogging in natural weathered soils is less studied. This paper studied the clogging when tunnelling in completely decomposed granite by laboratory tests, followed by field validation. In the laboratory tests, the torque and excavation speed were recorded and the soil distribution on the cutting device were analyzed. It appeared that when clogging happens, the excavation speed drops and the fluctuation in speed increases, while the torque rises as well as the fluctuations in the torque. Clogging first covers the cutters, then fill in the intervals between cutters, and finally blocked the openings on the cutting device. The opening at the central part of cutting device is of vital importance to prevent clogging. The process of clogging can be divided into three stages, the initial stage, the stabilized stage and the clogging stage. In-situ data from Guangzhou Metro Line 21 showed that clogging on cutterhead was effectively avoided when using the recommended soil conditioning scheme. Furthermore, the clogging evaluation method and process of clogging proposed are consistent with field validation and with current major clogging assessment method.

Assessment of hydraulic conductivity improvement due to vibration application at riverbank

Groundwater abstraction is a process of obtaining subsurface water sources for variety purpose of consumption. However, due to long and continuous pumping, the efficiency might decrease because of soil clogging. This decreased can be quantified and reflected as the change of hydraulic conductivity (K) values at the pumping site. This study aims to assess the variability of soil hydraulic conductivity at groundwater pumping site and also to study the effectiveness of vibration method to improve the hydraulic conductivity by comparing the result of before and after vibration is applied. The study was carried out by measuring the K values using slug test at wells MW01 and MW02 with two durations of vibration which were 45 minutes and 60 minutes. The result shows that values of hydraulic conductivity of the soil were found to have increased for both MW0l and MW02 wells. On first trial, the hydraulic conductivity increases for MW0l and MW02 are 16.7% and 39.3% while on second trial, the percentage increases for MW01 and MW02 are 54.3% and 11.1% respectively. Although the change for MW02 decreased for 60 minutes vibration, it can still be noted as there is a positive impact of vibration to the K value and further extensive data collection will be able to provide better assessment. Thus, it has been proven that the vibration method can be effective in reducing the soil clogging effect and also able to improve the hydraulic conductivity of the soil.

Soil Conditioning for EPB Shield Tunneling in Silty Clay and Weathered Mudstone

Soil conditioning technology is commonly applied to prevent mud caking and soil clogging in earth pressure balance (EPB) shield tunneling and to ensure continuous and efficient construction in highly viscous clay and weathered mudstone strata. In the note, the properties of soil conditioning agents and their interactions are investigated through a series of experimental tests and field construction applications in Changchun Metro Line 2, China. Tangential adhesion tests are carried out to learn the adhesion strength and the torque change relationship between the soil and the metal disk, by which the soil conditioning effect is evaluated. The results indicate that there is a certain interaction between the commercial foam agent and the customized anticlay agent and that the foam agent solution’s concentration and anticlay agent amount play an important role in determining the foam expansion ratio (FER) and the half-life time (HT). When the foam agent solution’s concentration is low, the anticlay agent can increase the FER and decrease the HT. When the foam agent solution’s concentration exceeds 4%, an opposite pattern is observed. It is also found that the composite application of an anticlay agent and a foam agent can significantly decrease the torque and adhesion strength of the weathered mudstone. Torque and adhesion strength can reflect the adhesion of chemically conditioned soil better than the consistency index, which has a good effect on the evaluation of unconditioned soil. Finally, field implementation indicates that mud caking and soil clogging were avoided by the application of the two conditioning agents in the EPB shield tunneling construction of Changchun Metro Line 2, China, and the thrust and torque of the shield were reduced.

Use of X-ray computed tomography for studying the desiccation cracking and self-healing of fine soil during drying–wetting paths

Managed aquifer recharge is an efficient approach using surface water for groundwater recharge. However, soil clogging in the infiltration systems represents a critical problem that reduces the efficiency of recharge systems. In recent years, much research has been conducted to investigate clogging in subsurface and surface soil (cake). Cake prevents infiltration into the water table and can drastically reduce the recharge rate. In arid and semi-arid areas, alternation of humid and dry seasons has an effect on cake cracking. In the present research, the propagation of desiccation cracking and self-healing of unconsolidated soil (cake), placed in Plexiglas columns, was investigated using X-ray computed tomography (CT) during drying–wetting (DW) paths. The results showed that during the drying path, cracks initiated at the base of the soil by friction with the bottom of the column and then propagated to the top surface of the cake. As the drying time increased, evaporation at the top surface led to more cracks growing from the surface than from the bottom of the cake. However, the cracks at the bottom tended to stabilize because the water content was greater than at the top surface. The initiation, propagation, and expansion of the cracks developed in the saturated condition of the cake. During the wetting path, some cracks were closed while others appeared. The cracks tended to close progressively with wetting time, highlighting the self-healing phenomenon, probably due to the high plasticity index of cake soil. The results showed that cake swelling is mainly related to an increase of the void ratio due to a decrease in suction between particles. The results demonstrate the capacity of the X-ray CT technique to investigate the evolution of cracks during DW paths.

Assessment of soil clogging and seed productivity of weeds on poplar black landings

Goal. Determination of soil contamination of plots planted for planting black poplar and evaluation of seed productivity of weeds.
 Methods. The level of seed productivity of the weeds was determined by the weighting method in the following sequence. In the experiment, 10 plants of one weed species were cut and manually threshed on a tarpaulin. The purified seeds were weighed and, after determining the mass of 1000 seeds, the average amount (thousand units /plant) of seeds per plant was converted.
 Results. The problem with perennial plantations of bioenergy crops is that the plants are grown for 10—15 years in monoculture on the same section of the field. Consequently, large stocks of certain weeds in the soil can significantly affect the growth and development and productivity level of cultivated plants. So, before planting a plantation, it is necessary to assess the clogging of the plots for the presence of problematic weed species, which can potentially breed on black poplar plantings and impede effective plant care. Virtually all arable land is mothballed with a different weed seed bank. Weed seed stocks depend on the direction of use of the plot, the culture of agriculture, the quality of agricultural operations on care, crop rotation, culture, etc. However, two areas with the same seed reserves in the soil are difficult to find, although the percentage of the main weed species may be identical.
 Conclusions. Weeds traditionally have high seed productivity and form large seed banks in the arable soil, reaching 1.5—2.0 million units / ha. Bioenergy crops, especially perennial species, are extremely sensitive to weeds in the first year of growing season. Because they form rather modest growths of vegetative mass and can not receive photosynthetically active energy to the soil, and therefore it is important to ensure the purity of the field from weeds during the first year of vegetation.

Micro-CT Scanning to Examine Soil Clogging Behavior of Natural Fiber Drains

AbstractThe use of jute and coir fibers as natural fiber drains to facilitate drainage and soft soil stabilization has been proposed for decades. However, their uncertain hydraulic behavior has oft...

Soil sealing by algae: An alternative to plastic pond liners for outdoor algal cultivation

Commercial production of algal biofuels is currently limited by high capital costs, particularly costs of synthetic pond liners that minimize seepage of cultivation fluids, salts, and nutrients into the subsurface beneath outdoor algae cultivation facilities. Even some profitable nutraceutical companies bear the high costs of pond liners. However, studies of animal waste holding ponds and aquaculture facilities have shown that underlying soils can effectively “self-seal”, potentially eliminating the need for plastic liners. Here, we explored the potential for self-sealing with algae to provide an alternative to synthetic pond liners in unlined algae cultivation ponds. Laboratory-scale soil column experiments were used to investigate soil clogging by algae, a topic rarely discussed in the literature. Columns composed of fine sand, loamy sand, and loam soil displayed reductions in saturated hydraulic conductivity of the entire soil column of up to two orders of magnitude in response to infiltration by the alga Scenedesmus dimorphus suspended in algal culture nutrient solution at a density of 5 × 108 cells L−1. Scanning electron microscope imaging showed a dense algal layer on the surface of each soil column, thickly coating mineral grains with algal material and filling pore spaces. The algal coating was absent in samples at >3 cm depth in the soil columns, and measurements of chlorophyll content also confirmed that algal cells were mostly confined to the soil surface. In this study, the application of an algal suspension contributed significantly to soil sealing. This new application of biological sealing technology should be studied further to determine its utility and durability as an alternative to plastic liners, perhaps in conjunction with soil compaction to achieve hydraulic conductivities beneath algal production ponds that are protective of groundwater quality.

Managed aquifer recharge: study of undisturbed soil column tests on the infiltration and treatment capacity using effluent of wastewater stabilization pond

ABSTRACT Managed Aquifer Recharge (MAR) is a useful tool for the treatment and use of sewage effluent because it complements conventional treatment, recovers the aquifer and minimizes risk of saltwater intrusion. This study aims to investigate technical data to determine the treatment of wastewater stabilization pond effluent using undisturbed soil columns collected from a coastal watershed study area within the BRAMAR (BRAzil Managed Aquifer Recharge) project. The treatment efficiency was monitored by measuring physico-chemical parameters (BOD 5, COD, DOC, TSS, NH3 and NO3) in two columns filled with undisturbed sandy soil in which sewage effluent was infiltrated under unsaturated condition for 72 days with an average input flow of 10 mm h-1. Results indicated reduction greater than 60% of organic matter, suspended solids and ammoniacal nitrogen. However, high concentrations of nitrate in the outflow were detected originating from nitrification of ammoniacal nitrogen. Moreover, difficulties in relation to soil clogging were observed. Furthermore, this study brought relevant contributions to understanding the influence of the infiltration rate and ability to treat effluent from wastewater stabilization ponds using undisturbed soil columns. Future research should be undertaken to improve the pretreatment methods and the operation of a MAR system in the study area.

Restoration of wetlands: successes and failures on scalds comprising an iron oxide clogged layer with areas of acid sulfate soils

This paper reports on successes and failures experienced over nearly two decades while attempting to remediate degraded scalds typified by iron clogged layersinterspersed with patches of acid sulphate soil on the Eastern Dundas Tablelands in Victoria, Australia. In 2004 (Gardner et al. I Overview Plant Soil 267:51–59, 2004a, Plant Soil 267:85–95, b), it was suggested that redox processes similar to acid sulfate soil reactions were acting to exacerbate and amplify salinity effects in the landscape. Soil permeability to 1 m depth was measured and compared to that at 3-5 m depths. Additional analysis of soils in the discharge zone were undertaken (mineralogy, SEM, XRF, XRD) to seek evidence of typical acid sulfate reactions which had not been found in 2004. Water quality (EC, pH) and hydraulic pressures were measured in 2005- 2006, after shallow trenchs were dug across the site, and revegetation attempted with a range of native species. Following observations of improved growth at leaking peizometers, those with above ground water levels were drilled to allow water to escape. Assessment of revegetation outcomes were conducted in 2006 and 2016. Soil permeability was lower in the upper 1 m layer of the soil than at 3-5m depth, Clear evidence of acid sulfate soil mineralogy was found, however small scale variation was the norm. Clogging of soil macropores was observed, which could be manually cleared. Fracturing the soil to increase discharge either with explosives or excavation of both shallow and deep trenchs failed because the increased discharge was insufficient to overcome evaporation and salt concentration, and redox processes continued which would eventually clog the soil again. Success was achieved with leaking piezometers to 4.5 m depth, which allowed the groundwater to reach the surface without reducing ferric oxides. Rushes planted at the discharge point maintained an oxidised environment thereby halting the redox processes. Evaporation effects were prevented because the increased discharge occurred at a point. This combination allowed a range of native species to flourish and after 10 years, to spread beyond what we estimate the leaking piezometers would support. Evaporation causing concentration of salts is very important, but this is linked to the redox processes, which cause soil clogging and reduced permeability, and thus the evaporation and salt issue. Success was achieved when the reduced groundwater could access the surface in an oxidised environment, at a sufficient rate to prevent salt concentration by evaporation. The revegetation has expanded beyond what could be supported by the original discharge, suggesting that the plants are breaking the clogged soil layers and increasing discharge. The successful colonising species typically produce specialised structures such as dauciform and proteoid roots which are able to reduce and chelate iron oxides.

A Review of Surfactant Role in Soil Clogging Processes at Wastewater Exfiltration Locations in Sewers.

Wastewater contains significant sources of pollutants and contaminants. often the failure of a pipe, inadequate sealing or corrupt pipe-connections cause the loss of raw sewage, which percolates into the nearby soil. As a consequence, a colmation layer in conjunction with soil clogging is developing, which regulates the exfiltration rate. Recently, literature has emerged that offers findings about the effects of wastewater surfactants on the change of physical properties of the soil. A survey of published literature in this field provides information highlighting the influential mechanisms of surfactants in soil clogging through physical, chemical and biological processes. Therefore, to provide a comprehensive approach, this review describes the adsorption mechanisms of surfactants on organic and inorganic particles, at gas-bubbles and at biomass. We also provided our own input to the description of the adsorption of surfactants at fluid/fluid and fluid/solid interfaces in porous media associated with the clogging process.

Research of Sands Clogging by Microbial-Induced

Experiments are designed to study the effect of soil clogging by microbial-induced calcite precipitation in the short term, and the differences clogging effect under different nutrient solution. Based on the constant head permeability test, microbial-induced calcite precipitation were performed in 2 groups of sand columns, where potato soup and nutrient solution (potato-Co(NH₂)₂-CaCl₂) were added. Changing trends of the hydraulic conductivity were presented by measuring piezometer readings regularly and soil micro-pore structure change was observed by scanning electron microscopy. Results show that clogging effects can be received for supply of potato soup and nutrient solution in order for the growth of microorganisms. The hydraulic conductivity of sand columns added potato soup could be reduced by 83.64% in 10 days, while that of sand columns added nutrient solution could be down to 99.14%. A piece of membrane material was observed, which made soil immersed in nutrient solution bond together. Few changes took place at the surface of soil that was immersed in potato soup and the soil was still in the decentralized state. Tests showed that microbial plugging technology is able to improve soil properties in a short time, achieve effective clogging, and clogging effect remains stable within a certain time.

Soil Conditioning for EPB Shield Tunneling in Argillaceous Siltstone with High Content of Clay Minerals: Case Study

AbstractSoil clogging occurred in the early construction stage of Nanchang Metro Line 1, China, when an earth balance pressure (EPB) shield passed through the argillaceous siltstone with a total content of clay minerals of 40.5%. This paper presents a new scheme for determining soil conditioning parameters to avoid the occurrence of soil clogging, taking both the slump value and the liquidity index of the soil into account. As indicated by the results of slump tests, the optimum slump value for the soil conditioning ranged from 17 to 20 cm, and a fitting function of slump value against foam injection ratio (FIR) and water content (w) was obtained. Considering the requirement for a liquidity index equal to ∼0.4–0.75 to ensure the stability of the excavation face, a chart was proposed for the soil conditioning. Based on the chart, the optimum FIR and w for the soil conditioning for tunneling in argillaceous siltstone were determined to be ∼19.2–23.2% and ∼14.2–36.6%, respectively. Taking shield parameters, ...

Numerical approach to modelling pulse-mode soil flushing on a Pb-contaminated soil

PurposeSoil flushing can represent a suitable technology in remediation of soils, sediments and sludge contaminated by persistent species (e.g. toxic metal). This paper presents a model specifically developed to evaluate the feasibility of chelating agent-enhanced flushing. The model, here applied to the remediation of real Pb-contaminated soils, was conceived also to simulate an innovative pulse-mode soil flushing technique.Materials and methodsThe soil flushing application was firstly carried out through columns laboratory experiments. Columns were filled with a real Pb-contaminated soil (3,000 mg kg−1 of dry soil) and flushing was operated in a pulse mode with different chelating agent dosages (3 and 4.3 mmol kg−1soil). Experimental results were used to calibrate and validate the developed reactive transport model that accounts for transport of ethylenediamine tetraacetic acid (EDTA) and EDTA–Pb chelate complexes, Pb residual concentration on soil and the reduction in permeability by soil dissolution. Determination of hydrodynamic and hydro-dispersive parameters was carried out through a numerical approach incorporating the use of neural network as interpolating function of breakthrough data obtained by a tracer test.Results and discussionThe EDTA dosage strongly influenced the efficiency in Pb extraction and soil permeability. Cumulative extractions of Pb were found to be 20 and 29 % for the EDTA concentrations of 3 and 4.3 mmol/kg of dry soil, respectively. The soil dissolution caused a significant flow rate decrease, as a consequence of the increase in chelating agent concentration. Therefore the recovery phase duration increased from 738 to 2,080 h. The ability of the model in simulating all the examined phenomena is confirmed by a good fit with experimental results in terms of (a) soil permeability reduction, (b) eluted Pb and (c) residual Pb in the soil.ConclusionsResults highlighted as the model, supported by a preliminary and careful characterization of the soil, can be useful to assess the feasibility of the flushing treatment (avoiding soil clogging) and to address the choice of the operating parameters (flow rate, chelating agent dosage and application method). On the basis of the present research results, a protocol is suggested for in situ soil pulse–flushing application.

Soil Clogging Genesis in Soil Treatment Units Used for Onsite Wastewater Reclamation: A Review

Onsite wastewater systems, widely used in the United States and abroad, often rely on infiltration of effluents into native soils for tertiary treatment and natural disinfection. The processes that govern soil clogging and hydraulic performance during infiltration into soil are complex and involve a dynamic interaction between physical, chemical, and biological processes. The authors link the development of soil clogging in onsite systems with the fundamental physical, chemical, and microbial processes that can occur during wastewater reclamation in soil environments. They provide a critical review of onsite wastewater systems, outlining the different types of wastewater-induced soil clogging, clogging locations, and clogging materials. The authors then focus on the influence of oxygen concentration on clogging and the environmental conditions that stimulate the accumulation of organic materials from microbial metabolism. Correlations are made between observational data in porous media studies and microbial metabolism. The objective of this review is to increase understanding of the processes that govern hydraulic performance of onsite wastewater systems during effluent infiltration and potentially improve system design and operation.

Laboratory assessment of factors affecting soil clogging of soil aquifer treatment systems

In this study the effect of soil type, level of pre-treatment, ponding depth, temperature and sunlight on clogging of soil aquifer treatment (SAT) systems was evaluated over an eight week duration in constant temperature and glasshouse environments. Of the two soil types tested, the more permeable sand media clogged more than the loam, but still retained an order of magnitude higher absolute permeability. A 6- to 8-fold difference in hydraulic loading rates was observed between the four source water types tested (one potable water and three recycled waters), with improved water quality resulting in significantly higher infiltration. Infiltration rates for ponding depths of 30 cm and 50 cm were higher than 10 cm, although for 50 cm clogging rates were higher due to greater compaction of the clogging layer. Overall, physical clogging was more significant than other forms of clogging. Microbial clogging becomes increasingly important when the particulate concentrations in the source waters are reduced through pre-treatment and for finer textured soils due to the higher specific surface area of the media. Clogging by gas binding took place in the glasshouse but not in the lab, and mechanical clogging associated with particle rearrangement was evident in the sand media but not in the loam. These results offer insight into the soil, water quality and operating conditions needed to achieve viable SAT systems.

Effect of soil fortified by polyurethane foam on septic tank effluent treatment

Fortified soil was made up of a mixture at a mass ratio 4/1000-6/1000 of sponge and natural soil according to the results of column experiment. The fortified soil had bigger porosity and higher hydraulic conductivity than the natural soil. The columns packed with 900 mm of the fortified soil endured a flow rate equivalent to 100 L/m(2)/d of septic tank effluent and the average chemical oxygen demand, nitrogen, and phosphorus removal rates were around 92%, 75% and 96%, respectively. After 100 weeks of operation, the saturated hydraulic conductivity of the fortified soil kept higher than 0.2 m/d. The bigger porosity of sponge improved the effective porosity, and the bigger specific surface area of sponge acted as an ideal support for biomat growth and ensured the sewage treatment performance of the fortified soil. The comparable performance was due to a similar and sufficient degree of soil clogging genesis coupled with bioprocesses that effectively purified the septic tank effluent given the adequate retention times.