Natural Soil Column Research Articles

An investigation into the role of treatment performance and soil characteristics of soil-based wastewater treatment systems.

Soil-based onsite wastewater treatment systems (OWTS) are becoming more important for the treatment and disposal of wastewater in areas that do not have central wastewater collection and treatment systems. However, there are concerns that OWTS may have adverse effects on public health and environment. The purpose of this study is to treat wastewater using a natural soil column in order to evaluate treatment system performance. Wastewater was applied to two different natural soils at different flow rates of 9, 18 and 36 L/day. The treatment performances of wastewater and geotechnical properties of the natural soils were examined. As a result of this study, the percentage of COD and SS removal in wastewater after soil column filtration ranged from 36.2% to 80.5% and 84.4% to 97.9% respectively. pH values of wastewater after the filtration were measured at between 7.75 and 8.12. TP and TN removal rates were found in the range of 23.9-76.8% and 12.4-83.0%, respectively. The column effluent water was classified as both 'high hardness class' in terms of hardness and 'polluted water' in terms of conductivity. Column effluent water was found in 'low, medium, and high hazard' classes in terms of SAR. Whereas the PL values of the natural soils were found to increase by up to 4.8% in the filtration area, specific gravity decreased by nearly 1.1%. The values of LL, PI, maximum dry density, optimum water content, and permeability changed depending on the soil type. The UCS of the natural soils after wastewater filtration decreased by about 5.9%. It was concluded that natural soils have positive effects on treatment of wastewater in a short time.

AN EXPERIMENTAL STUDY ON TREATMENT OF DOMESTIC WASTEWATER BY NATURAL SOIL

In recent centuries, issues such as efficient use of water resources, water quality and water supply have become important for many countries. Countries have focused on developing strategies that can protect water and using water in the most efficient way including treatment of wastewater. In addition, it has become important to provide sustainability of the natural treatment systems instead of complex and expensive wastewater treatment facilities that are rapidly developing. On the other hand, the researches on natural treatment of wastewater are still inadequate. Therefore, the feasibility and performance of new stragtegies about natural treatment systems should be developed and evaluated. For this purpose, a pilot facility was developed which utilizes a natural soil-column with different gradations in order to provide the treatment of domestic wastewater. In this way, not only the wastewater treatment performances of different soils but also some engineering properties of soils affected by wastewater filtration were examined. As a result of this research, it was found that soil filtration can be effective in the treatment of wastewater subjected to pre-sedimentation and can be affected by the pollutant load of the filtration environment.

Quantifying fate and transport of nitrate in saturated soil systems using fractional derivative model

Natural soil systems usually exhibit complex properties such as fractal geometry, resulting in complex dynamics for the movement of solutes and colloids in soils, such as the well-documented non-Fickian or anomalous diffusion for contaminant transport in saturated soils. The development of robust mathematical models to simulate anomalous diffusion for reactive contaminants at all relevant scales presents a contemporary problem in computational hydrology. This study aims to develop and validate a novel fractional derivative, advection-dispersion-reaction equation (fADRE) with first order decay to quantify nitrate contaminants transport in various soil systems. As an essential nutrient for crop growth, nitrogen in various forms (i.e., fertilizers) is typically applied to agricultural plots but a certain fraction or excess that is converted to nitrate or nitrite will serve as a critical pollutant to surface-water and groundwater. Applications show that the fADRE model can consider both hydrological and biogeochemical processes describing the fate and transport of nitrate in saturated soil. Here “fate” is a commonly used terminology in hydrology to describe the transformation and destination of pollutants in surface and subsurface water systems. The model is tested and validated using the results from three independent studies including: (1) nitrate transport in natural soil columns collected from the North China Plain agricultural pollution zone, (2) nitrate leaching from aridisols and entisols soil columns, and (3) two bacteria (Escherichia coli and Klebsiella sp.) transport through saturated soil columns. The qualitative relationship between model parameters and the target system properties (including soil physical properties, experimental conditions, and nitrate/bacteria physical and chemical properties) is also explored in detail, as well as the impact of chemical reactions on nitrate transport and fate dynamics. Results show that the fADRE can be a reliable mathematical model to quantify non-Fickian and reactive transport of chemicals in various soil systems, and it can also be used to describe other biological degradation and decay processes in soil. Hence, the mathematical model proposed by this study may help provide valuable insight on the quantification of various biogeochemical dynamics in complex soil systems, but needs to be tested in real-world applications in the future.

Nickel migration and retention dynamics in natural soil columns

Nickel migration measured in laboratory-scale, natural soil column experiments is shown to display anomalous (non-Fickian) transport, nonequilibrium adsorption and desorption patterns, and precipitation/dissolution. Similar experiments using a conservative tracer also exhibit anomalous behavior. The occurrence of ion exchange of nickel, mainly with calcium (but also with other soil components), is measured in both batch and flow-through column experiments; adsorption and desorption isotherms demonstrate hysteresis. Strong retention of nickel during transport in soil columns leads to delayed initial breakthrough (∼40 pore volumes), slow increase in concentration, and extended concentration tailing at long times. We describe the mechanisms of transport and retention in terms of a continuous time random walk (CTRW) model, and use a particle tracking formulation to simulate nickel migration in the column. This approach allows us to capture the non-Fickian transport and the subtle local effects of adsorption/desorption and precipitation/dissolution. Consideration also of preferential pathways accounts for the evolution of the measured breakthrough curve and measured spatial concentration profiles. The model uses non-Fickian transport parameters estimated from the conservative tracer and, as a starting point, adsorption/desorption parameters based on batch experiments and a precipitation parameter based on Ksp values. The batch parameters are found to underestimate the actual amount of adsorption. We suggest that the sorption and precipitation/dissolution dynamics, and resulting breakthrough curves, are influenced strongly by preferential pathways; such pathways significantly alter the availability of sorption sites and ion availability for precipitation. Analysis of these results provides further understanding of the interaction and dynamics among transport, precipitation, and sorption mechanisms in natural soil.

Mobility and Interaction of Heavy Metals in a Natural Soil

We study the mobility and interaction under competing conditions observed for copper (\(\text{ Cu}^{2+}\)) and zinc (\(\text{ Zn}^{2+}\)) ions in the context of laboratory-scale experiments performed in natural soil columns. The experiments focus on the analysis of solute breakthrough curves (BTCs) obtained after injection of an aqueous solution containing similar concentrations of the two metal ions into a soil column fully saturated with double deionized water. Transport of the competing ions is tested for the same soil under aerobic and anaerobic conditions. Measurements show that the species with lower affinity for the soil, \(\text{ Zn}^{2+}\), migrates occupying all available adsorption sites, and is then progressively replaced by the ion with higher affinity, \(\text{ Cu}^{2+}\). The two ions are displaced in the system with different effective retardation. The slowest species replaces the sorbed ions, resulting in observed \(\text{ Zn}^{2+}\) concentrations that display a non-monotonic behavior in time and which, for a certain period, are larger than the concentration supplied continuously at the inlet. In the absence of a complete geochemical characterization of the system, we show that the measured concentrations of both metals can be interpreted through simple models based on a set of coupled partial differential and algebraic equations, involving a small subset of aqueous and adsorbed species that are present in the system. Depending on the model considered, the relationship between aqueous and adsorbed ion concentrations is described at equilibrium by a Gaines–Thomas (GT) formulation, a competitive Sheindorf–Rebhun–Sheintuch (SRS) isotherm, or an Extended Langmuir (EL) isotherm, respectively. The GT formulation provides the best interpretation of the observed behavior among the models tested. We find that employing these simple models, which account only for the main governing reactive processes, allows reasonable estimation of the observed BTCs in experiments where only partial geochemical datasets are available.

Water Flow Monitored by Tracer Transport in Natural Porous Media Using Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) was applied to the study of flow processes in model and natural soil cores. Flow velocities in soils are mostly too slow to be monitored directly by MRI flow velocity imaging. Therefore, we used for the first time diethylenetriaminepentaacetate in the form Gd‐DTPA2− as a tracer in spin echo multislice imaging protocols with strong weighting of longitudinal relaxation time T1 for probing slow flow velocities in soils. Apart from its chemical stability, the main advantage of Gd‐DTPA2− is the anionic net charge in neutral aqueous solution. We showed that this property hinders adsorption at soil mineral surfaces and therefore retardation. We found that Gd‐DTPA2− is a very convenient conservative tracer for the investigation of flow processes in model and natural soil cores. With respect to the flow processes in the coaxial model soil column and the natural soil column, we observed totally different flow patterns. In the first case, the tracer plume moved quite homogeneously in the inner highly conductive core only and the migration into the outer fine material was very limited. A numerical forward simulation based on independently obtained parameters showed good agreement between experiment and simulation and thus proves the convenience of Gd‐DTPA as a tracer in MRI for soil physical investigations. The natural soil core, in contrast, showed a flow pattern characterized by preferential paths, avoiding dense regions and preferring loose structures. In the case of the simpler model column, the local flow velocities were also calculated by applying a peak tracking algorithm.

Bacterial Deposition of Gold on Hair: Archeological, Forensic and Toxicological Implications

BackgroundTrace metal analyses in hair are used in archeological, forensic and toxicological investigations as proxies for metabolic processes. We show metallophilic bacteria mediating the deposition of gold (Au), used as tracer for microbial activity in hair post mortem after burial, affecting results of such analyses.Methodology/Principal FindingsHuman hair was incubated for up to six months in auriferous soils, in natural soil columns (Experiment 1), soils amended with mobile Au(III)-complexes (Experiment 2) and the Au-precipitating bacterium Cupriavidus metallidurans (Experiment 3), in peptone-meat-extract (PME) medium in a culture of C. metallidurans amended with Au(III)-complexes (Experiment 4), and in non-auriferous soil (Experiment 5). Hair samples were analyzed using scanning electron microscopy, confocal microscopy and inductively coupled plasma-mass spectrometry. In Experiments 1–4 the Au content increased with time (P = 0.038). The largest increase was observed in Experiment 4 vs. Experiment 1 (mean = 1188 vs. 161 µg Kg−1, Fisher's least significance 0.001). The sulfur content, a proxy for hair metabolism, remained unchanged. Notably, the ratios of Au-to-S increased with time (linear trend P = 0.02) and with added Au and bacteria (linear trend, P = 0.005), demonstrating that larger populations of Au-precipitating bacteria and increased availability of Au increased the deposition of Au on the hair.Conclusion/SignificanceInteractions of soil biota with hair post mortem may distort results of hair analyses, implying that metal content, microbial activities and the duration of burial must be considered in the interpretation of results of archeological, forensic and toxicological hair analyses, which have hitherto been proxies for pre-mortem metabolic processes.

The use of stream flow routing for direct channel precipitation with isotopically-based hydrograph separations: the role of new water in stormflow generation

Understanding the pathways by which event water contributes to stream stormflow provides insight into stormflow generation mechanisms. We analyze the impact of storm size on the relative contribution of event water to stormflow by using natural variations in the oxygen isotopic composition of precipitation and stream water to separate multiple stormflow hydrographs from a single fourth-order, 1212 ha catchment. We extend previous isotope-based hydrograph separations by independently accounting for the contribution of event water via direct channel precipitation to the stream hydrograph. The direct channel precipitation contribution is determined using a numerical model of stream flow routing though the catchment, taking precipitation and digital elevation data as input variables. For the range of storm sizes sampled, having recurrence intervals ranging from less than a week to ∼4 months, essentially all the event water in stream stormflow can be attributed to direct channel precipitation. Event water not directly falling on the stream channel indirectly contributes to stormflow by increasing the subsurface discharge of pre-event water to the stream. Neither the hydrograph separation data, field observations during the precipitation events, nor experimental observations of flow in a large-scale natural soil column extracted from the watershed are consistent with macropore flow or groundwater ridging as the primary mechanism responsible for increasing subsurface discharge. Results from a series of artificial rain experiments using the unsaturated natural soil column are consistent with a preferential kinematic flow model and indicate that the discharge of pre-event water to the stream during a storm event may be controlled by kinematic flow processes within the watershed soils.

Modeling in situ ozonation for the remediation of nonvolatile PAH-contaminated unsaturated soils

Mathematical models were developed to investigate the characteristics of gaseous ozone transport under various soil conditions and the feasibility of in situ ozone venting for the remediation of unsaturated soils contaminated with phenanthrene. On the basis of assumptions for the mass transfer and reactions of ozone, three approaches were considered: equilibrium, kinetic, and lump models. Water-saturation-dependent reactions of gaseous ozone with soil organic matter (SOM) and phenanthrene were employed. The models were solved numerically by using the finite-difference method, and the model parameters were determined by using the experimental data of Hsu [The use of gaseous ozone to remediate the organic contaminants in the unsaturated soils, PhD Thesis, Michigan State Univ., East Lansing, MI, 1995]. The transport of gas-phase ozone is significantly retarded by ozone consumption due to reactions with SOM and phenanthrene, in addition to dissolution. An operation time of 156 h was required to completely remove phenanthrene in a 5-m natural soil column. In actual situations, however, the operation time is likely to be longer than the ideal time because of unknown factors including heterogeneity of the porous medium and the distribution of SOM and contaminant. The ozone transport front length was found to be very limited (<1 m). The sensitivity analysis indicated that SOM is the single most important factor affecting in situ ozonation for the remediation of unsaturated soil contaminated with phenanthrene. Models were found to be insensitive to the reaction mechanisms of phenathrene with either gas-phase ozone or dissolved ozone. More study is required to quantify the effect of OH ⋅ formation on the removal of contaminant and on ozone transport in the subsurface.

Kraft mill anaerobic effluent color enhancement by a fixed-bed adsorption system

An anaerobic reactor and a fixed-bed adsorption sequential system (FBAS) were applied to remove color from kraft mill effluent. Under anaerobic conditions, Biological Oxygen Demand (BOD5) removal was between 84 to 90% w/w, while Chemical Oxygen Demand (COD) removal ranged between 46 to 55% w/w. Total phenolic compounds were poorly removed (8 to 15% w/w) whereas the color was not removed by anaerobic digestion. For the FBAS system, three different columns were packed with natural and activated (calcinated and acidified) allophanic soil and fed with kraft mill anaerobic effluent. In activated soil columns, color and total phenolic compounds removal were around 95% w/w, whereas in the natural soil column the values were 87% w/w and 81% w/w, respectively.

Mobility of herbicides in natural soil columns

Abstract A description is offered of the equipment needed to determine herbicide mobility in natural soil columns. The devices were developed to extract intact soil cores from the field and to remove the soil cores from the stainless steel tubes. The method was applied to the mobility of metamitron in two soils. Herbicide distribution along the column was determined by bioassay. The results show that pH and other physical soil parameters are related to the mobility of this herbicide.

Analysis of cooling towers on a soft soil layer subjected to horizontal incident earthquake motions from base rock

An analysis of soil-structure interaction response of cooling towers was performed based on the frequency domain response. A cooling tower is assumed to rest on a soil layer subjected to an incident earthquake motion. The analytical method makes use of the finite element scheme of a rotational shell and solid elements. In the numerical model, dashpot elements are included at the sides and bottom boundaries, with a natural soil column at the sides. The effects of radiation damping on the horizontal and downward infinite regions, as well as the internal damping of soil layers, are revealed as important, and reduce the response of towers.