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Electrochemical treatment and associated chemical modifications of clayey soils: a review
Abstract
Electrochemical treatment of soil, ECT is the technique of deploying an external electric potential for introducing stabilizing chemicals into the intended zone of soil improvement. The current flow modifies the basic soil-electrolyte chemistry, reflected mostly in the form of soil pH. In view of this, the manuscript reviews the alterations in clay fabric and ionic-species interactions instigated with the modifications in surface charge due to soil pH alterations. The derived consequences of system chemistry changes are discussed concerning its impact on the migration mechanisms during ECT viz. electro-osmosis and electro-migration. Though ECT is familiar to the research fraternity for decades, the attempts made hitherto for compiling the available literature on ECT are limited. Given this, by depicting the pioneering developments over time, the present study also provides a concise review of the research carried out in the area of ECT by highlighting the impact of electrochemical modifications upon the treatment efficiency.
... Initially, as the voltage gradient is applied acidic and basic front was generated at anode and cathode which causes heterogeneous ion concentration in the soil-water system. This heterogeneous ion concentration reduces the electrical conductivity of soils and releases the H+ ions in the expelled pore fluid near the anode [29,42]. ...
... Soil properties and characteristics depend on the intermediate microstructure of dispersed and flocculated soil [43,[46][47][48]. The compressibility and consolidation characteristics are the results of clay matrices, interstitial pore spaces, diffuse double layer (DDL), and soil particles aggregation [42,49] These physical characteristics can be recognized with the SEM image for all microstructure features like particle arrangements, particle assemblage and pore spaces [50] At anode front Original soil At cathode front Figure 8. SEM images of marine soil at anode, original and cathode section Figure 8 shows the induced microfabric changes within the inter-electrode space for coupled loading (4V+4kg/cm 2 ) when compared with the original soil sample. An alteration in micro-fabric can be seen in the image. ...
... However, the major contributor in this regard is the electro-migration, which is the direct migration of chemical ions under the electrical potential. A detailed description of the various mechanisms involved in the electro-kinetic phenomena can be found the review by Kollannur and Arnepalli (2019a). ...
... Whereas for electro-kinetic remediation, the soil matrix should be acidic, in order that the contaminants will remain in the dissolved state without precipitation for easy recovery. In most of the electro-kinetic applications, ¾th of the soil becomes acidic, and this is due to the higher diffusivity of H + as well as the favourable electro-osmotic flow direction (Kollannur and Arnepalli 2019a). It is obvious that such soil pH profile can facilitate the remediation attempts. ...
Naturally prevailing biological processes viz. biomineralization, biofilm formation, bioaccumulation, production of extracellular polymeric substance (EPS), biodegradation, biotransformation, biosorption, biogas generation, in the surface and subsurface environments can be adapted for altering the nature of geomaterials. Among them, biomineralization is gaining huge attention due to its widespread application. This chapter reviews the role of bacteria and different metabolic pathways involved in the carbonate biomineral precipitation along with its feasibility to implement in the field. Field-scale implementation by augmentation or stimulation and challenges faced during the MICP application process has been reviewed. The different abiotic and biotic factors affecting the mineralization process are critically discussed with the requirement of future research. The chapter further sheds light on the perspective of MICP and its successful implementation in large commercial scale.
... However, the major contributor in this regard is the electro-migration, which is the direct migration of chemical ions under the electrical potential. A detailed description of the various mechanisms involved in the electro-kinetic phenomena can be found the review by Kollannur and Arnepalli (2019a). ...
... Whereas for electro-kinetic remediation, the soil matrix should be acidic, in order that the contaminants will remain in the dissolved state without precipitation for easy recovery. In most of the electro-kinetic applications, ¾th of the soil becomes acidic, and this is due to the higher diffusivity of H + as well as the favourable electro-osmotic flow direction (Kollannur and Arnepalli 2019a). It is obvious that such soil pH profile can facilitate the remediation attempts. ...
Bauxite residue also known as red mud (RM) is a by-product produced during the extraction of alumina in bauxite or aluminium industry, by the well-known Bayer process. The Enormous quantity of red mud with its alkaline constituents imposes a substantial threat to the environment. This chapter reviews the different RM storage or disposal system used worldwide and its effect on the ecosystem. A systematic review on the effective utilization of red mud in the field of construction material, cement and concrete industry, wastewater treatment, metal recovery, etc. and its feasibility has been discussed. Further, a detailed characterization of two different red muds was carried out to utilize in a large volume in the field of construction. Though extensive use of red mud has been revealed, consumption of RM in real field condition is still not environmentally acceptable due to its strong alkalinity. Given this, neutralization of RM is a highly feasible approach for its safe disposal and utilization. Hence, different ongoing research on neutralization techniques, such as seawater, using acidic waste, CO2, sintering, microbial neutralization have also been reviewed. This manuscript is an effort to analyze the research, developments, future scope and challenges to utilize the red mud efficiently in terms of environmental concerns.
... In recent years, great attention has been paid to the remediation of heavy metals contaminated soils due to their tremendous human health risks (Eijsackers et al., 2020). Many applicable technologies have been proved to be effective for soil remediation, including engineering techniques (e.g., excavation, leaching or washing, thermal treatment and electro-kinetics) (Hasan et al., 2019;Kollannur and Arnepalli, 2019), biological remediation (e.g., microbial immobilization and phytoremediation) (Bandara et al., 2020), and agrochemistry amendment (e.g., chemical immobilization with biochar modifier) (Bandara et al., 2020;Hasan et al., 2019;He et al., 2019b). Particularly, phytoremediation using hyperaccumulators has been considered as one of the most desirable and environmentally sound remediation techniques to remove heavy metals from contaminated soils due to its simplicity, high efficiency, low cost and favorable public acceptance (Keller et al., 2005;Suresh and Ravishankar, 2004). ...
Environmentally sound disposal of hyperaccumulator harvests is of critical importance to industrialization of phytoremediation. Herein, transformation behaviors and environmental risk of heavy metals were comprehensively examined during subcritical hydrothermal liquefaction of Sedum plumbizincicola. It is concluded that low temperature liquefaction favored resource recovery of heavy oil and hydrochars in terms of higher energy density, improved carbon sequestration and less energy consumption. Heavy metals were mainly distributed into hydrochars and water soluble phase with less than 10% in heavy oil. All metal elements except As could be accumulated in hydrochars by extending reaction time, whereas more than 96% of As was redistributed into water soluble phase. Prolonged liquefaction time facilitated immobilization of Cd, Cr and As in hydrochars, but fast liquefaction favored Pb stabilization. Liquefaction significantly reduced environmental risk level of Cd, Zn and As, but may mobilize Pb and Mn, especially for Mn to very high risk level at 240 ºC. High temperature with long reaction time tended to inhibit leaching rate of Mn, whereas low liquefaction temperature with short reaction time prevented the leaching of Zn and As from hydrochars. Overall, these findings are essential for downstream upgrading of heavy oil and metals recovery from hydrochars.
Soil has been the most widely explored material for construction purpose, since our ancestors stepped out from the cave dwellings and went in search for alternate shelters. As it is the plasticity and consequent mouldability of the soil, that attracted the early humans; it is evident that the clay minerals are the prime contributors for the desired properties. In modern times, the scope of soil as a building material became wider (viz. embankments, landfill liners etc.) and the clay fraction still plays the key role in deciding the material suitability. In this regard, it is necessary to have a thorough understanding of the various elements that influence the behaviour of the clayey fraction within the soil. Among the different factors that influence the clay behaviour, soil pH deserves the prime position, as it can alter the charge distribution of the clay surface and promote mineral dissolution. In view of this, the following chapter address the role of pH in moulding the current personality that we assigned to the clay minerals. In the initial part of the discussion, the different sources and nature of soil acidity/alkalinity, and the role of soil type and genesis in influencing the same has been reviewed. Further, the extent of pH buffering offered by the soil system is discussed, focussing on the various mechanisms involved in the pH-neutralisation. The later section of the chapter discuss the ways with which pH modifies the soil properties such as fabric arrangement and surface charge. Also, the special case of soil-electrokinetic treatment is considered to demonstrate the implications of the property changes in a real life applications.
Electrokinetic is an effective and innovative method to remediate different kinds of soils, especially low permeable fined-grain soils such as silty and clayey soils. In this method, by applying a direct-current electric field into a contaminated soil resulted in different transport phenomena, the soil is remediated. This paper’s objective is to propose a numerical model for Electrokinetic remediation of zinc and copper contaminated soils. Different transport phenomena including ion migration, electroosmosis flow, and diffusion were taken into account in the model. Chemical reactions such as precipitation/dissolution, adsorption onto the soil surface, and water chemical equilibrium were considered as well. Furthermore, instead of simplified boundary conditions (Neumann or Dirichlet) that cannot properly reflect the reality of the Electrokinetic remediation process, the realistic boundary conditions were used with consideration of flux and electrolysis reaction at the electrodes. The simulation results compared with the available experimental data in the literature. The coefficient of determination and the index of agreement indicated that the present model is consistent with the tests’ results. Thus, the assumptions considered in the present study are acceptable
Keywords:Electrokinetic; Numerical Model; Zinc; Copper; Chemical Reactions; Soil Remediation
The results of undrained shear strength (Su) and stiffness (Vs) of electrochemically stabilised residual tropical laterite soil (RTLS) are presented. Calcium (Ca2+) and phosphate (PO43-) ions from calcium chloride and phosphoric acid, respectively, were injected individually and together into remolded RTLS by applying 1 and 2 V/cm direct current electrical gradient for 5 d to facilitate cementation within the treated soil. Three different systems were employed using 1.0M calcium chloride or 0.01M sodium chloride as the anolyte and 1M phosphoric acid or 0.01Msodium chloride as the catholyte. Polarity reversal was also employed in some tests. The efficacy of the treatment was based on the soil Su and stiffness. The injection of Ca2+ led to a reduction in both the Su (90%) and stiffness (8%) of the treated RTLS. The injection of PO43- resulted in improvement in both the soil Su (151%) and stiffness (20%) of the treated RTLS. The study concluded that in stabilizing the RTLS, injection of PO43- is effective whereas the injection of Ca2+ is not.
Increasing number of failures of industrial structures due to distress caused by acid contamination of foundation soils prompted the present study. This study examines the effect of highly concentrated inorganic acids on the swelling and compressibility characteristics of commercially available bentonite and kaolin clay. Two concentrations of sulphuric acid and phosphoric acid are used as pore fluids. Experimental results showed that bentonite specimens contaminated with both acids exhibited significantly lower swelling and compressions than uncontaminated bentonite. Decrease in double layer due to replacement of sodium cations by hydrogen ions is responsible for lower swelling and compressions. On the other hand, kaolin clay exhibited higher swelling with both acids than uncontaminated kaolin clay. However, compressibility marginally increased with both sulphuric acid and phosphoric acid. Formation of flocculant fabric along with mineral dissolution is responsible for deviations in compressibility behaviour of contaminated kaolin clay. The structural alteration due to acid contamination was examined by FT-IR spectroscopy.
The electro-osmosis chemical treatment (ECT) is a useful method for improving soil strength. Some laboratory tests on ECT for strengthening high-salinity soft marine soils were investigated using self-designed laboratory facilities in this research. This study focused on improving the mechanical properties by using ECT method and analyzed the effects of using CaCl2 solution on soil strength owing to the electrolyte is an important factor for improving the bearing capacity of the high-salinity marine soils. Three groups of tests with different time for consolidation were performed to analyze the effective consolidation time on the ECT. In addition, several practical issues, including the current, voltage, energy consumption and the bearing capacity of the treated soils before and after experiments, were considered in the tests. The laboratory tests results demonstrated that the ECT technique is an effective method for improving the high-salinity marine soft soils. Furthermore, the definition of the effective time for consolidation was proposed for the ECT of high-salinity soft marine soils to improve the feasibility and economical efficiency of the ECT. This study provides some references and suggestions for practical application of the ECT technique for marine soft soils.
A calagem é uma prática comum para elevar o pH do solo e aumentar a biodisponibilidade de fósforo (P) nas regiões tropicais. Todavia, o efeito da calagem na adsorção e biodisponibilidade de fósforo tem sido relatado de forma controversa. A dessorção de fósforo é um processo mais importante do que a adsorção para definir a biodisponibilidade de fósforo. Apesar disso, poucos estudos sobre a relação entre pH do solo e dessorção de fósforo são disponíveis, sobretudo nos solos tropicais. Os efeitos do pH do solo na adsorção e dessorção de fósforo num Ultissolo da Bahia, Brasil, foram investigados. A adsorção de fósforo diminuiu até 21 e 34% com o aumento do pH de 4,7 para 5,9 e 7,0, respectivamente. O parâmetro K da equação de Langmuir diminuiu e os coeficientes de partição (Kd) diminuíram junto com o pH, mantendo esta tendência. A dessorção de fósforo foi positivamente influenciada pelo aumento do pH, como reflexo da quantidade total de fósforo dessorvido e da taxa dessorvida do fósforo inicialmente adsorvido. O parâmetro K diminuiu e o valor de Kd aumentou, especialmente no valor de pH mais alto e no nível mais alto de adição de fósforo, reforçando a ocorrência do fenômeno. A calagem deste solo teve efeitos duplos de reduzir a adsorção de fósforo (até 4,5 kgha-1 de P na solução) e de aumentar a dessorção de fósforo (até 2,7kgha-1 de P liberado adicionalmente para a solução).
Recent studies suggest that diffusion may be an important, if not dominant, mechanism of contaminant transport through waste containment barriers. This paper represents the first of two papers pertaining to the measurement of diffusion coefficients of inorganic chemicals diffusing in saturated soil. In this paper, both steady-state and transient equations describing the diffusive transport of inorganic chemicals are presented. Several factors affecting diffusion coefficients are identified. A method for measuring diffusion coefficients for compacted clay soil is described. The definition for the diffusion coefficient for diffusion in soil (known as the effective diffusion coefficient, D*) is shown to vary widely. In general, variations in the definition of D* result from consideration of the different factors that influence diffusion of solutes in soil and the different ways of including the volumetric water content in the governing equations. As a result of the variation in the definition of D*, errors in interpretation and comparison of D* values can result if the appropriate definition for D* is not used.
The purpose of this study is to study a feasibility of using an electrochemical technique for improving soil mechanical properties. The experiment is performed on a use of DC current applied to a cell that contains the soil between anolyte and catholyte solutions. As a result, it is found that there is the feasibility of using an electrochemical technique to improve the soil mechanical properties. Increase in strength up to 300kPa from almost cannot resist any applied load of kaolin soil can be obtained after treated by the electrochemical technique.
In this study on the surface charges and structural characterization of kaolinite clay, it is found that the highly pH dependent edge charges are important to the interparticle forces and associated fabric formations. When the pH is below the isoelectrical point of the edge surfaces, IEPedge, the Coulombian attraction between faces and edges dominates, which favors the formation of an opened edge-to-face (EF) association and a higher final sediment volume. At pH > IEPedge, the double-layer repulsion prevails at all surfaces to result in a deflocculated and dispersed fabric, which tends to form denser soil packing in the sediment. Increasing the ionic strength (with NaCl as the electrolyte) leads to the opposite behavior in clay suspensions below and above the IEPedge: the degree of fabric flocculation and the final sediment volume decrease with an increased ionic strength at pH < IEPedge but increase at pH > IEPedge. The measured pore-size distribution reveals a distinct dual-porosity characteristic in the pH 4 with salts (0.15 mol/L NaCl) specimen: it consists of inter-aggregate spaces (~1.10 µm) and intra-aggregate pores (~0.30 µm). Soils with a higher degree of EF flocculation due to the prevailing Coulombian or van der Waals attraction can render a higher liquid limit.Key words: pH, fabric associations, isoelectrical point, dual porosity, interparticle forces, liquid limit.
The electrochemical stabilization processes are studied in a calcareous soil recovered from the Western Australia coast and on the interface of calcareous soil and steel foundation. A series of experiments are performed to study the effects of two chemical agents used in electrochemical stabilization tests. The strengthening effects of electro kinetics and electrochemical treatments on the calcareous soil are investigated first. Significant increases in the undrained shear strength and effective cohesion are obtained after all tests, and the most significant improvement is found after the electrochemical treatment using a 15% CaCl2 solution as the stabilization agent. Subsequently, an electrochemical test is carried out on the calcareous soil with an embedded steel plate to simulate a part of a caisson foundation, using CaCl2 as the stabilization agent. In this test, the practical considerations for later large-scale tests and ultimately for field implementation are taken into account in the design, including factors such as the attachment of electrodes to the foundation, injection of the stabilization agent via perforated pipe electrodes, and distributions of voltage and electrical current in the soil. The result of this test reveals a 700% increase in the steel plate axial load capacity after 7 days of treatment with an applied voltage of 4 V. The main features of the approach are that it generates virtually no disturbance to the soil and the treatment is targeted at the soilstructure interface. With further development, the electrochemical treatment may be applied in offshore engineering for stabilization of foundations installed in weak calcareous soils.Key words: calcareous soil, offshore foundations, soil improvement, chemical stabilization, electrokinetics.
A thermodynamic analysis supported by experimental measurements show that electro-osmosis depends fundamentally on the exchange capacity of a soil, water content, and electrolyte concentration of the pore fluid. Electro-osmosis and streaming potential are equivalent phenomena; one can be determined from the other. Guidelines are established for judging the feasibility of electro-osmotic dewatering in soils.
This paper presents results of a laboratory investigation aimed at evaluating the influence of alkali on physico-chemical characteristics of kaolinitic clays. A series of experiments, atterberg limits, free swell index, specific gravity, cation exchange capacity, specific surface area, X-ray diffraction, scanning electron microscopy and Oedometer free swell test, were performed on two tropical kaolinitic clays. Based on the results, it was found that the amount of kaolinite mineral in clay significantly influences its behaviour . Once alkali attacked nucleus of clay mineral, the behaviour of clay was governed by the formation of sodium or potassium aluminosilicate complex (zeolite minerals), as evidenced by mineralogical and morphological studies. Swelling results on typical samples clearly illustrated that the plasticity properties could not be a true indication of swelling behaviour of alkali-contaminated clays unlike natural clays. Overall, mineralogical, chemical and physical analysis showed that the behaviour of alkali-contaminated clays cannot be elucidated without multi-phase characterization techniques.
Electro-kinetic properties of colloidal substance can be studied in terms of its zeta potential, which indicates the stability of the colloidal system. Numerous investigations have been made in the past several decades in areas of electro-kinetic remediation and stabilization of fine-grained soils. A proper understanding of the underlying mechanism of the above processes demands a thorough knowledge of the zeta potential of the system. Further, the electro-kinetic process can significantly alter the physio-chemical and electrical properties of the clay-water-electrolyte system which is also manifested as a change in the zeta potential value. Various environmental factors that affect the zeta potential include temperature, electrolytic concentration, cation valency and pH of the medium. The investigations made in view of understanding the role of zeta potential in determining electro-kinetic efficiency of various soils are widely scattered and no attempts have been made so far to interpret the available data, making it difficult to arrive at any conclusive inference. In this context, the present study attempts to evaluate the investigations carried out, by the previous researchers, to identify the factors that are influencing zeta potential and its role on electro-kinetic properties of clay minerals. In addition, zeta potential measurements are conducted on kaolinitic type and Na-bentonite soils over a wide range of pH and the results are compared with the data available in the literature.
The present study describes the calcium adsorption behavior of clays exhibiting distinct mineralogical composition. The adsorption characteristics were determined using conventional batch-equilibrium sorption method, and different theoretical models were applied to describe the equilibrium sorption isotherms. The variation in calcium adsorption capacity was determined as a function of clay mineralogy, temperature and pore fluid chemistry. Further, the thermodynamic parameters were also calculated to describe the nature of adsorption mechanisms. Significant variation in calcium adsorption potential was observed among the clays, primarily attributed to their mineralogical diversities and related unique surface charge properties. The adsorption density escalated with rise in calcium concentration, temperature and pH of the adsorption system. These observations can be attributed to surface charge modifications and mineral dissolution properties of the clays, which in turn resulted in higher electro-negativity of the clay surface and thereby enhancing the affinity for calcium ions.
Electroosmotic chemical treatment can be used to improve clay strength. However, this improvement is often limited to regions near the anode and/or cathode, while the areas between the electrodes remain weak. The objective of this study was to develop a suitable method to improve the clay strength throughout the entire sample. The characteristics of the test clay were studied by varying the concentration of the calcium chloride (CaCl2) solution, injecting a potassium hydroxide (KOH) solution to neutralize the acidic conditions in the anode area, using a fresh sodium silicate solution in the anode compartment, and constantly injecting deionized water after injection of the sodium silicate solution. The results indicated that an increase in the concentration of the CaCl2 solution reduced the efficiency of injecting the sodium silicate solution in the subsequent treatment stage. The use of a fresh sodium silicate solution may increase the efficiency of injecting the sodium silicate solution into clay, thereby extending the improvement range. When deionized water was injected constantly after injection of the sodium silicate solution, the Ca2 + ions in the clay migrated toward the cathode during treatment and, simultaneously, a highly alkaline condition formed near the cathode, leading to an enhancement of the pozzolanic reaction and a significant increase in the clay strength near the cathode. Based on these results, an ECT test was conducted using a fresh sodium silicate solution and constant injection of deionized water. The results indicated that the strength of the entire clay sample was improved.
Electro-osmosis has been extensively employed as an effective method for the de-water treatment of soils and thus the reinforcement of weak soils. At the microscopic level, this treatment process is inherently complex due to in situ chemical and electrochemical reactions, migration of ions and particles, and the dependence of Zeta potential of various particles on the local pH value in the soil. This complexity has hindered further understanding of mechanisms underlying the electro-osmosis technology. Here, we design an external electric field in which alternating pulse wave potentials were partially used to adjust the pH value of the soil and manipulate the dynamics of in situ formed nanoparticles and their inter-connectivity. The experimental results reveal that the in situ formation of Ca-rich particles, instead of water drainage, may serve as the main mechanism underlying the observed soil reinforcement when using calcium chloride as the treatment electrolyte. The inter-connectivity of such particles may be the key for the shear strength improvement without significant settlement of the soil.
We implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H⁺, (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction.
Electroconsolidation or electroosmosis of the soil is the movement of water from anode to the cathode when the electric current is applied to the soil through electrodes. The flow of water to the cathode is due to the electroosmosis (movement of water), electrophoresis (movement of soil particles), and electromigration of ions. In reclamation areas when the sediments of high moisture content are poured into the paddocks, they undergo a sedimentation process until the moisture content of the sediments reduces and the dredged sediments settle. Construction on these areas is not possible until the soil gains enough strength through consolidation, which takes a long time due to its low permeability. In this study, the potential application of electrokinetic stabilization to accelerate the settlement and dewatering of dredged sediments is investigated, along with the effect of irregular intermittent electric potential, type of drainage (singly and doubly), and efficiency of the method based on power consumption and soil resistivity.
Electro-osmosis is considered promising in effectively strengthening silts. This has been an urgent issue for engineers as large volumes of silts are being generated each year and need to be properly disposed. Electrode material is one of the key elements for the electro-osmosis technique. Inconsistent results have been reported in the existing literature on common electrode materials. To clarify these discrepancies and to optimize the electrode material, laboratory tests were performed with four common materials, namely, iron, graphite, copper and aluminum, under three levels of voltage gradient. Observations were performed from the perspectives of the electro-osmotic effect and the ionic strength. As for the former perspective, the electro-osmotic effect was denoted by the drainage, the water content and the effective potential. The graphite electrode was found to perform better at high potentials than iron or copper. The copper electrode exhibited a rapid decrease in the effective potential and current. As for the latter perspective, contents of Fe, Cu and Al were detected in the drainage and soils. Aluminum ions were demonstrated to have higher migration capacities than iron or cupric ions. Further analysis determined that electro-osmosis relies on ions in the original soils instead of those generated by electrode reactions. In conclusion, iron is recommended as the preferable electrode material for electro-osmosis. The performance of different electrode materials is directly reflected by the voltage loss rather than by the ion migration process. The voltage loss can be attributed to various factors, such as corrosion, electrochemical passivation, gas evolution, decomposition and electrochemical potential. The results of this paper provide deep insight into the influence of the electrode material on the electro-osmotic process.
A general model of electroosmosis for small Debye length is developed. It is applied to electroosmosis in a cylindrical capillary and by means of a capillary model to porous media. The model predicts the transient behavior of concentration fields for a set of chemical species in solution which are transported by convection, diffusion, and migration in an electric field. The species are also involved in rapid dissociation-association chemical equilibrium reactions and electrode reactions. Calculations based on the model are compared with experiments in compacted clay samples studying the transient process of electroosmotically displacing an initial saturating solution, which contains a dissolved organic acid, by a purging solution. The effect of organic acid concentration on the degree of removal is analysed. The results of preliminary experiments demonstrate that a high degree of removal (> 94%) can be achieved using electroosmosis. It is shown that the pH variations induced by electrode reactions can control the degree to which the organic will be removed by determining the valence of the acid molecule.
Stabilization of a kaolinite bed by the electrochemical injection of aluminium and phosphate ions has been investigated. Electrical gradients of 2 V / cm or less constituted the predominant driving force for ion transport under a 433 μA/cm2 constant direct current density. The changes in the kaolinite properties and pore fluid characteristics due to electrokinetic treatment were analysed. Average increases in undrained shear strength of 500-600% were observed for phosphoric acid and aluminium sulfate/phosphoric acid treatments of the kaolinite. Electrokinetic processing caused an average increase of 30% in the Atterberg limits. It is hypothesized that injection of phosphate and aluminium ions into the kaolinite specimens modified the pore fluid, leading to an increase in shear strength by ion exchange and precipitation mechanisms. However, the strength increase observed was not homogeneous throughout the specimen.
The results of shear box and consolidation tests on electrokinetically-treated tropical residual soil are presented. Injections of selected chemicals (calcium chloride, aluminium chloride and phosphoric acid) into the soil samples at the anodes or cathodes were carried out in cylindrical electrokinetic cells via applications of 30 V DC electrical potential for 168 h. Four different open-anode and open-cathode electrokinetic systems utilising different anolytes and catholytes were employed to treat the soil samples. The shear resistances of the treated soil utilising distilled water as the anolyte and 1.0 mol/l phosphoric acid as the catholyte was enhanced, whereas the treated soil near the cathode showed significant reduction in compressibility. Soil treated utilising the other chemicals showed no significant changes.
This paper describes the effect of improvement against liquefaction by using electrohoresis of Fixative materials in model ground. As a result of being electrohoresis at some Fixative materials, it was found that the case of using solution before mixing Sodium silicate No.3 and Calcium chloride is the most effective of soil improvement. And the effective voltage radient is 1.0V/cm, but the distance between electrodes is 100 cm, the strength of improved ground is decreased at the center part. There is a possibility that temperature variation in ground under electric loading has an influence on strength of improved ground.
Previous studies show that improved soil strength is usually limited to regions near the anode or cathode in electroosmotic chemical treatments. Laboratory studies have shown that a suitable operation process strengthens soft clay for the entire specimen, from the anode to the cathode. The suitable operation process first injects a calcium chloride solution until the current decreases, and then injects a sodium silicate solution until there is no drain from the cathode during electroosmosis. A field test was carried out in this study to verify the suitable operation process and to assess the effectiveness of this treatment. The results indicate that the region of improvement was expanded from the anode to the cathode (except near the anode) by the suitable operation process and reveal homogeneous strength distributions over the region of improvement and an overall increase in strength. The largest cone resistance was near the cathode and measured 4,500 kPa, an increase in 300 %. A significant increase in cone resistance was also found near the middle, between the anode and cathode, and measured 3,700 kPa, which is an increase in 280 %. The average cone resistance and undrained shear strength from the anode to the cathode increased 125–130 %. The suitable operation process of electroosmosis chemical treatment is therefore proven to be effective in a field-scale test.
The injection of calcium chloride solution through the anode during electroosmosis has been shown to be effective in strengthening soft clay. The objective of this study was to investigate the mechanism responsible for this improvement using a kaolinite. Several types of samples were prepared, including a sample directly taken from the clay near the cathode after the completion of an electroosmotic chemical treatment test and samples of kaolinite mixed with different concentrations of calcium ion solutions and cured for various times. A mechanical strength test and chemical and mineralogical analyses were performed to examine the properties and compositions of the samples. Results showed that some crystalline products could be formed in an alkaline environment of pH around 10 or after a short treatment time. The products filled some of the clay voids, causing a moderate increase in clay strength. In a strongly alkaline environment, calcium silicate and/or aluminum hydrate would be formed with a longer curing time, leading to a substantial increase in clay strength. Therefore, raising the concentration of the injected calcium chloride solution, enlargement of the applied electric voltage and extension of treatment time could result in greater clay strength.
a b s t r a c t In this research, four new chemical grout reagents were used, namely, sodium silicate, cal-cium chloride, calcium oxide, and aluminium hydroxide. The injection of the chemicals through the soil by using an electrokinetic method was successfully performed. Increase in the shear strength of stabilized soil was higher in the locations near the cathode and the calcium oxide showed the highest increment. The soil microstructure is comprehen-sively changed due to the change in the pH of the soil, and fluid flow during the electroki-netic application depends upon time and location of samples taken along the cell. The EDX output of natural peat showed the presence of oxygen (46.2%), carbon (29.3%), silica (5.1%), alumina (2.5%), and calcium (3.0%). However, after electrokinetic injection of the sodium silicate, calcium oxide, calcium chloride, and aluminium hydroxide, the concentration of these elements in the soil samples taken adjacent to the anode changed, with the carbon changing to 24.
Electro-osmotic stabilization has long been studied as a soft soil improvement technique, while the influence of an applied electrical field on the soil microfabric and minerals is always ignored. In this study, three laboratory experiments were conducted on sodium bentonite using copper, iron and graphite electrodes to investigate the microfabric and chemical composition change before and after electro-osmotic stabilization. The soil samples near the anode were identified using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The microfabric of the sodium bentonite changed from flocculated fabric to aggregated fabric after electro-osmotic stabilization. Regular calcium sulfate tubes were generated near the copper and iron anodes. EDX tests showed that the content of sodium near the anode decreased, while the copper, iron and calcium presented substantial increase, indicating that the sodium ions were substituted by copper, iron, and calcium ions in copper, iron and graphite experiments respectively. The change of microfabric and the ion exchange reactions between sodium, copper, iron and calcium ions are the main reasons for the significant decrease of the plasticity index and free swelling ratio.
The feasibility and efficiency of transporting lead under electric fields are investigated at pilot scale in three 1 t Georgia kaolinite specimens spiked with lead nitrate solution and at an electrode spacing of 72 cm. Enhancement methods such as cathode depolarization and/or catholyte neutralization techniques are not used in processing. A constant direct current density of 133 {micro}mA/cm{sup 2} is applied. Two of the tests are conducted on specimens spiked with lead at concentrations of 856 mg/kg and 1,533 mg/kg. The third test is conducted on a 1:1 mixture of compacted kaolinite/sand spiked with lead at a concentration of 5,322 mg/kg. Lead was transported toward the cathode and precipitated at its hydroxide solubility value within the basic zone in direct contact with the cathode compartment. Subsequent to 2,950 h of processing and an energy expenditure of 700 kWh/m{sup 3}, 55% of the lead removed across the soil was found precipitated within the last 2 cm close to the cathode, 15% was left in the soil before reaching this zone, 20% was found precipitated on the fabric separating the soil from the cathode compartment, and 10% was unaccounted. Heavy metals and species that are solubilized in the anodic acid front can be efficiently transported by electromigration under an electrical field applied across electrodes placed in soils.
A laboratory-floor experimental study was conducted on the electrochemical cementation of calcareous sand for offshore foundations. A caisson, 200 mm in diameter and 400 mm long, was embedded in a calcareous sand under seawater. The calcareous sand and seawater were recovered from the coast of Western Australia. Installed around the caisson were 12 electrodes, made of perforated steel pipes 14 mm in diameter and 450 mm long and filled with soluble CaCl2 granules as a cementing agent. A dc voltage of 8 volts with current intermittence and polarity reversal was applied over a period of 7 days to transport the cementing agent into the pores of the calcareous sand. The results of the treatment were assessed by a pullout resistance test, after which the caisson was pushed back into the soil and the treatment repeated to simulate post-failure recovery. The results showed that the pullout resistance of the foundation model after the electrochemical treatment increased by 140% prior to failure and increased by 255% post-failure, as compared with that of the control test. The cementation generated by the electrochemical treatment was evidenced by the attachment of cemented soil to the electrodes and caisson. The cementation effects were further confirmed by the mineralogical, chemical and XRF analyses, which indicated formation of synthetic calcite, calcium iron chlorate and iron oxide, compounds known as cementation agents in soils. Copyright © by The International Society of Offshore and Polar Engineers.
The electroosmotic improvement of silty clay using calcium chloride and sodium silicate solutions as injection materials was studied. A series of laboratory tests were performed on reconstituted samples in order to assess the probable effectiveness of electroosmotic treatment with injection. Results indicate that the two injection materials can be effectively introduced into silty clay by electroosmosis. Very stiff cemented soil, approximately 5–6 cm in diameter, surrounding the anode, was formed due to cementation reactions between the two injection materials and soil particles under the electric field. It is justified to assume that pozzolanic reactions were responsible for the formation of very stiff cemented soil. In addition to the area of very stiff cemented soil, the region of improvement was also expanded to the cathode, near which the undrained shear strength of soil was increased by an average of approximately 195%. It was also found that the technique of polarity reversal was unnecessary for the employment of calcium chloride and sodium silicate solutions as injection materials.
This paper describes work currently underway at the University of Birmingham concerning the application of electrokinetic stabilisation to clay soils. Electrokinetic stabilisation combines the processes of electroosmosis and chemical grouting, and is most effective in silty and clayey soils where the hydraulic conductivity is low. This paper introduces electroosmotic theory and an overview of the research performed to date. Field trials are reported in which electrokinetic stabilisation is performed in a silty clay to a depth of 1.1 m below ground level. The electrodes were perforated steel tubes driven into the ground at a spacing of 2.5 m. Sodium silicate and calcium chloride solutions were introduced at the cathode and anode respectively. The results indicated significant increases in the pore water pressure close to the anode and reductions generally in the pH along the test section. However, the pH was significantly raised close to the cathode, thereby potentially creating the conditions for traditional stabilisation reactions to occur. The pore water flow was sufficiently great to inhibit the migration of silicate ions from the cathode, and only when the silicate solution was injected between the two electrodes did it enter the ground. There was an increase in plastic limit midway between electrodes after 16 days, whereas closer to the anode there was a reduction, possibly as a result of electrode degradation.
A theory, based on the Nernst‐Planck equations, is presented for pH gradient development during the electrochemical processing of soils. Its premises and consequences are discussed in terms of using electrochemical techniques for the decontamination of polluted media. Formation of an acidic front at the anode from water electrolysis and the induced electro‐osmotic flow of pore fluid contribute to facilitate removal of contaminants. The model provides a first‐order, mathematical framework to examine the flow patterns and chemistry generated in electro‐osmosis. Analytical solutions are compared with the numerical results obtained by the finite element method (FEM) and with some preliminary experimental results. Upstream‐downstream effects are included but consolidation effects, neutralization, and ion exchange reactions need to be quantified and incorporated into the model. The physical basis of electro‐osmosis phenomenon needs to be better established. Modelling approaches of this type should assist scale‐up of this technology for common inorganic toxic pollutants removal.
The effect of electroosmosis with injection of saline solutions on a silty clay was studied. A laboratory testing program was performed to assess the probable effectiveness of electroosmosis with the injection of saline solutions. Results indicate that the effect of electroosmosis can be enhanced and the treatment time can be shortened by the injection of saline solutions during electroosmosis. The average undrained shear strength of the soil treated with electroosmosis for 7 days after initial injection of the CaCl2 solution was 5.0 times that of the untreated soil and 1.25 times that with electroosmosis only. The treatment time was also shortened by 40% for the injection of the CaCl2 solution during electroosmosis, compared with electroosmosis only. The quality of electroosmotic improvement could be enhanced by injecting solutions of higher valence, concentration and by applying higher electric potential. However, the improvement was limited to the area near the anode unless the treatment time was increased to ensure that no water was drained from the cathode.
(Cationic–electrokinetic) soil improvement was shown to be an effective technique for delivering, homogeneously, stabilizing agents into soils. The results of the electrokinetic-stabilization procedure using the K+ and Ca2+ ions as stabilizing agents varied according to the type of the stabilizing ions. The plasticity index of the natural soil (PI=40) was reduced to 32 for the Ca2+-stabilized soil, and to merely 8 for the K+-stabilized soil. The free swell value was reduced from 14% for the natural soil to 3.1% for the Ca2+-treated soil, and to only 0.4% for the K+-treated soil under identical conditions of dry density and initial moisture content. The friction angle was increased from ϕ=24° for the natural soil to 30.9° for the Ca2+-treated soil, and to 36° for the K+-treated soil under identical conditions.
Most previous studies and applications of electrochemical stabilization of soils through electroosmosis have been made on clayey soils. The object of this investigation was to find out if relatively small amounts of clay (1.5%-3.5%, by weight) present in a sandy soil would be enough for stabilization and strengthening to be possible. The results indicate increases of cohesion of the order of 100-200 lb./sq.ft. X-ray analyses of treated soils indicate that sheet structures of clays are reduced and silicates destroyed upon treatment by electroosmosis. Newly-formed minerals also cement the soil. These neoformations include gibbsite, limonite, calcite, hydrohematite, hydrogoethite (hydrolepidocrocite), hisingerite, allophane, allophanoid, gypsum, hematite, magnetite, nontronite, trona and natron (Na2 CO3, 10H2O). The process seems to be irreversible.
Electrochemical properties of silicate minerals govern their behavior in processes such as flocculation and enhanced oil recovery that can occur at elevated temperatures. Knowledge of these properties as a function of temperature can be helpful in developing an understanding of the role of these interfacial properties at non-ambient temperatures. The zeta potential of sodium kaolinite and quartz has been determined as a function of temperature in this work. Both systems exhibited markedly different behavior at higher temperatures and also exhibited significant hysteresis. The results were examined in terms of possible dissolution of the minerals and surface reactions at different temperatures.
The results of a laboratory study demonstrate the significant potential of electrogrouting, a new method for stabilizing soft soils with relatively low hydraulic conductivity. The experiments reported show that migration of stabilizing ions through soil pore fluid under applied direct current (dc) electric fields can be substantial. The method can achieve a more stable soil (i.e., less compressibility and higher shear strength, among other property improvements) without causing significant volume changes. In the experiments reported, the effect of stabilizing Boston Blue Clay (BBC) samples using phosphate ions was investigated. Initially, batch tests were conducted by mixing BBC samples with specific volumes of phosphoric acid solutions prepared at different concentrations. An increase of as much as 280% over the initial strength was achieved at the highest concentration of the acid used (10% of concentrated phosphoric acid solution). From the success of these batch tests, electrogrouting experiments were conducted by placing the soil in special treatment cells and applying a constant voltage gradient for 2 weeks. Electrogrouting the BBC under 1 V/cm dc is 15 times faster than is injection under a unit hydraulic gradient and produced increases in shear strength across the soil, with the greatest strength gain (160% of the initial shear strength) occurring in the soil section near the cathode (negatively charged probe). Additional results show the effects of electrogrouting on soil compressibility. A detailed review is given of the considerations necessary to implement the electrogrouting method in the field.
Synopsis
Clay soils were strengthened by introducing aluminium into the soil under an electrochemical gradient. Changes in both the composition and physical properties of the treated soils were investigated. The role of pH and pH buffering during treatment was also examined.
Strength increases or decreases in the treated samples were separated into three components: those caused by a change in water content, electroosmotic effects; those caused by age hardening, thixotropic effects; and those caused by electrochemical action, ion exchange and mineralization. Nearly all treated samples exhibited some degree of electrochemical hardening. Induration was most pronounced in ahigh water content, high pH, bentonitic soil due largely to hydroxy–aluminium interlayering in the clay. In a low pH. illitic soil interlayering was negligible and hardening appears to have resulted primarily from ion exchange.
Both X-ray diffraction and selective extraction methods were used to determinethe distribution and mode of occurrence of aluminium in the treated samples. Mineralization by aluminium in bentonitic soils was speeded and intensified by buffering the catholyte with carbon dioxide. Induration tended to occur slowly as evidenced by a time dependent strength increase, exclusive of reversible, thixotropic effects, in most samples after treatment.
Des sols argileux furent consolidés en introduisant de l'aluminiumdans le sol selon une tension électrochimique d'une valeur croissante. On examina des changements présentés à la fois par la composition et les propriétés physiques des sols traités. On examina aussi le rôle de pH et de l'effet stabilisateur du pH pendant le traitement.
On sépara les augmentations ou diminutions derésistance des échantillons traités en trois composantes: celles causées par un changement de la teneur en eau, les effets électro-osmotiques; celles causdées par un durcissement du à l'age, les effets thixotropiques: et celles causées par I'action électrochimique, échange d'ions et minéralisation. Presque tous les échantillons traités firent apparaitre un certain degré de durcissement électro-chimique. Le durcissement était le plus prononcé dans le cas d'une teneur en eau élevée, d'un pH élevé d'un sol bentonitique dû en grande par-tie à l'interposition de couches d'hydroxy-aluminium dans l'argile. Dans le cas d'un pH faible.l'interposition de couches de sol illitique était négligeable et le durcissement paraît avoir résult´ en premier lieu d'un échange d'ions.
On a utilisé à la fois la radiocristallographie par diffraction et les méthodes d'extraction sélective pour établir la répartition et le mode de présentation de l'aluminium dans les échantillons traités. La minéralisation au moyen de l'aluminium dans les sols bentonitiques se trouvait accélérée et intensifiée en stabilisant l'action du catholyte au moyen de gaz carbonique. Le durcissement avait tendance à se produire lentement comme en témoignait une augmentation de résistance en fonction du temps, les effets réversibles. thixotropiques mis à part, dans le cas de la plupartdes échantillons aprés leur traitement.
The physico-chemical changes in clay soils due to the application of electrokinetics are difficult to predict with accuracy
because of the very wide range of parameters interacting. The effects of the application of an electrical gradient across
controlled specimens of a pure form of kaolinite using stainless steel electrodes and a deionised water feed to the electrodes,
to mimic electrokinetic stabilisation without the stabiliser added, are reported. The specimens in which electrical and chemical
changes were induced over different time periods (3, 7, 14 and 28 days) were subsequently tested for Atterberg limits, undrained
shear strength, water content, pH, conductivity, Fe concentration and zeta potential. Changes in strength and plasticity indices
were attributed to electrolysis, electro-osmosis, electrode degradation, clay mineral dissolution, ion movement due to electromigration,
cation exchange reactions and precipitation of reaction products.
The effect of pH on the flocculation-dispersion behavior of noncrystalline aluminum and iron oxides, kaolinite, montmorillonite, and various mixtures of these materials was investigated. The clays were Na- or Ca-saturated and freeze-dried before use. Critical coagulation concentrations (CCC) of all materials and mixtures were found to be pH dependent. The A1 oxide was flocculated at pH >9.5 and the iron oxide was flocculated between pH 6.0 and 8.2; i.e., flocculation occurred at pHs near the point of zero charge (PZC). The CCC of both the Na- and Ca-clay systems increased with increasing pH. The effect of pH was greater for the Na-kaolinite (flocculated at pH 5.8 and having a CCC of 55 meq/liter at pH 9.1) than the Na-montmorillonite system (having a CCC of 14 meq/liter at pH 6.4 and a CCC of 28 meq/liter at pH 9.4). A 50/50 mixture of Na-kaolinite and Na-montmorillonite behaved more like montmorillonite (having CCCs of 13 and 33 meq/liter at pH 6.2 and pH 9.0, respectively). The presence of either noncrystalline oxide decreased the CCC over that of the clay(s) alone; the decrease occurred at pHs >7 for AI oxide and at pHs >6.5 for Fe oxide. Aluminum oxide produced a greater decrease in CCC than Fe oxide, especially at pHs > 8. The effect of each oxide on CCC was greatest near the PZC, 9.5 and 7.2 for A1 and Fe oxide, respectively.
Migration of ions from lime piles to bring about improvements in clay soils, into which the lime piles have been installed, has been observed by several researchers. Specific measurements have been taken to show how effective the improvement has been (in terms of distance, time, and magnitude of the physical change), and yet the observations have yet to be adequately explained. This paper aims to examine, via a series of controlled laboratory experiments, the physico-chemical phenomena in London clay brought about by the ion migration from a lime pile having the same initial water content as the clay. Ion migration was shown to occur under a combination of three drivers (chemical, electrical, and hydraulic gradients), the importance of each being discussed. Changes in the clay's properties were determined by shear strength, using a novel fall cone technique, and plasticity measurements, while measurement of pH, conductivity, and ion concentrations proved vital to understanding the processes taking place, notably in relation to the cation exchange and clay mineral dissolution effects of classic stabilization.
A field test was undertaken to assess the effectiveness of the electroosmotic strengthening of the soft sensitive (Champlain Sea) clay in the Gloucester Test Fill site by using specially designed copper electrodes to improve treatment efficiency. Tube samples, 127 mm in diameter, were recovered before and after field treatment for detailed laboratory tests. Isotropically consolidated undrained triaxial tests with pore-pressure measurements were performed. It was found that the failure envelope after treatment was significantly higher than the initial envelope, indicating that the strength in terms of effective stresses increased. Consolidation tests showed that, as a result of treatment, the preconsolidation pressure increased from 53 to 98 kPa. The soft clay is virtually "overconsolidated" by the process. Additional effects of electroosmosis on the properties of the soft clay are the increase in plasticity, carbonate content, and salinity and the decrease in sensitivity. There is, therefore, a general improvement in soil properties after treatment, both in terms of total and effective stresses. Key words: electroosmosis, soft sensitive clay, failure envelope, sensitivity, preconsolidation pressure, pH value.
Previous laboratory studies have shown that the injection of a calcium chloride solution followed by the injection of a sodium silicate solution during electroosmosis is effective in strengthening soft silty clay. Very stiff cemented soil near the anodes is formed after the treatment. This paper presents the effectiveness of the process in the field. Nine electrodes were installed using two grid arrangements with electrode spacings of 2.0 m × 2.5 m and 2.0 m × 5.0 m. The test procedure is similar to those employed in the laboratory. Test results show that the soil surrounding the anodes (within a diameter of 50–60 cm) became very stiff and cemented due to the effect of cementation between the two chemical solutions and soil particles under the electric field. Except for the areas of stiff cemented soil, the undrained shear strength of the soil between electrodes was increased substantially. Polarity reversal after normal polarity did not produce favorable improvement effects in terms of undrained shear strength of the soil and treatment time.
Electroosmosis in a copper-contaminated kaolinite was highly sensitive to chemical treatment schemes designed to remove the contamination. Nonuniform profiles of electric field intensity and pH as well as negative pore-water pressure develop during sustained electrokinetic treatment of clays. These nonlinearities and nonuniform pore-water pressures cannot be adequately described by classical analysis. Classical analysis is based on assumptions of a uniform and constant electroosmotic permeability coefficient, for instance. An extended capillary model which includes nonuniform contributions to electroosmosis and pore pressures that vary with space and time, is developed and compared with experimental findings. Subtle changes in initial and boundary conditions of the system chemistry have a very large effect on electroosmosis in soils. For instance, acid addition at the cathode reservoir may cause reversal of the direction of electroosmotic flow. Other species, such as the citrate, may form stable complexes with copper ions, thus reducing the impact of copper on the zeta potential of the clay. The model is used to simulate these effects.
A review of literature on soil stabilization by electrical methods is presented, with particular emphasis on the technique that might be applied by the military to improve mobility of surface vehicles over very wet and unstable fine-grained soils. The mechanics of the phenomenon of electroosmosis of soils are described, and the quantitative expressions for electroosmotic flow based on the theories of Helmholtz-Smoluchowski and Schmid are compared. It is apparent that the applicability of the theoretical concepts and their validity in relation to practical engineering problems remain to be established. Based on accounts of numerous successful practical field operations, it is known that certain definite benefits are derived from the application of an electric current to wet, fine-grained soils. In addition to enhancing drainage of soils of relatively low permeabilities, the process of electroosmosis results in a consolidation of the soil that contributes to an improved strength and stability. It has been demonstrated that an irreversible electrochemical hardening of soils containing clay occurs when aluminum electrodes are employed in the electroosmosis process.This phenomenon has resulted in the development of techniques for increasing the bearing capacity of piles, and has been explored for its possible applicability in soil reclamation and chemical injection processes.
One concern with UV disinfection of water is the production of nitrite when polychromatic UV sources are utilized. Based on previous work, it was hypothesized that a small addition of hydrogen peroxide (H(2)O(2)) may be useful in controlling nitrite during UV disinfection. However, it was found that H(2)O(2) addition (5 or 10mg/L) during polychromatic UV irradiation of drinking water at doses used for disinfection significantly increases the levels of nitrite produced relative to solutions without H(2)O(2). Enhancement rates ranged from approximately 15% to 40% depending upon pH and H(2)O(2) concentration; the relative increase in the NO(2)(-) yield was greater at pH 6.5 than at pH 8.3. The observed effects are tentatively ascribed to a combination of enhanced superoxide production and increased hydroxyl radical scavenging when H(2)O(2) is added. These results indicate that H(2)O(2) cannot be used to control nitrite production during UV disinfection and that enhanced nitrite formation will occur if H(2)O(2) is added during UV water treatment to achieve advanced oxidation of contaminants.