Groundwater Treatment Technology Research Articles

Arsenate removal using chitosan-coated bentonite via fixed-bed system: a process integration by fuzzy optimization.

Groundwater contamination is a global concern that has detrimental effect on public health and the environment. Sustainable groundwater treatment technologies such as adsorption require attaining a high removal efficiency at a minimal cost. This study investigated the adsorption of arsenate from groundwater utilizing chitosan-coated bentonite (CCB) under a fixed-bed column setup. Fuzzy multi-objective optimization was applied to identify the most favorable conditions for process variables, including volumetric flow rate, initial arsenate concentration, and CCB dosage. Empirical models were employed to examine how initial concentration, flow rate, and adsorbent dosage affect adsorption capacity at breakthrough, energy consumption, and total operational cost during optimization. The ε-constraint process was used in identifying the Pareto frontier, effectively illustrating the trade-off between adsorption capacity at breakthrough and the cost of the fixed-bed system. The integration of fuzzy optimization for adsorption capacity and its total operating cost utilized the global solver function in LINGO 20 software. A crucial equation derived from the Box-Behnken design and a cost equation based on energy and material usage in the fixed-bed system was employed. The results from identifying the Pareto front determined boundary limits for adsorption capacity at breakthrough (ranging from 12.96 ± 0.19 to 12.34 ± 0.42μg/g) and total operating cost (ranging from 955.83 to 1106.32 USD/kg). An overall satisfaction level of 35.46% was achieved in the fuzzy optimization process. This results in a compromise solution of 12.90μg/g for adsorption capacity at breakthrough and 1052.96 USD/kg for total operating cost. Henceforth, this can allow a suitable strategic decision-making approach for key stakeholders in future applications of the adsorption fixed-bed system.

Utilizing machine learning for reactive material selection and width design in permeable reactive barrier (PRB)

Permeable reactive barrier (PRB) is an important groundwater treatment technology. However, selecting the optimal reactive material and estimating the width remain critical and challenging problems in PRB design. Machine learning (ML) has advantages in predicting evolution and tracing contaminants in temporal and spatial distribution. In this study, ML was developed to design PRB, and its feasibility was validated through experiments and a case study. ML algorithm showed a good prediction about the Freundlich equilibrium parameter (R2 0.94 for KF, R2 0.96 for n). After SHapley Additive exPlanation (SHAP) analysis, redefining the range of the significant impact factors (initial concentration and pH) can further improve the prediction accuracy (R2 0.99 for KF, R2 0.99 for n). To mitigate model bias and ensure comprehensiveness, evaluation index with expert opinions was used to determine the optimal material from candidate materials. Meanwhile, the ML algorithm was also applied to predict the width of the mass transport zone in the adsorption column. This procedure showed excellent accuracy with R2 and root‐mean‐square‐error (RMSE) of 0.98 and 1.2, respectively. Compared with the traditional width design methodology, ML can enhance design efficiency and save experiment time. The novel approach is based on traditional design principles, and the limitations and challenges are highlighted. After further expanding the data set and optimizing the algorithm, the accuracy of ML can make up for the existing limitations and obtain wider applications.

ANALYSIS OF THE MATHEMATICAL MODEL OF "CHARGING"
 OXYGEN OF WATER-BEARING ROCKS IN THE PROCESS
 OF IN-SITU TREATMENT OF GROUNDWATER

The article describes the method of in-situ groundwater treatment technology, the conditions for modeling the process
 of water injection into the water-bearing rock, the analysis of the obtained mathematical equations.

Development of a new design of deironing granulated filter for joint removal of iron and ammonium nitrogen from underground water

ABSTRACT Providing the population with high-quality drinking water is one of the main state tasks. Rural water supply systems and water supply systems of small settlements in the region require special attention, namely, the development of technologies for individual, small-sized water treatment equipment, as well as equipment for collective use, designed to purify groundwater for drinking purposes. In many areas, there are groundwaters containing excess levels of several pollutants, which makes their purification much more difficult. Elimination of shortcomings in the known methods of water iron removal is possible by reconstructing existing water supply systems from underground sources in small settlements. A rational solution is to search for groundwater treatment technologies that make it possible to provide the population with high-quality drinking water at a lower cost. The result of increasing the concentration of oxygen in water was obtained in the process of modifying the filter by changing the excess air exhaust system, which was made in the form of a perforated pipeline located in the lower half of the granular filter layer connected to the upper branch pipe. At the same time, high-quality groundwater treatment, sufficient simplicity and reliability in operation are ensured, local conditions and the inaccessibility of many objects and settlements in the region are taken into account as much as possible. After the filter was upgraded, the concentration of iron decreased from 4.4 to 0.27 mg/L and ammonium nitrogen from 3.5 to 1.5 mg/L.

Efficacy of a Fine Bubble Diffuser in Enhancing Attached Biofilm Hydrogenotrophic Denitrification Reactor Performance

The efficacy of a fine bubble (FB) diffuser in enhancing the performance of an attached biofilm hydrogenotrophic denitrification (HD) reactor was evaluated. HD reactors equipped with an FB diffuser (FB reactor) and an air stone (AS) diffuser that produced ordinary bubbles (AS reactor) were operated in parallel at different hydraulic retention times (HRTs) in a synthetic groundwater treatment experiment. A reduction in H2 consumption of approximately 77% was achieved using the FB diffuser to reach a gas-liquid mass transfer coefficient similar to that of the AS diffuser. The high gas dissolution efficiency of the FB diffuser resulted in an effective nitrogen removal rate (NRR) enhancement, requiring less H2 supply. The highest value of NRR at 53.0±9.8 g-N/m3/d was obtained in the FB reactor at a minimum HRT of 3 h, which was two-fold higher than the corresponding value from the AS reactor. The FB reactor also had the lowest requirement of H2 for denitrification reaching 0.1 m3-H2/g-N in this condition, which was ten-fold lower than that in the AS reactor. Furthermore, the suspended sludge concentration in the FB reactor was lower than that in the AS reactor, indicating that the application of the FB diffuser can minimize excess suspended sludge accumulation inside the HD reactor. Microbial community analysis showed the predominance of Thauera spp. reaching a relative abundance of 15.7–27.3% in the FB reactor, suggesting a contribution to the HD. This finding can provide insight into the application of the FB diffuser for optimizing nitrate-contaminated groundwater treatment technology by HD.

Comparative Analysis of Natural and Synthetic Zeolite Filter Performance in the Purification of Groundwater

Zeolite materials are among the relatively cheap and readily available materials for wastewater treatment. However, the performance of zeolite-based systems can be highly affected by the material properties. In this study, the treatment system based on natural zeolite materials from Chankanai mines in Kazakhstan was compared with a synthetic zeolite treatment system for the purification of groundwater. Water quality indices were also developed from a set of selected water quality parameters to further assess the state of water quality of raw groundwater and the effluents treated with natural and synthetic zeolite. The lowest removal efficiency of natural zeolite (30%) was observed with zinc, while the lowest removal efficiency (36%) of synthetic zeolite was observed with arsenic. With turbidity and beryllium, we observed the maximum removal efficiency (100%) of natural zeolite, whereas with turbidity, we observed the highest removal efficiency (100%) of synthetic zeolite. When the groundwater samples were put through the natural zeolite treatment system, removal efficiency of 50% and above was obtained with 27 (79.4%) out of the 34 water quality parameters examined. On the other hand, when the groundwater samples were put through the synthetic zeolite treatment system, more than 50% removal efficiency was attained with 30 (88.2%) out of the 34 water quality parameters studied. The aggregated water quality index of raw groundwater was 3278.24, falling in the “water unsuitable for drinking” category. The effluent treated with natural zeolite generated 144.82 as a water quality index, falling in the “poor water” quality category. Synthetic zeolite generated 94.79 as a water quality index, falling in the “good water” quality category. Across the board, it was shown that the synthetic zeolite treatment system outperformed the natural zeolite treatment system according to a number of water quality parameters. The findings of this study offer substantial knowledge that can be used to develop more efficient groundwater treatment technologies.

Optimization of preparation parameters of ceramic pot water filters for potential application of microbial and fluoride removal from groundwater

The need to make clean water accessible and affordable for low-income countries is crucial. This study examines the suitability of various clays for Ceramic Pot Water Filters production and groundwater treatment for effective microbe and fluoride removal. For this study, three clays were collected from different geographical locations in Ethiopia,i.e., Hosaenna Clay, Babawuha Clay, and Leku Clay. Organic additives such as sawdust and eragrostis tef husks were used to increase the porosity of the Ceramic Pot Water Filters. The Atterberg limit and particle size distribution tests revealed that BC and HC have moderate to high plasticity and mouldability, making them suitable for CPWF production. The clay chemical composition, phase analysis, and thermal properties were determined using XRF, XRD, and TGA/DTA. The turbidity, fluoride level, total dissolved solids, and pH of the groundwater decreases, from 13 to 0.45 NTU, from 3.4 to 0.053 mg/100 mL, from 1245 to 360 mg/l, and from 8.4 to 7.3, respectively; all of which are within the acceptable range of WHO drinking water standards. Microbial removal tests show that the CPWFs removed 99.3%–100% of total coliform bacteria and 98.48%–100% of fecal coliform bacteria from groundwater. Therefore, this work paves the way to fabricate a clay-based ceramic water filter for low-income countries to provide affordable household groundwater treatment technology for microbial and excess fluoride removal.

Sustainable groundwater treatment technologies for underserved rural communities in emerging economies

Worldwide, about one out of two people depend on groundwater resources to satisfy their drinking water needs. While groundwater typically is of higher quality than surface water, pollution and geologic conditions may require treating groundwater to meet safe water quality criteria. Herein, a critical overview is presented of water treatment technologies for rural and underserved communities in emerging economies that depend on groundwater. Given that small to medium sized rural communities in emerging economies often lack the financial resources to support technologically complex and expensive centralized public water treatment systems, the focus is on proven technologies that are sustainable and acceptable by the rural population. After an overview of the underlying treatment mechanisms and the principal groundwater contaminants targeted by the traditional, advanced, and experimental water treatment technologies, we identify the groundwater quality parameters that may impact or interfere with the technology performance. We also introduce enabling environmental factors that might govern the implementation of water treatment technologies in the target communities and a brief discussion of safe storage of water after treatment to underline the importance of protecting the water from re-contamination. Our overview is further supported by tabulated summaries of the principal (dis)advantages of each technology covered herein, including cost considerations and social acceptance. Overall, our review suggests that underserved rural communities have sustainable and affordable options for cases where the quality of local groundwater resources requires treatment.

Analysis of the application of polluted groundwater treatment technology using shell-based activated carbon media filters

One source of clean water used by residents of Sendal Kopo Subvillage, Panenjoan Village, Carenang District, Serang Regency comes from dug wells (groundwater), has a problem with very cloudy, yellow, sour taste and smells due to contamination from residual waste and the rest of the rice field irrigation system. The clean water treatment unit for community-based sanitation (Sanimas) owned by residents is no longer functioning by the central government. One alternative in treating polluted groundwater is to design a water filter installation from PVC pipes using activated carbon media from coconut shells and additional media for filter foam, injuk, zeolite stone, activated carbon, and silica sand to produce good raw water quality. Simple water analysis by making a water filter. The results of the analysis showed that the water content of activated carbon as the main medium was made after adding the activating agent ZnCl 2 , CaCl, or KCl 25% for 12-18 hours, indicating that the results met the SNI 06-3730-1995 regarding the standard of quality requirements and testing of activated charcoal both for water content <15% and ash content <10%, namely 7.56% and 7.89% ash content. The tool was tested on water samples ranging from color, pH, and Fe content from Panenjoan Village. After being tested using a water filter, the color of the water showed very good results. Initially, it was cloudy yellowish after passing through the filter to become clear white, while the pH test showed the results of 6.9 were still within the threshold because according to the regulation of the minister of health, No 492/Menkes/ Per/IV/2010 the pH is 6.5-8.5 while the level of Fe produced is 0.65 mg/l while according to the regulation it is 0.3 mg/l. Salah satu sumber mata air bersih yang digunakan warga Kp. Sendal Kopo, Desa Panenjoan, Kecamatan Carenang, Kabupaten Serang berasal dari sumur galian (air tanah), memiliki masalah dengan kondisi air sangat keruh, kuning, berasa asam dan berbau akibat berasal dari pencemaran beberapa limbah dan sisa sistem pengairan sawah. Unit pengolahan air bersih sanitasi berbasis masyarakat (Sanimas) yang dimiliki warga sekitar sudah tidak berfungsi dari pemerintah pusat. Salah satu alternatif dalam pengolahan air tanah yang tercemar dengan mendisain instalasi filter air dari pipa PVC menggunakan media carbon aktif dari tempurung kelapa dan media tambahan busa filter, injuk, batu zeloit, carbon aktif dan pasir silika agar menghasilkan kualitas air baku yang baik. Analisis air sederhana dengan membuat filter air. Hasil analisis menujukan kadar air carbon aktif sebagai media utama yang di buat setelah menambahkan agen aktivator ZnCl 2 , CaCl atau KCl 25% selama 12-18 jam menujukan hasil memenuhi syarat standar SNI 06-3730-1995 tentang standard syarat mutu dan pengujian arang aktif baik untuk kadar air < 15% dan kadar abu <10%. yaitu 7,56 % dan kadar abu 7,89%. Alat tersebut di uji terhadap sample air mulai dari warna, pH, dan kadar Fe dari Desa Panenjoan. Warna air setelah di uji dengan menggunakan filter air menujukan hasil yang sangat baik, semula berwaran keruh kekuningan setelah melewati filter menjadi putih bening, sedangkan pengujian pH menunjukan hasil 6,9 masih dalam ambang batas karena menurut peraturan menteri kesehatan, No. 492/Menkes/Per/IV/2010 pH sebesar 6,5-8,5 sedangkan kadar Fe yang dihasilkan 0,65 mg/l sedangkan menurut peraturan yaitu 0,3 mg/l.

Compact groundwater treatment units

This thesis is dedicated to a systematic approach when choosing appropriate groundwater treatment technologies with regard to specific water consumers’ requirements. The groundwater analysis indicated that iron compounds were the main pollutants which could be found in biominerals, manganese, solution gases etc. This study represents the research results of compact groundwater treatment units which use nonchemical biological deferization methods and applied ozone treatment technologies. As the result, it was demonstrated that the source water with hydrogen-sulfide odor, 6.8 mg/l of iron content, 46 degrees of chromaticity and pH up to 7.6 was successfully treated in compliance with the statutory requirements. The authors also study wash water sediment structure and composition.

The properties of sludge formed as a result of coagulation of backwash water from filters removing iron and manganese from groundwater

The standard groundwater treatment technology is a simple, non-chemical reagent technology based on aeration and filtration processes. This treatment technology is resulted in the formation of groundwater treatment sludge (GWTS). Because one of the elements of sustainable development is the possibility of their reuse, that water treatment plant operators are looking for new ways of managing these sludges. At present, not all factors determining the adsorptive capacity of water treatment sludge are known. The explanation why the adsorption capacity of sludge with a similar structure and chemical composition may differ significantly will allow for their wider use as adsorbents. The information which must be known to ensure proper sludge management are the quality, chemical composition and texture characteristics of the GWTS. The sludges were characterized by X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy and N2 adsorption/desorption isotherms. The results showed that the composition and properties of the GWTS depend primarily on the quality parameters of the raw water and the processes and reagents used in its treatment technology. GWTS contains mainly amorphous iron oxides. Sludges are characterized by a large specific surface area (145 m2/g). Due to composition and textural parameters, GWTS demonstrates good adsorption properties toward different compounds such as heavy metals and metalloids. In this article, the authors describe the relationship between properties of resulting sludge and the properties of groundwater, the treatment technology and backwash water treatment from rapid filters.

Electric-field enhanced reactivity and migration of iron nanoparticles with implications for groundwater treatment technologies: Proof of concept

The extensive use of nanoscale zero-valent iron (nZVI) particles for groundwater treatment has been limited, in part, because of their non-selective reactivity and low mobility in aquatic environments. Herein, we describe and explore progressive changes in the reactivity and migration of aqueous dispersed nZVI particles under an applied DC electric field. Due to the applied electric field with an intensity of about 1 V cm−1, the solution oxidation-reduction potential (ORP) remained as low as −200 mV for at least 32 days, which was in agreement with the persistence of the reduced iron species (mainly Fe(II)), and led to substantially prolonged reactivity of the original nZVI. The treatment of chlorinated ethenes (DCE > PCE > TCE) was markedly faster, individual CHC compounds were eliminated with the same kinetics and no lesser-chlorinated intermediates were accumulated, following thus the direct dechlorination scheme. When nZVI-dispersion flows towards the anode through vertical laboratory columns filled with quartz sand, significant enhancement of nZVI migration was recorded because of lower extent of nanoparticle aggregation and increased repulsion forces between the nanoparticles and the surface of silica dioxide. The results of this study have significant consequences for groundwater remediation, mainly for the treatment of slowly degradable DCE in real CHC contaminated groundwater, where it could improve the reactivity, the longevity and the migration of nZVI particles.

MASALAH DAN ALTERNATIF TEKNOLOGI PENGOLAHAN AIR UNTUK MASYARAKAT MISKIN KOTA

Clean water to poor communities who live in crowded municipal area is stillexpensive and a luxury. This condition is evidenced by the number of people whouse ground water for their daily water, because water taps still seems expensivefor them. Diarrheal disease is still relatively high for Indonesia, where nearly 16thousand people suffer from diarrhea due to poor sanitation. To help the poor inthe city, there are several alternative technologies that can be applied to publicaccess to clean water and adequate low-cost, including ground water treatmenttechnology with a filter system equipped with an ultraviolet sterilizer, or ozonegenerators, or using ultrafiltration, if possible can also use the reverse osmosismembrane that for fresh water. Arsinum is the best alternative should be chosenfor fulfilled potable water in slump area.Keywords : Sanitation, water treatment technology, portable water, low-cost, slump area

LABORATORY TESTING OF THE POTENTIAL FOR THE INFLUENCE OF SUSPENDED SEDIMENTS ON THE ELECTROCHEMICAL REMEDIATION OF KARST GROUNDWATER.

Due to the complicated nature of karst aquifers, many groundwater treatment technologies are difficult to implement successfully. A particular challenge arises because sediments are ubiquitous and mobile in karst systems and may either facilitate contaminant transport or act as long-term substrates for storage via sorption. However, electrochemical remediation is a promising technology to be optimized for karst aquifers due to easy manipulation and control of groundwater chemistry as well as low cost, ability for in situ application, and performance under alternative power sources. This study investigates the effects of suspended karst sediments on the electrochemical remediation of groundwater via electro-Fenton (EF) mechanism. The EF mechanism relies on direct electrolysis (i.e., water electrolysis and ferrous iron release) and indirect, electrochemically-induced processes (i.e., Pd catalyzed H2O2 production). These processes can be optimized for H2O2 generation and support of its activation to hydroxyl radicals - a powerful oxidant capable of degrading and transforming a wide range of contaminants (e.g., chlorinated solvents). In this study, we tested sediments varying in concentrations of Fe, Mn and buffering capacities. When the sediments were introduced into the EF experiments, there were adverse effects on the H2O2 content: at steady state (120 min), Pd catalyzed formation of H2O2 decreased by 60%, 57%, and 75% in the presence of suspended sediment collected from three separate karst locations. Presented results imply that sediments' presence influences EF mechanism in electrochemical systems, but given the flexibility of the technology, it can be optimized in terms of electrode materials, current intensities and current regimes to address these challenges.

Configuration of a pilot station in a technological investigation of groundwater treatment

The purpose of pre-design technological investigations is to define the water treatment technology for a new or existing water treatment plant. The investigation is performed on model-scale equipment, making sure that the results can be extrapolated to the technological scale. The investigation should allow for the determination of unit process parameters and ensure the desired outcome i.e. treated water meeting the applicable quality standards. Indirectly, the investigation results can also be used as a basis for defining the estimated scope of the investment, the costs of its execution and the future equipment operating costs. Technological investigations are carried out on the grounds of existing or future treatment plants in order to take into account the variable composition and quality indicators of the raw water to be treated. The pilot station, being the main element of the technological investigation, should be designed, built and operated with a view to the possibility of formulating further design guidelines after the study is completed. In this article, the authors share their experience related to the configuration of a pilot station used in an investigation of a groundwater treatment technology.

Technology for treatment of groundwater simultaneously containing iron, manganese, ammonium and organic matter

The groundwater used as drinking water often contains unacceptable amounts of iron and manganese compounds and ammonium ions. These substances are efficiently removed using conventional technologies (aeration and filtration through granular media filters). However, the efficiency is drastically reduced for water containing considerable amounts of organic matter, which usually enters the water in wellfields linked with surface water. This paper presents a technology development for treating groundwater with such complex problems. A combination of open and closed aeration and filtering through three filters containing sand, zeolite and sand with oxidizing bacteria are used. Polyaluminium chloride acting as coagulant is the only chemical substance used in the technology. The developed water treatment technology was tested for eight months. The technology ensured the reduction of iron, manganese, ammonium, and organic compounds by 98%, 87%, 99%, and 80%, respectively. The efficiencies are sufficient to meet the requirements of the Council Directive 98/83/EC on the quality of water intended for human consumption for most wellfields fed by both underground and surface water.

Activated Zeolite and Magnesite as Potential Reactive Materials for Passive Acidic Groundwater Treatment Technology

Permeable reactive barriers (PRBs) are passive, in-situ remediation systems that comprise the filtration of a contaminated groundwater through a reactive media able to degrade, adsorb or precipitate the pollutants. Selection of the reactive media depends on the nature of the contamination. While the majority of PRBs are used to treat groundwater contaminated with chlorinated volatile organic compounds or acid mine drainage, the present study is focused on heavy metals, namely Fe, Al, Cu, Ni, Zn, Mn and As. To remove such inorganic pollutants, four methodologies are usually implemented: a) redox reaction, b) adsorption and ion exchange, c) biological treatment (e.g. metal sulphides precipitation) and d) pH control and precipitation. The present paper deals with the last methodology in which an adjustment of pH by alkalinity-generating materials leads to the precipitation of metal hydroxides and the decrease in the concentration of dissolved species. As the solubility of metals depends on their valence, redox-potential, concentrations and kinetics of reaction, the target pH varies with respect to the considered metal. A pH of about 10 allows the precipitation of hydroxides of divalent ions (zinc, manganese, copper, lead, nickel, cobalt and cadmium), while a pH of around 6-7 is adapted to trivalent ions (iron, aluminium and chromium). However, the accumulation of precipitates in the pore spaces can cause clogging of the pores, hence decrease the porosity and hydraulic conductivity of the reactive media and alter its efficiency. To validate this assumption, the neutralizing ability of alkaline materials such as activated zeolite and magnesite were examined in a test column by monitoring the resultant pH with attention to impact of precipitates on the hydraulic properties of reactive materials. Based on the test results, both materialls are considered suitable to remove the groundwater contaminants with high efficiency (up to 99%) and suitable grain size to encourage flow through the PRB.

Formulation of a Permeable Reactive Mixture for Groundwater Remediation Based on an Industrial Co-product: Permeability and Copper Retention Study

The objective of this research is to formulate a permeable material based on apatite gel having the ability to retain heavy metals, to be used in a permeable reactive barrier (PRB), an in situ passive groundwater treatment technology. This new material is produced from non-toxic waste in the research laboratory of a chemical company. It is characterised by a thixotropic behaviour and a high ion exchange capacity. The apatite gel is the active agent of the reactive material; it ensures the retention of heavy metals by ion exchange. Sand and an organic binder are also incorporated into the mixture, providing both high permeability and mechanical strength to the mixtures. An original experimental apparatus intended for measuring both water permeability and the retention of heavy metals has been specially designed and developed for this study. The mixture consisting of 95 % silica sand, 5 % apatite gel and 3 % epoxy was qualified as a suitable PRB mixture, due its high permeability, its good retention capacity and its acceptable mechanical strength.

Synthesis, characterization and stability of Cr(III) and Fe(III) hydroxides

Chromium is a common contaminant of soils and aquifers and constitutes a major environmental problem. In nature, chromium usually exists in the form of two oxidation states, trivalent, Cr(III), which is relatively innocuous for biota and for the aquatic environment, and hexavalent, Cr(VI) which is toxic, carcinogenic and very soluble. Accordingly, the majority of wastewater and groundwater treatment technologies, include a stage where Cr(VI) is reduced to Cr(III), in order to remove chromium from the aqueous phase and bind the element in the form of environmentally stable solid compounds. In the absence of iron the final product is typically of the form Cr(OH)3·xH2O whereas in the presence of iron the precipitate is a mixed Fe(1−x)Crx(OH)3 phase. In this study, we report on the synthesis, characterisation and stability of mixed (Fex,Cr1−x)(OH)3 hydroxides as compared to the stability of Cr(OH)3. We established that the plain Cr(III) hydroxide, abiding to the approximate molecular formula Cr(OH)3·3H2O, was crystalline, highly soluble, i.e. unstable, with a tendency to transform into the stable amorphous hydroxide Cr(OH)3(am) phase. Mixed Fe0.75Cr0.25(OH)3 hydroxides were found to be of the ferrihydrite structure, Fe(OH)3, and we correlated their solubility to that of a solid solution formed by plain ferrihydrite and the amorphous Cr(III) hydroxide. Both our experimental results and thermodynamic calculations indicated that mixed Fe(III)–Cr(III) hydroxides are more effective enhancers of groundwater quality, in comparison to the plain amorphous or crystalline Cr(III) hydroxides, the latter found to have a solubility typically higher than 50μg/l (maximum EU permitted Cr level in drinking water), while the amorphous Cr(OH)3(am) phase was within the drinking water threshold in the range 5.7<pH<11. In comparison, the mixed Fe0.75Cr0.25(OH)3 hydroxides studied were of extended stability in the 4.8<pH<13.5 range.

Review of Contaminated Sites Remediation Technology

The contaminated site remediation is an important content of site management. Plans for the introduction of measures and requirements to prevent and remediate soil contamination, particularly through the development of inventories of contaminated sites and the definition of targets for prioritization of remediation actions, are expected to have important consequences for site management practice and national site policies. Nowadays contaminated soil and groundwater treatment technologies can be sorted as three categories, that is bioremediation, chemical treatment and physical treatment. Biodegradation generally refers to the breakdown of organic compounds by living organism eventually resulting in the formation of carbon dioxide and water or methane. Chemical remediation is a kind of method that chemical reagent, chemical reaction and chemistry principles are used to reduce the mobility, organisms use ratio of heavy metals and decrease the heavy metals in the soil so as to remediate and repair the soil. Physical treatments in the remediation of contaminated site contains revising methods, capping methods, stabilization methods, electrokinetic methods and so on.