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The effects of humic acid (HA) on As(V) removal by zero-valent iron (Fe-0) from groundwater, associated with corrosion products analyses, were investigated using batch experiments. it was found that arsenic was rapidly removed from groundwater possibly due to its adsorption and co-precipitation with the corrosion products of Fe-0. The removal rate of arsenic by Fe-0 was inhibited in the presence of HA probably because of the formation of soluble Fe-humate in groundwater which hindered the production of iron precipitates. A longer reaction time was then required for arsenic removal. Such an influence of HA on arsenic removal increased with increasing HA concentration from 5 to 25 mg L-1. The binding capacity of HA for dissolved Fe was estimated to be about 0.75 mg Fe mg(-1) HA. When the complexation of HA with dissolved Fe was saturated, further corrosion of Fe-0 would produce precipitates, which significantly accelerated the removal of arsenic from groundwater via adsorption and co-precipitation with the corrosion products. Iron (hydr)oxides such as maghemite, lepidocrocite, and magnetite were characterized by XRD analyses as the corrosion products, while As(V) was found on the surface of these corrosion products as detected by fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. (c) 2009 Elsevier Ltd. All rights reserved.

Precipitation and dissolution are two main chemical reactions determining the fate of chemicals or contaminants in natural waters and in many water and wastewater treatment processes. Mineral precipitation and dissolution are the prime factors altering the chemical composition of natural water (Stumm and Morgan, 1996). Treatment processes, such as lime-soda softening, iron removal, coagulation with hydrolyzed metal salts and phosphate precipitation, are all based on the precipitation (Snoeyink and Jenkins, 1980).Likewise, the behavior of compounds containing carbon,nitrogen,sulfur,iron and manganese in the treatment processes and natural water is largely govermed by redox conditions in polluted areas is often a prerequisite in predicting the fate of pollutantss and for selecting suitable treatment or mitigation approaches. For instance, the redox condition information of a contaminant plume in subsurface allows evaluation of further plume development and potential risks to downgradient groundwater resources, and assessment of the appropriateness of natural attenuation as a remediation option.

The thickness of the zero-valent iron (Fe) packed media in full-scale permeable reactive barriers (PRBs) for the remediation of chlorinated aliphatic hydrocarbons (CAHs) in groundwater is conventionally designed using the kinetic data from laboratory column experiments and first-order equation. To study the reliability of this conventional approach for the PRB thickness design, the performance of the full-scale Fe PRB at Vapokon site, Denmark and the corresponding laboratory Fe packed columns (LFPCs) on CAH dechorination was studied and compared.

Redox reaction and precipitation are of paramount importance in both natural water as well as water and wastewater treatment processes. The behavior of compounds containing carbon, nitrogen, sulfur, iron and manganese etc in natural water and the treatment processes is largely influenced by redox reaction (Snoeyink and Jenkins 1980). Therefore, understanding the redox condition in polluted areas is often a prerequisite for selecting appropriate treatment or remediation approaches (Christensen et al. 2000).For example, knowledge of redox condition of contaminant plume in subsurface allows evaluation of the plume development and risks to downgradient groundwater resources as well as assessment of natural attenuation as a remediation option.

Tracer experiment is the most direct method for the evaluation of the hydraulic performance of zero-valent iron (Fe)-based permeable reactive barriers (PRBs). The implementation of tracer experiment involves (1) selection of suitable tracer materials;(2) groundwater modeling;(3) design and installation of tracer injection and groundwater sampling systems;(4) collection and chemical analysis of groundwater samples; and (5) data analysis. The findings obtained from the funneland-gate Fe PRB at Vapokon site,Denmark indicated that the natural gradient tracer experiment was able to identify and delineate the preferential flow of contaminated groundwater through the FE^0 reactive medium of the PRB. Besides, spatial moments analyssis of the tracer plume was capable of giving the arrival times and locations of the centre of mass of the tracer plume inside the upgradient and downgradient parts of the Fe^0 reactive medium, thereby resulting in the groundwater velocity of 99.5 m/yr within the Fe^0 reactive medium.

Reactive barrier technology was first proposed for groundwater remediation in the 1970s when an in situ barrier containing limestone was used for the attenuation of acidity and dissolved metals in acidic mine drainage (Pearson and McDonnell 1975; Hedin et al. 1994; Naftz et al. 2002). In the early 1990s, recognition of the efficacy of zero-valent iron (Fe) in the abiotic reduction of chlorinated aliphatic hydrocarbons (CAHs) led to the first Fe-based reactive barrier installation at the CAH contaminated Canadian Forces Base (CFB) Borden site subsequently initiated a period of active installations resulting in the construction of more than 40 reactive barriers between 1993 and 2001 to treat CAHs,metals, nutrients and radionuclides in groundwater.

Activated carbon was derived from waste wood pallets in Hong Kong via phosphoric acid activation and applied to adsorption of basic dye (methylene blue), acid dyes (acid blue 25 and acid red 151), and reactive dye (reactive red 23). The results showed that respective adjustment in phosphoric acid concentration, impregnation ratio, activation temperature, and activation time could maximize the surface area and pore volume of activated carbon. An increase of impregnation ratio or activation temperature significantly influenced the pore size distribution by expanding the porous structure and creating more macropores than micropores. The characterization of the carbon surface chemistry using Fourier-transform infrared (FTIR) spectroscopy, however, revealed a decrease in the amount of several functional groups with increasing activation temperature. The physical properties (surface area and pore volume) of the wood waste-derived activated carbon (using 36\% phosphoric acid with an impregnation ratio of 1.5 at an activation temperature of 550 degrees C for 1.5 h) were comparable to those of commercial activated carbon (Calgon F400). The contrasting pH effects on the adsorption of different classes of dyes signified the importance of both electrostatic interaction and chemical adsorption, which correlated to pH-dependent dissociation of surface functional groups. It is noteworthy that the physical properties of activated carbon were insufficient to account for the observed dye adsorption behavior, whereas the surface chemistry of activated carbon and the nature and chemical structure of dyes were more important. The fast kinetics and high capacity of dye adsorption of wood waste-derived activated carbon suggest that production of activated carbon from different types of wood waste should merit further investigation.

Performance monitoring of applied remediation technologies is an important part of site remediation. It involves periodic measurement of site parameters to evaluate whether the remediation technologies perform as expected or to determine the termination date of remediation projects. Performance monitoring can be a difficult undertaking if there are no well-defined and measurable remediation objectives, such as a reduction in mass discharge rate from a contaminant source. Besides, the selection of the site parameters to be monitored is highly dependent on the remediation objectives established and the remediation technologies applied. For instance, contaminant concentration in soil, soil vapor, and groundwater within a contaminant zone should be monitored if reduction of the mass or volume of a contaminant zone is the prime remediation objective, while contaminant concentration in groundwater just outside a contaminant zone should be the main monitoring parameter if the objective is to mitigate the contaminant migration. Furthermore, subsurface temperature is a unique monitoring parameter for in situ thermal remediation to ensure the proper operation of the technology, whereas groundwater oxidant concentration is the monitoring parameter only for in situ chemical oxidation technologies. This paper mainly covers the general criteria for establishing the site-specific remediation objectives and the key monitoring parameters for various remediation technologies, which help avoid waste of efforts to collect unnecessary site parameters during the performance monitoring. © 2007 ASCE.

Sponsored by the Hazardous, Toxic, and Radioactive Waste Management Committee of the Environmental and Water Resources Institute of ASCE. This report provides up-to-date technical information and state-of-the-art research findings on the use of zero-valent iron reactive materials to remove contaminants frequently found in groundwater. Covering both the theoretical and the practical, this book covers the comprehensive principles, latest research findings, and innovative developments in hazardous waste and inorganics removal. To establish a basic understanding of the reactive materials, the scientific principles of chemical reduction reactions, reductive precipitation, and adsorption processes are explained. Then the book describes the design methodology for the full-scale application of zero-valent iron in contaminated sites, as well as approaches to performance evaluation of the reactive materials. The book includes case studies and covers the design, installation, and performance evaluation of permeable reactive barriers based on zero-valent iron. This book will be beneficial to engineers, scientists, and decision makers applying zero-valent iron for hazardous waste and inorganics removal.

Configuration of zero-valent iron (Fe)-based permeable reactive barriers (PRBs) mainly refers to the configuration of the reactive materials and impermeable funnels emplaced in subsurface. Continuous, funnel-and-gate, trench and caisson PRBs, and GeoSiphon™/GeoFlow are the configurations currently used in PRB sites. Installation of Fe PRBs mainly involves emplacement of a permeable treatment zone containing Fe and impermeable funnels. Emplacement of the permeable treatment zone into subsurface currently can be achieved through the techniques of trench excavation, caisson- and mandrel-based emplacements, and continuous trenching. In addition, steel sheet piling barrier and slurry walls are the barriers conventionally used as impermeable funnels in PRB technology. Innovative techniques, such as jetting. hydraulic fracturing and deep soil mixing. provide alternatives to the conventional emplacement technique and all of them do not involve an excavation.

The application of zero-valent iron (Fe-0) in the funnel-and-gate permeable reactive barrier (PRB) installed at the Vapokon site, Denmark, was conducted in 1999 to remediate the groundwater contaminated by chlorinated aliphatic hydrocarbons (CAHs). Over the past 4 years, except in September 2002 and January 2003, about 92.4-97.5\% CAH removal Could be achieved with the PRB. Although there was a continuous decrease in total alkalinity (90.3\%), calcium (81.7\%), and sulfate (69.2\%) ions in the groundwater crossing the PRB, probably caused by mineral precipitation and resulting in 0.88\% porosity loss per year, no noticeable deterioration of the barrier's performance was observed between March 2000, and August 2003. Instead, chniatic variation in tile barrier's performance on CAH dechlorination was examined. The dechlorination rates in the cold season (January 2003 and March 2000) were generally smaller than those in the hot season (August 2003, September 2000, and September 2001). Besides, 1,2-dichloroethane and dichloromethane, which were proven to be not treatable by Fe-0, Could also be removed with the PRB, thereby suggesting enhancement from Fe-0 adsorption or microbial degradation.

Investigation of the hydraulic performance of a funnel-and-gate permeable reactive barrier (PRB), packed with zero-valent iron (Fe0) and installed at the Vapokon site, Denmark, has been conducted with a natural gradient tracer study. The purposes of this study were to evaluate the flow pattern and determine the seepage velocity (vx) of groundwater through the PRB. After collecting and analysing about 13 000 groundwater samples over a period of 10 months, the moving path of the tracer (i.e. lithium, Li+) was identified in which the Li+ plume was observed passing through the reactive barrier. However, probably owing to clogging caused by mineral precipitates, there was a preferential path inside the Fe 0 PRB. Comparison of the water table contour in the Vapokon site obtained in March 2000 and January 2003 showed formation of a low permeability zone within the reactive barrier, thereby further verifying clogging caused by mineral precipitates. Spatial moments analysis of the Li+ distribution illustrates the similarity of the maximum Li+ mass passing through the upgradient and downgradient locations of the Fe0 PRB and thereby indicated the conservative of the Li+ across the reactive barrier as well as the absence of bypassing flow. Based upon the results of first moment analysis, a vx of 99.5 m year-1 within the PRB was calculated. The vx just upgradient of the reactive barrier, however, was only about 6.86 m year-1, most likely owing to the effect of disturbance exerted by the clogged upgradient interface of the upper part of the Fe0 PRB.

Although permeable reactive barriers (PRB) technology appears to be a very suitable and cost effective option, the extent to which remediation results will be realized, greatly depends on the long-term integrity of the system. The formation of mineral precipitates is possibly a major factor in the long-term performance of PRB. Precipitates may passivate reactive surfaces by blocking electron-transfer sites, and thereby reduce the long-term reactivity of the granular iron to degrade groundwater contaminants. To evaluate the potential passivation impacts of inorganic groundwater chemistry, column experiments containing zero-valent iron (Fe-0) were performed under anoxic conditions to treat two contrasting Danish groundwater types spiked with trichloroethylene (TCE). For most of the experiments using Danish groundwater types, a soft low alkalinity groundwater produced slightly higher TCE dechlorination rate than did a hard high alkalinity groundwater. Compared to a soft low alkalinity baseline groundwater, it was also found the dechlorination of TCE in the column was enhanced in the presence of 1 mM CaCO3 and 1 mM NaHCO3. The dechlorination of TCE in the presence of 1 mM KNO3 and 1 mM Na2SiO3 was found to decrease considerably compared with the baseline solution. The results suggest that the composition of field groundwater is likely to strongly affect the ability of Fe-0 barriers to degrade TCE.

A funnel-and-gate permeable reactive barrier (PRB) packed with zero valent iron (Fe0) was constructed at Vapokon site, Denmark in September 1999 to remediate the groundwater contaminated by chlorinated aliphatic hydrocarbons (CAHs). In order to understand the variation of the performance of the PRB over the past 4 years and identify the major factor(s) affecting the iron barrier's performance, comprehensive monitoring of the behaviour of the Fe0 PRB was conducted between March 2000 and August 2003. Although there was a continuous decrease in total alkalinity (90.3%), calcium (81.7%) and sulphate (69.2%) ions in the groundwater across the PRB, probably caused by mineral precipitation and resulting in 0.88% porosity loss per year, no noticeable trend of deterioration of the barrier's performance was observed. Virtually, over the past 4 years, about 92.4-97.5% removal of CAHs from the groundwater could be achieved across the PRB, except in September 2002 and January 2003. Instead, climatic variation of the barrier's performance on CAHs dechlorination was examined in which the dechlorination rates in cold season (January 2003 and March 2000) were generally smaller than those in hot season (August 2003, September 2000 and September 2001). The high DO content in the groundwater caused by the recharge from rainfall precipitation may also be one of the factors affecting the performance of PRB on CAHs dechlorination.

The salinity levels of wastewater and sludge are relatively high in some coastal cities as they may use saline water for toilet flushing, and as such,the sludge dewaterability can be affected by it. The salinity effect on sludge dewaterability was therefore investigated through experimental testing of specific resistance in filtration (SRF), time to filter (TTF) and final solid content of sludge. SRF and TTF were determined using Buchner funnel tests. The final solid content was estimated by centrifuging the sludge at four levels of rotational speed. Sludge with three salinity levels (5 000, 10 000 and 20 000 ppm) were considered in this study, Coagulants such as alum iron(II) sulfate, and organic polyelectrolytes were added to the sludge to study the dewaterability of such sludge with chemical conditioning. Experimental results show that doubling the salinity level of the sludge from 10 000 to 20 000 ppm shows not much change in SRF and TTF Compared with the sludge without chemical conditioning, the addition of the coagulants to the sludge at a salinity level of 5000 ppm drastically reduces its SRF and TTF However, sludge with and without chemical conditioning at a salinity of 20 000 ppm has similar SRF and TTF The final solid content of sludge increases almost linearly with salinity. Among the coagulants used in this study, the cationic polyelectrolyte is found to be better in improving sludge dewaterability, while iron(II) sulfate performs slightly better in enhancing the final solid content of the sludge.

Examples of successful, top-down technical approaches for stabilising and improving the productivity of shifting cultivation systems are difficult to find. However, there are many compelling examples of shifting cultivators who are successfully managing local resources to intensify land use. The Indigenous Fallow Management Network, initiated by ICRAF-SE Asia, has documented and analysed many such cases