Use of iron-based technologies in contaminated land and groundwater remediation: a review

Reactions involving iron play a major role in the environmental cycling of a wide range of important organic, inorganic and radioactive contaminants. Consequently, a range of environmental clean-up technologies have been proposed or developed which utilise iron chemistry to remediate contaminated land and surface and subsurface waters, e.g. the use of injected zero zero-valent iron nanoparticles to remediate organic contaminant plumes; the generation of iron oxyhydroxide-based substrates for arsenic removal from contaminated waters; etc. This paper reviews some of the latest iron-based technologies in contaminated land and groundwater remediation, their current state of development, and their potential applications and limitations.     

Slow sand filters effectively reduce Phytophthora after a pathogen switch from Fusarium and a simulated pump failure

Slow sand filtration has been shown to effectively reduce Phytophthora zoospores in irrigation water. This experiment tested the reduction of Phytophthora colony forming units (CFUs) by slow sand filtration systems after switching the pathogen contaminating plant leachate from Fusarium to Phytophthora and the resilience of the system to a short period without water, as might be caused by a pump failure. The slow sand filtration system greatly reduced Phytophthora CFUs and transmission after switching the pathogens. In addition, Phytophthora reduction by the slow sand filter was equally effective before and after the simulated pump failure. Reduction of Fusarium was not seen by the SSFs, before or after the simulated pump failure. The results suggest that slow sand filters are effective at reducing larger organisms, such as Phytophthora zoospores, even after a pump failure or a change in pathogens.     

Gefährdung des Grundwassers durch Freisetzung organischer Schadstoffe: Methoden zur Berechnung der in-situ-Schadstoffkonzentrationen

The release of pollutants from contamined soils can be due to desorption and dissolution from residual phase blobs or pools. Volatile compounds can diffuse from contaminated soil air into the groundwater. This paper discusses the basic release processes and presents methods for the calculation of the rates of desorption, dissolution and diffusion. These rates are a prerequisite for the determination of the in-situ contaminant concentration in groundwater. The necessary parameters can be estimated from empirical correlations or may be measured directly in laboratory experiments. Column experiments, e. g., yield maximum release rates in the case of slow diffusion limited desorption whereas dissolution of contaminants from blobs of residual phase results in maximum concentration (solubility) in the column effluent.     

Modeling antimicrobial contaminant removal in slow sand filtration

Slow sand filters are used in rural regions where source water may be subjected to antimicrobial contaminant loads from waste discharges and diffuse pollution. A numerical model (LETA) was derived to calculate aqueous antimicrobial concentrations through time and depth of a slow sand filter and estimate accumulating contaminant mass in the schmutzdecke. Input parameters include water quality variables easily quantified by water system personnel and published adsorption, partitioning, and degradation coefficients. Simulation results for the tetracycline, quinolone, and macrolide classes of antimicrobials suggested greater than 3-log removal from 1 microg/L influent concentrations within the top 40 cm of the sand column, with schmutzdecke antimicrobial concentrations comparable to other land-applied waste biosolids. A 60-day challenge experiment injecting 1 microg/L tylosin to a pilot slow sand filter showed an average 0.1mg/kg of the antimicrobial remaining in the schmutzdecke layer normally removed during filter maintenance, and this value was the same order of magnitude as the sorbed concentration predicted by the LETA model.     

Untersuchungen zum Langzeiteinsatz der In-situ-Aktivkohlefiltration zur Entfernung von organischen Schadstoffen aus Grundwasser

Long-term in-situ removal of organic contaminants using activated carbon was investigated within the framework of the SAFIRA-Project. Common problems are plugging and chemo- or biofouling, which can reduce the sorption capacity or permeability of the activated carbon filter. The tests involved three different types of granular activated carbon (TL 830, INP Reac, both from Chemviron and ROW 0.8 supra, from Norit). The groundwater predominately contaminated with monochlorobenzene (MCB) was treated successfully and efficient over a time period of two years by the activated carbon filtration. In none of the in-situ operated activated carbon filters plugging, chemo- or biofouling was observed, which is believed to be due to the strategy of keeping the natural groundwater chemistry stable. The loading of the activated carbon with the contaminants agreed very well with expectations from modeling (PSDM). The results of this long term investigation demonstrate, that in-situ activated carbon filtration is a very successful method to remove hydrophobic contaminants from groundwater without bio- or chemofouling.     

Arsenic Removal from Contaminated Groundwater by Zero Valent Iron: a Mechanistic and Long-Term Performance Study

The present study investigated the application of zero valent iron to remediate the arsenic in naturally contaminated groundwater. A performance evaluation was conducted in the laboratory on groundwater contaminated with artificial arsenic using sodium arsenate (Na₂HAsO₄.7H₂O) to simulate the arsenic concentration in the groundwater. Batch and column experiments were performed to evaluate the arsenic removal capacity by zero valent iron and the removal mechanism. The flow rate (up-flow mode) was maintained for 180 days in each column. The results from both the batch and the column experiments showed that more than 99% of the arsenic was removed successfully. In the column experiments, the arsenic was efficiently removed and the arsenic concentration in the treated water decreased to below the limit of 10 μg /L (WHO's standard) even when the columns were packed with only 25% ZVI by volume. We used SEM and XRD to characterize the surface morphology and the corrosion layer which formed on pristine ZVI and arsenic-treated ZVI to elucidate the arsenic removal mechanism. XRD and SEM results revealed that ZVI gradually converted to a magnetite/maghemite corrosion product mixed with lepidocrocite. Adsorption followed by co-precipitation was an important pathway to removing the arsenic by ZVI. Our results suggest that ZVI, combined with sand, is a suitable candidate for the ex-situ treatment of groundwater in the neutral pH range and in the presence of dissolved oxygen.     

Validation of two tropical marine bivalves as bioindicators of mining contamination in the New Caledonia lagoon: Field transplantation experiments

The bioaccumulation and retention capacities of some key local contaminants of the New Caledonia lagoon (Ag, As, Cd, Co, Cr, Cu, Mn, Ni and Zn) have been determined in the oyster Isognomon isognomon and the edible clam Gafrarium tumidum during transplantation experiments. In a first set of experiments, oysters and clams from a clean site were transplanted into contaminated sites. Uptake kinetics determined in the field indicated that for Cr and Cu in oysters and Co, Ni, and Zn in clams, concentrations in transplanted bivalves reached those of resident organisms after 100d, whereas for the other elements, it would require a longer time for transplanted bivalves to reach the same levels as in the resident populations (e.g., up to 3 years for Cd). However, the slow uptake rate for metals observed in the latter transplantation is rather related to low bioavailability of metals at the contaminated sites than to low bioaccumulation efficiency of the organisms. Indeed, results of a second transplantation experiment into two highly contaminated stations indicated a faster bioaccumulation of metals in both bivalves. Results of both transplantations point out that the clam G. tumidum is a more effective bioindicator of mining contamination than I. isognomon, since it is able to bioaccumulate the contaminants to a greater extent. However the very efficient metal retention capacity noted for most elements indicates that organisms originating from contaminated sites would not be suitable for monitoring areas of lower contamination. Hence, geographical origin of animals to be transplanted in a monitoring perspective should be carefully selected.     

The environmental impact of gold mine tailings footprints in the Johannesburg region, South Africa

 Gold mining in South Africa resulted in vast volumes of tailings, which have been deposited in impoundments. Poor management of most of the tailings dams resulted in the escape of seepage, adversely affecting soils and water quality. Some tailings dams have been partially or completely reclaimed leaving contaminated footprints. These zones pose a serious threat to the underlying dolomitic aquifers. In this study, the footprints of seven selected sites situated near Johannesburg have been investigated. It was found that the topsoil is highly acidified and only a minor portion of contaminants is bioavailable. However, phytotoxic contaminants such as Co, Ni and Zn could complicate rehabilitation measures as they limit the soil function. In addition, soil samples contain trace element concentrations, which often exceed background concentrations in soils. As a result, the depletion of buffer minerals and the subsequent acidification could result in the long-term remobilization of large quantities of contaminants into the groundwater. Soil management measures such as liming are required to prevent the contaminant migration from the topsoil into the subsoil and groundwater as well as to provide suitable recultivation conditions to enable future land use. Received: 20 April 1999 · Accepted: 27 September 1999     

A sand/granular carbon filtration treatment system for removing aqueous pesticide residues from a marine toxicology laboratory effluent

Flow-through toxicity tests using marine organisms can generate large volumes of contaminated seawater effluent which should be treated to remove the contaminants before discharge into the environment. We have developed a sand filtration/carbon treatment system that removes from these effluents a diversity of organophosphate, organochlorine and pyrethroid pesticide residues down to their detection limit. The sand filter removed an average of 72% (range 4–99%) of the chemicals by continuously filtering suspended particulates and chemicals associated with the particulate. Following sand filtration, effluent water slowly percolates through granular carbon. Overall, organic removal efficiencies average 91% (range 24–99%). Initial construction cost was less than $20,000.     

Removal of heavy metals from storm and surface water by slow sand filtration: the importance of speciation

The removal of heavy metals from storm and surface waters by slow sand filtration is described. The importance of speciation as a technique for exploring and improving the mechanisms of removal is identified. Laboratory-scale slow sand filters operating at conventional flow rate and depth were shown to be able to reduce concentrations of selected heavy metals (Cu, Cr, Pb and Cd) found in road runoff, surface water and sewage effluents to drinking water standard. Nitrogen, volatile solids and modified Stover speciation were used to differentiate between the potential mechanisms of removal, i.e. active biomass, organic adsorption and simple adsorption or precipitation on the surface of the sand. The data presented show that adsorption via organic ligands was the predominant mechanism for metal removal at the surface of the filter but chemical adsorption was the more important deeper in the filter. In the lower layers the adsorbed metals were more easily exchanged than the organically bound metals. The precise chemical ligands were not identified and varied from metal to metal. The most important operational factors affecting performance were therefore the concentration of organic matter, filter depth and the flow velocity.     

Effect of residues from a burnt oil refinery on the compaction parameters and strength of clayey sand

Soil contamination by petroleum contaminants and their derivatives has harmful effects on the environment, including groundwater and marine contamination and on the geotechnical properties of the soil. It decreases the soil strength, bearing capacity of foundations, and slope and trench stability. Petroleum contaminants can also alter the structure of cohesive granular soil. The present study examined the effect of acidic sludge and dirt filter contaminants from a burnt oil refinery on the compaction parameters and strength of clayey sand. Proctor compaction and direct shear tests were performed on soil samples containing 0%, 3%, 6%, and 9% of these pollutants. Direct shear tests were performed at different depths and stresses on soil samples from sandy soil contaminated with the residue from a burnt oil refinery. The results showed that with approximately 4 to 5% increase in pollution, the maximum dry soil unit weight increases and decreases with the addition of more contaminants. Also, the friction and dilatancy angles of the soil decreased. The sample containing 9% pollutants recorded the most significant decrease in these values. The effect of surface-active agents on acidic sludge caused an increase in the Van der Waals force between the particles, resulting in an increase in soil cohesion. Contamination with 47.7% SiO₂ from the dirt filter increased the soil cohesion parameter. Under similar experimental and loading conditions, an increase in the acidic sludge and dirt filter contents decreased the soil shear strength and dilatancy angle.

     

Examining metal migration through geotextiles during dewatering

This paper presents a study conducted to assess the influence that a filter cake deposited on the surface of the geotextile has on the mobility of three metals (Cu, Pb, Zn) during filtration of a contaminated sediment. Two chemical additives (cationic coagulant and cationic polymer) were introduced to the sediment to increase the particle size and improve the filtration efficiency. Bench scale experimentation was conducted to identify contaminant reduction using a small volume of sediment. A field test was applied to observe what effect three-dimensional filtration and a larger filter cake had on metal mobility. Analysis of the effluent was conducted to determine total and dissolved metal contaminants, as well as particulate matter. Effluent chemical properties (pH, E_h, and zeta potential) were analyzed to identify a possible rationale for variations in concentration during filtration. The results of the study show that as an increasing buildup of filter cake on the surface of a geotextile developed, filtrate quality was improved with respect to the metal and particulate contaminants considered. In addition, the metals detected in the effluent were primarily in the solid state, suggesting further reduction could be achieved through subsequent filtration (if desired).     

BAF/O_3预处理工艺后砂滤池的除污效果

以珠江广州段源水为处理对象,考察了曝气生物滤池（BAF）／臭氧（O3）预处理工艺后砂滤池的除污效果。结果表明,砂滤池出水CODMn、NH4^＋ -N和浊度的平均值分别为2．19、0．099mg／L和0．225NTU,NO2^- -N的最高值为0．003mg／L;相对于沉淀池出水,砂滤池对上述指标的平均去除率分别为27．60％、66．88％、69．88％和98．53％。BAF和臭氧塔提高了源水的DO浓度,其对浊度和有机物的去除作用降低了砂滤池的反冲洗频率,从而有利于提高生物膜中微生物的数量和活性;臭氧氧化可提高源水的可生化性,且水中没有残留臭氧,也为砂滤池的生物降解作用提供了有利条件。     

复合污染地下水的两级处理工艺中试研究

开展了石英砂+生物活性炭的两级处理工艺净化复合污染地下水的中试研究。结果表明,当石英砂滤料未成熟时,单级过滤对铁、锰的去除效果较好,但是对氨氮及CODMn的去除效果不理想;二级过滤工艺可以明显提高水中氨氮和CODMn的去除效果;滤料成熟后系统对铁、锰、氨氮及CODMn的平均去除率分别达到99.5%,99.9%,93.7%和34.5%。该处理工艺出水水质较好,抗水质冲击负荷能力强,且运行稳定性高。     

The role of aluminum in slow sand filtration

Engineering enhancement of slow sand filtration has been an enigma in large part because the mechanisms responsible for particle removal have not been well characterized. The presumed role of biological processes in the filter ripening process nearly precluded the possibility of enhancing filter performance since interventions to enhance biological activity would have required decreasing the quality of the influent water. In previous work, we documented that an acid soluble polymer controls filter performance. The new understanding that particle removal is controlled in large part by physical chemical mechanisms has expanded the possibilities of engineering slow sand filter performance. Herein, we explore the role of naturally occurring aluminum as a ripening agent for slow sand filters and the possibility of using a low dose of alum to improve filter performance or to ripen slow sand filters.     

Comparison of injection well patterns for remediating benzene‐contaminated groundwater

Ten alternative injection well patterns and a no‐action plan were evaluated for bioremediating benzene‐contaminated groundwater. Evaluations were made for a silty‐sand aquifer using a contaminant fate and transport model. Wells injected water containing 8 mg/L dissolved oxygen. The study's objective was to rank the alternative schemes based upon mass of contaminant removed and area of residual groundwater contamination. Interior configurations with injection wells at areas of high benzene concentration outperformed the other remediation schemes. Interior wells supply oxygen quickly to areas of a plume where it is most needed. Alternative configurations rely upon groundwater to transport the oxygen, an inefficient process. No action was the least effective strategy.     

Composition of bacterial and archaeal communities in freshwater sediments with different contamination levels (Lake Geneva, Switzerland)

The aim of this study was to compare the composition of bacterial and archaeal communities in contaminated sediments (Vidy Bay) with uncontaminated sediments (Ouchy area) of Lake Geneva using 16S rRNA clone libraries. Sediments of both sites were analysed for physicochemical characteristics including porewater composition, organic carbon, and heavy metals. Results show high concentrations of contaminants in sediments from Vidy. Particularly, high contents of fresh organic matter and nutrients led to intense mineralisation, which was dominated by sulphate-reduction and methanogenesis. The bacterial diversity in Vidy sediments was significantly different from the communities in the uncontaminated sediments. Phylogenetic analysis revealed a large proportion of Betaproteobacteria clones in Vidy sediments related to Dechloromonas sp., a group of dechlorinating and contaminant degrading bacteria. Deltaproteobacteria, including clones related to sulphate-reducing bacteria and Fe(III)-reducing bacteria (Geobacter sp.) were also more abundant in the contaminated sediments. The archaeal communities consisted essentially of methanogenic Euryarchaeota, mainly found in the contaminated sediments rich in organic matter. Multiple factor analysis revealed that the microbial community composition and the environmental variables were correlated at the two sites, which suggests that in addition to environmental parameters, pollution may be one of the factors affecting microbial community structure.     

Evaluation of a laboratory-scale bioreactive in situ sediment cap for the treatment of organic contaminants

The development of bioreactive sediment caps, in which microorganisms capable of contaminant transformation are placed within an in situ cap, provides a potential remedial design that can sustainably treat sediment and groundwater contaminants. The goal of this study was to evaluate the ability and limitations of a mixed, anaerobic dechlorinating consortium to treat chlorinated ethenes within a sand-based cap. Results of batch experiments demonstrate that a tetrachloroethene (PCE)-to-ethene mixed consortium was able to completely dechlorinate dissolved-phase PCE to ethene when supplied only with sediment porewater obtained from a sediment column. To simulate a bioreactive cap, laboratory-scale sand columns inoculated with the mixed culture were placed in series with an upflow sediment column and directly supplied sediment effluent and dissolved-phase chlorinated ethenes. The mixed consortium was not able to sustain dechlorination activity at a retention time of 0.5 days without delivery of amendments to the sediment effluent, evidenced by the loss of cis-1,2-dichloroethene (cis-DCE) dechlorination to vinyl chloride. When soluble electron donor was supplied to the sediment effluent, complete dechlorination of cis-DCE to ethene was observed at retention times of 0.5 days, suggesting that sediment effluent lacked sufficient electron donor to maintain active dechlorination within the sediment cap. Introduction of elevated contaminant concentrations also limited biotransformation performance of the dechlorinating consortium within the cap. These findings indicate that in situ bioreactive capping can be a feasible remedial approach, provided that residence times are adequate and that appropriate levels of electron donor and contaminant exist within the cap.     

滴滤池-人工湿地组合工艺处理农村生活污水

采用滴滤池-人工湿地组合工艺处理农村生活污水,考察了其除污效果及两工艺对污染物去除的贡献率.中试结果表明,在稳定运行状态下,滴滤池对COD、氨氮、总氮和总磷去除的贡献率分别为74.5%、79.2%、33.8%、47.5%,人工湿地的则分别为25.5%、20.8%、66.2%、52.5%.滴滤池能有效完成对有机物的降解和硝化作用,人工湿地系统则能进一步去除氮、磷等污染物,两者结合可使污水中的各类污染物得到有效去除.     

The Use of Limestone Bed Filtration for the Treatment of Ferruginous Groundwater

A pilot plant, consisting of limestone bed and sand filtration units, has been built 15 km south of Cairo to serve about 400 people. The plant comprises three limestone filter units (operated in series) and two sand filters. Operation of the pilot plant has shown that a packed limestone filter unit is a simple and cheap method of removing iron from ferruginous groundwater. The results demonstrate an iron removal rate of about 60% after passing through one 1.15?m deep limestone filter operating with a surface loading rate up to 1.4 m³/m². h. The overall iron removal after one limestone filter followed by sand filtration was more than 90%.