The paper reports a pilot injection test of microsized zerovalent iron (mZVI) dispersed in a guar gum shear thinning solution. The test was performed in the framework of the EU research project AQUAREHAB in a site in Belgium contaminated by chlorinated aliphatic hydrocarbons (CAHs). The field application was aimed to overcome those critical aspects which hinder mZVI field injection, mainly due to the colloidal instability of ZVI-based suspensions. The iron slurry properties (iron particles size and concentration, polymeric stabilizer type and concentration, slurry viscosity) were designed in the laboratory based on several tests (reactivity tests towards contaminants, sedimentation tests and rheological measurements). The particles were delivered into the aquifer through an injection well specifically designed for controlled-pressure delivery (approximately 10 bars). The well characteristics and the critical pressure of the aquifer (i.e. the injection pressure above which fracturing occurs) were assessed via two innovative injection step rate tests, one performed with water and the other one with guar gum. Based on laboratory and field preliminary tests, a flow regime at the threshold between permeation and preferential flow was selected for mZVI delivery, as a compromise between the desired homogeneous distribution of the mZVI around the injection point (ensured by permeation flow) and the fast and effective injection of the slurry (guaranteed by high discharge rates and injection pressure, resulting in the generation of preferential flow paths). A monitoring setup was designed and installed for the real-time monitoring of relevant parameters during injection, and for a fast determination of the spatial mZVI distribution after injection via non-invasive magnetic susceptibility measurements.

In the framework of the research project AQUAREHAB (FP7 - G. A. Nr. 226565), a pilot injection test of guar gum stabilized microsized zerovalent iron has been designed and performed under low pressure in a CAHs contaminated site in Belgium, characterized by fine sand (hydraulic conductivity in the order of 2•10-5 m/s) and an effective velocity equal to 0.005 m/day (1). The field application was aimed to overcome those critical aspects which hinder mZVI particles field injection, mainly due to ZVI-based colloidal suspensions instability. A shear thinning guar gum solution (2 g/l) was selected as an environmentally friendly stabilizer. The relevant properties of the iron slurry (iron particles size and concentration, polymeric stabilizer type and concentration, slurry viscosity) were designed in the laboratory based on several tests (namely iron reactivity tests towards contaminants, sedimentation tests and rheological measurements).The slurry preparation was successfully up-scaled to the field application, allowing a fast preparation of large volumes (1 m3 at a time) of slurry with good dissolution of guar gum and effective dispersion of mZVI. Since the injection regime of iron slurries depends on subsurface geotechnical parameters, aquifer hydraulic conductivity, and fluid properties, a specific injection well and monitoring strategy have been developed in order to achieve high discharge rates and radii of influence, and a more homogeneous distribution of the iron particles through low pressure injection. The injection well has been designed and sealed in order to sustain average to high discharge rates, preventing the daylighting of the product. Moreover the well has been hydraulically tested by means of innovative water and guar gum step rate tests in order to determine the most suitable injection rate for the iron slurry. The injection of 50 kg of microsized iron particles (BASF, Germany), dispersed in 5 m3 of a 2 g/l guar gum suspension, was performed at a discharge rate of 1.5 m3/h. The monitoring of the process has been conducted measuring injection rate and pressure as well as iron concentration by means of a magnetic susceptometer. After the injection, the iron distribution in the subsurface was determined through liners extraction and the iron concentration measured both via non-invasive magnetic susceptibility measurements and chemical analysis. Even if the field test was specifically designed to inject in a permeation regime, or on the threshold between permeation and fracturing, the results of monitoring injection pressure and iron distribution proved that particles migration in the porous medium occurred via preferential flow. Results will be presented as well as considerations about critical aspects related to injection via permeation

In the framework of the research project AQUAREHAB (FP7 - G. A. Nr. 226565), a pilot injection test of guar gum stabilized microsized zerovalent iron (mZVI) was designed and performed under low pressure in a CAHs contaminated site in Belgium. Since the injection regime of iron slurries depends on subsurface geotechnical parameters, aquifer hydraulic conductivity, and fluid properties, a specifically designed injection well was installed and a monitoring set-up developed in order to achieve high discharge rates and radii of influence, and a likely homogeneous distribution of the iron particles through low pressure injection. The injection well was designed and sealed in order to sustain average to high discharge rates, preventing the daylighting of the product. Moreover it was hydraulically tested by means of innovative water and guar gum step rate injection tests in order to determine the most suitable injection rate for the iron slurry. A subsequent injection of 50 kg of microsized iron particles (BASF, Germany), dispersed in 5 m3 of a 2 g/l guar gum suspension, was performed at a discharge rate of 1.5 m3/h. The monitoring of the process was conducted measuring injection rate and pressure as well as iron concentration by means of a magnetic susceptometer. After the injection, the iron distribution in the subsurface was determined through liners extraction and the iron concentration measured both via non-invasive magnetic susceptibility measurements and chemical analysis. The field test was specifically designed to inject in a permeation regime, or on the threshold between permeation and fracturing. A radius of influence in the order of 1 m was obtained. The presence of mZVI particles was detected up to 1.7 m from the injection point

We investigated if in-situ metal bioprecipitation (ISMP) is applicable to remediate a highly permeable zinc-contaminated aquifer at a metal-processing factory in Maasmechelen, Belgium. A large (more than 200m long and 70m wide) groundwater contamination plume has developed, with zinc concentrations in the range of 1-100mg/L, whereas the legal Flemish clean-up standard is 0.5mg/L. The estimated groundwater flow velocity is in the range 0.2-1m/d. The groundwater is relatively oxidized, naturally low in DOC (<1mg/L) and relatively low in sulfate (40-50mg/L). We conducted both laboratory feasibility tests as well as a long-term field pilot test in two sections of the plume. In the laboratory microcosm tests, zinc bioprecipitation (following addition of organic substrate and sulfate) removed more than 99% of the zinc from the water phase. Lactate, glycerol and vegetable oil were equally effective as substrates. 28-day anaerobic leaching tests indicated that the metal precipitates that were formed are stable, but they also suggested that substrate addition increases the solubility (leachability) of arsenic and manganese. In the field test, Zn concentrations were reduced by 2 to 3 orders of magnitude within the 232 day testing period and stayed low for the following 6 months in both pilot zones. In the field, no mobilization of arsenic occurred but manganese groundwater concentrations increased from 0.01-0.6mg/L to 0.4-6.5mg/L. Dissolved iron concentrations also increased markedly from below detection limits to concentrations as high as 67mg/L. Zinc concentrations in groundwater were closely correlated to pH and redox potential (Eh): plotting y=[Zn] against x=pH/log(Eh), an exponential relationship was found:

Groundwater contamination with heavy metals is a recurring major problem for mining and metallurgical sector worldwide. Expensive and non sustainable remedial methods such as Pump&Treat are currently applied. An extensive pilot program is under execution to design an in-situ remediation system (metals precipitation) for historic groundwater contamination with heavy metals underneath three nonferrous industrial sites. This program is funded by EU LIFE program. Tracers tests, data acquisition and groundwater & hydrochemical models were performed to simulate, monitor and optimize the injection design. Batch and column tests were performed to select an economic and efficient electron donor. Laboratory tests concluded that biochemical precipitation, inducing sulphate reduction and subsequent metal sulphide precipitation, is a feasible option.

The groundwater chemistry of an industrial site near the centre of a historical town in Flanders is characterized by chromium(VI) contamination. Since the potential for natural attenuation was not sufficient to control the groundwater plume as observed from different analyses like pH, Eh, soil oxidation and reduction capacity, the feasibility of site remediation based on in-situ bioprecipitation of Cr was examined in lab microcosm studies. By creating reducing conditions by addition of a carbon source in the groundwater, Cr(VI) can be biologically reduced to Cr(III), which can form an insoluble hydroxide precipitate. Between pH 6 and pH 12, the precipitated phase Cr(OH)3 predominates (Loyauw-Lawniczak et al., 2001). Microcosms contained contaminated groundwater and aquifer samples that were collected and manipulated under anaerobic conditions. A rapid conversion of Cr(VI) to Cr(III) was observed for all conditions tested (three different carbon sources). However, extensive removal of Cr from the groundwater by precipitation was only achieved for a limited number of conditions. In general, lactate was found to be the most effective carbon source, slightly better than the lowest concentration of sugar molasses that was tested, which itself was more effective than molasses based on potato. Higher concentrations of molasses, although causing a steeper decline in redox potential, resulted in less effective Cr removal. Typically, the fermentation of molasses results in acidification and this drop in pH may hinder the formation of insoluble Cr(III)-hydroxides. It may also be possible that certain components of the molasses form soluble complexes with Cr(III). For lactate, no significant drop in pH was observed. Since the outcome of these tests was positive, a pilot scale test was implemented in the field in April 2005 until June 2006. Two different substrates, the cheap waste product sugar molasses and lactate were injected creating two different impact zones and typical parameters were monitored. Frequent re-injections were important to maintain reduced conditions and are carried out three-weekly up to now. To study the stability of precipitates formed, mesocosm socks containing aquifer material were installed in the monitoring wells and harvested at regular intervals. Results of this pilot test showed efficient chromate removal from the groundwater for the lactate injection zone within 200 days, while for the molasses zone efficient removal was observed only after injecting additional substrate at a depth between 8-12 m-bg after +/- 400 days. Based on the success of this field test, a full scale process will be designed and implemented as remediation strategy.

An extensive pilot program is performed in order to design an in-situ remediation system for historic groundwater contamination with heavy metals near a non ferrous metals producing plant in Belgium. A profound site characterization has been performed, in order to obtain a detailed cross-section of the subsoil and a detailed understanding of the contaminated aquifer(s) present in the water bearing strata. Characterization of soil and groundwater has been done through drilling, borehole geophysical measurements and sampling. The hydraulic characteristics of the water bearing strata were determined through aquifer tests and piezometric campaigns. The selected site was characterized by a relative shallow contamination (< 10 m-bg) of mainly Co (30-300 mg/L) and containing typical sulphate concentrations in the range of 300-1200 mg/L. The aquifer was characterized as clayey sand. The information obtained during this characterization allowed to develop and calibrate a hydraulic groundwater model, using the USGS’s Modflow Package and a hydrochemical model using the Modflow MT3D Package. The models were used to simulate the dispersion of the injection fluid, by implementing different scenario’s regarding injection fluid constitution, volume, flow and pressure. On basis of the simulation, the interdistances, depths and equipment of the wells were optimized in function of the lithological, hydrogeological and chemical characters of the site. Lab tests, including batch and column tests have been done for the selection of an economic and efficient electron donor for each site. For the selected site, the lab tests allowed to conclude that biochemical precipitation, inducing sulphate reduction and subsequent metal sulphide precipitation, is a feasible option using Lactate as a C-source containing additional nutrients, i.e. nitrogen and phosphorus. On basis of the results of the site characterization, modeling and lab tests, the final lay-out of the pilot test has been fixed and injections started. Results should be available by the end of 2007.

We conducted a 10-month anaerobic microcosm test and a 15-month field test to investigate the effects of carbon source addition on the in-situ 1,1,1-trichloroethane (TCA) degradation in a polluted aquifer at an industrial site near Antwerp, Belgium. In the microcosms TCA decreased from 15000 μ g/L to 1500 μ g/L. 1,1-Dichloroethane (DCA) end-concentrations were about the same as the concentrations at the start of the tests (1500 μ g/L). 1,1-Dichloroethene (DCE) decreased from 1200 μ g/L to 800 μ g/L. Carbon source unamended and amended microcosms showed equal concentration trends. Neither chloroethane (CA) nor vinyl chloride (VC) were produced in the microcosms. In the field test TCA dropped from 15000 μ g/L to below 2000 μ g/L. Upstream, TCA levels remained elevated proving that the C-source injection had stimulated degradation. Sulphate reducing bacteria were stimulated; FeS was produced in the microcosms and aquifer. Dehalococcoides species were stimulated in some microcosms and in the HRC-amended aquifer. Neither sulphate reducers nor Dehalococcoidesspecies are however believed to be responsible for the observed TCA degradation. The carbon source injection however did yield environmental conditions that increased TCA degradation.

A lab scale study has been set-up to evaluate the possibilities of an inoculated bioreactor for the on-site treatment of MTBE-contaminated groundwater. Activated carbon was inoculated with two different MTBE-degrading cultures, an axenic strain (Rubrivivax sp. PM-1) and an MTBE-degrading enrichment culture. Based on batch experiments the cultures were found to degrade MTBE in the presence of the activated carbon. Column-experiments have been started to evaluate MTBE-degradation in a continuous system. Oxygen uptake was detected in the inoculated column as well as in the non-inoculated column. Based on the available preliminary data it is difficult to make a distinction between sorption and degradation of MTBE. Formation of TBA indicates that at least a part of the MTBE is removed by biodegradadation.

Chlorinated aliphatic hydrocarbons are common groundwater contaminants. One possible remediation option is in-situ reductive dechlorination by zero-valent iron, either by direct injection or as reactive barriers. Chlorinated ethenes (tetrachloroethene: PCE; trichloroethene: TCE) have received extensive attention in this context. However, another common groundwater pollutant, 1,1,1-trichlorethane (TCA), has attracted much less attention. We studied TCA reduction by three types of granular zero-valent irons in a series of batch experiments using polluted groundwater, with and without added aquifer material. Two types of iron were able to reduce TCA completely with no daughter product concentration increases (1,1-dichloroethane: DCA; chloroethane: CA). One type of iron showed slower reduction, with intermediate rise of DCA and CA concentrations. When evaluating the formation of daughter products, the tests on the groundwater alone showed different results than the groundwater plus aquifer batches: DCA did not temporarily accumulate in the batches with added aquifer material, contrary to the batches without added aquifer material. 1,1-dichloroethene (DCE, also present in the groundwater as an abiotic degradation product of TCA) was also reduced slower in the batches without added aquifer material than in the batches with aquifer material. Redox potentials gradually decreased to low values in batches with aquifer material without iron, while the batches with groundwater alone maintained a constant higher redox potential. Either adsorption processes or microbiological activity in the samples could explain these phenomena. Polymerase Chain Reaction (PCR: a targeted gene probe technique) for chlorinated aliphatic compound (CAH)-degrading bacteria confirmed the presence of Dehalococcoides sp. (chloroethene-degraders) but was negative for Desulfobacterium autotrophicum (a known co-metabolic TCA degrader). DCA reduction was rate determining: first-order half-lives of 300–350 h were observed. TCA was fully removed within hours. CA is resistant to reduction by zero-valent iron but it is known to hydrolyze easily. Since CA did not accumulate in our batches, it may have disappeared by the latter mechanism or it may not have formed as a major daughter product.

Bench-scale feasibility tests were carried out to evaluate if in-situ bioprecipitation and adsorption should be considered as remediation treatment for heavy metal impacted groundwater. The remedial goals are 1) controlling further off-site spreading, 2) mitigating source areas, and 3) reducing risks. In-situ metal bioprecipitation batch tests, based on the sulphate reduction and metalsulphide precipitation process using sulphate-reducing bacteria, were carried out. High metals removal rates were obtained using an appropriate electron donor or bio-augmentation (Desulfovibrio desulfotomaculum Dd8301 and the Postgate medium). The use of a sorption barrier (secondary polishing step) to prevent further spreading of the heavy metal groundwater contamination has been validated using batch tests with various aluminosilicates (zeolites and Metasorb) and aerobic/anaerobic compost (with/without crushed limestone for pH adjustment). The compost mixtures demonstrated significant heavy metal removal, the best results were obtained with the anaerobic compost. Feasibility tests were done in batch and at column level.

In situ bioremediation of oil-contaminated soils by means of bioventing is seen as a cost effective technology for remediation of oil contaminated sites. Laboratory microcosms containing a long-term heavy oil contaminated soil were treated as a bioventing simulation system, applying different system parameters (i.e., the amendment of different nutrient compositions: mineral nutrients and a commercial oleophylic nutrient) with or without oxygen. In addition, in some microcosms extra diesel fuel was added in order to examine the influence of the oil concentration on the developing microbial populations. The changes in microbial populations were followed by means of Denaturing Gradient Gel Electrophoresis (DGGE) of 16S rDNA fragments generated by PCR using general eubacterial primers, and by CFU counts after microbial extraction. Analysis of the hydrocarbon content was performed to investigate the biodegradation capacity. Bacteria capable of using high oil concentrations as a C-source, were isolated and characterised for their hydrocarbon utilization pattern. Based on the clustered DGGE patterns, the CFU counts, and the hydrocarbon content, an effect on the microbial oil degrading soil population could be observed for those soil samples to which nutrients were added. Aeration did not seem to make any difference.

The use of bacteria for the removal of heavy metals from contaminated groundwater is presented by two examples. The first one utilizes in situ bioprecipitation of the heavy metals in the unsaturated zone. The system is based on the induction of sulphate reducing bacteria by addition of a specific carbon source. The second system is based on a pump & treat system and utilizes san filters inoculated with heavy metals bioprecipitating and biosorbing bacteria to remove the metals from the pumped groundwater on site. Special attention is also paid to the biodegradation of BTEX in the presence of heavy metals (mixed waste).