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.     

Fate of N-nitrosomorpholine in an anaerobic aquifer used for managed aquifer recharge: a column study

The fate of N-nitrosomorpholine (NMOR) was evaluated at microgram and nanogram per litre concentrations. Experiments were undertaken to simulate the passage of groundwater contaminants through a deep anaerobic pyritic aquifer system, as part of a managed aquifer recharge (MAR) strategy. Sorption studies demonstrated the high mobility of NMOR in the Leederville aquifer system, with retardation coefficients between 1.2 and 1.6. Degradation studies from a 351 day column experiment and a 506 day stop-flow column experiment showed an anaerobic biologically induced reductive degradation process which followed first order kinetics. A biological lag-time of less than 3 months and a transient accumulation of morpholine (MOR) were also noted during the degradation. Comparable half-life degradation rates of 40-45 days were observed over three orders of magnitude in concentration (200 ng L⁻¹ to 650 μg L⁻¹). An inhibitory effect on microorganism responsible to the biodegradation of NMOR at 650 μg L⁻¹ or a threshold effect at 200 ng L⁻¹ was not observed during these experiments.     

Biosorption of phenol and chlorophenols by acclimated residential biomass under bioremediation conditions in a sandy aquifer

Phenol and chlorophenols are common environmental contaminants. The fate and transport of these chemicals must be sufficiently understood to predict detrimental environmental impacts and to develop technically and economically appropriate remedial action to minimise environmental degradation. In order to gain a better understanding of the many mechanisms influencing the fate of phenol and chlorophenols in a sandy aquifer, we conducted biosorption experiments with biomass collected from a simulated aquifer polluted by consecutive accidental spills of phenol, 2-monochlorophenol, 2,4,6-trichlorophenol and pentachlorophenol under continuous bioremediation conditions following a closed-loop configuration during 180 days. A comparative study of the biosorption capacity of phenol and chlorophenols characterised by different physicochemical properties, at different pHs in the range of 6.0+/-0.1 to 9.0+/-0.1 showed the following: (i) the biosorption of phenol and chlorophenols on resident biomass was rapid (equilibrium reached in less than 2h); (ii) the experimental data followed the Freundlich isotherm; (iii) changes in pH from 6.0+/-0.1 to 9.0+/-0.1 resulted in a decrease in the equilibrium biosorption capacity (qeq); (iv) both Freundlich parameters (KF, n) should be used together as predictive parameters in mathematical models to simulate the fate of phenol and chlorophenols in the aquifer; (v) qeq of phenol and chlorophenols investigated in this study were satisfactorily correlated to their hydrophobicity (Kow) with a correlation factor 0.98. In addition, available data from other reported studies fell in the same correlation curve. The results of the present study should be introduced in mathematical models developed to predict the effect of biomass fate and transport of contaminants in aquifers during bioremediation conditions.     

Mutagenic assessment of Prestige fuel oil spilled on the shore and submitted to field trials of bioremediation

The mutagenicy of the slightly weathered fuel oil from the Prestige oil spill and the effects of different bioremediation products (nutrients and/or microorganisms and biodiesel) on the potential mutagenic activity of this heavy fuel oil spilled on the shore were evaluated for a period of 1 year using the Ames Salmonella assay with strains TA98, TA100, TA1535 and TA1537 in the absence and presence of exogenous metabolic activation (S9 fraction from rat liver). The in situ bioremediation experiment was performed using tiles located in the supra-littoral and intertidal zones of a beach seriously affected by the fuel oil spill. The results obtained showed the mutagenic activity of the slightly weathered fuel oil extracts at the beginning of the experiment in strain TA98 that persisted for more than 150 days in both the untreated control and treated tiles independently of the zone of the beach considered. However, after 360 days neither the control nor the treated tiles in the intertidal zone showed mutagenic activity and a weak positive response in strain TA98 was detected for the control fuel oil extracts from supra-littoral tiles. The application of biodiesel to accelerate the biodegradation of this type of fuel oil may constitute a further genotoxic hazard to the environment, since the mutagenic response achieved from the biodiesel-fuel oil mixture in the first samplings (days 0 and 30) was more potent than that obtained from the control tiles. The mutagenic activity was detected along the study with S. typhimurium TA98 in both the presence and absence of S9 microsomal fraction, but the addition of S9 fraction in the assay always increased the number of revertants induced. In general, these findings suggest that the bioremediation strategies used were not effective in eliminating the genotoxic hazard associated with this heavy fuel oil attached to rocky substrate since they did not achieve a decrease in the mutagenic response with respect to the untreated control tiles. These data also confirm that genotoxicity assays should be used to evaluate the effectiveness of bioremediation efforts associated with oil spills for a better risk assessment.     

In situ disinfection of sewage contaminated shallow groundwater: a feasibility study

Sewage-contaminated shallow groundwater is a potential cause of beach closures and water quality impairment in marine coastal communities. In this study we set out to evaluate the feasibility of several strategies for disinfecting sewage-contaminated shallow groundwater before it reaches the coastline. The disinfection rates of Escherichia coli (EC) and enterococci bacteria (ENT) were measured in mixtures of raw sewage and brackish shallow groundwater collected from a coastal community in southern California. Different disinfection strategies were explored, ranging from benign (aeration alone, and aeration with addition of brine) to aggressive (chemical disinfectants peracetic acid (PAA) or peroxymonosulfate (Oxone)). Aeration alone and aeration with brine did not significantly reduce the concentration of EC and ENT after 6 h of exposure, while 4-5 mg L⁻¹ of PAA or Oxone achieved >3 log reduction after 15 min of exposure. Oxone disinfection was more rapid at higher salinities, most likely due to the formation of secondary oxidants (e.g., bromine and chlorine) that make this disinfectant inappropriate for marine applications. Using a Lagrangian modeling framework, we identify several factors that could influence the performance of in-situ disinfection with PAA, including the potential for bacterial regrowth, and the non-linear dependence of disinfection rate upon the residence time of water in the shallow groundwater. The data and analysis presented in this paper provide a framework for evaluating the feasibility of in-situ disinfection of shallow groundwater, and elucidate several topics that warrant further investigation.     

Occurrence of sessile Pseudomonas oryzihabitans from a karstified chalk aquifer

Pseudomonas oryzihabitans is an uncommon pathogen that may cause opportunistic infections. Although it has been previously isolated from the environment, the source of human infection has not been well documented. In this study, we describe the presence of P. oryzihabitans adhering on suspended particulate matters recovered from karst groundwaters. The isolated pathogen was capable of forming biofilms on silicon supports and clay beads. Adherent P. oryzihabitans cells displayed a high resistance to chlorine as compared with the same organisms cultured in the planktonic mode. These results demonstrate that aquifer biofilms are potential environmental sources for water-born P. oryzihabitans infections and that bacterial attachment might affect drinking water purification.     

Metabolism of the soil and groundwater contaminants,ethylene dibromide and trichloroethylene,by the tropical leguminous tree,Leuceana leucocephala

Ethylene dibromide (EDB; dibromoethane) and trichloroethylene (TCE) are hazardous environmental pollutants. The use of plants to treat polluted sites and groundwater, termed phytoremediation, requires plants that can both effectively remove the pollutant as well as grow in the climatic region of the site. In this paper, we report that the tropical leguminous tree, Leuceana leucocephala var. K636, is able to take up and metabolize EDB and TCE. The plants were grown in sterile hydroponic solution without its symbiont, Rhizobium. EDB and TCE were both metabolized by the plant, as indicated by the formation of bromide ion from EDB and trichloroethanol from TCE. Each plant organ was independently capable of debromination of EDB. L. leucocephala is being used to treat perched groundwater as part of a remedial alternative to address an accidental EDB spill in Hawaii. Bromide levels of plant tissues from the trees grown in the phytoremediation treatment cells at the Hawaii Site were elevated, indicating uptake and degradation of brominated compounds in the trees. This report is the first evidence of a tropical tree effectively metabolizing these common organic pollutants.     

Identification of microorganisms involved in reductive dehalogenation of chlorinated ethenes in an anaerobic microbial community

In this study, we report on phylogenetic and physiological characterization of an anaerobic culture capable of reductive dehalogenation of tetrachloroethene (PCE) obtained from a PCE-contaminated site. The culture was enriched using different combinations of electron donors (hydrogen and acetate) and electron acceptors (PCE, cis-1,2-dichloroethene (cDCE) and controls without chlorinated ethenes). The resulting subcultures were analyzed using three different approaches: chemical analysis to document conversion of chlorinated ethenes; polymerase chain reaction (PCR) of 16S rRNA gene fragments and denaturing gradient gel electrophoresis (DGGE) to compare community compositions; fluorescence in situ hybridization (FISH) to quantify specific groups of microorganisms using oligonucleotide probes previously designed or newly designed based on the sequences retrieved from sequence analysis of specific DGGE bands. Members of two genera which contain bacteria capable of reductive dehalogenation were detected in the culture: Dehalococcoides and Desulfitobacterium. The combined analyses suggested that Dehalococcoides-like bacteria are associated with complete dehalogenation of chlorinated ethenes to ethene with hydrogen as electron donor; and Desulfitobacterium-like bacteria, in contrast, are associated with incomplete PCE dehalogenation to cDCE and appear to be able to use acetate as electron donor. In addition, Sporomusa-like bacteria were identified, which most likely act as homoacetogens. The results demonstrated that combination of culture enrichment with different substrates, DGGE, and FISH allowed a detailed qualitative and quantitative characterization of the dominant microorganisms associated with reductive dehalogenation.     

Enhanced removal of polychlorinated biphenyls from alfalfa rhizosphere soil in a field study: The impact of a rhizobial inoculum

Polychlorinated biphenyls (PCB) are persistent pollutants in soil environments where they continue to present considerable human health risks. Successful strategies to remediate contaminated soils are needed that are effective and of low cost. Bioremediation approaches that include the use of plants and microbial communities to promote degradation of PCB have significant potential but need further assessment under field conditions. The effects of growth of alfalfa (Medicago sativa L.) and inoculation with a symbiotic nitrogen fixing bacterium (Rhizobium meliloti) on the removal of polychlorinated biphenyls (PCB) from rhizosphere soil were evaluated in a field experiment. The initial PCB content of the soil ranged from 414 to 498 µg kg⁻¹. PCB removal for the rhizosphere soil was enhanced in the planted treatments, an average of 36% decrease in PCB levels compared to a 5.4% decrease in the unplanted soil, and further enhanced when plants were inoculated with the symbiotic Rhizobium (an average of 43% decrease) when evaluated at 90 days after planting. Plant biomass production was higher in the inoculated treatment. The total PCB content was increased from 3.30 µg kg⁻¹ to 26.72 µg kg⁻¹ in plant shoots, and from 115.07 µg kg⁻¹ to 142.23 µg kg⁻¹ in roots in the inoculated treatment compared to the planted treatment. Increased colony forming units (cfu) of total heterotrophic bacteria, biphenyl-degrading bacteria and fungi were observed in the rhizosphere of inoculated plants. PCB removal from the rhizosphere soil was not significantly correlated with the direct PCB uptake by the plants in any of the treatments but was significantly correlated with the stimulation of rhizosphere microflora. Changes in the soil microbial community structure in the planted and inoculated treatment were observed by profiling of bacterial ribosomal sequences. Some bacteria, such as Flavobacterium sp., may have contributed to the effective degradation of PCB and deserve further investigation.     

In situ characterization of nitrifying biofilm: Minimizing biomass loss and preserving perspective

Methods for characterizing nitrifying bacteria within biofilms are of key importance to understand and optimize the nitrification kinetics of attached growth treatment facilities. In this work, we propose an analytical protocol based upon environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy (CSLM) in combination with fluorescent in situ hybridization (FISH) to characterize the structure of nitrifying biofilm as it remains attached to the original reactor substratum. This protocol minimizes the loss of mass and distortion of in situ perspective commonly associated with traditionally applied microscopic techniques and thereby enables a more accurate estimation of the nitrifying biomass within biofilm attached to the substratum. The use of ESEM eliminates the destructive preparatory procedures associated with traditional scanning electron microscopy and thus the loss of mass and shrinking of the samples. ESEM is used in this study to evaluate the percent coverage of the substratum with biofilm and the biofilm thickness. CLSM-FISH is used to determine cell counts in the biofilm and to characterize the undisturbed substratum/biofilm interface. By hybridizing and analyzing the nitrifying biofilm using CLSM as it remains attached to the substratum, the loss of material and distortion of in situ perspective associated with the biofilm detachment process is minimized. Moreover, by conducting the CLSM analysis directly on the nitrifying biofilm as it remains attached to the substratum it is shown that cell counts at the substratum/biofilm interface differ significantly from that located above the interface.     

Benzoate and salicylate degradation by Halomonas campisalis, an alkaliphilic and moderately halophilic microorganism

Alkaliphiles and halophiles have considerable potential to treat organic pollutants in industrial wastewaters having high pH and salinity. As model aromatic compounds, benzoate and salicylate at concentrations up to 380 mg/L were degraded as carbon and energy sources by Halomonas campisalis, an alkaliphile and moderate halophile. Aerobic batch experiments were performed at 50 and 100g/L NaCl and pH 9. Detected metabolites, catechol and cis, cis-muconate, indicated that H. campisalis used the ortho degradation pathway for both substrates. For benzoate concentrations up to 1600 mg/L, the intermediate 2-hydroxymuconic semialdehyde (2HMSA), characteristic of the meta pathway, was not detected. Improved understanding and characterization of these degradation processes in high pH, high salt systems may lead to improved application of haloalkaliphiles for industrial wastewater treatment.     

1,4-Dioxane biodegradation at low temperatures in Arctic groundwater samples

1,4-Dioxane biodegradation was investigated in microcosms prepared with groundwater and soil from an impacted site in Alaska. In addition to natural attenuation conditions (i.e., no amendments), the following treatments were tested: (a) biostimulation by addition of 1-butanol (a readily available auxiliary substrate) and inorganic nutrients; and (b) bioaugmentation with Pseudonocardia dioxanivorans CB1190, a well-characterized dioxane-degrading bacterium, or with Pseudonocardia antarctica DVS 5a1, a bacterium isolated from Antarctica. Biostimulation enhanced the degradation of 50 mg L⁻¹ dioxane by indigenous microorganisms (about 0.01 mg dioxane d⁻¹ mg protein⁻¹) at both 4 and 14 °C, with a simultaneous increase in biomass. A more pronounced enhancement was observed through bioaugmentation. Microcosms with 50 mg L⁻¹ initial dioxane (representing source-zone contamination) and augmented with CB1190 degraded dioxane fastest (0.16 ± 0.04 mg dioxane d⁻¹ mg protein⁻¹) at 14 °C, and the degradation rate decreased dramatically at 4 °C (0.021 ± 0.007 mg dioxane d⁻¹ mg protein⁻¹). In contrast, microcosms with DVS 5a1 degraded dioxane at similar rates at 4 °C and 14 °C (0.018 ± 0.004 and 0.015 ± 0.006 mg dioxane d⁻¹ mg protein⁻¹, respectively). DVS 5a1 outperformed CB1190 when the initial dioxane concentration was low (500 μg L⁻¹, which is representative of the leading edge of plumes). This indicates differences in competitive advantages of these two strains. Natural attenuation microcosms also showed significant degradation over 6 months when the initial dioxane concentration was 500 μg L⁻¹. This is the first study to report the potential for dioxane bioremediation and natural attenuation of contaminated groundwater in sensitive cold-weather ecosystems such as the Arctic.     

In situ aquatic bioassessment of pesticides applied on rice fields using a microalga and daphnids

This study assessed the effects of episodic contamination on a drainage canal adjacent to an area of intensive rice production (Coimbra, Portugal). Four monitoring periods were considered [i) before herbicide application (day -14), ii) at the first application day (day 0), iii) 3 or 5 and iv) 6 days after]. Each one consisted in three complementary evaluation lines: a) physico-chemical analyses, b) whole effluent toxicity (WET) assays with Pseudokirchneriella subcapitata, c) in situ bioassays to assess microalgae (P. subcapitata) growth, and the feeding rate and survival of Daphnia longispina and Daphnia magna. Study sites were located upstream, in a protected wetland (L1), and downstream, in the vicinity of rice fields (L2). Along with the application of agrochemicals, there was a general decrease of the water quality, especially in L2, due to nutrient and herbicide inputs. Herbicide peaks (on days 0, 5 and 6) in L2 water samples were recorded concomitantly or immediately after their application. Regarding the in situ bioassessment, the algae growth decrease from day 0 onwards in L1, whilst in L2 its inhibition was generally coherent with the decline of the water quality. Apparently, WET tests indicated that the limitation of nutrients could be affecting algae growth in L1, however, conclusions should be cautious. The feeding depression of daphnids occurred on days 0 and 5 for D. longispina and only on day 0 for D. magna, while significant reductions on survival were restricted to day 0 for both species. The impairments occurring on day 0 were linked to a potential increased toxicity driven by the ingestion of particle-bound herbicides and suspended particles. The feeding rate of daphnids provided an earlier indication of toxic impairments, though it is prompted the use of complementary endpoints and trophic levels in order to understand the cumulative effects due to various herbicide pulses.     

Filtering activity of Spongia officinalis var. adriatica (Schmidt) (Porifera, Demospongiae) on bacterioplankton: implications for bioremediation of polluted seawater

A study on the filtering activity has been carried out on reared specimens of the demosponge Spongia officinalis var. adriatica coming from an off-shore farm displaced off the Apulian coast (Ionian Sea). The experience was carried out under laboratory conditions, by using natural seawater collected from the sponge environment. The study demonstrates a high efficiency of the sponge in removing bacteria. Bacterial concentration significantly decreases in presence of the sponge, with a marked drop after 2 h from the start of the experience. The maximum clearance rate was 210 ml h(-1) g(-1) DW at 60 min. Retention efficiency reached the highest value of 61% at 120 min. The bacterial density removed by the S. officinalis filtering activity was 12.3 +/- 1.8 x 10(4) cells ml(-1) corresponding to a biomass of about 11.7 +/- 1.4 microg Cl(-1). The sponge fed preferentially large- and medium-size bacteria, whereas the small ones are fed after the removal of the largest size categories. The results obtained suggest that S. offcinalis is a suitable species for marine environmental bioremediation.     

Recurrent recovery of Pseudomonas oryzihabitans strains in a karstified chalk aquifer

Pseudomonas oryzihabitans is an uncommon pathogen that may cause catheter-associated infections, particularly in immunocompromised patients. Although it has been isolated from environment, the source of human infection is not well documented. In the present study, 14 isolates of P. oryzihabitans were recovered over a 28-month period from a karstified chalk aquifer, allowing to advance that distributed natural water could be a source of contamination. Microbiological analyses showed that the bacterium was mainly associated with suspended particulate matters. To investigate the clonality of P. oryzihabitans environmental isolates, 16S rRNA gene sequencing, antibiogram and randomly amplified polymorphic DNA (RAPD) typings were performed. Results demonstrated (i) the presence of at least three clones within the aquifer and (ii) that the presence of the bacterium in groundwater is not only the result of a biofilm bloom but also of an exogenous contamination.     

Intensive exploitation of a karst aquifer leads to Cryptosporidium water supply contamination

Groundwater from karst aquifers is an important source of drinking water worldwide. Outbreaks of cryptosporidiosis linked to surface water and treated public water are regularly reported. Cryptosporidium oocysts are resistant to conventional drinking water disinfectants and are a major concern for the water industry. Here, we examined conditions associated with oocyst transport along a karstic hydrosystem, and the impact of intensive exploitation on Cryptosporidium oocyst contamination of the water supply. We studied a well-characterized karstic hydrosystem composed of a sinkhole, a spring and a wellbore. Thirty-six surface water and groundwater samples were analyzed for suspended particulate matter, turbidity, electrical conductivity, and Cryptosporidium and Giardia (oo)cyst concentrations. (Oo)cysts were identified and counted by means of solid-phase cytometry (ChemScan RDI^®), a highly sensitive method. Cryptosporidium oocysts were detected in 78% of both surface water and groundwater samples, while Giardia cysts were found in respectively 22% and 8% of surface water and groundwater samples. Mean Cryptosporidium oocyst concentrations were 29, 13 and 4/100 L at the sinkhole, spring and wellbore, respectively. Cryptosporidium oocysts were transported from the sinkhole to the spring and the wellbore, with respective release rates of 45% and 14%, suggesting that oocysts are subject to storage and remobilization in karst conduits. Principal components analysis showed that Cryptosporidium oocyst concentrations depended on variations in hydrological forcing factors. All water samples collected during intensive exploitation contained oocysts. Control of Cryptosporidium oocyst contamination during intensive exploitation is therefore necessary to ensure drinking water quality.     

In situ feeding assay with Gammarus fossarum (Crustacea): Modelling the influence of confounding factors to improve water quality biomonitoring

In situ feeding assays implemented with transplanted crustacean gammarids have been claimed as promising tools for the diagnostic assessment of water quality. Nevertheless the implementation of such methodologies in biomonitoring programs is still limited. This is explained by the necessity to improve the reliability of these bioassays. The present study illustrates how modelling the influence of confounding factors could allow to improve the interpretation of in situ feeding assay with Gammarus fossarum. We proceeded in four steps: (i) we quantified the influence of body size, temperature and conductivity on feeding rate in laboratory conditions; (ii) based on these laboratory findings, we computed a feeding inhibition index, which proved to be robust to environmental conditions and allowed us to define a reference statistical distribution of feeding activity values through the data compilation of 24 in situ assays among diverse reference stations at different seasons; (iii) we tested the sensitivity of the feeding assay using this statistical framework by performing 41 in situ deployments in contaminated stations presenting a large range of contaminant profiles; and (iv) we illustrated in two site-specific studies how the proposed methodology improved the diagnosis of water quality by preventing false-positive and false-negative cases mainly induced by temperature confounding influence. Interestingly, the implementation of the developed protocol could permit to assess water quality without following an upstream/downstream procedure and to compare assays performed at different seasons as part of large-scale biomonitoring programs.     

Mobilisation of arsenic from a mining soil in batch slurry experiments under bio-oxidative conditions

Laboratory investigations were performed to estimate the potential mobility of arsenic (As) from a highly contaminated gold-mining soil under bio-oxidative aerobic conditions as a potential remediation process. The selected soil was sampled from a gold-mining site in the South of France. It contained 27700 mg kg(-1) total As, with only 0.01% present under water-soluble forms. The nature of the immobilization mechanisms was identified by using complementary physical and chemical techniques. As was found to be strongly associated to iron (oxy)hydroxide solid phase by adsorption and/or co-precipitation. Determination of iron (Fe) and As mobility as a function of pH showed that the release of As was related with the dissolution of Fe (oxy)hydroxide at very low pH values. Bioleaching experiments were conducted with the objective to enhance the mobilization of As from the source material via biological oxidation of elemental sulfur (S degree) into sulfuric acid by autotrophic exogenous or indigenous bacteria naturally located in the soil (i.e. Acidithiobacillus species). Tests conducted at 30 degrees C in shaker flasks supplemented with S degree resulted in very acidic (pH < 1) and oxidative conditions (oxidation/reduction potential (ORP) around +800 mV vs. NHE) and induced the extraction of up to 35% of As over 84 days of incubation. Under the experimental conditions of the study (batch experiments), As mobilization was strongly correlated to the dissolution of Fe solid phases. As mobilization was probably limited by the saturation of the liquid phase. Chimiolithotrophic exogenous population appeared to have a minor effect on As bioleaching. Endogenous populations were shown to rapidly develop their capacity to oxidize S degree and mobilize As from the mining soil in the form of arsenate when elemental S degree was supplemented. The use of microbial population adapted to high As concentrations reduced significantly the lag period to reach optimal pH/ORP conditions, and increased As extraction rate to a maximum of 41% within 70 days of incubation. However, As reprecipitation was subsequently observed, suggesting that the solution should be periodically replaced in order to optimize the process.     

Quantification of pathogenic microorganisms and microbial indicators in three wastewater reclamation and managed aquifer recharge facilities in Europe

Managed Aquifer Recharge (MAR) is becoming an attractive option for water storage in water reuse processes as it provides an additional treatment barrier to improve recharged water quality and buffers seasonal variations of water supply and demand. To achieve a better understanding about the level of pathogenic microorganisms and their relation with microbial indicators in these systems, five waterborne pathogens and four microbial indicators were monitored over one year in three European MAR sites operated with reclaimed wastewater. Giardia and Cryptosporidium (oo)cysts were found in 63.2 and 36.7% of the samples respectively. Salmonella spp. and helminth eggs were more rarely detected (16.3% and 12.5% of the samples respectively) and Campylobacter cells were only found in 2% of samples. At the Belgian site advanced tertiary treatment technology prior to soil aquifer treatment (SAT) produced effluent of drinking water quality, with no presence of the analysed pathogens. At the Spanish and Italian sites amelioration of microbiological water quality was observed between the MAR injectant and the recovered water. In particular Giardia levels decreased from 0.24-6.14 cysts/L to 0-0.01 cysts/L and from 0.4-6.2 cysts/L to 0-0.07 cysts/L in the Spanish and Italian sites respectively. Salmonella gene copies and Giardia cysts were however found in the water for final use and/or the recovered groundwater water at the two sites. Significant positive Spearman correlations (p < 0.05, r_s range: 0.45-0.95) were obtained, in all the three sites, between Giardia cysts and the most resistant microbial markers, Clostridium spores and bacteriophages.