An examination of groundwater discharge and the associated nutrient fluxes into the estuaries of eastern Hainan Island, China using 226Ra

The nutrient concentrations and stoichiometry in a coastal bay/estuary are strongly influenced by the direct riverine discharge and the submarine groundwater discharge (SGD). To estimate the fluxes of submarine groundwater discharge into the Bamen Bay (BB) and the Wanquan River Estuary (WQ) of eastern Hainan Island, China, the naturally occurring radium isotope (²²⁶Ra) was measured in water samples collected in the bay/estuary in August 2007 and 2008. Based on the distribution of ²²⁶Ra in the surface water, a 3-end-member mixing model was used to estimate the relative contributions of the sources to these systems. Flushing times of 3.9 ± 2.7 and 12.9 ± 9.3 days were estimated for the BB and WQ, respectively, to calculate the radium fluxes for each system. Based on the radium fluxes from groundwater discharge and the Ra isotopic compositions in the groundwater samples, the estimated SGD fluxes were 3.4 ± 5.0 m³ s⁻¹ in the BB and 0.08 ± 0.08 m³ s⁻¹ in the WQ, or 16% and 0.06%, respectively, of the local river discharge. Using this information, the nutrient fluxes from the submarine groundwater discharge seeping into the BB and WQ regions were estimated. In comparison with the nutrient fluxes from the local rivers, the SGD-derived nutrient fluxes played a vital role in controlling the nutrient budgets and stoichiometry in the study area, especially in the BB.     

Application of the Nernst-Planck approach to lead ion exchange in Ca-loaded Pelvetia canaliculata

Ca-loaded Pelvetia canaliculata biomass was used to remove Pb²⁺ in aqueous solution from batch and continuous systems. The physicochemical characterization of algae Pelvetia particles by potentiometric titration and FTIR analysis has shown a gel structure with two major binding groups - carboxylic (2.8 mmol g⁻¹) and hydroxyl (0.8 mmol g⁻¹), with an affinity constant distribution for hydrogen ions well described by a Quasi-Gaussian distribution. Equilibrium adsorption (pH 3 and 5) and desorption (eluents: HNO₃ and CaCl₂) experiments were performed, showing that the biosorption mechanism was attributed to ion exchange among calcium, lead and hydrogen ions with stoichiometry 1:1 (Ca:Pb) and 1:2 (Ca:H and Pb:H). The uptake capacity of lead ions decreased with pH, suggesting that there is a competition between H⁺ and Pb²⁺ for the same binding sites. A mass action law for the ternary mixture was able to predict the equilibrium data, with the selectivity constants α_Ca^H = 9 ± 1 and α_Ca^Pb = 44 ± 5, revealing a higher affinity of the biomass towards lead ions. Adsorption (initial solution pH 4.5 and 2.5) and desorption (0.3 M HNO₃) kinetics were performed in batch and continuous systems. A mass transfer model using the Nernst-Planck approximation for the ionic flux of each counter-ion was used for the prediction of the ions profiles in batch systems and packed bed columns. The intraparticle effective diffusion constants were determined as 3.73 × 10⁻⁷ cm² s⁻¹ for H⁺, 7.56 × 10⁻⁸ cm² s⁻¹ for Pb²⁺ and 6.37 × 10⁻⁸ cm² s⁻¹ for Ca²⁺.     

Delineation of Pb contamination pathways in two Pectinidae: The variegated scallop Chlamys varia and the king scallop Pecten maximus

Bioaccumulation of Pb was determined in Chlamys varia and Pecten maximus exposed to ²¹⁰Pb via seawater, food and sediment. Both scallops readily concentrated dissolved Pb with whole-body 7-d concentration factors of 250 ± 40 and 170 ± 70, respectively. In both species, more than 70% of Pb taken up from seawater was strongly retained within tissues (biological half-life > 1.5 month) whereas Pb ingested with phytoplankton was poorly assimilated (< 20%). As P. maximus lives buried in the sediment, this exposure pathway was assessed and showed low bioaccumulation efficiency for sediment-bound Pb (transfer factor < 0.015). Despite the poor transfer efficiency of Pb from food and sediment, the use of a global bioaccumulation model indicated that the particulate pathway (food and/or sediment) constituted the major bioaccumulation route of Pb in both scallops. Whatever the exposure pathway, the digestive gland and kidneys always played a major role in Pb accumulation. In scallop tissues, Pb was predominantly associated with the insoluble subcellular fraction, suggesting a low bioavailability of Pb for scallop consumers.     

Free-radical-induced oxidative and reductive degradation of N,N′-diethyl-m-toluamide (DEET): Kinetic studies and degradation pathway

N,N′-Diethyl-m-toluamide (DEET) is widely used as an insect repellent and has therefore been detected as a contaminant in numerous waste and surface waters. In this study we have determined the absolute reaction rate constants of DEET with the hydroxyl radical and the hydrated electron in aqueous solution as (4.95 ± 0.18) × 10⁹ and (1.34 ± 0.04) × 10⁹ M⁻¹ s⁻¹, respectively, using pulse radiation. To provide additional information on the radicals formed upon oxidation, transient spectra were measured from 1 to 150 μs, with transient decay rates determined from the time-dependence of the maximum absorption at 330 nm. These data suggest simple decay of the initially formed radical to stable products. Radical-based destruction mechanisms for destruction of DEET are proposed based on the LC-MS determination of the stable compounds produced by ⁶⁰Co γ-irradiation of DEET solutions. These data will be useful in evaluating potential advanced oxidation/reduction processes for the control of DEET and understanding its fate and transport in surface water where analogous radical chemistry is operative.     

Spatial isolation favours the divergence in microcystin net production by Microcystis in Ugandan freshwater lakes

It is generally agreed that the hepatotoxic microcystins (MCs) are the most abundant toxins produced by cyanobacteria in freshwater. In various freshwater lakes in East Africa MC-producing Microcystis has been reported to dominate the phytoplankton, however the regulation of MC production is poorly understood. From May 2007 to April 2008 the Microcystis abundance, the absolute and relative abundance of the mcyB genotype indicative of MC production and the MC concentrations were recorded monthly in five freshwater lakes in Uganda: (1) in a crater lake (Lake Saka), (2) in three shallow lakes (Lake Mburo, George, Edward), (3) in Lake Victoria (Murchison Bay, Napoleon Gulf). During the whole study period Microcystis was abundant or dominated the phytoplankton. In all samples mcyB-containing cells of Microcystis were found and on average comprised 20 ± 2% (SE) of the total population. The proportion of the mcyB genotype differed significantly between the sampling sites, and while the highest mcyB proportions were recorded in Lake Saka (37 ± 3%), the lowest proportion was recorded in Lake George (1.4 ± 0.2%). Consequently Microcystis from Lake George had the lowest MC cell quotas (0.03-1.24 fg MC cell⁻¹) and resulted in the lowest MC concentrations (0-0.5 μg L⁻¹) while Microcystis from Lake Saka consistently showed maximum MC cell quotas (14-144 fg cell⁻¹) and the highest MC concentrations (0.5-10.2 μg L⁻¹). Over the whole study period the average MC content per Microcystis cell depended linearly on the proportion of the mcyB genotype of Microcystis. It is concluded that Microcystis populations differ consistently and independently of the season in mcyB genotype proportion between lakes resulting in population-specific differences in the average MC content per cell.     

Assessment of in vivo bioaccessibility of arsenic in dietary rice by a mass balance approach

A pilot dietary experiment was conducted over 10 days to evaluate whether a simple yet often underutilized approach of constructing mass balance of arsenic metabolites can be used to assess in vivo bioaccessibility of arsenic in cooked rice. Two volunteers were involved in this study. The quantity of drinking water, food and urine samples, together with arsenic concentration and speciation of these samples was monitored to construct a mass balance of arsenic intake and excretion. In the first five days, the two volunteers on a wheat diet had an average arsenic daily intake of 15.4 ± 2.6 µg and 9.6 ± 0.7 µg, respectively. In the next five days, these volunteers switched to a rice diet, increasing the average arsenic daily intake to 36.4 ± 2.8 µg and 34.1 ± 7.7 µg, respectively. Daily excretion of urinary arsenic, mostly as dimethylarsenic acid (DMA), doubled from 9.8 ± 0.3 µg to 21.0 ± 3.0 µg, and from 6.5 ± 0.8 µg to 11.6 ± 4.5 µg, respectively. The percentage of ingested arsenic excreted in urine remained constant at ∼ 58% for one volunteer before and after the rice diet, and was ∼ 69% for another. Mass balance established during a controlled dietary experiment over 10 days is shown to be a useful approach to evaluate in vivo bioaccessibility and metabolism of arsenic uptake from diet and is applicable to study with more subjects.     

Sensitivity of Cylindrotheca closterium to copper: Influence of three test endpoints and two test methods

The present study checked the suitability of Cylindrotheca closterium (Bacillariophyceae) as a test species for ecotoxicology studies. To date, only limited use has been made of microphytobenthos in ecotoxicology, and C. closterium has been employed as a target organism in this study because the biological group is considered to be very relevant ecologically. The main objective was to assess the response of C. closterium to a contaminant-type (copper) using three different test endpoints (esterase activity, chlorophyll fluorescence and population growth) and two different test methods (Erlenmeyer flasks and microplates), to evaluate which combination of test conditions would provide the most sensitive approach for assessment of effects. Regardless of the endpoints, the response of C. closterium to copper was very similar; however lower sensitivity (EC₅₀ of 27.8 ± 0.7 µg Cu L^− 1) was observed when tests were carried out in microplates. Chlorophyll fluorescence measured by flow cytometry as total FL3 was slightly more sensitive (EC₅₀ of 4.7 ± 0.1 µg Cu L^− 1) than the other parameters measured, probably because it takes into account the effect on chlorophyll fluorescence and cell density simultaneously. The test method (Erlenmeyer flask or microplate) was the determining factor for the observed differences in sensitivity. These differences found for the two methods are explained by the higher metal adsorption capacity of microplate vessel walls (more than 40%), which decreases the available copper. C. closterium was demonstrated to be a suitable organism for adoption in ecotoxicological studies, given the reliability of the three endpoints and also of the two test methods evaluated here.     

Environmental occurrence and degradation of the herbicide n-chloridazon

A sampling campaign was carried out for n-chloridazon (n-CLZ) and its degradation product desphenyl-chloridazon (DPC) in the Hesse region (Germany) during the year 2007: a total of 548 environmental samples including groundwater, surface water and wastewater treatment plant (WWTP) effluent were analysed. Furthermore, aerobic degradation of n-CLZ has been studied utilising a fixed bed bioreactor (FBBR).In surface water, n-CLZ was detected at low concentrations (average 0.01 ± 0.06 μg L⁻¹; maximum 0.89 μg L⁻¹) with a seasonal peak, whereas DPC was present throughout the year at much higher concentrations (average 0.72 ± 0.81 μg L⁻¹; maximum 7.4 μg L⁻¹). Higher n-CLZ concentrations were observed in the North compared with South Hesse, which is ascribed to a higher density of agricultural areas. Furthermore, methylated DPC (Me-DPC), another degradation product, was detected in surface water.In the degradation test, n-CLZ was completely converted to DPC at all concentrations tested (Me-DPC was not formed under the test conditions). DPC was resistant to further degradation during the whole experimental period of 98 days. The results obtained suggest persistence and high dispersion of DPC in the aquatic environment.     

Efficient electricity generation from sewage sludge using biocathode microbial fuel cell

Microbial fuel cells (MFCs) with abiotic cathodes require expensive catalyst (such as Pt) or catholyte (such as hexacynoferrate) to facilitate oxidation reactions. This study incorporated biocathodes into a three-chamber MFC to yield electricity from sewage sludge at maximum power output of 13.2 ± 1.7 W/m³ during polarization, much higher than those previously reported. After 15 d operation, the total chemical oxygen demand (TCOD) removal and coulombic efficiency (CE) of cell reached 40.8 ± 9.0% and 19.4 ± 4.3%, respectively. The anolyte comprised principally acetate and propionate (minor) as metabolites. The use of biocathodes produced an internal resistance of 36-46 Ω, lower than those reported in literature works, hence yielding higher maximum power density from MFC. The massively parallel sequencing technology, 454 pyrosequencing technique, was adopted to probe microbial community on anode biofilm, with dominant phyla belonging to Proteobacteria (45% of total bacteria), Bacteroidetes (19%), Uncultured bacteria (9%), Actinobacteria (7%), Firmicutes (7%), Chloroflex (7%). At genera level, Rhodoferax, Ferruginibacter, Propionibacterium, Rhodopseudomonas, Ferribacterium, Clostridium, Chlorobaculum, Rhodobacter, Bradyrhizobium were the abundant taxa (relative abundances > 2.0%).     

Protection against UV disinfection of E. coli bacteria and B. subtilis spores ingested by C. elegans nematodes

Nematodes, which occur abundantly in granular media filters of drinking water treatment plants and in distribution systems, can ingest and transport pathogenic bacteria and provide them protection against chemical disinfectants. However, protection against UV disinfection had not been investigated to date.In this study, Caenorhabditis elegans nematodes (wild-type strain N2) were allowed to feed on Escherichia coli OP50 and Bacillus subtilis spores before being exposed to 5 and 40 mJ/cm² UV fluences, using a collimated beam apparatus (LP, 254 nm). Sonication (15 W, 60 s) was used to extract bacteria from nematode guts following UV exposure in order to assess the amount of ingested bacteria that resisted the UV treatment using a standard culture method. Bacteria located inside the gut of C. elegans were shown to benefit from a significant protection against UV. Approximately 15% of the applied UV fluence of 40 mJ/cm² (as typically used in WTP) was found to reach the bacteria located inside nematode guts based on the inactivation of recovered bacteria (2.7 log reduction of E. coli bacteria and 0.7 log reduction of B. subtilis spores at 40 mJ/cm²). To our knowledge, this study is the first demonstration of the protection effect of bacterial internalization by higher organisms against UV treatment, using the specific case of E. coli and B. subtilis spores ingested by C. elegans.     

Remediation of petroleum contaminated soils by joint action of Pharbitis nil L. and its microbial community

The plot-culture experiments were conducted for examining the feasibility of Pharbitis nil L. and its microbial community to remedy petroleum contaminated soils. The petroleum contaminated soil, containing 10% (w/w) of the total petroleum hydrocarbons (TPHs), was collected from the Shengli Oil Field, Dongying City, Shandong Province, China. The collected soil was applied and diluted to a series of petroleum contaminated soils (0.5%, 1.0%, 2.0% and 4.0%). Root length, microbial populations and numbers in the rhizosphere were also measured in this work. The results showed that there was significantly (p < 0.05) greater degradation rate of TPHs in vegetated treatments, up to 27.63-67.42%, compared with the unvegetated controls (only 10.20-35.61%), after a 127-day incubation. Although various fractions of TPHs had an insignificant concentration difference due to the presence of the remediation plants, there was a much higher removal of saturated hydrocarbon compared with other components. The biomass of P. nil L. did not decrease significantly when the concentration of petroleum hydrocarbons in soil was ≤ 2.0%. The trends of microbial populations and numbers in the rhizosphere were similar to the biomass changes, with the exception that fungi at 0.5% petroleum contaminated soil had the largest microbial populations and numbers.     

Feeding characteristics of a golden alga (Poterioochromonas sp.) grazing on toxic cyanobacterium Microcystis aeruginosa

Microcystis aeruginosa has quickly risen in infamy as one of the most universal and toxic bloom-forming cyanobacteria. Here we presented a species of golden alga (Poterioochromonas sp. strain ZX1), which can feed on toxic M. aeruginosa without any adverse effects from the cyanotoxins. Using flow cytometry, the ingestion and maximal digestion rates were estimated to be 0.2∼1.2 and 0.2 M. aeruginosa cells (ZX1 cell)⁻¹ h⁻¹, respectively. M. aeruginosa in densities below 10⁷ cells mL⁻¹ could be grazed down by ZX1, but no significant decrease was observed when the initial density was 3.2 × 10⁷ cells mL⁻¹. ZX1 grazing was a little influenced by the light intensity (0.5∼2500 lx) and initial pH of the medium (pH = 5.0∼9.5). ZX1 could not survive in continuous darkness for longer than 10 days. The pH value was adjusted to 8 by ZX1 while to 10 by M. aeruginosa. This study may shed light on understanding the ecological interactions between M. aeruginosa and mixotrophic Poterioochromonas sp. in aquatic ecosystems.     

Specificity and sensitivity evaluation of novel and existing Bacteroidales and Bifidobacteria-specific PCR assays on feces and sewage samples and their application for microbial source tracking in Ireland

Three novel ruminant-specific PCR assays, an existing ruminant-specific PCR assay and five existing human-specific PCR assays, which target 16S rDNA from Bacteroidales or Bifidobacteria, were evaluated. The assays were tested on DNA extracted from ruminant (n = 74), human (n = 59) and non-ruminant animal (n = 44) sewage/fecal samples collected in Ireland. The three novel PCR assays compared favourably to the existing ruminant-specific assay, exhibiting sensitivities of 91-100% and specificities of 95-100% as compared to a sensitivity of 95% and specificity of 94%, for the existing ruminant-specific assay. Of the five human-specific PCR assays, the assay targeting the Bifidobacterium catenulatum group was the most promising, exhibiting a sensitivity of 100% (with human sewage samples) and a specificity of 87%. When tested on rural water samples that were naturally contaminated by ruminant feces, the three novel PCR assays tested positive with a much greater percentage (52-87%) of samples than the existing ruminant-specific assay (17%). These novel ruminant-specific assays show promise for microbial source tracking and merit further field testing and specificity evaluation.     

Biohydrogen production from xylose at extreme thermophilic temperatures (70 °C) by mixed culture fermentation

Biohydrogen production from xylose at extreme thermophilic temperatures (70 °C) was investigated in batch and continuous-mode operation. Biohydrogen was successfully produced from xylose by repeated batch cultivations with mixed culture received from a biohydrogen reactor treating household solid wastes at 70 °C. The highest hydrogen yield of 1.62 ± 0.02 mol-H₂/mol-xylose_consumed was obtained at initial xylose concentration of 0.5 g/L with synthetic medium amended with 1 g/L of yeast extract. Lower hydrogen yield was achieved at initial xylose concentration higher than 2 g/L. Addition of yeast extract in the cultivation medium resulted in significant improvement of hydrogen yield. The main metabolic products during xylose fermentation were acetate, ethanol, and lactate. The specific growth rates were able to fit the experimental points relatively well with Haldane equation assuming substrate inhibition, and the following kinetic parameters were obtained: the maximum specific growth rate (μ_max) was 0.17 h⁻¹, the half-saturation constant (K_s) was 0.75 g/L, and inhibition constant (K_i) was 3.72 g/L of xylose. Intermittent N₂ sparging could enhance hydrogen production when high hydrogen partial pressure (>0.14 atm) was present in the headspace of the batch reactors. Biohydrogen could be successfully produced in continuously stirred reactor (CSTR) operated at 72-h hydraulic retention time (HRT) with 1 g/L of xylose as substrate at 70 °C. The hydrogen production yield achieved in the CSTR was 1.36 ± 0.03 mol-H₂/mol-xylose_sonsumed, and the production rate was 62 ± 2 ml/d·L_reactor. The hydrogen content in the methane-free mixed gas was approximately 31 ± 1%, and the rest was carbon dioxide. The main intermediate by-products from the effluent were acetate, formate, and ethanol at 4.25 ± 0.10, 3.01 ± 0.11, and 2.59 ± 0.16 mM, respectively.     

Kinetic of benzotriazole oxidation by ozone and hydroxyl radical

Ozonation experiments were performed in batch reactors in order to determine the rate constants for the reaction of molecular ozone and OH radicals with benzotriazole (BT) at different pHs. The first group of ozonation experiments was carried out for the determination of the rate constant for the direct reactions between ozone and BT. Two different kinetic models were used for the determination of kinetic rate constants: (i) the log-reduction of BT with ozone in excess, (ii) the competition kinetic model. The second-order rate constants for BT with molecular ozone were determined to be 36.4 ± 3.8 M⁻¹ s⁻¹ and 18.4 ± 0.8 M⁻¹ s⁻¹ at pH 2 from the two methods respectively. With the competition method, the value at pH 5 was found to be 22.0 ± 2.0 M⁻¹ s⁻¹. In a following stage, the reaction of BT with OH radicals was investigated at pH values ranging from 2 to 10.2. Using a method involving two probe compounds during the ozonation, the second-order rate constants of the BT reaction with hydroxyl radicals were determined. The rate constants were found to vary from 6.2 × 10⁹ M⁻¹ s⁻¹ at pH 10.2 to 1.7 × 10¹⁰ M⁻¹ s⁻¹ at pH 2.     

Effects of local point source polychlorinated biphenyl (PCB) contamination on bone mineral density in deer mice (Peromyscus maniculatus)

A former local source of PCBs has contaminated soil and the terrestrial food web at Saglek, Labrador. The relationship between PCB exposure and bone mineral density as an osteoporosis biomarker in deer mice (Peromyscus maniculatus) was investigated at two sites at Saglek: a contaminated Beach and a reference area. Bone mineral density was measured on the femur of twenty-six deer mice using dual-energy X-ray absorptiometry (DXA) technology. Bone mineral density was significantly lower in deer mice from the high exposure site (average whole body ∑PCB = 5769 ng/g wet weight, n = 20) than at the reference site (average whole body ∑PCB = 79.8 ng/g wet weight, n = 7). We used T-scores from the World Health Organization to determine the degree of decreased bone mineral density in exposed mice. Assuming the same biomechanical forces apply as for humans, and using a conservative factor of 1.5 (fracture risk increases 1.5 to 3 fold for every standard deviation decrease in bone mineral density), mice from the contaminated Beach are up to five folds more susceptible to fracture risk than mice from the reference area. Therefore, the PCB concentrations found locally at contaminated military sites such as Saglek are high enough to affect local wildlife.     

Impact of toxic cyanobacteria on gastropods and microcystin accumulation in a eutrophic lake (Grand-Lieu, France) with special reference to Physa (= Physella) acuta

Hepatotoxic microcystins (MCs) produced by cyanobacteria are known to accumulate in gastropods following grazing of toxic cyanobacteria and/or absorption of MCs dissolved in water, with adverse effects on life history traits demonstrated in the laboratory. In the field, such effects may vary depending on species, according to their relative sensitivity and ecology. The aims of this study were to i) establish how various intensities of MC-producing cyanobacteria proliferations alter the structure of gastropod community and ii) compare MC tissue concentration in gastropods in the field with those obtained in our previous laboratory experiments on the prosobranch Potamopyrgus antipodarum and the pulmonate Lymnaea stagnalis. We explored these questions through a one-year field study at three stations at Grand-Lieu Lake (France) affected by different intensities of cyanobacteria proliferations. A survey of the community structure and MC content of both cyanobacteria and gastropods was associated with a caging experiment involving P. antipodarum and L. stagnalis. In total, 2592 gastropods belonging to 7 prosobranch and 16 pulmonate species were collected. However, distribution among the stations was unequal with 62% vs 2% of gastropods sampled respectively at the stations with the lowest vs highest concentrations of MC. Irrespective of the station, pulmonates were always more diverse, more abundant and occurred at higher frequencies than prosobranchs. Only the pulmonate Physa acuta occurred at all stations, with abundance and MC tissue concentration (≤ 4.32 µg g DW^− 1) depending on the degrees of MC-producing cyanobacteria proliferations in the stations; therefore, P. acuta is proposed as a potential sentinel species. The caging experiment demonstrated a higher MC accumulation in L. stagnalis (≤ 0.36 µg g DW^− 1 for 71% of individuals) than in P. antipodarum (≤ 0.02 µg g DW^− 1 for 12%), corroborating previous laboratory observations. Results are discussed in terms of differential gastropod sensitivity and MC transfer through the food web.     

Factors controlling mobility of 127I and 129I species in an acidic groundwater plume at the Savannah River Site

In order to quantify changes in iodine speciation and to assess factors controlling the distribution and mobility of iodine at an iodine-129 (¹²⁹I) contaminated site located at the U.S. Department of Energy's Savannah River Site (SRS), spatial distributions and transformation of ¹²⁹I and stable iodine (¹²⁷I) species in groundwater were investigated along a gradient in redox potential (654 to 360 mV), organic carbon concentration (5 to 60 μmol L^− 1), and pH (pH 3.2 to 6.8). Total ¹²⁹I concentration in groundwater was 8.6 ± 2.8 Bq L^− 1 immediately downstream of a former waste seepage basin (well FSB-95DR), and decreased with distance from the seepage basin. ¹²⁷I concentration decreased similarly to that of ¹²⁹I. Elevated concentrations of ¹²⁷I or ¹²⁹I were not detected in groundwater collected from wells located outside of the mixed waste plume of this area. At FSB-95DR, the majority (55-86%) of iodine existed as iodide for both ¹²⁷I and ¹²⁹I. Then, as the iodide move down gradient, some of it transformed into iodate and organo-iodine. Considering that iodate has a higher K_d value than iodide, we hypothesize that the production of iodate in groundwater resulted in the removal of iodine from the groundwater and consequently decreased concentrations of ¹²⁷I and ¹²⁹I in downstream areas. Significant amounts of organo-iodine species (30-82% of the total iodine) were also observed at upstream wells, including those outside the mixed waste plume. Concentrations of groundwater iodide decreased at a faster rate than organo-iodine along the transect from the seepage basin. We concluded that removal of iodine from the groundwater through the formation of high molecular weight organo-iodine species is complicated by the release of other more mobile organo-iodine species in the groundwater.     

Alcohol production through volatile fatty acids reduction with hydrogen as electron donor by mixed cultures

In this research we demonstrated a new method to produce alcohols. It was experimentally feasible to produce ethanol, propanol and butanol from solely volatile fatty acids (VFAs) with hydrogen as electron donor. In batch tests, VFAs such as acetic, propionic and butyric acids were reduced by mixed microbial cultures with a headspace of 1.5 bar of hydrogen. Observed alcohol concentrations were 3.69 ± 0.25 mM of ethanol, 8.08 ± 0.85 mM of propanol and 3.66 ± 0.05 mM of n-butanol. The conversion efficiency based on the electron balance was 55.1 ± 5.6% with acetate as substrate, 50.3 ± 4.7% with propionate and 46.7 ± 2.2% with n-butyrate. Methane was the most predominant by-product in each batch experiment, 33.6 ± 9.6% of VFA and hydrogen was converted to methane with acetate as substrate; which was 27.1 ± 7.1% with propionate and 36.6 ± 2.2% with n-butyrate. This VFAs reducing renewable fuel production process does not require carbohydrates like fermentable sugars, but uses biomass with high water content or low sugar content that is unsuitable as feedstock for current fermentation processes. This so-called low-grade biomass is abundantly present in many agricultural areas and is economically very attractive feedstock for the production of biofuels.