Bioremediation of Perchlorate-Contaminated Groundwater Using a Packed Bed Biological Reactor

The objective of this study was to assess the efficacy of a bench-scale, acetate-fed, packed bed bioreactor (PBR) to treat low concentrations (>1 mg L^?1) of perchlorate (ClO₄ ^?) in groundwater collected from an impacted site. The PBR consisted of a cylindrical plexiglass column packed with Celite, a diatomaceous earth product, as a solid support medium. The reactor was inoculated with a ClO_?4 ^?-reducing bacterial isolate, perclace. Results showed that with influent ClO₄ ^? concentrations of approximately 800 μg L^?1, nondetectable effluent concentrations (>4 μg L^?1) were achieved with the PBR/perclace system at residence time as low as 0.3 h. Influent acetate concentrations of less than 500 mg L^?1 yielded nondetectable effluent ClO^? ₄ concentrations, and acetate concentrations generally less than 50 mg L^?1 were present in the effluent. Nitrate (NO^? _?3) was also removed in this system, while sulfate (SO₄ ^2?) reduction was not observed. The pH remained relatively constant during the process.     

Aerobic granulation and nitrogen removal with the effluent of internal circulation reactor in start-up of a pilot-scale sequencing batch reactor

Aerobic granular sludge was successfully cultivated with the effluent of internal circulation (IC) reactor in a pilot-scale sequencing batch reactor (SBR) using activated sludge as seeding sludge. N removal was investigated in the start-up of aerobic granulation process. Initially, the phenomenon of partial nitrification was observed and nitrite accumulation rates (NO₂ ^?-N/NO _x ^? -N) were between 84.6 and 99.1?%. It was potentially caused by ammonium oxidizing bacteria (AOB) in the seeding activated sludge, high external environmental temperature (~32?°C) and free ammonia (FA) concentration. After 50?days’ running, the aerobic granules-based bioreactor demonstrated perfect performance in simultaneous removal of organic matter and ammonia nitrogen, and average removal efficiencies were maintained above 93 and 96?%, respectively. The maximum nitrogen removal efficiency of 83.1?% was achieved after the formation of aerobic granules. The average diameter of mature aerobic granular sludge mostly ranged from 0.5 to 1.0?mm. Furthermore, one typical cyclic test indicated that pH and DO profiles could be used as effective parameters for biological reactions occurring in the aerobic/anoxic process. The obtained results could provide further information on the cultivation of aerobic granular sludge with practical wastewater, especially with regard to nitrogen-rich industrial wastewater.     

Spatial distribution,exposure, and potential health risk assessment from nitrate in drinking water from semi-arid region of South India

Abstract

Elevated nitrate concentration in groundwater is a worldwide problem. Continuous exposure to high levels of nitrate in groundwater may cause adverse health effects among residents who use groundwater for consumption. Therefore, this study was conducted to identify the nitrate distribution and its potential health risk assessment from semi-arid region of Peddavagu in Central Telangana (PCT), South India. Groundwater samples were collected from thirty five locations and analyzed for nitrate and other water quality parameters. Nitrate (NO₃^-) in groundwater was observed to vary from 17 to 120?mg/L, with a mean of 58.74?mg/L. About 57% of samples exceeded the maximum acceptable limit of Indian drinking water standard. About, 40% of groundwater samples drinking water quality index (DWQI) is good, while 60% of groundwater falls in poor quality for drinking purposes. Health risk maps were created based on hazard quotient to quantify the potential health risk of the residents using US Environmental Protection Agency (US EPA) health risk assessment model. Health risk assessment revealed that mean total hazard index (HI_total) for men, women, and children were found as 1.42E?+?00, 1.67E?+?00, and 1.95E?+?00, respectively. Results exhibited that children are at high health risk than men and women in the PCT. Further, the human exposure to the NO₃^- contaminated water was above the critical limit of non-carcinogenic risk.     

Anaerobic submerged membrane bioreactor (AnSMBR) treating low-strength wastewater under psychrophilic temperature conditions

An anaerobic submerged membrane bioreactor (AnSMBR) treating low-strength wastewater was operated for 90 days under psychrophilic temperature conditions (20 °C). Besides biogas sparging, additional shear was created by circulating sludge to control membrane fouling. The critical flux concept was used to evaluate the effectiveness of this configuration. Biogas sparging with a gas velocity (U_G) of 62 m/h together with sludge circulation (94 m/h) led to a critical flux of 7 L/(m² h). Nevertheless, a further increase in the U_G only minimally enhanced the critical flux. A low fouling rate was observed under critical flux conditions. The cake layer represented the main fouling resistance after 85 days of operation. Distinctly different volatile fatty acid (VFA) concentrations in the reactor and in the permeate were always observed. This fact suggests that a biologically active part of the cake layer contributes to degrade a part of the daily organic load. Hence, chemical oxygen demand (COD) removal efficiencies of up to 94% were observed. Nevertheless, the biogas balance indicates that even considering the dissolved methane, the methane yield were always lower than the theoretical value, which indicates that the organic compounds were not completely degraded but physically retained by the membrane in the reactor.     

Pretreatment with alum or powdered activated carbon reduces bacterial predation-associated irreversible fouling of membranes

This study evaluated the co-application of bacterial predation by Bdellovibrio bacteriovorus and either alum coagulation or powdered activated carbon adsorption to reduce fouling caused by Escherichia coli rich feed solutions in dead-end microfiltration tests. The flux increased when the samples were predated upon or treated with 100 ppm alum or PAC, but co-treatment with alum and predation gave the best flux results. The total membrane resistance caused by the predated sample was reduced six-fold when treated with 100 ppm PAC, from 11.8 to 1.98 × 10¹¹ m^?1, while irreversible fouling (R_p) was 2.7-fold lower. Treatment with 100 ppm alum reduced the total resistance 14.9-fold (11.8 to 0.79 × 10¹¹ m^?1) while the R_p decreased 4.25-fold. SEM imaging confirmed this, with less obvious fouling of the membrane after the combined process. This study illustrates that the combination of bacterial predation and the subsequent removal of debris using coagulation or adsorption mitigates membrane biofouling and improves membrane performance.     

An assessment of karstic submarine groundwater and associated nutrient discharge to a Mediterranean coastal area (Balearic Islands, Spain) using radium isotopes

Short and long-lived radium isotopes (²²³Ra, ²²⁴Ra, ²²⁶Ra, ²²⁸Ra) were used to quantify submarine groundwater discharge (SGD) and its associated input of inorganic nitrogen (NO₃ ^?), phosphorus (PO₄ ^3?) and silica (SiO₄ ^4?) into the karstic Alcalfar Cove, a coastal region of Minorca Island (Western Mediterranean Sea). Cove water, seawater and groundwater (wells and karstic springs) samples were collected in May 2005 and February 2006 for radium isotopes and in November 2007 for dissolved inorganic nutrients. Salinity profiles in cove waters suggested that SGD is derived from shallow brackish springs that formed a buoyant surface fresh layer of only 0.3 m depth. A binary mixing model that considers the distribution of radium activities was used to determine the cove water composition. Results showed that cove waters contained 20% brackish groundwater; of which 6% was recirculated seawater and 14% corresponded to freshwater discharge. Using a radium-derived residence time of 2.4 days, a total SGD flux of 150,000 m³ year^?1 was calculated, consisting of 45,000 m³ year^?1 recirculated seawater and 105,000 m³ year^?1 fresh groundwater. Fresh SGD fluxes of NO₃ ^?, SiO₄ ^4? and PO₄ ^3? were estimated to be on the order of 18,000, 1,140 and 4 μmol m^?2 day^?1, respectively, and presumably sustain the high phytoplankton biomass observed in the cove during summer. The total amount of NO₃ ^? and SiO₄ ^4? supplied by SGD was higher than the measured inventories in the cove, while the reverse was true for PO₄ ^3?. These discrepancies are likely due to non-conservative biogeochemical processes that occur within the subterranean estuary and Alcalfar Cove waters.     

Cooperation of Three Denitrifying Bacteria in Nitrate Removal of Acidic Nitrate- and Uranium-Contaminated Groundwater

In uranium-contaminated aquifers co-contaminated with nitrate, denitrifiers play a critical role in bioremediation. Six strains of denitrifying bacteria belonging to Rhizobium, Pseudomonas, and Castellaniella were isolated from the Oak Ridge Integrated Field Research Challenge Site (OR-IFRC), where biostimulation of acidic (pH 3.5–6.5), nitrate-contaminated (up to 140 mM) groundwater occurred. Three isolates were characterized in regards to nitrite tolerance, denitrification kinetic parameters, and growth on different denitrification intermediates. Kinetic and growth experiments showed that Pseudomonas str. GN33#1 reduced NO^? ₃ most rapidly (V_max = 15.8 μmol e^?·min^?1·mg protein^?1) and had the fastest generation time (gt) on NO^? ₃ (2.6 h). Castellaniella str. 4.5A2 was the most low pH and NO^? ₂ tolerant and grew rapidly on NO^? ₂ (gt = 4.0 h). Rhizobium str. GN32#2 was also tolerant of low pH values and reduced NO^? ₂ rapidly (V_max = 10.6 μmol e^?·min^?1·mg protein^?1) but was far less NO^? ₂ tolerant than Castellaniella str. 4.5A2. Growth of and denitrification by these three strains incubated together and individually were measured in OR-IFRC groundwater at pHs 5 and 7 to determine whether they cooperate or compete during denitrification. Mixed assemblages reduced NO^? ₃ more rapidly and more completely than any individual isolate over the course of the experiment. The results described in this article demonstrate 1) that this synthetic assemblage comprised of three physiologically distinct denitrifying bacterial isolates cooperate to achieve more complete levels of denitrification and 2) the importance of pH- and nitrite-tolerant bacteria such as Castellaniella str. 4.5A2 in minimizing NO^? ₂ accumulation in high-NO^? ₃ groundwater during bioremediation. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental files.     

Enhanced biological denitrification of high concentration of nitrite with supplementary carbon source

Nitrite accumulates during biological denitrification processes when carbon sources are insufficient. Acetate, methanol, and ethanol were investigated as supplementary carbon sources in the nitrite denitrification process using biogranules. Without supplementary external electron donors (control), the biogranules degraded 200 mg l^?1 nitrite at a rate of 0.27 mg NO₂–N g^?1?VSS h^?1. Notably, 1,500 mg l^?1 acetate and 700 mg l^?1 methanol or ethanol enhanced denitrification rates for 200 mg l^?1 nitrite at 2.07, 1.20, and 1.60 mg NO₂–N g^?1?VSS h^?1, respectively; these rates were significantly higher than that of the control. The sodium dodecyl sulfate polyacrylamide gel electrophoresis of the nitrite reductase (NiR) enzyme identified three prominent bands with molecular weights of 37–41 kDa. A linear correlation existed between incremental denitrification rates and incremental activity of the NiR enzyme. The NiR enzyme activity was enhanced by the supplementary carbon sources, thereby increasing the nitrite denitrification rate. The capacity of supplementary carbon source on enhancing NiR enzyme activity follows: methanol?>?acetate?>?ethanol on molar basis or acetate?>?ethanol?>?methanol on an added weight basis.     

Exploring the relationship between groundwater geochemical factors and denitrification potentials on a dairy farm in southeast Ireland

Nitrate (NO₃⁻) loss from agriculture to shallow groundwater and transferral to sensitive aquatic ecosystems is of global concern. Denitrifying bioreactor technology, where a solid carbon (C) reactive media intercepts contaminated groundwater, has been successfully used to convert NO₃⁻ to di-nitrogen (N₂) gas. One of the challenges of groundwater remediation research is how to track denitrification potential spatially and temporally within reactive media and subsoil. First, using δ¹⁵N/δ¹⁸O isotopes, eight wells were divided into indicative transformational processes of ‘nitrification’ or ‘denitrification’ wells. Then, using N₂/argon (Ar) ratios these wells were divided into ‘low denitrification potential’ or high denitrification potential’ categories. Secondly, using falling head tests, the saturated hydraulic conductivity (K_sat) in each well was estimated, creating two groups of ‘slow’ (0.06 m day⁻¹) and ‘fast’ (0.13 m day⁻¹) wells, respectively. Thirdly, two ‘low denitrification potential’ wells (one fast and one slow) with high NO₃⁻ concentration were amended with woodchip to enhance denitrification. Water samples were retrieved from all wells using a low flow syringe to avoid de-gassing and analysed for N₂/Ar ratio using membrane inlet mass spectrometry. Results showed that there was good agreement between isotope and chemical (N₂/Ar ratio and dissolved organic C (DOC)) and physio-chemical (dissolved oxygen, temperature, conductivity and pH) parameters. To explain the spatial and temporal distribution of NO₃⁻ and other parameters on site, the development of predictive models using the available datasets for this field site was examined for NO₃⁻, Cl⁻, N₂/Ar and DOC. Initial statistical analysis was directed towards the testing of the effect of woodchip amendment. The analysis was formulated as a repeated measures analysis of the factorial structure for treatment and time. Nitrate concentrations were related to K_sat and water level (p < 0.0001 and p = 0.02, respectively), but did not respond to woodchip addition (p = 0.09). This non-destructive technique allows elucidation of denitrification potential over time and could be used in denitrifying bioreactor technology to assess denitrification hotspots in reactive media, while developing a NO₃⁻ spatial and temporal predictive model for bioreactor site specific conditions.     

NO 3 − transport across the plasma membrane of Arabidopsis thaliana root hairs: Kinetic control by pH and membrane voltage

High-affinity nitrate transport was examined in intact root hair cells of Arabidopsis thaliana using electrophysiological recordings to characterise the response of the plasma membrane to NO ₃ ^? challenge and to quantify transport activity. The NO ₃ ^? -associated membrane current was determined using a three-electrode voltage clamp to bring membrane voltage under experimental control and to compensate for current dissipation along the longitudinal cell axis. Nitrate transport was evident in the roots of seedlings grown in the absence of a nitrogen source, but only 4–6 days postgermination. In 6-day-old seedlings, additions of 5–100 μm NO ₃ ^? to the bathing medium resulted in membrane depolarizations of 8–43 mV, and membrane voltage (V _m) recovered on washing NO ₃ ^? from the bath. Voltage clamp measurements carried out immediately before and following NO ₃ ^? additions showed that the NO ₃ ^? -evoked depolarizations were the consequence of an inward-directed current that appeared across the entire range of accessible voltages (?300 to +50 mV). Both membrane depolarizations and NO ₃ ^? -evoked currents recorded at the free-running voltage displayed quasi-Michaelian kinetics, with apparent values for K_m of 23 ± 6 and 44 ± 11 μm, respectively and, for the current, a maximum of 5.1 ± 0.9 μA cm^?2. The NO ₃ ^? current showed a pronounced voltage sensitivity within the normal physiological range between ?250 and ?100 mV, as could be demonstrated under voltage clamp, and increasing the bathing pH from 6.1 to 7.4–8.0 reduced the current and the associated membrane depolarizations 3- to 8-fold. Analyses showed a well-defined interaction between the kinetic variables of membrane voltage, pH_o and [NO ₃ ^? ]_o. At a constant pH_o of 6.1, depolarization from ?250 to ?150 mV resulted in an approximate 3-fold reduction in the maximum current but a 10% rise in the apparent affinity for NO ₃ ^? . By contrast, the same depolarization effected an approximate 20% fall in the K_m for transport as a function in [H⁺]_o. These, and additional characteristics of the transport current implicate a carrier cycle in which NO ₃ ^? binding is kinetically isolated from the rate-limiting step of membrane charge transit, and they indicate a charge-coupling stoichiometry of 2(H⁺) per NO ₃ ^? anion transported across the membrane. The results concur with previous studies showing a high-affinity NO ₃ ^? transport system in Arabidopsis that is inducible following a period of nitrogen-limiting growth, but they underline the importance of voltage as a kinetic factor controlling NO ₃ ^? transport at the plant plasma membrane.     

Performance of an anaerobic membrane bioreactor in which granular sludge and dynamic filtration are integrated

To alleviate the fouling of a filter, simple substrates, dynamic filtration, and granular sludge were applied in an anaerobic membrane bioreactor (AnMBR). The results showed that under a transmembrane pressure < 20 kPa, the filter flux ranged between 15 and 20 l (m^?2 h)^?1 for a period of 30 days. The flux was higher than the typical flux of AnMBRs with conventional membranes and most current dynamic filters. In addition, the low cost of the filter avoided the need for a higher flux. Moreover, a stable granular sludge bed, which consumed all volatile fatty acids, was maintained. A compact fouling/filtration layer formed on the filter, which contributed to low effluent chemical oxygen demand concentrations and turbidity. In addition, substrate scarcity in the filtration zone resulted in the evolution of diverse bacteria on the filter.     

Bacterial Perchlorate Reduction in Simulated Reverse Osmosis Rejectate

Reverse osmosis (RO) is capable of removing perchlorate (ClO₄ ^?) from contaminated groundwater and producing potable effluent; however, RO does not destroy ClO₄ ^?, but collects it in a concentrated waste stream (rejectate) that must be treated or disposed of appropriately. A packed bed bioreactor, inoculated with the pure culture perclace, was tested for its ability to remove ClO₄ ^? from a simulated RO rejectate. Perchlorate concentrations were lowered from 5 mg/L to <0.004 mg/L with a residence time of 0.8 h. In addition, this system removed 98% of ClO₄ ^? from a twice-concentrated rejectate with an influent ClO₄ ^? concentration of 8 mg/L and a residence time of 2.0 h. In both experiments, nitrate (NO₃ ^?) was removed simultaneously with ClO₄ ^? from an initial concentration as high as 900 mg/L NO₃ to below 4 mg/L. Despite the efficiency of ClO₄ ^? removal, the system suffered from clogging due to the high total dissolved solids (TDS) of the twice-concentrated rejectate.     

Indirect N2O emissions from shallow groundwater in an agricultural catchment (Seine Basin, France)

Production and accumulation of nitrous oxide (N₂O), a major greenhouse gas, in shallow groundwater might contribute to indirect N₂O emissions to the atmosphere (e.g., when groundwater flows into a stream or a river). The Intergovernmental Panel on Climate Change (IPCC) has attributed an emission factor (EF_5g) for N₂O, associated with nitrate leaching in groundwater and drainage ditches—0.0025 (corresponding to 0.25% of N leached which is emitted as N₂O)—although this is the subject of considerable uncertainty. We investigated and quantified the transport and fate of nitrate (NO₃ ^?) and dissolved nitrous oxide from crop fields to groundwater and surface water over a 2-year period (monitoring from April 2008 to April 2010) in a transect from a plateau to the river with three piezometers. In groundwater, nitrate concentrations ranged from 1.0 to 22.7 mg NO₃ ^?–N l^?1 (from 2.8 to 37.5 mg NO₃ ^?–N l^?1 in the river) and dissolved N₂O from 0.2 to 101.0 μg N₂O–N l^?1 (and from 0.2 to 2.9 μg N₂O–N l^?1 in the river). From these measurements, we estimated an emission factor of EF_5g = 0.0026 (similar to the value currently used by the IPCC) and an annual indirect N₂O flux from groundwater of 0.035 kg N₂O–N ha^?1 year^?1, i.e., 1.8% of the previously measured direct N₂O flux from agricultural soils.     

Enhanced Vadose Zone Nitrogen Removal by Poplar During Dormancy

A pilot-scale, engineered poplar tree vadose zone system was utilized to determine effluent nitrate (NO₃^?) and ammonium concentrations resulting from intermittent dosing of a synthetic wastewater onto sandy soils at 4.5°C. The synthetic wastewater replicated that of an industrial food processor that irrigates onto sandy soils even during dormancy which can leave groundwater vulnerable to NO₃^? contamination. Data from a 21-day experiment was used to assess various Hydrus model parameterizations that simulated the impact of dormant roots. Bromide tracer data indicated that roots impacted the hydraulic properties of the packed sand by increasing effective dispersion, water content and residence time. The simulated effluent NO₃^? concentration on day 21 was 1.2 mg-N L^?1 in the rooted treatments compared to a measured value of 1.0 ± 0.72 mg-N L^?1. For the non-rooted treatment, the simulated NO₃^? concentration was 4.7 mg-N L^?1 compared to 5.1 ± 3.5 mg-N L^?1 measured on day 21. The model predicted a substantial “root benefit” toward protecting groundwater through increased denitrification in rooted treatments during a 21-day simulation with 8% of dosed nitrogen converted to N₂ compared to 3.3% converted in the non-rooted test cells. Simulations at the 90-day timescale provided similar results, indicating increased denitrification in rooted treatments.     

GIS based evaluation of fluoride contamination and assessment of fluoride exposure dose in groundwater of a district in Uttar Pradesh,India

Groundwater is the main source of drinking water in both rural and urban areas of the Pratapgarh district in the eastern Uttar Pradesh. Fifty-five groundwater samples were collected from 17 blocks of the Pratapgarh district and analyzed for fluoride (F^?) and other water quality parameters (pH, EC, TDS, turbidity, Cl^?, HCO₃^?, SO₄^2?, NO₃^?, Ca²⁺, Mg²⁺, Na⁺, K⁺, silica and total hardness) to assess its suitability for drinking uses. The fluoride concentration in the analyzed groundwater of the Pratapgarh district varied between 0.41 and 3.99 mg/L. Fluoride concentration in about 78% of the groundwater samples exceeded the acceptable level of 1.0 mg/L, while in 70% samples it exceeded the maximum permissible limit of 1.5 mg/L. A geographic information system (GIS) tool was used to study the spatial variation of fluoride concentrations in the groundwater of the Pratapgarh district. Fluoride is positively correlated with pH (0.36) and HCO₃^? (0.22) and negatively with Ca²⁺ (?0.23) and Mg²⁺ (?0.08), suggesting dissolution of fluoride-bearing minerals with the precipitation of Ca/Mg carbonate in the alkaline environment. The maximum exposure dose to fluoride for adults in the study area was found to be 6.8 times higher than the minimum risk level (MRL) of 0.05 mg kg^?1 day^?1 estimated by the Agency for Toxic Substances and Disease Registry (ATSDR).     

The Effect of Exogenous IAA and Kinetin on Nitrate Reductase,Nitrite Reductase and Glutamate Dehydrogenase Activities in Excised Pea Roots

Nitrate reductase (NO₃R) activity, nitrite reductase (NO₂R) activity and NADH₂ dependent glutamate dehydrogenase (GDH) activity were followed in extracts from excised pea roots incubated under aseptic conditions for 9 and 24 h in nitrate containing nutrient medium to which IAA was added in concentrations promoting lateral root formation (1 × 10^?5; 3 × 10^?5; 5 × 10^?5 M) and kinetin in concentrations which reduce lateral root formation (0.1; 1; 5 mg 1^?1, that is 4.65 × 10^?7;4.65 × 10^?6 and 2.3 × 10^?5 M). NO₃R activity was not influenced by IAA, NO₂R activity was slightly depressed by IAA after 24 h incubation and GDH activity was slightly increased after 24 h incubation in the presence of IAA. Kinetin decreased NO₃R activity significantly both after 9 h and 24 h incubation, slightly increased NO₂R activity after 9 h incubation but slightly decreased it after 24 h incubation, and did not affect GDH activity after 24 h incubation. However, when applied together with IAA, kinetin abolished the promoting effect of IAA on GDH activity. IAA neither reversed nor accentuated the effect of kinetin on NO₂R activity. Nevertheless the depressing effect of kinetin on NO₃R activity was emphasized by the presence of IAA after 9 h incubation. The results obtained indicate that reduced nitrate assimilation due to the depression of nitrate reductase activity caused by kinetin probably contributes to the negative growth effect of kinetin in pea root segments grown in nitrate medium.     

Porewater nitrate profiles in sandy sediments hosting submarine groundwater discharge described by an advection�Cdispersion-reaction model

In order to separate the effects of reaction from those of transport on vertical porewater concentration profiles of nitrate at an intertidal groundwater seepage site (Ria Formosa, Portugal), a free-boundary solution of an Advection?CDispersion-Reaction (ADR) model was used to describe the shape of NO₃ ^? concentration profiles collected in situ. The model includes three sequential reaction layers, postulated with basis on the local distribution of the benthic organic C:N ratio and major identifiable changes in concentration gradients with depth. The advective nature of the system was used to propose a mass balance simplification to the constitutive equations permitting a free-boundary solution, which in turn allowed prediction of sediment?Cwater fluxes of NO₃ ^?. Sensitivity analysis confirmed that in similarly advective-dominated environments, both the porewater concentration distribution and the interfacial fluxes are strongly dependant on seepage rate and benthic reactivity. The model fitted the measured profiles with high correlation (usually higher than 90%), and model-derived sediment?Cwater NO₃ ^? fluxes were in good agreement to fluxes measured in situ with Lee-type seepage meters (0.9948 slope, R² = 0.8672, n = 8). Nitrate oxidation and reduction rates extracted from model fits to the data (10^?2?C10⁰ mmol m^?2 h^?1) agreed with literature values. Because dispersive effects are not included in direct mass balances based on the porewater concentrations, the model presented here increases the accuracy of apparent reaction rate estimates and geochemical zonation at Submarine Groundwater Discharge (SGD) sites. The results establish the importance of sandy sediments as reactive interfaces, able to modulate mass transfer of continental-derived contaminants into coastal ecosystems. We suggest that tools such as the one described here might be used to advantage in preparing further experimental studies to elucidate how benthic reactivity affects nitrate distribution and fluxes in sediments affected by SGD.     

Optimization of growth and production of toxins by three dinoflagellates in photobioreactor cultures

A bioreactor system for biotoxin production was appraised against traditional methods of growing dinoflagellate cultures. In an optimised bioreactor culture (5.4?L) operated in batch mode, growth of Karenia selliformis was more efficient than in 15-L bulk carboy culture in terms of growth rate (μ?=?0.07?day^?1 versus 0.05?day^?1) and growth maximum (G _max, 169.10⁶ versus 41.10⁶ cells L^?1). Maximal gymnodimine concentration (1200?μg L^?1) in bioreactor culture was 8-fold higher than in bulk carboy culture, and the yield per cell (pg cell^?1) was 2-fold higher. Similarly the bioreactor batch culture of Alexandrium ostenfeldii performed more efficiently than carboy cultures in terms of growth rate (1.6-fold higher), growth maximum (15-fold higher) and desmethyl C spirolide (SPX-desMe-C) yield (5-fold higher [μg L^?1], though the yield [pg cell^?1basis] was lower). When bioreactor cultures of K. selliformis were operated in continuous mode, the yield of gymnodimine was substantially higher than a carboy or the bioreactor run in batch mode to growth max (793?μg day^?1 over 58?days in continuous culture was achieved versus an average of 60?μg day^?1 [carboy over 40?days] or 249?μg day^?1 [batch mode] over 26?days). Likewise in continuous bioreactor cultures of A. ostenfeldii run over 25?days, the yield of SPX-desMe-C (29?μg day^?1) was substantially higher than in same cultures run in batch mode or carboys (10.2 day^?1 and 7.7?μg day^?1 respectively). Similarly 5.4?L bioreactor batch cultures of K. brevisulcata reached 3.8-fold higher cell densities than carboy cultures, and when operated in continuous mode, the brevisulcatic acids were more efficiently produced than in batch culture (12?μg day^?1 versus 7?μg day^?1). When the bioreactor system was upscaled to 52?L, the maximum cell densities and toxin yields of K. brevisulcata cultures were somewhat less than those achieved in the smaller reactor, which was attributed to reduced light penetration.     

Effect of Previous Nitrate Deprivation on 15N-nitrate Absorption and Assimilation by Wheat Seedlings

Nitrate uptake and assimilation were examined in intact 18 days old wheat (Triticum aestivum, cv Capitole) seedlings either permanently grown on nitrate (high-N seedlings) or N-stressed by transfer to an 0 N-solution for the final 7 days (low-N seedlings). The N-stressed seedlings were characterized by a lower organic N content (2.5 mg instead of 4.9 mg per seedling) and an increased root dry weight.The seedlings received ¹⁵NO₃K for 7 h in the light. Nitrate uptake was 2.8 times higher in low-N than in high-N seedlings. The assimilation rate was 35 and 16 μmol NO₃^?·^h?1· g^?1 dry weight respectively. Partitioning of NO₃^? to reduction and assimilation was the very same in both kinds of seedlings. The results support the view that 50 % of the nitrate reduction in Triticum aestivum, cv Capitole could be achieved in the roots.The present observations are interpreted as evidence that factors closely associated with the seedling N-status may have a major role in regulating NO₃^? uptake and assimilation. In low-N seedlings, the high amount of carbohydrates in roots may add its stimulus to the specific inducing effect of nitrate whereas in high-N seedlings, excess of nitrate or amino-acids may set the pace by negative feedback control.     

Inoculum effects on community composition and nitritation performance of autotrophic nitrifying biofilm reactors with counter‐diffusion geometry

The link between nitritation success in a membrane‐aerated biofilm reactor (MABR) and the composition of the initial ammonia‐ and nitrite‐oxidizing bacterial (AOB and NOB) population was investigated. Four identically operated flat‐sheet type MABRs were initiated with two different inocula: from an autotrophic nitrifying bioreactor (Inoculum A) or from a municipal wastewater treatment plant (Inoculum B). Higher nitritation efficiencies (NO₂^‐‐N/NH₄⁺‐N) were obtained in the Inoculum B‐ (55.2–56.4%) versus the Inoculum A‐ (20.2–22.1%) initiated reactors. The biofilms had similar oxygen penetration depths (100–150 µm), but the AOB profiles [based on 16S rRNA gene targeted real‐time quantitative PCR (qPCR)] revealed different peak densities at or distant from the membrane surface in the Inoculum B‐ versus A‐initiated reactors, respectively. Quantitative fluorescence in situ hybridization (FISH) revealed that the predominant AOB in the Inoculum A‐ and B‐initiated reactors were Nitrosospira spp. (48.9–61.2%) versus halophilic and halotolerant Nitrosomonas spp. (54.8–63.7%), respectively. The latter biofilm displayed a higher specific AOB activity than the former biofilm (1.65 fmol cell^?1 h^?1 versus 0.79 fmol cell^?1 h^?1). These observations suggest that the AOB and NOB population compositions of the inoculum may determine dominant AOB in the MABR biofilm, which in turn affects the degree of attainable nitritation in an MABR.