Continuous Flow-through System Research Articles

Porous Iron Electrodes Reduce Energy Consumption During Electrocoagulation of a Virus Surrogate: Insights into Performance Enhancements Using Three-Dimensional Neutron Computed Tomography.

Electrocoagulation has attracted significant attention as an alternative to conventional chemical coagulation because it is capable of removing a wide range of contaminants and has several potential advantages. In contrast to most electrocoagulation research that has been performed with nonporous electrodes, in this study, we demonstrate energy-efficient iron electrocoagulation using porous electrodes. In batch operation, investigation of the external pore structures through optical microscopy suggested that a low porosity electrode with sparse connection between pores may lead to mechanical failure of the pore network during electrolysis, whereas a high porosity electrode is vulnerable to pore clogging. Electrodes with intermediate porosity, instead, only suffered a moderate surface deposition, leading to electrical energy savings of 21% and 36% in terms of electrocoagulant delivery and unit log virus reduction, respectively. Neutron computed tomography revealed the critical role of electrode porosity in utilizing the electrode's internal surface for electrodissolution and effective delivery of electrocoagulant to the bulk. Energy savings of up to 88% in short-term operation were obtained with porous electrodes in a continuous flow-through system. Further investigation on the impact of current density and porosity in long-term operation is desired as well as the capital cost of porous electrodes.

Sequential Fractionation of Spruce Bark in a Continuous Flow-through System

Sequential Fractionation of Spruce Bark in a Continuous Flow-through System

The single atom Fe loaded catalytic membrane for effective peroxymonosulfate activation and pollution degradation

A novel iron-based single-atom catalyst (Fe SAC) integrated into a catalytic membrane was developed for peroxymonosulfate (PMS) activation and organic pollutant degradation. The Fe SAC membrane was synthesized using a co-precipitation method and acid leaching treatment, and its catalytic activity was evaluated in a continuous flow-through system using nitenpyram (NPR) as a model pollutant. The Fe SAC membrane/PMS system achieved over 90% NPR removal efficiency with low iron leaching (2.85–8.05 μg/L) during 10 hours of continuous operation, and maintained over 80% NPR removal in tap water, Yellow River water, and Yangtze River water. Experimental and theoretical analyses revealed that the strong chemisorption and electron transfer between PMS and FeN4 led to the dominant production of singlet oxygen for NPR degradation. This study demonstrates the potential of SAC-based catalytic membranes for efficient and stable attenuation of refractory organic pollutants in water treatment applications.

Partial Replacement of Fish Meal with an Aquatic Macrophyte, Ceratophyllum demersum in the Diet of Common Carp, Cyprinus carpio var. communis Fingerlings

A 12-week feeding trial was conducted to investigate the nutrient utilization, growth performance, and hematological indices of Cyprinus carpio var. communis fingerlings fed diets based on aquatic macrophyte, Ceratophyllum demersum as a replacement of fish meal (FM). Six isonitrogenous and isocaloric diets containing graded levels of C. demersum 0%, 5%, 10%, 15%, 20%, and 25%, respectively, as replacer of FM were formulated. Total of 360 fingerlings with an initial weight of 3.65 ± 0.98 g were randomly stocked in 70 L plastic tanks water volume 60 L connected with a continuous flow-through system (1–1.5 L/min) for each treatment and were run in triplicate having 20 fish in each tank. At the end of the feeding trial, it was observed that the C. carpio var. communis fingerlings receiving 5% and 10% C. demersum in the diet showed improvements in live weight gain (LWG), specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency rate (PER). While further addition of C. demersum as a replacement of FM from 15% to 25% led to the progressive decline in the values of LWG, SGR, FCR, and PER. Hematological data also exhibited a linear declining trend beyond the 10% C. demersum replacement level. The fish fed with higher inclusions of C. demersum in each diet significantly (P<0.05) affected whole body composition with the lowest protein and fat amounts recorded at higher replacement levels significantly (P<0.05). The highest protein and fat contents were observed at 5% and 10% diets. Except serum glucose, cholesterol, alanine aminotransferase (ALT), and aspartate aminotransferase (AST), the other serum indices exhibited a decreasing trend with increasing inclusion of C. demersum in the diet. The results of the present study clearly demonstrated that the inclusion of 10% C. demersum did not affect the growth and other parameters of C. carpio var. communis fingerlings compared to the 50% FM diet. However, it is recommended that 10% FM can be substituted without compromising the growth and nutritional quality of fish.

Wavelength synergistic effects in continuous flow-through water disinfection systems

The past decade's development of UV LEDs has fueled significant research in water disinfection, with widespread debate surrounding the potential synergies of multiple UV wavelengths. This study analyses the use of three UV sources (265, 275, and 310 nm) on the inactivation of Escherichia coli bacteria in two water matrixes. At maximum intensity in wastewater, individual inactivation experiments in a single pass set-up (Flow rate = 2 L min−1, Residence time = 0.75 s) confirmed the 265 nm light source to be the most effective (2.2 ± 0.2 log units), while the 310 nm led to the lowest inactivation rate (0.0003 ± 7.03×10−5 log units). When a combination of the three wavelengths was used, an average log reduction of 4.4 ± 0.2 was observed in wastewater. For combinations of 265 and 275 nm, the average log reductions were similar to the sum of individual log reductions. For combinations involving the use of 310 nm, a potential synergistic effect was investigated by the use of robust statistical analysis techniques. It is concluded that combinations of 310 nm with 265 nm or 275 nm devices, in sequential and simultaneous mode, present a significant synergy at both intensities due to the emission spectra of the selected LEDs, ensuring the possibility of two inactivation mechanisms. Finally, the electrical energy per order of inactivation found the three-wavelength combination to be the most energy efficient (0.39 ± 0.05, 0.36 ± 0.01 kWh m−3, at 50% and 100% dose, respectively, in wastewater) among the synergistic combinations.

TOXICITY OF CHLORPYRIFOS TECHNICAL GRADE AND 20% EC TO THE FRESHWATER FISH, CHANNA PUNCTATA (BLOCH)

The toxicity studies of chlorpyrifos technical grade (TG) and 20% EC are conducted in the prevailing laboratory conditions of the fish Channa punctata in vivo to determine the median lethal concentrations i.e., LC50 values for 24, 48, 72 and 96 hrs duration by employing both static renewal and continuous flowthrough systems. The most preferred and palatable fish and mostly used pesticide the organophosphate are selected for study. The static renewal values are 6.02 µg/L, 5.82 µg/L, 5.62 µg/L, 5.38 µg/L for technical grade and for 20% EC 3.01 µg/L, 2.71 µg/L, 2.61 µg/L, and 2.51 µg/L for 24, 48, 72 and 96 hrs respectively. Similarly, for the continuous flow through system (CFTS) the values are 3.11 µg/L, 2.87 µg/L, 2.81 µg/L and 1.61 µg/L for technical grade and for 20% EC 1.91 µg/L, 1.81 µg/L, 1.61 µg/L and 1.41 µg/L respectively for 24, 48, 72 and 96 hrs. The toxicity is the concentration and duration dependent and the LC50 values in both methods decreased as well as concentrations also. The static renewal values are higher to CFTS and 20% EC is sufficiently toxic, which had synergistic effect on target and tested organism. The values are useful for data base and also in prescribing the permissible limits.

Retention and recycling of granules in continuous flow-through system to accomplish denitrification and perchlorate reduction

This study employed a completely anoxic reactor and a gravity-settling design for continuously capturing and separating granules from flocculated biomass, and recycling granules back to the main reactor. The average chemical oxygen demand (COD) removal in the reactor was 98%. Average nitrate (NO3−-N) and perchlorate (ClO4−) removal efficiencies of 99% and 74 ± 19% were observed, respectively. Preferential utilization of NO3− over ClO4− led to COD limiting conditions, which resulted in ClO4− in the effluent. The average granule diameter in continuous flow-through bubble-column (CFB) anoxic granular sludge (AxGS) bioreactor was 6325 ± 2434 µm, and the average SVI30/SVI1 was >90 % throughout its operation. 16s rDNA amplicon sequencing revealed Proteobacteria (68.53%–88.57%) and Dechloromonas (10.46%–54.77%) to be the most abundant phylum and the genus present in reactor sludge representing the denitrifying and ClO4− reducing microbial community. This work represents a pioneering development of CFB-AxGS bioreactor.

Impact of the anaerobic feeding mode on substrate distribution in aerobic granular sludge

There is a growing interest to implement aerobic granular sludge (AGS) in existing conventional activated sludge (CAS) systems with a continuous flow-through configuration. The mode of anaerobic contact of raw sewage with the sludge is an important aspect in the adaptation of CAS systems to accommodate AGS. It remains unclear how the distribution of substrate over the sludge by a conventional anaerobic selector compares to the distribution via bottom-feeding applied in sequencing batch reactors (SBRs). This study investigated the effect of the anaerobic contact mode on the substrate (and storage) distribution by operating two lab-scale SBRs; one with the traditional bottom-feeding through a settled sludge bed similar to full-scale AGS systems, and one where the synthetic wastewater was fed as a pulse at the start of the anaerobic phase while the reactor was mixed through sparging of nitrogen gas (mimicking a plug-flow anaerobic selector in continuous flow-through systems). The distribution of the substrate over the sludge particle population was quantified via PHA analysis, combined with the obtained granule size distribution. Bottom-feeding was found to primarily direct substrate towards the large granular size classes (i.e. large volume and close to the bottom), while completely mixed pulse-feeding gives a more equal distribution of substrate over all granule sizes (i.e. surface area dependant). The anaerobic contact mode directly controls the substrate distribution over the different granule sizes, irrespective of the solids retention time of a granule as an entity. Preferential feeding of the larger granules will enhance and stabilise the granulation compared to pulse-feeding, certainly under less advantageous conditions imposed by real sewage.

Transcriptomic and metabolomic integration to assess the response of gilthead sea bream (Sparus aurata) exposed to the most used insect repellent: DEET.

DEET is one of the most frequently detected insect repellents in the environment reaching concentrations of several μg L−1 in surface water. There is scarce information available regarding its mode of action in non-target organisms. Here, we have used an integrated metabolomic and transcriptomic approach to elucidate the possible adverse effects of DEET exposure in the marine fish gilthead sea bream (Sparus aurata). Individuals were exposed at an environmentally relevant concentration of DEET (10 μg L−1) for 22 days in a continuous flow-through system. Transcriptomic analysis revealed 250 differentially expressed genes in liver, while metabolomic analysis identified 190 differentially modulated features in liver and 98 in plasma. Multi-omic data integration and visualization allowed elucidation of the modes of action of DEET exposure, including: energy depletion through the disruption of carbohydrate and amino acids metabolisms, oxidative stress leading to DNA damage, lipid peroxidation, and damage to cell membrane and apoptosis. Activation of xenobiotic pathway as well as the inmune-inflammatory reaction was evidenced in the present work.

P22-09 Dissolution kinetics of three different nanoparticles using the continuous flow-through system

P22-09 Dissolution kinetics of three different nanoparticles using the continuous flow-through system

Oxygen-vacancy-enriched substrate-less SnOx/La-Sb anode for high-performance electrocatalytic oxidation of antibiotics in wastewater

Electrocatalytic oxidation is a promising technology for treating toxic organic pollutants in water and wastewater, but conventional Ti-based anodes often exhibit a short service life and low efficiency in application. Oxygen vacancy (OV)-based defect engineering is an effective activation method for enhancing the electrocatalytic activity of electrodes. Herein, the controllable formation of OV on the surface of a freestanding SnO2-Sb anode was achieved by the quantitative doping of La3+ into the SnO2 crystal structure of the anode for high-performance electrochemical wastewater treatment. The resultant SnOx/La-Sb anode degraded nearly 100% moxifloxacin (MOX, 10 mg L−1) in 30 min, with a low energy consumption of 0.09 kWh m−3. The SnOx/La-Sb anode with an OV density of 1.09% had the highest degradation rate constant (0.226 min−1), 8 times higher than that of the SnO2-Sb anode and 16 times higher than that of the state-of-the-art boron-doped diamond anode. La3+ doping-induced OV activated the anode surface for electrochemical reactions by boosting the interfacial electron transfer and •OH generation (103% increase). The novel 3D permeable SnOx/La-Sb anode also exhibited remarkable stability (predicted service life of 59 years) and high-rate performance (>98%) in a continuous flow-through treatment system (<1 min through the anode).

Pilot-scale direct UV-C photodegradation of pesticides in groundwater and recycled wastewater for agricultural use

Pesticides widely used for intensive agriculture may leach to groundwater and pose problems to drinking water and irrigation. UV-C disinfection systems (UV-DS) for water disinfection can be used also for the abatement of organic micropollutants. A pilot-scale continuous flow-through UV-DS system was evaluated for its degradation efficiency of atrazine (ATR), malathion (MAL) and glyphosate (GLY) from 40 L water. Groundwater used to irrigate potato fields and recycled wastewater used to wash potatoes were treated without catalysts to avoid any toxicity effect on potatoes. Chromatographic methods were used to quantify very low pesticide levels before and after UV-C treatments (<10 µg L−1), while a specific method was adapted to analyse traces of GLY (0.0008–10 µg L−1) in recycled wastewater containing suspended particulate matter (SPM). ATR was completely eliminated from groundwater after 15 min photodegradation while 80% was removed from the turbid wastewater after 25 min. For MAL, 70–80% was removed in 25 min from the groundwater. For wastewater, the initial concentration was important for the performance of the photolytic process. An amount of 75% of GLY was eliminated after 10 min irradiation at concentrations higher than those found in natural groundwater. In wastewater, the UV-C treatment was less efficient because GLY was mainly adsorbed to SPM which obstruct the photodegradation process. Therefore, the pilot-scale UV-DS using a turbulent flow and a multiple-lamp system was performed to remove quantitatively traces of pesticides from large volumes of water, by direct photolytic oxidation, when the turbidity of the treated water was limited.

Syntheses of Ag[Cu@Ag]\\APTMS\\boehmite as a photocatalyst for methylene blue degradation in batch and continuous flow systems under visible light

A novel nano-composite photo-catalyst, called Ag[Cu@Ag]\\APTMS\\boehmite, was developed and tested for the degradation of methylene blue (MB) dye as a representative of dye pollutants. The synthesized boehmite nanoparticles (NPs) were functionalized by 3-aminopropyltrimethoxysilane and then anchored by Cu@Ag core–shell NPs. The MB degradation was investigated in the batch and continuous flow-through system. In the batch system, the MB solution was degraded by synthesized photo-catalyst under irradiation by visible light (500-W lamp) and solar light. In this system, different parameters including pH, catalyst dosage, initial dye concentration, and time were optimized. The optimum condition obtained for photocatalytic rate was at pH = 6, an initial dye concentration of 10 mg.L−1, catalyst dosage of 2 g.L−1 and a reaction time of 47 h under visible light irradiation. The MB solution was degraded by 80.3% under visible light irradiation over 34.7 h, and it was degraded by 40.7% over 8 h under solar light irradiation in the optimum condition. In the continuous flow-through system, the MB degradation was studied by considering initial dye concentration and flow rate as variables. Results indicated that the MB degradation rate increased by decreasing the initial concentration of MB and flow rate, as seen 90.4% of initial concentration reduced in 8 h under solar irradiation.

Genomic analysis of high copy-number sequences for the targeted detection of Listeria species using a flow-through surveillance system

The bacterial foodborne pathogen Listeria monocytogenes has been implicated in fresh produce outbreaks with a significant economic impact. Given that L. monocytogenes is widespread in the environment, food production facilities constantly monitor for the presence of Listeria species. To develop a surveillance platform for food processing facilities, this study conducted a comparative genomic analysis for the identification of conserved high copy sequences in the ribosomal RNA of Listeria species. Simulated folding was performed to assess RNA accessibility in the identified genomic regions targeted for detection, and the developed singleplex assay accurately detected cell amounts lower than 5 cells, while no signals were detected for non-targeted bacteria. The singleplex assay was subsequently tested with a flow-through system, consisting of a DNA aptamer-capture step, followed by sample concentration and mechanical lysis for the detection of Listeria species. Validation experiments indicated the continuous flow-through system accurately detected Listeria species at low cell concentrations.

Nitrogen Dynamics of Inundated Sediments in an Emerging Coastal Deltaic Floodplain in Mississippi River Delta Using Isotope Pairing Technique to Test Response to Nitrate Enrichment and Sediment Organic Matter

Nitrate (NO3–) enrichment in rivers over the last four decades has potentially shifted how coastal ecosystems process nitrogen (N). Shifts in N dynamics may be particularly significant in coastal deltaic floodplains when sediments are inundated during river flood stage as this may change the fate of NO3– transported to the coastal ocean. We evaluated the relative importance of denitrification, dissimilative nitrate reduction to ammonium (DNRA), and anaerobic ammonium oxidation (anammox) in intact sediment cores of Wax Lake Delta (WLD) using continuous flow-through system. We manipulated this experimental system with two concentrations of riverine NO3– (lower concentration at 5 μM and ambient concentration at 100 μM) to test how nitrate-enriched waters may modify N cycling in coastal deltaic floodplains. Inundated sediments in a coastal deltaic floodplain removed bio-reactive N as a function of sediment organic matter (SOM) concentrations, indicating how N dynamics vary as a result of deltaic succession. Direct denitrification was the dominant N pathway in inundated sediments in WLD, which was several times greater than coupled nitrification-denitrification, DNRA, and anammox. Gross denitrification (direct denitrification + coupled nitrification-denitrification) rates generally increased with SOM concentrations and ranged from 4 to 12 μmol N m–2 h–1 under lower NO3– enrichment (5 μM) and 68 to 276 μmol N m–2 h–1 under higher NO3– enrichment (100 μM). Most of these changes in N fluxes with SOM and NO3– enrichment resulted from the increase in direct denitrification rates rather than coupled nitrification-denitrification rates. DNRA rates varied from 0 to 65 μmol N m–2 h–1, and the relative significance of DNRA increased as a percentage of total NO3– reduction (%DNRA) with increasing ratio of organic carbon to NO3– concentrations (OC/NO3–). Anammox rates increased among sites as SOM increased, but rates were lower from 0.0 to 38 μmol N m–2 h–1. The dominance of direct denitrification and increased anammox rates with SOM concentrations indicate that dynamic deltaic floodplains can permanently remove bio-reactive N in the proximal zone of river deposition of tidal freshwater wetlands.

A continuous flow-through system with integration of electrosorption and peroxi-coagulation for efficient removal of organics

A flow-through reactor with integration of electrosorption (ES) and peroxi-coagulation (PC) processes was designed for organics removal. Impacts of key parameters (solution pH, flow rate, initial concentration of organics, applied voltage) on the removal efficiency of Orange II were explored. Under the optimized conditions, 93% removal efficiency and 1043 mg g−1 removal capacity of Orange II could be obtained with an energy consumption of 31.9 kWh m−3 order−1. Controlled experiments of ES for pollutants removal, and the detections of dissolved irons and the generated hydroxyl radicals (•OH) were conducted, demonstrating the coupling effect and contribution ratio of ES and PC for organics removal in this flow-through system. The spatiotemporal efficiency of the integrated flow-through system was more than 10 times of conventional ES system, providing more potential for practical application of wastewater treatment. The flow-through system was also verified to be advantageous for removal of other organic pollutants including 2,4-dichlorophenoxyacetic acid, phenol and methylene blue with high removal efficiencies. This study proved that the integrated flow-through process was an efficient, comparative and applicable method for wastewater treatment.

Contrasting responses of DOM leachates to photodegradation observed in plant species collected along an estuarine salinity gradient

A series of abiotic processes affected by salinity changes involve light-mediated reactions and different degradation pathways of organic compounds, including altered photo-oxidation, photo-degradation, and photolysis of organic matter (OM). Sunlight is known to degrade, oxidize, or mineralize dissolved organic matter (DOM) in waterways, creating large changes in compositional structure of DOM near the water surface and ultimately in the mixed layer. DOM derived from various vegetation types has differing levels of susceptibility to photolytic degradation depending on initial chemical composition and in what matrix degradation takes place (e.g., salinity). The effect of sunlight and salinity on degradation of leached DOM derived from three dominant vegetative species, Avicennia germinans, Juncus romerianus, and Taxodium distichum, along a riverine continuum in northeast Florida was determined. Leachates from these three sources in a deionized or seawater matrix were irradiated in a continuous flow-through photolytic system over the course of 20 h. Avicennia germinans and Juncus roemerinaus DOM readily degraded as indicated by decreases in absorbance across all wavelengths during the irradiation period, while Taxodium distichum DOM was found to increase in absorbance across all wavelengths in the freshwater matrix, but not in seawater. PARAFAC analysis indicated differences in photochemical components and % change of absorbance and fluorescence over time indicate the importance and variability of individual contributions to the DOM pool across an estuarine continuum. This work characterizes the photochemical properties of three individual DOM sources, exhibits the need for further research on this topic, and explores the salinity effect on photo-degradation of DOM from unique plant-derived DOM.

High-Resolution Carbonate System Dynamics of Netarts Bay, OR From 2014 to 2019

Netarts Bay is a shallow, temperate, tidal lagoon located on the northern coast of Oregon and the site of the Whiskey Creek Shellfish Hatchery (WCSH). Data collected with an autonomous continuous flow-through system installed at WCSH capable of high-resolution (1 Hz) partial pressure of aqueous CO2 (pCO2) and hourly total dissolved inorganic carbon (TCO2) measurements, with combined measurement uncertainties of &amp;lt; 2.0% and 0.5%, respectively, is analyzed over the 2014–2019 interval. Summer upwelling, wintertime downwelling, and in situ bay biogeochemistry represent significant modes of the observed variability in carbonate system dynamics. Summer upwelling is associated with large amplitude diel pCO2 variability, elevated TCO2 and alkalinity, but weak variability in salinity. Wintertime downwelling is associated with bay freshening by both local and remote sources, a strong tidal signature in salinity, TCO2, and alkalinity, with diel pCO2 variability much less amplified when compared to summer. Further, analysis of alkalinity-salinity relationships suggests multiple water masses inhabiting the bay during 1 year: mixing of end-members associated with direct precipitation, coastal rivers, southward displacement of the Columbia River plume, California Current surface and deep upwelled waters. The importance of in-bay processes such as net community metabolism during intervals of high productivity are apparent. These direct measurements of pCO2 and TCO2 have been useful to local hatchery owners who have monitored intake waters following historic seed-production failures related to high-CO2 conditions exacerbated by ocean acidification.

A mineralogical perspective on the recovery of uranium from brannerite-rich ore at Cooke Section, West Rand Goldfield, South Africa

Abstract The recovery of uranium from quartz-pebble conglomerates of the Witwatersrand Basin is accomplished through sulphuric acid dissolution under oxidising conditions. At Cooke Section on the West Rand Goldfield, the extraction process has been plagued by low to moderate yields on the order of 40 to 75%, as opposed to a target recovery of 80%. This has been ascribed to the high abundance of brannerite in the ore, which has traditionally been more problematic to leach. In addition to brannerite, poor metallurgical recoveries may also be associated with processing inefficiencies related to comminution, residence time, acid dosage and leach temperature. In view of this, a range of ore samples (channel samples) were collected from four uranium-bearing conglomerate horizons at Cooke Section (the A1, A5, E9EC and UE1A reefs) for detailed mineralogical and metallurgical characterisation, involving automated mineralogical analysis, and laboratory-scale leach testwork. The mineralogical results show that the major uranium-bearing minerals of uraninite, coffinite and brannerite are fine-grained (~80% passing 32 micron) and exhibit high degrees of mineral exposure to the lixiviant (~99%). Despite these favourable attributes, the elemental deportment data indicate that brannerite accounts for approximately 43% of the combined uranium budget. Further inspection shows that brannerite can be subdivided into three compositional subtypes: uraniferous brannerite (~13% U deportment), brannerite (~25% U deportment) and titaniferous brannerite (~5% U deportment). Baseline laboratory leach tests, which replicated plant leach conditions of 30 kg/ton acid, 4 kg/t oxidant, 24 hour residence time and 60°C leach temperature, yielded elevated dissolutions between ~77% and ~96%, with a combined overall uranium recovery of ~94%. These results are not consistent with the low yields obtained at the processing plant, and suggest that the high level of uranium recovery can be attributed to the effective leaching of brannerite (most likely uraniferous brannerite and brannerite). In view of prevailing market conditions, variability tests were carried out on a representative bulk composite sample to investigate the potential to achieve similar yields under more cost-effective leaching conditions. In these tests, a single parameter was varied (e.g. acid dosage), while the remaining parameters remained at baseline conditions. The results demonstrate that uranium recoveries of ~80% can be achieved on Cooke Section ores at low acid dosages and high temperatures (18 kg/t, 60°C) or at moderate acid dosages and low temperatures (23 kg/t, 30°C). The associated reduction of input costs would represent a significant cost-saving for the Ezulwini gold and uranium recovery plant. It is concluded that the poor uranium yields encountered during commercial processing of the ore are most likely related to undiagnosed inefficiencies in the treatment plant, such as excessive acid consumption related to elevated temperatures/oxidant addition and/or insufficient leach residence times, especially when recirculating, continuous flow-through leaching systems are in use. The broader implication of this study is that uranium processing operations beyond Cooke Section may be able to optimise their process designs and reduce input costs by quantifying the different types of brannerite within their ores through automated mineralogical analyses. The present study thus demonstrates the value of a geometallurgical approach in enhancing the understanding of uranium recovery through acid leaching.

Benthic fluxes of dissolved oxygen and nutrients across hydrogeomorphic zones in a coastal deltaic floodplain within the Mississippi River delta plain

We tested the hypothesis that benthic fluxes will increase spatially in a coastal deltaic floodplain as sediment organic matter increases in response to developing hydrogeomorphic zones along a chronosequence of the active Mississippi River Delta. A continuous flow-through core system was used to incubate intact sediment cores from three hydrogeomorphic zones along a chronosequence in the emerging Wax Lake Delta (WLD). Organic matter content increased from younger to older deltaic sediments from subtidal to supratidal hydrogeomorphic zones, which were coupled with increasing benthic oxygen and nitrogen fluxes. Mean net denitrification rate in spring was 100 µmol N2–N m−2 h−1 with significantly lower rates occurring in the younger intertidal zones (T4 transect, − 22 µmol N2–N m−2 h−1) and higher rates occurring in the older supratidal zones (T2 and T1 transects, 330 and 262 µmol N2–N m−2 h−1, respectively). Mean net denitrification rate in summer was 397 µmol N2–N m−2 h−1 without significant site-to-site variability except for the supratidal-T2 site (911 µmol N2–N m−2 h−1) showing higher denitrification rate than the other sites. Based on seasonal temperature and inundation time, annual rates of benthic NO3− removal varied from − 0.5 to − 3.4 mol m−2 y−1 and N2–N production rates varied from 1.0 to 3.2 mol N m−2 y−1 across WLD. The subtidal zone had the lowest fluxes associated with lower organic matter content, but was the hydrogeomorphic zone with the largest area and longest flood duration, and therefore contributed over half of N removal in WLD. The estimated annual NO3− removal of 896 Mg N y−1 in WLD accounts for 10 to 27% of total NO3− load to WLD, most of which is converted to N2 through denitrification. As a small prograding coastal deltaic floodplain under early stages of delta development, WLD is a continuously emerging ecosystem where the capacity of N removal increases by 0.2 to 2% per year prior to riverine NO3− is export to coastal ocean. These results highlight the contribution of the coastal deltaic floodplain in an active coastal basin in processing elevated riverine NO3− at continental margins with coastal ocean. The potential loss of this ecosystem service in N removal may increase in global significance as delta areas decline as result of accelerated relative sea level rise and decreased sediment loading in major river basins around the world.