Salt-water Systems Research Articles

Chemistry of salts in aqueous solutions: Applications, experiments, and theory

Salts comprise a very large and important group of chemical compounds. Natural occurrence of salts and industrial processes of their recovery, conversion, purification, and use depend on solubility phenomena and their chemistry in aqueous solutions, mostly in multi-ion systems. Modeling of these processes as well as developing new ones requires knowledge of the properties of the aqueous salt solutions in extended T-p-x ranges including a growing number of components in solutions (CO2, SO2, lithium salts, salts of rare earth metals, actinides, etc.). At least for the thermodynamic properties, the general accepted methodology is to use thermodynamic databases of aqueous species and solids in combination with an appropriate ion-interaction model to perform equilibrium calculations for species distributions in solution and phase equilibria. The situation in respect to available thermodynamic models and data for their parameterization is discussed at selected examples. Thereby, the importance of accurate experimental determinations of phase equilibrium data for derivation of model parameters is emphasized. Furthermore, it is concluded that experimental investigations should follow a chemical systematic. Simple physical models or quantum chemical calculations cannot predict unknown quantities in the databases with sufficient accuracy. Finally, solubility changes in salt-water systems at enhanced temperatures are considered. Systems, which can be considered as molten hydrates, display interesting phase behavior and chemical reactivity as protic ionic liquids. The latter can be exploited in chemical syntheses to substitute mixtures of concentrated acids like HNO3/H2SO4 by simple salts like ferric nitrate. For an understanding of the chemical and phase behavior of water-salt systems in terms of structure–property relations, a renaissance of chemical guided basic investigations of such systems would be worthwhile.

Gold and copper partitioning in magmatic-hydrothermal systems at 800 °C and 100 MPa

Porphyry-type ore deposits sometimes contain fluid inclusion compositions consistent with the partitioning of copper and gold into vapor relative to coexisting brine at the depositional stage. However, this has not been reproduced experimentally at magmatic conditions. In an attempt to determine the conditions under which copper and gold may partition preferentially into vapor relative to brine at temperatures above the solidus of granitic magmas, we performed experiments at 800 °C, 100 MPa, oxygen fugacity ( f O 2 sys ) buffered by Ni–NiO, and a S 2 sys fixed at either 3.5 × 10 −2 by using intermediate solid solution–pyrrhotite, or 1.2 × 10 −4 by using intermediate solid solution–pyrrhotite–bornite. The coexisting vapor (∼3 wt.% NaCl eq.) and brine (∼68 wt.% NaCl eq.) were composed initially of NaCl + KCl + HCl + H 2O, with starting HCl set to <1000 μg/g in the aqueous mixture. Synthetic vapor and brine fluid inclusions were trapped at run conditions and subsequently analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Our experiments demonstrate that copper and gold partitioned strongly into the magmatic volatile phase(s) (MVP) (i.e., vapor or brine) relative to a silicate melt over the entire imposed range of a S 2 sys . Nernst style partition coefficients between coexisting brine (b) and melt (m), D b/m (±1 σ), range from 3.6(±2.2) × 10 1 to 4(±2) × 10 2 for copper and from 1.2(±0.6) × 10 2 to 2.4(±2.4) × 10 3 for gold. Partition coefficients between coexisting vapor (v) and melt, D v/m range from 2.1 ± 0.7 to 18 ± 5 and 7(±3) × 10 1 to 1.6(±1.6) × 10 2 for copper and gold, respectively. Partition coefficients for all experiments between coexisting brine and vapor, D b/v (±1 σ), range from 7(±2) to 1.0(±0.4) × 10 2 and 1.7(±0.2) to 15(±2) for copper and gold, respectively. Observed average D b/v at an a S 2 sys of 1.2 × 10 −4 were elevated, 95(±5) and 15 ± 1 for copper and gold, respectively, relative to those at the higher a S 2 sys of 3.5 × 10 −2 where D b/v were 10(±5) for copper and 7(±6) for gold. Thus, there is an inverse relationship between the a S 2 sys and the D b/v for both copper and gold with increasing a S 2 sys resulting in a decrease in the D b/v signifying increased importance of the vapor phase for copper and gold transport. This suggests that copper and gold may complex with volatile S-species as well as Cl-species at magmatic conditions, however, none of the experiments of our study at 800 °C and 100 MPa had a D b/v ⩽ 1. We did not directly determine speciation, but infer the existence of some metal–sulfur complexes based on the reported data. We suggest that copper and gold partition preferentially into the brine in most instances at or above the wet solidus. However, in most systems, the mass of vapor is greater than the mass of brine, and vapor transport of copper and gold may become more important in the magmatic environment at higher a S 2 sys , lower f O 2 sys , or near the critical point in a salt-water system. A D b/v ⩽ 1 at subsolidus hydrothermal conditions may also occur in response to changes in temperature, f O 2 sys , a S 2 sys , and/or acidity. Additionally, both copper and gold were observed to partition into intermediate solid solution and bornite much more strongly than into vapor, brine or silicate melt. This suggests that, although vapor and brine are both efficient at removing copper and gold from a silicate melt, the presence of Cu–Fe sulfides can sequester a substantial portion of the copper and gold contained within a silicate melt if the Cu–Fe sulfides are abundant.

A study of partial replacement of fish meal with sunflower meal on growth, amino acid retention, and body composition of sharpsnout seabream, &lt;I&gt;Diplodus puntazzo&lt;/I&gt; (Actinopterygii: Perciformes: Sparidae)

Background. Our previous study demonstrated that sharpsnout seabream, Diplodus puntazzo (Walbaum, 1792),can be fed with up to 34.8% sunflower meal (SFM), with excellent results in growth parameters and feed efficiency.&nbsp; The aim of the current study was to test the replacement of fish meal with SFM in the diet formulation for sharpsnout seabreamand to evaluate growth, nutritive parameters, amino acid retention, and body composition of the fish during the fattening period. Materials and methods. Sixteen baskets (300 L capacity), each with thirteen fish, were distributed in a recirculated saltwater system to allow four experimental diets containing 40% crude protein (CP) and 20% crude lipid (CL) with 0%, 11.7%, 23.5%, and 34.8% SFM partially replacing fish meal to be used in quadruplicate for this experiment.&nbsp; The fish were fed these diets ad libitum during the experiment, which lasted for 162 days.&nbsp; Growth, nutrition efficiency, biometrics, carcass composition, amino acid composition, and amino acid retention of the experimental fish were evaluated. Results. There were no statistical differences in the growth parameters among the treatments.&nbsp; However, fish fed a diet containing 34.8% SFM had the lowest feed intake (FI), lowest feed conversion ratio (FCR), and the highest protein efficiency ratio (PER).&nbsp; There were also no statistical differences in the biometric parameters although fish fed the diet containing 10% SFM had the lowest CP levels.&nbsp; Leucine was the only difference in the essential amino acid (EEA) profile with fish fed a diet containing 11.7% SFM having the lowest levels of leucine.&nbsp; Although there were fluctuations among the amino acid retentions, they were not statistically significant. Conclusion. SFM (up to 34.8%) can be included in the diets of sharpsnout seabream, thereby, replacing 27% of the fish meal without altering the fish growth.&nbsp

Solute and Heat Transport Model of the Henry and Hilleke Laboratory Experiment

SEAWAT is a coupled version of MODFLOW and MT3DMS designed to simulate variable-density ground water flow and solute transport. The most recent version of SEAWAT, called SEAWAT Version 4, includes new capabilities to represent simultaneous multispecies solute and heat transport. To test the new features in SEAWAT, the laboratory experiment of Henry and Hilleke (1972) was simulated. Henry and Hilleke used warm fresh water to recharge a large sand-filled glass tank. A cold salt water boundary was represented on one side. Adjustable heating pads were used to heat the bottom and left sides of the tank. In the laboratory experiment, Henry and Hilleke observed both salt water and fresh water flow systems separated by a narrow transition zone. After minor tuning of several input parameters with a parameter estimation program, results from the SEAWAT simulation show good agreement with the experiment. SEAWAT results suggest that heat loss to the room was more than expected by Henry and Hilleke, and that multiple thermal convection cells are the likely cause of the widened transition zone near the hot end of the tank. Other computer programs with similar capabilities may benefit from benchmark testing with the Henry and Hilleke laboratory experiment.

Non-equilibrium State Salt-forming Phase Diagram: Utilization of Bittern Resource in High Efficiency

Salt-forming regions for a complex salt-water system in non-equilibrium state of evaporation process are usually different from those in solubility diagrams. To understand the solid-forming region of NaCl and improve the utilization of bittern resources, experiments were carried out to evaporate 20 representative mixture solution samples of Na +, Mg 2+//Cl −, -H 2O system with an average evaporation intensity of (1.4±0.4) g·L −1·min −1 (water) at boiling temperature 348 K, and determine the NaCl solid-forming regions in non-equilibrium state. Because of the complexity of salt-forming region, a maximal region and a minimal region were proposed to express the non-equilibrium state salt-forming region with different crystal seed, and a conditional salt-forming region was proposed to present the characteristic region of non-equilibrium salt-forming phase diagram. The areas of the maximal and minimal regions are 2.00 and 1.56 times those in solubility diagram, so it is possible to utilize bittern resources in high efficiency. The recovery rates of NaCl were 99.65%, 93.14%, 88.57%, 72.76%, and 83.68% for six typical bittern sources from Tulantai Salt Lake (China), Dongtai Salt Lake (China), Jilantai Salt Lake (China), Qarun Salt Lake (Egypt) and seawater, respectively. It is testified that the non-equilibrium state salt-forming phase diagram can be used in industrial processes.

Effect of Ammonia and Sulphide Environment on 90/10 and 70/30 Cupronickel Alloy

Copper nickel alloys 90/10 and 70/30 are used extensively in saltwater systems operating on marine platforms and offer high corrosion and biofouling resistance. However, systems using these materials were reported to fail prematurely. Preliminary investigations revealed pollution of harbor waters with tangible levels of ammonia and sulphides which was reported to be the primary cause of failure. The present author(s) have performed laboratory and field investigations to identify the stress-material-environment interaction of the copper nickel alloys extensively in use on seawater system of marine platforms. Results obtained point to the fact that polluted seawaters can affect the material properties of the alloy leading to premature failure(s) of systems at stresses well below the designed stress. The paper presents the correlation of the results of the laboratory and field tests of 90/10 and 70/30 copper–nickel alloys in seawaters polluted with ammonia and sulphide pollutants.

Tidal exchange between a freshwater tidal marsh and an impacted estuary: the Scheldt estuary, Belgium

Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary.

Phase Separation of Phosphatidylcholine–Water Systems below the Main Transition Temperature Induced by Monovalent Ions

Abstract Effects of 1:1 electrolytes (LiCl, NaCl, NaBr, KCl, RbCl, and NH4Cl) on the stacked multilamellar structure of phosphatidylcholine–water systems below the acyl-chain melting temperature were examined by means of small-angle X-ray scattering and differential scanning calorimetry. For the ternary DPPC–salt–water system at 20 °C, the lamellar repeating distance, D, jumped from 64 to 72 Å at certain thresholds of electrolyte concentration; 4.0, 2.1, and 1.4 mol kg−1 when LiCl, NaCl, or KCl were added, respectively. The temperature-dependent D jump from 72 to 64 Å at 20 °C was also confirmed for DPPC in 2.1 mol kg−1 NaCl accompanying the small latent heat of ca. 0.033 J g−1. For the DMPC–NaCl–water system at 5 °C, the salt-induced D jump, at a threshold NaCl concentration of 1.2 mol kg−1, was also observed. A triangular phase diagram of DPPC–NaCl–water at 20 °C was constructed based on X-ray scattering data. It was confirmed that the DPPC–NaCl–water system had a three-phase coexisting region, i.e., two lamellar phases with different repeating distances of 64 or 72 Å, respectively, and the NaCl bulk solution. Some qualitative aspects are discussed concerning the interpretation of the phase separation into the two different lamellar phases based on the lipid–monovalent ion interactions.

In situ measurements of the solubilities of salt–water systems by a fiber sensor

A novel fiber sensor for measuring solid solubilities of salt-water systems in situ is described. The sensor consists of a diode laser as light source, three couplers, two sensing fiber ends with protective cladding, and two photodetectors. The measurement principle is based on relative Fresnel reflective intensity. This method enabled us to observe in situ transitional process of the equilibration of a solid-liquid system with a small quantity of specimens. By the relatively simple technique, fast determination of the solid solubility is possible. We applied this method to measure a temperature dependence of the solubility of potassium chloride in water in situ and compared with the previous data obtained by other techniques. The measured result has the long-term standard deviation of the concentration of 0.1%, and agrees with the data obtained by the classical method within the error of +/-1%. This method is precise and sample saving and is suitable to measure the solubilities of rare and expensive materials.

Speciation of Zinc Mixed Ligand Complexes in Salt Water Systems

Amalgam voltammetric method has been used to study heavy metal interaction in model lake water in KNO3 at 23¼C at concentration levels of genuine lake water of total ionic strength 1.44 M. Hanging drop amalgam electrode was prepared in situ before exchanging the medium containing Zn2+ ions for the sample solution with ligands of known concentrations. Half-wave potentials at the actual metal ion concentration in the lake and at a much lower one (10-2 times) were experimentally determined. Shifts in half-wave potentials are used to compute metal complex formation constants. The study reveals the existence of various species and a prediction is made of the distribution of the major labile complex species of Zn2+ present in the lake water. The concentration level of Zn2+ ions in the lake seems to play a role in determining the number of complexes formed and their stabilities. The results show that hydroxo/chloro and hydroxo/fluoro mixed ligand complexes have free Zn2+ ions as predominant species at the natural pH of the lake water and these systems are, therefore, potentially polluting. However, the contribution of OH- ions to the speciation of Zn is of no consequential effect because in its normal state, the [OH-] of the lake water is quite low and the aquatic life is, therefore, not threatened. The CO3 2- ions are the major contributors to the speciation of zinc in the lake water because the natural [CO3 2-] of 0.5 M is high. The normal lake water is thus, dominated by the carbonato complexes [ZnCO3Cl4]4-, [ZnCO3Cl2]2-, [ZnCO3Cl]- and to a less extent, ZnCO3. Keywords : Heavy metals, hanging drop electrode, amalgam voltammetry, speciation. Discovery and Innovation Vol. 19 (3) 2007: pp. 188-194

In situ X-ray absorption spectroscopy measurement of vapour-brine fractionation of antimony at hydrothermal conditions

AbstractDespite the growing geological evidence that fluid boiling and vapour-liquid separation affect the distribution of metals in magmatic-hydrothermal systems significantly, there are few experimental data on the chemical status and partitioning of metals in the vapour and liquid phases. Here we report on an in situ measurement, using X-ray absorption fine structure (XAFS) spectroscopy, of antimony speciation and partitioning in the system Sb2O3-H2O-NaCl-HCl at 400°C and pressures 270—300 bar corresponding to the vapour-liquid equilibrium. Experiments were performed using a spectroscopic cell which allows simultaneous determination of the total concentration and atomic environment of the absorbing element (Sb) in each phase. Results show that quantitative vapour-brine separation of a supercritical aqueous salt fluid can be achieved by a controlled decompression and monitoring the X-ray absorbance of the fluid phase. Antimony concentrations in equilibrium with Sb2O3 (cubic, senarmontite) in the coexisting vapour and liquid phases and corresponding SbIII vapour-liquid partitioning coefficients are in agreement with recent data obtained using batch-reactor solubility techniques. The XAFS spectra analysis shows that hydroxy-chloride complexes, probably Sb(OH)2Cl0, are dominant both in the vapour and liquid phase in a salt-water system at acidic conditions. This first in situ XAFS study of element fractionation between coexisting volatile and dense phases opens new possibilities for systematic investigations of vapour-brine and fluid-melt immiscibility phenomena, avoiding many experimental artifacts common in less direct techniques.

Global survey of diversity among environmental saltwater Bacteriovoracaceae

Halophilic Bacteriovorax (Bx), formerly known as the marine Bdellovibrio, are Gram-negative, predatory bacteria found in saltwater systems. To assess their genetic diversity and geographical occurrence, the small subunit rRNA (ssu-rRNA) gene sequences were analysed from 111 marine, salt lake and estuarine isolates recovered from 27 locations around the world. Phylogenetic analysis of these isolates using Geobacter as the outgroup revealed eight distinct ribotype clusters each with at least two isolates. Each cluster was composed of isolates with >or= 96.5% similarity in ssu-rRNA sequences. Three single isolate outliers were observed. Many of the Bx ribotypes were widely dispersed among different types of ecosystems (e.g. cluster III was recovered from the Great Salt Lake, the Atlantic Ocean, Pacific Ocean, Chesapeake Bay and gills of aquarium fish). However, cluster V was only recovered from a single ecosystem, estuaries. Cluster V was originally detected in the Chesapeake Bay and subsequently in the Pamlico Sound/Neuse River system. Principal coordinate analysis revealed that the sequences of the isolates from different environments were distinct from each other. The results of this study reveal the saltwater Bx to be phylogenetically and environmentally more diverse than was previously known.

Removal of phenanthrene from saltwater solutions using activated carbon

Activated carbon (AC) is used for the removal of organic compounds from freshwater and saltwater systems. The effect of salinity on the sorption of organic compounds by sorbents with pores such as AC is not yet well understood. Phenanthrene sorption equilibrium and kinetic experiments are performed in the present work. An EPA granular AC bed model is employed to demonstrate the effect the salinity has on the breakthrough curves at different phenanthrene initial concentrations. At high relative to the solubility phenanthrene concentrations (200–50 μg/L), sorption is higher in the saltwater than in the freshwater solutions. At low relative to the solubility phenanthrene concentrations (3 μg/L), sorption is lower in the saltwater than in the freshwater solutions. Activated carbon is less efficient in removing phenanthrene from saltwater than from freshwater solutions when phenanthrene is present at low relative concentrations (<10 μg/L).

Paleo-fluid composition determined from individual fluid inclusions by Raman and LIBS: Application to mid-proterozoic evaporitic Na–Ca brines (Alligator Rivers Uranium Field, northern territories Australia)

Detailed determination of the composition of individual fluid inclusions in the H 2O–NaCl–Ca(Mg)–Cl 2 system from microthermometry data may be difficult because (i) the melting of salt hydrates is often unclear, (ii) salts or salt hydrates are often metastable, and iii) eutectic temperatures are often difficult to relate precisely to a unique salt–water system. These problems can be circumvented by using a Raman microprobe to identify the salt hydrates and to measure the chlorinity, by using Laser Induced Breakdown Spectroscopy (LIBS) to determine cation ratios, and by cross-checking the data from these independent techniques at each step in the determination of the fluid inclusion composition. Data from individual inclusion analysis are then completed by crush–leach technique data on bulk samples. This methodology was applied to a case study, the mineralized faults and associated breccia located in the Alligator Rivers Uranium Field (middle Proterozoic Kombolgie Subgroup, Northern Territory, Australia). Faults are cemented by euhedral quartz containing a variety of fluid inclusions with a wide range of ice-melting temperatures, from near 0 °C down to about − 50 °C. The approach has permitted the identification of three types of fluids: an Na-rich brine with variable Mg concentrations, a Ca-rich brine with low Mg concentrations, and a lower salinity fluid. The Ca and Na-brines mixed with each other and a less saline end-member. On the basis of Cl/Br and cation ratios, the Na-brine is interpreted as a primary brine, resulting from the evaporation of seawater. It is inferred that the Na-brine evolved chemically during its interaction with the Ca-rich lithologies from Proterozoic basement, forming subsequently a Ca-brine through Na–Ca exchange reactions. Thus, the fault system, which affects both the base of the Kombolgie sandstone and its basement, represents active drainage zones where different fluid reservoirs were connected, and thus a place where fluid mixing was highly favored.

Primer on Invasive Species in Coastal and Marine Waters

Now available online! SGEB-60, a 28-page full-color circular by Charles Jacoby, Linda Walters, Shirley Baker, and Karen Blyler, provides important background information on invasive species, especially invasive species in saltwater systems. Includes bibliography, glossary, a list of international laws and conventions related to invasive species, a directory of experts, and additional sources of information. Published by Florida Sea Grant, University of Florida IFAS Extension, July 2004.

A high temperature equation of state for the H 2O-CaCl 2 and H 2O-MgCl 2 systems

An equation of state (EOS) is developed for salt-water systems in the high temperature range. As an example of the applications, this EOS is parameterized for the calculation of density, immiscibility, and the compositions of coexisting phases in the CaCl 2-H 2O and MgCl 2-H 2O systems from 523 to 973 K and from saturation pressure to 1500 bar. All available volumetric and phase equilibrium measurements of these binaries are well represented by this equation. This EOS is based on a Helmholtz free energy representation constructed from a reference system containing hard-sphere and polar contributions plus an empirical correction. For the temperature and pressure range in this study, the electrolyte solutes are assumed to be associated. The water molecules are modeled as hard spheres with point dipoles and the solute molecules, MgCl 2 and CaCl 2, as hard spheres with point quadrupoles. The free energy of the reference system is calculated from an analytical representation of the Helmholtz free energy of the hard-sphere contributions and perturbative estimates of the electrostatic contributions. The empirical correction used to account for deviations of the reference system predictions from measured data is based on a virial expansion. The formalism allows generalization to aqueous systems containing insoluble gases (CO 2, CH 4), alkali chlorides (NaCl, KCl), and alkaline earth chlorides (CaCl 2, MgCl 2). The program of this model is available as an electronic annex (see EA1 and EA2) and can also be downloaded at: http://www.geochem-model.org/programs.htm.

Impact of rapid impulse operating disturbances on ammonia removal by trickling and submerged-upflow biofilters for intensive recirculating aquaculture

Biofilters are regularly used in aquaculture production systems to remove ammonia and nitrite and are the only economically feasible ammonia removal devices in saltwater systems. Six identical 5.23L biofilters, three trickling and three submerged-upflow filters, were operated at predetermined water quality conditions (pH 7.5, temperature 25°C, salinity 5ppt, TAN 1mg/L), and then perturbed to simulate a number of possible operating disturbances, e.g. increased fish load, flushing of culture tanks, closing off of valves. Each disturbance was a controlled impulse change in ammonia concentration, temperature, pH or salinity. The maximum water quality ranges were pH 6–9, TAN 0.5–4.0mg/L, temperature 15–35°C, and salinity 0–10ppt. After each disturbance, the water quality was immediately returned to the predetermined (baseline) values. The ammonia removal across the filters was monitored during the disturbance and the recovery period for loss and subsequent restoration of biofilter removal efficiency. Baseline nitrification rates resumed within 1–2h after cessation of the shock. Some impulse shocks were temporarily detrimental to both filter types—especially low pH (−29% efficiency), low salinity (−13% to −18% efficiency), and low temperature (−11% to −13% efficiency). Raising the temperature (+9% to +12% efficiency) and TAN concentration (+0.30 to +0.36mg/L of filter additional TAN removal) appears to be beneficial to the biofilter.

Impact of positive ramp short-term operating disturbances on ammonia removal by trickling and submerged-upflow biofilters for intensive recirculating aquaculture

Biofilters are regularly used in freshwater aquaculture production systems to remove ammonia and nitrite and are the only economically feasible ammonia removal devices in saltwater systems. Six identical 5.23l biofilters, i.e., three trickling and three submerged-upflow filters, were operated at predetermined baseline water quality conditions (pH 7.5, temperature 25°C, salinity 5ppt, TAN 1mg/L), and then perturbed to simulate a number of possible operating disturbances, e.g. increased fish load, flushing of culture tanks, closing off of valves. Each disturbance was a controlled positive ramp short-term change in ammonia concentration (with other water quality parameters held constant) or temperature or pH or salinity. Ammonia removal across the biofilters was monitored during the disturbance and recovery period for loss and subsequent restoration of ammonia removal efficiency. Baseline water quality to the filters was resumed at the end of each disturbance and baseline ammonia removal occurred within 1 to 2h after end of disturbance. Ranges of variation in water quality were pH 7.5–9, TAN 1.0–4.0mg/L, temperature 25–35°C, and salinity 5–35ppt. Salinity increases over a 5–10h period reduced biofilter removal efficiency (−12 to −30% TAN removal); temperature increases, over a 1.6–10h period, offered about a 5% increase in TAN removal while gradual TAN increases, over a 3–12h period, although providing an approximately extra 1mg/L of removal did not significantly change removal efficiency; and gradual pH increases, over a 3–7.5h period, did not change biofilter removal efficiency significantly.

A new water column profiler for shallow aquatic systems

Coupled physical and biogeochemical processes in shallow (<2 m deep) productive systems must be observed on fine temporal and spatial scales with automated sampling and monitoring devices. We developed a pump profiler system that can sample six to eight depths at 10-cm resolution every 30 min. The system is economical, secure from vandalism, portable, and capable of integration with a real-time remote monitoring system. Solenoid valves select the suction depth, and a diaphragm pump delivers water to a flow cell where temperature, oxygen, pH, specific conductivity, turbidity, oxidation reduction potential, and fluorescence are measured with probes mounted on a water quality sonde. A microcontroller is used to direct the operation of the system. Water column disturbance and maintenance requirements are minimized by eliminating exposed moving parts. The data can be retrieved remotely and graphically displayed on the Internet in real time. The system has been deployed successfully in two freshwater ponds and a tidal saltwater system. The pump profiler is used to study coupled physical biogeochemical processes in shallow systems with strong diel cycles and large density and chemical gradients. Applications may include studies in aquaculture ponds, storm water retention ponds, shallow lakes, and small estuaries.

A computational fluids dynamics study of buoyancy effects in reverse osmosis

In order to advance the understanding of membrane transfer processes and their optimisation, models are required that can address all of the important physical processes occurring in membrane systems. This paper describes an extension of our previously validated computational fluid dynamics (CFD) model of a pressure-driven system to include a mechanistic model for permeate flux and buoyancy effects. As an example application, the effect of buoyancy in reverse osmosis of salt–water separation in a flat sheet system is examined. We show that for the salt–water system, buoyancy effects are important only for low flow rates that allow a significant increase in the salt concentration at the membrane surface and when the flow direction is aligned with the direction of gravity (i.e. in a vertical channel). No buoyancy effects are predicted for this system when the flow is oriented normal to the direction of gravity (i.e. for a horizontal channel).