Synthetic Salt Water Research Articles

Nutrients in overlying water affect the environmental behavior of heavy metals in coastal sediments

Excessive nutrients in aquatic ecosystems are the main driving factors for eutrophication and water quality deterioration. However, the influence of nutrients in overlying water on sediment heavy metals is not well understood. In this study, the effects of nitrate nitrogen (NO3–N) addition and phosphate addition in the overlying water on the environmental behaviors of chromium (Cr), copper (Cu), and cadmium (Cd) in coastal river sediments were investigated. Fresh estuary sediments and synthetic saltwater were used in microcosm studies conducted for 13 d. To determine the biological effect, unsterilized and sterilized treatments were considered. The results showed that the diffusion of Cr and Cu was inhibited in the unsterilized treatments with increased NO3–N. However, under the NO3–N sterilized treatments, Cr and Cu concentrations in the overlying water increased. This was mostly related to changes in the microbial regulation of dissolved organic carbon and pH in the unsterilized treatments. Further, in the unsterilized treatments, NO3–N addition considerably increased the concentrations of the acid-soluble (Cr, Cu, and Cd increased by 5%–8%, 29%–41%, and 31%–42%, respectively) and oxidizable (Cr, Cu, and Cd increased by 10%, 5%, and 14%, respectively) fractions. Additionally, compared with that in the unsterilized treatments, Cu and Cd concentrations in P-3 treatments decreased by 7% and 63%, respectively. By producing stable metal ions, microorganisms reduced the amount of unstable heavy metals in the sediment and heavy metal concentration in the overlying water, by considerably enhancing the binding ability of phosphate and heavy metal ions. This study provides a theoretical basis for investigating the coupling mechanisms between heavy metals and nutrients.

Calorimetry based temperature and specific enthalpy measurements associated with ice-water phase change in saline systems for freeze desalination

Ice based Freeze Desalination (FD) offers a potential alternative to recover fresh water from seawater. However, ice-water phase change data in saline water in the range of practical interest and of importance in FD process design is limited. In this study, reliable and accurate measurements related to ice–water phase change temperatures and specific enthalpies have been carried out using a Micro–Differential Scanning Calorimeter (μ–DSC). The runs were carried out using pure water, synthetic salt water (0.5 to 5 wt% NaCl) and seawater. The NaCl concentrations covered a range of values of practical interest in FD. In the case of pure water, the specific enthalpy value was found to be in excellent agreement to within ± 0.51% of the value reported in literature, i.e. 333 J/g which validated the experimental protocols adopted in this study. Phase change temperature and specific enthalpy values for salt water were found to decrease with an increase in salt concentration. Test runs conducted subsequently using seawater were consistent with the results obtained from the synthetic salt water test runs. The experimental protocol adopted and data presented in this study can be used in design of an ice based FD process.

Process intensification using a novel continuous U-shaped crystallizer for freeze desalination

Ice based Freeze Desalination (FD) offers a potential alternative to recover fresh water from seawater. There has been increased interest over the years in the development of continuous crystallizer configurations to address the combined challenge of ice yield and salinity reduction in FD. In this work, experimental studies have been conducted to establish the potential of a novel continuously operated U-shaped crystallizer for ice based Freeze Desalination (FD). Unlike conventional FD crystallizers researched till date, this crystallizer integrates pre-cooling, chilling and freezing of saline water in a single unit along with in-situ ice removal. Preliminary experiments were carried out using synthetic salt water to investigate the effect of salt water flow rate and coolant temperature on product water yield and salinity. Salinity was found to increase with water yield. The overall phase change heat transfer coefficient has also been estimated. Subsequently test runs were carried out using seawater samples under prescribed operating conditions identified from the synthetic salt water runs. Salinity reduction was observed to increase with an increase in number of washing steps and wash water requirement. The results obtained provide a strong case to promote the use of the U-shaped crystallizer for ice based FD.

Investigation of the fouling effect on a commercial semi-permeable membrane in the pressure retarded osmosis (PRO) process

Abstract One of the main challenges for generating osmotic power by using PRO technology is the membrane fouling which reduces the permeate flux and consequently increases the cost and decreases the osmotic power generation. In this research, different feed waters with various qualities were used to investigate the effect of fouling on a commercial membrane in PRO mode in continuous conditions. Also, the fouling mechanisms were investigated in order to study the cleaning of the membrane in PRO mode in the future research. In addition, four classic fouling models such as complete blocking model (CBM), intermediate blocking model (IBM), standard blocking model (SBM) and cake filtration model (CFM) were used. Cake enhanced osmotic pressure as a new mechanism for osmotically driven membranes was studied as well. According to the results, the fouling rate when the draw solution was synthetic salt water followed the order of: untreated river water > multimedia sand filter > microfiltration > ultrafiltration effluents. The fouling rate in ultrafiltration and microfiltration effluents using sea water occurred faster compared to the results for untreated synthetic salt water. Complete fouling (permeate flux was negligible) occurred after 580 h using feed water from ultrafiltration unit. It was observed that cake filtration and cake enhanced osmotic pressure were the main fouling mechanisms that governed the membrane fouling. These models could describe the membrane fouling in PRO processes.

Identification of the type of foulants and investigation of the membrane cleaning methods for PRO processes in osmotic power application

Pressure retarded osmosis (PRO) is a membrane based technology used for generation of osmotic power as a sustainable energy. The main challenge of PRO technology is the membrane fouling which reduces the permeate flux and osmotic power generation which consequently increases the cost. In this research, different quality feed waters were used to identify the main foulants on the surface of a commercial semi permeable membrane in the PRO process. In addition, two cleaning methods were investigated to determine the desirable cleaning methods. According to the results, the main inorganic foulants using synthetic salt water were iron, aluminum, calcium, sodium, and silica and when sea water was used as the draw solution, the same foulants, in addition to magnesium and potassium were detected. The organic foulants were humic substances, polysaccharides and proteins for both synthetic salt and sea water draw solutions. According to the results, the water flux recoveries were 98.4%, 98%, 97.5%, 97.3%, and 97.2% after each sequential chemical cleaning, respectively. Therefore, the most successful cleaning method was with acidic and basic cleaners. This research indicates that chemical cleaning can decrease the membrane fouling in PRO processes and consequently improve the osmotic power generation.

Removal of Pollutants from Water by Using Single-Walled Carbon Nanotubes (SWCNTs) and Multi-walled Carbon Nanotubes (MWCNTs)

Water crisis is one of the supreme challenges worldwide as clean water is the ultimate need for human civilization and all other life on earth. In the present study, continuous adsorption experiments were carried out in an adsorption column to survey the efficiency of the carbon nanotubes (CNTs) for removal of pollutants from water/wastewater in terms of physicochemical parameters, such as electrical conductivity, total dissolved solids (TDS), pH, chemical oxygen demand (COD) and total organic carbon (TOC), by using both single-walled carbon nanotubes and multi-walled carbon nanotubes. Sample solutions were allowed to flow in down-flow mode through the fixed-bed of CNTs. The CNTs column showed a reduction efficiency of electrical conductivity 80 % from effluent treatment plant (ETP) treated water sample, 69.23 % from raw effluent sample, and 53.33 % from the synthetic salt water sample. Similarly, the efficiency of TDS reduction was 78.61 % from raw effluent sample, 66.86 % from ETP treated water sample, and 62.02 % from the synthetic salt water sample. COD also reduced 84.71 % from raw effluent sample and 39.58 % from the ETP treated water sample. In case of TOC, the column showed a reduction efficiency of 85.88 % from the ETP treated water sample and 70.79 % from the raw effluent sample. These findings suggested that CNTs present a great potential in removal of pollutants in terms of physicochemical parameters from water/wastewater.

Synthetic salt water desalination by electrodialysis using reinforced ion exchange membranes for acid–base production

The demand for clean water is vast, whether it is used for human consumption, agricultural activities or industrial applications. To find a solution for this important issue, a small attempt has been made in the present work towards developing reinforced monopolar and bipolar membranes based on functionalized polysulfone and evaluated for electrodialysis of salt water. Polyvinyl pyrrollidone was used as the intermediate layer for the preparation of the bipolar membrane. The concentration of salt water taken for the bipolar membrane electrodialysis (BPMED) process ranged from 5 to 25 g/L. A commercially procured monopolar and bipolar membranes made of polystyrene divinyl benzene was also evaluated for the purpose of comparison. The BPMED performance reached a highest current efficiency of 75.8 and 53.6 % with the energy consumption of 0.36 and 1.39 Wh for the synthesized and commercial membranes respectively. Also the performance of the fabricated unit was assessed in terms of electrical conductivity, salinity and ion (sodium and chloride) concentrations in the feed solution after 8 h duration. The reproducibility performance of the membranes was also analyzed for various concentrations of the synthetic salt solution.

Analysis of impact of temperature and saltwater on Nannochloropsis salina bio-oil production by ultra high resolution APCI FT-ICR MS

Concentrated Nannochloropsis salina paste was reconstituted in distilled water and synthetic saltwater and processed at 250°C and 300°C via hydrothermal liquefaction. The resulting bio-oils yielded a diverse distribution of product classes, as analyzed by ultra high resolution APCI FT-ICR MS. The organic fractions were analyzed and both higher temperatures and distilled water significantly increase the number of total compounds present and the number of product classes. Major bio-oil products consisted of N1O1, hydrocarbon, and O2 classes, while O1, O4, S1, N1O2, and N2O2 classes represented the more significant minor classes. Both chlorine and sulfur containing compounds were detected in both distilled and saltwater reactions, while fewer numbers of chlorine and sulfur containing products were present in the organic fraction of the saltwater reactions. Further refinement to remove the chlorine and sulfur contents appears necessary with marine microalgal bio-oils produced via hydrothermal liquefaction. The higher heating value (MJ/kg) as calculated by the Boie equation of classes of interest in the bio-oil reveals a significant potential of algal hydrothermal liquefaction products as a sustainable and renewable fuel feedstock.

Evaluation of synthetic salt water desalination by using a functionalized polysulfone based bipolar membrane electrodialysis cell

The work reported herein describes the study of desalination of synthetic salt water at laboratory scale in five different feed concentrations using a lab-made functionalized high molecular weight polysulfone (PSu) polymer based monopolar (cation exchange and anion exchange) and bipolar ion exchange membranes (with PVA as the intermediate layer) using bipolar membrane electrodialysis cell. Various parameters such as conductivity, solution pH, feed concentration, current efficiency, energy consumption, transport number, fluxes and water dissociation efficiency were determined. During the 8h treatment under optimal conditions (i.e. time, current, higher acid and base concentrations), for the various initial feed concentrations (from 10g/L to 50g/L), the current efficiencies obtained ranged from 27% to 75%. And for the highest feed concentration, the highest current efficiency (≈max. of about 75% for PSu and 63% for polystyrene divinylbenzene (PSDVB)) with lowest energy consumption (≈max. of about 1.2Wh/mol for PSu and 2.6Wh/mol for PSDVB) in addition to acid-base production (≈max. of about 0.018N acid: 0.016N base for PSu and 0.012N acid: 0.013N base for PSDVB) was observed. The results of the study demonstrated the promising potential of functionalized polysulfone based ion exchange membranes for greater water dissociation efficiency in desalination of water.

The effect of air bubbles on optical backscatter sensors

The sensitivity of an optical backscatter sensor (OBS) to bubbles is tested using a variety of bubble generating mechanisms that span the range of bubble sizes typically observed in surf zone studies. Over 1200 one-minute runs were performed in a stirred test tank by altering the bubbler type, water type, air-flow rate and sand or mud concentration. The laboratory data shows a strong dependence of OBS response to bubble size and concentration. For sand or mud sediments, the optical backscatter sensor voltage is increased by the presence of bubbles and smaller bubbles had a larger effect. The effect was more pronounced in salt water than fresh water. We conservatively report that OBS output voltage is increased due to the presence of bubbles by 25% for the trials undertaken here. In the cases performed in vigorously stirred salt and synthetic salt water, bubbles were smaller than those measured under quiescent water conditions due to bubble shattering at the bubbler orifices and by the pumps used for stirring. It was found in those cases that the bubble effect on OBS was larger than the 25% reported here, but the extension of this finding to a natural setting, such as in the direct vicinity of the breakpoint or a bore, is not known.

Oxides Formed on Titanium by Polishing, Etching, Anodizing, or Thermal Oxidizing

Abstract Photoelectrochemistry (PEC), glancing angle x-ray diffraction (GAXRD), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) in synthetic salt water were uti...

Predator avoidance in mummichog larvae from a polluted habitat

Previous work has shown that adult mummichogs (Fundulus heteroclitus) from a polluted site (Piles Creek, PC, New Jersey) were more vulnerable to predation by blue crabs than fish from a more pristine site (Tuckerton, TK, New Jersey). The present study was conducted to compare the spontaneous activity, swimming performance and predator avoidance of fish of the two populations at early life stages. When raised in synthetic salt water, both newly hatched and 1–month‐old mummichog larvae from TK had greater spontaneous activity, swimming performance, and stamina than those from PC. In comparison to TK, PC larvae were less vulnerable to predation by yearling mummichogs at 1 week old, but were more vulnerable at 1 month old. Variation in behaviour and swimming ability of TK and PC larvae accounted for the differences in vulnerability to predation. TK larvae employed greater swimming and irregular movement, which was more successful for survival of older larger larvae. In contrast, PC larvae hid, often remaining motionless, which was advantageous for survival of young smaller larvae. Contaminants had been assumed responsible for the behavioural differences in the PC population. However, since differences were seen in larvae raised in synthetic salt water, it is possible that maternally transferred neurotoxicants (possibly delayed effects) and/or inherent factors also play a role.