Increasing Solution Salinity Research Articles

Microbially-induced calcium carbonate precipitation by a halophilic ureolytic bacterium and its potential for remediation of heavy metal-contaminated saline environments

Heavy metal contamination is widespread in the environment and has resulted in numerous adverse consequences for the ecosystem. Ureolytic microorganisms are known to immobilize heavy metals by co-precipitation with calcium carbonates, which are formed during microbial hydrolysis of urea. In this work, we described a novel halophilic ureolytic bacterium (Exiguobacterium sp. JBHLT-3) and examined the relationship between ureolytic-driven mineralization of CaCO3 and heavy metal mitigation. The growth of strain JBHLT-3 occurred at salinities between 3 and 12% with an optimum at 6%. This strain was capable of precipitating calcite and vaterite under non-growth conditions. Lead (Pb) was selected as a model heavy metal for this study and amended into the bio-precipitation systems at a starting concentration of 1 mM. The strain JBHLT-3 efficiently removed Pb from saline solutions via incorporation within microbially-induced calcium carbonates. Mineralogical analysis showed that calcite had higher uptake of Pb2+ than vaterite. The increasing solution salinity progressively increased the vaterite fraction in the bio-precipitates but reduced the removal efficiency of Pb2+. Nevertheless, the removal efficiency could be still as high as 89% in the cultures incubated in a 12% salinity medium. Our results highlight the positive role of halophilic ureolytic microbes in remediating heavy metal-contaminated saline environments.

Effect of salinity on adsorption and interaction forces of hydrophobically modified polyacrylamide on silica and alumina surfaces

In this work, the adsorption behaviors and interaction forces of different polymers on silica and alumina surfaces have been investigated under the effect of KCl concentration using quartz crystal micro-balance with dissipation (QCM-D) monitoring technique, viscosity measurement and atomic force microscopy (AFM) colloidal probe technique. Polyacrylamide (PAM) and hydrophobically modified polyacrylamide (HMPAM) with hydrophobic monomer (i.e., hexadecyl dimethyl allyl ammonium chloride (C16DMAAC)) have been investigated as model polymers. It is found that the adsorption amounts of HMPAM and PAM polymers on negatively charged silica and positively charged alumina surfaces increase with increasing solution salinity (1–100 mM KCl). HMPAM displays higher adsorption capacity than PAM on both silica and alumina surfaces, which is attributed to the hydrophobic interaction originated from the long hydrocarbon chains of HMPAM. Furthermore, the measured adhesion between the polymers and the substrate surfaces is found to decrease for the alumina cases and increase for the silica cases with increasing the salinity, which is due to the weakened electrostatic interactions between the polymers and substrate surfaces under high salinity (i.e., 100 mM KCl). The viscosities of PAM and HMPAM solutions are found to decrease with increasing solution salinity, which could be caused by the much more coiled conformation of PAM and HMPAM chains at higher salinity. Both the interactions between the polymer and substrate surface and the polymer conformational changes play important roles in the polymer adsorption behaviors on silica and alumina surfaces.

Effects of the electrical conductivity of a soilless culture system on gamma linolenic acid levels in borage seed oil.

Borage is a well-known plant of great importance in human nutrition and health. Expanding knowledge of particular plants that have anti-cancer products is a global concern. There is substantial information regarding the benefits, presence and extraction of gamma linolenic acid (GLA; 18:3n6) in different plants around the world, especially in borage seeds. However, there is little information concerning the effects of the salinity of the nutrient solution on the growth and presence of GLA in borage seeds. The objective of this work was to determine the optimal salinity of the nutrient solution for obtaining GLA in soilless cultivation systems. Borage plants were grown in coconut fibre and provided three treatments of nutrient solution of 2.20, 3.35 and 4.50 dS m-1, increasing solution salinity with the standard nutrient solution of concentrated macronutrients as a reference. Vegetative growth, seed production and GLA ratio were measured. The results of vegetative development and GLA production doubled and tripled with the increase in salinity of the nutrient solution, respectively.

Efficiency of ionic liquids for chemical enhanced oil recovery

Substantial amount of crude oil remains in the reservoir after primary and secondary production. Chemical flooding is one of the enhanced oil recovery (EOR) methods; however, chemicals (i.e., Surfactant) used are sensitive to the harsh environment characterizing the local reservoirs. The current study aimed at investigating the utilization of ionic liquids (ILs), known as environment friendly salt with good solubility, thermal stability and effective surface activity, as an alternative to conventional organic surfactants in enhanced oil recovery process. In this work, screening tests of nine ILs were performed. These ILs were diluted in different brine solutions of different salt compositions at 10 % (w/w) salinity and their solubility, thermal stability and surface activity in presence of Saudi medium crude oil were tested. Tetra alkyl ammonium sulfate known as Ammoeng 102 was found to be the ionic liquid of choice. Further investigations on Ammoeng 102 solutions at 10 and 20 % (w/w) salinity were conducted and IFT measurements indicate enhanced surface activity of Ammoeng 102 with increasing solution salinity. Effects of pressure and temperature on interfacial tension (IFT) were also tested and the results indicate minor effects. Adsorption test indicates high Ammoeng 102 adsorption tendency with more adsorption for higher salinity solution. Different flooding scenarios were conducted in sandstone rock samples to investigate the effectiveness of Ammoeng 102 IL as an EOR chemical. The findings indicate promising results for ionic solution flooding in secondary mode at irreducible water saturation (S wirr). Ultimate recovery obtained is higher than that obtained with combined secondary brine flooding followed by tertiary ionic solution flooding at residual oil saturation (S or). Injection of slug of ionic solution in secondary mode provides lower recovery compared to that recovered with continuous ionic solution injection in the same mode. Rock water content affects recovery efficiency indicating higher oil recovery for secondary brine and tertiary ionic solution flooding at low S wirr. Contact angle and relative permeability measurements demonstrate the role of wettability alteration behind the extra oil recovery which is very much affected by ionic liquid concentration that can be altered by dilution with formation and injected brines.

Release of Cryptosporidium and Giardia from dairy calf manure: impact of solution salinity.

Studies were initiated to determine the release behavior of Cryptosporidium oocysts and Giardia cysts from dairy calf manure to waters of various salinities. Experiments were conducted by sprinkling a particular aqueous solution over a manure disk and collecting the runoff water. Effluent concentrations of manure and (oo)cysts were initially several orders of magnitude below their starting concentration in the manure, after continued application of water the concentrations gradually decreased, and then exhibited persistent concentration tailing. Solution salinity significantly affected the shape and magnitude of the manure and (oo)cyst concentration curves. Increases in solution salinity tended to decrease the manure and (oo)cyst concentrations at a particular time. This was attributed to a stabilization of manure by compression of the double layer thickness between negatively charged components of the manure phase. Calculated release efficiencies of the (oo)cysts (relative to manure release) also decreased with increasing solution salinity. Experimental observations indicate that onlythe surface layer of manure was depleted of finer manure materials and (oo)cysts and that the manure will act as a long-term source of contamination. A conceptual model to describe and predict manure and (oo)cyst release rates and cumulative loading for the various solution salinities was proposed and applied to the experimental data. The calibrated model yielded a reasonable description of the experimental results.