A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

The controversy related to the environment pollution is increasing in human life and in the eco-system. Especially, the water pollution is growing rapidly due to the wastewater discharge from the industries. The only way to find the new water resource is the reuse of treated wastewater. Several remediation technologies are available which provides a convenience to reuse the reclaimed wastewater. Heavy metals like Zn, Cu, Pb, Ni, Cd, Hg, etc. contributes various environmental problems based on their toxicity. These toxic metals are exposed to human and environment, the accumulation of ions takes place which causes serious health and environmental hazards. Hence, it is a major concern in the environment. Due to this concern, the significance of developing technology for removing heavy metals has been increased. This paper contributes the outline of new literature with two objectives. First, it provides the sketch about treatment technologies followed by their heavy metal capture capacity from industrial effluent. The treatment performance, their remediation capacity and probable environmental and health impacts were deliberated in this review article. Conclusively, this review paper furnishes the information about the important methods incorporated in lab scale studies which are required to identify the feasible and convenient wastewater treatment. Moreover, attempts have been made to confer the emphasis on sequestration of heavy metals from industrial effluent and establish the scientific background for reducing the discharge of heavy metals into the environment.

Efficient techniques for the removal of toxic heavy metals from aquatic environment: A review

Adsorption materials for volatile organic compounds (VOCs) and the key factors for VOCs adsorption process: A review

Eutrophication of water bodies is a serious and widespread environmental problem. Achieving low levels of phosphate concentration to prevent eutrophication is one of the important goals of the wastewater engineering and surface water management. Meeting the increasingly stringent standards is feasible in using a phosphate-selective sorption system. This critical review discusses the most fundamental aspects of selective phosphate removal processes and highlights gains from the latest developments of phosphate-selective sorbents. Selective sorption of phosphate over other competing anions can be achieved based on their differences in acid-base properties, geometric shapes, and metal complexing abilities. Correspondingly, interaction mechanisms between the phosphate and sorbent are categorized as hydrogen bonding, shape complementarity, and inner-sphere complexation, and their representative sorbents are organic-functionalized materials, molecularly imprinted polymers, and metal-based materials, respectively. Dominating factors affecting the phosphate sorption performance of these sorbents are critically examined, along with a discussion of some overlooked facts regarding the development of high-performance sorbents for selective phosphate removal from water and wastewater.

Selective Phosphate Removal from Water and Wastewater using Sorption: Process Fundamentals and Removal Mechanisms.

Morphological evolution from a unicellular to multicellular state provides greater opportunities for organisms to attain larger and more complex living forms. As the most common freshwater cyanobacterial genus, Microcystis is a unicellular microorganism, with high phenotypic plasticity, which forms colonies and blooms in lakes and reservoirs worldwide. We conducted a systematic review of field studies from the 1990s to 2017 where Microcystis was dominant. Microcystis was detected as the dominant genus in waterbodies from temperate to subtropical and tropical zones. Unicellular Microcystis spp. can be induced to form colonies by adjusting biotic and abiotic factors in laboratory. Colony formation by cell division has been induced by zooplankton filtrate, high Pb2+ concentration, the presence of another cyanobacterium (Cylindrospermopsis raciborskii), heterotrophic bacteria, and by low temperature and light intensity. Colony formation by cell adhesion can be induced by zooplankton grazing, high Ca2+ concentration, and microcystins. We hypothesise that single cells of all Microcystis morphospecies initially form colonies with a similar morphology to those found in the early spring. These colonies gradually change their morphology to that of M. ichthyoblabe, M. wesenbergii and M. aeruginosa with changing environmental conditions. Colony formation provides Microcystis with many ecological advantages, including adaption to varying light, sustained growth under poor nutrient supply, protection from chemical stressors and protection from grazing. These benefits represent passive tactics responding to environmental stress. Microcystis colonies form at the cost of decreased specific growth rates compared with a unicellular habit. Large colony size allows Microcystis to attain rapid floating velocities (maximum recorded for a single colony, ∼ 10.08 m h-1 ) that enable them to develop and maintain a large biomass near the surface of eutrophic lakes, where they may shade and inhibit the growth of less-buoyant species in deeper layers. Over time, accompanying species may fail to maintain viable populations, allowing Microcystis to dominate. Microcystis blooms can be controlled by artificial mixing. Microcystis colonies and non-buoyant phytoplankton will be exposed to identical light conditions if they are evenly distributed over the water column. In that case, green algae and diatoms, which generally have a higher growth rate than Microcystis, will be more successful. Under such mixing conditions, other phytoplankton taxa could recover and the dominance of Microcystis would be reduced. This review advances our understanding of the factors and mechanisms affecting Microcystis colony formation and size in the field and laboratory through synthesis of current knowledge. The main transition pathways of morphological changes in Microcystis provide an example of the phenotypic plasticity of organisms during morphological evolution from a unicellular to multicellular state. We emphasise that the mechanisms and factors influencing competition among various close morphospecies are sometimes paradoxical because these morphospecies are potentially a single species. Further work is required to clarify the colony-forming process in different Microcystis morphospecies and the seasonal variation in this process. This will allow researchers to grow laboratory cultures that more closely reflect field morphologies and to optimise artificial mixing to manage blooms more effectively.

Colony formation in the cyanobacterium Microcystis

The removal and recovery of phosphate from water by Fe 3 O 4 @alkali-treated calcium-silicate composite (Fe 3 O 4 @ASC) was investigated. The adsorbent was characterized by XRF, BET, XRD and zeta-potential analyses. The characterization results showed the successful synthesis of Fe 3 O 4 @ASC with a high specific surface area (129 m 2 /g). In batch experiments, the kinetic data and isotherm data fitted well to the pseudo-second-order model and Langmuir model, respectively, and the maximum adsorption capacity calculated by Langmuir model was 128 mg/g. The phosphate adsorption of Fe 3 O 4 @ASC performed well over a wide pH range from 2.5 to 13 and exhibited a good selective property even with 10 times higher molar concentration of other anions. Fe 3 O 4 @ASC could remove nearly 100% phosphate from real lake solution with phosphate concentration of 10 mg/L at the dosage of 0.25 g/L. In the column experiment, the breakthrough point of Fe 3 O 4 @ASC column was nearly 6000 mL for the initial phosphate concentration of 18.02 mg/L. Experimental data showed a good agreement with Yoon and Nelson model and Thomas model, the saturation adsorption capacity was 92 mg/g. Phosphate fractionation, XRD, and FTIR spectra analysis indicated that Ca-P precipitation generated during the phosphate adsorption process. Besides, the adsorbed phosphate could be successfully recovered by 2% citric acid solution, which implied that recovered phosphate could be reused as fertilizer.

Removal and recovery of phosphate from water by a magnetic Fe3O4@ASC adsorbent

This study isolated extracellular polysaccharides (EPS) as a powder material from cyanobacterial blooms and the powdered EPS was used to trigger colony formation of dispersed unicellular M. aeruginosa by controlling EPS concentration in culture medium. The effect of Ca2+ ions on the colony formation of M. aeruginosa was also investigated, then the interaction between EPS and Ca2+ ions on colony formation was discussed. The results showed that the addition of the powdered EPS into the medium did not cause morphological changes of M. aeruginosa, suggesting that EPS alone would not induce the colony formation of M. aeruginosa. On the other hand, a high concentration of calcium ions (1000 mg/l) caused colony formation. When EPS and Ca2+ ions in the culture medium were adjusted to 200 and 1000 mg/l, respectively, the colony density, the average cell number per colony and the particle size of M. aeruginosa showed ca. 1.7–2.0 times greater values than those in the Ca2+ added medium. Calcium ion contributed to the aggregation of M. aeruginosa via crosslinked reaction with negatively charged M. aeruginosa cells, and the addition of EPS possessing negatively charged functional groups such as carboxy groups could enhance the reaction, promoting the crosslinked reaction between EPS and Ca2+ ions.

Colony formation of highly dispersed Microcystis aeruginosa by controlling extracellular polysaccharides and calcium ion concentrations in aquatic solution

An activated carbon fiber was oxidized with ammonium persulfate solutions (APS) and used for the adsorption of Pb(II) from aqueous solutions. A comprehensive study on the effect of the oxidation process conditions—oxidant concentration, oxidation temperature and time—on the obtained fibers Pb(II) adsorption capacity and their chemical and physical properties was done. Samples were characterized by elemental analysis, Boehm titration, N2 adsorption–desorption isotherms and infrared spectroscopy. Adsorption isotherms were obtained for the activated carbon fibers and for two commercial ion-exchange resins, and they showed good agreement with the Langmuir model. For the first time, an activated carbon fiber with a high adsorption capacity for aqueous Pb(II) was obtained (2.70 mmol g−1, ca. 559 mg g−1). This value was more than 10 times higher than that of the pristine fiber and superior to those of the commercial ion-exchange resins. The adsorption kinetics data of the oxidized activated carbon fiber were studied by different kinetic models and found to be better described by the pseudo-second order model, while the adsorption equilibrium could be reached in less than 2 h. It was confirmed that the adsorption process mainly occurred by an ion-exchange mechanism. The obtained results showed that APS oxidation is capable of producing activated carbon fibers with high adsorption capacities for aqueous Pb(II), making them promising materials for industrial wastewater treatment applications.

Ammonium persulfate oxidized activated carbon fiber as a high capacity adsorbent for aqueous Pb(II)

The removal and recovery of phosphate from water by calcium-silicate composite (CSC) and alkali-treated calcium-silicate composite (ASC) was investigated. ASC had a higher specific surface area and total pore volume, and exhibited better performance of phosphate adsorption than CSC. In the batch mode adsorption studies, the isotherm adsorption experiments data fitted well the Langmuir isotherm model and the maximum adsorption capacities were 120 and 73.0 mg/g for ASC and for CSC, respectively. For the kinetic study, the experimental data fitted very well the pseudo-second-order kinetic model. The uptake of phosphate could be performed well over a wide pH range, from 3.0 to 13.0 for ASC and from 4.0 to 13.0 for CSC. The adsorption of phosphate by ASC was very selective even with 10 times higher concentration of other coexistent anions. For the adsorption of low phosphate concentration (10 mg/L), ASC could efficiently remove phosphate at the dosage of 0.8 g/L, while CSC was even difficult to remove phosphate at the dosage of 4.0 g/L. Phosphate fractionation results and FTIR spectra showed that phosphate-Ca complex was formed through phosphate adsorption process. The adsorbed phosphate could be successfully desorbed by 2% citric acid solution, indicating that the adsorbent after adsorbed phosphate could be reusable as fertilizer in the agricultural field.

Removal and recovery of phosphate from water by calcium-silicate composites-novel adsorbents made from waste glass and shells

In this study, introduction of acidic functional groups onto a carbon surface and their removal were carried out through two oxidation methods and outgassing to investigate the adsorption mechanism of aromatic compounds which have different polarity (benzene and nitrobenzene). Adsorption experiments for these aromatics in aqueous solution and n-hexane solution were conducted in order to obtain the adsorption isotherms for commercial activated carbon (BAC) as a starting material, its two types of oxidized BAC samples (OXs), and their outgassed samples at 900 °C (OGs). Adsorption and desorption kinetics of nitrobenzene for the BAC, OXs and OGs in aqueous solution were also examined. The results showed that the adsorption of benzene molecules was significantly hindered by abundant acidic functional groups in aqueous solution, whereas the adsorbed amount of nitrobenzene on OXs gradually increased as the solution concentration increased, indicating that nitrobenzene can adsorb favourably on a hydrophilic surface due to its high dipole moment, in contrast to benzene. In n-hexane solution, it was difficult for benzene to adsorb on any sample owing to the high affinity between benzene and n-hexane solvent. On the other hand, adsorbed amounts of nitrobenzene on OXs were larger than those of OGs in n-hexane solution, implying that nitrobenzene can adsorb two adsorption sites, graphene layers and surface acidic functional groups. The observed adsorption and desorption rate constants of nitrobenzene on the OXs were lower than those on the BAC due to disturbance of diffusion by the acidic functional groups.

Yoshimasa Amano

Papers

Removal and recovery of phosphate from water by a magnetic Fe3O4@ASC adsorbent

Colony formation of highly dispersed Microcystis aeruginosa by controlling extracellular polysaccharides and calcium ion concentrations in aquatic solution

Ammonium persulfate oxidized activated carbon fiber as a high capacity adsorbent for aqueous Pb(II)

Removal and recovery of phosphate from water by calcium-silicate composites-novel adsorbents made from waste glass and shells

Effect of Polarity of Activated Carbon Surface, Solvent and Adsorbate on Adsorption of Aromatic Compounds from Liquid Phase.