Synergistic Removal of Pb(II), Cd(II) and Humic Acid by Fe3O4@Mesoporous Silica-Graphene Oxide Composites

The synergistic adsorption of heavy metal ions and humic acid can be very challenging. This is largely because of their competitive adsorption onto most adsorbent materials. Hierarchically structured composites containing polyethylenimine-modified magnetic mesoporous silica and graphene oxide (MMSP-GO) were here prepared to address this. Magnetic mesoporous silica microspheres were synthesized and functionalized with PEI molecules, providing many amine groups for chemical conjugation with the carboxyl groups on GO sheets and enhanced the affinity between the pollutants and the mesoporous silica. The features of the composites were characterized using TEM, SEM, TGA, DLS, and VSM measurements. Series adsorption results proved that this system was suitable for simultaneous and efficient removal of heavy metal ions and humic acid using MMSP-GO composites as adsorbents. The maximum adsorption capacities of MMSP-GO for Pb(II) and Cd (II) were 333 and 167 mg g⁻¹ caculated by Langmuir model, respectively. HA enhances adsorption of heavy metals by MMSP-GO composites due to their interactions in aqueous solutions. The underlying mechanism of synergistic adsorption of heavy metal ions and humic acid were discussed. MMSP-GO composites have shown promise for use as adsorbents in the simultaneous removal of heavy metals and humic acid in wastewater treatment processes.     

Characteristics of PAHs adsorption on inorganic particles and activated sludge in domestic wastewater treatment

The occurrence of polycyclic aromatic hydrocarbons (PAHs) in a domestic wastewater treatment plant (WWTP) was investigated in a 1 year period. In order to understand how PAHs were removed at different stages of the treatment process, adsorption experiments were conducted using quartz sand, kaolinite, and natural clay as inorganic adsorbents and activated sludge as organic adsorbent for adsorbing naphthalene, phenanthrene, and pyrene. As a result, the adsorption of PAHs by the inorganic adsorbents well followed the Langmuir isotherm while that by the activated sludge well followed the Freundlich isotherm. By bridging equilibrium partitioning coefficient with the parameters of adsorption isotherm, a set of mathematical models were developed. Under an assumption that in the primary settler PAHs removal was by adsorption onto inorganic particles and in the biological treatment unit it was by adsorption onto activated sludge, the model calculation results fairly reflected the practical condition in the WWTP.     

Lignin--from natural adsorbent to activated carbon: a review

The present review compiles the work done over the last few decades on the use of lignin and lignin-based chars and activated carbons as adsorbents for the removal of substances from water and focuses on the utilisation of lignin as adsorbent, its conversion to chars and activated carbons and the use of these materials as adsorbents. Moreover, the review also examines the textural and surface chemical properties of lignin-based activated carbons. The work so far carried out indicates that lignin is relatively non-reactive and probably the component of lignocellulosic precursors primarily responsible for the microporosity of activated carbons. Under appropriate conditions of activation it is possible to obtain materials with surface areas and pore volumes approaching 2000 m(2)g(-1) and 1cm(3)g(-1), respectively, and these materials have capacities for the aqueous phase adsorption of metallic pollutants that are comparable to those of commercial activated carbons. Relatively little work has so far been published and there is considerable scope for more detailed studies on the preparation, characterisation and adsorption applications of lignin-based activated carbons.     

Covalent immobilization of proteins on carbon nanotubes using the cross-linker 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide--a critical assessment

Functionalization of carbon nanotubes (CNTs) with proteins is often a key step in their biological applications, particularly in biosensing. One popular method has used the cross-linker 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) to covalently conjugate proteins onto carboxylated CNTs. In this article, we critically assess the evidence presented in these conjugation studies in the literature. As CNTs have a natural affinity for diverse proteins through hydrophobic and electrostatic interactions, it is therefore important to differentiate protein covalent attachment from adsorption in the immobilization mechanism. Unfortunately, many studies of conjugating proteins onto CNTs using EDC lacked essential controls to eliminate the possibility of protein adsorption. In studies where the attachment was claimed to be covalent, discrepancies existed and the observed immobilization appeared to be due to adsorption. So far, bond analysis has been lacking to ascertain the nature of the attachment using EDC. We recommend that this approach of covalent immobilization of proteins on CNTs be re-evaluated and treated with caution.     

Significance of exploiting non-living biomaterials for the biosorption of wastewater pollutants

Industrial effluents from various sectors have become a matter of major environmental concern. The treatment of wastewater in recent year plays a significant role in order to remove the pollutants and to safeguard the water resource. The conventional wastewater treatment is considered costlier and associated with problem of sludge generation. Biosorption methods are considered as the potential solution due to their economical efficiency, good adsorption capacity and eco-friendliness. In this review, an extensive list of biosorbents from algae, bacteria, fungi and agricultural byproducts have been compiled. The suitability of biosorbents towards the eradication of heavy metals, textile dyes and phenolic compounds were highlighted. It is evident from the literature survey of recently published research articles that the biosorbents have demonstrated outstanding removal potential towards the wastewater pollutants. Therefore, biosorbents from the source of dead microbial and agricultural byproduct can be viable alternatives to activated carbon for the wastewater treatment.     

改性微生物吸附剂在重金属废水处理中的应用进展

高效、低耗、环境友好的重金属废水处理方法是当前的研究热点之一,微生物吸附法因具有优良的吸附性能、不产生二次污染、环境友好性等优点,在重金属废水处理中有巨大的应用潜力。细菌、真菌、藻类等微生物可通过静电吸附、络合作用等将重金属结合到细胞壁表面。但未经处理的微生物往往吸附效果不佳,通过对微生物进行物理、化学等方法的改性处理,能显著增加微生物与重金属离子结合的活性位点,提高去除效果。本文对国内外微生物的改性方法以及改性微生物吸附剂对废水中重金属的吸附能力和影响因素进行阐述,讨论微生物吸附剂存在的相关问题,并对其未来的研究方向做简要展望。     

A review on economically adsorbents on heavy metals removal in water and wastewater

Heavy metals contamination in water has been an issue to the environment and human health. The persisting contamination level has been observed and concerned by the public due to continuous deterioration of water quality. On the other hand, conventional treatment system could not completely remove the toxic metals in the water, thus alternative purification methods using inexpensive materials were endeavor to improve the current treatment process. Wide ranges of low cost adsorbents were used to remove heavy metal in aqueous solution and wastewater. The low cost adsorbents were usually collected from agricultural waste, seafood waste, food waste, industrial by-product and soil. These adsorbents are readily available in a copious amount. Besides, the pretreatment are not complicated to be conducted on the raw products, which is economically sound for an alternative treatment. The previous studies have provided much evidence of low cost adsorbents’ efficiency in removing metal ions from aqueous solution or wastewater. In this review, several low cost adsorbents in the recent literature have been studied. The maximum adsorption capacity, affecting factors such as pH, contact times, temperature, initial concentration and modified materials were revised and summarized in this review for further reference. Comparisons of the adsorbent between the modified and natural products were also demonstrated to provide a clear understanding on the kinetic uptake of the selected adsorbents. Some of the natural adsorbents appeared as good heavy metal removal, while some were not and require further modifications and improvements to enhance the adsorption capacity. SWOT analysis (strength, weakness, opportunities, threat) was also performed on the low cost adsorbents to identify the advantages of using low cost adsorbents and solve the weaknesses encountered by the utilization of low cost materials. This tool helps to determine the potential quality of low cost materials in the application for water and wastewater treatment.     

Removal of fluoride from aqueous solution by TiO2 and TiO2–SiO2 nanocomposite

Adsorption plays an important role in the removal of pollutants such as fluoride from aqueous solutions. With the rapid development of environmental technology, TiO₂ particle has become promising material to adsorb fluoride ion because of its low cost, non-toxic, good chemical stability, and good sorption ability. This work used sol-gel and hydrothermal synthesis methods to prepare TiO₂ particles and load them onto SiO₂ particles. The physicochemical properties such as heat stability, particle size, and surface area of the resulting TiO₂ adsorbents were characterized with various analytical methods. In addition, their adsorption abilities to fluoride were determined under various conditions including different initial fluoride concentration, pH and coexisting ions. The maximum adsorption capacity of the TiO₂ adsorbents can reach up to 94.3 mg/g. The adsorption isotherms of fluoride onto the TiO₂ adsorbents can be closely described by the Langmuir model, suggesting the monolayer adsorption process.     

Detergent removal by non-polar polystyrene beads

Detergent removal from lipid-protein-detergent micellar solutions is the most successful strategy for reconstitution of integral membrane proteins into proteoliposomes or into two-dimensional crystals. This review establishes the potential of polystyrene beads as a simple alternative to other conventional detergent removing strategies such as dialysis, gel chromatography and dilution. Kinetics and equilibrium aspects of removal of different detergents by hydrophobic adsorption onto polystyrene beads have been systematically investigated. A mechanism of adsorption onto polystyrene beads is proposed and provide useful information about the use of these beads in reconstitution experiments. The usefulness of this detergent removal strategy to produce quasi-ideal proteoliposomes is evaluated by considering the morphology and the size of the reconstituted vesicles, the homogeneity in size and protein distribution, the final protein orientation and the permeability of resulting proteoliposomes. Finally, the advantages of detergent removal by polystyrene beads as an alternative to conventional dialysis in two-dimensional crystallization trials are evaluated through review of recent structural reconstitution studies. Received: 1 December 1997 / Revised version: 6 February 1998 / Accepted: 6 February 1998     

Adsorption thermodynamics to clean up wastewater; critical review

The current review paper deals with critical evaluation of the thermodynamic parameters of adsorption equilibrium uptakes of heavy metals, dyes and other organic pollutants from the wastewater using low-cost adsorbents, activated carbon derived from agricultural waste, industrial wastes and other important adsorbent materials. Present review paper focus the spontaneity of adsorption processes when the thermodynamic parameters were assessed with the compensation effects of standard enthalpy change (ΔH^o) and standard entropy change (ΔS^o) with temperature. This paper also investigates the spontaneity of adsorption on the basis of thermodynamic criteria of spontaneity and the temperature range to predict feasibility of the adsorption processes.     

Removal of cesium ions from aqueous solutions using various separation technologies

Cesium is the major fission product of uranium, which widely exists in radioactive wastewater. Radiocesium has potential adverse effects on human health and ecological environment. Different methods such as chemical precipitation, coagulation/co-precipitation, solvent extraction, membrane process, chemical reduction, and adsorption have been used to remove radioactive cesium from aqueous solution. However, the development of innovative technologies capable of selectively removing radioactive cesium is still imperative yet challenging. This review focused on cesium removal using various separation technologies, including chemical precipitation, solvent extraction, membrane separation, and adsorption. The key restraints for cesium removal, as well as the recent progress of these methods have also been discussed. Particular attention has been paid to the adsorption methods, which has been highlighted by introducing the latest advances in inorganic adsorbents (such as metal hexacyanoferrates, clay minerals, carbon-based-adsorbents, and ammonium molybdophosphate), organic adsorbents (such as ion exchange resin, metal–organic frameworks and supramolecular/indicator grafting adsorbents), and biosorbents (such as agroforestry wastes and microbial biomass). Adsorption-based methods are high efficient in separation of cesium ions from aqueous streams, and adsorption of cesium ions has been investigated intensively and even used in practical applications, there is still considerable scope for improvement in terms of adsorption capacity and selectivity.

     

Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: a review

The application of low-cost adsorbents obtained from plant wastes as a replacement for costly conventional methods of removing heavy metal ions from wastewater has been reviewed. It is well known that cellulosic waste materials can be obtained and employed as cheap adsorbents and their performance to remove heavy metal ions can be affected upon chemical treatment. In general, chemically modified plant wastes exhibit higher adsorption capacities than unmodified forms. Numerous chemicals have been used for modifications which include mineral and organic acids, bases, oxidizing agent, organic compounds, etc. In this review, an extensive list of plant wastes as adsorbents including rice husks, spent grain, sawdust, sugarcane bagasse, fruit wastes, weeds and others has been compiled. Some of the treated adsorbents show good adsorption capacities for Cd, Cu, Pb, Zn and Ni.     

污水处理工艺的生态安全性研究进展

污水经处理后,排放和回用时常规指标通常都能达到设计标准,但出水水质并未达到无害化.从可持续发展的角度来讲,为保障生态环境及人群的安全,需要将污水的综合毒性纳入排放标准.为此,在工艺的选择及优化时应将毒性削减效果纳入其中,提高污水处理工艺的生态安全性.本文着重综述了以特定污水处理为目的、以污水回用为目的及以受纳水体安全为目的各类污水处理工艺的生态安全性研究,指出传统生物处理与高级氧化技术相结合,在去除污染物质的基础上可以强化对毒性的削减;对于以污水回用为目的处理工艺,对各种工艺进行集成可实现常规污染物去除和毒性削减的优势互补;以受纳水体生态安全为目的的污水处理工艺,应重点基于工艺运行参数和工艺单元选择进行毒性削减优化.最后对研究中存在的问题以及未来的学科发展方向提出了建议.     

Removal of ammonium from aqueous solutions using alkali-modified biochars

Biochars converted from agricultural residuals can effectively remove ammonium from water. This work further improved the sorption ability of biochars to aqueous ammonium through alkali modification. Three modified biochars were prepared from agricultural residuals pre-treated with NaOH solution through low-temperature (300 °C) slow pyrolysis. The modified biochars effectively removed ammonium ions from water under various conditions with relatively fast adsorption kinetics (reached equilibrium within 10 h) and extremely high adsorption capacity (>200 mg/g). The Langmuir maximum capacity of the three modified biochars were between 313.9 and 518.9 mg/g, higher than many other ammonium adsorbents. Although the sorption of ammonium onto the modified biochar was affected by pH and temperature, it was high under all of the tested conditions. Findings from this work indicated that alkali-modified biochars can be used as an alternative adsorbent for the removal of ammonium from wastewater.     

Microwave-assisted preparation of bagasse and rice straw for the removal of emulsified oil from wastewater

The present study was carried out to examine modified bagasse and rice straw as absorbents for the removal of emulsified oil by a microwave-assisted technique. The raw adsorbents were chemically modified with sodium hydroxide and surfactant solution for better adsorption of oil. The surface modification was confirmed through Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) analysis. Batch studies were performed to identify the influence of contact time, pH, dosage, speed, and temperature on the percentage of removal of emulsified oil from the wastewater. A maximum oil removal of 98.07% and 98.72% was achieved in microwave-assisted bagasse and rice straw at 313 K. The obtained data were compared with isotherm and kinetic models to understand the mechanism behind the adsorption. From the Langmuir isotherm model, a maximum adsorption capacity of 192.58 and 276.82 mg/g was observed for modified bagasse and rice straw. The oil-loaded raw and microwave-assisted adsorbents can act as a potential energy source for renewable energy.     

Dye adsorption by sewage sludge-based activated carbons in batch and fixed-bed systems

The present research work deals with the production of activated carbons by chemical activation and pyrolysis of sewage sludges. The adsorbent properties of these sewage sludges based activated carbons were studied by liquid-phase adsorption tests. Dyes removal from colored wastewater being a possible application for sludge based adsorbents, methylene blue and saphranine removing from solution was studied. Pure and binary adsorption assays were performed in batch and fixed bed systems. In all cases studied, the adsorbents produced from sewage sludges were able to adsorb both the compounds considered here. Nevertheless, time required for reaching equilibrium, adsorptive capacity and fixed bed characteristic parameters were different for these two compounds. Methylene blue adsorption occurred faster than that of saphranine, and it was preferably adsorbed when treating binary solutions. It could be concluded that the sewage sludge-based activated carbons may be promising for dyes removal from aqueous streams.     

Advances in water treatment by adsorption technology

Among various water purification and recycling technologies, adsorption is a fast, inexpensive and universal method. The development of low-cost adsorbents has led to the rapid growth of research interests in this field. The present protocol describes salient features of adsorption and details experimental methodologies for the development and characterization of low-cost adsorbents, water treatment and recycling using adsorption technology including batch processes and column operations. The protocol describes the development of inexpensive adsorbents from waste materials, which takes only 1-2 days, and an adsorption process taking 15-120 min for the removal of pollutants. The applications of batch and column processes are discussed, along with suggestions to make this technology more popular and applicable.     

How to avoid pharmaceuticals in the aquatic environment

Pharmaceuticals and other micropollutants in wastewater pose a new challenge to wastewater professionals as well as to the pharmaceutical industry. Although there is a great deal of uncertainty concerning the possible detrimental effects on the aquatic ecosystems, the precautionary principle--or possibly new scientific evidence--may give rise to more stringent demands on wastewater treatment in the future. In conventional wastewater treatment plants, a combination of biological treatment with high sludge residence times and ozonation of the effluent seems to be the most promising technology. Ozonation, however, is an energy-intensive technology. Moreover, in conventional end-of-pipe systems a large part of the pollutants will always be lost to the environment due to leaking, primarily during rain. In the long term, source separation offers the more sustainable solution to the entire wastewater problem, including organic micropollutants. Urine source separation is an elegant solution to the problems of nutrients and pharmaceuticals alike and losses of untreated pollutants to the environment can be minimized. Although few technologies for the separate treatment of urine have been developed to date, the 100-500 times higher concentrations of micropollutants promise more efficient conditions for all removal technologies known from conventional wastewater treatment.     

MOLECULARLY IMPRINTED POLYMERS FOR SOME REACTIVE DYES

Depending upon their structure, azo- and anthraquinonic dyes are the two major classes and together represent 90% of all organic colorants. Adsorption of dye molecules onto a sorbent can be an effective, low-cost method of color removal. Most of the techniques used for removal of dyes are of high production cost, and the regeneration also makes them uneconomical. There is much interest in the development of cheaper and effective newer materials for use as adsorbents. Molecular imprinting is a new kind of materials that can be alternative adsorbents. In this study, molecularly imprinted polymers of three textile dyes (Cibacron Orange P-4R, Cibacron Red P-4B, Cibacron Black PSG) were prepared. Methacrylic acid was used as a monomer for red and orange dyes and acrylamide was used for black dye. Methanol:acetonitrile was used as a porogen. The selective recognition ability of the molecularly imprinted polymers was studied by an equilibrium–adsorption batch method. The adsorption data are for Cibacron Black PSG 65% and nonimprinted polymer (NIP) 25%; Cibacron Red P-4B 72% and NIP 18%; and Cibacron Orange P-4R 45% and NIP 10%, respectively. Dye-imprinted polymers were used as a solid-phase extraction material for selective adsorption from wastewater of textile factory.     

Removal of organic pollutants from aqueous solutions by adsorbents prepared from an agroalimentary by-product

Two series of crosslinked starch polymers were tested for their ability to adsorb organic pollutants in aqueous solutions. The polymers were prepared by a crosslinking reaction of starch-enriched flour using epichlorohydrin as the crosslinking agent, without and in the presence of NH(4)OH. These polymers were used as sorbent materials for the removal of phenolic derivatives from wastewater. The influence of several parameters (kinetics, pH and polymer structure) on the sorption capacity was evaluated using the batch and the open column methods. Results of adsorption experiments showed that the starch-based materials exhibited high sorption capacities toward phenolic derivatives. The study of the kinetics of pollutant uptake revealed that the adsorbents presented a relatively fast rate of adsorption. The experimental data were examined using the Langmuir and Freundlich models and it was found that the Freundlich model appeared to fit the isotherm data better than the Langmuir model.