Iron, chromium, lead, europium, silver, copper, strontium, cesium, zinc and nickel are some of the most frequently found heavy metal ions in wastewater and can cause serious health problems. Hence, their removal is essential from the environmental point of view. Recent studies show that graphene oxide (GO) can efficiently remove heavy metal ions from wastewater. A great deal of effort has been made to enhance the waste removal performance of GO using a variety of techniques. The performance of GO as an adsorbent agent to remove various organic pollutants, radioactive wastes and dyes has already been reviewed by various authors. However, the capability of GO and its derivatives to remove heavy metal ions has not been reviewed in detail. This paper reviews the wastewater removal efficiency and sorption mechanism of GO, functionalized GO and their composites for five of the most extensively studied heavy metal ions: Cr(III), Cr(VI), Cu(II), Pb(II) and Au(III). The waste removal kinetics of the adsorbents and the condition for the maximum adsorption are analysed for each of these heavy metal ions.

Graphene oxides for removal of heavy and precious metals from wastewater

Presently, there is an emerging research trend in the fabrication of Phytogenic Magnetic Nanoparticles (PMNPs) and their applications in the water/wastewater treatment (WWT), due to their dynamic morphology, desired size, super paramagnetic behavior and high saturation magnetization value. Green fabrication of PMNPs is clean, non-toxic, eco-friendly, fast and cost-effective as compared to other physico-chemical technologies, which make it a promising technology. However, certain aspects such as the optimization of the fabrication protocol in order to produce desired quality of PMNPs, regeneration and reusability, are the main hindrances in the transfer of this technology from the laboratory scale to the commercial applications. Therefore, the present study highlights the performance of PMNPs for the removal of aqueous pollutants from wastewater. In addition, the research developments of PMNPs regarding fabrication mechanism, regeneration and reusability for WWT are discussed. The study also provides a model of PMNPs based on zero effluent discharge and consequently, the WWT process is proposed. Finally, future perspectives and challenges are discussed to make PMNPs based green nanotechnology technically more feasible and economically sustainable.

https://pubs.rsc.org/en/Content/ArticlePDF/2017/RA/C7RA04738J

Phytogenic magnetic nanoparticles for wastewater treatment: a review

Magnetotactic bacteria (MTB) have started to be employed for the biosynthesis of magnetic nanoparticles, due to the rapidly increasing demand for nanoparticles in biomedical, biotechnology and environmental protection. MBT are the group of prokaryotes that have the ability to produce bio-magnetic minerals or bio-magnetic crystals of either magnetite (Fe3 O4 ) or greigite (Fe3 S4 ) in numerous shapes and size ranges, known as magnetosomes (MS). MS compel MTB to respond to the applied external magnetic field. However, it is extremely difficult to grow MTB and produce high yield of MS under artificial environmental conditions, thus creating a major hurdle to relocate MTB technology from laboratory scale to industrial or commercial level. Therefore, to best of our knowledge this review is the first attempt to highlight existing research developments about the laboratory scale and mass production of MS by MTB. Moreover, the optimum culture media and environmental conditions used for the cultivation of MTB were also considered. Finally, future research is encouraged for the improvement of MS yield which will result in the development of advanced nanotechnology/magnetotechnology.

Yield cultivation of magnetotactic bacteria and magnetosomes: A review.

Magnetotactic bacteria (MTB) represent a heterogeneous group of Gram-negative aquatic prokaryotes with a broad range of morphological types, including vibrioid, coccoid, rod and spirillum. MTBs possess the virtuosity to passively align and actively swim along the magnetic field. Magnetosomes are the trademark nano-ranged intracellular structures of MTB, which comprise magnetic iron-bearing inorganic crystals enveloped by an organic membrane, and are dedicated organelles for their magnetotactic lifestyle. Magnetosomes endue high and even dispersion in aqueous solutions compared with artificial magnetites, claiming them as paragon nanomaterials. MTB and magnetosomes offer high technological potential in modern science, technology and medicines. This review focuses on the applicability of MTB and magnetosomes in various areas of modern benefits.

Magnetotactic bacteria: nanodrivers of the future.

An overview of heavy metal removal from wastewater using magnetotactic bacteria

A magnetotactic bacterial isolate was found a good biosorbent for removing Au(III) from wastewater in our preliminary studies. In this study, the process and the mechanism of biosorption were investigated from several aspects, including surface complexation, ion exchange, electrostatic attraction, and oxidation–reduction reaction. According to the water treatment experiments, these bacteria were confirmed to quickly purify the wastewater-containing Au(III). The results showed that the role of ion exchange was a secondary mechanism in the biosorption process. The molecular dynamics simulation revealed that electrostatic attraction and thermal motion had effects on the motion of Au(III), and the electrostatics of different functional groups was dissimilar. Using chemical modified and unmodified biomass as absorbents, it was found that the functional groups (including carboxylate, hydroxyl, and phosphoryl groups present on cell wall) were the main reason for the adsorption. The experimental data cou...

Theoretical and experimental study of Au(III)-containing wastewater treatment using magnetotactic bacteria

Magnetotactic bacterium has the characteristics of both magnetotaxis and adsorbing the precious metal ions, which makes it possible to recycle the precious metal from wastewater in the combination of high gradient magnetic separation. Nickel wires were used as media which producing gradient magnetic field to separate the magnetotactic bacteria (MTB) which had adsorbed Au(III) with high gradient magnetic field from wastewater. The magnetic separation model including the material balance equation and the separation rate equation were developed to describe this process. The movement process of metal loaded bacteria in magnetic field was investigated both experimentally and theoretically. The magnetic separator developed by our research team used for separating Au loaded biomass showed high separation efficiency, with nearly 100% biomass removed at the magnetic intensity of 1200 GS in 100 min. Experimental and simulation results all showed that the trapped bacteria were deposited in multi-layers, imp...

Simulation and experimental study on magnetic separation of Au loaded biomass from wastewater

Flotation Mechanism of Soluble Salts with High Ionic Strength

The magnetotactic bacteria have the properties of both capturing heavy metal ions and being quickly separated out from the wastewater, which makes them high quality adsorbents. The adsorption of ions usually shows selectivity in the multi component aqueous solutions. This paper investigated the mechanism of adsorption selectivity using the molecular dynamics method on the basis of periodic law of elements. A universal equation with respect to the mass, volume and charge of ions was deduced. Based on the analysis of the surficial properties, a model was built to describe the structure of magnetotactic bacteria using the organic groups. Then, the interface system of bacterium surface, aqueous solutions and heavy metal ions was developed and dynamics simulation was performed. It was found that the ion having smaller charge-mass ratio according to the periodic system of elements might be easier to be adsorbed. The ionic thermal motion could depress the adsorption of ions and might be one of the reasons which cause adsorption selectivity. Furthermore, the larger charge-mass ions were more inclined to be drifting away from the bacteria in the simulation.

	 

	Key words: Magnetotactic bacteria, heavy metal, adsorption, charge-mass ratio, periodic law of elements, molecular simulation.

Cheng Huaigang

Papers

Theoretical and experimental study of Au(III)-containing wastewater treatment using magnetotactic bacteria

Simulation and experimental study on magnetic separation of Au loaded biomass from wastewater

Flotation Mechanism of Soluble Salts with High Ionic Strength

The effect of ion charge-mass ratio on adsorption of heavy metals on magnetotactic bacteria