Cadmium (Cd) and lead (Pb) are toxic heavy metals commonly used in various industries. The simultaneous presence of these metals in wastewater amplifies the toxicity of wastewater and the complexity ...of the treatment process. This study has investigated the selective behavior of an aluminosilicate-based mesoporous adsorbent. It has been demonstrated that when equimolar quantities of the metals are present in wastewater, the adsorbent uptakes the Pb²⁺ ions selectively. This has been attributed to the higher electronegativity value of Pb²⁺ compared to Cd²⁺ which can be more readily adsorbed on the adsorbent surface, displacing the Cd²⁺ ions. The selectivity can be advantageous when the objective is the separation and reuse of the metals besides wastewater treatment. In non-equimolar solutions, a complete selectivity can be observed up to a threshold Pb²⁺ molar ratio of 30%. Below this threshold value, the Cd²⁺ and Pb²⁺ ions are uptaken simultaneously due to the abundance of Cd²⁺ ions and the availability of adsorption sites at very low Pb²⁺ molar ratios. Moreover, the total adsorption capacities of the adsorbent for the multi-component system have been shown to be in the same range as the single-component system for each metal ion which can be of high value for industrial applications.
It is well known that enzymatic hydrolysis is hampered by soluble inhibitors, while lignosulfonate (LS) generated from the sulfite pretreatment could enhance saccharification under certain ...conditions. To explain the roles of the LS during the hydrolyzing process, two types of LS were tested on selected lignocellulosic substrates and investigated through surface activity analysis and designed hydrolyzing experiments. The results showed that the LS with higher surface activity bound to and saturated the enzyme at a lower dosage and more effectively influenced the enzymatic hydrolysis. Both lignosulfonates, irrespective of their molecular weight and sulfonation degree, inhibited or enhanced the enzymatic saccharification related to two opposing mechanisms, i.e., competitive inhibition by the LS and its beneficial role on the enzyme activity. According to the Michaelis-Menten equation, the rate of cellulase-substrate complex conversion into product did not change with the introduction of the LS, whereas the specific binding affinity of the enzyme to the substrate was noticeably altered. With the introduction of LS, the stability of the enzyme increased, which increased the final hydrolysis yield. The hypothesis that the inhibition effects of LS could be effectively overcome by increasing the substrate content and the buffer concentration of the hydrolysates was confirmed through additional experiments.
This study involves the sustainable development of an ion exchange material with ultrahigh heavy metal uptake capacity from a waste material, originally destined for landfills. In this study, a ...promising thermo-alkaline reaction has been employed to simultaneously alter the surface chemistry and tune the textural properties of the waste-derived aluminosilicate. The effects of several reaction variables on the formation of mesotunnels in the structure of the material have been examined. Also, the surface characterization of the functionalized aluminosilicate has demonstrated that the functionalization reaction results in the cleavage of the robust T–O–T′ linkages (where T and T′ = Si or Al) into T–O– moieties, counterbalanced by an alkali metal cation, resulting in the coverage of the aluminosilicate surface with active ion exchange sites. Comparison of the ion exchange capacity of the functionalized aluminosilicate with those of the commercial ion exchange resins has proven exceptionally higher heavy metal uptake for the former. The ultrahigh heavy metal uptake of this material is ascribed to the high concentration of developed counterbalancing cations on the material surface. The attractiveness of this innovative approach is manifested by the dual environmental benefit, i.e., sustainable upcycling of a waste formerly deposited in landfills and its utilization for heavy metal-laden wastewater treatment.
•Preparing pellets from a novel aluminosilicate-based adsorbent was investigated.•Binder type and content, water content, and compaction pressure were optimized.•Calcium carbonate was selected as the ...binder of choice.•The compaction process was successful at producing high quality pellets.
Pelletization is an important part of the commercialization of adsorbents. Two factors must be considered in determining the pelletization conditions, namely mechanical strength of the pellets and their water resistance in aqueous environments. The primary objective of this study was the preparation of pellets from an aluminosilicate-based adsorbent for industrial fixed-bed adsorption columns. The pellet formation conditions, including binder type and content, water content, and compaction pressure, were optimized. Calcium carbonate was demonstrated to be the most promising binder for the aluminosilicate material. The experiments showed that with a water content of 30% and final applied compaction pressure of 80MPa, the amount of binder required for pelletization can be as low as 2.5wt%. Although higher compaction pressures produced pellets with higher mechanical strength, there exists a trade-off between the mechanical strength and the cost of the compaction process. Overall, the compaction process was successful at producing pellets with ample mechanical strength (as high as 800kN/m2) and satisfactory water resistance (pellet integrity not affected by immersion).
This study aimed at unfolding the role and mechanisms of chemically enhanced cleaning-in-place (CIP) regimes in fouling control of polytetrafluoroethylene (PTFE) made flat sheet (FS) membrane ...bio-reactors (MBRs). The trans-membrane pressure (TMP) was successfully maintained below 10 kPa using a daily CIP regime consisting of 100 to 600 mg l
−1
of NaOCl and cake layer resistance control was shown to be critical for effective high-flux MBR operation. In contrast, in the control unit without the CIP, the TMP exceeded 35 kPa at a flux of 40 LMH. The extracellular polymeric substances associated with proteins (EPS
protein
) were also controlled effectively with a daily application of the CIP to the fouled membrane. Moreover, the CIP prompted a thinner and looser bio-cake layer on the membrane surface, suggesting that in situ CIP can be a favorable method to control FS membrane fouling at high-flux MBR operation.
Development of next-generation porous sorbents to overcome the challenges, such as low uptake capacity, slow sorption rate, and non-recyclability, associated with conventional sorbents is of utmost ...importance. Herein, we report the synthesis of a highly porous graphene aerogel (GA) with a unique three-dimensional hierarchical bimodal porous network of macro and meso-pores
via
a facile hydrothermal technique; this aerogel has sorption capacity that is more than 5 times that of conventional commercial sorbents. Fluoroalkyl silane functionalization of the GA surface results in a significant reduction in its water sorption from 20 g g
−1
to 5 g g
−1
due to the GA surface becoming more hydrophobic, which renders it useful in practical application to selectively remove oil from seawater. Moreover, the sorption rate of the GA for oils and organic solvents has been found to be extremely fast, and saturation of the GA is completed in a few seconds. This is attributed to its unique meso-macro bimodal porous structure with large pore channels called macro-pores or voids of various sizes ranging from 300 nm to over 10 μm, which facilitate mass transport into its inner mesopores of 14-18 nm at high rate. Finally, the GA is shown to be a highly recyclable material due to its good mechanical strength, where the oil- and organic solvent-sorbed GA can be efficiently recovered using thermal or chemical methods for several sorption-desorption cycles without significant loss in its capacity, which also makes the process cost effective and environmentally friendly.
Development of graphene based porous sorbent to overcome the challenges, such as low uptake capacity, slow sorption rate, and non-recyclability, associated with conventional sorbents.
Most of the landfill sites are suffering from the toxicity problems which exert pollution to their soil and underground water rendering it unusable for further applications. Printed circuit boards ...(PCBs) constitute one of the major sources of such toxicity in the landfill areas throughout the world. Hence, PCB recycling and separation of its metallic and nonmetallic components has been considered a major breakthrough in this direction. There are a lot of studies focusing on the metallic fraction of the PCBs due to its economic benefits whereas the nonmetallic fraction (NMP) has been left isolated. This work investigates the feasibility of producing adsorbent from waste NMP and its possible application to remove the positively-charged toxic heavy metal ions from effluents. In the first phase of the study, the NMP is activated under various conditions, namely impregnation time, impregnation ratio, impregnation temperature, furnace temperature and activation time. The optimum condition in terms of surface areas of the samples has been determined and the optimum sample (A-NMP) has been fully characterized. The mechanism of the activation has been hypothesized by comparing the characteristics of the optimum sample with those of the untreated material. It is considered that it is possible to use this activated material for heavy metal adsorption purposes due to the development of a porous structure and surface functional moieties on the material. The second phase involves the employment of the produced material for wastewater treatment. Therefore, the adsorption capacity of this material for copper, lead, zinc, nickel and cobalt has been evaluated in both the single- and multi-component systems. It has been shown that the untreated material has no adsorption capacity for any of the metals, whereas the adsorption capacity of the modified material is 3 mmol Cu, 3.4 mmol Pb, 2 mmol Zn, 3.4 mmol Ni and 3.5 mmol Co per gram of the adsorbent. These values are not only higher than the untreated material, but also much higher than the adsorption capacities of the three widely-used commercial adsorbents used in this study. It has also been shown that the adsorption capacity of this material does not decrease in multi-component systems and in some cases, even shows a synergistic effect. Furthermore, depending on the difference between the electronegativity of the metal ions present in the solution, this material can have either selective or simultaneous adsorption in multi-component systems. The single-component modeling shows that this material exhibits a completely Langmuir behavior indicative of monolayer adsorption in a homogeneous surface. The extended modified Freundlich model was the best-fit equation for the multicomponent system.
Toward environmentally-benign utilization of nonmetallic fraction of waste printed circuit boards as modifier and precursor Hadi, Pejman; Chao NingauthorChemical and Biomolecular Engineering Department, Hong Kong University of Science and Technology, Clear Water Bay Road, Hong Kong Special Administrative Region; Weiyi OuyangauthorChemical and Biomolecular Engineering Department, Hong Kong University of Science and Technology, Clear Water Bay Road, Hong Kong Special Administrative Region ...
2015
Journal Article
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