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.
Climate change is receiving an ever-increasing attention due to the accelerated global warming. Undoubtedly, CO2 from anthropogenic sources is the major contributor to this undesirable effect and ...thus, there has been a growing attempt to curb it. Utilization of biofuels to replace fossil fuels has been considered a viable method to mitigate CO2 emissions. However, there has been some concern about the indirect greenhouse gas emissions from the production and consumption of biofuels, such as land-use change, carbon leakage, and biomass transportation. It was suggested that these indirect factors can increase the CO2 emission and may offset the benefits of CO2 sequestration from biofuel utilization. In this study, all these challenges in biofuel production have been comprehensively reviewed and the importance of using the agricultural residues for biofuel production in countries with high reliance on agricultural development has been emphasized upon. A case study for the utilization of the agricultural residues in the Great Mekong Subregion (GMS) for biofuel production has been presented and the carbon balance for different bioenergy production scenarios in five Southeast Asian countries has been calculated. The results of the regression models show that Thailand and Lao PDR have the highest and lowest amounts of biomass residues per unit mass crop, respectively, suggesting the substantial differences in the harvesting technologies and/or economics of those countries. The overall annual CO2 sequestration potentials of the biomass for replacing gasoline through bioethanol production, and for substituting coal for power generation via anaerobic digestion and gasification have been determined to be approximately 104/Tg and 488Tg, respectively. It has been suggested that using the crop residues as feedstock for the second generation biofuel production without affecting the food market could indeed provide considerable carbon credits for sustainable agricultural development as the major industry in the developing countries.
In this study, anionic dialdehyde cellulose (DAC) and cationic dialdehyde cellulose (c-DAC) nanofibrous adsorbents were prepared via a two-step reaction from bamboo pulp, using sodium periodate and ...Girard’s reagent T as oxidizing and cationizing agents, respectively. The performance of DAC and c-DAC for selective dye adsorption and separation was evaluated by six different organic dyes (with varying charge properties) and certain binary mixtures. Both adsorbents could remove the dyes but with different capability, where DAC exhibited high adsorption efficiency against cationic dyes (e.g., the maximum adsorption capacity for Bismarck brown Y was 552.1 mg/g) and c-DAC exhibited high adsorption efficiency against anionic dyes (e.g., the maximum adsorption capacity for Congo red was 540.3 mg/g). To investigate the adsorption mechanism for these adsorbents, effects of contact time, initial pH value, initial dye concentration, and ionic strength on the adsorption activity against Congo red were investigated. The adsorption equilibrium data of DAC were found to fit best with the Langmuir isotherm model, whereas that of c-DAC were found to fit best with the Freundlich model. Both DAC and c-DAC adsorption kinetic data could be described by the pseudo-second-order kinetic model, and these adsorbents possessed stable adsorption efficiency in the pH range of 4–10. Furthermore, their dye adsorption capabilities were found to increase with increasing ionic strength (salt concentration). The distinctive complementary features of DAC and c-DAC will allow them to remove a wide range of organic dyes from industrial wastewater.
•The investigation of fouling control mechanism via the CEB method in FS-MBRs.•Effect of the CEB method on the removal of the cake layer and fouling resistances.•Evaluation of the effect of the ...foulant type on the efficiency of the CEB method.•Optimization of the chemical concentration and cleaning run time for an enhanced foulant removal.
This study attempts to demonstrate the applicability of chemically enhanced backflush (CEB) to flat sheet (FS) membranes and aims at examining the membrane resistance fraction of complex organic foulants without applying hydraulic cleaning. With sodium hypochlorite (NaOCl) applied (i.e., 100–600mg/L) as an oxidant chemical, complex soluble microbial products (SMP) foulants were effectively removed from the membrane in 60–90min, and the membrane resistance is governed by the CEB bulk reaction and the transport, penetration and back transport of NaOCl. An in-depth study has proved that the cake resistance associated from the SMP foulants is more sensitive to CEB runtime, whereas the fouling resistance is more sensitive to the concentration of NaOCl. Nevertheless, for the foulant which mainly compose of dissolved organic matters, the cake resistance can be effectively removed in a shorter runtime and with a lower concentration of NaOCl as compared with the SMP foulant. However, high concentration of NaOCl is still needed to remove its fouling resistance. In addition, this study demonstrates that even in the absent of hydraulic backflush CEB is still highly compatible with FS membrane and the effectiveness is comparable to that of hollow fiber membrane.
•Environmental impacts of electronic waste and specifically waste printed circuit boards.•Review of the recycling techniques of waste printed circuit boards.•Advantages of physico-mechanical ...recycling techniques over chemical methods.•Utilization of nonmetallic fraction of waste printed circuit boards as modifier/filler.•Recent advances in the use of nonmetallic fraction of waste printed circuit boards as precursor.
Electronic waste, including printed circuit boards, is growing at an alarming rate due to the accelerated technological progress and the shorter lifespan of the electronic equipment. In the past decades, due to the lack of proper economic and environmentally-benign recycling technologies, a major fraction of e-waste generated was either destined to landfills or incinerated with the sole intention of its disposal disregarding the toxic nature of this waste. Recently, with the increasing public awareness over their environment and health issues and with the enaction of more stringent regulations, environmentally-benign recycling has been driven to be an alternative option partially replacing the traditional eco-unfriendly disposal methods. One of the most favorable green technologies has been the mechanical separation of the metallic and nonmetallic fraction of the waste printed circuit boards. Although metallic fraction, as the most profitable component, is used to generate the revenue of the separation process, the nonmetallic fraction (NMF) has been left isolated. Herein, the recent developments in the application of NMF have been comprehensively reviewed and an eco-friendly emerging usage of NMF as a value-added material for sustainable remediation has been introduced.
•A review on the applications of nonmetallic fraction (NMF) of waste printed circuit boards (PCBs).•Examining the production and characterization of a novel adsorbent (A-NMF) from NMF.•Study on the ...heavy metal removal efficiency of A-NMF in single- and multi-component systems.•Best fit equilibrium isotherm modeling in single and binary component systems.
The recycling of waste printed circuit boards (PCBs) has become one of the global challenges in the technological era. The colossal volume of waste PCB generated annually coupled with its toxic nature and the existence of highly-precious metals in its composition intensifies the problems associated with waste PCB management and recycling. The two prevalent waste management options, landfill disposal and incineration, are being phased out for this special waste as a result of public health concerns. Hence, in the past few decades, several PCB recycling schemes are being introduced. The most efficient and environmentally-sound practice for waste PCB recycling has been the separation of metallic and nonmetallic fraction of PCBs by extensively-studied physico-mechanical approaches. Although the metallic fraction can be directly rendered into the market due to its high value, the nonmetallic fraction (NMF) is either disposed of in landfills causing secondary pollution or used as a low-value filler with the sole purpose of its safe disposal. This study presents a brief overview of the utilization of NMF as a filler in various industries. The main objective of the present review is to thoroughly examine the novel, highly efficient application of NMF as precursor for the production of a mesoporous structured adsorbent and its application in the removal of a myriad of heavy metals in single- and multi-component systems. In addition, the effects of the operational parameters on the adsorption behavior of the adsorbent material have been provided. Moreover, a comprehensive overview of the adsorption system modelling for single and binary-component systems for this novel material has been compiled.
The removal of copper ions from wastewater has been studied using ion exchange with an iminodiacetate resin. The effects of agitation time, pH value of the solution, and initial concentration of the ...copper solution have been evaluated. It has been found that the equilibrium is obtained after 72 h. Also, the capacity of the resin for the copper ions has been determined to be 2.2 mmol/g by measuring the equilibrium isotherm at a pH value of 5.0. When the pH value of the solution is lower than 3.2, the adsorption capacity of the resin is reduced drastically. It has been verified that the Langmuir-based isotherm models are the best-fit models for the equilibrium isotherm system. A series of fixed bed column runs have been performed to remove copper from solution and study the effects of solution flow rate, initial copper concentration, and resin particle size. The empty bed residence time model, EBRT, has been used to correlate the fixed bed pilot plant experimental results. The original form of the EBRT model was modified using a time dependent bed depth adsorption capacity to determine the bed exhaustion rate in order to improve the original model which utilized the equilibrium adsorption capacity. The modified model demonstrates that the EBRT can be used to more accurately model copper removal using the chelating ion exchange resin.
Simultaneous removal of heavy metals coupled with high adsorption capacity of an adsorbent material is an ultimate target in industry for the purification of wastewater. A novel adsorbent prepared ...from an electronic waste-based material has been used for this purpose. The results exhibit very high removal capacities of the adsorbent for both cobalt and nickel in the single-component systems. These capacities have been compared with those of three widely-used industrial adsorbents and it has been shown that the removal capability of this novel material is well above those of the industrial ones. Moreover, the effect of pH has also been explored and it has been shown that the pH value has a drastic effect on the metal removal capacity at pH values lower than 3. Furthermore, a synergistic effect of two metals has been observed and studied in the binary metal system. The results indicate that not only the simultaneous presence of the two metals does not reduce the adsorption capacity, but also enhances their removal from the effluent.
In this study, the effects of activation time and temperature, as two of the most prominent parameters affecting the porous structure of the carbonaceous materials, have been evaluated. It has been ...demonstrated that increasing the activation degree enhances the porous structure of the prepared activated carbons. The Methylene Blue (MB) adsorption capacity of the activated carbon with the highest surface area has been determined to be higher than that of a commercial activated carbon, F400, although the surface areas of these two adsorbents are very close. It has been attributed to the higher “effective” surface area of the former adsorbent and thus accessibility of more pores for dye adsorption. Also, the mechanism of Methylene Blue adsorption by tyre char activated carbon has been elucidated by isotherm modeling. It has been demonstrated that since the exponent of the best-fit isotherm model, Redlich–Peterson, approaches unity, a monolayer dye adsorption on a surface with homogeneous active sites can be assumed. Considering the MB adsorption capacities of the produced activated carbons, the MB molecule size and the effective surface areas of the adsorbents, the MB coverage factors have been calculated and the possible MB adsorption orientation has been proposed and modeled.
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