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•Sustainable hydrothermal synthesis of zeolite from kaolinite.•Factors affecting the hydrothermal synthesis of zeolite from kaolinite.•Optimal conditions for the hydrothermal ...synthesis of zeolites from kaolinite.
Synthesis of zeolite through hydrothermal process has been commonly used for decades. However, it does not satisfy the serious terms of sustainability that leads to reduction of costs, reduction of waste, eliminating negative environmental impacts and improvement of any system efficiency. The bottom line of this review paper is to highlight the current trends in the hydrothermal synthesis of zeolite, attention is paid to the utilization of natural resources and manufacturing wastes as raw materials to synthesize zeolite. Optimum conditions for sustainable hydrothermal synthesis of zeolites from kaolinite natural resources are also studied and discussed in this paper.
Tapping into solar energy seems to be a viable and sustainable solution for the ongoing global challenges of water scarcity and clean energy shortage. However, the natural mechanism of solar ...energy-driven water evaporation is often compromised by low evaporation rate and water and solar absorption spectrum mismatch. Therefore, localized heating on the water vapor-liquid interface by light-absorbing materials, known as photothermal materials, has been proposed. This allows the harvesting of energy from the full solar spectrum and high efficiency of light-to-heat conversion. With the emerging advances of photothermal nanomaterials and the urgent demand for a green transition of water treatment technology, the establishment of a photothermal-driven membrane distillation system has been reinvigorated, as seen by the number of publications recently. The efficiency of light absorption and light-to-heat conversion of photothermal materials are critical factors in determining the membrane performances. This review aims to assess the state-of-the-art photothermal materials, including innovative modifications that have been made. The second part is devoted to the emerging aspects and new directions of using these photothermal materials for the development of photothermal membranes. Lastly, the prospects of photothermal membrane for clean water production in the near future are also discussed.
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•There is an urgent demand for a green transition of water treatment process.•The state-of-the-art of photothermal materials is discussed.•The utilization of photothermal membrane for various applications is highlighted.•Photothermal membranes for water-energy-environment nexus•Prospect of photothermal membrane for water reclamation and purification
•It is attempted to provide critical considerations on various biogas upgrading techniques.•Membrane is an environmentally and economically sound technique for purification.•Purified biogas in ...compressed form is a substitute of compressed natural gas for vehicles.•Charged mass and compressor input work are the most important factors for storage.
Biogas upgrading is a widely studied and discussed topic and its utilisation as a natural gas substitute has gained a significant attention in recent years. The production of biomethane provides a versatile application in both heat and power generation and as a vehicular fuel. This paper systematically reviews the state of the art of biogas upgrading technologies with upgrading efficiency, methane (CH4) loss, environmental effect, development and commercialisation, and challenges in terms of energy consumption and economic assessment. The market situation for biogas upgrading has changed rapidly in recent years, making the membrane separation gets significant market share with traditional biogas upgrading technologies. In addition, the potential utilisation of biogas, efficient conversion into bio-compressed natural gas (bio-CNG), and storage systems are investigated in depth. Two storing systems for bio-CNG at filling stations, namely buffer and cascade storage systems are used. The best storage system should be selected on the basis of the advantages of both systems. Also, the fuel economy and mass emissions for bio-CNG and CNG filled vehicles are studied. There is the same fuel economy and less carbon dioxide (CO2) emission for bio-CNG. Based on the results of comparisons between the technical features of upgrading technologies, various specific requirements for biogas utilisation and the relevant investment, and operating and maintenance costs, future recommendations are made for biogas upgrading.
The overgeneration of non-biodegradable waste in Indonesia requires empty lands for landfilling, which contravenes with the landscape of sustainable cities. As local landfills have become ...overburdened, the solid waste is disposed of in uncontrolled manners that seriously affect public health and the environment. To address this problem, Indonesian gradually moves towards digitalization for waste recycling. To reflect its novelty, this work investigates how to add economic value to recycled waste using digital technology and how economic incentives can be promoted to avoid generating waste. The roles and implications of digitalization on resource recovery are elaborated from Cleaner Production perspectives. As a driving force of social innovation, it was found that the digital transformation of waste industry encouraged community in Yogyakarta to sell waste online via Rapel app installed in their smartphones. On average, customers sell their waste nearly 15 kg per transaction and earn USD 0.1/kg as a point balance. When their waste ranges from 15 to 20 kg, the sellers get USD 1.4. Recovering polyethylene (PET) bottles via a mixed-recyclables could yield about USD 150–300/Mt, while a bottle-only collection ranges from USD 360 to 590/Mt. As the implications of this study, digitalization has created new jobs (780 waste collectors) in Yogyakarta (@20 persons/subdistrict). Digitalization in waste management also promotes waste avoidance up to 65%. Potential monthly turnover from the waste recycling's transaction through the app is about USD 2,000/waste bank. Overall, the findings imply that the digital transformation in the waste sector not only promotes the resource recovery of non-biodegradable waste for a circular economy, but also enables local community to do online transactions of recycled goods through mobile-based applications. By moving towards digitalization, it is projected that the country's waste recycling industry would create over 120,000 new jobs and absorb about 3.3 million informal workers such as waste collectors.
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•Digitalization enables industry to recover valuable materials in waste streams.•When their waste ranges from 15 to 20 kg, sellers get USD 1.4.•Digitalization of non-biodegradable waste promoted waste avoidance up to 65%.•Potential monthly turnover in the online platform was about US$ 2,000/waste bank.
This article reviews the various techniques of immobilizing a photocatalyst into and onto the polymer membrane for pollutant removal and as a problem solver in handling suspended photocatalyst issues ...from the previous literature. A particular focus is given to the preparation of mixed matrix membranes and deposition techniques for photocatalytic degradation in applications for wastewater treatment. Advantages and disadvantages in this application are evaluated. Various operating conditions during the process are presented. About 90 recently published studies (2008-2020) are reviewed. From the literature, it was found that TiO
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is the most favoured photocatalyst that is frequently used in photocatalytic water treatment. Dry-wet co-spinning and sputtering techniques emerged as the promising technique for immobilizing a uniformly distributed photocatalyst within the polymeric membrane, and exhibited excellence pollutant removal. In general, the technical applicability is the key factor in selecting the best photocatalyst immobilizing technique for water treatment. Finally, the scope of various techniques that have been reviewed may provide potential for future photocatalytic study.
This article reviews the various techniques of immobilizing a photocatalyst into and onto the polymer membrane for pollutant removal and as a problem solver in handling suspended photocatalyst issues from the previous literature.
In China, environmental pollution due to municipal solid waste (MSW) over-generation is one of the country’s priority concerns. The increasing volume and complexity of the waste poses serious risks ...to the environment and public health. Currently, the annual growth of MSW generation is estimated to be approximately 8–10% and will increase to 323 million metric tons (Mt) by 2030. Based on the secondary data collected from a literature survey, this article critically evaluates the recent progress of MSW management (MSWM) in China and offers new insights into the waste sector in the era of Industry 4.0. This helps decision makers in China to plan a smooth transition nationwide to a circular economy (CE) in the waste sector. It is evident that digitalization is a driving force for China to move towards low-carbon development strategies within the framework of CE. Through digitalization, the waste sector has promoted prevention, reduction, reuse, and recycling (3Rs) of waste before waste disposal in landfills. A proper implementation of digitalization-based waste recycling has contributed to an efficient cooperation between the government and private sector, increased job opportunities, and promoted the conservation of resources. It is anticipated that this work not only contributes to the establishment of an integrated MSWM system in China, but also improves local MSWM through digitalization in the framework of a CE.
•Rosa damascene was an effective biosorbent for heavy metal removal.•Functional groups of the biosorbent were involved in metal adsorption.•Metal adsorption capacities were 97.68 mg/g for Pb(II) and ...90.8 mg/g for Cd(II).•Metal adsorption by R. damascene followed the Langmuir and Elovich models.
Due to their toxicity to public health, the presence of inorganic pollutants in the aquatic environment have become a global concern. This work investigates the technical feasibility of R. damascena waste as a biosorbent (RWB) in batch studies for the removal of Cd(II) and Pb(II) from synthetic wastewater. The biomass waste is abundantly available from rose oil industries in Lahore (Pakistan). To improve its treatment performance for metals removal, the biomass waste is pretreated with H2SO4 and NaOH, respectively. To understand the roles of functional groups on the RWB during biosorption, Fourier Transform infrared (FT-IR) spectroscopy and scanning electron microscope (SEM) analyses were used to compare its surface area before and after adsorption. At the same initial metal concentration of 25 mg/L, it was found that the chemically modified R. damascena could remove 95% and 91% of Pb(II) and Cd(II), respectively, under the optimum conditions: pH 6.5, reaction time: 2 h, 10 g/L of dose, and 120 rpm of shaking speed. Its metal adsorption capacities were 24.9 and 24.8 mg/g for Pb(II) and Cd(II), respectively. The Langmuir isotherm was applicable to simulate the adsorption of both target metals, while the pseudo-second order fitted well their kinetics. The characterization results implied the roles of certain functional groups of the biosorbent as electron donors. This indicates that H-bonding was involved in the chemisorption of target metals by the biosorbent. In spite of their encouraging findings, treated effluents were still unable to meet the required discharge limits of 0.05 and 0.005 mg/L for Pb(II) and Cd(II), respectively, mandated by local legislation. This reveals that another subsequent treatment using biological process such as activated sludge is required to complement their removal from wastewater samples. Overall, this work reveals the applicability of R. damascena waste as a biosorbent for heavy metal removal.
Hydrogen has received significant attention as a carbon-free energy carrier for power generation. Water is an environmentally-benign source for hydrogen production either through electrolysis or ...catalytic splitting, and the latter has a relatively low equilibrium constant. Coupling catalytic water splitting with a mixed ionic–electronic conducting (MIEC) membrane reactor has been demonstrated as a very promising approach to enhance the hydrogen production rate by extracting the oxygen produced. This review provides a comprehensive coverage of critical aspects included in this process, including membrane materials, structure, morphology, catalysts, and operating conditions for water splitting. Moreover, process intensification can be further achieved by integrating methane-related oxidation reactions to facilitate oxygen removal, so as to improve the hydrogen production rate. Some trends for future development have also been summarized.
The application of low cost ceramic membrane from kaolin has attracted much interest due to its excellent mechanical stability, chemical and thermal resistivity and most importantly, because it is ...cost effective, in some cases, compared to polymeric membranes. The advantage of kaolin based ceramic membrane is its thermal properties that allow sintering at much lower temperature than alumina. Although many studies have been made on the application of kaolin based ceramic membranes, detailed discussions were scarcely made and the information on the fabrication of ceramic membrane from kaolin is very limited. This article is aimed to make a comprehensive review on ceramic membrane from kaolin for its fabrication methods and applications. An attempt is also made to show the future direction of the R and D on the kaolin based ceramic membrane.
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•Magnetic biochar was prepared from Fe-enriched sludge without any modification.•Sludge biochar prepared at 900 °C temperature enhanced Cr(VI) removal.•Maximum Cr removal by sludge ...biochar was attained at pH 6.8.•Interfering ions were SO42− and NO3− that co-existed with Cr(VI) in wastewater.•α-Fe0 in sludge biochar facilitated the reduction and adsorption of Cr(VI).
In this work, inexpensive biochar derived from different feedstock was synthesized, characterized, and tested for Cr(VI) removal from synthetic wastewater. The physical properties of the sludge-based magnetic biochars (SSB) were analyzed using FT-IR, XRD, BET surface area, SEM-EDS, and XPS techniques. The effects of pyrolysis temperature (300–900 ℃), initial Cr(VI) concentration (2–30 mg/L), rotation speed (50–200 rpm), pH (3–11), and co-ions (Na+, Ca2+, Mg2+, K+, Cl−, HCO3− and SO42−) on Cr(VI) removal by the SSB were determined in batch modes. It was found that the SSB had the highest Cr(VI) removal (43.7%), as compared to the other feedstock-derived biochars (p ≤ 0.05; Anova test). The characterization data indicated that with an increasing pyrolysis temperature from 300 to 900℃, the surface area, pore volume, and pore size decreased, while the Fe3O4 on SSB was gradually reduced to α-Fe0. With respect to Cr(VI) removal, under the optimized conditions of 900℃ of pyrolysis temperature, 2 mg/L of Cr(VI) concentration, 200 rpm of agitation speed, and pH 6.8, a complete Cr(VI) removal could be attained by the SSB900. Its treated effluents could comply with the required Cr(VI) discharge limit of <0.01 mg/L (GB3838-2002) mandated by local legislation. Therefore, further treatment was not required, avoiding additional cost. Coexisting ions experiments showed that all of them inhibited the Cr(VI) removal by the adsorbent after 1 h of reaction. The Cr(VI) removal followed the pseudo-second-order kinetics and the Langmuir isotherm model. The removal mechanism was based on the reduction of Cr(VI) by nZVI on the SSB900 and the Fe leakage might have facilitated the Cr(VI) removal. Overall, iron-enriched sewage sludge biochar is promising and cost-effective for treatment of low-level Cr(VI)-contaminated wastewater.
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