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Plastic waste accumulation has been recognized as one of the most critical challenges of modern societies worldwide. Traditional waste management practices include open burning, landfilling, and incineration, resulting in greenhouse gas emissions and economic loss. In contrast, emerging techniques for plastic waste management include microwave-assisted conversion, plasma-assisted conversion, supercritical water conversion, and photo reforming to obtain high-value products. Problems with poorly managed plastic waste are particularly serious in developing countries. This review article examines the emerging strategies and production of various high-value-added products from plastic waste. Additionally, the uses of plastic waste in different sectors, such as construction, fuel production, wastewater treatment, electrode materials, carbonaceous nanomaterials, and other high-value-added products are reviewed. It has been observed that there is a pressing need to utilize plastic waste for a circular economy and recycling for different value-added products. More specifically, there is limited knowledge on emerging plastic waste conversion mechanisms and efficiency. Therefore, this review will help to highlight the negative environmental impacts of plastic waste accumulation and the importance of modern techniques for waste management.

Menthol synthesis is possible through citral and citronellal hydrogenations via following multistage chemical reactions such as hydrogenation and cyclization. This research mainly focuses on a design of selective, active and cost-effective metal-acid (bifunctional) catalysts for menthol production via citral and citronellal hydrogenations. More specifically, Pd and Ni metals were impregnated over acidic support (e.g., hetero-poly acid supported montmorillonite, HPA_MM). The prepared catalysts were characterized by BET, pyridine adsorption and amine titration methods. Some of the most important parameters such as metal type and loading; applied pressure and reaction time have been investigated throughout this work. The obtained results reveals that the 8 wt% Ni-HPA-MM catalyst (Cat-5) has produced 63% menthols (initial reaction rate 0.126 mmol/min) from citral hydrogenation (80 °C, 1.0 MPa) within 24 h. Similarly, during lower applied pressure (0.5 MPa), the production of menthol was significantly improved (approximately 98% of menthol, initial reaction rate ~ 0.138 mmol/min) with the application of 8 wt% Ni-HPA-MM catalyst (Cat-5) in citronellal hydrogenation. Higher menthol selectivity was achieved from both reactions (citral and citronellal hydrogenation) which might be due to the presence of strong Lewis and medium Bronsted acid sites.

An air-breathing cathode electrocoagulation (ACEC) process with a sacrificial aluminum anode was used to treat arsenite (As(III)) from aqueous systems. Its performance was investigated by controlling operational parameters. As(III) removal efficiency of the ACEC increased from 81 to 86% with an increase in NaCl concentration from 10 to 20 mM. Furthermore, we were able to observe the oxidation of As(III) into its corresponding ions as well as the production of an aluminum oxide hydroxide in the form of boehmite. This study describes ACEC as one of the most energy-efficient treatment methods for As(III) removal based on its performance evaluation.

Airborne benzene is hazardous even at sub-ppm levels. Therefore, an effective strategy is required for its removal, such as the use of a sorbent with large adsorption capacity or high breakthrough volume. To meet the goal, the performance for the removal of benzene was assessed by loading benzene at 5 Pa inlet partial pressure against seven types of biowaste-derived biochar: (1) paper mill sludge, (2) conventional biochar with magnetic properties, (3) biochar composites with carbon nanotubes (CNTs), (4) gasification biochar from mixed feedstock, (5) gasification biochar from a single feedstock, (6) modified gasification biochar, and (7) activated carbon (AC) as a reference. The 298 K maximum adsorption capacities (mg g−1), when measured at a benzene inlet pressure of 5 Pa (or 50 ppm in ultrapure nitrogen) and flow rate of 50 mL atm min−1, varied widely for different biochars, from 0.35 (MS: Swine manure + plastic mulch film waste) to 144 mg g−1 (XC-1: biochar from mixed feedstock); their 10% breakthrough volumes (BTV) were in the range of 0.22–492 L g−1, respectively. The experimental data (capacity vs. benzene outlet partial pressure) could be fitted to either two or three linearized Langmuir isotherms with distinctive sorption mechanisms ((1) a retrograde region (Type III isotherm: 0 to ∼0.2 Pa), (2) an intermediate pressure region (0.2 and 2.0 Pa), and (3) a higher pressure region (>2 Pa)) which was also confirmed similarly by Freundlich, Dubinin–Radushkevich, and Elovich fitting. About 65% of the maximum capacity was achieved in the retrograde region. The strongest biochar sorbent, XC-1, showed similar performance as activated carbon to prove its feasibility toward air quality management (AQM) applications.

Metal-air fuel cell electrocoagulation is one of the most cost-effective and innovative treatment options for metals in water. Here, the removal mechanism of chromium (Cr(VI)) was assessed using an iron-air fuel cell electrocoagulation (IAFCEC) system. Simultaneously, the effects of such treatment were also investigated with respect to a list of parameters controlling groundwater quality. During the IAFCEC operation, in-situ production of stable iron hydroxides (e.g., maghemite, hematite, and goethite) was experienced due to the sacrificial oxidation of the iron anode electrode. Therefore, these iron hydroxides were responsible for direct co-precipitation of aqueous Cr(VI). The removal efficiency of the system was assessed by varying the initial concentrations of Cr(VI) such as1, 5, and 10 mg L−1). The IAFCEC, when operated with low concentrations of competing anions (e.g., silicate, phosphate, magnesium, and calcium), was capable of treating 6 L of water containing 1 mg L−1 Cr(VI) per day with an operating cost of 0.2 USD m−3. This study demonstrates the IAFCEC as one of the most cost-effective treatment methods for Cr(VI) removal based on evaluation of performance relative to other options commonly available.

There is growing interest in advanced, novel water treatment technologies that are simple, cheap, and highly efficient for removal of pollutants because of the widespread pollution of fresh water sources accompanied by the increase in the world's population. Thus, one of the most persistent challenges in the 21st century is to develop adequate clean water supply technologies for natural aquifers that are contaminated by various pollutants, e.g., arsenic (As). Electrocoagulation (EC) is a promising and efficient electrochemical process for nutrient recovery and remediation of a wide range of contaminants including heavy metals and organic matter. However, its large electric consumption is considered a main limiting factor. Further, the formation of an oxide (or passivation) layer on the metal anode electrode surface may reduce removal efficiency. The addition of gelatinous hydroxide (as a supporting electrolyte) is also required to increase solution conductivity. Recently, an alternative approach known as metal-air fuel cell electrocoagulation (MAFCEC) was proposed to address many shortcomings related to conventional EC process. This combined concept of EC and a fuel cell was effectively optimized to treat As contained in water. This review was organized to describe MAFCEC as one of the most energy-effective treatment methods for As based on a performance evaluation and a comparison to other relevant options. This review will help in the development of sustainable, cost-effective, and efficient technologies for removal of pollutants.

The implementation of sustainable industrial development based on energy/cost-effective techniques with zero/low rate of pollutant emission is an ideal strategy for the proper management of a natural environment. Gaseous ammonia released from a variety of anthropogenic sources (e.g., agriculture, pharmaceuticals, commercial cleaning products, and refrigerant) is estimated to be as high as 150 million tons∙year

Commercial membranes typically suffer from fouling and wetting during membrane distillation (MD). In contrast, reverse osmosis (RO) can be subject to the fouling issue if applied for highly saline feed solutions containing foulants (e.g., organics, oils, and surfactants). Among the diverse treatment options, the nanomaterial-based membranes have recently gained great interest due to their advantageous properties (e.g., enhanced flux and roughness, better pore size distribution, and higher conductivity). This review focuses on recent advances in the mechanical properties, anti-fouling capabilities, salt rejection, and economic viability of metal oxide (SiO2, TiO2, and ZnO) and carbon nanomaterial (graphene oxide/carbon nanotube)–based membranes. Current challenges in applying nanomaterial-based membranes are also discussed. The study further describes the preparation methods, mechanisms, commercial applications, and economical feasibility of metal oxide– and carbon nanomaterial–based membrane technologies.

The thermochemical conversion of different feedstocks is a technology capable of reducing the amount of biowaste materials produced. In addition, the gasification of feedstock using steam as a gasifying agent also produces hydrogen, which is a clean energy fuel. This article aimed to encapsulate the current status of biowaste gasification and to explain, in detail, the advantages and limitations of gasification technologies. In this review paper, different gasifying agents such as steam, air, and oxygen, as well as their effects on the quality of syngas production, are discussed. In addition, the effects of reactor configuration and different operating parameters, such as temperature, pressure, equivalence ratio, and incorporation of a catalyst, as well as their effects on the ratio of H2/CO, LHV, syngas yield, and tar production, were critically evaluated. Although gasification is a sustainable and ecologically sound biomass utilization technology, tar formation is the main problem in the biomass gasification process. Tar can condense in the reactor, and clog and contaminate equipment. It has been shown that an optimized gasifier and a high-activity catalyst can effectively reduce tar formation. However, key biowaste treatment technologies and concepts must first be improved and demonstrated at the market level to increase stakeholder confidence. Gasification can be the driving force of this integration, effectively replacing fossil fuels with produced gas. In addition, support policies are usually needed to make the integration of biomass gasification technology into the industry profitable with fully functional gasification plants. Therefore, to address such issues, this study focused on addressing these issues and an overview of gasification concepts.

Aluminum–air fuel cell electrocoagulation was evaluated for arsenate removal during power production. Effects of operational parameters (type and concentration of individual and mixed supporting electrolytes and initial pH) were investigated. 1 mg L −1 arsenate in 1 L of anolyte (with 10 mM NaCl) was reduced to 1 μg L −1 in 4 h, power density produced was 112 mW/m 2 . 8 mM Na 2 SO 4 mixed with 10 mM NaCl created optimal conditions as mixed supporting electrolyte. Power density increased to 308 mW/m 2 and arsenate was reduced to 15 μg L −1 after 24 h. This indicates aluminum–air fuel cell electrocoagulation is useful treatment process.

Electrocoagulation with an iron-air fuel cell is an innovative arsenate removal system that can operate without an external electricity supply. Thus, this technology is advantageous for treating wastewater in remote regions where it is difficult to supply electricity. In this study, the possibility of real applications of this system for arsenate treatment with electricity production was verified through electrolyte effect investigations using a small-scale fuel cell and performance testing of a liter-scale fuel cell stack. The electrolyte species studied were NaCl, Na2SO4, and NaHCO3. NaCl was overall the most effective electrolyte for arsenate treatment, although Na2SO4 produced the greatest electrical current and power density. In addition, although the current density and power density were proportional to the concentrations of NaCl and Na2SO4, the use of concentrations above 20 mM of NaCl and Na2SO4 inhibited arsenate treatment due to competition effects between anions and arsenate in adsorption onto the iron hydroxide. The dominant iron hydroxide produced at the iron anode was found to be lepidocrocite by means of Raman spectroscopy. A liter-scale four-stack iron-air fuel cell with 10 mM NaCl electrolyte was found to be able to treat about 300 L of 1 ppm arsenate solution to below 10 ppb during 1 day, based on its 60-min treatment capacity, as well as produce the maximum power density of 250 mW/m2.

Dual-chambered fuel cells with an iron anode and an air-carbon cathode separated by an ion exchange membranes have been used to treat arsenate during power production. To select an effective catholyte, the dual-chambered fuel cell consisted 90 mL of 0.1 M HCl or 0.5 M NaCl as the catholyte and 1 L of 0.1 M NaHCO3 as the anolyte at an initial pH 5. The 0.1 M HCl was an effective catholyte, with which 1 ppm arsenate in 1 L of anolyte was reduced to 5 ppb in 1 h, and the maximum power density was about 6.3 w/m2 with an anion exchange membrane fuel cell (AEM_FC) and 4.4 w/m2 with a cation exchange membrane fuel cell (CEM_FC). Therefore, 90 mL of 0.1 M HCl was used as a catholyte to treat 20 L of 0.1 M NaHCO3 anolyte containing 1 ppm arsenate at an initial pH of 5 or 7. The arsenate level at pH 5 decreased to less than 5 ppb in 4 h, and the maximum power density was 5.9 W/m2 and 4.7 W/m2 with AEM_FC and CEM_FC, respectively. When using 0.01 M NaHCO3 as the anolyte at pH 5, arsenate was reduced to less than 5 ppb in 8 and 24 h for AEC_FC and CEM_FC, respectively. However, when using an anolyte at pH 7, arsenate could not be effectively removed in 24 h. Therefore, when using carbonate as an anolyte, the solution should be adjusted to a weakly acidic pH in order to remove arsenate.

Petroleum processing wastewater (PPW) is a complex mixture of free, soluble, and emulsive hydrocarbons that often contain heavy metals and/or solid particles. As these hazardous constituents can accumulate in human beings and the environment, exposure to the PPW can have harmful effects in various respects. The use of environmental nanotechnologies (E-Nano) is considered an attractive option to resolve the problems associated with PPW. Among different treatment technologies, E-Nano-based sorption (adsorption/absorption) and membrane filtration approaches have been proven to have outstanding efficacy in remediation of PPW pollutants. It is, however, crucial to determine the appropriate technological option (e.g., low-cost operational conditions) for the practical application of such technologies. In this review, the potential of E-Nano-based sorption and membrane technologies in the treatment of various PPW pollutants is discussed based on their performances in comparison to traditional technologies. Their suitability is evaluated further in relation to their merits/disadvantages and economic feasibility with the goal of constructing a perspective map to efficiently implement the E-Nano technologies.

Covalent-organic polymers (COPs) are recognized for their great potential for treating diverse pollutants via adsorption. In this study, the sorption behavior of benzene and toluene was investigated both individually and in a binary mixture against two types of COPs possessing different –NH2 functionalities. Namely, the potential of COPs was tested against benzene and toluene in a low inlet partial pressure range (0.5–20 Pa) using carbonyl-incorporated aromatic polymer (CBAP)-1-based diethylenediamine (EDA) [CD] and ethylenetriamine (DETA) [CE]. The maximum adsorption capacity and breakthrough values of both COPs showed dynamic changes with increases in the partial pressures of benzene and toluene. The maximum adsorption capacities (Amax) of benzene (as the sole component in N2 under atmospheric conditions) on CD and CE were in the range of 24–36 and 33–75 mg g−1, respectively. In contrast, with benzene and toluene in a binary mixture, the benzene Amax decreased more than two-fold (range of 2.7–15 and 6–39 mg g−1, respectively) due to competition with toluene for sorption sites. In contrast, the toluene Amax values remained consistent, reflecting its competitive dominance over benzene. The adsorption behavior of the targeted compounds (i.e., benzene and toluene) was explained by fitting the adsorption data by diverse isotherm models (e.g., Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich). The current research would be helpful for acquiring a better understanding of the factors affecting competitive adsorption between different VOCs in relation to a given sorbent and across varying partial pressures.

The aim of this work was to develop the scale-up microbial fuel cell technology for actual ethanolamine wastewater treatment, dual anode/cathode MFC stacks connected in series to achieve any desired current, treatment capacity, and volume capacity. However, after feeding actual wastewater into the MFC, maximum power density decreased while the corresponding internal resistance increased. With continuous electricity production, a stack of eight MFCs in series achieved 96.05% of COD removal and 97.30% of ammonia removal at a flow rate of 15.98L/d (HRT 12h). The scaled-up dual anode/cathode MFC stack system in this research was demonstrated to treat actual ETA wastewater with the added benefit of harvesting electricity energy.

The potential use of activated carbon (AC) as an inexpensive and effective alternative sorbent material in thermal desorption is presented and validated for the analysis of aromatic volatile organic compounds (VOCs) such as benzene, toluene, m-xylene, and styrene (BTXS) in air. The optimum desorption conditions of an AC sampling tube (2 mg AC bed) were determined and compared with a commercial three-bed (Carbopack; C + B + X) tube sampler as a reference. The AC sampler exhibited good linearity (R2 > 0.99) and reproducibility (RSE of 2.38 ± 0.21%) for BTXS analysis. The AC tube sampler showed good storability (up to 3 d) and excellent recyclability (up to 50 cycles). An analysis of BTXS in ambient air showed excellent agreement between AC and CBX (bias AC as a suitable medium for sampling VOCs as reliable as high-cost commercial sorbent products.

A microbial fuel cell (MFC) with biological Fe(III) reduction was implemented for simultaneous ethanolamine (ETA) degradation and electrical energy generation. In the feasibility experiment using acetate as a substrate in a single-chamber MFC with goethite and ammonium at a ratio of 3.0(mol/mol), up to 96.1% of the ammonium was removed through the novel process related to Fe(III). In addition, the highest voltage output (0.53V) and maximum power density (0.49Wm(-2)) were obtained. However, the ammonium removal and electrical performance decreased as acetate was replaced with ETA. In the long-term experiment, the electrical performance markedly decreased where the voltage loss increased due to Fe deposition on the membranes.

BACKGROUND The objective of this study was to investigate the feasibility of developing an integrated bio-electrochemical system for the removal of ethanolamine from wastewater by combining an Fe(III)-based microbial fuel cell (MFC) with a continuous Fe(II) oxidation system for simultaneous oxidation and reduction of iron in the same compartment. The ethanolamine in the Fe(III)-based MFC can be effectively converted to electrical energy by using the catalytic activity of microorganisms. In this respect, the authors investigated whether the introduction of a system for Fe(III) regeneration could enhance the sustainability of both power generation and the removal of ethanolamine in this integrated system. RESULTS The experimental results obtained with a traditional Fe(III)-based MFC, operated with a ferric sulfate solution of 25 or 50 mmol L−1 Fe(III) mixed with ethylenediaminetetraacetic acid (EDTA) solution of 10 mmol L−1, showed that increasing the Fe(III) concentration leads to improved performance of the MFC; the maximum power density, open circle voltage (OCV), and Coulombic efficiency (CE) were all improved. However, the effluents from the cathode chamber contained a low concentration of Fe(III) due to deficient regeneration of Fe(III). In the integrated bio-electrochemical system developed in this work (enhanced Fe(III)-based MFC), the generated Fe(II) was oxidized at the air cathode via favorable oxygen diffusion and a Fe(II)-based fuel cell (FC). CONCLUSION Electricity was sustainably generated from the enhanced MFC with 25 mmol L−1 Fe(III); the highest performance, in terms of maximum power density, OCV and CE, was achieved using 50 mmol L−1 Fe(III), thus indicating the increased efficiency of this integrated system. © 2015 Society of Chemical Industry

Sustainable development and the restoration of ecosystems are the important goals for civilization. Currently, heavy metal contamination of aquatic environments has become a serious issue. Chromium (Cr) is simultaneously an essential metallic element and one of 20 chemicals posing a maximum threat to living beings. To mitigate that threat, various treatment methods have been developed, including adsorption, electrocoagulation, photoelectrocatalysis, fuel cells, bioremediation, chemical precipitation, ultrafiltration, ion exchange, and co-precipitation. However, selection of the most energy- and cost-efficient wastewater treatment option has proven challenging, as each approach is subject to shortcomings involving energy consumption, treatment capacity, and efficiency. This review describes the potential role of diverse functional nanomaterials (e.g., iron/iron oxide nanoparticles, carbon nanostructures, metal organic frameworks, and their commercial counterparts) in treatment of Cr in aqueous environments with respect to key figure of merits, such as, adsorption capacity, removal efficiency, and partition coefficient. In addition, their performance was compared with the most common treatment options. The results of this study will help determine the most effective and economical options for control of Cr in aquatic environments. Keywords: Cr(VI) removal, Adsorption, Electrocoagulation, Photoelectrocatalysis, Fuel cell, Performance evaluation

Dual-chambered fuel cells with an iron anode and an air-carbon cathode separated by an ion exchange membranes have been used to treat arsenate during power production. To select an effective catholyte, the dual-chambered fuel cell consisted 90 mL of 0.1 M HCl or 0.5 M NaCl as the catholyte and 1 L of 0.1 M NaHCO