NOx removal and copper recovery from the leaching process for waste printed circuit boards: performance evaluation and potential environmental impact assessment.

Resource recovery is crucial for small- and medium-sized enterprises to attain a circular economy. The economic benefits of recovering precious metals from electronic waste, such as waste printed circuit boards (WPCBs), are hindered by secondary pollutant emissions from pretreatment processes. This study aims to recover copper from the WPCB acid leaching process and reduce NOx emissions through the use of a high gravity rotating packed bed (RPB). The results indicate that the copper recovery ratio increases to 99.75% through the displacement reaction between iron powder and copper nitrate. The kinetic analysis of copper dissolution was employed to simulate the NOx emissions during acid leaching, with an R-squared value of 0.872. Three oxidants, including H2O2(aq), ClO2(aq), and O3(g), with pH adjusted to different NaOH concentrations, were used to remove NOx. The greatest NOx removal rate was achieved using a 0.06 M NaOH solution, with a removal rate of 91.2% for ozone oxidation at a 152-fold gravity level and a gas-to-liquid (G/L) ratio of 0.83. The gas-side mass transfer coefficients (KGa) for NOx range from 0.003 to 0.012 1/s and are comparable to previous studies. The results of a life cycle analysis indicate that the NOx removal rate, nitric acid recycling rate, and copper recovery rate are 85%, 80%, and 100%, respectively, reducing the environmental impact on the ecosystem, human health, and resource depletion by 10% compared to a scenario with no NOx removal.

Synthesis of Calcium Peroxide Nanoparticles with Starch as a Stabilizer for the Degradation of Organic Dye in an Aqueous Solution.

One of the most significant environmental problems in the world is the massive release of dye wastewater from the dyeing industry. Therefore, the treatment of dyes effluents has received significant attention from researchers in recent years. Calcium peroxide (CP) from the group of alkaline earth metal peroxides acts as an oxidizing agent for the degradation of organic dyes in water. It is known that the commercially available CP has a relatively large particle size, which makes the reaction rate for pollution degradation relatively slow. Therefore, in this study, starch, a non-toxic, biodegradable and biocompatible biopolymer, was used as a stabilizer for synthesizing calcium peroxide nanoparticles (Starch@CPnps). The Starch@CPnps were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET), dynamic light scattering (DLS), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM). The degradation of organic dyes, methylene blue (MB), using Starch@CPnps as a novel oxidant was studied using three different parameters: initial pH of the MB solution, calcium peroxide initial dosage and contact time. The degradation of the MB dye was carried out via a Fenton reaction, and the degradation efficiency of Starch@CPnps was successfully achieved up to 99%. This study shows that the potential application of starch as a stabilizer can reduce the size of the nanoparticles as it prevents the agglomeration of the nanoparticles during synthesis.

Synthesis of Controlled-Release Calcium Peroxide Nanoparticles Coated with Dextran for Removal of Doxycycline from Aqueous System.

Nanoscale calcium peroxide (nCP) has turned out to be one of the effective and environmentally friendly approaches for wastewater remediation purposes. The rapid hydrolysis of nCPs and burst oxygen release caused by the high surface-to-volume ratio of nCPs could surpass the appropriate demand for oxygenation and pollutant degradation in the aqueous system. Thus, coated oxidants (COs) have been prepared using polymeric materials to ensure long-term efficacy and slow-release capability. Therefore, the nCPs were first prepared using dextran as a stabilizer to prevent irreversible agglomeration by the chemical precipitation method and had an average mean size of 2.33 ± 0.81 nm. The synthesized nCPs were then coated with dextran to produce dextran-coated nCPs. Their characteristics and effectiveness in doxycycline (DOX) degradation were assessed. The characterization of nCPs and dextran-coated nCPs was performed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), fourier transform infrared spectroscopy (FTIR), Brunauer, Emmett and Teller analysis (BET), dynamic light scattering (DLS) and thermogravimetric analysis (TGA) techniques. This work suggests that dextran-coated nCPs are beneficial in wastewater treatment practice in terms of the long-term efficacy of DOX degradation potential.

Stabilization-solidification-utilization of MSWI fly ash coupling CO2 mineralization using a high-gravity rotating packed bed.

Municipal solid waste incineration fly ash (MSWI-FA) has been regulated as a hazardous waste that needs to treat with stabilization, solidification and landfill due to its amount of heavy metals, chlorides, sulfates and dioxin. While the proper treated MSWI-FA can be utilized as pozzolanic material to reduce the usage of Portland cement. The present article aims to develop an integrated wet-extraction and carbonation process for MSWI-FA stabilization, solidification and utilization via the high-gravity technology. A benchtop experiment demonstrated the dechlorination and CO2 sequestration of MSWI-FA and the carbonated product was applied as a supplementary cementitious material (SCM) in the cement mortar. Physical, chemical and thermal characteristics of raw, wet-extracted, and carbonated MSWI-FA were addressed in terms of the mean diameter, micropore area, micropore volume, chemical compositions, mineralogy and morphology. The effects of the liquid-to-solid ratio and high gravity factor were evaluated. Overall, a chloride extraction ratio of 36.35% and a CO2 capture capacity of 258.5 g-CO2 kg-FA-1 were achieved in the batch experiment. The results of water-energy consumption of chloride removal and CO2 fixation provided a novel insight into the future process criterion. In addition, the carbonated FA was found as binder to partially substitute Portland cement due to its large content of calcium carbonate. The workability and mechanical strength of cement mortar with partial substitution of stabilized FA were evaluated to determine the potential FA utilization pathway. Finally, the continuous process tests determined the key operation indexes for future process scale-up.

Source and sectoral contribution analysis of PM2.5 based on efficient response surface modeling technique over Pearl River Delta Region of China.

Identifying and quantifying source contributions of pollutant emissions are crucial for an effective control strategy to break through the bottleneck in reducing ambient PM2.5 levels over the Pearl River Delta (PRD) region of China. In this study, an innovative response surface modeling technique with differential method (RSM-DM) has been developed and applied to investigate the PM2.5 contributions from multiple regions, sectors, and pollutants over the PRD region in 2015. The new differential method, with the ability to reproduce the nonlinear response surface of PM2.5 to precursor emissions by dissecting the emission changes into a series of small intervals, has shown to overcome the issue of the traditional brute force method in overestimating the accumulative contribution of precursor emissions to PM2.5. The results of this case study showed that PM2.5 in the PRD region was generally dominated by local emission sources (39-64%). Among the contributions of PM2.5 from various sectors and pollutants, the primary PM2.5 emissions from fugitive dust source contributed most (25-42%) to PM2.5 levels. The contributions of agriculture NH3 emissions (6-13%) could also play a significant role compared to other sectoral precursor emissions. Among the NOX sectors, the emissions control of stationary combustion source could be most effective in reducing PM2.5 levels over the PRD region.

Real-time source contribution analysis of ambient ozone using an enhanced meta-modeling approach over the Pearl River Delta Region of China.

The nonlinear response of O3 to nitrogen oxides (NOx) and volatile organic compounds (VOC) is not conducive to accurately identify the various source contributions and O3-NOx-VOC relationships. An enhanced meta-modeling approach, polynomial functions based response surface modeling coupled with the sectoral linear fitting technique (pf-ERSM-SL), integrating a new differential method (DM), was proposed to break through the limitation. The pf-ERSM-SL with DM was applied for analysis of O3 formation regime and real-time source contributions in July and October 2015 over the Pearl River Delta Region (PRD) of Mainland China. According to evaluations, the pf-ERSM-SL with DM was proven to be effective in source apportionment when the traditional sensitivity analysis was unsuitable for deriving the source contributions in the nonlinear system. After diagnosing the O3-NOx-VOC relationships, O3 formation in most regions of the PRD was identified as a distinctive NOx-limited regime in July; in October, the initial VOC-limited regime was found at small emission reductions (less than 22-44%), but it will transit to NOx-limited when further reductions were implemented. Investigation of the source contributions suggested that NOx emissions were the dominated contributor when turning-off the anthropogenic emissions, occupying 85.41-94.90% and 52.60-75.37% of the peak O3 responses in July and October respectively in the receptor regions of the PRD; NOx emissions from the on-road mobile source (NOx_ORM) in Guangzhou (GZ), Dongguan&Shenzhen (DG&SZ) and Zhongshan (ZS) were identified as the main contributors. Consequently, the reinforced control of NOx_ORM is highly recommended to lower the ambient O3 in the PRD effectively.

Large-scale optimization of multi-pollutant control strategies in the Pearl River Delta region of China using a genetic algorithm in machine learning.

A scientifically sound integrated assessment modeling (IAM) system capable of providing optimized cost-benefit analysis is essential in effective air quality management and control strategy development. Yet scenario optimization for large-scale applications is limited by the computational expense of optimization over many control factors. In this study, a multi-pollutant cost-benefit optimization system based on a genetic algorithm (GA) in machine learning has been developed to provide cost-effective air quality control strategies for large-scale applications (e.g., solution spaces of ~1035). The method was demonstrated by providing optimal cost-benefit control pathways to attain air quality goals for fine particulate matter (PM2.5) and ozone (O3) over the Pearl River Delta (PRD) region of China. The GA was found to be >99% more efficient than the commonly used grid searching method while providing the same combination of optimized multi-pollutant control strategies. The GA method can therefore address air quality management problems that are intractable using the grid searching method. The annual attainment goals for PM2.5 (< 35 µg m-3) and O3 (< 80 ppb) can be achieved simultaneously over the PRD region and surrounding areas by reducing NOx (22%), volatile organic compounds (VOCs, 12%), and primary PM (30%) emissions. However, to attain stricter PM2.5 goals, SO2 reductions (> 9%) are needed as well. The estimated benefit-to-cost ratio of the optimal control strategy reached 17.7 in our application, demonstrating the value of multi-pollutant control for cost-effective air quality management in the PRD region.

Implementation of green chemistry principles in circular economy system towards sustainable development goals: Challenges and perspectives.

Green chemistry principles (GCP) are comprehensively deployed in industrial management, governmental policy, educational practice, and technology development around the world. Circular economy always aims to balance the economic growth, resource sustainability, and environmental protection. This article offers a highlight on issues of significance within GCP and circular economy, and proposes the integrated strategies for GCP implementation from the aspects of governance, industry and education. At first, we developed a new categorizing system for GCP dividing to (i) pollution and accident prevention, (ii) safety and resource sustainability, and (iii) energy and resource sustainability. To assess the GCP practice towards the circular economy, the implementation of international movement of GCP in worldwide policy, especially those of Canada, China, Germany, Japan, South Korea, Sweden, Taiwan, United States and United Kingdom were reviewed. The policy implementation of GCP practices among governance, industries and education was analyzed. To integrate GCP into the circular economy concept, we also proposed five strategies of priority governance direction as follows: (i) establishment of cross-departmental collaboration, (ii) development of cleaner production and green product, (iii) provision of integrated chemical management system, (iv) implementation of green chemistry education program, and (v) construction of a business model. Finally, we discussed the prospects of disciplinary elements including the establishment of redesign-reduction-recovery-recycle-reuse (5R) practices for wastes reclamation, deployment of water-energy-food nexus with GCP to improve the food security and resource sustainability, and implementation of GCP in the green smart industrial park.

Removal of fine particles from IC chip carbonization process in a rotating packed bed: Modeling and assessment.

A high-gravity rotating packed bed (HiGee RPB) is very efficient at removing pollution because it exerts a strong high centrifugal and allows tiny droplets to form, which allows the control of gaseous and particulate air pollution. In this study, fine particles that are removed from integrated circuit (IC) chip carbonization process using a RPB are evaluated under different high gravity factors and liquid-to-gas ratios. The greatest number of particles captured per energy consumption is 17.77 mg kWh-1 in a RPB. This allow greater energy efficiency for the HiGee technology prevents an air-energy nexus. The maximum available particle removal efficiency for a RPB is determined using a response surface model (RSM). 99.5% of particles are removed at a high gravity factor of 262 and a liquid-to-gas ratio of 0.24. A semi-theoretical model is developed to determine the particle removal efficiency individually in packing and cavity zones of the RPB. More particles are removed in a cavity zone than in the packing zone as the high gravity factor increases. An empirical model shows that the particle removal efficiency depends on the operating factors. Finally, a comparison analysis of particulate matter treatment in various types of RPB is used to validate the performance in terms of particle removal using high-gravity technology for different industries.

An engineering-environmental-economic-energy assessment for integrated air pollutants reduction, CO2 capture and utilization exemplified by the high-gravity process.

In this study, a high-gravity (HiGee) process incorporating CO2 and NOx reduction from flue gas in a petrochemical plant coupled with petroleum coke fly ash (PCFA) treatment was established. The performance of HiGee was systematically evaluated from the engineering, environmental, economic, and energy aspects (a total of 15 key performance indicators) to establish the air pollution, energy efficiency, waste utilization nexus. The engineering performance was evaluated that lower energy consumption of 78 kWh/t-CO2 can be achieved at a capture capacity of 600 kg CO2/t-PCFA. A net emission reduction of 327.3 kg-CO2/t-PCFA could be determined based on six environmental impact indicators. A cost-benefit analysis was conducted using operating cost, product sale, carbon credit, and savings in air pollution fees to present a better technological selection compared to existing carbon capture and storage plants. The waste heat recovery from the flue gas via the HiGee process could be measured via moisture condensation and attendant elimination of white smog emissions. Retrofitted heat recovery and energy intensity up to 131.8 kJ/t-PCFA and 0.21 kWh/t-PCFA were assessed. Finally, a comprehensive analysis of the HiGee process based on three daily load scenarios of CO2 capture scale were conducted, suggesting an optimal operating condition of the HiGee for generating profitability.

Red soil amelioration and heavy metal immobilization by a multi-element mineral amendment: Performance and mechanisms.

This field study aims to identify the performance and mechanisms of red soil amelioration and heavy metal immobilization by a multi-element mineral amendment (MMA) mainly containing a mixture of zeolites (laumontite and gismondine), montmorillonite, gehlenite, grossular and calcium silicate powder. The results indicated that the acidity of red soil was neutralized, and the soil EC, CEC, and content of montmorillonite and illite were increased after application of MMA, improving the soil fertility as well as the ability of heavy metals immobilization. The high amounts and reactivity of dissolved and colloidal Fe provided by the ferralsol (red soil) combined with the abundant available Si, Ca, Mg, Na and K supplied by MMA, readily destabilizes kaolinite and facilitates the formation of 2:1 type clay minerals. Meanwhile, the application of MMA was effective in reducing the bioavailability of soil heavy metals due to the activated mineralogical compositions of MMA as well as the increase of pH and 2:1 type clay minerals in the soil, which significantly decreased the up-taking and accumulation of Cd, Pb, Cr and Hg in lettuce tissues (p < 0.05). Compared with the untreated soil, the plant height, the total yield and content of vitamin C in the edible parts of lettuce in MMA-treated soil was increased by 7.6%, 23.6%, and 12.8%, respectively. These results showed that MMA could be a promising amendment for red soil amelioration and heavy metal immobilization.

Development and deployment of integrated air pollution control, CO2 capture and product utilization via a high-gravity process: comprehensive performance evaluation.

In this study, a proposed integrated high-gravity technology for air pollution control, CO2 capture, and alkaline waste utilization was comprehensively evaluated from engineering, environmental, and economic perspectives. After high-gravity technology and coal fly ash (CFA) leaching processes were integrated, flue gas air emissions removal (e.g., sulfate dioxide (SO2), nitrogen oxides (NOx), total suspended particulates (TSP)) and CO2 capture were studied. The CFA, which contains calcium oxide and thus, had high alkalinity, was used as an absorbent in removing air pollution residues. To elucidate the availability of technology for pilot-scale high-gravity processes, the engineering performance, environmental impact, and economic cost were simultaneously investigated. The results indicated that the maximal CO2, SO2, NOx, and TSP removal efficiencies of 96.3 ±â€¯2.1%, 99.4 ±â€¯0.3%, 95.9 ±â€¯2.1%, and 83.4 ±â€¯2.6% were respectively achieved. Moreover, a 112 kWh/t-CO2 energy consumption for a high-gravity process was evaluated, with capture capacities of 510 kg CO2 and 0.468 kg NOx per day. In addition, the fresh, water-treated, acid-treated, and carbonated CFA was utilized as supplementary cementitious materials in the blended cement mortar. The workability, durability, and compressive strength of 5% carbonated CFA blended into cement mortar showed superior performance, i.e., 53 MPa ±2.5 MPa at 56 days. Furthermore, a higher engineering performance with a lower environmental impact and lower economic cost could potentially be evaluated to determine the best available operating condition of the high-gravity process for air pollution reduction, CO2 capture, and waste utilization.

Performance evaluation of modified bioretention systems with alkaline solid wastes for enhanced nutrient removal from stormwater runoff.

Bioretention systems have been found to be potential candidates for the removal of various pollutants/nutrients from rainfall or stormwater runoff. Despite bioretention has been widely developed for the removal of nutrients from stormwater, effective removal of both phosphorus and nitrogen is still a challenge. Hence, in this study, bioretention systems modified by alkaline solid waste media have been reported for the effective removal of nutrients. Six different types of solid wastes were first assessed using leaching and adsorption tests, and then the bottom ash from a refuse incineration plant was selected as a modifier. The bottom ash was mixed with soil to form a special media as the filter layer in the bioretention systems. The nutrient removal efficiencies of the modified bioretention systems were evaluated and also compared with those of the unmodified control. For this purpose, the design of the modified filter media with a saturated zone was combined to enhance the simultaneous removal of nitrogen and phosphorus. The effect of different rainfall intensities and nutrient concentrations in stormwater runoff on the removal efficiency of nutrients was evaluated. The results indicated that the modified bioretention with bottom ash modified soil media and saturated zone could exhibit the excellent removal efficiency of nitrogen and phosphorus from stormwater runoff. The extent of removal of total nitrogen, total Kjeldahl nitrogen, and total phosphorus was found to be 58-70%, 66-82% and 82-97%, respectively. The performed correlation analysis showed that the bioretention cell using the special media could simultaneously enhance the removal of phosphorus and nitrogen. As a part of this study, the adsorption isotherms of phosphorus removal by the modified bioretention systems have also been determined. Finally, the implications and opportunities for deploying modified bioretention systems for optimizing water-energy nexus and stormwater management were illustrated. In overall, this study demonstrated that the modified bioretention systems could substantially enhance the removal efficiencies of nutrients from stormwater runoff.

Integration of Green Energy and Advanced Energy-Efficient Technologies for Municipal Wastewater Treatment Plants.

Wastewater treatment can consume a large amount of energy to meet discharge standards. However, wastewater also contains resources which could be recovered for secondary uses under proper treatment. Hence, the goal of this paper is to review the available green energy and biomass energy that can be utilized in wastewater treatment plants. Comprehensive elucidation of energy-efficient technologies for wastewater treatment plants are revealed. For these energy-efficient technologies, this review provides an introduction and current application status of these technologies as well as key performance indicators for the integration of green energy and energy-efficient technologies. There are several assessment perspectives summarized in the evaluation of the integration of green energy and energy-efficient technologies in wastewater treatment plants. To overcome the challenges in wastewater treatment plants, the Internet of Things (IoT) and green chemistry technologies for the water and energy nexus are proposed. The findings of this review are highly beneficial for the development of green energy and energy-efficient wastewater treatment plants. Future research should investigate the integration of green infrastructure and ecologically advanced treatment technologies to explore the potential benefits and advantages.

Characterization and flocculation evaluation of a novel carboxylated chitosan modified flocculant by UV initiated polymerization.

In this work, carboxylated chitosan modified flocculant (CC-g-PCD) was prepared by graft copolymerization technique to enhance the charge-attracting and adhesion of bridges and net-sweeping capacity of flocculants. The dimethyldiallylammonium chloride (DMDAAC), carboxylated chitosan (CMCS), and 3-chloro-2-chloropropyltrimethylammonium chloride (CTA) were utilized for synthesis of CC-g-PCD via photopolymerization techniques. The synthesized CC-g-PCD was characterized by 1H NMR, SEM, XRD, and FTIR, and the characteristic groups on the main chain and surface morphological structure of CC-g-PCD were investigated. The obtained results indicated that CTA and DMDAAC were successfully grafted into the CPCTS. In ordered to evaluate the flocculation performance of CC-g-PCD at various dosages, stirring intensity (G value), and pH value by detecting Chl a, COD, and turbidity, the actual lake water that contains algae was used for flocculation assessment tests. The experimental results of the water sample with flocculation showed that the maximum flocculation efficiency of turbidity (91.1%), Chl a (97.2%), and COD (97.0%) can be achieved by CC-g-PCD at pH 7, G value 200 s-1, and 4.0 mg/L. The comparison results demonstrated that CC-g-PCD had better flocculation efficiency than commercial flocculants. Finally, based on the analysis of algae removal in combination with Zeta potential measurements, the flocculation mechanisms in actual lake water at various dosages and pH values were adsorption bridging and electrical neutralization.

Performance evaluation of integrated adsorption-nanofiltration system for emerging compounds removal: Exemplified by caffeine, diclofenac and octylphenol.

Emerging pollutants introduced into surface water pose potential hazards to the safety of drinking water. In this study, the removal performance of three emerging compounds (exemplified by caffeine, diclofenac and octylphenol, with different physico-chemical properties) from synthetic water and source water by combining activated carbon (AC) adsorption and nanofiltration (NF) membrane processes was evaluated and analyzed. Results from synthetic water showed that the adsorption isotherms modeled well with the Langmuir equation. The removal performance of target compounds by AC-NF system was more remarkable than that of NF-AC combination. In the source water system, the integrated AC-NF process with coagulation pretreatment (the alum dosage of 60 mg/L) achieved satisfactory performance (the removal efficiencies of three target compounds reached > 95%). Results showed the electrostatic interaction and pollutant hydrophobicity determined the behavior and the fate of selected PPCPs/EDCs during the sequential treatment process of coagulation, activated carbon adsorption, and NF membrane separation. Finally, the AC and NF membranes were analyzed by Fourier transform infrared spectroscopy and scanning electron microscopy to understand the mechanisms, i.e. electrostatic and hydrophobic effects on the total removal process. It suggests that the integrated AC-NF process with coagulation pretreatment should be a feasible approach for removing emerging compounds in waterworks.

Electrocatalytic oxidation of tetracycline by Bi-Sn-Sb/γ-Al2O3 three-dimensional particle electrode.

In this work, highly efficient Bi-Sn-Sb/γ-Al2O3 particle electrodes were prepared for effectively degrading tetracycline. The effects of a mass ratio (Sn: Sb), the mass ration of Bi:(Sn + Sb), impregnation times, calcination temperature, and calcination time on the electrocatalytic oxidation capacity of Bi-Sn-Sb/γ-Al2O3 particle electrode was investigated. Conditions in which mass ratio of (Sn: Sb) = 10:1, the mass ratio of Bi:(Sn/Sb) = 1:1, impregnation times 2 h, calcination temperature 500 °C., and calcination time 3 h were considered as optimal preparation conditions for Bi-Sn-Sb/γ-Al2O3 particle electrode. It was cherecterized by infrared spectroscopy (IR), scanning electron microscope (SEM), energy dispersive X-ray detector (EDX), X-Ray Diffraction (XRD), and X-ray fluorescence (XRF) techniques to conforming that the triclinic Bi2O3 formed in the preparation conditions has superior electrocatalytic activity. The electrocatalytic oxidation mechanism of tetracycline by Bi-Sn-Sb/γ-Al2O3 particle electrode is proposed by determining degradation intermediates through LC-MS detection. Electrocatalytic oxidation experiments by adding tert-butyl alcohol indicate that the formation of OH is the primary responsibility for degradating tetracycline. Electrocatalytic degradation of tetracycline at different initial concentration shows that the degradation of tetracycline meets the pseudo first-order kinetics. Results suggest that the three-dimensional electrochemical reactor with Bi-Sn-Sb/γ-Al2O3 particle electrodes could be an alternative for the pretreatment of antibiotic wastewater before biological treatment.

Mechanism of organic pollutants sorption from aqueous solution by cationic tunable organoclays.

A variety of quaternary ammonium salts with different carbon chain lengths were used to modify and convert montmorillonite clay to organoclays. The surface modification attributing to the wettability was investigated using various techniques. The zeta-potential values of all clays showed pH dependency. The prepared organoclays were utilized for phenol (protic) and nitrobenzene (aprotic) adsorption in a batch system, with pH and contact time as variables. The optimized removal for phenol and nitrobenzene within 30 min of equilibrium observed at pH 9.0 and 5.0, respectively. Observed equilibrium data followed the Langmuir monolayer adsorption kinetics with two adsorption sites (outer-layer and interlayer) for purified clay, and third additional sites for organoclays. Kinetic studies revealed that the adsorption of phenol was in the order of mono- > tetra- > di- > benzyl-substituted organoclays, which is similar to the hydrophilicity order. However, the exact opposite trend of adsorption was observed for nitrobenzene. From the performed quantitative study, it is inferred that -OH functional phenol and -NO2 functional nitrobenzene have an affinity towards the hydrophilic clay surface and hydrophobic surfaces of quaternary ammonium salts as its first preference, respectively. This study brings promising observations and implications to the vital structural-property relationship for selective adsorption of pollutants from aqueous solutions.

Advances and challenges in sustainable tourism toward a green economy.

This paper provides an overview of the interrelationships between tourism and sustainability from a cross-disciplinary perspective. The current challenges and barriers in the tourism sustainability, such as high energy use, extensive water consumption and habitat destruction, are first reviewed. Then the key cross-disciplinary elements in sustainable tourism, including green energy, green transportation, green buildings, green infrastructure, green agriculture and smart technologies, are discussed. To overcome the challenges and barriers, a few implementation strategies on achieving sustainable tourism from the aspects of policy/regulation, institution, finance, technology and culture are proposed, along with the framework and details of a key performance indicator system. Finally, prospects of the potential for tourism to contribute to the transformative changes, e.g., a green economy system, are illustrated. This paper shine a light on issues of importance within sustainable tourism and encourage researchers from different disciplines in investigating the inter-relationships among community/culture, environment/ecology, and energy/water/food more broadly.

CO2 Mineralization and Utilization using Steel Slag for Establishing a Waste-to-Resource Supply Chain.

Both steelmaking via an electric arc furnace and manufacturing of portland cement are energy-intensive and resource-exploiting processes, with great amounts of carbon dioxide (CO2) emission and alkaline solid waste generation. In fact, most CO2 capture and storage technologies are currently too expensive to be widely applied in industries. Moreover, proper stabilization prior to utilization of electric arc furnace slag are still challenging due to its high alkalinity, heavy metal leaching potentials and volume instability. Here we deploy an integrated approach to mineralizing flue gas CO2 using electric arc furnace slag while utilizing the reacted product as supplementary cementitious materials to establish a waste-to-resource supply chain toward a circular economy. We found that the flue gas CO2 was rapidly mineralized into calcite precipitates using electric arc furnace slag. The carbonated slag can be successfully utilized as green construction materials in blended cement mortar. By this modulus, the global CO2 reduction potential using iron and steel slags was estimated to be ~138 million tons per year.