Optimizing refuse-derived fuel production from scheduled wastes through Aspen plus simulation.

This study aims to improve the quality of fuel with high calorific value namely Sfuel - a commercial high-quality refuse-derived fuel (RDF) from hazardous waste via modifying the process design and operating parameters of thermal conversion process. The study analyses key parameters of RDF quality, such as calorific value and heavy metal content, before and after process modifications based on the combination of experimental and simulation using Aspen Plus. In this study, the temperature and pressure of the simulation system are varied from 100 to 700 °C and from 1 to 5 bar, respectively. Findings indicate that there are a total of eleven heavy metals and 179 volatile compounds in the "Sfuels". The quality of the targeted product is greatly improved by the metal evaporation at high temperatures and pressures. However, the calorific value of RDF significantly decreases at 700 °C due to a large amount of the carbon content being evaporated. Although the carbon content at high temperatures is significantly lost, the heat from the vapour stream reactor outlet, which is reused to preheat the nitrogen gas stream supplied to the system, reduces energy consumption while improving the thermal conversion efficiency of the system. Besides, low pressure along with high temperature are not the optimal conditions for quality Sfuels improvement by thermal conversion. Results also indicate that electric heating is more economically efficient than natural gas heating.

Adsorptive removal of benzene and toluene from aqueous solutions by oxygen-functionalized multi-walled carbon nanotubes derived from rice husk waste: A comparative study.

One of the current directions for sustainable development is to use waste resources to create materials that reduce environmental pollution. In this study, multi-walled carbon nanotubes (MWCNT) and their oxygen-functionalized forms (HNO3/H2SO4-oxidized MWCNT, NaOCl-oxidized MWCNT, and H2O2-oxidized MWCNT) were first synthesized from activated carbon (AC) derived from rice husk waste. A comprehensive comparison of the morphological and structural properties of these materials was conducted using FT-IR, BET, XRD, SEM, TEM, TGA, Raman spectroscopy, and surface charge analysis. The morphology study suggests that the synthesized MWCNTs have an average outer and inner diameter of about 40 and 20 nm, respectively. Additionally, the NaOCl-oxidized MWCNT possesses the largest interspaces between nanotubes, while the HNO3/H2SO4-oxidized CNT has the most oxygen-functional groups, including -COOH, (Ar)-OH, and C-OH. The adsorption capacities of these materials were also compared for the removal of benzene and toluene. Experimental results have shown that while porosity is the primary factor governing the benzene and toluene adsorption onto AC, functionalization degree and surface chemical characteristics are the determining factors in the adsorption capacity of the as-prepared MWCNTs. The adsorption capacity of these aromatic compounds in an aqueous solution increases in the following order: AC < MWCNT < HNO3/H2SO4-oxidized MWCNT < H2O2-oxidized MWCNT < NaOCl-oxidized MWCNT, and in all cases, toluene is more readily adsorbed than benzene under similar adsorption conditions. Wherein the uptake of both pollutants by the prepared adsorbents in this study is best described by the Langmuir isotherm and obeys the pseudo-second-order kinetic model. The adsorption mechanism was discussed in a detailed manner.

Isolation of organophosphate pesticides from water using gold nanoparticles doped magnetic three-dimensional graphene oxide.

Pesticides are a large group of pristine organic contaminants, which are widely discharged into environmental water due to agricultural activities. Hence, extraction, determination, and removal of pesticides from water resources are necessary for human health. In this study, novel adsorbent was developed based on three-dimensional magnetic graphene coated with gold nanoparticles (3D-MG@AuNPs) for extraction of chlorpyrifos, dicrotophos, fenitrothion, and piperophos as four specific organophosphorus pesticides (OPPs) from wastewater and tap water samples. The proposed nanocomposite was characterized; FTIR and EDX are performed for the expected functional groups and elemental analysis, SEM showed the unique and spherical AuNPs are well dispersed over graphene sheets. In this investigation, the important parameters that have effect on the extraction efficiency, including the desorbing solvent, desorbing solvent volume, vortex time, the extraction time, adsorbent dosage, pH of sample solutions, and salt effect were evaluated. In conclusion, the measured amounts of the chosen OPPs were determined using the gas chromatography microelectron capture (µECD-GC) method. Limits of quantification (S/N ratio of 10) and detection (S/N ratio of 3) were attained at concentrations of 0.26-0.43 µg.L-1 and 0.08-0.14 µg.L-1, respectively. According to the results of the investigations, the synthesized 3D-MG@AuNPs did not require any complicated sample preparation methods; therefore, it is a very good choice for solid magnetic phase extraction studies.

A hybrid nanocomposite based on CuFe layered double hydroxide coated graphene oxide for photocatalytic degradation of trimethoprim.

Photocatalytic activation of persulfate (PS) has recently been considered an effective and environmentally friendly approach for antibiotic decomposition due to its high treatment efficiency, low energy consumption, and high reliability. The development of safe and high-performance catalysts is important for PS-based advanced oxidation processes. In this study, a CuFe-layered double hydroxide (LDH) coated graphene oxide (CuFe-LDH/GO) composite was constructed as a photocatalyst for trimethoprim (TMP) decomposition. The CuFe-LDH/GO catalyst was prepared via the co-precipitation method and characterized through Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and X-ray electron microscopy (XPS) techniques. Characterization results revealed that GO was entirely covered by LDH platelets which also kept its hydrotalcite structure in the as-prepared nanocomposite. The average crystallite size of CuFe-LDH/GO was 28.22 nm. The results confirmed that CuFe-LDH/GO exhibited excellent performance for the PS activation with a TMP removal efficiency of 90.8% under UV-light irradiation. Compared with pristine CuFe-LDH, the rate constant of TMP degradation of CuFe-LDH/GO was doubled. The results also indicated that acidic and alkaline conditions were not favorable for TMP degradation, and the catalytic activity of the used photocatalyst has not decreased significantly after 720 h of continuous recycling. Overall, CuFe-LDH/GO could be a promising photocatalyst for the treatment of wastewater containing antibiotics.

Electrochemical degradation of indigo carmine, P-nitrosodimethylaniline and clothianidin on a fabricated Ti/SnO2-Sb/Co-ßPbO2 electrode: Roles of radicals, water matrices effects and performance.

In this study, the kinetic degradation of several typical organic pollutants was performed on a synthetic electrode (Ti/SnO2-Sb/Co-ßPbO2). The surface structure and the electrochemical properties of the prepared electrode were investigated, confirming the successful preparation of the electrode using an electrochemical deposition method. The outer layer (Co-ßPbO2) played an important role in reducing the resistance of the electrode and improving its degradation efficiency. The results showed that indigo carmine (IC), p-nitrosodimethylaniline (RNO), and clothianidin (CLO) were effectively degraded within 20 min of electrolysis. Their degradation in the electrochemical process followed the first-order kinetic model with the degradation rate constant of IC being higher than that of RNO and CLO. This was proved by the difference in the reactivity of the target pollutants toward oxidizing radicals (i.e., •OH, SO4•-, and Cl•). Their second-order rate constant towards radicals were in the range of 109 - 1010 M-1 s-1 with the highest value being that for IC: k·OH,IC = 15.1 × 109 M-1 s-1 and [Formula: see text]  = 7.4 × 109 M-1 s-1. The study calculated the contribution of some oxidizing species, including direct electron transfer (DET), •OH, SO4•-, and other reactive oxygen species (ROS). Solution pH, supporting electrolyte, and water matrix affected the degradation efficiency of pollutants and the contribution of the oxidizing species. Br- and I- ions enhanced the degradation rate of organic pollutants, while Fe2+, HCO3-, and humic acid (HA) reduced it. In addition, the toxicity, total organic carbon (TOC) removal, mineralization current efficiency (MCE), energy consumption, recyclability and stability of the prepared electrode were studied, suggesting that the prepared Ti/SnO2-Sb/Co-ßPbO2 is a good candidate for treating organic pollutants using the electrochemical oxidation process.

Kinetic study on methylene blue removal from aqueous solution using UV/chlorine process and its combination with other advanced oxidation processes.

This study investigated the kinetic degradation of methylene blue (MB) by a UV/chlorine process and its combination with other advanced oxidation processes. The ∙OH and reactive chlorine species (RCS: Cl∙, ClO∙, etc.) were the primary reactive species, which accounted for 56.7% and 37.6% of MB degradation at pH 7, respectively. The second-order rate constant of Cl∙ towards MB was calculated to be 2.8 × 109 M-1 s-1. When the pH increased from 3 to 7, kMB by ∙OH increased from 0.15 to 0.21 min-1 before being reduced to 0.11 min-1 at pH 11. kMB by RCS continuously reduced from 0.16 to 0.13 min-1 when the pH was increased to 11. Humic acid (HA), Br-, and Cl- inhibited the degradation with kMB in the order: kMB (in HA) < kMB (in Br-) < kMB (in Cl-). HCO3- increased kMB from 0.37 to 0.48 min-1. The experimental and modeling methods fit well, indicating the effectiveness of using Kintecus® in predicting concentrations of free radicals in complex water matrices. TOC removal was achieved at 60% after 30 min in a control process and it was strongly inhibited by the presence of HA, with 22% removal achieved at 5 mgc L-1 HA. UV/chlorine/electrochemical oxidation (UV/chlorine/EO) significantly improves kMB from 0.37 to 0.94 min-1 at a high current (240 mA), while UV/chlorine/H2O2 decreased kMB at a low concentration of 0.01 mM H2O2 (kMB decreased by 6.1%). The results indicate that the energy cost for UV irradiation was the main cost in MB treatment in both UV/chlorine and UV/persulfate (UV/PS) processes, accounting for 91% and 84%, respectively.

Recent progress on adsorption of cadmium ions from water systems using metal-organic frameworks (MOFs) as an efficient class of porous materials.

Various articles have been written about MOFs, which are organic-inorganic polymer structures that are unique in three-dimensional porosity, crystalline structure, and their ability to adsorb cadmium ion pollutants from aqueous solutions. These materials possess active metal sites, highly porous structures, high specific surfaces, high chemical functionality, and porous topologies. It is necessary to study adsorption kinetics, isotherms, and mechanisms in order to better understand the adsorption process. Adsorption kinetics can provide information about the adsorption rate and reaction pathway of adsorbents. Adsorption isotherms analyze the possibility of absorbances based on the Gibbs equation and thermodynamic theories. Moreover, in practical applications, knowledge of the adsorption mechanism is essential for predicting adsorption reactions and designing MOFs structures. In this review, the latest suggested adsorption mechanisms, kinetics, and isotherms of MOFs-based materials for removing cadmium ions are presented. A comparison is then conducted between different MOFs and the mechanisms of cadmium ion removal. We also discuss the future role of MOFs in removing environmental contaminants. Lastly, we discuss the gap in research and limitations of MOFs as adsorbents in actual applications, and probable technology development for the development of cost-efficient and sustainable MOFs for metal ion removal.

Assessment and treatment of floodwater in the Vietnamese Mekong Delta using a simple filter system based on silver nanoparticles coated onto activated carbon derived from rice husk.

The floods in the Vietnamese Mekong Delta have long caused a shortage of clean water supply, which has a significant impact on the indigenous people in the region. We have conducted a preliminary survey of the water quality of the Hau Giang River (one of the two main branches of the Mekong River) before, during, and after the flood season. The obtained results demonstrated that the water in the Hau Giang River was highly turbid and contaminated with a large number of harmful microorganisms. Thus, in this study, a simple filter system based on silver nanoparticles coated onto activated carbon derived from rice husk (AgNPs@AC) has been proposed for treating floodwater from the Hau Giang River. The optimal conditions for AgNPs@AC preparation were established. The prepared AgNPs@AC was then characterized using various surface analyses such as SEM, TEM, XRD, BET, FTIR, and DLS. The initial floodwater source would be pre-treated with polyaluminum chloride using the coagulation-sedimentation method to remove the suspended solids before being discharged into the filtration column containing AgNPs@AC. The results showed that the filter system based on AgNPs@AC performed well in removing turbidity, dissolved solids, suspended solids, color, and bacteria from the floodwater. In addition, it was determined that the filter column with a 30 mm thick AgNPs@AC layer could continuously process 1300 m3 of the floodwater and had a service life of more than two months. The findings of this study not only added to our understanding of the floodwater treatment capacity of activated carbon coated nanoparticles, but they also provided valuable information for water treatment plants along the Hau Giang River, aquatic ecosystem researchers, and public health researchers.

Natural core-shell structure activated carbon beads derived from Litsea glutinosa seeds for removal of methylene blue: Facile preparation, characterization, and adsorption properties.

In this study, natural core-shell structure activated carbon beads (ACBs) from Litsea glutinosa seeds were successfully produced, characterized, and applied for adsorption of methylene blue (MB). The ACBs were prepared using single-step carbonization-activation with NaHCO3 at the optimized activation temperature, time, and activating agent concentration of 450 °C, 60 min, and 5%, respectively. Batch experiments were performed to determine the optimum adsorption conditions, suitable kinetic and isotherm models, and thermodynamic parameters for the adsorption of MB onto ACBs. The results showed that the ACBs were displayed as highly porous natural core-shell spheres with a diameter of about 5 mm. The adsorption of MB dye on ACBs was a spontaneous endothermic process, followed the Langmuir isotherm and the pseudo-second-order kinetic models with the rate-controlling step of both external diffusion and intra-particle diffusion. At the optimum conditions (pH of 9, the contact time of 10 h, the temperature of 40 °C, and an adsorbent dosage of 6 g/L), the maximum adsorption capacity reached 29.03 mg/g. The thermal method turned out to be more suitable for regenerating ACBs compared to the chemical method. The ACBs exhibited high reusability and stability, its adsorption efficiency could maintain more than 90% after five consecutive cycles of use. The electrostatic attraction, π-π interaction, hydrogen bonding, and pore-filling were identified as primary contributions to the adsorption mechanism. The overall results revealed that the ACBs could be used as a potential adsorbent for removing MB from water media.