Low-energy production of a monolithic catalyst with MnCu-synergetic enhancement for catalytic oxidation of volatile organic compounds.

Producing a low-cost catalyst by a low-cost method is one of the hottest topics in the field of catalytic oxidization of volatile organic compounds (VOCs). In this work, a catalyst formula with a low-energy requirement was optimized in the powdered state, and verified in the monolithic state. An effective MnCu catalyst was synthesized at a temperature as low as 200 °C. Removals were all bigger than 88% for toluene, ethyl acetate, hexane, formaldehyde, and cyclohexanone at a low temperature of 240 °C. The MnCu catalyst was then loaded on a honeycomb cordierite, which was also effective for toluene removal at 240 °C. After characterizations, active phases were Mn3O4/CuMn2O4 in both the powdered and monolithic catalysts. The enhanced activity was attributed to balanced distributions of low-valence Mn and Cu, as well as abundant surface oxygen vacancies. The obtained catalyst is produced by low energy and effective at low temperature, which suggests a perspective application.

Quantifying the effect of socio-economic-geo drivers on the change of municipal waste disposal in China by an integrated TWFE-PRF-SDM methodology.

Municipal solid waste management and disposal in China have significantly evolved since 2000. Due to China's vast land area and significant socioeconomic and geographic disparities, nationwide waste management strategies need to be further evaluated. This study quantified the effect of social, economic, and geographic drivers on municipal waste disposal activities in 31 provincial-level administrative regions from 2003 to 2020, by establishing a methodology integrated by two-way fixed effects regression model, panel random forest, and spatial Durbin model. The results showed, in the past two decades, socio-economic-geo indicators significantly co-decided the landfill and incineration activities. In particular, the explanatory ability of GDP per capita was above 45%, while land resources and city size also showed great significance. Spatial autocorrelation analysis showed that the relationship between landfill/incineration rates and socio-economic-geo drivers changed notably from unobvious to significant with economic growth. Furthermore, the local economy and land resources displayed more impact than those of the neighboring regions, while sci-tech and education showed clear spatial spillover effects. Chinese government would carefully assess the full-scale promotion policy of incineration plants, landfill is still hold as a reasonable option for regions with specific socio-economic-geo conditions.

Recycling electroplating sludge as a monolithic catalyst for effective catalytic purification of volatile organic compounds.

Electroplating sludge had a high content of heavy metals and usually lacked high-value-added utilization. In this work, Cu-containing sludge was used to synthesize a spinel catalyst, which was applied in catalytic oxidization of toluene. As a result, the sludge-derived spinel removed 50% of toluene (1000 ppm, 9600 h-1) at 280 °C. In comparison, a reagent-synthesized spinel with a similar component removed 50% of pollutant at 294 °C. The sludge-derived spinel also showed a stable performance for over 50 h at 370 °C. Even when the initial concentration was increased to 5000 ppm, or the gas hourly space velocity was increased to 40,000 h-1, the temperature for 50% removal was only increased to 303 °C. According to characterizations, surface oxygens of the sludge-derived spinel were more active than those in the reagent-synthesized one. Besides, the former had more active surface oxygens (207.9 µmol/g) than the latter (183.1 µmol/g). Furthermore, the sludge-derived spinel was coated on a monolithic honeycomb, which were also effective in catalytic oxidization of toluene. The main results of this work were in favor of high-value-added utilization of hazardous solid waste and promoting its real industry application.

Implementation effect of municipal solid waste mandatory sorting policy in Shanghai.

In Shanghai, the biggest metropolis in China, the source classification of domestic waste began in the 1990s but achieved little success over the past thirty years. Surprisingly, the compulsory classification provision of Shanghai residents' domestic waste since 2019 has been successful. In this work, the overall status, and challenges of municipal solid waste (MSW) management in Shanghai under compulsory waste sorting rules are investigated. We tracked the classification efficiency of municipal solid waste, physicochemical characteristics of separated waste, and the carbon emissions arising from waste disposal system. It was found that almost 83.62 % of household food waste has been effectively separated with high purity of 99.50 %, while the lower heating value (LHV) of residual waste was increased by 96.4 % compared to previous years. With effective waste classification, the net carbon emission of separated processing was reduced to 0.11 ton CE/ton waste. However, this system generated some negative outcomes as well such as the lower recovery value of metal in bottom ash and the higher chloride content in fly ash. Moreover, we have documented and discussed several challenges of sustainable waste management system in Shanghai in the text. In order to overcome those challenges, we recommend to: (i) establish a finer source separation and recycling system; (ii) develop highly-efficient resource recovery technologies of byproducts from waste disposal system; and (iii) propose optimization adjustment strategy for overcapacity in incineration facilities.

Synthesis of a perovskite-type catalyst from Cr electroplating sludge for effective catalytic oxidization of VOC.

Chromium-containing electroplating sludge usually lacked proper disposal and recycling. High-temperature melting was a technology aiming to form glass-phase slag for the stabilizations of heavy metals. This work investigated the possibility of forming perovskite-like phase by chromium-containing sludge using high-temperature melting. The formed material was applied in catalytic oxidization of volatile organic compound. As a result, Ca2+-doped LaCrO3 was formed according to XRD and HRTEM. When Ca2+ doping reached 33%, i.e., La0.67Ca0.33CrO3, surface oxygen species of the obtained catalyst was increased to 65.7%, which was detected by XPS, resulting in a toluene removal of 50% at 302 °C. Besides, the activity was stable for over 50 h. In addition, the doping amount was as high as 40 mol% of Cr in the catalyst. Based on these results, a high-value-added catalyst was produced by the hazardous waste, which was in favor of hazardous-waste recycling as well as high-temperature-melting development.

Resident risk attitude analysis in the decision-making management of waste incineration construction.

Environmental pollutants generated by waste incineration plants, such as heavy metals and dioxin, make surrounding residents very sensitive to the construction of such facilities. This sensitivity and anxiety of residents may induce group events, which further leads to the emergence of social risks. Based on risk perception theory, a total of 320 questionnaires was designed and handed out to residents neighboring to Jiangqiao Waste Incineration Plant in Shanghai, China to detect the factors affecting risk attitude toward such plants. Using ordered logit model, it is found that there are four decisive factors including impact on health, information cognitive, objective characteristics, and the attitude of the neighbors. These factors have different influence on resident risk attitudes, in which the attitude of the neighbors is of most significance, followed by the economic-geography characteristics of residents, the information cognitive has minimal impact.

Production of an effective catalyst with increased oxygen vacancies from manganese slag for selective catalytic reduction of nitric oxide.

Manganese slag is a solid waste produced by the steel industry and usually lacks a proper recycling. In this paper, the manganese slag was used to synthesize a catalyst via microwave assistant method and applied in selective catalytic reduction of nitric oxide. As a result, the catalyst exhibited an excellent low-temperature activity. It removed 78.31% of nitric oxide at 100 °C, 44.44% higher than that of a slag-derived catalyst synthesized by ammonia impregnation, and 63.18% higher than that of a commercial catalyst. Even after a hydrothermal treatment, the catalyst still showed a removal of 69.26% at 150 °C. After a detailed characterization, the low-temperature activity was attributed to an increased amount of oxygen vacancies, which were generated during the microwave synthesis. The generated oxygen vacancies provided adsorption sites for chemisorbed oxygens, which then promoted the electron transfer for reduction of nitric oxide. The main result of this work will help to develop a low-cost catalyst and obtain a high-value-added utilization of manganese slag at the same time.

Heavy metal leaching and distribution in glass products from the co-melting treatment of electroplating sludge and MSWI fly ash.

Melting is a common solidification treatment that concentrates and encapsulates heavy metals into a glass matrix for waste containing heavy metals (Chae et al., 2016). To control the risk of heavy metal leaching into the glass product, a reduction in the amount of heavy metal was achieved in a pilot-scale furnace by co-melting electroplating sludge (EPS) and municipal solid waste incineration fly ash (MSWI FA). Through the melting process, the chloride from MSWI FA led to heavy metals volatilization in the form of chlorine salts. The fly ash additionally increased heavy metals volatilization by 4%-91%. The highest volatilization ratios of Zn, Pb, Cu, Cd, Cr and Ni were 33%, 96%, 33%, 79%, 81% and 31%, respectively. The concentrations of Pb and Zn in the secondary fly ash were close to the Pb and Zn concentrations in lead-zinc ore that are required in smelting industry. Moreover, glass sand was produced after the melting treatment. With an increase in the fly ash mixing ratio, the leaching concentration of Zn and Cu decreased to 3.8 mg/L and 2.1 mg/L. The leaching concentrations of other heavy metals stayed below 1 mg/L in all cases. When the ratio of MSWI FA reached 10%, the glass sand contained the least amount of impurities and a large amount of phosphate and silicate, which were probably responsible for the stability of the heavy metals. Therefore, our results provided a promising approach to the stability of the waste by the recovery of heavy metals in the co-treatment of heavy metal-bearing wastes.

Rapid evaluation of leaching potential of heavy metals from municipal solid waste incineration fly ash.

Municipal solid waste incineration fly ash is directly landfilled after solidification in the industry. The rapid evaluation of contaminant leaching is required before the landfill of fly ash. In order to reduce the time to evaluate the effect of solidification, a set of rapid evaluation method was developed through the determination of characteristic index, heavy metal leaching analysis, principal component analysis, and mathematical model construction. It was found that f-CaO, acid neutralizing capacity, pH and soluble calcium were negatively correlated with heavy metal leaching. The soluble chlorine was positively correlated with heavy metal leaching. The effect of each feature indicators on heavy metal leaching was evaluated using principal component analysis and mathematical analysis software R.3.4.4. Furthermore, R.3.4.4 was used to detect the optimal model and the excess probability formula by stepwise linear regression and logistic regression analysis method. By introducing the measured value of feature indicator into the excess probability formula, the rate of excess-standard of heavy metals leaching can be preliminarily determined. Based on the above ideas, a rapid detection and evaluation system could be developed according to the local leaching standards and the components of fly ash selected locally.

Driving forces of impervious surface in a world metropolitan area, Shanghai: threshold and scale effect.

Shanghai is one of the largest metropolitan areas in the world, during the rapid urbanization of the past decades, impervious surface expanded dramatically and became a main factor influencing surface water quality. Thus, exploring the driving forces of impervious surface has great implications in such metropolitan area. In this study, an impervious surface coefficient method (ISC) was used to measure the percentage of total impervious area (PTIA) of Shanghai; regression analysis was conducted to define the relationship between PTIA and three socio-economic factors, population density, unit area gross domestic product, and unit area industrial output at the city and district scale. Results showed that the industrial land use generated the highest ISC value, followed by high-density residential. Strong correlations were showed between PTIA and socio-economic indicators, in which population density was the most significant. Threshold effect was presented that when population density was higher than 15000 per/km2, this relationship would become less significant and PTIA remained stable. Similar effects were found when unit area gross domestic product exceeded 125 million yuan/km2. Scale effect was also discussed that the relationship was more significant at city scale than district. An improved understanding of the threshold effect and scale effect will help guide future urban planning and design new urban ecosystem policies.

The Transformation of Hybrid Silica Nanoparticles from Solid to Hollow or Yolk-Shell Nanostructures.

Here, a facile self-templating approach is presented for synthesis of hollow and yolk-shell mesoporous silica nanoparticles (HMSNs and YMSNs) through a selective etching of hybrid silica nanoparticles. The hybrid silica nanoparticles are from the co-condensation of tetraethylorthosilicate (TEOS) and N-[3-(trimethoxysilyl)propyl]ethylenediamine (TSD) by a simple one-step process. Two kinds of products including HMSNs and YMSNs can be easily prepared only by tuning the TSD amounts in the precursor. Significantly, the transformation of hollow structure does not use any sacrificial template and surface-protective agent. The etching mechanism and formation process are systematically investigated by SEM, TEM, TG, CHN elemental analysis and Si MAS NMR spectroscopy. The results reveal that the selective etching is mainly attributed to the discrepancy in density between the outer layer and inner area of hybrid silica, where its inner section is more readily dissolved while the outer shell is robust in hydrofluoric acid (HF) aqueous solution. Specifically, the new understanding is further extended to precisely prepare multi-shelled hollow/yolk-shell silica nanoparticles.

Shape-Controlled Hollow Mesoporous Silica Nanoparticles with Multifunctional Capping for In Vitro Cancer Treatment.

A series of multifunctional shape-controlled nonspherical hollow mesoporous silica nanoparticles (HMSNs) drug carriers have been prepared by employing Fe2 O3 with four morphologies (capsule, cube, rice, and rhombus) as a sacrificial template and a multifunctional cap as the encapsulating shell. The resulting shape-controlled nonspherical HMSNs perfectly replicate the original morphology of the Fe2 O3 templates, which possess a high specific surface area, good monodispersity, perpendicular mesoporous channels, and excellent biocompatibility. After modification of polyethylene glycol (PEG) and folic acid (FA), the shape-controlled HMSN core and functional shell can then be integrated into a single device (HMSNs-PEG-FA) to provide an efficient and tumor-cell-selective drug-delivery system. The shape-controlled HMSNs and HMSNs-PEG-FA all show controlled pH-responsive release behavior for the anticancer drug doxorubicin hydrochloride (DOX). The in vitro results indicate that HMSNs-PEG-FA is biocompatible and selectively targets HeLa cells (overexpressed folate receptors). Fluorescence images show that desirable surface modification and the nonspherical shape effectively facilitate cellular internalization of HMSNs. It is expected that the construction of these unique nanomaterials with controlled morphology through the hard-templating technique may also provide useful information for the design of nanoscale multifunctional systems.

Theoretical and Experimental Evidence for the Carbon-Oxygen Group Enhancement of NO Reduction.

The relation between a catalytic center and the surrounding carbon-oxygen groups influences the catalytic activity in various reactions. However, the impact of this relation on catalysis is usually discussed separately. For the first time, we proved that carbon-oxygen groups increased the reducibility of Fe-C bonds toward NO reduction. Experimentally, we compared the reductive activities of materials with either one or both factors, i.e., carbon-oxygen groups and Fe-C bonds. As a result, graphene oxide-supported Fe (with both factors) showed the best activity, duration of activity, and selectivity. This material reduced 100% of NO to N2 at 300 °C. Moreover, theoretical calculations revealed that the adsorption energy of graphene for NO increased from -13.51 (physical adsorption) to -327.88 kJ/mol (chemical adsorption) after modification with Fe-C. When the graphene-supported Fe was further modified with carboxylic acid groups, the ability to transfer charge increased dramatically from 0.109 to 0.180 |e-|. Therefore, the carbon-oxygen groups increased the reducibility of Fe-C. The main results will contribute to the understanding of NO reduction and the design of effective catalysts.

Electroplating sludge derived zinc-ferrite catalyst for the efficient photo-Fenton degradation of dye.

A zinc-dominant ferrite catalyst for efficient degradation of organic dye was prepared by the calcination of electroplating sludge (ES). Characterizations indicated that zinc ferrite (ZnFe2O4) coexisted with Fe2O3 structure was the predominant phase in the calcined electroplating sludge (CES). CES displayed a high decolorization ratio (88.3%) of methylene blue (MB) in the presence of H2O2 combined with UV irradiation. The high efficiency could be ascribed to the photocatalytic process induced by ZnFe2O4 and the photo-Fenton dye degradation by ferrous content, and a small amount of Al and Mg in the sludge might also contribute to the catalysis. Moreover, the degradation capability of dye by CES was supported by the synthetic ZnFe2O4 with different Zn to Fe molar ratio (n(Zn): n(Fe)), as 84.81%-86.83% of dye was removed with n(Zn): n(Fe) ranged from 1:0.5 to 1:3. All synthetic ferrite samples in the simulation achieved adjacent equilibrium decolorization ratio, the flexible proportioning of divalent metal ions (M2+) to trivalent metal ions (M3+) applied in the synthesis indicated that the catalyst has a high availability. Therefore, an efficacious catalyst for the degradation of dye can potentially be derived from heavy metal-containing ES, it's a novel approach for the reutilization of ES.

Algal uptake of dissolved organic nitrogen in wastewater treatment plants.

The algal uptake of dissolved organic nitrogen (DON) in the anaerobic-anoxic-oxic (A2O) process was investigated in this study. Anaerobic, aerobic and effluent DON samples from two wastewater treatment plants (WWTPs) were separated into hydrophilic and hydrophobic fractions using a DAX-8 resin coupled with an anion exchange resin and a nanofiltration (NF) pretreatment. Hydrophilic DON accounted for 66.66%-88.74% of the entire DON for the two plants evaluated. After a 15-day incubation, 16.95%-91.75% DON was bioavailable for algal growth, and untreated samples exhibited higher DON bioavailability, with 52.83% DON average uptake rates, compared with the hydrophilic and hydrophobic fractions (45.53% and 44.40%, respectively) because the pretreatment caused the inorganic salt to be resistant to algae. Anaerobic untreated samples, hydrophilic fractions and hydrophobic fractions showed higher DON reduction rates and higher biomass accumulation compared with the other DON fractions due to the decomposition of resistant organics by anaerobic and anoxic bacteria. DON in aerobic and effluent samples of plant A was more bioavailable than that of plant B with usages of 27.49%-55.26% DON. DON bioavailability in the anaerobic-anoxic-oxic process decreased in the following order: anaerobic>effluent>aerobic. The DON contents were reduced after anaerobic treatment in the two plants. The EEM-PARAFAC model identified three DON components, including two humic acid-like substances and one protein-like substance in plant A and two protein-like substances and one humic acid-like substance in plant B.

Microbial bioavailability of dissolved organic nitrogen (DON) in the sediments of Lake Shankou, Northeastern China.

Dissolved organic nitrogen (DON) extracted from Lake Shankou sediments using KCl was isolated into hydrophobic and hydrophilic fractions. The bioavailabilities of the hydrophobic and hydrophilic fractions to three types of bacterial communities collected from sediments, activated sludge and compost products were examined. The DON recoveries obtained by DAX-8 and cation exchange resins treatment were 96.17%±1.58% and 98.14%±0% for the samples obtained from N4 and N14 stations, respectively. After 25 days of incubation at 25°C, most DON (59% to 96%) was degraded. Hydrophilic DON exhibited a higher reduction rate than hydrophobic DON during the growth phase. Untreated wastewater from Changshuihe town was the main degradable DON source to station N4, and 93% of hydrophilic DON and 80% of hydrophobic DON were degraded. Station N14 received a large amount of refractory DON from forest soils and exhibited DON degradation rates of 82% and 71% for the hydrophilic and hydrophobic fractions, respectively. Amino acid contents and fluorescence intensities were also analyzed. Approximately 27% to 74% of amino acids were taken up by day 5, and their concentration gradually increased in the following days due to the decomposition of dissolved proteins. Parallel factor analysis resulted in identification of tryptophan-like proteins, tyrosine-like proteins and FA-like substances. During the growth phase, 40%-51% of the tryptophan-like proteins were taken up by bacteria, and the accumulation of tyrosine-like proteins was attributed to the release of biotic substances. The concentration of the FA-like substances decreased due to microbial decomposition.

Can washing-pretreatment eliminate the health risk of municipal solid waste incineration fly ash reuse?

Although the reuse of washing-pretreated MSWI fly ash bas been a hot topic, the associated risk is still an issue of great concern. The present study investigated the influence of washing-pretreatment on the total contents and bioaccessibility of heavy metals in MSWI fly ash. Furthermore, the study incorporated bioaccessibility adjustment into probabilistic risk assessment, to quantify the health risk from multi-pathway exposure to the concerned chemicals as a result of reusing washed MSWI fly ash. The results revealed that both water-washing and acid-washing process have resulted in the concentrated heavy metal content, and have reduced the bioaccessibility of heavy metals. Besides, the acid-washing process increased the cancer risk in most cases, while the effect of water-washing process was uncertain. However, both water-washing and acid-washing pretreatment could decrease the hazard index based on bioaccesilbility. Despite the uncertainties accompanying these procedures, the results indicated that, in this application scenario, only water-washing or acid-washing process cannot reduce the actual risk from all samples to acceptable level, especially for cancer risk.

Aqueous Cr (VI) removal by Friedel's salt adsorbent prepared from calcium aluminate-rich cementitious materials.

This research paper investigated a novel absorbent of calcium aluminate-rich cementitious materials (Friedel's salt adsorbent, FA) for aqueous hexavalent chromium (VI) removal. The adsorption kinetics showed that the maximum adsorption capacities of FA were 3.36, 14.66, and 26.17 mg/g when the initial Cr(VI) concentration was 10, 50, and 100 mg/L, respectively. The adsorption fitted with the pseudo-second-order kinetic model, suggesting the important roles of intercalation in the adsorption process with increasing Cr(VI) concentrations. This Friedel's salt adsorbent is suggested as an adaptive and effective adsorbent for Cr(VI) removal in contaminated groundwater.

Decomposition of potent greenhouse gas sulfur hexafluoride (SF6) by Kirschsteinite-dominant stainless steel slag.

In this investigation, kirschsteinite-dominant stainless steel slag (SSS) has been found to decompose sulfur hexafluoride (SF6) with the activity higher than pure metal oxides, such as Fe2O3 and CaO. SSS is mainly made up of CaO·FeO·SiO2(CFS)/MgO·FeO·MnO(RO) phase conglomeration. The SF6 decomposition reaction with SSS at 500-700 °C generated solid MF2/MF3 and gaseous SiF4, SO2/SO3 as well as HF. When 10 wt % of SSS was replaced by Fe2O3 or CaO, the SF6 decomposition amount decreased from 21.0 to 15.2 or 15.0 mg/g at 600 °C. The advantage of SSS over Fe2O3 or CaO in the SF6 decomposition is related to its own special microstructure and composition. The dispersion of each oxide component in SSS reduces the sintering of freshly formed MF2/MF3, which is severe in the case of pure metal oxides and inhibits the continuous reaction of inner components. Moreover, SiO2 in SSS reacts with SF6 and evolves as gaseous SiF4, which leaves SSS with voids and consequently exposes inner oxides for further reactions. In addition, we have found that oxygen significantly inhibited the SF6 decomposition with SSS while H2O did not, which could be explained in terms of reaction pathways. This research thus demonstrates that waste material SSS could be potentially an effective removal reagent of greenhouse gas SF6.

Efficient selective catalytic reduction of NO by novel carbon-doped metal catalysts made from electroplating sludge.

Electroplating sludges, once regarded as industrial wastes, are precious resources of various transition metals. This research has thus investigated the recycling of an electroplating sludge as a novel carbon-doped metal (Fe, Ni, Mg, Cu, and Zn) catalyst, which was different from a traditional carbon-supported metal catalyst, for effective NO selective catalytic reduction (SCR). This catalyst removed >99.7% NO at a temperature as low as 300 °C. It also removed NO steadily (>99%) with a maximum specific accumulative reduced amount (MSARA) of 3.4 mmol/g. Gas species analyses showed that NO removal was accompanied by evolving N2 and CO2. Moreover, in a wide temperature window, the sludge catalyst showed a higher CO2 selectivity (>99%) than an activated carbon-supported metal catalyst. Structure characterizations revealed that carbon-doped metal was transformed to metal oxide in the sludge catalyst after the catalytic test, with most carbon (2.33 wt %) being consumed. These observations suggest that NO removal over the sludge catalyst is a typical SCR where metals/metal oxides act as the catalytic center and carbon as the reducing reagent. Therefore, our report probably provides an opportunity for high value-added utilizations of heavy-metal wastes in mitigating atmospheric pollutions.