Photocatalytic oxidation through semiconductor photocatalysis is an efficient and green technology for pollutant removal, which has been widely applied to degrade volatile organic chemicals under ambient conditions. However, most of reports focus on the reduction of VOCs concentration while ignore the generation of toxic intermediates, as well as the corresponding secondary pollution. Therefore, it is necessary to further explore how to timely achieve efficient and deep oxidation of VOCs. In this review, we undertake a detailed analysis of photocatalytic degradation of toluene, a representative compound of aromatic hydrocarbon VOCs, and identify the most capable phenolized pathway governed by hydroxyl radicals (•OH). With this pathway, no toxic intermediate like benzene is produced during the photocatalysis. The driving factor, oxygen vacancy (OV), for fueling the generation of •OH is highlighted and the specific approaches including doping engineering and co-catalyst loading that can create rich OVs in semiconductor photocatalysts are described. Furthermore, the challenges and opportunities faced by the phenolized pathway in the future development are prospected.
Germanium, a critical yet often overlooked metal, has experienced significant shifts in its global market, largely driven by China’s dominant role. However, concerns are growing over the sustainability of germanium supply in China due to imbalances in mining, manufacturing, recycling, and rising demand. In this study, we employ substance flow analysis to provide a quantitative assessment of China’s germanium flow system in 2019, and we project future demand and anthropogenic mineral generation up to 2050 using stock-driven models. Our results indicate that by 2050, domestic demand for germanium will increase to 164–187 t—double the demand in 2019—with infrared optics and solar cells being the primary drivers. A supply shortage is anticipated before 2040, although recycling through urban mining could meet around 30% of the demand. These findings underscore the urgent need to address emerging supply challenges and offer critical insights for policymakers and stakeholders to inform strategic decision-making.
Chlorite (ClO2− or COI) is used to establish the advanced reduction and oxidation process (AROP). The iron/biochar-based particles (iron-based hydrothermal carbon with hinge-like structure, FebHCs, 20 mg/L) can be utilized to activate COI (2 mmol/L) to present selective oxidation in removing triphenylmethane derivatives (15 min, 90%). The protonation (H+ at ~102 μmol/L level) played a huge role (k-2nd = 0.136c-H+ − 0.014 (R2-adj = 0.986), and rapp = − 0.0876/c-H+ + 1.017 (R2-adj = 0.996)) to boost the generation of the active species (e.g., high-valent iron oxidizing species (HVI=O) and chlorine dioxide (ClO2)). The protonation-coupled electron transfer promoted Fe-substances in Feb/HCs activating COI (the calculated kobs ranging from 0.066−0.285 min−1). The form of ClO2 mainly attributed to proton-coupled electron transfer (1e/1H+). The HVI=O was generated from the electron transfer within the coordination complex. Moreover, carbon particles in FebHCs serve as the bridge for electron transfer. The above roles contribute to the fracture and formation of coordination-induced bonds between Lx-FeII/III and ClO2− at phase interface to form AROP. The ultrasonic (US) cavitation enhanced the mass transfer of active species in bulk solution, and the HVI=O and ClO2 attack unsaturated central carbon atoms of triphenylmethane derivatives to initiate selective removal. Furthermore, the scale-up experiment with continuous flow (k values of approximately 0.2 min−1, COD removal efficiency of approximately 80%) and the reactor with COMSOL simulation have also proved the applicability of the system. The study offers a novel AROP and new insights into correspondingly heterogeneous interface activation mechanisms.
Insights into the microbial communities in municipal wastewater treatment plants (WWTPs) are critical for the optimization of biological nutrient removal process. However, our understanding about the spatiotemporal characteristics of the microbial communities in WWTPs remains limited. In the present study, 264 samples were collected biweekly from four spatially independent corridors in a typical municipal WWTP. The annual compositional and metagenomic characteristics were investigated based on multiple ecological indicators using statistical tests. The results revealed that the microbial community compositions from the four corridors showed significantly high similarities, as revealed by the statistical analysis at the operational taxonomic unit (OTU) level. Consistent with the OTU level results, the functionality of the microbial communities in the four independent corridors also showed significant similarity. In comparison, the dynamics of the microbial community over the year showed two successional peaks of the microbial communities with the spatial similarity, and this resulted in three alternative stable states of the microbial communities in a calendar year. The microbial communities only drifted in July and November, suggesting an uneven community succession pattern driven by seasonal variation in environmental conditions. The functional characteristics were found to be relatively conservative compared to the microbial community succession, which revealed the decoupling between the composition and functionality of the microbial community in the municipal WWTP. The present study provides an in-depth overview of the microbial communities in a municipal WWTP and will be useful for the establishment of the connection between ecological characteristics and the operational stability of WWTPs.
The catalytic degradation of single-component VOCs has been widely studied. However, several types of VOCs may be present in an actual industrial emission stream. Efficient synergistic removal of multicomponent VOCs is currently a popular research topic. Herein, Mn–Co samples with various Mn/Co ratios (1:2, 1:1, and 2:1) were successfully prepared, and the catalytic oxidation performance characteristics toward benzene and toluene over these samples under single and binary VOC oxidation conditions were studied. Compared with pure MnOx and CoOx, the prepared Co–Mn composite oxide samples exhibited significantly improved catalytic performance. MnCoOx and MnCo2Ox showed optimum catalytic performance, with 100% benzene and 100% toluene conversion in the mixtures at 300 and 350 °C, 100% CO2 selectivity. Characterization methods were employed to elucidate the relevance of the catalytic activity to the structures, acidity, redox properties, Mn–Co valence state and oxygen species. Moreover, the interactions between benzene and toluene during their synergistic degradation, as well as the intermediates and potential reaction mechanisms of their simultaneous elimination, were investigated. Utilizing Mn–Co oxide compounds for cooperative catalytic oxidation of benzene and toluene represents a viable and effective technique for the practical and synergist elimination of multicomponent VOCs.
This study evaluates the performance of small-scale high-temperature treatment facilities for managing rural domestic waste on the Tibetan Plateau and investigates the emission characteristics of dioxin pollutants. Seven small-scale facilities (with capacities ranging from 3 to 25 t/d) selected from a total of 183 different facilities in the Tibetan Plateau region, underwent on-site sampling and laboratory multi-threaded pollutant analysis of pollutants. The results revealed that dioxin emission concentrations in the flue gas ranged from 0.085 to 53.6 ng I-TEQ/Nm3. The primary mechanism for dioxin synthesis in the flue gas of small-scale gasification incinerators and high-temperature pyrolysis furnaces consisted of the precursor formation mechanism, whereas de novo synthesis was observed in conventional incinerators. Dioxin concentrations in fly ash varied from 0.0060 to 11.59 ng I-TEQ/g, with precursor synthesis as the dominant pathway. The distribution of dioxin in activated carbon and desulfurization lye notably differed significantly from that in the flue gas and fly ash congeners. Additionally, the dioxin content in the pyrolysis products exceeded both the concentrations in purchased-coal and the relevant emission limits. The total emission factors for these facilities ranged from 0.49 to 326.92 μg I-TEQ/t, with variations of the distribution of dioxin emission factors observed across different facilities.
Currently, there is an increasing interest in developing efficient and cost-effective treatment technologies to remediate per- and polyfluoroalkyl substances (PFAS) in water. Biochars (pristine and modified/engineered) can be a good candidate among porous pyrogenic carbonaceous materials for the sorptive removal of PFAS from water/wastewater. There is a need to focus on developing efficient, environmentally friendly, and cost-effective techniques for desorbing PFAS from spent biochars (pristine and modified/engineered) to enable potential reuse or suitable disposal of these adsorbents, facilitating their future full-scale application in the water sector. This review article briefly compiles the state-of-the-art knowledge on the: (i) application of pristine and modified/engineered biochars for the sorptive removal of PFAS from aqueous samples; (ii) regeneration/reuse techniques for the spent biochars; and (iii) economic analysis of their use in PFAS removal from water/wastewater. Further investigations on (i) better modifying/engineering biochars to remove specially short-chain PFAS species in real environmental water samples due to challenging nature of their removal using conventional treatment technologies; (ii) feasible low-energy, environmentally friendly, and cost-effective strategies for regeneration/reuse of the spent biochars (pristine and modified/engineered) and management of their end-of-life; and (iii) large-scale and continuous column sorption operation for the real water/wastewater samples are still desirable to apply biochars for PFAS removal at full-scale in the future.
Aeration is pivotal in accelerating landfill stabilization. Biodegradation kinetic models of landfills have not fully accounted for the uneven distribution of oxygen during aerobic in situ stabilization, owing to the high heterogeneity of landfills. In this study, a successive degradation of organic matter (SDOM) model is proposed to calculate the reaction rate constant of municipal solid waste (MSW). The SDOM model assumes that organic matter (OM) is composed of n independent shares, with each share starting to degrade at different times. However, all fractions degrade according to first-order kinetics once they enter the reaction phase. In this study, degradation tests of typical organic matter in landfills were conducted under varying oxygen concentrations, and the reaction rates for each degradation test were calculated using the SDOM model. Subsequently, a model was developed to simulate the variation in the reaction rate constant with the oxygen concentration. Superposition tests on multiple types of organic matter were conducted to further validate the superposition principle of the degradation process. Model verification using real waste data revealed a reaction rate constant of 0.12, demonstrating a better fit compared to the Monod model and traditional first-order kinetic model, as well as the highest accuracy in the calculation of CO2 produced in the degradation process. The SDOM model can help to understand the degradation mechanism of the aerobic in situ stabilization of landfills in a better manner.
Perfluorinated acids (PFAs) are a new class of persistent organic pollutants that are difficult to defluorinate or remove. The reductive degradation of various representative PFAs in a biomimetic system composed of vitamin B12 (VB12) as a catalyst and nano-zero-valent iron-nickel bimetal (nFe0/Ni0) as a reductant was investigated in this study. The effects of the self-structures of PFAs and the coexisting substances in natural water were also discussed. The results indicated that the defluorination and removal rates of PFAs were highly dependent on the length and terminal functional groups of the perfluorocarbon chain. Only Perfluorocarboxylates with C > 11 and Perfluorosulfonates with C > 6 were significantly degraded. Based on the analysis of the degradation products of perfluorobutanesulfonate (PFBS), perfluorohexanesulfonate (PFHxS), prefluorooctanesulfonate (PFOS), and 2-perfluoroctyl ethanol (8:2 FTOH), hydrolysis followed by the scission of C–S or C–C connecting the terminal functional groups was the dominant degradation pathway of long-chain PFAs instead of cleavage of C–C in the perfluorocarbon chain. The perfluorocarbon chain length affects the product type. It is speculated that the high bond dissociation energies of C–F bonds in short-chain PFAs hinder the occurrence of the decarboxylation-hydroxylation-elimination-hydrolysis (DHEH) pathway and make the addition of (–CF2–)n dominant. Meanwhile, the inhibition of SO42– removal by PFOS was significant, whereas humic acid, Cl–, and dissolved oxygen had only a slight influence. Overall, this study provides new insights on the degradation of PFAs containing multiple structures and highlights the impact of the self-structure on PFAs removal.
Polyethylene-based plastic mulch films are widely utilized in agriculture due to their benefits in improving soil conditions and crop yield. However, their degradation into microplastics has been shown to negatively impact plant growth and development, posing a significant source of plastic pollution in the agroecosystem. In response to this issue, the present study aimed to design an innovative bioremediation system based on PGPR (Pseudomonas aeruginosa), biochar, and UV treatment for the degradation of plastics. Additionally, the phytotoxic effects of plastic residues on the growth of Spinacia oleracea (spinach) were evaluated to understand the impact of plastic contamination on plant health. Bacterial strains were isolated from vegetable-cultivated soil with plastic mulch. The bacterial strain demonstrating the most effective plant growth-promoting properties and plastic degradation efficiency was identified as Pseudomonas aeruginosa (OP007126). Biochar was prepared from food waste and thoroughly characterized. Polyethylene (PE) was exposed to UV radiation to induce degradation. A glass house experiment was then designed to assess the effect of PGPR, biochar, and UV radiation on mitigating plastic-induced stress and promoting plant growth. Fourier transform infrared spectroscopy (FTIR) and weight loss measurement showed a maximum degradation of 62% with a combination of all treatments. PE negatively affected the morphology of the plant as it decreased the shoot and root fresh weight by up to 60%. Biochemical parameters of spinach were also affected by PE, as proline content increased by up to 45%. The use of amendments demonstrated effectiveness in alleviating the detrimental impact of PE on spinach plants, as evidenced by improvements in morphological, physiologic, and biochemical parameters. This approach presents a promising strategy to mitigate the detrimental effects of plastic mulch and warrants further investigation through field trials.
The Ningxia region in Northwest China, a significant grain-producing area, heavily relies on the Yellow River for agricultural irrigation. Maintaining the ecological health of the Yellow River is crucial due to its role as the primary water source. This research comprehensively assessed heavy metal (HM) levels in surface water and sediments within the Ningxia section of the Yellow River basin. It specifically examined the concentrations of Sr, Zn, Mn, Cu, As, Cd, Cr, Co, Sb, Pb, Tl, Ni, and Hg, detailing their spatial distribution and associated risks. Sources of pollution were identified, and their relationships were explored using statistical analysis and positive matrix factorization (PMF). The risk assessment results indicated elevated pollution levels of Tl and slight pollution of Hg in surface water. Integrated Nemerow Pollution Index (
Microplastics have received increasing attention in soil ecosystems, and their potential impacts on soil properties have raised concerns. Pesticides are the most prevalent pollutants in soil, but their combined effects with microplastics on the soil environment have not been elucidated. In this study, polystyrene microplastics (PS MPs) and imidacloprid (IMI) were added to the soil to investigate their combined effects on soil physicochemical characteristics, nitrogen and phosphorus contents, related transformation activities, and the composition of nitrogen- and phosphorus-transforming microorganisms. The results revealed that the coexistence of PS MPs and IMI led to a significantly higher soil pH level and lower water-stable aggregate (WSA) content. Additionally, it increased the relative abundance of nitrogen- and phosphorus-transforming microorganisms, including ammonia-oxidizing archaea and bacteria, nitrite-oxidizing bacteria, heterotrophic denitrifying bacteria, phosphate-solubilizing bacteria. PS MPs increased the soil potential denitrification rate by 14.53% owing to a significantly higher pH level. However, this promotion disappeared when they combined with IMI. The coexistence of PS MPs and IMI caused a significant decrease in WSA content, thereby improving soil aeration and increasing the relative abundance of phosphate-solubilizing bacteria, which led to a 14.54% and 44.79% increase in soil phosphatase activity and Olsen-P content, respectively. Variance partitioning analysis revealed that the coexistence of PS MPs and IMI mainly influenced nitrogen and phosphorus transformations by altering soil pH and WSA content. These results reveal the combined effects of PS MPs and IMI on soil nitrogen and phosphorus transformations and elucidate soil environmental risks associated with microplastics and pesticides.
Phytoplankton serve as vital indicators of eutrophication levels. However, relying solely on phytoplankton parameters, such as chlorophyll-a, limits our comprehensive understanding of the intricate eutrophication conditions in natural lakes, particularly in terms of timely analysis of changes in limiting nutrients and their concentrations. This study presents machine learning (ML) models for predicting and identifying lake eutrophication. Five tree-based ML models were developed using the latest data on hydrological, water quality, and meteorological parameters obtained from 34 sites in the Huating Lake basin over 5 months. The extreme gradient boosting model exhibited high accuracy in predicting the total nitrogen/total phosphorus ratio (TN/TP) (R2 = 0.88; RMSE = 24.60; MAPE = 26.14%). Analysis of the TN/TP ratio and output eigenvalue weight revealed that phosphorus plays a crucial role in eutrophication, probably because of the low-flow and deep-water characteristics of the basin. Furthermore, the light gradient boosting machine model exhibited outstanding performance and high accuracy in predicting phytoplankton parameters, especially the Shannon index (H′) (R2 = 0.92; RMSE = 0.11; MAPE = 4.95%). The mesotrophic classification of the Huating Lake determined using the H′ threshold, coincided with the findings from the H′ analysis. Future research should cover a wider range of pollution sources and spatiotemporal dimensions to further validate our findings. Overall, this study highlights the potential of incorporating the TN/TP ratio and phytoplankton parameters into ML techniques for effective monitoring and management of environmental conditions.
