Interaction of Ca2+ and Fe3+ in co-precipitation process induced by Virgibacillus dokdonensis and its application.

Biomineralization has garnered significant attention in the field of wastewater treatment due to its notable cost reduction compared to conventional methods. The reinjection water from oilfields containing an exceedingly high concentration of calcium and ferric ions will pose a major hazard in production. However, the utilization of biomineralization for precipitating these ions has been scarcely investigated due to limited tolerance among halophiles towards such extreme conditions. In this study, free and immobilized halophiles Virgibacillus dokdonensis were used to precipitate these ions and the effects were compared, at the same time, biomineralization mechanisms and mineral characteristics were further explored. The results show that bacterial concentration and carbonic anhydrase activity were higher when additionally adding ferric ion based on calcium ion; the content of protein, polysaccharides, deoxyribonucleic acid and humic substances in the extracellular polymers also increased compared to control. Calcium ions were biomineralized into calcite and vaterite with multiple morphology. Due to iron doping, the crystallinity and thermal stability of calcium carbonate decreased, the content of OC = O, NC = O and CO-PO3 increased, the stable carbon isotope values became much more negative, and ß-sheet in minerals disappeared. Higher calcium concentrations facilitated ferric ion precipitation, while ferric ions hindered calcium precipitation. The immobilized bacteria performed better in ferric ion removal, with a precipitation ratio exceeding 90%. Free bacteria performed better in calcium removal, and the precipitation ratio reached a maximum of 56%. This research maybe provides some reference for the co-removal of calcium and ferric ions from the oilfield wastewater.

Simultaneous immobilization of multiple heavy metal(loid)s in contaminated water and alkaline soil inoculated Fe/Mn oxidizing bacterium.

Two strains of Fe/Mn oxidizing bacteria tolerant to high concentrations of multiple heavy metal(loid)s and efficient decontamination for them were screened. The surface of the bio-Fe/Mn oxides produced by the oxidation of Fe(II) and Mn(II) by Pseudomonas taiwanensis (marked as P4) and Pseudomonas plecoglossicida (marked as G1) contains rich reactive oxygen functional groups, which play critical roles in the removal efficiency and immobilization of heavy metal(loid)s in co-contamination system. The isolated strains P4 and G1 can grow well in the following environments: pH 5-9, NaCl 0-4%, and temperature 20-30°C. The removal efficiencies of Fe, Pb, As, Zn, Cd, Cu, and Mn are effective after inoculation of the strains P4 and G1 in the simulated water system (the initial concentrations of heavy metal(loid) were 1 mg/L), approximately reaching 96%, 92%, 85%, 67%, 70%, 54% and 15%, respectively. The exchangeable and carbonate bound As, Cd, Pb and Cu are more inclined to convert to the Fe-Mn oxide bound fractions in P4 and G1 treated soil, thereby reducing the phytoavailability and bioaccessible of heavy metal(loid)s. This research provides alternatives method to treat water and soil containing high concentrations of multi-heavy metal(loid)s.

Effect of gradual increase of salt on performance and microbial community during granulation process.

Salinity was considered to have effects on the characteristics, performance microbial communities of aerobic granular sludge. This study investigated granulation process with gradual increase of salt under different gradients. Two identical sequencing batch reactors were operated, while the influent of Ra and Rb was subjected to stepwise increments of NaCl concentrations (0-4 g/L and 0-10 g/L). The presence of filamentous bacteria may contribute to granules formed under lower salinity conditions, potentially leading to granules fragmentation. Excellent removal efficiency achieved in both reactors although there was a small accumulation of nitrite in Rb at later stages. The removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Ra were 95.31%, 93.70% and 88.66%, while the corresponding removal efficiencies in Rb were 94.19%, 89.79% and 80.74%. Salinity stimulated extracellular polymeric substances (EPS) secretion and enriched EPS producing bacteria to help maintain the integrity and stability of the aerobic granules. Heterotrophic nitrifying bacteria were responsible for NH4+-N and NO2--N oxidation of salinity systems and large number of denitrifying bacteria were detected, which ensure the high removal efficiency of TN in the systems.

Disentangling microbial coupled fillers mechanisms for the permeable layer optimization process in multi-soil-layering systems.

The multi-soil-layering (MSL) systems is an emerging solution for environmentally-friendly and cost-effective treatment of decentralized rural domestic wastewater. However, the role of the seemingly simple permeable layer has been overlooked, potentially holding the breakthroughs or directions to addressing suboptimal nitrogen removal performance in MSL systems. In this paper, the mechanism among diverse substrates (zeolite, green zeolite and biological ceramsite) coupled microorganisms in different systems (activated bacterial powder and activated sludge) for rural domestic wastewater purification was investigated. The removal efficiencies performed by zeolite coupled with microorganisms within 3 days were 93.8% for COD, 97.1% for TP, and 98.8% for NH4+-N. Notably, activated sludge showed better nitrification and comprehensive performance than specialized nitrifying bacteria powder. Zeolite attained an impressive 89.4% NH4+-N desorption efficiency, with a substantive fraction of NH4+-N manifesting as exchanged ammonium. High-throughput 16S rRNA gene sequencing revealed that aerobic and parthenogenetic anaerobic bacteria dominated the reactor, with anaerobic bacteria conspicuously absent. And the heterotrophic nitrification-aerobic denitrification (HN-AD) process was significant, with the presence of denitrifying phosphorus-accumulating organisms (DPAOs) for simultaneous nitrogen and phosphorus removal. This study not only raises awareness about the importance of the permeable layer and enhances comprehension of the HN-AD mechanism in MSL systems, but also provides valuable insights for optimizing MSL system construction, operation, and rural domestic wastewater treatment.

Efficient magnetic capture of PE microplastic from water by PEG modified Fe3O4 nanoparticles: Performance, kinetics, isotherms and influence factors.

Due to their resistance to degradation, wide distribution, easy diffusion and potential uptake by organisms, microplastics (MPs) pollution has become a major environmental concern. In this study, PEG-modified Fe3O4 magnetic nanoparticles demonstrated superior adsorption efficiency against polyethylene (PE) microspheres compared to other adsorbents (bare Fe3O4, PEI/Fe3O4 and CA/Fe3O4). The maximum adsorption capacity of PE was found to be 2203 mg/g by adsorption isotherm analysis. PEG/Fe3O4 maintained a high adsorption capacity even at low temperature (5°C, 2163 mg/g), while neutral pH was favorable for MP adsorption. The presence of anions (Cl-, SO42-, HCO3-, NO3-) and of humic acids inhibited the adsorption of MPs. It is proposed that the adsorption process was mainly driven by intermolecular hydrogen bonding. Overall, the study demonstrated that PEG/Fe3O4 can potentially be used as an efficient control against MPs, thus improving the quality of the aquatic environment and of our water resources.

Enhanced Cd2+ removal from aqueous solution using olivine and magnesite combination: New insights into the mechanochemical synergistic effect.

In this study, an efficient stabilizer material for cadmium (Cd2+) treatment was successfully prepared by simply co-milling olivine with magnesite. Several analytical methods including XRD, TEM, SEM and FTIR, combined with theoretical calculations (DFT), were used to investigate mechanochemical interfacial reaction between two minerals, and the reaction mechanism of Cd removal, with ion exchange between Cd2+ and Mg2+ as the main pathway. A fixation capacity of Cd2+ as high as 270.61 mg/g, much higher than that of the pristine minerals and even the individual/physical mixture of milled olivine and magnesite, has been obtained at optimized conditions, with a neutral pH value of the solution after treatment to allow its direct discharge. The as-proposed Mg-based stabilizer with various advantages such as cost benefits, green feature etc., will boosts the utilization efficiency of natural minerals over the elaborately prepared adsorbents.

Immobilization of laccase on magnetic PEGDA-CS inverse opal hydrogel for enhancement of bisphenol A degradation in aqueous solution.

Endocrine disruptors such as bisphenol A (BPA) adversely affect the environment and human health. Laccases are used for the efficient biodegradation of various persistent organic pollutants in an environmentally safe manner. However, the direct application of free laccases is generally hindered by short enzyme lifetimes, non-reusability, and the high cost of a single use. In this study, laccases were immobilized on a novel magnetic three-dimensional poly(ethylene glycol) diacrylate (PEGDA)-chitosan (CS) inverse opal hydrogel (LAC@MPEGDA@CS@IOH). The immobilized laccase showed significant improvement in the BPA degradation performance and superior storage stability compared with the free laccase. 91.1% of 100 mg/L BPA was removed by the LAC@MPEGDA@CS@IOH in 3 hr, whereas only 50.6% of BPA was removed by the same amount of the free laccase. Compared with the laccase, the outstanding BPA degradation efficiency of the LAC@MPEGDA@CS@IOH was maintained over a wider range of pH values and temperatures. Moreover, its relative activity of was maintained at 70.4% after 10 cycles, and the system performed well in actual water matrices. This efficient method for preparing immobilized laccases is simple and green, and it can be used to further develop ecofriendly biocatalysts to remove organic pollutants from wastewater.

Adsorption removal of mercury from flue gas by metal selenide: A review.

Mercury (Hg) pollution has been a global concern in recent decades, posing a significant threat to entire ecosystems and human health due to its cumulative toxicity, persistence, and transport in the atmosphere. The intense interaction between mercury and selenium has opened up a new field for studying mercury removal from industrial flue gas pollutants. Besides the advantages of good Hg° capture performance and low secondary pollution of the mineral selenium compounds, the most noteworthy is the relatively low regeneration temperature, allowing adsorbent regeneration with low energy consumption, thus reducing the utilization cost and enabling recovery of mercury resources. This paper reviews the recent progress of mineral selenium compounds in flue gas mercury removal, introduces in detail the different types of mineral selenium compounds studied in the field of mercury removal, reviews the adsorption performance of various mineral selenium compounds adsorbents on mercury and the influence of flue gas components, such as reaction temperature, air velocity, and other factors, and summarizes the adsorption mechanism of different fugitive forms of selenium species. Based on the current research progress, future studies should focus on the economic performance and the performance of different carriers and sizes of adsorbents for the removal of Hg0 and the correlation between the gas-particle flow characteristics and gas phase mass transfer with the performance of Hg0 removal in practical industrial applications. In addition, it remains a challenge to distinguish the oxidation and adsorption of Hg0 quantitatively.

Electrochemical removal of nitrate in high-salt wastewater with low-cost iron electrode modified by phosphate.

Nitrate (NO3-) is a widespread pollutant in high-salt wastewater and causes serious harm to human health. Although electrochemical removal of nitrate has been demonstrated to be a promising treatment method, the development of low-cost electro-catalysts is still challenging. In this work, a phosphate modified iron (P-Fe) cathode was prepared for electrochemical removal of nitrate in high-salt wastewater. The phosphate modification greatly improved the activity of iron, and the removal rate of nitrate on P-Fe was three times higher than that on Fe electrode. Further experiments and density functional theory (DFT) calculations demonstrated that the modification of phosphoric acid improved the stability and the activity of the zero-valent iron electrode effectively for NO3- removal. The nitrate was firstly electrochemically reduced to ammonium, and then reacted with the anodic generated hypochlorite to N2. In this study, a strategy was developed to improve the activity and stability of metal electrode for NO3- removal, which opened up a new field for the efficient reduction of NO3- removal by metal electrode materials.

Dissolved organic matter characteristics linked to bacterial community succession and nitrogen removal performance in woodchip bioreactors.

Woodchip bioreactors are an eco-friendly technology for removing nitrogen (N) pollution. However, there needs to be more clarity regarding the dissolved organic matter (DOM) characteristics and bacterial community succession mechanisms and their association with the N removal performance of bioreactors. The laboratory woodchip bioreactors were continuously operated for 360 days under three influent N level treatments, and the results showed that the average removal rate of TN was 45.80 g N/(m3·day) when the influent N level was 100 mg N/L, which was better than 10 mg N/L and 50 mg N/L. Dynamic succession of bacterial communities in response to influent N levels and DOM characteristics was an important driver of TN removal rates. Medium to high N levels enriched a copiotroph bacterial module (Module 1) detected by network analysis, including Phenylobacterium, Xanthobacteraceae, Burkholderiaceae, Pseudomonas, and Magnetospirillaceae, carrying N-cycle related genes for denitrification and ammonia assimilation by the rapid consumption of DOM. Such a process can increase carbon limitation to stimulate local organic carbon decomposition to enrich oligotrophs with fewer N-cycle potentials (Module 2). Together, this study reveals that the compositional change of DOM and bacterial community succession are closely related to N removal performance, providing an ecological basis for developing techniques for N-rich effluent treatment.

Acute inhibitory effects of tire wear particles on the removal of biological phosphorus：The critical role of aging in improving environmentally persistent free radicals.

A comparative study explored how photoaging, ozonation aging, and Fenton aging affect tire wear particles (TWPs) and their phosphorus (P) removal in activated sludge. Aging altered TWPs' properties, increasing surface roughness, porosity, and generating more small particles, especially environmental persistent free radicals (EPFRs) in ozonation and Fenton aging. Post-aging TWPs (50 mg/L) inhibited sludge P removal significantly (p < 0.05), with rates of 44.3% and 59.6% for ozonation and Fenton aging, respectively. In addition, the metabolites involved in P cycling (poly-ß-hydroxyalkanoates: PHA and glycogen) and essential enzymes (Exopolyphosphatase: PPX and Polyphosphate kinase: PPK) were significantly inhibited (p < 0.05). Moreover, TWPs led to a decrease in microbial cells within the sludge and altered the community structure, a situation exacerbated by the aging of TWPs. P-removing bacteria decreased (e.g., Burkholderia, Candidatus), while extracellular polymeric substance-secreting bacteria increased (e.g., Pseudomonas, Novosphingobium). Pearson correlation analysis highlighted EPFRs' role in TWPs' acute toxicity to microbial cells, yet, emphasizing particle size's impact on the sludge system's purification and community structure.

Study on the key parameters of ice particle air jet ejector structure.

Existing ice particle jet surface treatment technology is prone to ice particle adhesion during application, significantly affecting surface treatment efficiency. Based on the basic structure of the jet pump, the ice particle air jet surface treatment technology is proposed for the instant preparation and utilization of ice particles, solving the problem of ice particle adhesion and clogging. To achieve efficient utilization of ice particles and high-speed jetting, an integrated jet structure for ice particle ejection and acceleration was developed. The influence of the working nozzle position (Ld), expansion ratio (n), and acceleration nozzle diameter ratio (Dn) length-to-diameter ratio (Ln) on the ice particle ejection and acceleration was systematically studied. The structural parameters of the ejector were determined using the impact kinetic energy of ice particles as the comprehensive evaluation index, and the surface treatment test was conducted to verify the results. The study shows that under 2 MPa air pressure, the ejector nozzle parameters of n = 1.5, Dn = 4.0, Ld = 4, and Ln = 0 mm can effectively eject and accelerate the ice particles. The aluminum alloy plate depainting test obtained a larger paint removal radius and resulted in a smoother aluminum alloy plate surface, reducing the surface roughness from 3.194 ± 0.489 µm to 1.156 ± 0.136 µm. The immediate preparation and utilization of ice particles solved the problems of adhesion and storage in the engineering application of ice particle air jet technology, providing a feasible technical method in the field of material surface treatment.

Virtual reality use in pediatric patients for orthopedic clinical procedures: A randomized prospective trial of efficacy.

Background: Distraction therapy use such as virtual reality is novel in the pediatric orthopedic field. In this study, we use subjective and objective metrics to evaluate virtual reality efficacy to reduce anxiety and pain in a pediatric orthopedic cohort. Methods: A prospective randomized controlled trial included patients between age 5 and 17 years, presenting to a tertiary care pediatric orthopedic clinic. Parallel groups underwent orthopedic procedures in clinic, utilizing immersive and interactive virtual reality distraction therapies versus standard of care. Procedures included cast application, cast removal, bone pin removal, and fracture reduction. All preprocedure parameters were similar between the groups. Primary outcome was the difference between maximum procedural heart rate and baseline. Secondary outcomes included Wong Baker FACES Rating Scale (Wong & Baker, 1988, Oklahoma, USA) for pain and Visual Analog Scale scores for anxiety. Results: Ninety-five patients (66 M, 29 F) underwent 59 cast removals, 26 cast applications, 7 percutaneous pin removals, and 3 fracture reductions. Average patient age in the virtual reality and control cohorts was 10.1 (5-17) and 10.6 (5-17), respectively. Average change in maximum heart rate in the virtual reality and control groups was 10.6 ± 10.1 versus 18.4 ± 11.0 (p = 0.00048). The virtual reality group demonstrated trends toward lower perceived anxiety (1.7 ± 2.8 versus 2.9 ± 3.6, p = 0.0666) when compared to controls. Conclusions: This level 1 study is the first to utilize objective biometric measurements to evaluate use of interactive virtual reality during multiple types of pediatric orthopedic procedures in the clinical setting. The findings suggest that an interactive and immersive virtual reality experience can be effective in reducing pain and anxiety. Level of evidence: Level 1, Randomized Controlled Trial.

Composition of the microbial community in surface flow-constructed wetlands for wastewater treatment.

Traditionally constructed wetlands face significant limitations in treating tailwater from wastewater treatment plants, especially those associated with sugar mills. However, the advent of novel modified surface flow constructed wetlands offer a promising solution. This study aimed to assess the microbial community composition and compare the efficiencies of contaminant removal across different treatment wetlands: CW1 (Brick rubble, lignite, and Lemna minor L.), CW2 (Brick rubble and lignite), and CW3 (Lemna minor L.). The study also examined the impact of substrate and vegetation on the wetland systems. For a hydraulic retention time of 7 days, CW1 successfully removed more pollutants than CW2 and CW3. CW1 demonstrated removal rates of 72.19% for biochemical oxygen demand (BOD), 74.82% for chemical oxygen demand (COD), 79.62% for NH4 +-N, 77.84% for NO3 --N, 87.73% for ortho phosphorous (OP), 78% for total dissolved solids (TDS), 74.1% for total nitrogen (TN), 81.07% for total phosphorous (TP), and 72.90% for total suspended solids (TSS). Furthermore, high-throughput sequencing analysis of the 16S rRNA gene revealed that CW1 exhibited elevated Chao1, Shannon, and Simpson indices, with values of 1324.46, 8.8172, and 0.9941, respectively. The most common bacterial species in the wetland system were Proteobacteria, Spirochaetota, Bacteroidota, Desulfobacterota, and Chloroflexi. The denitrifying bacterial class Rhodobacteriaceae also had the highest content ratio within the wetland system. These results confirm that CW1 significantly improves the performance of water filtration. Therefore, this research provides valuable insights for wastewater treatment facilities aiming to incorporate surface flow-constructed wetland tailwater enhancement initiatives.

Revealing the functional potential of microbial community of activated sludge for treating tuna processing wastewater through metagenomic analysis.

Reports regarding the composition and functions of microorganisms in activated sludge from wastewater treatment plants for treating tuna processing wastewater remains scarce, with prevailing studies focusing on municipal and industrial wastewater. This study delves into the efficiency and biological dynamics of activated sludge from tuna processing wastewater, particularly under conditions of high lipid content, for pollutant removal. Through metagenomic analysis, we dissected the structure of microbial community, and its relevant biological functions as well as pathways of nitrogen and lipid metabolism in activated sludge. The findings revealed the presence of 19 phyla, 1,880 genera, and 7,974 species, with Proteobacteria emerging as the predominant phylum. The study assessed the relative abundance of the core microorganisms involved in nitrogen removal, including Thauera sp. MZ1T and Alicycliphilus denitrificans K601, among others. Moreover, the results also suggested that a diverse array of fatty acid-degrading microbes, such as Thauera aminoaromatica and Cupriavidus necator H16, could thrive under lipid-rich conditions. This research can provide some referable information for insights into optimizing the operations of wastewater treatment and identify some potential microbial agents for nitrogen and fatty acid degradation.

Removing information from working memory with a delay: Effective but not beneficial.

Ideally, removing outdated information from working memory (WM) should have two consequences: The removed content should be less accessible (removal costs), and other WM content should benefit from the freeing up of WM capacity (removal benefits). Robust removal benefits and removal costs have been demonstrated when people are told to forget items shortly after they were encoded (immediate removal). However, other studies suggest that people might be unable to selectively remove items from an already encoded set of items (delayed removal). In two experiments (n = 219; n = 241), we investigated the effectiveness and consequences of delayed removal by combining a modified version of Ecker's et al. (Journal of Memory and Language, 74, 77-90, 2014) letter updating task with a directed-forgetting in WM paradigm. We found that while delayed removal resulted in reduced memory for the to-be-forgotten item-location relations (removal costs), it failed to enhance performance for existing WM content. This contrasts sharply with immediate removal, where removal benefits can be observed. A fine-grained analysis of removal benefits shows that removal from WM proactively facilitates the subsequent encoding of new information but does not retroactively aid stored WM content.

Ventriculoperitoneal shunt tube migration into the heart and pulmonary artery: successful tube removal. Illustrative case.

BACKGROUND: Ventriculoperitoneal (VP) shunt tube migration is recognized as an occasional complication; however, migration into the cardiac system is rare. The authors report a case of VP shunt tube migration into the heart and pulmonary artery and the safe removal of the tube. OBSERVATIONS: The patient had a VP shunt implanted for hydrocephalus after a subarachnoid hemorrhage. The screening chest radiograph taken a few months later showed the migration of the abdominal tube into the heart. Examinations revealed that the abdominal tube had migrated from the left subclavian vein, passed through the superior vena cava, right atrium and ventricle, and looped into the pulmonary artery. The patient had no symptoms; however, there were some risks, such as damage to the valves or fatal arrhythmia. The authors therefore decided to remove the tube. To avoid various intraoperative risks, in particular tube knot formation, the tube was removed under fluoroscopy with a guidewire inserted, which was 0.035 inches for the angiography catheter. The tube was successfully removed without any complications. LESSONS: Knot formation can be one of the fatal complications of shunt tube removal. The authors' technique is an effective method for safe removal. https://thejns.org/doi/10.3171/CASE24127.

Fabrication and characterization of biodegradable hydrogel beads of guar gum for the removal of chlorpyrifos pesticide from water.

A new guar gum hydrogel beads were fabricated by dropping method from an aqueous solution of guar gum (GG) using ammonium persulphate and polyethylene glycol as initiator and crosslinker respectively, for the adsorption of chlorpyrifos (CP) from water. The semi-crystalline nature of the synthesized beads was confirmed by FESEM analysis. The TGA studies implied that the beads were thermally stable up to 600 °C. The maximum swelling ratio of 1400 gg-1 was attained at pH 9.2 and 80 min. The evidence of a strong absorption band was found in FTIR spectrum at 584 cm-1 due to -P=S of the adsorbed pesticide CP. The maximum adsorption of CP was found to be 220.97 mgg-1. The adsorption followed pseudo second-order kinetics and Langmuir adsorption isotherm with regression coefficients 0.9998 and 0.9938 which followed the chemisorption process. It is due to the hydrolysis of CP at pH 9.2 to yield 3,5,6-trichloropyridinol which in turn reacts with the carboxylic group present in GG giving -N-C=O linkage. A -ΔG indicates that the process is spontaneous and involves chemisorption which is thermodynamically and kinetically favorable and a -ΔH value (-10.37 kJ/mol) suggests that the adsorption is exothermic.

Deep-root respiration: The unknown CO2 removed from the atmosphere.

Carbon (C) sequestration in soils is a promising CO2 removal approach. So far, the focus has been on how to increase the content of soil organic C (SOC), while the management soil inorganic C (SIC), i.e. carbonate minerals, has received little attention, because SIC is thought to be much less involved in biotic C cycling than SOC. However, in principle SIC management potentially provides a long-term solution, with a much greater capacity for C sequestration than SOC. The forgotten link is the dissolved inorganic carbon (DIC), i.e. CO2 species dissolved in soil solution, and its fate throughout the unsaturated zone (USZ). The return of CO2 respired by deep roots to the atmosphere, either directly through CO2 degassing or indirectly through DIC leaching, may not necessarily take place over decades or centuries. CO2 diffusion decreases sharply with depth due to reduced porosity of the subsoil and more water-filled pores. The downward water percolation rate is often only a few centimeters per year, and the large amount of respired CO2 compared to the leached DIC results in a relatively small amount of CO2 being transferred to the groundwater. Therefore, respired CO2 at deeper soil depth can be defined as a hitherto unknown ecosystem service of deep-rooted plants i.e. providing a net C sink as inorganic C in the USZ. A conservative estimation suggests a C sink as SIC of at least 80 kg C ha-1 y-1, comparable to reported annual C sequestration as SOC in temperate grasslands.

Evaluating MODIS cloud-free snow cover datasets using massive spatial benchmark data in the Tibetan Plateau.

Accurate snow cover data is crucial for understanding climate change, managing water resources, and calibrating models. The MODIS (Moderate-resolution Imaging Spectroradiometer) and its cloud-free snow cover datasets are widely used, but they have not been systematically evaluated due to different benchmark data and evaluation parameters. Conventional methods using station observations as a ground truth suffer from underrepresentation and mismatches in temporal and spatial scales. This study established a scale-matched spatial benchmark dataset, compiling from 18,433 Landsat series and 11,172 Sentinel-2 images over two decades, totaling ∼1.86 billion samples and ∼320 million snow samples. We evaluated seven MODIS cloud-free snow cover datasets for seasons, elevation zones, land covers and subregions using this benchmark data. For the clear-sky part, NIEER_MODIS_SCE (MODIS snow cover extent product over China) performs best due to its use of optimal NDSI thresholds suitable for each land use type. This highlights the importance of regional customization in snow mapping algorithms, and it can be further improved in spring, forests and zone 1 by combining it with M*D10A1GL06. For the cloud removed part, one-step integrated spatiotemporal cloud removal datasets perform better than any other approach does. The second-best dataset is obtained from a simple but effective single temporal cloud removal method using nearby time information. For the whole dataset, the best NIEER_MODIS_SCE has an overall accuracy of 0.82 and snow retrieval accuracy of 84.56 %. It performs excellently in most settings but weakest in forests thus requiring more efficient strategies. This research provides new perspectives and methods for objectively assessing MODIS snow cover products and other relevant datasets. These methods can be readily extended to other regions and adapted to future satellite missions. And such findings may guide the selection of more valid snow cover data and the developing of even better snow detecting strategies.