Small Molecular Organic Acids Research Articles

Remediation of heavy metal-contaminated estuarine sediments by strengthening microbial in-situ mineralization

The production of in-situ iron-sulfide minerals through sulfate reduction is commonly used to immobilize heavy metals in sediments and waste residues from abandoned non-ferrous mines. Ensuring a consistent supply of organic carbon sources, such as small molecular organic acids, under optimal reduction conditions, is essential for effective biomineralization. In this study, we developed a technique to enhance the biomineralization (iron-sulfide minerals) capacity of native sulfate-reducing bacteria to immobilize heavy metals, using the facultative anaerobic fermentation bacterium Bacillus coagulans to bind to waste olivine, providing small molecular organic acids required by sulfate-reducing bacteria while providing more reduction conditions for remediation systems.Our results showed that, compared with the control group (Control) and the group added with medium (Cul), the groups added with Bacillus coagulans (Cul+Bio) and the combination of Bacillus coagulans and olivine (Cul+Bio+Oli), significantly increased the overlying water pH value, pH remained above 8 in the final stage of remediation, and decreased the redox potential and sulfate concentration, ORP remained -80 mV, SO42- concentration below 600 mg/L at the end of remediation. The addition of Bacillus coagulans and olivine helped stabilize heavy metals Cu, Pb, Zn, and Cd by reducing their release into the liquid phase. Cd and Pb were found to be in more stable forms within the solid phase. In the Cul+Bio and Cul+Bio+Oli groups, sulfur primarily existed as more reductive FeS, accounting for 55% and 75% of the sulfur speciations, respectively. Desulfuromonadia, Desulfuromonas, Desulfofustis, and Geothermobacter have been identified in the Cul+Bio+Oli experimental group in high abundance and are capable of dissimilatory sulfate reduction. The combined application of microorganisms and waste olivine offers an effective strategy for remediating in-situ heavy metal-contaminated soils/sediments, thereby establishing a theoretical and practical foundation for employing microbial mineralization in the in-situ remediation of heavy metals in sediment.

Using red mud to prepare the iron-bearing catalyst for the efficient degradation of phenol in the Fenton-like process

Phenol pollution is widely environmental and health problems that require new insights and urgent attention. A iron-bearing catalyst (FRM/2%A) was prepared with red mud by HCl dissolution, ascorbic acid reducing and precipitation of filter liquor, and activated H2O2 to degrade the phenol in synthetic wastewater. Results show that FRM/2%A had the highest degradation efficiency (99.3 %) in the reaction time of 5 min among investigative samples, due to the production of ferrous polymetallic oxides on the catalyst and the formation of mesoscopic particles and microcellular structures. The optimal conditions were 1 g/L of catalyst dosage, 5 mM of H2O2 concentration, 3–6 of initial pH and 100 mg/L of initial concentration of phenol in the FRM/2%A/H2O2 system. The degradation data fit into the pseudo-first-order kinetics model and the reaction rate constant (k) of FRM/2%A was 0.865 min−1. The removal efficiency (77 %) of COD below the value (99.3 %) of phenol degradation implied the intermediates generating during the phenol degradation. The possible degradation pathway was proposed as phenol → catechol → benzoquinone → muconic acid → small molecular organic acids → CO2 and H2O. The findings suggested a new way for the synthesis of the efficient catalyst with RM and optimal operating strategies for the treatment of phenol wastewater.

Positive profile of natural small molecule organic matters on emerging antivirus pharmaceutical elimination in advance reduction process: A deep dive into the photosensitive mechanism of triplet excited state compounds

Natural small molecular organic matter (NSOM), ubiquitous in natural waters and distinct from humic acid or fulvic acid, is a special type of dissolved organic matter (DOM) which is characterized as strong photosensitivity and simple molecular structure. However, little study had been directed on the role of NSOM in eliminating emerging contaminants in advanced reduction process (ARP). This study took three small molecular isomeric organic acids (p−hydroxybenzoic acid, pHBA; salicylic acid, SA; m−hydroxybenzoic acid, mHBA) as the representative substances of NSOM to explore these mechanisms on promoting Ribavirin (RBV, an anti COVID−19 medicine) degradation in ultraviolet activated sulfite (UV/Sulfite) process. The results demonstrated that the observed degradation rate constant of RBV (kobs-RBV) was 7.56 × 10−6 s−1 in UV/Sulfite process, indicating that hydrated electron (eaq−) from UV/Sulfite process could not effectively degrade RBV, while it increased by 178 and 38 times when pHBA and SA were introduced into UV/Sulfite process respectively, suggesting that pHBA and SA strongly promoted RBV degradation while mHBA had no promotion on RBV abatement in UV/Sulfite process. Transient absorption spectra and reactive intermediates scavenging experiment indicated that the triplet excited state pHBA and SA (3pHBA* and 3SA*) contributed to the degradation of RBV through non−radical process. Notably, eaq− played the role of key initiator in transforming pHBA and SA into their triplet states. The difference of kobs-RBV in UV/Sulfite/pHBA and UV/Sulfite/SA process was attributed to different generation pathways of 3pHBA* and 3SA* (high molar absorptivity at the wavelength of 254 nm and photosensitive cycle, respectively) and their second order rate constants towards RBV (kRBV-3pHBA* = 8.60 × 108 M−1 s−1 and kRBV-3SA* = 6.81 × 107 M−1 s−1). mHBA could not degrade RBV for its lack of intramolecular hydrogen bond and low molar absorptivity at 254 nm to abundantly transform into its triplet state. kobs-RBV increased as pH increased from 5.0 to 11.0 in UV/Sulfite/SA process, due to the high yield of eaq− in alkaline condition which promoted the generation of 3SA* and the stable of the absorbance of SA at 254 nm. By contrast, kobs-RBV underwent a process of first increasing and then decreasing in UV/Sulfite/pHBA process as the increase of pH, and its highest value achieved in a neutral condition. This lied in the exposure of eaq− increased as the increase of pH which promoted the generation of 3pHBA*, while the molar absorptivity of pHBA at 254 nm decreased as the increase of pH in an alkaline condition which inhibited the yield of 3pHBA*. The RBV degradation pathways and products toxicity assessment indicated that UV/Sulfite/pHBA had better detoxification performance on RBV than UV/Sulfite/SA process. This study disclosed a novel mechanism of emerging contaminants abatement through non-radical process in NSOM mediated ARP, and provide a wide insight into positive profile of DOM in water treatment process, instead of only taking DOM as a quencher of reactive intermediates.

Copper-zinc nanoparticle-decorated nitrogen-doped carbon composite for electrochemical determination of triclosan.

Anew sensor based on copper-zinc bimetal embedded and nitrogen-doped carbon-based composites (CuZn@NC) was prepared for triclosan (TCS) detection by pyrolyzing the precursor of Cu-Zn binuclear metal-organic framework (MOF). The performance for detecting TCS was evaluated using linear scanning voltammetry (LSV) and differential pulse voltammetry (DPV), and the proton and electron numbers during TCS oxidation have been proved to be one-to-one. The results indicated that CuZn@NC can present a satisfactory analysis performance for TCS detection. Under the optimized conditions, the linear response range was 0.2-600 µM and the detection limit was 47.9nM. The sensor presented good stability (signal current dropped only 2.5% after 21days) and good anti-interference of inorganic salts and small molecular organic acids. The good recovery (97.5-104.1%) for detecting spiked TCS in commercial products (toothpaste and hand sanitizer) suggested its potential for routine determinationof TCS in real samples.

Screening of microalgae strains for efficient biotransformation of small molecular organic acids from dark fermentation biohydrogen production wastewater

Dark fermentation biohydrogen production is a rapidly advancing and well-established field. However, the accumulation of volatile organic acid (VFAs) byproducts hinder its practical applications. Microalgae have demonstrated the ability to efficiently utilize VFAs while also treating waste gases and other nutrient elements. Integrating microalgae cultivation with dark fermentation is a promising approach. However, low VFAs tolerance and slow VFAs consumption restrict their application. To find suitable wastewater treatment microalgae, this work screened eight microalgae strains from five family. The results demonstrated that Chlamydomonas reinhardtii exhibited significant advantages in VFAs utilization, achieving a maximum removal of 100% for acetate and 52.5% for butyrate. Among the tested microalgae strains, CW15 outperformed in terms of photobioreactor adaptability, VFAs utilization, biomass productivity, and nutrient removal, making it the most promising microalgae for practical applications. This research demonstrates the feasibility of integrating microalgae cultivation with dark fermentation and providing a viable technical solution for integrated-biorefining.

Lithium extraction from typical lithium silicate ores by two bacteria with different metabolic characteristics: Experiments, mechanism and significance

Microorganisms obtain inorganic nutrients or energy from specific minerals to selectively weather minerals, but few studies on the differences in metabolic components of different functional bacteria lead to different weathering effects. This study evaluated the leaching effects of two bacteria with distinct metabolic characteristics on lithium silicate minerals with different structures. We aimed to understand the microscopic mechanism of crystal destruction of lithium silicate minerals with different structures under the action of microorganisms. The results showed that the metabolites produced by an acid producing silicate strain Raoultella sp. Z107 (strain Z107) had a high content of organic acids, among which lactic acid was up to about 11 g/L. Bacillus mucilaginosus 21,699 (strain BM) secreted capsular polysaccharide with a high content of 14.84 mg/L. The metabolic activities of the two strains were significantly different. Through the analysis of the leaching residue, it was found that the lithium silicate minerals were acid etched, interlayer domains expanded, crystallinity decreased, and metal bonds were broken under the action of bacteria. The dissolution of lithium silicate minerals by bacteria is a combination of bacterial adsorption, organic acid corrosion, and complexation of small molecular organic acids and macromolecular polymers with metal ions. The acid erosion and complexation effects of organic acids are greater than the single complexation of capsular polysaccharides, and the layered lepidolite is more likely to be decomposed by the weathering of bacterial metabolites than the chain structure spodumene. These results indicate that the diversity of metabolic activity of bacteria from different sources and the sequence and decomposition mechanism of metal ions released from minerals after lattice destruction are also different. Microorganisms decompose minerals for energy and nutrients, and eventually become the main players in the transformation of elements in biogeology.

High-throughput screening of multi-pesticide residues in animal-derived foods by QuEChERS-online gel permeation chromatography-gas chromatography-tandem mass spectrometry

Improvements in living standards have led to an increase in the consumption of animal-derived foods. Pesticides may be used illegally during animal breeding as well as meat production and processing for pest control and preservation. Pesticides applied to crops may also be enriched in animal tissues through the food chain, thereby increasing the risk of pesticide residue accumulation in muscles and visceral tissues and endangering human health. China has stipulated maximum residue limits for pesticide residues in livestock and poultry meat and their viscera. Many other major developed countries and organizations, including the European Union, Codex Alimentarius Commission, and Japan, have also set maximum residue limits for these residues (0.005-10, 0.004-10, and 0.001-10 mg/kg, respectively). Research on pretreatment technologies for pesticide residue detection in plant-derived foods is widely available, but insufficient attention has been paid to animal-derived foods. Thus, high-throughput detection technologies for pesticide residues in animal-derived foods are limited. The impurities that can interfere with the detection process for plant-derived foods mainly include organic acids, polar pigments, and other small molecular compounds; by contrast, the matrix of animal-derived foods is much more complex. Macromolecular proteins, fats, small molecular amino acids, organic acids, and phospholipids can interfere with the detection of pesticide residues in animal-derived foods. Thus, selecting the appropriate pretreatment and purification technology is of great importance. In this study, the QuEChERS technique was combined with online gel permeation chromatography-gas chromatography-tandem mass spectrometry (GPC-GC-MS/MS) to determine 196 pesticide residues in animal-derived foods. The samples were extracted with acetonitrile, purified using the QuEChERS technique coupled with online GPC, detected by GC-MS/MS, determined in multiple reaction monitoring mode (MRM), and quantified using the external standard method. The effects of the extraction solvent and purification agent type on the extraction efficiency and matrix removal of the method were optimized. The purification effect of online GPC on the sample solution was investigated. The optimal distillate receiving time was obtained by studying the recoveries of the target substances and matrix effects over different distillate receiving periods to achieve the effective introduction of target substances and efficient matrix removal. Further, the advantages of the QuEChERS technique combined with online GPC were evaluated. The matrix effects of 196 pesticides were assessed; ten pesticide residues showed moderate matrix effects, while four pesticide residues showed strong matrix effects. A matrix-matched standard solution was used for quantification. The 196 pesticides showed good linearity in the range of 0.005-0.2 mg/L, with correlation coefficients greater than 0.996. The limits of detection and quantification were 0.002 and 0.005 mg/kg, respectively. The recoveries of 196 pesticides at spiked levels of 0.01, 0.05, and 0.20 mg/kg were 65.3%-126.2%, with relative standard deviations (RSDs) of 0.7%-5.7%. The proposed method is rapid, accurate, and sensitive; thus, it is suitable for the high-throughput screening and detection of multiple pesticide residues in animal-derived foods.

Colonization Mechanism of Endophytic Enterobacter cloacae TMX-6 on Rice Seedlings Mediated by Organic Acids Exudated from Roots

Small molecular organic acids (SMOAs) in root exudates are critical for plant-microbe interaction, especially under environmental stresses. However, the dominant organic acids driving the process and promoting the colonization are unclear. Here, using a target metabolomics, 20 main SMOAs of rice root exudates were identified and analyzed in control and 10 mg/L thiamethoxam-treated groups. The composition of these SMOAs differed significantly between the two treatments. Among which, malic acid, citric acid, succinic acid, and proline induced a chemotactic response, swimming ability, and biofilm formation of Enterobacter cloacae TMX-6 in a dose-dependent manner. The maximal chemotactic response of TMX-6 was induced by proline at 10 mg/L, and a strong chemotactic response was even observed at 0.01 mg/L. The recruitment assay confirmed that the addition of these four compounds promoted the colonization of TMX-6. The results provide insight for directional regulation of plant-microbe interactions for beneficial outcomes.

Construction of magnetically recoverable MnZnFe2O4@Ag3PO4 Z-scheme photocatalyst for rapid visible-light-driven phenol degradation.

Visible-light-driven magnetic heterojunction as a promising photocatalysts has received much attention in environmental remediation. In this work, novel Z-scheme heterojunction MnZnFe2O4@Ag3PO4 (MZFO@APO) magnetic photocatalysts with excellent visible-light-driven photocatalytic activity are successfully constructed and characterized. The photocatalytic activity for phenol degradation is measured, and photodegradation mechanism is investigated with EPR, radical trapping experiments, and LC-MS. It turns out that the heterojunction introduced MZFO exhibits good adsorption effect on visible light and the direct Z-scheme bandgap alignment of MZFO and APO significantly improves charge separation and electron transfer, outperforming that of pure APO. MZFO@APO-40% with 40% APO content shows the rapid photodegradation performance, obtaining a 100% removal efficiency of phenol (25mg L-1) after 12-min visible light irradiation, and its kinetic constants are approximately 25.3 and 4.9 times higher than that of P25 TiO2 and pure APO, respectively. Especially, MZFO@APO-40% also possesses a high magnetic separation property and can be efficiently reused for 5 cycles. Additionally, EPR and radical trapping experiments confirm that h+, O2-, and 1O2 are the main active species in the photocatalytic process. Hydroquinone and small molecular organic acids such as maleic acid and oxalic acid are detected by LC-MS, which further indicates that the pathway of phenol degradation involves hydroxylation, open-ring reactions, and mineralization reactions. The novel addition of MZFO in photocatalyst construction has the potential to promote its application in environmental remediation.

NMR method for simultaneous determination of 21 chemical components in Danhong Injection

Danhong Injection, a compound Chinese medicine injection prepared from Salviae Miltiorrhizae Radix et Rhizoma and Carthami Flos, is used in the clinical treatment of coronary heart disease, cerebral thrombosis, myocardial infarction, angina pectoris and other cardiovascular and cerebrovascular diseases. In this study, a quantitative method for simultaneous determination of multiple components in Danhong Injection was developed based on ~1H-qNMR technology and then methodological verification was carried out. The results showed that the established method had good methodological indexes. This method can simultaneously determine the content of 21 chemical components including 6 amino acids, 4 small molecular organic acids, 5 sugars and their derivatives, 1 nucleoside, and 5 aromatic compounds in Danhong Injection. The total content accounted for about 85% of the total solid mass, which reflected the great advantage of ~1H-qNMR method in the analysis of Chinese medicine injections. The ~1H-qNMR method for simultaneous determination of multiple components in Danhong Injection developed in this study has simple operation, short analysis time, and wide application range, which has practical significance for the quality evaluation of Danhong Injection and provides reference for the development of quality control methods for Chinese medicine injections.

Accelerated catalytic ozonation for aqueous nitrobenzene degradation over Ce-loaded silicas: Active sites and pathways

Cerium oxides loaded silica catalysts were synthesized by an impregnation method by simply mixing Ce precursor with silica spherule (Ce/SS) and ordered MCM-41 zeolites (Ce/MCM-41), followed by a mild calcination. Compared with pure SS and MCM-41, Ce modified Ce/SS and Ce/MCM-41 demonstrate much improved catalytic ozonation activities for mineralization of recalcitrant nitrobenzene (NB). At solution pH of 6, 86 and 97% TOC mineralization rates were achieved within 60 min for Ce/MCM-41 and Ce/SS, respectively. Characterization results suggest that Ce loading significantly increases the surface Lewis acidic sites, which would synergize with Ce3+/Ce4+ redox cycle for the activity improvement. With the aid of in situ electron paramagnetic resonance (EPR) spectra and quenching tests, hydroxyl radical (·OH), superoxide radical (O2•–), and singlet oxygen (1O2) are identified as the O3 catalytic decomposition products, while ·OH mainly accounts for NB mineralization. The detailed degradation route of NB was further investigated by the multi-chromatography analysis. NB is firstly oxidized into polyhydroxy compounds, followed by small molecular organic acids, and finally being mineralized into CO2 and H2O. This study established a facile strategy to synthesize highly active and stable Ce/SiO2 catalysts for catalytic ozonation, and elucidated the in-depth mechanisms for the activity origins of the Ce loaded silica-based materials in catalytic ozonation processes (COP).

Solar Boosting Pollutant Removal plus Hydrogen Production by Lifting-Heat and Lowering-Potential Chemical Synergy.

Solar-boosted oxidation plus hydrogen production for pollutant removal in wastewater, driven by a high thermal and low-potential electrochemical combination, is facilitated and demonstrated from theory to experiments. One sun fully offers both thermal and electrical energy powered thermo- and electrochemistry for pollutant oxidation. Solar thermal action provides high temperatures for the activation of the pollutant molecules to gear up for solar-driven electrochemical oxidation. Taking wastewater containing phenol as an example, the cyclic voltammetry (CV) curves display two redox processes at less than 100 °C, while only one redox process of single oxidation of phenol appears at more than 100 °C. The oxidation of phenol is accompanied by an efficient evolution of hydrogen, in which the yield of 0.627 mL at 30 °C is increased to 2.294 mL at 210 °C. The phenol removal is enhanced to 80.50% at 210 °C. Tracking the reaction progress shows that small molecular organic acids are detected as the only intermediate at the high temperatures, which suggests the easy realization of full mineralization. The kinetic reaction of the phenol oxidation is fitted to the first order with an increase of the rate constant of 10 times compared with that at low temperatures. Solar engineering of oxidation of organic pollutants not only solves the issue of energy demand for the tough wastewater treatment but also realizes fast and efficient oxidation of organic pollutants. This study opens up new avenues to achieve solar wastewater treatment and simultaneous hydrogen production.

Integrating high-throughput sequencing and metabolomics to investigate the stereoselective responses of soil microorganisms to chiral fungicide cis-epoxiconazole

The use of the chiral triazole fungicide cis-epoxiconazole in agricultural production continues to increase; however, little is known about the stereoselective and toxic responses of soil microorganisms to cis-epoxiconazole in the soil microenvironment. High-throughput sequencing and metabolomics were integrated to investigate the stereoselective response of soil microbial community structure, metabolic profile to cis-epoxiconazole exposure, and the correlation between the microbiomes and different metabolites. Soil microbial community structure and soil metabolic profile were significantly altered and exhibited significant enantioselectivity. The alpha diversity (Chao, Shannon, and Simpson diversity) of bacterial and fungus was not significantly affected, whereas the beta diversity (Bray-Curtis dissimilarity and PLS-DA) of bacterial and fungus was significantly altered in treatment of cis-epoxiconazole and its enantiomers (p-value < 0.05). The variation in bacterial and fungus community structure was the highest under (+)-enantiomer exposure, followed by exposure to racemate and (−)-enantiomer. Soil metabolomic analysis revealed that exposure to high or low doses of cis-epoxiconazole and its enantiomers resulted in different degrees of reprogramming of the soil metabolic pool. The 39 significantly changed metabolites mainly included small molecular organic acids, amino acids and their intermediates, and purine and adenosine intermediates. Six metabolic pathways were significantly disrupted. Different correlation patterns were observed between the significantly altered metabolites and microbes (p-value < 0.05) by Pearson correlation-based analysis. In conclusion, as xenobiotic pollutant, epoxiconazole altered the structure and metabolism of soil microorganisms with significant stereoselectivity mainly driven by 2R, 3S-(+)-cis-epoxiconazole. This study provided a more robust assessment of the risks of epoxiconazole exposure to soil microorganisms. Given the importance of the soil environment in agricultural production, characterization of the soil microbiome and metabolome can provide new insights into the ecological risks posed by exposure to the chiral triazole pesticide cis-epoxiconazole and its enantiomers.

Fingerprint of Shenmai Injection based on ~1H-NMR technique

Shenmai Injection is a Chinese medicinal injection prepared from Ginseng Radix et Rhizoma Rubra and Ophiopogonis Radix, which is widely used in clinical practice for the treatment and adjuvant therapy of cardiovascular diseases with significant pharmacological effects. Proton nuclear magnetic resonance spectroscopy(~1H-NMR) has the advantages of simple and nondestructive sample pretreatment, fast analysis, abundant chemical information, quantification and no need to follow the standard curve. It is widely used in the analysis and research of complex mixtures of traditional Chinese medicine, clinical blood and urine samples. In this study, the ~1H-NMR fingerprint of Shenmai Injection was established. Thirty-two chemical components were identified, including seven amino acids, eight small molecular organic acids, one alkaloid, four sugars, two nucleosides, seven saponins, and three other components. Pearson's correlation coefficient and multivariate analysis of variance(principal component analysis combined with hierarchical cluster analysis) were applied based on the ~1H-NMR fingerprint to evaluate the quality consistency. The results showed high-quality consistency of 82 batches of Shenmai Injection. This study confirms that the ~1H-NMR fingerprint has great potential in the application of quality control of Chinese medicinal injection.

Magnetically separable NiFe2O4/sepiolite catalyst for enhanced ozonation treatment of quinoline and bio-treated coking wastewater in a catalytic ozonation system

In a quest to eliminate the bio-refractory organic pollutants in industrial wastewater, the NiFe2O4/SEP composites were synthesized via a sol-gel method and investigated by XRD, SEM, XPS, FTIR, VSM. The TOC removal increased from 16.82% to 69.35% in NiFe2O4/SEP+O3 system using quinoline as a target contaminant after 30 min, which is about 4.12 times as that in O3 system. The evolution of acetic acid, oxalic acid and formic acid in quinoline degradation was analyzed, saturated carboxylic acids were inertia to ozone molecules. However, 93.54% of oxalic acid was removed after 10 min, and 77.66% of acetic acid was degraded after 30 min in catalytic ozonation. The generation of small molecular organic acids could promote the Fe3+/Fe2+ redox cycle by complexing with Fe3+ on NiFe2O4/SEP, and then accelerated the formation of reactive oxygen species. In the presence of NiFe2O4/SEP, the high oxidation potential of •OH and •O2- contributed to an excellent TOC removal rate. Meanwhile, NiFe2O4/SEP was proved to be active for bio-treated coking wastewater in catalytic ozonation. The naturally fluorescent constituents in bio-treated coking wastewater were almost entirely removed by NiFe2O4/SEP+O3 system in 60 min. These findings indicated the good potential of NiFe2O4/SEP for practical applications in industrial wastewater treatment.

Study on the properties of denitrifying carbon sources from cellulose plants and their nitrogen removal mechanisms

Abstract Carbon sources of cellulose plants are promising materials that enhance the activities of denitrifying bacteria in the groundwater system. To further verify the denitrification performance of cellulose plants and the main factors of affecting the denitrifying system, six cellulose plants from agricultural wastes (wood chip, corn cob, rice husk, corn straw, wheat straw, and sugar cane) were selected for bioavailable organic matter leaching experiments, carbon denitrification experiments, functional bacteria identification, and analysis experiments. The results show that the extracts of cellulose plants contain a mixed carbon sources system including small molecular organic acids, sugars, nitrogen-containing organic components, and esters. The qPCR results showed that the denitrifying bacteria had obvious advantages compared to anaerobic ammonia-oxidizing bacteria during the stable period; the denitrification experiment showed that each of six cellulose plants removed more than 80% of nitrogen, and the denitrification rates reached 1.00–2.00 mg N cm−3·d−1. The supplement of cellulose plants promotes the metabolism rate of denitrifying bacteria, and the additional denitrifying bacteria have little effect on nitrate removal. In summary, the expected denitrification reaction occurred in the cellulose plant system, which is suitable as a carbon source material for water body nitrogen pollution remediation.

Simultaneous Cu-EDTA oxidation decomplexation and Cr(VI) reduction in water by persulfate/formate system: Reaction process and mechanisms

The heavy metal-organic complexes and heavy metal ions pose great threats to human health, and their elimination from water environment is quite urgent. Simultaneous decomplexation of heavy metal complex Cu-EDTA and reduction of Cr(VI) was performed in a persulfate (PS)/formate (FA) system. Oxidizing species and reductive species were simultaneously produced in this PS/FA system, which realized 96.6% of Cu-EDTA decomplexation and 100% of Cr(VI) reduction within 90 min treatment under the solution pH 3.60. Higher solution temperature and acidic conditions favored Cu-EDTA decomplexation and Cr(VI) reduction. There existed an appropriate molar ratio of FA and PS to simultaneously realize high-efficient Cu-EDTA decomplexation and Cr(VI) reduction. SO4•-, •OH, and 1O2 drove the Cu-EDTA decomplexation, which destroyed the chelating sites of Cu and EDTA, and finally it was oxidized to small molecular alcohols, organic acids, and Cu2+. Reductive species CO2•− was produced by the reaction of SO4•− and FA, as well as •OH and FA, which dominated the reduction of Cr(VI) to Cr3+. Carbonates, hydroxides, and oxides including Cu(OH)2, CuCO3, Cu2CO3(OH)2, CuO, Cr(OH)3, and Cr2O3 were the main composites in precipitates after Cu2+ and Cr3+ were precipitated. Furthermore, Cu-EDTA decomplexation and Cr(VI) reduction processes induced by PS/FA were put forward.

Co/Fe co-doped porous graphite carbon derived from metal organic framework for microelectrolysis-Fenton catalytic degradation of Rhodamine B

Co/Fe co-doped porous graphite carbon (Co/Fe-PGC) nanocomposites were successfully prepared by one-step pyrolysis with CoFe-MOF, in which the Co/Fe nanoparticles were uniformly coated on porous graphite carbon derived from MOF. It was used to microelectrolysis-Fenton degrade rhodamine B through the main active substance ∙OH. The color and TOC removal rate of 100 mg/L rhodamine B reached 99.41% and 64.6%, respectively, for 30 min. Rhodamine B was degraded into small molecular organic acids, alcohols and lipids by N-demethylation and chromophore cleavage, until it was finally degraded into CO2 and H2O, and no new colored organics were produced in the degradation process. The degradation process follows the first-order reaction kinetics, and its rate constant is much higher than that of the previous similar studies. The excellent catalytic performance of Co/Fe-PGC catalyst is attributed to the coupling effect of micro-electrolysis and Fenton reaction, and the acceleration of cobalt on electron transport and Fe2+ reduction. Co0/Fe0 undergoes galvanic corrosion to generate Co2+/Fe2+ and H2O2, and then these products undergo Fenton reaction to generate Co3+/Fe3+ and ∙OH, thus forming a circulating system of Co3+/Fe3+ and Co2+/Fe2+, enhancing the activation of H2O2 and ensuring the efficient degradation of RhB.

Bio-dissolution process and mechanism of copper phosphate hybrid nanoflowers by Pseudomonas aeruginosa and its bacteria-toxicity in life cycle

Copper phosphate hybrid nanoflowers (HNF) have been widely used in chemical industries and wastewater treatment owing to its excellent catalytic activity and high stability. However, their fate and ecological risks have not received due attention after being discharged into natural environment. The significance of bacteria on the dissolution and fate of HNF and its toxicity to bacteria was evaluated from the perspective of its life cycle. Results showed that in the presence of Pseudomonas aeruginosa, HNF was gradually ‘disassembled’ into smaller nanoparticles (NPs), and then dissolved completely. More than half of the dissolution products (Cu2+) entered biological phase, and PO43- was absorbed and utilized by bacteria as a phosphorus source. The mechanisms of HNF bio-dissolution are as follows: the metabolites of bacteria dissolve HNF through complexation and acidification, in which small molecular organic acids and amino acids play an important role. Bacteria toxicity experiments of HNF in its cycle life show that HNF exhibits lower cell toxicity, but its intermediate (smaller NPs) and final dissolved products (Cu2+) exhibit stronger cytotoxicity by increasing the level of intracellular ROS and membrane permeability of bacteria. This research is helpful to provide ecological risk assessment, develop targeted applications, and rationally design future nanomaterials.

Effective removal of the heavy metal-organic complex Cu-EDTA from water by catalytic persulfate oxidation: Performance and mechanisms

It is difficult to remove heavy metal-organic complexes from water by chemical precipitation because of the strong complexation ability between heavy metal ions and organics. In this study, the removal of the Cu-ethylenediaminetetraacetic acid (Cu-EDTA) complex using autocatalytic persulfate (PS) oxidation was investigated. The Cu-EDTA removal efficiency reached up to 96.57% after 90 min of treatment by PS oxidation. A higher PS concentration favored Cu-EDTA removal; An increase in the initial concentration of Cu-EDTA benefited PS activation, and a greater removal performance was obtained at a lower Cu-EDTA initial concentration (0.1 mmol L−1). Excessive Cu2+ accelerated Cu-EDTA removal, while superfluous EDTA suppressed it. Relatively lower initial solution pH value favored Cu-EDTA removal. SO4•-, •OH, and 1O2 displayed significant roles in the Cu-EDTA removal process, as they destroyed the chelating sites of the Cu(II) and EDTA molecules; finally small molecular organic acids, alcohols, and NO3− were produced. The released Cu(II) existed in the precipitates in the forms of Cu-based carbonates, Cu-based hydroxides, and copper oxide. A possible decomposition pathway of Cu-EDTA was proposed. Overall, multipathway activation of PS induced by heavy metal complexes could be an effective technique for the removal of the heavy metal complexes.