Development of a New Permanganate/Chlorite Process for Water Decontamination.

Development of new technologies with strong selectivity for target pollutants and low sensitivity toward a water matrix remains challenging. Herein, we introduced a novel strategy that used chlorite as an activator for Mn(VII) at pH 4.8, turning the inert reactivity of the pollutants toward Mn(VII) into a strong reactivity. This paved a new way for triggering reactions in water decontamination. By utilizing sulfamethoxazole (SMX) as a typical pollutant, we proposed coupled pathways involving electron transfer across hydrogen bonds (TEHB) and oxidation by reactive manganese species. The results indicated that a hydrogen bonding complex, SMX-ClO2-*, formed through chlorite binding the amino group of SMX initially in the TEHB route; such a complex exhibited a stronger reduction capability toward Mn(VII). Chlorite, in the hydrogen bonding complex SMX-ClO2-*, can then complex with Mn(VII). Consequently, a new reactive center (SMX-ClO2--Mn(VII)*) was formed, initiating the transfer of electrons across hydrogen bonds and the preliminary degradation of SMX. This is followed by the involvement of the generated Mn(V)-ClO2-/Mn(III) in the reduction process of Mn(VII). Such a process showed pH-dependent degradation, with a removal ratio ranging from 80% to near-stagnation as pH increased from 4.8 to 7. Combining with pKa analysis showed that the predominant forms of contaminants were crucial for the removal efficiency of pollutants by the Mn(VII)/chlorite process. The impact of the water matrix was demonstrated to have few adverse or even beneficial effects. With satisfactory performance against numerous contaminants, this study introduced a novel Mn(VII) synergistic strategy, and a new reactivity pattern focused on reducing the reduction potential of the contaminant, as opposed to increasing the oxidation potential of oxidants.

Unraveling the Role of Humic Acid in the Oxidation of Phenolic Contaminants by Soluble Manganese Oxo-Anions.

Humic acid (HA) is ubiquitous in natural aquatic environments and effectively accelerates decontamination by permanganate (Mn(VII)). However, the detailed mechanism remains uncertain. Herein, the intrinsic mechanisms of HA's impact on phenolics oxidation by Mn(VII) and its intermediate manganese oxo-anions were systematically studied. Results suggested that HA facilitated the transfer of a single electron from Mn(VII), resulting in the sequential formation of Mn(VI) and Mn(V). The formed Mn(V) was further reduced to Mn(III) through a double electron transfer process by HA. Mn(III) was responsible for the HA-boosted oxidation as the active species attacking pollutants, while Mn(VI) and Mn(V) tended to act as intermediate species due to their own instability. In addition, HA could serve as a stabilizer to form a complex with produced Mn(III) and retard the disproportionation of Mn(III). Notably, manganese oxo-anions did not mineralize HA but essentially changed its composition. According to the results of Fourier-transform ion cyclotron resonance mass spectrometry and the second derivative analysis of Fourier-transform infrared spectroscopy, we found that manganese oxo-anions triggered the decomposition of C-H bonds on HA and subsequently produced oxygen-containing functional groups (i.e., C-O). This study might shed new light on the HA/manganese oxo-anion process.

Effect of Tb3+ and Ce3+ Co-doping on the Structure and Photoluminescence Properties of Hexagonal Boron Nitride Phosphors.

In the paper, we have successfully prepared hexagonal boron nitride (h-BN:Tb3+, Ce3+) phosphors with melamine as the nitrogen source. The X-ray powder diffraction patterns confirm that the sample possesses a hexagonal crystal structure within the P 6 ¯ m2 space group. It is interesting that the co-doping combination of Tb3+ and Ce3+ can markedly enhance the threshold concentration of doped activators within the limited solid solution of h-BN phosphors. Under 302 nm excitation, the h-BN:Ce3+ phosphors exhibit broadband blue light emission at 406 nm. In h-BN:Tb3+, Ce3+ phosphors, the co-doping of Ce3+ not only ensures high phase purity but also results in strong green light emission. The energy transfer efficiency from Ce3+ to Tb3+ is about 55%. The fluorescence lifetime increases with the increase of Ce3+ and Tb3+ concentration, and the fluorescence lifetime of h-BN:0.025Tb3+, 0.05Ce3+ phosphor reached 2.087 ms. Additionally, the h-BN:0.025Tb3+, 0.05Ce3+ phosphor exhibits excellent thermal performance with an activation energy value of 0.2825 eV. Moreover, the photoluminescence quantum yield of the sample exceeds 52%. Therefore, the h-BN:Tb3+, Ce3+ samples can be used as green phosphors for solid state lighting and fluorescent labeling.

A Novel Source of Radicals from UV/Dichloroisocyanurate for Surpassing Abatement of Emerging Contaminants Versus Conventional UV/Chlor(am)ine Processes.

Ultraviolet (UV)/chlor(am)ine processes are emerging advanced oxidation processes (AOPs) for water decontamination and raising continuous attention. However, limitations appear in the UV/hypochlorite and UV/monochloramine for removing specific contaminants ascribed to the differences in the sorts and yields of free radicals. Here, this study reports UV/dichloroisocyanurate (NaDCC) as a novel source of radicals. NaDCC was demonstrated to be a well-balanced compound between hypochlorite and monochloramine, and it had significant UV absorption and a medium intrinsic quantum yield. The UV/NaDCC produced more substantial hydroxyl radicals (·OH) and reactive chlorine species (RCSs, including Cl·, ClO·, and Cl2·-) than conventional UV/chlor(am)ine, thereby generating a higher oxidation efficiency. The reaction mechanisms, environmental applicability, and energy requirements of the UV/NaDCC process for emerging contaminants (ECs) abatement were further investigated. The results showed that ·OH and ·NH2 attacked ECs mostly through hydrogen atom transfer (HAT) and radical adduct formation, whereas Cl· destroyed ECs mainly through HAT and single electron transfer, with ClO· playing a certain role through HAT. Kinetic model analyses revealed that the UV/NaDCC outperformed the conventional UV/chlor(am)ine in a variety of water matrices with superior degradation efficiency, significantly saving up to 96% electrical energy per order. Overall, this study first demonstrates application prospects of a novel AOP using UV/NaDCC, which can compensate for the deficiency of the conventional UV/chlor(am)ine AOPs.

Synergy between UV light and trichloroisocyanuric acid on methylisothiazolinone degradation: Performance, kinetics and degradation pathway.

Methylisothiazolinone (MIT) is widely used in daily chemicals, fungicides, and other fields and its toxicity has posed a threat to water system and human health. In this study, ultraviolet (UV)/trichloroisocyanuric acid (TCCA), which belongs to advanced oxidation processes (AOP), was adopted to degrade MIT. Total chlorine attenuation detection proved that TCCA has medium UV absorption and a strong quantum yield (0.49 mol E-1). At a pH of 7.0, 93.5% of MIT had been decontaminated after 60 min in UV/TCCA system (kobs = 4.4 × 10-2 min-1, R2 = 0.978), which was much higher than that in the UV alone system and TCCA alone system, at 65% (1.7 × 10-2 min-1, R2 = 0.995) and 10% (1.8 × 10-3 s-1, R2 = 0.915), respectively. This system also behaved well in degrading other five kinds of contaminants. Tert-butanol (TBA) and carbonate (CO32-) were separately used in quenching experiments, and the degradation efficiency of MIT decreased by 39.5% and 46.5% respectively, which confirmed that HO• and reactive chlorine species (RCS) were dominant oxidants in UV/TCCA system. With TCCA dosage increasing in a relatively low concentration range (0.02-0.2 mM) and pH decreasing, the effectiveness of this AOP system would be strengthened. The influences of coexisting substances (Cl-, SO42-, CO32-, NO2- and NO3-) were explored. MIT degradation pathways were proposed and sulfur atom oxidation and carboxylation were considered as the dominant removal mechanisms of MIT. Frontier orbital theory and Fukui indexes of MIT were employed to further explore the degradation mechanism.

The variation of microorganisms and organics during methane production from lignite under an electric field.

OBJECTIVES: The succession of microbial communities and intermediates during methane production was determined by pyrosequencing and GC-MS to investigate the mechanism of biomethanation enhancement from coal. RESULTS: The maximum methane production at 1.2 V was significantly higher than that at 0 V. Bacterial flora have been changed as a result of the addition of an electric field, e.g., the abundance of Pseudomonas significantly increased to enhance the coal degradation which improved the methane yield by facilitating the electron transfer. The fungal structure was also found stabilized by the electric field when compared to the control after 7 days of cultivation. The predominance of Methanosarcina could also stimulate interspecies electron transfer. The GC-MS analysis revealed that the electric field can selectively promote the metabolism of refractory intermediates such as esters and aromatics during coal biodegradation. CONCLUSION: The application of an electric field could enhance methane production from coal by changing the structure and succession of microbial communities, improving electron transfer, and enhancing the fermentation of intermediates during coal biodegradation.

Determining Factors for Nitrite Accumulation in an Acidic Nitrifying System: Influent Ammonium Concentration, Operational pH, and Ammonia-Oxidizing Community.

Acidic nitrification is attracting wide attention because it can enable robust suppression of nitrite-oxidizing bacteria (NOB) in wastewater treatment. This study reports a comprehensive assessment of the novel acidic nitrification process to identify the key factors that govern stable nitrite accumulation. A laboratory-scale moving-bed biofilm reactor receiving low-alkalinity wastewater was continuously operated under acidic conditions (pH < 6) for around two years, including nine stages varying influent and operational conditions. The results revealed that nitrite accumulation was related to three factors, i.e., influent ammonium concentration, operating pH, and ammonia-oxidizing microbial community. These three factors impact nitrite accumulation by altering the in situ concentration of free nitrous acid (FNA), which is a potent inhibitor of NOB. The critical FNA concentration is approximately one part per million (ppm, ∼1 mg HNO2-N/L), above which nitrite accumulation is stably maintained in an acidic nitrifying system. The findings of this study suggest that stable nitrite accumulation via acidic ammonia oxidation can be maintained under a range of influent and operational conditions, as long as a ppm-level of FNA is established. Taking low-strength mainstream wastewater (40-50 mg NH4+-N/L) with limited alkalinity as an example, stable nitrite accumulation was experimentally demonstrated at a pH of 4.35, under which an in situ FNA of 2.3 ± 0.6 mg HNO2-N/L was attained. Under these conditions, Candidatus Nitrosoglobus became the only ammonia oxidizer detectable by 16S rRNA gene sequencing. The results of this study deepen our understanding of acidic nitrifying systems, informing further development of novel wastewater treatment technologies.

Impact of hydrological factors on the dynamic of COVID-19 epidemic: A multi-region study in China.

Considering the live SARS-CoV-2 was detected and isolated from the excrement and urine of infected patients, the potential public health risk of its waterborne transmission should be paid broad and close attention. The purpose of the current study is to investigate the associations between COVID-19 incidences and hydrological factors such as lake area, river length, precipitation and volume of water resources in 30 regions of China. All confirmed cases for each areas were divided into two clusters including first cases cluster driven by imported cases during the period of January 20th to January 29th, 2020 and second cases cluster driven by local cases during the period of January 30th to March 1st, 2020. Based on the results of descriptive analysis and nonlinear regression analysis, positive associations with COVID-19 confirmed numbers were observed for migration scale index (MSI), river length, precipitation and volume of water resources, but negative associations for population density. The correlation coefficient in the second stage cases cluster is apparently higher than that in the first stage cases cluster. Then, the negative binomial-generalized linear model (NB-GLM) was fitted to estimate area-specific effects of hydrological variables on relative risk (RR) with the incorporation of additional variables (e.g., MSI) and the effects of exposure-lag-response. The statistically significant associations between RR and river length, the volume of water resources, precipitation were obtained by meta-analysis as 1.24 (95% CI: 1.22, 1.27), 2.56 (95% CI: 2.50, 2.61) and 1.59 (95% CI: 1.56, 1.62), respectively. The possible water transmission routes of SARS-CoV-2 and the potential capacity of long-distance transmission of SARS-CoV-2 in water environment was also discussed. Our results could provide a better guidance for local and global authorities to broaden the mind for understanding the natural-social system or intervening measures for COVID-19 control at the current or futural stage.

The role of nonacid reflux in laryngopharyngeal reflux diseases.

OBJECTIVE: To analyze the role of nonacid reflux in laryngopharyngeal reflux diseases (LPRD). METHODS: From January 2014 to April 2019, 344 patients associated with LPRD underwent 24-h multichannel intraluminal impedance-pH monitoring, and their reflux symptom index (RSI) and reflux finding score (RFS) were recorded. The numbers of acid, weakly acidic and alkaline reflux events in the laryngopharynx were counted, and the consistency analysis of the results with the results of the RSI and RFS was conducted. RESULTS: Among the 344 patients, nonacid reflux events accounted for 74.1% (1367/1845) of the all reflux events. There were 111 patients with ≥ 3 acid reflux events, 218 patients with ≥ 3 any kinds of reflux events, and 257 patients with positive results of RSI or RFS. Taking the results of the RSI and or RFS as a reference, the sensitivity, specificity and consistency test Kappa value for the diagnosis of LPRD according to the existence of ≥ 3 acid reflux events were 41.2%, 94.2% and 0.228, respectively. With the existence of three or more all kinds of reflux events as the standard, the sensitivity, specificity and consistency test Kappa value were 76.7%, 74.7% and 0.449, respectively. CONCLUSION: The nonacid reflux events account for the highest proportion of laryngopharyngeal reflux events, and the consistency of the results of RSI and or RFS with all reflux events is higher than that with only acid reflux events, that indicates nonacid reflux may play an important role in LPRD.

Enhanced bioremediation of diesel range hydrocarbons in soil using biochar made from organic wastes.

Hydrocarbon contamination due to anthropogenic activities is a major environmental concern worldwide. The present study focuses on biochar prepared from fruit and vegetable waste and sewage sludge using a thermochemical approach and its application for the enhanced bioremediation (biostimulation and bioaugmentation) of diesel-polluted soil. The biochar was characterized using FTIR (Fourier-transform infrared spectroscopy), elemental analysis, surface area analysis, and pore analysis. Adsorption experiments showed that hydrocarbon degradation was attributed to biological processes rather than adsorption. The study found that various biochar amendments could significantly increase the rate of hydrocarbon biodegradation with removal efficiencies > 70%. Bioaugmentation using cow dung further improved the removal efficiency to 82%. Treatments showing the highest degree of removal efficiency indicated the presence of 27 different bacteria phyla with Proteobacteria and Actinobacteria as the most abundant phyla. The present study concludes that biochar amendments have great potential for enhancing the bioremediation of soils contaminated with diesel range hydrocarbons.

Coal-derived compounds and their potential impact on groundwater quality during coalbed methane production.

Coalbed methane (CBM) is an important unconventional energy source and accounts for a substantial portion of the overall natural gas production in the USA. The extraction of CBM generates significant amounts of produced water, where the withdrawal of groundwater may disturb the subsurface environment and aquifers. The release of toxic recalcitrant compounds from the coal seam is of great concern for those who use groundwater for irrigation and potable water sources. Experiments were conducted that determined a small fraction of coal carbon can be extracted and solubilized in water during the CBM formation and production. These soluble components included long-chain alkanes, aromatic hydrocarbons, and humic compounds. Biometer flask assays demonstrated that these compounds are bioamenable and can be potentially degraded by microorganisms to produce methane and carbon dioxide, where these biodegradation processes may further impact groundwater quality in the coal seam.

A contribution of hydrogenotrophic methanogenesis to the biogenic coal bed methane reserves of Southern Qinshui Basin, China.

The activity of methanogens and related bacteria which inhabit the coal beds is essential for stimulating new biogenic coal bed methane (CBM) production from the coal matrix. In this study, the microbial community structure and methanogenesis were investigated in Southern Qinshui Basin in China, and the composition and stable isotopic ratios of CBM were also determined. Although geochemical analysis suggested a mainly thermogenic origin for CBM, the microbial community structure and activities strongly implied the presence of methanogens in situ. 454 pyrosequencing analysis combined with methyl coenzyme-M reductase (mcrA) gene clone library analysis revealed that the archaeal communities in the water samples from both coal seams were similar, with the dominance of hydrogenotrophic methanogen Methanobacterium. The activity and potential of these populations to produce methane were confirmed by the observation of methane production in enrichments supplemented with H2 + CO2 and formate, and the only archaea successfully propagated in the tested water samples was from the genus Methanobacterium. 454 pyrosequencing analysis also recovered the diverse bacterial communities in the water samples, which have the potential to play a role in the coal biodegradation fueling methanogens. These results suggest that the biogenic CBM was generated by coal degradation via the hydrogenotrophic methanogens and related bacteria, which also contribute to the huge CBM reserves in Southern Qinshui Basin, China.

Comparative analysis of UV-initiated ARPs for degradation of the emerging substitute of perfluorinated compounds: Does defluorination mean the sole factor?

Due to the increasing attention for the residual of per- and polyfluorinated compounds in environmental water, Sodium p-Perfluorous Nonenoxybenzenesulfonate (OBS) have been considered as an alternative solution for perfluorooctane sulfonic acid (PFOS). However, recent detections of elevated OBS concentrations in oil fields and Frontal polymerization foams have raised environmental concerns leading to the decontamination exploration for this compound. In this study, three advanced reduction processes including UV-Sulfate (UV-SF), UV-Iodide (UV-KI) and UV-Nitrilotriacetic acid (UV-NTA) were selected to evaluate the removal for OBS. Results revealed that hydrated electrons (eaq-) dominated the degradation and defluorination of OBS. Remarkably, the UV-KI exhibited the highest removal rate (0.005 s-1) and defluorination efficiency (35 %) along with the highest concentration of eaq- (K = -4.651). Despite that nucleophilic attack from eaq- on sp2 carbon and H/F exchange were discovered as the general mechanism, high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC/Q-TOF-MS) analysis with density functional theory (DFT) calculations revealed the diversified products and routes. Intermediates with lowest fluorine content for UV-KI were identified, the presence nitrogen-containing intermediates were revealed in the UV-NTA. Notably, the nitrogen-containing intermediates displayed the enhanced toxicity, and the iodine poly-fluorinated intermediates could be a potential-threat compared to the superior defluorination performance for UV-KI.

From challenge to opportunity: Revolutionizing the monitoring of emerging contaminants in water with advanced sensors.

Emerging contaminants in water represent long-term and unpredictable threats to both environmental and human health due to their persistence and bioaccumulation. Current research predominantly focuses on their removal rather than sustained monitoring. This review comprehensively investigates advanced sensor technologies for detecting these contaminants in water, critically evaluating biosensors, optical sensors, electrochemical sensors, and nanomaterial sensors. Elucidating the operational principles, performance metrics such as detection thresholds, and the pros and cons of their practical applications, the review addresses a significant research gap in environmental monitoring. Moreover, it enhances understanding of sensor effectiveness, which in turn guides researchers in selecting the right sensor types for various environmental scenarios. Furthermore, by emphasizing the integration of nanotechnology and the standardization of evaluation protocols, it promotes the development of robust, deployable sensing solutions. Ultimately, this leads to the proposal of a strategic framework aimed at significantly improving the detection capabilities of emerging contaminants and supporting the preservation of environmental health.

Methane production from the biodegradation of lignite with different sizes by mixed fungi-methanogen microflora.

Biogenic coalbed methane (CBM) is a developing clean energy source. However, it is unclear how the mechanisms of bio-methane production with different sizes of coal. In this work, pulverized coal (PC) and lump coal (LC) were used for methane production by mixed fungi-methanogen microflora. The lower methane production from LC was observed. The aromatic carbon of coal was degraded slightly by 2.17% in LC, while 11.28% in PC. It is attributed to the proportion of lignin-degrading fungi, especially Penicillium, which was reached 67.57% in PC on the 7th day, higher than that of 11.38% in LC. The results suggested that the limited interaction area in LC led to microorganisms hardly utilize aromatics. It also led the accumulation of aromatic organics in the fermentation broth in PC. Increasing the reaction area of coal and facilitating the conversion of aromatic carbon are suggested means to increase methane production in situ.

Insights into the carbon nanotubes-mediated activation of permanganate for decontamination under high salinity.

Radical-based advanced oxidation process (AOPs) has attracted great interests in wastewater treatment field. However, by the traditional radical-based method, the degradation of organic pollution is greatly suppressed when radicals react with the co-existing anions in the solution. Herein, an efficient method for degrading of contaminant under high salinity conditions is discussed through a non-radical pathway. Carbon nanotubes (CNTs) was employed as an electron transfer medium to facilitate the electron conversion from contaminants to potassium permanganate (PM). Based the results of quenching experiments, probe experiments, and galvanic oxidation process experiments, the degradation mechanism of CNTs/PM process was demonstrated to be electron transfer, rather than reactive intermediate Mn species. As a result, typical influencing factors including salt concentration, cations, and humic acid have less of an impact on degradation during CNTs/PM processes. In addition, the CNTs/PM system exhibits superior reusability and universality of pollutants, which has the potential to be applied as a non-radical pathway for the purification of contaminant in the large-scale high salinity wastewater treatment.

Insights into the electron transfer regime of permanganate activation on carbon nanomaterial reduced from carbon dioxide.

Simultaneously eliminating novel contaminants in the water environment while also achieving high-value utilization of CO2 poses a significant challenge in water purification. Herein, a CO2-reduced carbon catalyst (CRC) was synthesized via the chemical vapor deposition method for permanganate (PM) activation, fulfilling the ultra-efficient removal of bisphenol A (BPA). The primary mechanism responsible for the BPA degradation in the CRC/PM process is electron transfer. Hydroxyl groups and defect structures on CRC act as electron mediators, facilitating the transfer of electrons from contaminants to PM. On the basis of the quantitative structure-activity relationship, the elimination performance of the CRC/PM process exhibited variability in accordance with the inherent characteristics of pollutants. In addition, the yield of manganese intermediates was also observed in the CRC/PM process, which only serve as redox intermediates rather than active species attacking organics. Ascribed to nonradical mechanisms, the CRC/PM system exhibited remarkable stability and demonstrated significant resistance to the presence of background substances. Moreover, BPA degradation pathways were clarified via mass spectrometry analysis and density functional theory calculations, with intermediate products exhibiting lower toxicity. This study provided new insights into the employment of carbon catalysts derived from CO2 for PM nonradical activation to degrade contaminants in various water matrices.

Reevaluation for UV photolysis of Fe(III) inducing tetracycline abatement: Overlooked significance of complexation-assistance in environmental fates of antibiotics.

Interaction of antibiotics with metal ions in aquatic environments, commonly occurring to form complexes, may affect the migration, transformation and reactivity of residual antibiotics. This study demonstrates the photolysis of Fe(III) by UV irradiation at pH 3.5, as an advanced oxidation process, to produce •OH for the abatement of a common broad-spectrum antibiotic compound, tetracycline (TET). The dimethylamino (-N(CH3)2) and hydroxyl (-OH) groups of TET were determined as the binding sites for the complexation with Fe(III) via a series of novel characterization approaches. The complexation stoichiometry of Fe(III)-TET complexation, including the complexation ratio, constants and percentages, was determined via a complexometric titration based on the UV differential spectroscopy. The complexation constant was determined to be 21,240 ± 1745 L·mol-1 under the designed conditions. Complexation of TET with Fe(III) enhanced its degradation in the UV/Fe(III) process, through the promotion of the •OH generation by inhibiting hydrolysis-precipitation process of Fe(III) and enhancing Fe(III)/Fe(II) cycle and the acceleration of mass transfer between •OH and TET. This finding provides new insights into the role of complexation in the fate of residual antibiotics in the UV/Fe(III) process. The reduced overall ecotoxicity during the TET abatement, evaluated by the toxicity variation through ECOSAR program, provides the UV/Fe(III) process with a theoretical feasibility for water decontamination in actual applications.

Trade-off effect of dissolved organic matter on degradation and transformation of micropollutants: A review in water decontamination.

The degradation of micropollutants by various treatments is commonly affected by the ubiquitous dissolved organic matter (DOM) in the water environment. To optimize the operating conditions and decomposition efficiency, it is necessary to consider the impacts of DOM. DOM exhibits varied behaviors in diverse treatments, including permanganate oxidation, solar/ultraviolet photolysis, advanced oxidation processes, advanced reduction process, and enzyme biological treatments. Besides, the different sources (i.e., terrestrial and aquatic, etc) of DOM, and operational circumstances (i.e., concentration and pH) fluctuate different transformation efficiency of micropollutants in water. However, so far, systematic explanations and summaries of relevant research and mechanism are rare. This paper reviewed the "trade-off" performances and the corresponding mechanisms of DOM in the elimination of micropollutants, and summarized the similarities and differences for the dual roles of DOM in each of the aforementioned treatments. Inhibition mechanisms typically include radical scavenging, UV attenuation, competition effect, enzyme inactivation, reaction between DOM and micropollutants, and intermediates reduction. Facilitation mechanisms include the generation of reactive species, complexation/stabilization, cross-coupling with pollutants, and electron shuttle. Moreover, electron-drawing groups (i.e., quinones, ketones functional groups) and electron-supplying groups (i.e., phenols) in the DOM are the main contributors to its trade-off effect.

The effect of organics transformation and migration on pore structure of bituminous coal and lignite during biomethane production.

Biomethane generation by coal degradation not only can increase coalbed methane (CBM) reserves, namely, microbially enhanced coalbed methane (MECBM), but also has a significant effect on the pore structure of coal which is the key factor in CBM extraction. The transformation and migration of organics in coal are essential to pore development under the action of microorganisms. Here, the biodegradation of bituminous coal and lignite to produce methane and the cultivation with inhibition of methanogenic activity by 2-bromoethanesulfonate (BES) were performed to analyze the effect of biodegradation on coal pore development by determining the changes of the pore structure and the organics in culture solution and coal. The results showed that the maximum methane productions from bituminous coal and lignite were 117.69 µmol/g and 166.55 µmol/g, respectively. Biodegradation mainly affected the development of micropore whose specific surface area (SSA) and pore volume (PV) decreased while the fractal dimension increased. After biodegradation, various organics were generated which were partly released into culture solution while a large number of them remained in residual coal. The content of newly generated heterocyclic organics and oxygen-containing aromatics in bituminous coal was 11.21% and 20.21%. And the content of heterocyclic organics in bituminous coal was negatively correlated with SSA and PV but positively correlated with the fractal dimension which suggested that the retention of organics contributed greatly to the decrease of pore development. But the retention effect on pore structure was relatively poor in lignite. Besides, microorganisms were observed around fissures in both coal samples after biodegradation which would not be conducive to the porosity of coal on the micron scale. These results revealed that the effect of biodegradation on pore development of coal was governed by the combined action of organics degradation to produce methane and organics retention in coal whose contributions were antagonistic and determined by coal rank and pore aperture. The better development of MECBM needs to enhance organics biodegradation and reduce organics retention in coal.