1. 题目: Effects of fulvic acids on the electrochemical reactions and mass transfer properties of organic cation toluidine blue: Results of measurements by the method of rotating ring-disc electrode
This study examined effects of aquatic and soil natural organic matter (NOM) exemplified by standard Suwannee River fulvic acid (SRFA) and Pahokee Peat fulvic acid (PPFA), respectively, on the electrochemical (EC) reactivity and mass transfer properties of the cationic organic probe toluidine blue (TB) that forms complexes with NOM. EC measurements that were carried out using the method of rotating ring-disc electrode (RRDE) showed that for disc potentials below −0.4 V vs. the standard Ag/AgCl reference electrode, TB molecules undergo EC reduction accompanied by the formation of EC-active products that undergo oxidation at the ring electrode. EC reactions of TB in the range of potentials −0.2 to −0.4 V were determined to involve free TB+ cations and TB species adsorbed on the electrode surface. The EC reduction of TB species at the disc potentials < −0.4 V was controlled by the mass transfer of the free TB+ cations and TB/NOM complexes to the electrode surface. Formation of TB/NOM complexes caused the mass transfer-controlled TB currents to undergo a consistent decrease. The observed changes were correlated with the extent of TB/NOM complexation and decreases of the diffusion coefficients of TB/NOM complexes that have higher molecular weights (MW) than the free cations. Properties of the intermediates formed upon the reduction of TB+ cations were also affected by NOM. These results demonstrate that RRDE measurements of EC reactions of TB or possibly other EC active probes allow probing the complexation of EC-active organic species with NOM and mass transfer properties of NOM complexes and ultimately NOM itself.
2. 题目: Fate and removal of aromatic organic matter upon a combined leachate treatment process
Mature leachates contain extremely recalcitrant aromatic organic matter, and require appropriate treatment before discharge. The combined process for treating mature landfill leachate is a common and proper due to its inexpensiveness and high performance. Identification of refractory components and insights into the physicochemical properties transformations of the organics are essential for the development of efficient treatment process. Optical, three-dimensional chromatography and electrochemical techniques were applied to characterize aromatic organic matter in leachate from a pilot landfill leachate treatment plant. Results showed that the combination of biological contact oxidation, iron-carbon micro-electrolysis, Fenton, coagulation and integrated activated sludge system could efficiently remove 95.5% COD and 88.3% DOC in leachate organic matter, together with a simultaneous reduction in its molecular weight (MW), aromaticity, polarity, and humification degree. The low MW proteinaceous, carboxylic acid and amine-containing fractions were preferentially removed in biological contact oxidation process, whereas the hydrophilic humic substances with the MW > 4.0 kDa were the main species against biological treatment. Conversely, the advanced oxidation processes (AOPs) could efficiently destroy high MW, aromatic rings and conjugated moieties fractions, resulting in an increase in the leachate biodegradability. The oxygen-containing moieties generated in the AOPs were bridged by the flocculants to promote precipitate during the coagulation process, and the polymerized metastable organic fractions formed during the process were partly biodegraded in the integrated activated sludge system. This study highlights the potential of combined optical-electrochemical measurements to monitor the intrinsic reactivity of aromatic organic matter and guide the practical leachate treatment.
3. 题目: Carbon balance by priming as controlled by single versus repeated addition and soil fertility
Labile carbon (C) inputs strongly alter soil organic matter (SOM) turnover by priming, thus affecting soil C dynamics and over long-term the soil fertility. The input patterns of labile C regulating priming effect (PE) intensity, and consequently the soil C balance may differ between the experimentally single addition compared to naturally ongoing continuous inputs via rhizodeposits or litter decomposition. We evaluated the effects of single versus repeated additions of 13C-labeled glucose (with added 13C corresponding to 2% of soil organic C content) to five soils with increasing fertility level on the PE intensity and soil C balance. Repeated glucose addition induced 61–108% higher positive SOM priming than the single addition across the five soils. The PE intensity declined with soil fertility level and mineral nitrogen (N) content, but increased with activities of enzymes for N-acquisition (N-acetyl-glucosaminidase and leucine amino peptidase). Consequently, the decrease in N availability strongly increased PE intensity via enhancing microbial N mining from SOM. Considering the C balance between SOM losses by priming and glucose-C retention, glucose addition induced net C losses in the low and moderate fertility soils (−14.0 to −0.30 mg C g−1 SOC over 14 weeks) but C gains in the high fertility soils (+0.44 to +4.36 mg C g−1 SOC). The increase in soil fertility reduced priming intensity and increased glucose-C retention via high N availability and intensive microbial growth, thus promoting microbial necromass formation and so, soil C sequestration. Compared to single addition, repeated glucose addition caused larger net C losses or lower C gains due to stronger SOM priming. In conclusion, substrate addition pattern and soil fertility are crucial for regulating SOM priming and the C balance. This knowledge should be integrated to evaluate soil C dynamics in response to labile C inputs caused by agricultural managements.
4. 题目: Rapid, high-sensitivity analysis of oxyhalides by non-suppressed ion chromatography-electrospray ionization-mass spectrometry: application to ClO4−, ClO3−, ClO2−, and BrO3− quantification during sunlight/chlorine advanced oxidation
5. 题目: Characteristics of DOM in 14 AAO processes of municipal wastewater treatment plants
The characteristics of dissolved organic matter (DOM) such as chemical composition, molecular weight (MW) distribution and hydrophobic/hydrophilic distribution can affect wastewater treatment efficiency, effluent quality and ecological risk. Fluorescence spectroscopy could provide a quick estimate of DOM characteristics during the monitoring of wastewater treatment plants (WWTPs). In this study, the characteristic and quantitative correlation of DOM from 14 anaerobic-anoxic-oxic (AAO) processes of WWTPs located in different provinces (municipalities) of China were investigated. The results showed that DOM of MW <1 kDa was the largest group of DOM in influent and secondary effluent, and DOM removal increased as the MW increased. Hydrophilic (HPI) fraction and hydrophobic acid (HPO-A) comprised the major portion of DOM in influent and secondary effluent and exhibited the lowest rate of removal. In addition, DOM concentrations in the northern provinces were higher than in the southern provinces, which were related to the water quality, economy and population. There were positive correlations between specific fluorescence intensity (SFI) and the MW <1 kDa, 1–5 kDa and <10 kDa fractions. The smaller the molecular weight, the better the correlation. Strong positive correlations between regional fluorescence proportion (fi) and HPI were found. SFI and fi may be explored as potential indicators of the MW fractions and the hydrophobic/hydrophilic distribution of DOM in AAO processes WWTPs.
6. 题目: Deciphering organic matter sources and ecological shifts in blue carbon ecosystems based on molecular fingerprinting
7. 题目: Reduction mechanism of Cd accumulation in rice grain by Chinese milk vetch residue: Insight into microbial community
Chinese milk vetch is an efficient approach to reduce Cd accumulation in rice, nevertheless, its reduction mechanism is not well understood. In this study, we investigated the rice grain Cd, soil properties and microbial community in a Cd-polluted paddy field amended with milk vetch residue (MV) or without (CK) during rice growth period. We found that milk vetch residue averagely decreased the Cd content in rice grain by 45%. Decrease of Cd in rice mainly attributed to the inhibition of Cd activation by milk vetch residue at heading stage probably by the formation of HA-Cd (Humic Acid) and CdS. Increased pH and organic matter (OM) promoted the reduction of available Cd. In addition, nonmetric multidimensional scaling (NMDS) analysis revealed that microbial community structure was significantly different between MV and CK treatment (r = 0.187, p = 0.002), and the core functions of differentially abundant genera were mainly associated with N-cycling, organic matter degradation and sulfate-reducing. The application of milk vetch residue increased the abundance of sulfate-reducing bacteria (SRB) by 8–112% during the rice growth period, which may involve in promoting the transformation of Cd to a more stably residual Cd (CdS). Canonical correspondence analysis (CCA) and mantel test analysis indicated that available K (p = 0.004) and available N (p = 0.005) were the key environmental factors of shaping the SRB. Altogether, changes in soil properties affected microbial structure and functional characteristics, especially the response of SRB in MV treatment would provide valuable insights into reducing the bioavailability of Cd in soil.
8. 题目: Seagrass losses since mid‐20th century fuelled CO2 emissions from soil carbon stocks
Seagrass meadows store globally significant organic carbon (Corg) stocks which, if disturbed, can lead to CO2 emissions, contributing to climate change. Eutrophication and thermal stress continue to be a major cause of seagrass decline worldwide, but the associated CO2 emissions remain poorly understood. This study presents comprehensive estimates of seagrass soil Corg erosion following eutrophication‐driven seagrass loss in Cockburn Sound (23 km2 between 1960s and 1990s) and identifies the main drivers. We estimate that shallow seagrass meadows (<5 m depth) had significantly higher Corg stocks in 50 cm thick soils (4.5 ± 0.7 kg Corg/m2) than previously vegetated counterparts (0.5 ± 0.1 kg Corg/m2). In deeper areas (>5 m), however, soil Corg stocks in seagrass and bare but previously vegetated areas were not significantly different (2.6 ± 0.3 and 3.0 ± 0.6 kg Corg/m2, respectively). The soil Corg sequestration capacity prevailed in shallow and deep vegetated areas (55 ± 11 and 21 ± 7 g Corg m−2 year−1, respectively), but was lost in bare areas. We identified that seagrass canopy loss alone does not necessarily drive changes in soil Corg but, when combined with high hydrodynamic energy, significant erosion occurred. Our estimates point at ~0.20 m/s as the critical shear velocity threshold causing soil Corg erosion. We estimate, from field studies and satellite imagery, that soil Corg erosion (within the top 50 cm) following seagrass loss likely resulted in cumulative emissions of 0.06–0.14 Tg CO2‐eq over the last 40 years in Cockburn Sound. We estimated that indirect impacts (i.e. eutrophication, thermal stress and light stress) causing the loss of ~161,150 ha of seagrasses in Australia, likely resulted in the release of 11–21 Tg CO2‐eq since the 1950s, increasing cumulative CO2 emissions from land‐use change in Australia by 1.1%–2.3% per annum. The patterns described serve as a baseline to estimate potential CO2 emissions following disturbance of seagrass meadows.
9. 题目: Optical and chemical analysis of absorption enhancement by mixed carbonaceous aerosols in the 2019 Woodbury, AZ fire plume
Wildfires emit mixtures of light‐absorbing aerosols (including black and brown carbon, BC and BrC, respectively) and more purely‐scattering organic aerosol (OA). BC, BrC and OA interactions are complex and dynamic and evolve with aging in the atmosphere resulting in large uncertainties in their radiative forcing. We report microphysical, optical and chemical measurements of multiple plumes from the Woodbury Fire (AZ, USA) observed at Los Alamos, NM after 11‐18 hours of atmospheric transit. This includes periods where the plumes exhibited little entrainment as well as periods that had become more dilute after mixing with background aerosol. Aerosol mass absorption cross‐sections (MAC) were enhanced by a factor of 1.5‐2.2 greater than bare‐BC at 870 nm suggesting lensing by non‐absorbing coatings following a core‐shell morphology. Larger MAC enhancement factors of 1.9‐5.1 at 450 nm are greater than core‐shell morphology can explain and are attributed to BrC. MAC of OA (MACOrg) at 450 nm was largest in intact portions of the plumes (peak value bounded between 0.6‐0.9 m2/g (Org)) and decreased with plume dilution. We report a strong correlation between MACOrg(450 nm) with the fC2H4O2 (a tracer for levoglucosan‐like species) of coatings and of bulk OA indicating that BrC in the Woodbury Fire was co‐emitted with levoglucosan, a primary aerosol. fC2H4O2 and MACOrg(450 nm) are shown to vary between the edge and the core of plumes demonstrating enhanced oxidation of OA and BrC‐bleaching near plume edges. Our process‐level finding can inform parameterizations of mixed BC, BrC and OA properties for wildfire plumes in climate models.
10. 题目: Hydroxyl radical scavenging factor measurement using a fluorescence excitation-emission matrix and parallel factor analysis in ultraviolet advanced oxidation processes
The performance of the UV/H2O2 advanced oxidation process (AOP) is dependent on water quality parameters, including the UV absorbance coefficient at 254 nm and hydroxyl radical (•OH) water background demand (scavenging factor, s−1). The •OH scavenging factor represents the •OH scavenging rate of the background substances in the water matrix, and it is known to be one of the key parameters to predict the performance of the UV/H2O2 process. The •OH scavenging factor has been determined experimentally by using a probe compound such as pCBA and rhodamine B. The experimental method has been validated to accurately predict the micropollutants removal in the UV/H2O2 process, but there is a need for an easier and simple method of determining the OH scavenging factor. We evaluated the alternative method to analyze the •OH scavenging factor using fluorescence excitation-emission matrix and parallel factor analysis (F-EEM/PARAFAC). The correlation between •OH scavenging factor and the spectroscopic characteristics and structure of different organic matter types was evaluated. Organic matter was characterized using a fluorescence excitation-emission matrix, parallel factor analysis, and liquid chromatography-organic carbon detection. Second-order reaction rates of humic acid sodium salt, sodium alginate, Suwannee River humic acid and bovine serum albumin were calculated as 1.30 × 108 M−1 s−1, 1.39 × 108 M−1 s−1, 1.03 × 108 M−1 s−1, and 3.17 × 107 M−1 s−1, respectively. Results of PARAFAC analysis, the ratio of humic and fulvic fluorescence component 2 to terrestrial humic-like fluorescence component 1 (C2/C1), and •OH scavenging factor showed high linearity. A predictive model, which combines with the F-EEM/PARAFAC method, predicted the optimal UV and H2O2 dose to achieve target compound removal.
11. 题目: The modern phosphorus cycle informs interpretations of Mesoproterozoic Era phosphorus dynamics
The cycles of phosphorus, carbon and oxygen are intimately linked. Indeed, in many models, phosphorus is considered the driver of the carbon and oxygen cycles, and low concentrations of atmospheric oxygen during the Mesoproterozoic Era have been linked to extreme phosphorus limitation in the Mesoproterozoic oceans. To evaluate the Mesoproterozoic Era phosphorus cycle, we analyze the concentrations of phosphorus, organic carbon, and selected trace metals in several geological formations of Mesoproterozoic age. We combine these analyses with literature data to explore the relationship between phosphorus and organic carbon removal into Mesoproterozoic-Era sediments through a variety of water depths and water-column chemistries. We find that the ratio of organic carbon to reactive phosphorus (Corg/Preact) is largely invariant between different paleo-settings with average Corg/Preact that is either equal to or less than the Redfield ratio of 106/1 through all environments we explored. We put these results in the context of the modern phosphorus cycle which is reviewed here. Compared to modern phosphorus dynamics, we see no evidence for an anoxic-euxinic feedback between phosphorus burial, carbon burial and oxygen production during Mesoproterozoic Times. However, we do identify an additional potential phosphorus feedback related to the relationship between anoxia and deep-sea phosphorus dynamics that could have importance and oxygen regulation through time. We find the average value of Corg/Preact during the Mesoproterozoic Era is greater than the average for modern sediments. This result suggests that equal or more organic carbon was buried per unit of phosphorus during Mesoproterozoic times compared to today, a conclusion broadly consistent with the carbon isotope record. These results offer the possibility of a strong oxygen source to the atmosphere during the Mesoproterozoic Era, raising the conundrum as to why atmospheric oxygen levels were lower then, when compared to now. We suggest that a variety of factors may explain these differences in oxygen concentration including elevated rates of mantle degassing, reduced rates of phosphorus weathering and the lack of a terrestrial biosphere.
12. 题目: Glycerol dialkyl glycerol tetraethers in surface sediments from three Pacific trenches: Distribution, source and environmental implications
Glycerol dialkyl glycerol tetraethers (GDGTs) have been widely used to elucidate sources of sediment total organic carbon (TOC), past temperature and presence of methanogenesis in diverse environments. However, their applicability to hadal trenches with their unique deposition dynamics remains unknown. Here, we analyzed GDGTs and their stable isotope values and content of TOC in surface sediments from the Kermadec Trench region (KT; 6080–10010 m), New Britain Trench region (NBT; 1553–8931 m), and Atacama Trench region (AT; 2560–8085 m). These regions are at very different distances from terrestrial sources and have varying net primary productivity (NPP) in the waters above them. The GDGT concentration was highly variable (54.5–2416 μg g-1 TOC) within and between trench regions and was not directly related to local NPP or apparent terrestrial inputs. This finding is presumably due to complex deposition dynamics within the trench interior. Isoprenoidal GDGTs (isoGDGTs; 75.4–99.1%) were dominant over branched GDGTs (brGDGTs, 0.91–24.6%) in all samples, leading to low levels of Branched versus Isoprenoidal Tetraether (BIT) index (0.01–0.27). Thus, sediment TOC is mainly derived from marine sources. However, compared to adjacent non-hadal sites, trench axis sites have a higher BIT index, lower acyclic hexa-/pentamethylated brGDGT and lower δ13C, supporting relative enrichment of terrestrial organic carbon at the trench axis. The application of TetraEther indeX of tetraethers consisting of 86 carbon atoms (TEX86) resulted in sea surface temperature (SST) estimates of 18.9–23.7 ℃ in the KT, 28.6–30.2 ℃ in the NBT, and 17.9–20.4 ℃ in the AT. The close agreement between TEX86-SST with observed in situ SST suggests that isoGDGTs are not selectively degraded during the transport towards the hadal realm, and that TEX86 from hadal settings robustly records an integrated regional SST signal.
13. 题目: Amelioration of copper toxicity to a tropical freshwater microalga: Effect of natural DOM source and season
Australian tropical freshwaters can experience extreme seasonal variability in rainfall and run off, particularly due to pulse events such as storms and cyclones. This study investigated how seasonal variability in dissolved organic matter (DOM) quality impacted the chronic toxicity of copper to a tropical green alga (Chlorella sp.) in the presence of two concentrations of DOM (low: ∼2 mg C/L; high: ∼10 mg C/L) collected from three tropical waters. Copper speciation and lability were explored using diffusive gradients in thin-films (DGT) and modelled maximum dynamic concentrations (cdynmax) using data derived from the Windermere Humic Aqueous Model (WHAM VII). Relationships between copper lability and copper toxicity were assessed as potential tools for predicting toxicity. Copper toxicity varied significantly with DOM concentration, source and season. Copper toxicity decreased with increasing concentrations of DOM, with 50% growth inhibition effect concentrations (EC50) increasing from 1.9 μg Cu/L in synthetic test waters with no added DOM (0.34 mg C/L) up to 63 μg Cu/L at DOM concentrations of 9.9 mg C/L. Copper toxicity varied by up to 2-fold between the three DOM sources and EC50 values were generally lower in the presence of wet season DOMs compared to dry season DOMs. Linear relationships between DGT-labile copper and dissolved copper were significantly different between DOM source, but not concentration or season. Modelled cdynmax consistently under-predicted labile copper in high DOM treatments compared to DGT measurements but performed better in low DOM treatments, indicating that this method is DOM-concentration dependent. Neither speciation method was a good surrogate for copper toxicity in the presence of different sources of natural DOM. Our findings show that DOM source and season, not just DOM concentration, affect copper toxicity to freshwater biota. Therefore, DOM quality should be considered as a toxicity-modifying factor for future derivation of bioavailability-based site-specific water quality guideline values.
14. 题目: Biochar amendment increases tree growth in nutrient-poor, young Scots pine stands in Finland
Biochar is charred material formed by the pyrolysis of organic matter. The addition of biochar to soil may offer a chance to mitigate climate change by increasing soil carbon stocks, improving soil fertility and enhancing plant growth. Vast majority of biochar studies are conducted in agricultural soils, and field experiments studying the effect of biochar on tree growth in boreal forests are lacking. We applied spruce biochar amendments of 5 and 10 Mg ha−1 to the soil surface in young boreal Scots pine (Pinus sylvestris L.) forests in Southern Finland and studied the responses in tree growth and needle nitrogen (N) and 15N concentrations during the first three years after treatment. The biochar amendment of 10 Mg ha−1 increased the diameter growth of dominant trees significantly, on average by 1 mm year−1, which corresponded to 25% increase compared to control during the three years study period. The positive growth responses were less pronounced in height than in diameter growth. The biochar amendment of 5 Mg ha−1 increased the height growth of dominant trees by 0.16 m or 12% compared to the control during three years. Biochar amendments did not affect N and 15N concentrations in needles. The results suggest that wood biochar amendment can be a climate-friendly method to increase tree biomass production in nutrient poor, xeric, young Scots pine forests.
15. 题目: The degradation of chloramphenicol by O3/PMS and the impact of O3-based AOPs pre-oxidation on dichloroacetamide generation in post-chlorination
The frequent detection of chloramphenicol (CAP) in wastewater and surface water gives rise to concerns on its fatal myelosuppression and aplastic anemia. Recently, the combination of ozone and peroxymonosulfate (O3/PMS) has received wide attention in removing pollutants due to the multiple oxidants (i.e., O3, hydroxyl radicals (OH) and sulfate radicals (SO4−)) existed therein. This study showed that O3/PMS could effectively degrade CAP under various conditions. The second-order rate constant of CAP with O3, OH and SO4− was , and , respectively. The degradation efficiency of CAP was significantly enhanced as PMS concentration or pH increased. Bicarbonate (HCO3−) at concentration of 5 mM slightly inhibited CAP degradation at pH 7. Chloride (Cl−) at concentration of 0.5 mM enhanced CAP removal at pH 7, while this enhancement gradually weakened as Cl− concentration further increased. The degradation efficiency of CAP first increased with increasing natural organic matter (NOM) concentrations (0.1–0.3 mg/L), while it was completely suppressed at higher NOM concentrations (0.5 mg/L). Four degradation products in total of CAP were identified in O3-based processes (i.e., O3, O3/TBA, O3/H2O2, O3/PMS and O3/PMS/tert-butyl alcohol (TBA) systems. Besides, these transformation products by OH, SO4− and/or O3 were also distinguished. Finally, the impact of O3/PMS pre-oxidation on the formation of dichloroacetamide (DCAcAm) from CAP during post-chlorination process was investigated. Compared with the traditional O3 and O3/H2O2 processes, O3/PMS pre-oxidation generally led to the least generation of DCAcAm under similar conditions, where SO4− rather than OH was conducive to relieve the formation of DCAcAm. Moreover, the presence of NOM obviously alleviated the formation of DCAcAm by O3/PMS pre-oxidation.
16. 题目: Soil macroinvertebrates alter the fate of root and rhizosphere carbon and nitrogen in a turfgrass lawn
Soil invertebrates, especially larger macroinvertebrates, move soil, fragment organic matter and change resource accessibility for soil microorganisms. Macroinvertebrates also affect the formation and turnover of aggregates, which are important controls of soil organic matter dynamics because they physically protect organic matter from degradation and influence many belowground processes ranging from microbial activity to nutrient sorption and water flow. We still lack a complete understanding of how different soil invertebrate functional groups affect the incorporation of root derived carbon and nitrogen into belowground pools. We assessed the effects of macroinvertebrates on soil aggregate abundance and composition and quantified the fate of organic matter derived from roots using a two-year macroinvertebrate exclusion-based field mesocosm study coupled with stable isotope labeling in a turfgrass lawn ecosystem. We hypothesized that macroinvertebrates change soil aggregates dynamics by increasing macroaggregates and decreasing microaggregates and enhancing the incorporation of root-derived organic matter into macroaggregates. Macroinvertebrate effects on rhizosphere organic matter dynamics were assessed using both size-based exclusion mesocosms and tracing of stable isotopes of carbon and nitrogen for two years. We found that within the turfgrass root zone, macroinvertebrates increased the proportion of macroaggregates and decreased free microaggregates. In addition, macroinvertebrates increased carbon and nitrogen incorporation into macroaggregates, microaggregates and coarse particulate organic matter, detected via isotopic enrichment of those soil fractions. We found that macroinvertebrates affect the fate of recently fixed root- and rhizodeposit-derived organic matter in a turfgrass lawn ecosystem, and particularly its incorporation into soil aggregates, similar to findings in forest and agricultural systems.
17. 题目: Effect of no-tillage on soil bacterial and fungal community diversity: A meta-analysis
No-tillage farming is widespread globally; however, the impact of no-tillage on soil microbial diversity is debatable. The existing research literature needs to be synthesized and a comprehensive and unified standard analysis conducted to examine the effects of no-tillage on soil microbial diversity. To this end, we conducted a meta-analysis based on 43 peer-reviewed articles from around the world, with 141 observations on microbial community changes under no-tillage. No-tillage had different effects on bacterial and fungal community diversity—increasing soil bacterial diversity, with no significant change to fungal diversity—and soil type and stubble had a significant impact on soil bacterial diversity. Neither low (0–100 kg ha–1) nor high (> 200 kg ha–1) nitrogen applications could simultaneously promote soil organic carbon and total nitrogen under no-tillage, but a medium (100–200 kg ha–1) nitrogen application level accomplished this goal. A medium nitrogen application level significantly changed soil microbial diversity under no-tillage, while excessively high or low nitrogen application levels had no significant effect. No-tillage significantly increased the relative abundance of Acidobacteria, decreased Actinobacteria, and had little effect on Proteobacteria, Chloroflex, Firmicute, and Bacteroides. A structural equation model showed that retaining stubble under no-tillage had the most significant effect on soil microbial diversity by changing soil organic carbon and total nitrogen contents. Field management with long-term no-tillage, stubble, and medium nitrogen application can improve soil bacterial diversity.
18. 题目: KOH-activated porous biochar with high specific surface area for adsorptive removal of chromium (VI) and naphthalene from water: Affecting factors, mechanisms and reusability exploration
Herein, a high-performance porous biochar described as PBCKOH was successfully synthesized by two-step pyrolysis of corn straw with chemical activation of KOH, and was employed for the elimination of Cr(VI) and naphthalene (NAP) from water. Benefiting from KOH activation, the PBCKOH was found to possess huge specific surface area of 2183.80 m2/g and many well-developed micropores with average particle size of 2.75 nm and main pore diameters distribution from 1 to 2 nm. The PBCKOH presented an excellent adsorption performance with a theoretical monolayer uptake of 116.97 mg/g for Cr(VI) and a heterogeneous adsorption capacity of 450.43 mg/g for NAP. The uptake equilibrium was attained within about 120 min for Cr(VI), while about 180 min for NAP following avrami fractional-order model, revealing the existence of multiple kinetics during the adsorption. The thermodynamic results showed that the uptake of both Cr(VI) and NAP occurred spontaneously (-ΔG°), while in an endothermic nature for Cr(VI) (+ΔH°) and an exothermic characteristic for NAP (-ΔH°) with different randomness. Furthermore, the PBCKOH was believed to enhance the Cr(VI) adsorption mainly through the combination of electrostatic attraction, complexation, ion exchange and reduction action, while achieving the high NAP uptake by pore filling and π-π stacking interactions.
19. 题目: Characterization of reversible and irreversible foulants in membrane bioreactor (MBR) for eucalyptus pulp and paper mill wastewater treatment using fluorescence regional integration
Membrane bioreactors (MBRs) are an alternative technology to achieve high quality effluent for water reuse for eucalyptus pulp and paper (P&P) industries, but membrane fouling is still a challenging factor that restricts its application. This study aims to investigate characteristics of reversible and irreversible fouling of the submerged polyvinylidene fluoride (PVDF) MBR for treating eucalyptus P&P wastewater. Six batches of MBR experiments with different mixed liquor suspended solids (MLSS) concentrations were performed. The membrane cleaning protocol included three-steps: backwashing with DI water and subsequently NaOH solution, and then soaking with NaOCl solution, for which achieved 54.6 ± 11 %, 76.6 ± 10 % and 97.8 ± 2 % of flux recovery, respectively. Formation of a cake layer comprised of organic substance and soluble microbial products (SMPs), mostly polysaccharides and proteins, was the main contributor to flux decline of the MBR. Concentration of proteins in the irreversible foulant was found to be positively correlated with degree of membrane fouling. Using fluorescence excitation-emission matrix (EEM) with fluorescence regional integration (FRI) analysis revealed that, during MBR treatment, protein-like substances in the permeate water significantly decreased, simultaneously with the increase in relative proportions of humic-like and fulvic-like substances. Further analysis on the irreversible foulants showed that protein-like substances, including tyrosine-like and tryptophan-like substances, were disproportionately more important to membrane fouling than humic-like substances relative to their respective concentration in raw P&P wastewater.
20. 题目: Low-dose biochar added to sediment improves water quality and promotes the growth of submerged macrophytes
Biochar is a good adsorbent for water pollutants. However, the effects of biochar on aquatic organisms are not well understood. In this study, different amounts of biochar (CK, 0 mg/g; T1, 10 mg/g; T2, 30 mg/g) were added to sediment to study changes in water quality and its impact on three submerged macrophytes (Hydrilla verticillata, Vallisneria natans, and Ceratophyllum demersum) and the sediment microbial community. The results indicated that biochar treatments significantly increased the water pH and conductivity. Compared with the initial values, the total phosphorus (P) contents in the water of the CK, T1, and T2 treatments decreased by 78.5%, 95.0%, and 58.3%, respectively, while the total nitrogen contents increased by 26.26%, −5.81%, and 19.70%, respectively. Compared with those in CK, the relative growth rates of H. verticillata, V. natans, and C. demersum in T1 increased by 28.4%, 163.1%, and 61.3%, respectively, while those in T2 showed no significant difference except that the growth rates of H. verticillata decreased by 17.7%. The P contents of the three submerged macrophytes increased with the increase of biochar addition, except that there was no significant difference between T2 and CK for H. verticillata. Biochar treatments reduced the biomass of total microbial, bacterial, and fungal phospholipid fatty acids in the sediment for H. verticillata and V. natans, and they increased fungal: bacterial ratios in the low-dose biochar treatments for V. natans and C. demersum. This study demonstrates that the addition of biochar to sediment significantly increased the pH and conductivity, and decreased total P contents in the water. Low-dose biochar treatments were more beneficial for water quality improvements and the growth of submerged macrophytes than high-dose biochar.