12881. 题目: A new insight on enhanced Pb(II) removal by sludge biochar catalyst coupling with ultrasound irradiation and its synergism with phenol removal
The applicability of sludge biochar catalyst (SBC) coupling with ultrasound (US) irradiation for the simultaneous removal of Pb(II) and phenol was firstly investigated in this study. Results indicate that Pb(II) removal of SBC/US process was superior to that of SBC without US. The inhibitory order of the coexisting anions on Pb(II) removal was PO43− > HCO3− > NO3− > F− > SO42− > Cl−. Also, several coexisting metals ions inculding Cr(VI), Ni(II) and Cu(II) could be removed in a simultaneous manner with Pb(II). A high removal performance of Pb(II) by SBC/US process and its synergism with phenol oxidation had been successfully achieved. The simultaneous removal efficiencies of Pb(II) and phenol were high up to 95% within 60 min at optimum reaction conditions. Four kinds of Pb species inculding Pb0, PbCO3, PbO and Pb(OH)2 were formed during the reaction, whereas five kinds of transformation compounds of phenol such as 1,4-benzoquinone, acetic acid, formic acid, maleic acid and propionic acid were detected. Both HO and O2− contributed to the oxidation of phenol by SBC/US process, but HO was dominant radical. A reaction mechanism for the synergistic removal of Pb(II) and phenol by SBC/US process involving in four stages-namely adsorption, precipitation, reduction and Fenton-like oxidation processes was proposed. This study demonstrates that SBC/US process could be considered as a potential candidate for the remediation of real wastewaters containing Pb(II) and phenol.
12882. 题目: Behaviour of neonicotinoids in contrasting soils
Neonicotinoids are widely used to control insect pests in agriculture. Their presence in the environment can affect the health of non-target insects and aquatic animals. The behaviour of four neonicotinoids, namely imidacloprid, acetamiprid, thiacloprid and thiamethoxam, has been investigated in soils with contrasting characteristics to understand their migration in soil and ecological risk. Among the study neonicotinoids, thiamethoxam and thiacloprid were found to be the least and most sorbed neonicotinoids by all the soils, respectively (up to 186 time greater adsorption of thiacloprid), and their uptake was affected by the content of organic matter in the soil. Leaching studies in columns confirmed that thiamethoxam leached out of the soils readily, pointing out to a relatively high risk of ground water contamination with possible ecological impact when thiamethoxam is used in soils with low organic matter. In soil column studies, the soil with the lowest organic matter presents the greatest residue of neonicotinoids in the sub-surface (≤5 cm). In contrast the soil richer in organic matter presented most of the contamination deeper down in the column; a factor to be considered in the remediation from soil.
12883. 题目: Fossil fuel carbon contamination impacts soil organic carbon estimation in cropland
Fossil fuel consumption for centuries has led to widespread deposition of coal or soot particles in agricultural soils of industrialized areas. However, little is known about the impact of fossil fuel carbon (C) contamination on soil organic C (SOC) estimates. This study investigated topsoil (0–10 cm) coal C and soot C derived from incomplete combustion of fossil fuels (SfC) in the coal-contaminated soils (CCS) and coal-free soils (CFS) from the Jiaozuo coal-crop overlapping zone in China. We explored the impact of fossil fuel C by comparing the SOC measurements determined by dry combustion and two modified Walkley-Black (WB175 and WB135) methods with counterparts derived from the stable C isotope technique. The results showed that the coal C and SfC fractions accounted for 52 ± 25% and 7 ± 4% of total organic C (TOC) in the CCS. The SfC fraction accounted for 8 ± 2% of the TOC in the CFS. No significant difference in SOC concentration was observed between the CCS and CFS (P > 0.05). Both coal C and SfC can be completely oxidized by the dry combustion method and highly oxidized by the WB methods (WB175: 46–95%; WB135: 53–100%). Using the three methods to quantify SOC produced an overestimation of 20% to 7.4-fold for the CCS. Moreover, the contribution of coal C to the SOC overestimation was significantly higher than that of SfC (P < 0.001). For the CFS, a significant overestimation (5–15%) of SOC was also detected for the dry combustion method (P < 0.001). The results suggest that direct application of routine dry combustion and WB methods can lead to serious overestimation of SOC when ignoring fossil fuel C contamination. Interestingly, we observed a sharp decrease in SOC concentration when the coal C fraction exceeded 68%, which implies that the incorporation of crop straw into highly coal-contaminated soils can act as a C source for the atmosphere. Therefore, distinguishing fossil fuel C from SOC is crucial for accurately estimating SOC in fossil fuel-contaminated soils when dry combustion and WB methods are applied.
12884. 题目: The addition of biochar as a sustainable strategy for the remediation of PAH–contaminated sediments
The contamination of sediments by polycyclic aromatic hydrocarbons (PAHs) has been widely spread for years due to human activities, imposing the research and development of effective remediation technologies for achieving efficient treatment and reuse of sediments. In this context, the amendment of biochar in PAH–contaminated sediments has been lately proposed as an innovative and sustainable technology. This review provides detailed information about the mechanisms and impacts associated with the supplementation of biochar to sediments polluted by PAHs. The properties of biochar employed in these applications have been thoroughly examined. Sorption onto biochar is the main mechanism involved in PAH removal from sediments. Sorption efficiency can be significantly improved even in the presence of a low remediation time (i.e. 30 d) when a multi–PAH system is used and biochar is provided with a high dosage (i.e. by 5% in a mass ratio with the sediment) and a specific surface area of approximately 360 m2 g−1. The use of biochar results in a decrease (i.e. up to 20%) of the PAH degradation during bioaugmentation and phytoremediation of sediments, as a consequence of the reduction of PAH bioavailability and an increase of water and nutrient retention. In contrast, PAH degradation has been reported to increase up to 54% when nitrate is used as electron acceptor in low–temperature biochar–amended sediments. Finally, biochar is effective in co–application with Fe2+ for the persulfate degradation of PAHs (i.e. up to 80%), mainly when a high catalyst dose and an acidic pH are used.
12885. 题目: Disinfection by-products in Croatian drinking water supplies with special emphasis on the water supply network in the city of Zagreb
The occurrence of disinfection by-products (DBPs) was investigated in 48 drinking water systems across Croatia. Eleven DBPs were studied: chlorite (ClO2−), chlorate (ClO3−), four trihalomethanes (THMs), and five haloacetic acids (HAAs). Furthermore, an intensive sampling program was conducted in the distribution system in the city of Zagreb where, aside from DBP analyses, natural organic matter (NOM) was characterized using fluorescence spectroscopy. In the drinking waters examined across Croatia, DBP values were found in the range from 0.7 μg/L to 32.8 μg/L for THMs, below LOQ to 17.2 μg/L for HAAs (primarily di- and trichloroacetic acids), below LOQ to 720 μg/L for ClO2− and below LOQ to 431 μg/L for ClO3−. The results obtained showed higher chlorite concentrations in the systems treated with hypochlorite compared to systems treated with chlorine dioxide. DBPs in the Zagreb distribution network were generally low (the average values were below 6 μg/L and 2 μg/L for total THM and total HAA respectively). In contrast to our observations throughout Croatia, dibromoacetic acid (DBAA) was found to be the predominant HAA within Zagreb, most likely due to the degradation of chlorinated carboxylates (di-/tri-chloroacetic) in the network. Characterization of NOM by Parallel Factor Analysis (PARAFAC) fluorescence spectroscopy across the Zagreb network showed distinct temporal variations arising from groundwater inputs, as evident from variable humic-, tyrosine-, and tryptophan-like peaks. Statistical correlations between fluorescence data and DBPs highlight its potential for monitoring the presence of DBPs in distribution networks.
12886. 题目: Sustainable use of biochar for resource recovery and pharmaceutical removal from human urine: A critical review
12887. 题目: Metal sorption onto nanoscale plastic debris and trojan horse effects in Daphnia magna: Role of dissolved organic matter
There is a debate on whether the Trojan horse principle is occurring for nanoscale plastic debris (NPD < 1 µm). It is realized that NPD have a high capacity to sorb environmental contaminants such as metals from the surrounding environment compared to their microplastic counterparts, which influences the sorbed contaminants' uptake. Herein, we studied the influence of dissolved organic matter (DOM) on the time-resolved sorption of ionic silver (Ag+) onto polymeric nanomaterials, as models of NPD, as a function of particle size (300 and 600 nm) and chemical composition [polystyrene (PS) and polyethylene (PE)]. Subsequently, the toxicity of NPD and their co-occurring (adsorbed and absorbed) Ag+ on Daphnia magna was determined. Silver nitrate was mixed with 1.2 × 105 NPD particles/mL for 6 days. The extent of Ag+ sorption onto NPD after 6 days was as follows: 600 nm PS-NPD > 300 nm PS-NPD > 300 nm PE-NPD. The presence of DOM in the system increased the sorption of Ag+ onto 300 nm PS-NPD and PE-NPD, whereas DOM decreased the sorption onto 600 nm PS-NPD. Exposure to 1 mg/L NPD or 1 µg/L Ag+ was not toxic to daphnids. However, the mixture of these concentrations of PS-NPD and Ag+ induced toxicity for both sizes (300 and 600 nm). The addition of DOM (1, 10 and 50 mg/L) to the system inhibited the combined toxicity of Ag+ and NPD regardless of the size and chemical composition. Taken together, in natural conditions where the concentration of DOM is high e.g. in freshwater ecosystems, the sorption of metals onto NPD depends on the size and chemical composition of the NPD. Nevertheless, under realistic field conditions where the concentration of DOM is high, the uptake of contaminants in D. magna that is influenced by the Trojan horse principles could be negligible.
12888. 题目: Comparison of soluble microbial product (SMP) production in full-scale anaerobic/aerobic industrial wastewater treatment and a laboratory based synthetic feed anaerobic membrane system
This study focused on the characterisation of soluble microbial products (SMPs) produced from a full-scale multi-stage (anaerobic/aerobic) industrial wastewater treatment plant, and contrasted them to the SMPs detected in the effluent of a lab-scale AnMBR treating synthetic wastewater to determine if there were any common solutes detected irrespective of the feed organics. Recently developed analytical methods using gas chromatography coupled mass spectrometry (GC–MS) and liquid chromatography coupled quadrupole-time-of-flight (LC-Q-ToF) for SMP characterisation in a wide molecular weight (MW) range of 30–2000 Da (Da) were applied. Samples collected from the Industrial Wastewater plant were the upflow anaerobic sludge blanket (UASB) influent and effluent, and aerobic membrane bioreactor (MBR) effluent before discharge. The GC–MS detected a spike in cyclooctasulphur in the UASB effluent, an indicator of shock-loading, which disappeared after the MBR process. Alkanes, acids and nitrogenous compounds were found to be the end-products from the GC–MS results, while LC-Q-ToF analysis revealed that eicosanoids, a group of cell-signalling molecules, were produced in the aerobic MBR, and made up 71% of its effluent. A comparison of the submerged anaerobic membrane bioreactor (SAMBR) and aerobic MBR effluents using GC–MS showed that there was only a small degree of similarity between the SMPs, comprising mainly long chain alkanes and phthalate. On the other hand, LC-Q-ToF showed a large contrast in compound composition, mostly having cell-signalling functions, which deepened our understanding of the different metabolic processes occurring in aerobic and anaerobic systems. These data could be useful for future work in various areas such as controlling quorum-sensing and biofilm formation, process optimisation and control, and microbial ecology.
12889. 题目: Sorptive removal of disinfection by-product precursors from UK lowland surface waters: Impact of molecular weight and bromide
The current study compared the impact of three different unit processes, coagulation, granular activated carbon (GAC), and a novel suspended ion exchange (SIX) technology, on disinfection by-product formation potential (DBPFP) from two UK lowland water sources with medium to high bromide content. Specific attention was given to the influence of the organic molecular weight (MW) fraction on DBPFP as well as the impact of bromide concentration. Whilst few studies have investigated the impact of MW fractions from Liquid Chromatography with Organic Carbon Detection (LC-OCD) analysis on dissolved organic carbon (DOC) removal by different processes, none have studied the influence of DOC MW fractions from this analysis on DBP formation. The impact of higher bromide concentration was to decrease the total trihalomethane (THM) and haloacetic acid (HAA) mass concentration, in contrast to previously reported studies. Results indicated that for a moderate bromide concentration source (135 μg/L), the THM formation potential was reduced by 22% or 64% after coagulation or SIX treatment, respectively. For a high bromide content source (210 μg/L), the THM formation potential removal was 47% or 69% following GAC or SIX treatment, respectively. The trend was the same for HAAs, albeit with greater differences between the two processes/feedwaters with reference to overall removal. A statistical analysis indicated that organic matter of MW > 350 g/mol had a significant impact on DBPFP. A multiple linear regression of the MW fractions against DBPFP showed a strong correlation (R2 between 0.90 and 0.93), indicating that LC-OCD analysis alone could be used to predict DBP formation with reasonable accuracy, and offering the potential for rapid risk assessment of water sources.
12890. 题目: Assessing impacts of nitrogen management on nitrous oxide emissions and nitrate leaching from greenhouse vegetable systems using a biogeochemical model
Greenhouse vegetable (GV) fields with intensive nitrogen application and frequent flood irrigation may substantially contribute to reactive nitrogen (Nr) losses, such as nitrous oxide (N2O) emissions and nitrate (NO3−) leaching. In this study, we applied a biogeochemical model, Denitrification-Decomposition (DNDC), to assess impacts of N management on vegetable yields, N2O emissions, and NO3−-N leaching from GV systems. The model was evaluated using multi-year (2011–2013) field measurements of vegetable yields, N2O emissions, and NO3−-N concentrations in the surface soil layer and soil leachate under three treatments with different N management. The model evaluations demonstrated that the simulations of the vegetable yields and seasonal cumulative N2O emissions were consistent with the corresponding observations after calibration. In addition, DNDC generally captured the seasonal variations of the N2O fluxes and NO3−-N concentrations in the surface soil layer and the seasonal patterns and magnitudes of the measured NO3−-N concentrations in soil leachate in 2011. We then assessed impacts on the vegetable yields, N2O emissions, and NO3−-N leaching of different N management practices by conducting simulations under scenarios with changes in rate of the applied N-fertilizers and the application of nitrification inhibitor (NI). The results suggested that 1) the increasing of organic or synthetic N application rate generally increased the N2O emissions and NO3−-N leaching, but did not persistently increase the vegetable yields, 2) urea N application could induce more N2O emissions and NO3−-N leaching in comparison with organic N amendment, and 3) the NI application could decrease the N2O emissions and NO3−-N leaching while maintaining the vegetable yields at the GV fields. The optimum management practice identified in this study was applying organic manure at a rate of 320 kg N ha−1 four season−1 and urea at a rate of 334 kg N ha−1 four season−1, combined with the NI application. The optimum management practice reduced the rates of organic manure (1600 kg N ha−1 four season−1) and urea (1670 kg N ha−1 four season−1) under the farm's conventional practice by 80%. This practice maintained or slightly increased the yields and mitigated the N2O emissions and NO3−-N leaching by 81% to 90% and 92% to 95%, respectively, among different vegetable growing seasons.
12891. 题目: Vegetation and soil covariation, not grazing exclusion, control soil organic carbon and nitrogen in density fractions of alpine meadows in a Tibetan permafrost region
The accrual of soil organic carbon (SOC) and nitrogen (N) in grassland is an important management option to improve the ecosystem functions of grassland. However, how abiotic (such as grazing exclusion (GE)) and biotic factors influence SOC and N and their different fractions in Tibetan alpine meadows remains unclear. In this study, we evaluated the relative importance of abiotic and biotic factors that drive SOC and N contents in soil density fractions by performing redundancy analysis based on three long-term (10 years) fenced alpine meadows maintained in the permafrost region of the Tibetan Plateau in China. Biotic factors comprise plant aboveground biomass, cover and diversity, whereas abiotic factors include soil properties (i.e. soil moisture, pH, clay, silt, sand, total phosphorus, available phosphorus, microbial biomass carbon and N, available N, C:N ratio and C:P ratio) and GE. Site rather than GE has significant effects on the SOC and N contents. GE caused no increase in the SOC and N contents in the whole soil and fractions. Redundancy analysis showed that 96.7% of the variations in SOC and N fractions can be explained by the selected explanatory variables. Aboveground biomass, cover, soil moisture and clay contents were key factors that affected the SOC and N fractions. The SOC and N fractions were mainly explained by the interaction between vegetation and soil, followed by soil, vegetation and GE. The study highlighted the importance of considering the covariation of vegetation and soil for evaluating the SOC and N dynamics in alpine meadows. The effect of GE (such as 10 years) on the SOC and N contents in alpine meadows can be weak in the permafrost region of the Tibetan Plateau.
12892. 题目: CrVI reductive transformation process by humic acid extracted from bog peat: Effect of variables and multi-response modeling
The present paper reports the efficiency of bog peat-derived humic acid (HA) in the reductive removal of hexavalent chromium (CrVI) from aqueous solution as affected by solution pH, the dose of FeIII and reaction time (numeric variables) and light irradiation (categorical variable). A three-level Box-Behnken design (BBD) applied to design experimental matrix, model the effects and interactions of variables on four determined responses (residual concentration of dissolved CrVI, dissolved CrIII, dissolved FeII and total CrVI) and optimize the experimental conditions for highest CrVI removal efficiency (CrVI RE). Reaction mechanisms are also well discussed. Regression models were developed and analyzed by the ANOVA test and models determination coefficient R2. Obtained models were significant (F values > 13) and an excellent relationship between experimental and predicted responses (R2: 98.1–99.6%) was observed. The optimum conditions were established corresponding to the residual concentration of dissolved CrVI as an index for CrVI removal efficiency (RE). In the dark system, the highest CrVI RE (98.1%) was obtained under the following conditions: pH = 1, reaction time = 7 d and FeIII dosage = 0.110 mM. In the light-irradiated system, the optimal CrVI RE of 98.3% was observed in pH = 1, reaction time = 5 d and FeIII dosage = 0.075 mM. Almost all reduced CrIII remained in the solution even at high pH value. No adsorption or precipitation of CrIII on the HA surface at pH 5 was confirmed by surface analyses of HA using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).
12893. 题目: The dissolved organic carbon flux from the UK – A new Bayesian approach to flux calculation
The study of regional and national-scale fluxes of biogeochemically relevant elements (e.g. carbon) has been hampered by inconsistency of long-term sampling. In this study we solve the issue of sporadic, low-density and low-frequency sampling for nutrients by using Bayesian hierarchical generalised linear modelling. The Bayesian approach means that it is possible to estimate a distribution of the expected value of the nutrient of interest for each location within a survey, no matter whether it was surveyed in a particular year, as long as that site was sampled sometime during the entire study period and that somewhere within the wider survey was sampled in the particular year, i.e. there is no minimum number of samples for a site to be included save that the site was sampled during the entire study period. The method developed was applied to problem of understanding the long-term flux of dissolved organic carbon (DOC) for the UK. The method was applied to 251 monitoring sites across the UK from 1974 to 2019 and the approach was similarly applied to river discharges so as to infill gaps in flow records. The results showed that:
12894. 题目: The passivation effect of heavy metals during biochar-amended composting: Emphasize on bacterial communities
Available information on passivation effect of biochar on heavy metals (HMs) through regulating bacterial communities remains limited. Thus, this study investigated the correlation between bacterial diversity and HM-fractions (Zn, Cu, Cd, Cr and Pb) during composting with different dose of biochar (5% and 10%, dry weight basis), in order to ascertain the passivation effect on HMs under the influence of bacterial community. The addition of 10% biochar showed better passivation effect with reduction in bioavailability factor (BF) of Zn, Cu, Cd and Pb by 4.10%, 44.12%, 18.75% and 30.06%, respectively. In addition, it brought forward the variation in primary bacterial phylum to the thermophilic phase. The results of redundancy analysis (RDA) and structural equation models (SEMs) indicated that C:N ratio was an important factor in controlling the morphological transformation of HM by affecting the bacterial community structure. Our results maybe provide a novel insight into HM-passivation from an interaction mechanism on C:N ratio and bacterial community.
12895. 题目: Carbon isotope systematics of leaf wax n-alkanes in a temperate lacustrine depositional environment
The carbon isotope ratio (δ13C) of plant-derived organic carbon preserved in geological archives can be a valuable proxy for the relative abundance of terrestrial plants using C3 and C4 photosynthesis. In certain sedimentary archives, however, mixing of terrestrial C3 and aquatic macrophyte-sourced carbon will result in sedimentary organic matter (OM) δ13C signatures that could be misinterpreted as shifts in the abundance of C3 and C4 vegetation. There is potential for this problem to be mitigated using leaf wax n-alkane compound-specific δ13C measurements because n-alkane production differs between terrestrial vegetation and aquatic macrophytes. This approach requires an increased understanding of how mixing of terrestrial plant and aquatic macrophyte n-alkane inputs to lacustrine sedimentary archives manifests in the δ13C values of different n-alkane homologues in diverse environmental settings. This study examines a Pleistocene lacustrine sequence in southeastern Australia in which the inputs from terrestrial and aquatic macrophytes vary naturally through time, enabling the characterization of the mixing dynamics for different n-alkane homologues. Relative contributions of terrestrial vegetation and aquatic macrophytes were estimated using the relative abundance of mid-chain to long-chain n-alkanes and compared to the δ13C values of discrete n-alkane homologues. We find that δ13C values of mid- and some long-chain n-alkanes (C23–C29) are strongly impacted by mixing between C3 terrestrial and non-emergent aquatic macrophyte-derived n-alkanes. In contrast, δ13C values of very long chain (C31–C35) n-alkanes integrated in sediments are the least affected by isotopic mixing. These results indicate that aquatic macrophyte inputs can significantly influence C29 isotopic signatures and thus the δ13C values of the very long chain n-alkanes ( C31) will provide the most robust quantification of n-alkane inputs from terrestrial plants and will be most useful for reconstructing the abundance C3 and C4 vegetation from temperate lake sediments.
12896. 题目: Fluorescence Signatures of Dissolved Organic Matter Leached from Microplastics: Polymers and Additives
12897. 题目: Two-Phase System Model to Assess Hydrophobic Organic Compound Sorption to Dissolved Organic Matter
12898. 题目: Investigation of the spatio-temporal heterogeneity and optical property of water-soluble organic carbon in atmospheric aerosol and snow over the Yulong Snow Mountain, southeastern Tibetan Plateau
Atmospheric aerosols are a branch of active research in recent decades. The deposition of light-absorbing substances on high-altitude glaciers causes substantial adverse impacts on the cryospheric environment, cryosphere-hydrology, and climate system. Although, the concentrations of water-soluble organic carbon (WSOC) in snow/ice on glaciers of Tibetan Plateau (TP) have been reported, their transfer processes and optical properties in the context of summer precipitation-atmosphere-snow-river water continuum are seldom studied. In this study, we have systematically examined some scientific issues associated with WSOC concentrations and light absorption properties of WSOC in various forms of samples from the Mt. Yulong region. Statistical results demonstrate that the spatial distribution of WSOC in the snow of Baishui glacier was heterogeneous. The average WSOC concentrations of each snowpit were significantly decreased, and its light-absorbing properties were significantly elevated with the time extension. Aerosol WSOC concentrations and light absorption have distinct spatial disparity and seasonal variation. Pre-monsoon and monsoon have the highest and lowest WSOC content, respectively. Whereas the light-absorbing properties present contrasting seasonal trends. Rivers of which runoff was supplied by glacier meltwater have significantly lower WSOC concentrations (e.g., 0.42 ± 0.03 mg L−1) compared with other forms of water bodies. Mass absorption cross-section of WSOC (MAC-WSOC) in multiple snow and meltwater samples was significantly different and type-dependent. Atmospheric aerosol has the lowest MAC-WSOC value among the four types of samples, which was likely associated with exhaust emissions from private vehicles and tour buses. Statistical results indicated that the average AAE330-400 values of various snow/ice samples are subequal. Snow of glaciers supplies a desirable platform for the deposition of gaseous materials which experienced long-range transport in high altitude zones. Biomass-burning emissions made an immense contribution to the WSOC deposition over the study area, as demonstrated by the distribution of active fire points. However, this preliminary study represents the first systematic investigation of WSOC deposition in southeastern TP. Further robust in-situ field investigations and laboratory measurements are urgently necessary to improve our understanding of the transfer process and optical property of WSOC.
12899. 题目: Rhizosphere priming effects of Lolium perenne and Trifolium repens depend on phosphorus fertilization and biological nitrogen fixation
Live roots can stimulate microbial soil organic matter (SOM) decomposition and nutrient cycling, which is termed as the rhizosphere priming effect (RPE). Compared to nitrogen (N) availability, fewer studies have focused on the effect of phosphorus (P) availability on the RPE. Here we investigated the RPEs of ryegrass (Lolium perenne) and clover (Trifolium repens) with and without P fertilization (4 g P m−2) at three sampling times (Day 30, Day 44, and Day 58 after planting). A continuous 13C–CO2 labeling method was used to separate soil-derived CO2 from root-derived CO2. A nutrient budget method was applied to evaluate the rhizosphere effect on net soil N and P release for plant uptake. We found that ryegrass and clover induced positive RPEs in most plant-soil combinations, ranging from −1% to 134%. Ryegrass exhibited a larger RPE than clover by Day 30, but clover exhibited a larger RPE than ryegrass by Day 44 and Day 58, possibly due to larger shoot biomass regrowth rates, root activity, and rhizodeposition during the later stages. P fertilization significantly decreased the RPE of ryegrass by Day 44 and Day 58, but did not change the RPE of ryegrass by Day 30 and clover at all three sampling times. The reduced RPE of ryegrass with P fertilization was associated with increased microbial biomass N, more root-derived microbial C, and less shoot biomass and root-derived CO2. These findings suggest that P fertilization coupled with C supply from root exudates induced more microbial N immobilization, which reduced the RPE of ryegrass during later stages when soil N limitation negatively impacted plant growth. However, P-induced microbial N immobilization did not affect clover as much because its biological N fixation, on average 37% of total plant N, may have alleviated soil N limitation. We further observed significant positive relationships between excess net soil N and P release and the RPE by Day 58 across all planted treatments, indicating that soil N and P release by plants can be directly linked to rhizosphere C mineralization. Overall, our results demonstrate the importance of C–N–P interactions for understanding the RPE, which have significant implications for P cycling in plant-soil systems.
12900. 题目: A novel modified method for the efficient removal of Pb and Cd from wastewater by biochar: Enhanced the ion exchange and precipitation capacity
The purpose of this research was to improve the sorption ability of Pb and Cd by promoting the ion exchange and precipitation capacity of biochar. The adsorption performance and mechanisms of Pb and Cd in wastewater using coconut shell biochar modified with magnesium were investigated. After modification, the total adsorption capacity (Qt) of Pb and Cd on Mg-coated biochar (MgBC400) increased by 20 and 30 times compared with the unmodified biochar (BC400), respectively. The removal of Pb and Cd to biochar was attributed to ion exchange (Qe), mineral precipitation (Qp), interaction with oxygen functional groups (OFGs) [(Qf)], and metal-π electron coordination (Qπ). Compared with the BC400, the adsorption capacity of the four fractions of MgBC400 increased especially the ion exchange and precipitation. The Qe values of MgBC400 were almost 49 and 59 times that of BC400 in the adsorption of Pb and Cd, respectively. The Qp values of MgBC400 increased by 214.4 and 81.7 mg/g, respectively. Ion exchange and mineral precipitation dominated the adsorption of Pb and Cd by MgBC400.