Exploring the trophic transfer and effects of microplastics in freshwater ecosystems: A focus on Bellamya aeruginosa to Mylopharyngodon piceus.

Microplastics (MPs) can enter aquatic food webs through direct ingestion from the environment or indirectly via trophic transfer, but their fate and biological effects within local freshwater food chains remain largely unexplored. In this study, we conducted the first investigation on the trophic transfer and impacts of fluorescently labeled polystyrene microplastics (PS-MPs) (100-nm and 10-µm) in a model freshwater food chain consisting of the snail Bellamya aeruginosa and the commercially important fish Mylopharyngodon piceus, both prevalent in Chinese freshwater ecosystems. Quantitative analysis revealed substantial accumulation of MPs in B. aeruginosa, reaching an equilibrium state within 12 h of exposure. While steady-state was not observed, a pronounced time-dependent bioaccumulation of MPs was evident in M. piceus over a five-week period following dietary exposure through the consumption of contaminated B. aeruginosa. Notably, MPs of both sizes underwent translocation from the gastrointestinal tract to the muscle tissue in M. piceus. High-throughput sequencing of the gut microbiota revealed that exposure to 100-nm MPs significantly altered the microbial community composition in M. piceus, and both particle sizes led to increased relative abundance of potentially pathogenic bacterial genera. Our findings provide novel insights into the trophic transfer, tissue accumulation, and biological impacts of MPs in a model freshwater food chain, highlighting the need for further research to assess the ecological and food safety risks associated with microplastic pollution in freshwater environments.

Synergistic control potential of flue gas pollutants under Ultra-Low emission standards in waste incineration plants.

As the dominant waste disposal process, incineration is regarded as the main incentive for the "not-in-my-backyard" syndrome, and faces an inescapable pressures of ultra-low emissions (ULE). Establishing precise response relationships between emission factors (EFs) and full-process influencing factors can provide guidance for the synergistic mitigation of flue gas pollutants (FGPs). In this work, the multi-dimensional EFs of FGPs were identified by initially integrating FGPs concentration monitoring data of existing 1,226 processing lines in China, technologies applied and operational experience (OE), local economic and political characteristics. Significant regional imbalance performance was observed, which EFs in the coastal regions were 3.55-92.39 % lower than those of the inland areas. NOx, SO2, HCl were identified as critical components requiring further reduction under the ULE standards, with exceedance rates recorded at 73.07 %, 38.90 %, and 56.69 %, respectively. An indicative value of 20 mg/m3 for PM is recommended for the control of heavy metals of Cd + Tl and Sb + As + Pb + Cr + Co + Cu + Mn + Ni based on the correlation coefficients of r = 0.28 (p < 0.001) and r = 0.20 (p = 0.002), respectively. Waste composition and OE were quantified as the main contributors of EFs' disparities by the tree-branching controlled variable approach established in this study. Predictive models for FGPs control process and corresponding EFs were constructed. EFs of nine FGPs in 2030 would decrease by 0.97-65.42 %, due to more complex purification processes employed to meet ULE's limitations, such as the application of five-stage processes growing from 45.60 % to 58.28 %. While regional imbalance in EFs-SO2 and EFs-HCl were extended with increases from 25.83 % to 33.07 % and 9.91 % to 32.32 %, respectively, due to the consistent disparities of OE and growing heterogeneity of control policies. Enhancing interregional empirical exchanges, reducing the regional market monopolies, and formulating technical guidelines would be beneficial to synergize the reduction of FGPs emissions and alleviate regional imbalance.

Impact of polystyrene microplastics on the growth and photosynthetic efficiency of diatom Chaetoceros neogracile.

The increasing prevalence of microplastic pollution in aquatic environments has raised concerns about its impact on marine life. Among the different types of microplastics, polystyrene microplastics (PSMPs) are one of the most commonly detected in aquatic systems. Chaetoceros neogracile (diatom) is an essential part of the marine food web and plays a critical role in nutrient cycling. This study aimed to monitor the ecotoxicological impact of PSMPs on diatoms and observe enzymatic interactions through molecular docking simulations. Results showed that diatom growth decreased with increasing concentrations and exposure time to PSMPs, and the lowest photosynthetic efficiency (Fv/Fm) value was observed after 72 and 96 h of exposure to 200 mg L-1 of PSMPs. High concentrations of PSMPs led to a decrease in chlorophyll a content (up to 64.4%) and protein content (up to 35.5%). Molecular docking simulations revealed potential interactions between PSMPs and the extrinsic protein in photosystem II protein of diatoms, suggesting a strong affinity between the two. These findings indicate a detrimental effect of PSMPs on the growth and photosynthetic efficiency of diatoms and highlight the need for further research on the impact of microplastics on marine microbial processes.

Treatment of Landfill Leachate Reverse Osmosis Concentrates by Advanced Oxidation-Heterotrophic Nitrification-Aerobic Denitrification Combination process.

This study aimed to develop a multistage treatment system for highly toxic wastewater named reverse osmosis concentrates of landfill leachate. Therefore, a combination of the ammonia stripping process (ASP), catalytic ozone oxidation process (COP), and heterotrophic nitrification-aerobic denitrification process (HNADP) was proposed and the quality of effluent was evaluated for the concentration of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total nitrogen (TN). ASP had moderate removal efficiency of NH4+-N, and TN in the effluent. COP was catalyzed by cerium-supported-activated carbon achieved good performance in disposal of COD. The effluent of HNADP had the most significant removal efficiency of COD, NH4+-N, and TN. As a result, the effluent of combined process successfully met the discharge standards for NH4+-N and TN according to Table 1 of GB 16889-2008 in China. To investigate the microbial mechanism of pollutant removal in HNADP, 16S rRNA high-throughput sequencing was performed and the results suggested that the relative abundance and diversity of microorganisms fluctuated with the changes of COD/TN ratio in HNADP. Truepera and Halomonas were identified as the key genera involved in the simultaneous degradation of COD and nitrogen-containing pollutants, the functional genes (hao, amoA, nirS, and nirK) were predicted in nitrification and denitrification process. Overall, this study demonstrates a feasible multistage system for treatment of concentrates and propose that further explorations of combined techniques may lead to even more satisfactory removal efficiencies.

Exploring into a light-avoided environment: Mechanical-thermal coupled conditions responsible for the aging behavior of plastic waste in landfills.

Plastics in landfills undergo a unique micronization process due to multi-factor and light-avoided conditions, but their aging process in such a typical environment remains unexplored. This study investigated the aging behavior of polyethylene plastics, representative of landfills, under simulated dynamic mechanical forces and high temperature-two prevalent environmental factors in landfills. The study explored the individual and combined contributions of these factors to the aging process. Results indicated that high temperature played a primary role in aging plastics by depolymerization and degradation through ·OH production, while mechanical forces contributed mainly to surface structure breakdown. The combined effect leads to more serious surface damage, creating holes, cracks, and scratches that provide access for free radical reactions to plastic bulk, thereby accelerating the aging and micronization process. The resulting microplastics were found to be 14.25 ± 0.53 µg L-1. Aged plastics exhibit a rapid aging rate of depolymerization and oxidation compared to virgin plastics due to their weak properties, suggesting a higher potential risk of microplastic generation. This study fills a knowledge gap regarding the aging behavior of plastics under complex and light-avoided landfill conditions, emphasizing the need for increased attention to the evolution process of microplastics from aged plastic waste in landfills.

The Typical Polybrominated Diphenyl Ethers (PBDEs) and Heavy Metals Distributions in a Formal e-Waste Dismantling Site.

Understanding the release of pollutants from the formal e-waste dismantling site could provide the basic information and potential risk to guide the normative regulation of the process. In this study, the distribution of typical polybrominated diphenyl ethers (PBDEs) and heavy metals in a relocating site of a formal e-waste dismantling company was firstly investigated down to the saturated zone, with a maximum depth of 3.0 m. The mean concentrations of Σ13PBDEs were ranged from 2.815 to 7.178 ng/g, with a peak value of 7.178 ng/g in storage area. BDE-209 was the predominant congener of PBDEs in the soil, with the value ranged from 1.688 to 2.483 ng/g. A higher pollution of PBDEs and HMs was presented in the storage area. The risk assessment of PBDEs mostly posed a low environmental risk (RQ ≤ 0.01) and pentaBDE was found to be the most harmful driver for the potential environmental risk.

Carbon sequestration for high-quality sludge-based carbon preparation via K/Na bi-molten salts pyrolysis.

Pyrolysis carbonization of sewage sludge is employed to achieve carbon sequestration and access carbon resources, while the quality of the obtained sludge-based carbon (SBC) is poor due to high ash contents and volatile organic matter. Here, carbonization in KOH/Na2CO3 (K/Na) bi-molten salts was developed for SBC preparation, improvement of carbon exploitation from biomass, and to reduce the contents of ash and volatile organic matter. The results showed that the surface area and pore volume of SBC under optimized conditions reached 1631 m2 g-1 and 1.312 cm3 g-1 at 700 °C, respectively, with a K/Na bi-molten salts/sludge ratio of 2:1 (K:Na = 5:5). Moreover, over fivefold the higher surface area and 43.61% amount of carbon element could be obtained, with a decrease in the mass loss rate for sludge pyrolysis of 25%. The mechanism behind the higher surface area of the SBC was identified and divided into three stages: intense dehydration and dehydrogenation caused by molten salt-enhanced polycondensation of protein and polysaccharide (200-400 °C), strongly reduced carbon-oxygen structure after deoxygenation reactions (400-600 °C), aromatization and cyclization of long-chain fatty acids triggered by deamidation of tar catalyzed by molten salts (600-900 °C). Eventually, 14.63% carbon was sequestered for the high-surface-area SBC prepared by K/Na bi-molten salts system.

Successive choline addition enhancing the methanogenesis of waste activated sludge anaerobic digestion: Insight from hydrophilicity, electrochemical performance and microbial community.

Anaerobic digestion (AD) is a promising technology to treat waste-activated sludge, previous study proved that methane production could be enhanced with the addition of choline, this work aimed to solve the problem of rapid biodegradability of choline in the AD process by changing its dosing method. With 0.75 g/L as the optimal choline dosing concentration, experimental results showed that successive choline dosing during the first 3-6 days of AD (experimental groups, EGs) performed better than the single dosing. The accumulative biogas production in EGs was increased by 35.55-36.73%, which could be caused by the simultaneous promotion of hydrolysis-acidification and methanogenesis processes. Especially, the electron exchange capacity of digested sludge in EGs was increased by 16.71-34.58%. In addition, the surface Gibbs free energy (△GSL) of sludge in EGs was 105.51-172.21% higher (corresponding to stronger hydrophilicity and repulsion), which might help disperse sludge flocs and improve mass transfer efficiency, and the △GSL values were positively correlated with the accumulative methane production (R2 = 0.7029). Microbiological analysis showed that microbial communities in EGs were richer and Methanosaeta was regarded as the dominant species with 15.93-30.08% higher relative abundance with choline addition. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, EGs were found to be more active in metabolism clusters. Collectively, these findings demonstrated that successive choline dosing during the first 3-6 days is an effective and novel method to enhance methane production in AD process.

Identifying the fate of nitrogenous species during sewage sludge pyrolysis via in-situ tracing of protein-sludge inherent components interactions.

The effect of interactions between different components in sewage sludge on the thermochemical transformation of nitrogenous species is usually neglected, which is important to explain the generation mechanism of some key nitrogenous by-products. Here, we investigated the distribution, form, and chemical properties of the products from sludge-extracted protein (PR) under different pyrolysis scenarios using several in-situ probe techniques, to elucidate the critical role of typical sludge organics/inorganics on the evolution of nitrogenous intermediates and by-products. The results suggested that Ca/Fe/Si/Al-containing inorganics significantly affected the pyrolytic behavior of PR and the thermal transformation of nitrogenous species, while sludge organics, including humic acids and polysaccharides, had limited effects on the temperature-dependent evolution of nitrogenous species in PR. Among them, calcium oxide catalyzed the ring-opening reaction of heterocyclic-N with aromatic-like structures, resulting in a 21.1 %-68.8 % reduction in nitrogen fixation efficiency in the char. At lower temperatures (350-450 °C), calcium oxide caused more nitrogen to be transferred to the gas/tar phases in the form of NH3 and heterocyclic-N, and it also enhanced the conversion of nitrile-N → HCN → NO at temperatures above 450 °C. In contrast, polyferric salts inhibited the devolatilization of mono-heterocyclic-N and enhanced the thermal stability of poly-heterocyclic-N, resulting in a maximum increase of 18.5 mg·g-1 of nitrogen content in the char, while reducing the release of NH3 and HCN by 71.1 % and 32.0 %. This work elucidated the interaction between PR and inherent components in sludge, providing key information for the control of nitrogenous volatiles and NOx.

Low-molecular-weight dissolved organic nitrogen transformation behavior in concentrated leachate by O3 and •OH: Partition, molecular insight, and potential precursor-product relationship.

Low-molecular-weight dissolved organic nitrogen (LMW-DON) is an emerging issue in concentrated leachate (CL). Ozonation is crucial to remove LMW-DON, but selectivity mechanisms of different reactive oxygen species were unknown. Here, reactions of O3 and •OH with LMW-DON at different dosages were determined from composition, unsaturation/redox potential, and precursor-product relationship. The molecular weight of LMW-DON in CL presented a normal distribution and 76.5% was below 450 Da. LMW-DON with 400-1000 Da increased to 55.6%-66.7% and O/Cwa increased by over 40.0% due to electrophilic substitution of O3. LMW-DON with <400 Da and 550-1000 Da were preferentially degraded by •OH at the low and high O3 dosage, respectively. O3 preferred to remove lipid-like (69.1%), protein-like (58.2%), and amino sugars-like (72.8%) LMW-DON, whereas •OH preferred to the refractory LMW-DON, such as carbohydrates-like (71.1%), lignin-like (49.6%), and tannins-like (72.5%) LMW-DON. Forty-three transformation reactions were quantified using mass difference analysis, and O3 preferred to oxygen addition (e.g., +2O) and conversed amino to nitro groups, and saturated LMW-DON increased via unsaturated bonds rupture. •OH attacked the carbon groups (e.g., -CH2) and nitrogen groups (e.g., -NH3+O, -NO2+H). These findings provide molecular evidence for the selectivity of oxidants with LMW-DON and improve the ozonation application in wastewater treatment.

Medium-Low Temperature Conditions Induce the Formation of Environmentally Persistent Free Radicals in Microplastics with Conjugated Aromatic-Ring Structures during Sewage Sludge Pyrolysis.

Medium-low temperature pyrolysis is an effective method of retaining active components in sludge char. However, we found that incomplete cracking reactions resulted in residues of microplastics (MPs) remaining in the char; moreover, high levels of environmentally persistent free radicals (EPFRs) were detected in these MPs. Here, we investigated the temperature-dependent variations in the char-volatile products derived from sludge and MPs under different pyrolysis scenarios using multiple in situ probe coupling techniques and electron paramagnetic resonance spectroscopy, thereby identifying the sources of EPFRs and elucidating the corresponding formation-conversion mechanisms. The temperature was the key factor in the formation of EPFRs; in particular, in the 350-450 °C range, the abundance of EPFRs increased exponentially. Reactive EPFR readily formed in MPs with conjugated aromatic-ring structures (polyethylene terephthalate and polystyrene) at a temperature above 350 °C; EPFR concentrations were 5-17 times higher than those found in other types of polymers, and these radicals exhibited half-lives of more than 90 days. The EPFR formation mechanism could be summarized as solid-solid/solid-gas interfacial interactions between the polymers and the intermediate products from sludge pyrolysis (at 160-350 °C) and the homolytic cleavage-proton transfer occurring in the polymers themselves under the dual action of thermal induction and acid sites (at 350-450 °C). Based on the understanding of the evolution of EPFRs, temperature regulation and sludge components conditioning may be effective approaches to inhibit the formation of EPFRs in MPs, constituting reliable strategies to diminish the environmental risk associated with the byproducts of sludge pyrolysis.

Booming microplastics generation in landfill: An exponential evolution process under temporal pattern.

Landfills are the main plastic sinks and microplastics (MPs) sources in the anthropogenic terrestrial system. Understanding the dynamic process of generating MPs is a prerequisite to reducing their potential risk, which remains unexplored because of the complex stabilization process of landfills. In this study, we investigated the evolution process of MPs generated in a partitioned landfill, with well-recorded disposal ages of over 30 years. Considering the initial plastic proportions in fresh landfilled waste, the occurrence of MPs increased exponentially with the disposal age. A booming generation of MPs occurred from 71.3 ± 17.7 items/(g plastic) to 653.1 ± 191.5 items/(g plastic). The generation rates of MPs varied greatly depending on the individual polymer types, with polyethylene (PE) having the highest generation rate of 28.4 items/(g plastic) per year at 31 years, compared to that of polypropylene (PP) and polystyrene (PS) at 15.0 and 9.6 items/(g plastic) per year, respectively. The variation in the carbonyl index indicated that environmental oxidation might facilitate the fragmentation of plastic waste. The relative abundance of plastic-degrading microbes increased more than three times in the plastisphere after 30 years of landfilling, indicating that the potential biodegradation might be a nonnegligible driver for plastic fragmentation after long-term natural acclimatization. This study revealed the dynamic evolution process of MPs in landfills and predicted the booming stage, which might provide an important guideline for reducing the leakage risk of MPs during the reclamation of old landfills or dumping sites.

A comparative and modeled approach for three biochar materials in simultaneously preventing the migration and reducing the bioaccessibility of heavy metals in soil: Revealing immobilization mechanisms.

The effectiveness and feasibility of the three biochar materials for remediation of arsenic (As) and lead (Pb) contaminated soil were explored in this study. Significant reduction of bioaccessibility and migration risks of both heavy metals have been explained mechanistically by incubation, column experiments and numerical simulation. Langmuir equation fitted As and Pb sorption isotherms better in the control and biochar (BC) amended soils, while Freundlich model was more suitable for iron modified biochar (Fe-BC) and sulfur/iron modified biochar (S/Fe-BC) amended soils, indicating that modified biochar promoted chemical adsorption process for As and Pb. For the three biochar materials, S/Fe-BC showed the best effects on reducing the bioavailability of As and Pb, with a decrease of 40.42%-64.21%. The reduction in bioaccessibility by metal portioning into available and non-available fractions was better for illustrating the mechanisms including adsorption, precipitation/coprecipitation and As(III) oxidation behind S/Fe-BC efficacy. Moreover, S/Fe-BC can effectively inhibit the leaching behavior of As and Pb under acid rain, which increased by 99.89% and 90.18%, respectively, compared with the control. The HYDRUS-1D modeling indicated that S/Fe-BC could continuously treat As (100 mg/L) and Pb (1000 mg/L) contaminated water for 16.22 years and 40.86 years, respectively, and ensure the groundwater quality criteria being met. Based on these insights, we believe that our study will provide meaningful information about the potentials of biochar derived materials for soil heavy metals' remediation.

Cr(VI) immobilization in soil using lignin hydrogel supported nZVI: Immobilization mechanisms and long-term simulation.

A novel nanocomposite, named as nZVI@LH, was prepared by nanoscale zero-valent iron (nZVI) supported on lignin hydrogel and was used in the remediation of Cr(VI)-contaminated soil collected from an industrial site. Meanwhile, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and X-ray diffractometry (XRD) results determined that nZVI nanoparticles disperse uniformly on hydrogel. After the 14 days remediation, the immobilization efficiency of Cr(VI) could reach over 87% in the treatment of 3% (w/w%) nZVI@LH and 26% in the treatment of bare-nZVI. Leaching experiment results showed that the treatment group with 3% (w/w%) nZVI@LH was up to the national leaching toxicity identification standard, and there was no threat in simulation of acid rain over the long term. The water-soluble (WS) fraction in 3# nZVI@LH treatment decreased 31.1%, while the Fe-Mn oxide bound (OX) fraction and organic matter-bound (OM) fraction increased 10.9% and 13.4%, respectively. Moreover, nZVI@LH had limited impact on soil properties and the capability to immobilize Cr over a long period exposure to acid rain. This work prove that nZVI@LH has the potential to remediate Cr contaminated soil. Furthermore, details of possible mechanistic insight into the Cr remediation were carefully discussed.

Environmental impacts and nutrient distribution routes for food waste separated disposal on large-scale anaerobic digestion/ composting plants.

Centralized biological treatments, i.e., anaerobic digestion (AD) and in-vessel composting (IVC), were supposed to be the promising processes for the disposal of food waste (FW) after source separation, while the systematic benefits were unclear for FW with high water content, salt and oil and thus influenced the selection by the local decision-makers. In this study, two large-scale working AD and IVC plants were compared for environmental impacts, nutrient recovery and economic benefits. For unit amount of FW, 89.26 kg CO2-eq was released in IVC mainly due to 47.89 kWh electricity consumption, and 57.02 kg CO2-eq was produced in AD. With the application of compost and energy recovery, 26.88 and 93.55 kg CO2-eq savings were obtained in IVC and AD, respectively. NH3 emissions were the main contributor to acidification (0.35 kg SO2-eq) in IVC, while AD exerted less impact on acidification (0.09 kg SO2-eq) and nutrient enrichment (0.25 kg NO3-eq) attributed to the counteract of energy recovery. 2029 would be the inflection point for global warming potential in AD with more clean energy applied in electricity mix in China. For nutrient recovery, more C (8.3%), N (37.9%) and P (66.7%) could be recovered in compost, while those were discharged via leachate and biogas residue in AD. The cost of IVC was 16 CNY/t (2.40 USD/t) lower than AD. Combing the three key indexes and the sale routes of products, IVC was recommended to be used in areas dominated by agriculture and forestry industries, and AD was more suitable for large cities.

A novel lignin hydrogel supported nZVI for efficient removal of Cr(VI).

A novel hydrogel-supported nanoscale zero-valent iron (nZVI) composite (nZVI@LH) was synthesized by ion exchange and in-situ reduction. The removal efficiency was tested, and the mechanism was also explored. The nZVI@LH at the precursor Fe(II) ion concentration of 0.1 mol/L presented an enhanced Cr(VI) removal capacity of 310.86 mg/g Fe0 at pH 5.3, which was 11.6 times more than that of the pure nZVI. The removal efficiency of the composite at pH 2.1 was more than double compared with alkaline or neutral conditions. Scanning electron microscopy (SEM) suggested that the nZVI particles were uniformly immobilized in the lignin hydrogel. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) provided evidence supporting the removal mechanism. According to the XPS results, the high removal capacity of the composite was attributed to chemical reduction/precipitation (69.7%), surface sorption (19.7%), and swelling uptake (10.6%). The pseudo-first-order reduction kinetics and pseudo-second-order kinetic model were employed to simulate the kinetic data, which supported the mechanism that chemical reduction and surface sorption could simultaneously remove Cr(VI). The electron acceptor and electron donor affected the reaction rate, and the presence of humic acid significantly inhibited the reaction. The present study demonstrated that lignin hydrogel acted as a carrier to prevent aggregation of nZVI particles. nZVI particles loaded on lignin hydrogel showed high reactivity and high degree of utilization compared with bare-nZVI. These results exhibited the great potential of nZVI@LH in practical water treatment due to its high activity.

Variations of nitrogen-metabolizing enzyme activity and microbial community under typical loading conditions in full-scale leachate anoxic/aerobic system.

Influent loading determines the performance of leachate treatment plant (LTP) facing the dynamic conditions, but enzyme expression in microbial community is unclear. Here, six nitrogen-metabolizing enzymes were detected during nitrification failures (NF), high loading (HL), low loading (LL), and low carbon/nitrogen (LCN) in a 500 m3/d LTP. Nitrogen removal in LL was 15 ± 5% higher than that in HL. The activity of hydroxylamine oxidoreductase decreased by 90% as the influent total nitrogen increased from 2450 mg/L to 3100 mg/L, which might be a critical enzyme causing the nitrification failure. Denitrifying enzyme abated by 1.3% as the carbon/nitrogen dropped by 1% in LCN. With the influent chemical oxygen demand decreased from 22000 mg/L to 12000 mg/L, the relative abundance of norank_f_Saprospiraceae dropped from 33.66% to 11.94%, and finally disappeared, which seems to be an indicator of the high load operation. These findings provide the basis for improving the efficiency of LTPs.

Molecular transformation and composition flow of dissolved organic matter in four typical concentrated leachates from the multi-stage membrane system.

Concentrated leachate (CL), characterized with high content salts and compositional complexity of dissolved organic matter (DOM), is difficult to degrade. Understanding the CL from molecular insight level is the requirement for further disposal based on their components. Here, typical CL samples were collected from the multi-stage membrane separation process in a large-scale leachate plant, including nanofiltration (NF), primary ultrafiltration (PUF), secondary nanofiltration (SNF), and reverse osmosis (RO). More than 95% of DOM was removed from raw CL, of which about 3/4 flowed into PUFCL and 1/5 flowed into SNFCL. DOM with macro-molecular weight (>500 Da, 30.46%) and highly unsaturated compounds (double-bond equivalents >15) were detected in PUFCL. Nearly half of DOM was CHO-only compounds (42.04%) in SNFCL. PUFCL was abundant in heteroatom species with higher-order oxygen (O ≥ 10), which was coincident with the trend of humic substance distribution (humic substance >1/2). Based on these properties results, advanced oxidation processes, such as ozonation, might be the right process for SNFCL rich in heteroatom species with low-order oxygen (O < 10). Abundant disulfides (S2O2-6 classes, 20.19%) and monovalent salts existed in ROCL, which should be removed from the system. These findings might provide basic information for the treatment of CLs from different membranes.

Systematic understanding of char-volatile evolution and interaction mechanism during sewage sludge pyrolysis through in-situ tracking solid-state reaction and products fate.

The complexity of sludge components and the heterogeneity of pyrolysis products make it challenging to trace char-volatile evolutions and interaction mechanisms during pyrolysis. Herein, we systematically dissected the solid-state reactions and volatile dynamic variations via in-situ infrared/mass spectral probes coupled signal amplification techniques. The identification of hidden reactions was further enhanced by comparing the discrepancies in the pyrolysis of three systems: raw sludge, sludge-extracted organics, and pseudo-components of organics. A three-stage sludge pyrolysis of bond cleavage (α = 0.2-0.5), intermediates diffusion (α = 0.5-0.7), and interface interaction (α = 0.7-0.8) was proposed through solid-state reaction tracing, and the pyrolysis reaction was found to be dominated by the first two stages. The generation of reactive intermediates accelerated the collision frequency between reactants, which increased the order of solid-state reactions and raised the energy barrier from 148 to 180-261-297 kJ/mol. The temperature-response sequence of the major pyrolysis volatiles was H2O/CO2/furans/alcohols (<250 °C), amine-N/acids/ketones/esters (250-350 °C), heterocyclic-N/phenols/C2-3 (300-400 °C), CH4/aromatics/nitrile-N (350-450 °C), and CO/HCN (>450 °C). The temperature-dependent evolution of these volatiles was consistent with the variations of chars in terms of pyrolysis behaviors, reaction models, and surface characteristics. The comprehensive understanding of the staged pyrolysis pathways and the char-volatile interaction mechanisms may provide critical information for pyrolysis procedure design and product targeted regulation.