Landfill Leachate Treatment Research Articles

The Performance of Iron Nanocomposites as Persulfate Activators in Permeable Reactive Barrier Technology for Treatment of Landfill Leachate

Landfill leachate contains a large organic load and a wide spectrum of pollutants, and it needs appropriate treatment to reduce the severity of these contaminants. Therefore, the present study aimed to remove chemical oxygen demand (COD) and ammonia (NH3 ) as target contaminants from the landfill leachate. To this end, the zero-valent iron nanofibers/reduced ultra-large graphene oxide (ZVINFs/rULGO) and converter sludge (CS) were used as persulfate (PS) activators in permeable reactive barrier (PRB) technology for removing COD and NH3 . The Box–Behnken design (BBD) was employed to determine the possibility of using each activator and optimize three parameters: activator, pore volume (PV), and flow (mL/min) using target contaminants. In the Batch process, the effects of pH, activator concentration, and PS/COD mass ratio on COD removal were examined. The BBD experiments provided a satisfactory predictive model, indicating that ZVINFs/rULGO is superior to CS when used as activators of PS in PRB technology. The biochemical oxygen demand (BOD5 )/COD ratio increased from 0.24 in raw leachate to 0.67 in treated leachate, and leachate toxicity was reduced by more than 85%. Additionally, the ZVINFs/rULGO and CS contributed to the activation of PS.

Enhanced anaerobic digestion of landfill leachate based on a novel redox mediator: Synergistic mechanism of enhancing extracellular electron transfer

The presence of recalcitrant compounds and toxic substances in landfill leachate results in low anaerobic digestion (AD) efficiency and poor methane production performance. Strengthening the extracellular electron transfer of microorganisms represents an effective approach to promote the AD of landfill leachate. In this study, a novel redox mediator (FeNC-RM) was synthesized through the combination of metal and non-metal doping, intensifying the stable operation of the landfill leachate AD system. Through characterization techniques including X-ray photoelectron spectroscopy and X-ray diffraction, it was observed that FeNC-RM possesses a larger specific surface area, abundant functional groups, and exceptional electrochemical performance. By adding FeNC-RM, the stability and efficiency of the medium-temperature AD system in the treatment of landfill leachate were improved: Obtained a high removal of chemical oxygen demand which was increased by 30 % compared to the control group and enhanced the specific methanogenic activity by 57.5 % compared to the control group. The electron transport system (ETS) activities of the experimental groups with the addition of RMs were all significantly higher than those of the control group, and the ETS activity of the sludge from the FeNC-RM group was 79.6 % higher than that of the control group. Through a comprehensive analysis of the underlying mechanism, it was determined that three aspects synergistically facilitated electron transfer: FeNC-RM, endowed with electrochemical capabilities, assumed a pivotal role in establishing a conduit for electron transport, thus promoting the synthesis of extracellular humic substances and augmenting electron transport activity. Furthermore, the microbial community was optimized by FeNC-RM, thereby fostering a co-nutritional mechanism between hydrolytic acidification bacteria and methanogens, establishing a direct interspecific electron transport pathway. In this study, an “endogenous + exogenous” electron transport model based on the enhanced extracellular electron transport pathway facilitated by FeNC-RM was proposed. This study offered valuable contributions to the advancement of anaerobic treatment technology for landfill leachate.

Nitrogen removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions by simultaneous partial nitrification anammox and denitrification

In this study, a SNAD-SBBR process was implemented to achieve ammonia removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions (0.051 mg/L) for a continuous operation of 266 days. The process demonstrated excellent removal performance, with ammonia nitrogen removal efficiency reaching 100 %, total nitrogen removal efficiency reaching 87.56 %, and an average removal rate of 0.180 kg/(m3·d). The recalcitrant organic compound removal efficiency reached 34.96 %. Nitrogen mass balance analysis revealed that the Anammox process contributed to approximately 98.1 % of the nitrogen removal. Candidatus Kuenenia achieved a relative abundance of 1.49 % in the inner layer of the carrier. In the SNAD-SBBR system, the extremely low DO environment created by the highly efficient partial nitrification stage enabled the coexistence of AnAOB, denitrifying bacteria, and Nitrosomonas, synergistically achieving ammonia removal and carbon reduction. Overall, the SNAD-SBBR process exhibits low-cost and high-efficiency characteristics, holding tremendous potential for landfill leachate treatment.

Nutrient removal and emission of nitrous oxide and methane by a sequencing batch reactor treating wastewater with and without landfill leachate

Wastewater and landfill leachate treatment processes have the potential to generate nitrous oxide (N2O) and methane (CH4), both significant greenhouse gases (GHG). However, little is known about these emissions when a combined treatment approach (wastewater with leachate) is utilized. This study aimed to assess the emissions of these gases and nutrient removal in an anaerobic/aerobic/anoxic sequencing batch reactor (SBR) employed for treating wastewater with landfill leachate (1% v/v). Leachate contributes significantly to the removal of organic matter and nutrients, primarily phosphorus. The production and emission of N2O occurred during the aerobic phase, whereas CH4 was produced in the anaerobic and anoxic phases. This gas was emitted at the beginning of the aerobic phase and in the end of anoxic phase. The emission factors obtained in this work were 0.0108 and 0.0119 kg N2O-N per kg TNinfluent and 0.000225 and 0.000253 kg CH4-C per kg CODinfluent with and without landfill leachate, respectively. Regarding CO2-equivalent, the N2O was the major contributor, accounting for 99% of the emitted GHG by the process. Further studies are required; however, the main findings of this study suggest that this system may be appropriate when lower GHG emissions are required.

Electrochemical-coupled sulfur-driven autotrophic denitrification for nitrogen removal from raw landfill leachate: Evaluation of performance and mechanisms

The cost-effective and environment-friendly sulfur-driven autotrophic denitrification (SdAD) process has drawn significant attention for advanced nitrogen removal from low carbon-to-nitrogen (C/N) ratio wastewater in recent years. However, achieving efficient nitrogen removal and maintaining system stability of SdAD process in treating low C/N landfill leachate treatment have been a major challenge. In this study, a novel electrochemical-coupled sulfur-driven autotrophic denitrification (ESdAD) system was developed and compared with SdAD system through a long-term continuous study. Superior nitrogen removal performance (removal efficiency of 89.1 ± 2.5 %) was achieved in ESdAD system compared to SdAD process when treating raw landfill leachate (influent total nitrogen (TN) concentration of 241.7 ± 36.3 mg-N/L), and the effluent TN concentration of ESdAD bioreactor was as low as 24.8 ± 5.1 mg-N/L, which meets the discharge standard of China (< 40 mg N/L). Moreover, less sulfate production rate (1.3 ± 0.2 mg SO42−−S/mgNOx−−N vs 1.7 ± 0.2 mg SO42−−S/mgNOx−−N) and excellent pH modulation (pH of 6.9 ± 0.2 vs 5.8 ± 0.4) were also achieved in the ESdAD system compared to SdAD system. The improvement of ESdAD system performance was contributed to coexistence and interaction of heterotrophic bacteria (e.g., Rhodanobacter, Thermomonas, etc.), sulfur autotrophic bacteria (e.g., Thiobacillus, Sulfurimonas, Ignavibacterium etc.) and hydrogen autotrophic bacteria (e.g., Thauera, Comamonas, etc.) under current stimulation. In addition, microbial nitrogen metabolic activity, including functional enzyme (e.g., Nar and Nir) activities and electron transfer capacity of extracellular polymeric substances (EPS) and cytochrome c (Cyt-C), were also enhanced during current stimulation, which facilitated the nitrogen removal and maintained system stability. These findings suggested that ESdAD is an effective and eco-friendly process for advanced nitrogen removal for low C/N wastewater.

Electro-controlled membrane coupling heterogeneous electro-Fenton (EM-HEF) in treating acetaminophen: performance, mechanism, DFT calculation, and application

The utilization of hybrid electro-Fenton (EF) processes has gained considerable attention, which can combine the advantages of two or more treatment methods resulting in efficient removal of refractory pollutants from water. Here, an electro-controlled membrane coupling heterogeneous EF (EM-HEF) system was constructed for the degradation of acetaminophen (APAP) in water. In the EM-HEF system, a bifunctional ACF/CC-FeOCl-Cu cathode material was synthesized to enhance the HEF reaction, while a tubular Ti microfiltration membrane was used as both cathode and membrane. Degradation experiments indicated the EM-HEF system exhibited remarkable removal efficiency (97.0 %) towards APAP within 30 min under the conditions of flow rate at 60 mL min−1, initial pH at 7.1, and current density at 3 mA cm−2. Notably, the cathode materials showed low metal leaching rate and high APAP removal rate in the 10 cyclic experiments. The common inorganic anions (Cl−, HCO3−, HPO42−, and NO3−) did not inhibit the removal of APAP significantly, whereas humic acid exhibited a more pronounced inhibitory effect only at concentrations exceeding 10 mg L−1. Quenching experiments and electron spin resonance (ESR) tests confirmed the pivotal role of hydroxyl radicals in the decomposition of APAP. Combining density functional theory (DFT) and LC-MS results, three pathways were proposed. The overall toxicity of intermediates was relieved during EM-HEF degradation of APAP. Furthermore, it also achieved good performance in the treatment of landfill leachate, with increasing BOD5/COD ratio from 0.11 to 0.34. This work provides an efficient strategy for the removal of refractory pollutants in water.

Perspectives on sustainable process control optimization through reusability of non-regenerated Fenton sludge in landfill leachate treatment

The production of iron-rich waste (Fenton sludge) and the high chemical dosage required in the Fenton-based advanced oxidation process (AOP) harm the environment, making disposal challenges and the technique unsustainable. Thus, finding adequate Fenton sludge (FS) reuse alternatives is critical to addressing the Fenton process's drawbacks in addition to environmental protection. This study signifies that FS could be employed satisfactorily without requiring costly regeneration operations or chemical dosages, such as landfill leachate, during wastewater treatment. In this study, two sets of experiments were carried out utilizing the most often used optimization tools: design of experiments (DOE) (central composite design (CCD)/response surface methodology (RSM). Under optimized conditions, reasonably high chemical oxygen demand (COD) removal of 62 %, total suspended solids (TSS) removal of >95 %, and colour removal of >80 % was obtained after 48 min of reaction time with 84 mL/L sludge reused at pH 3.6. The method's key influencing factors were sludge volume, pH, and reaction time. Furthermore, reused FS exhibited lower toxicity and total volatile solids, indicating that sludge reuse is superior to direct disposal. According to the techno-economic analysis, using non-regenerated sludge as proposed reduces toxic iron-based waste and total wastewater treatment costs.

Performance evaluation of Anaerobic-Aerobic Hybrid Baffled Reactor Coupled with an Anaerobic Filter treating Landfill Leachate.

The Anaerobic Baffled Reactor (ABR) is an effective solution for landfill leachate treatment using an anaerobic fermentation process, which helps to reduce operating costs and sludge volume. To better understand the biological, chemical, and physical processes involved, especially when combining the ABR with an aerobic component, the study aimed to investigate the performance of an Anaerobic-Aerobic Hybrid Baffled Reactor (AABR) that includes an Anaerobic Filter (AF) for treating landfill leachate. This research utilized two glass reactors. The first reactor, designated as AABR-AF, consisted of six independent rectangular glass chambers arranged side by side. The third and sixth chamber designed for aerobic treatment and AF, respectively. The second reactor was used as a control reactor and did not include any aerobic chamber. The highest Removal Efficiencies (REs) for turbidity, COD, BOD, TP, TKN, nitrate, TOC, and TSS in the AABR-AF and ABR-AF were found to be (65.4% and 56.3%), (98.3% and 94.1%), (98.1% and 93.2%), (86.4% and 65%), (89.2% and 76.7%), (81.2% and 64.4%), (88.2% and 79.4%), and (72.4% and 68.5%), respectively. These optimal REs were achieved at an HRT of 48 h and an OLR of 10 kg/m3.d. Also, the highest and the lowest REs in Heavy Metals (HMs) were 89.57% for manganese in AABR-AF and 6.59% for nickel in ABR-AF, in an OLR of 10 kg/m3.d, respectively. The effective removal of Organic Matters (OMs) from landfill leachate using the AABR-AF and ABR-AF was found to be strongly influenced by HRT and OLR. The AABR-AF configuration, featuring a single aerobic chamber in the reactor, exhibited a higher efficiency in removing OMs compared to the ABR-AF configuration.

Internal Electric Field Facilitates Facet-Dependent Photocatalytic Cl- Utilization on BiOCl in High-Salinity Wastewater for Ammonium Removal.

High Cl- concentration in saline wastewater (e.g., landfill leachate) limits wastewater purification. Catalytic Cl- conversion into reactive chlorine species (RCS) arises as a sustainable strategy, making the salinity profitable for efficient wastewater treatment. Herein, aiming to reveal the structure-property relationship in Cl- utilization, bismuth oxychloride (BiOCl) photocatalysts with coexposed {001} and {110} facets are synthesized. With an increasing {001} ratio, the RCS production efficiency increases from 75.64 to 96.89 μg L-1 min-1. Mechanism investigation demonstrates the fast release of lattice Cl- as an RCS and the compensation of ambient Cl-. Correlation analysis between the internal electric field (IEF, parallel to [001]) and normalized efficiency on {110} (kRCS/S{110}, perpendicular to [001]) displays a coefficient of 0.86, validating that the promoted carrier dynamics eventually affects Cl- conversion on the open layered structure. The BiOCl photocatalyst is well behaved in ammonium (NH4+-N) degradation ranging from 20 to 800 mg N L-1 with different chlorinity (3-12 g L-1 NaCl). The sustainable Cl- conversion into RCS also realizes 85.4% of NH4+-N removal in the treatment of realistic landfill leachate (662 mg of N L-1 NH4+-N). The structure-property relationship provides insights into the design of efficient catalysts for environment remediation using ambient Cl-.

Simulation of landfill leachate treatment systems involving self-designed disk tube reverse osmosis (DTRO) model integrated with mechanical vapor recompression (MVR)

Four landfill leachate treatment systems involving self-designed disk tube reverse osmosis (DTRO) module integrated with mechanical vapor recompression (MVR) were established in Aspen Plus. To assess the treatment efficiency and the economic feasibility of landfill leachate treatment techniques, simulation of leachate treatment by four systems were conducted, and the corresponding recovery rate Y, removal rate Rt, energy consumption and operating cost were obtained. Results indicate that for the two-stage DTRO system, the optimal operational pressures in compliance with emission standards are 5.6 MPa in the first stage and 3.5 MPa in the second stage. Adding an MVR system to further treat the membrane concentrate (MC) can greatly reduce the pollutant recharge and the energy consumption of the DTRO system. When Y in MVR is not strictly required, the single-stage MVR system is the most energy-saving one. When a high Y (≥80 %) is required, the series double-stage MVR system affords the highest energy-efficiency, offering a 3.14 % lower operating cost, a 3.27 % lower unit COD removal cost, and a 7.29 % lower unit water production cost as compared to the single-stage MVR system.

Treatment of mature landfill leachate using chemical and electrical Fenton with novel Fe-loaded GAC heterogeneous catalysts

In this study, heterogeneous Fenton catalysts were prepared by loading iron oxides on granular activated carbon (GAC), with which as heterogeneous Fenton catalysts, mature landfill leachate (MLL) was treated by chemical and electrical Fenton method. For chemical Fenton treatment of MIL, the optimum conditions were optimised by orthogonal experiments and the removal of COD, NH3-N and colour reached 93.7 %, 65.5 % and 84 % respectively for static experiments, whereas the heterogeneous Fenton fluidized bed reactor removed >90 % of COD in all the 12 h of continuous operation. For electrical Fenton treatment of MIL, the removal rates of COD, colour, NH3-N, and TN were 97.4 %, 99 %, 100 %, and 94.2 %, respectively under the optimum treatment conditions of pH = 5, the GAC/α-FeOOH catalyst dosage of 13.3 g L−1, and the applied voltage of 8 V with the energy consumption of only 0.23 kWh (g COD)−1. Upon characterization, humic acid, fulvic acid and xanthohumic acid in the MLL were completely degraded and the complex macromolecules such as polycyclic aromatic hydrocarbons and heterocyclic rings were reduced and converted to simple small molecules such as alkanes. The quenching experiments verified that the ·OH produced in the heterogeneous electrical Fenton system plays an important role in the degradation of MLL, while the removal of NH3-N also relies on indirect oxidation with the active chlorine produced by the electrochemical system. GAC-based heterogeneous Fenton catalysts with high catalytic capacity and easy recycling have good application prospects in treating MLL.

A novel integrated microbial and laccase-anchored carbon catalyst system for the effective treatment of toxic organic and recalcitrant-rich municipal landfill leachate

A novel integrated microbial and laccase-anchored carbon catalyst system for the effective treatment of toxic organic and recalcitrant-rich municipal landfill leachate

Simultaneous ammonia and organics degradation from municipal landfill leachate by electrochemical oxidation

ABSTRACT The two primary issues for wide implementation of the electrochemical oxidation of wastewater are the significant cost of electrode and high energy consumption. On the other side, conventional biological processes and membrane technology have several drawbacks for recalcitrant landfill leachate (LL) treatment. To address these issues, graphite/PbO2 anode was used to treat medium to mature age (biodegradability index, 5-day biochemical oxygen demand/chemical oxygen demand: 0.25) LL. To reduce the cost of the oxidation process and maximize the efficiency, operating conditions were optimized. The optimum parameter values were obtained as 24.7 mA cm−2, 180 ± 3 rpm, and 1.9 cm of current density, stirring rate, and electrode gap, respectively. Dissolved organic carbon (DOC), chemical oxygen demand (COD), and ammonia-N removal efficiencies of 55 ± 1.4%, 81 ± 1.9%, and 56 ± 3% were obtained after 8 h of degradation at optimum conditions. The decrease in aromatic substances and ultraviolet (UV) quenching materials were evaluated by UV-Visible spectroscopy and Specific UV absorbance. The conversion of aromatic compounds into simpler molecule compounds was also verified by Fourier-transform infrared spectroscopy analysis. The lab-scale anode synthesis cost was evaluated as 0.42 USD.

Utilization of UV–Vis and synchronous fluorescence heterospectral two-dimensional correlation analysis on the structural variation of landfill leachate during membrane bioreactor-reverse osmosis process

Landfill leachate, a complex organic effluent generated during the sanitary landfilling process, poses a significant environmental threat if not properly managed. This study utilized fluorescence and UV–Vis spectroscopy in conjunction with two-dimensional correlation spectroscopy (2DCOS) to investigate the removal and transformation properties of landfill leachate during membrane bioreactor (MBR) and reverse osmosis (RO) processes. The results revealed that the MBR process effectively reduced the concentrations of chemical oxygen demand and total organic carbon, but had limited impact on complex structures and bio-refractory organic matter. Conversely, the RO process demonstrated effective trapping of organic pollutants, including both fluorescent and non-fluorescent components. Furthermore, 2DCOS analysis identified the sequence of changes in landfill leachate substances: unsaturated aldehydes and ketones > fulvic-like component/protein-like component > aromatic compounds. These findings offer valuable insights for the development of economical and efficient landfill leachate treatment procedures.

Analysis of landfill leachate promoting efficient application of weathered coal anaerobic fermentation

This research aimed to develop a new method for clean utilization and treatment of landfill leachate and solid waste weathered coal. Landfill leachate and weathered coal were adopted for combined anaerobic fermentation for methane production. The characteristics of microbial community, mechanism of biological methane production, and utilization characteristics of fermentation broth and solid residue for co-fermentation were analyzed through metagenomics, soluble organic matter detection and thermogravimetric (TG) analysis. The obtained results revealed that combined anaerobic fermentation increased methane production by 80.1%. Syntrophomonas, Salipiger, Methanosaeta and Methanothrix were highly correlated. Gene abundances of 2-oxoacid ferredoxin oxidoreductase and enolase were increased in methane conversion pathway mainly by acetic acid. Pyruvate-ferroredoxin oxidoreductase, 2-oxoglutarate synthase and succinate dehydrogenase acetate synthase intensified electron transfer pathways among microorganisms. Fulvic acid, tyrosine and tryptophan contents were high in fermentation broth. Volatile decomposition temperature, ignition point and residual char combustion temperature of residual coal were decreased and combustion was more stable. The obtained results showed that the co-fermentation of landfill leachate and weathered coal improved biological methane gas production, degraded weathered coal and improved combustion performance, which provided a new idea for weathered coal clean utilization.

Treatment of membrane-concentrated landfill leachate by heterogeneous chemical and electrical Fenton processes with Iron-loaded granular activated carbon catalysts

The composition of the membrane-concentrated landfill leachate (MCLL) is complex with a high concentration of organic matter and inorganic ions. In this study, a chemical and an electro-Fenton system were constructed to treat MCLL from a mature landfill using granular activated carbon loaded with iron oxides as heterogeneous Fenton catalysts. In the chemical Fenton treatment optimized by orthogonal experiments, the COD and colour removal rates were 93.9% and 80.2%. For the electro-Fenton system, the best COD, colour, and TN removal rates of MCLL reached 95.7%, 99%, and 94.9% with an energy consumption (EC) of 0.098 kWh·(g COD)−1 under the condition of pH 6, applied voltage 8 V, the reaction time 4 h, and the catalyst dosage 16.67 g L−1. Various spectral analyses confirmed that refractory organic matter and toxic substances in the MCLL were effectively degraded. The synergistic effect study of the factors in chemical Fenton indicated that as far as the effect on COD removal is concerned, heterogeneous Fenton system > catalyst adsorption > activated carbon/H2O2 system > activated carbon adsorption. The results of free radical quenching experiments illustrate that a large amount of ·OH was produced in the chemical heterogeneous Fenton system, while both ·OH and active chlorine play important roles in the removal of pollutants for the electro-Fenton system. MCLL can be disposed of costly and effectively by chemical and electrical Fenton processes with Iron-loaded granular activated carbon catalysts.

Advanced treatment of landfill leachate by catalytic ozonation with MnCeOx/γ-Al2O3 catalyst

Ozonation combined with an efficient and stable catalyst has been demonstrated to be a feasible solution in for removing refractory contaminants from landfill leachate. In this study, MnCeOx/γ-Al2O3 catalyst fabricated with impregnation method was adopted as ozone catalyst for advanced treatment of landfill leachate biochemical effluent (LLBE). The optimized Mn80Ce20Ox/γ-Al2O3 catalyst was fabricated with Mn/Ce molar ratio of 4:1, a metal oxide loading amount of 3.1 wt%, and calcination temperature of 500 °C. By treating LLBE, the removal of chemical oxygen demand (COD) and UV254 in 120 min reached 82.4 % and 96.3 %, respectively, with ozone dose of 15.3 mg L−1, catalyst dosage of 250 g L−1, and the initial pH of 5. The Mn80Ce20Ox/γ-Al2O3 catalyzed ozonation process conformed to pseudo-first-order kinetics with degradation rate constants of 0.0171 min−1 and 0.0313 min−1 for COD and UV254, respectively, which were 3.4 and 2.8 times higher than those of ozonation alone. The MnCeOx/γ-Al2O3 also showed satisfactory catalytic activity and stability based on eight times catalytic ozonation treatments on LLBE.

Prospects of industrial membrane concentrates: treatment of landfill leachates by coupling reverse osmosis and wet air oxidation.

Stabilized landfill leachates are characterized by a high chemical oxygen demand and limited biodegradability. This study investigates the removal of the organic fraction (chemical oxygen demand and total organic carbon) using a treatment approach that couples membrane processes and wet air oxidation (operating at 200-300 °C and 18 MPa). The aim is to address the challenges posed by landfill leachate membrane concentrates considering variations throughout the year across three different seasons. The efficiency of the treatment path was assessed through the removal of the chemical oxygen demand and total organic carbon, with additional insights provided by fluorescence spectroscopy to evaluate the degradation of the organic compounds' complexity. The most favorable results were achieved at the highest temperature (300 °C) with removals over 90% for total organic carbon and 87% for chemical oxygen demand, along with a complete elimination of fluorescence. The coupling of membrane processes and wet air oxidation has demonstrated its effectiveness in degrading the organic compounds of landfill leachates. The overall mass balance on the treatment path indicates the feasibility of discharging the treated effluent into the environment, meeting regulatory thresholds for total organic carbon and chemical oxygen concentrations.

Excess sludge-based biochar loaded with manganese enhances catalytic ozonation efficiency for landfill leachate treatment

This study developed an efficient and stable landfill leachate treatment process, which was based on the combination of biochar catalytic ozonation and activated sludge technology for intensive treatment of landfill leachate, aiming to achieve the standard discharge of leachate. The focus is to investigate the effect of manganese loading on the physicochemical properties of biochar and the mechanism of its catalytic ozonation. It was found that more surface functional groups (CO, Mn–O, etc.) and defects (ID/IG = 1.27) were exposed via the change of original carbon structure by loading Mn, which is conducive to the generation of lattice oxygen. Meanwhile, generating different valence states of Mn metal can improve the redox properties and electron migration rate, and encourage the production of reactive oxygen species (ROS) during the reaction process and enhance the catalytic efficiency. The synergistic action of microorganisms, especially denitrifying bacteria, was found to play a key role in the degradation of nitrogenous pollutants during the activated sludge process. The concentration of NH+4-N was reduced from the initial 1087.03 ± 9.56 mg/L to 9.05 ± 1.91 mg/L, while COD was reduced from 2290 ± 14.14 mg/L to 86.5 ± 2.12 mg/L, with corresponding removal rates of 99.17% and 99.20%, respectively. This method offers high efficiency and stability, achieving discharge standards for leachate (GB16889-2008). The synergy between Mn-loaded biochar and microorganisms in the activated sludge is key to effective treatment. This study offers a new approach to solving the challenge of waste leachate treatment.

A mixed blessing of influent leachate microbes in downstream biotreatment systems of a full-scale landfill leachate treatment plant

In landfill leachate treatment plants (LLTPs), the microbiome plays a pivotal role in the decomposition of organic compounds, reduction in nutrient levels, and elimination of toxins. However, the effects of microbes in landfill leachate influents on downstream treatment systems remain poorly understood. To address this knowledge gap, we collected 23 metagenomic and 12 metatranscriptomic samples from landfill leachate and activated sludge from various treatment units in a full-scale LLTP. We successfully recovered 1,152 non-redundant metagenome-assembled genomes (MAGs), encompassing a wide taxonomic range, including 48 phyla, 95 classes, 166 orders, 247 families, 238 genera, and 1,152 species. More diverse microbes were observed in the influent leachate than in the downstream biotreatment systems, among which, an unprecedented ∼30 % of microbes with transcriptional expression migrated from the influent to the biological treatment units. Network analysis revealed that 399 shared MAGs across the four units exhibited high node centrality and degree, thus supporting enhanced interactions and increased stability of microbial communities. Functional reconstruction and genome characterization of MAGs indicated that these shared MAGs possessed greater capabilities for carbon, nitrogen, sulfur, and arsenic metabolism compared to non-shared MAGs. We further identified a novel species of Zixibacteria in the leachate influent with discrete lineages from those in other environments that accounted for up to 17 % of the abundance of the shared microbial community and exhibited notable metabolic versatility. Meanwhile, we presented groundbreaking evidence of the involvement of Zixibacteria-encoded genes in the production of harmful gas emissions, such as N2O and H2S, at the transcriptional level, thus suggesting that influent microbes may pose safety risks to downstream treatment systems. In summary, this study revealed the complex impact of the influent microbiome on LLTP and emphasizes the need to consider these microbial characteristics when designing treatment technologies and strategies for landfill leachate management.