Landfill Leachate Treatment Research Articles

Membrane technology as a strategy for microplastics removal from landfill leachate: a review

ABSTRACT This study offers a comprehensive review of global microplastic (MP) contamination in landfill leachate (LL) and examines remediation strategies using membrane technologies such as ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and membrane bioreactors (MBRs). Research investigations and full-scale applications of these technologies for treating LL demonstrate their efficacy as viable solutions for on-site leachate treatment, providing promise in mitigating LL toxicity and reducing the environmental and human health risks associated with MP pollution. While the size of MPs in LL may raise questions about the necessity of using NF and RO membranes for MP removal, these processes are commonly employed in many landfills to serve as barriers for MP retention. Despite the high efficacy of MBR systems in removing MPs, the accumulation of MPs in the biological sludge can adversely affect biological performance and membrane fouling, necessitating further exploration. In general, membrane technologies face challenges such as membrane fouling and the release of MPs. Therefore, further research is needed to address MP removal, understand membrane–MP interactions, explore cleaning strategies in LL treatment and their impact on MP release from membranes, and study the integrity of membranes after continuous exposure to LL under varied operating conditions.

Bioaerosols and VOC emissions from landfill leachate treatment processes: Regional differences and health risks

The landfill leachate treatment process (LLTP) is a crucial anthropogenic source of bioaerosols and volatile organic compounds (VOCs) with potential environmental impacts and on-site health risks to plant workers. However, factors influencing microbial aerosol and VOC emissions remain poorly understood. We sampled and analyzed bioaerosols and VOCs in two process sections (oxidation ditch [OD] and reverse osmosis membrane [RO]) of LLTPs in northern (NLF) and southern (SLF) China. Bioaerosol concentrations were highest in OD, and particle size predominantly ranged from 0.654.7 µm. Microbial community analysis revealed distinct differences between geographical locations and process sections, with 332 genera identified. Genera such as Paenibacillus, Bacillus, and Pseudomonas were prevalent at all sampling sites. Oxygen-containing compounds (e.g., acetophenone and propionic acid) were the dominant VOCs, particularly in SLF-OD. Network analysis showed complex interactions, with Sphingomonas and ketones playing central roles in microbial and VOC communities, respectively. Partial least squares (PLS) modeling indicated a significant correlation between bioaerosols and VOCs. Specific microorganisms, such as TK10, Adhaeribacter, and Lachnospiraceae, were major contributors to emissions of hazardous VOCs (e.g., toluene and styrene). The ozone-generation potential and olfactory effect of the OD were significantly higher than those of RO; and those of SLF were higher than those of NLF. Health risk assessments indicated potential chronic toxicity and cancer risks associated with VOC exposure to specific compounds, such as trichloroethylene. Bioaerosol exposure occurred primarily through inhalation, particularly in male workers. This study establishes a theoretical foundation for the prevention and control of air-phase pollutant risks associated with LLTPs.

Sustainable approach for landfill leachate treatment through dielectric barrier discharge/ferrate (DBD/Fe(VI)) enhanced nanofiltration

Landfill leachate, with its high concentrations of persistent organic pollutants, salts, heavy metals, and emerging contaminants, presents significant environmental challenges. This study investigated the combination of dielectric barrier discharge (DBD) and ferrate (Fe(VI)) pretreatment technology in landfill leachate treatment, focusing on its effectiveness in enhancing oxidation performance and mitigating membrane fouling. The results indicated that after DBD/Fe(VI) treatment, TOC and UV254 removal efficiencies increased by 44 % and 67 %, respectively. Additionally, the DBD/Fe(VI) system excelled in removing fluorescent substances and high molecular weight organic compounds, thereby reducing the formation of the cake layer on the nanofiltration membrane. This system enhanced oxidation performance through the synergistic production of reactive intermediates, with Fe(V)/Fe(IV) and •OH being the main active species, O2•-, and 1O2 also contributing significantly. The degradation pathway of perfluorooctanoic acid was investigated by utilizing it as the representative pollutant. Compared to the raw landfill leachate system, the DBD/Fe(VI) increased membrane flux by 104 %, while reducing reversible and irreversible fouling resistances by 67 % and 75 %, respectively. Furthermore, the advantages and practical application potential of the DBD/Fe(VI) system were evaluated from energy consumption, economic cost, and carbon dioxide emissions. The study offers an innovative method for landfill leachate treatment and fouling mitigation.

Landfill leachate treatment by incorporating MWCNTs assisted adsorption and coagulation process

Landfill leachate treatment by incorporating MWCNTs assisted adsorption and coagulation process

Single-atom cobalt enables efficient catalytic ozonation for advanced wastewater treatment: Mechanisms and application

Heterogeneous catalytic ozonation (HCO) triggered by single-atom catalysts (SACs) is an emerging and promising advanced wastewater treatment technology. The catalytic ozonation mechanisms involving single-atom sites and the application of SACs-based HCO require further exploration. Herein, a single-atom Co catalyst with Co-N4 active sites was synthesized for HCO. Oxalic acid (OA) and p-hydroxybenzoic acid (pHBA) with different structural and chemical properties were utilized as the model contaminants. Compared with ozonation and Co nanoparticle-based HCO, single-atom Co-based HCO exhibited superior removal for the two model pollutants, with the removal rate constants of 0.098 and 0.076 min−1 for OA and pHBA, respectively. In the single-atom Co-based HCO, ozone was decomposed and converted to nonradical ROS of surface-adsorbed atomic oxygen (*Oad) and singlet oxygen (1O2). OA was mainly removed on the catalyst surface, relying on the adsorption by the catalyst and the oxidation of *Oad, while electron-rich pHBA was oxidized by O3 and 1O2 in solution. Furthermore, using 3-5 mm Al2O3 pellets as the carrier, single-atom Co doped carbon-Al2O3 pellets were fabricated and applied for the advanced treatment of landfill leachate, and the COD decreased from 110 mg/L to 38 mg/L after treatment. This work provided new insights into the oxidation mechanisms and applications of SACs-based HCO.

A new approach on the management of landfill leachate reverse osmosis concentrate: Solar distillation coupled with struvite recovery and biological treatment

The management of reverse osmosis (RO) concentrate remains a challenging task for operators of Landfill Leachates Treatment Plants. In this article we suggest an integrated treatment scheme for RO concentrate that combines solar distillation, struvite precipitation to reduce ammonia content of the distillate and biological treatment of the supernatant either with mixed cultures of bacteria or with microalgae. Experiments in a pilot-scale solar still, equipped with underfloor heating system, showed that the production rate of the distillate ranged up to 3.17 L/d m2. The distillate was characterized by elevated average concentrations of ammonium nitrogen; 2028 mg/L and 1358 mg/L in the two experiments conducted, respectively. A decreasing trend on concentrations of NH4+-N was noticed during these experiments, while the opposite was observed for COD. Struvite recovery experiments showed that the optimum Mg:NH4:PO3 ratio was that of 2:1:5.8. Under these conditions, the NH4+-N removal reached 88%. Further treatment of the process supernatant into a 4-L hybrid sequencing batch reactor with biocarriers and activated sludge achieved NH4+-N removal higher than 98% in Phases C and D, where 450 and 600 mL of supernatant were added, respectively. Similar removal was also observed in a 2-L bioreactor with microalgae Chlorella sorokiniana when 150 mL of struvite supernatant were added (Phase B) while further increase of the amount of added supernatant to 200 mL resulted to a sharp stop of NH4+-N consumption (Phase C). Calculations for a landfill serving 20,000 inhabitants and a daily RO concentrate production of 6 m3/d showed that the required area for the construction of the solar still was 1893 m2 and the volumes of the hybrid and the microalgae reactor were 54 m3 and 60 m3, respectively. The recovered solid material of struvite process, after characterization for heavy metals and organic micropollutants, could be reused to the fertilizers industry.

Determination of three dechloranes in environmental water by magnetic solid-phase extraction-gas chromatography-negative chemical ionization mass spectrometry based on the covalent organic framework material

Dechloranes are additive-type chlorine flame retardants that are widely used in processing industrial products, such as electronic equipment and textiles. Dechloranes, which can enter the human body through various routes, pose significant health risks because of their toxicity, persistence, and bioaccumulation. In 2023, dechlorane plus was listed in the Stockholm Convention on Persistent Organic Pollutants. In the same year, China recognized this compound as a priority-controlled substance. Dechloranes are commonly found at trace levels in water, which is extremely harmful to the environment and human health. Therefore, the development of detection methods for dechloranes is crucial. Magnetic solid-phase extraction (MSPE) has attracted considerable attention because of its low organic solvent consumption, simplicity of adsorbent separation, and ease of operation. In general, the selectivity and efficiency of MSPE depend on the characteristics of the adsorbent. Covalent organic frameworks (COFs) have regular porosity, structural predictability and stability, high specific surface areas, and adjustable pore sizes, which are advantageous for a wide range of separation and analysis applications. In this study, Fe3O4 magnetic nanoparticles and a COF material (TpBD) were combined to prepare Fe3O4@TpBD as an adsorbent for dechloranes. Subsequently, an effective method for analyzing dechlorane in environmental water was established by coupling MSPE with gas chromatography-negative chemical ionization mass spectrometry (GC-NCI/MS). The successful synthesis of Fe3O4@TpBD was confirmed using transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometry. A single-factor method was used to optimize the extraction conditions, including the Fe3O4@TpBD dosage, pH of water sample, elution solvent type and volume, extraction time, elution time, and ionic strength. The target analytes were separated on a TG-5SILMS column (30 m×0.25 mm×0.25 μm) and quantified using the external standard method in the selected-ion monitoring (SIM) mode. Under the optimal extraction conditions, the method validation results showed a linear range of 2-1000 ng/L. The limits of detection (LODs) and quantification (LOQs) were 0.18-0.27 ng/L and 0.60-0.92 ng/L, respectively, for the three analytes. The intra-day and inter-day precisions at three spiked levels were 4.2%-16.2% and 6.9%-15.7%, respectively. This method was successfully applied to the determination of dechloranes in environmental water samples (laboratory tap water, reservoir water, wastewater treatment plant effluent, and landfill leachate treatment effluent). The recoveries of the three dechloranes at different spiked levels ranged from 77.8% to 113.3% with relative standard deviations (RSDs) of 2.5%-16.3% (n=3). With the advantages of operational simplicity, high sensitivity, and good reproducibility, the proposed method is suitable for the qualitative and quantitative determination of dechloranes in environmental water.

매립지 침출수 처리에서 질산화 공정 최적화 : pH 및 무기탄소원농도가 질소 제거에 미치는 영향

This study was conducted to solve problems that arise in the nitrification of landfill leachate due to the increase in waste generation and diversification of components associated with domestic economic growth. Landfill leachate contains high concentrations of nitrogen compounds and organic substances thus, it is a potential cause of environmental pollution. The study findings confirmed that the nitrification process was inhibited when the metal (Cu) concentration was more than 2.5ppm: further, the nitrification rate could be greatly improved by replenishing alkalinity and adjusting pH. Additionally, appropriate Do and pH alone did not have a sufficient effect on nitrification. This study is expected to contribute to the development of new treatment technology that can minimize the use of chemicals and suppress the generation of secondary toxic substances in the landfill leachate treatment process.

Effects of suspended titanium dioxide (TiO2) nanoparticles on cake layer formation in submerged anaerobic membrane bioreactor (AnMBR) for landfill leachate treatment (LFL)

In recent years, TiO2 NPs have attracted great attention among the semiconductors because of stability, commercial availability, and ease of preparation. For this reason, NPs are widely used in wastewater treatment and membrane bioreactor (MBRs) In this study, the effect of titanium dioxide (TiO2) nanoparticle material was investigated on both the landfill leachate (LFL) treatment and membrane fouling performance. The system performance was evaluated for under varying TiO2 concentrations (50–300 mg/L TiO2), constant HRT (24 h), and constant backwashing (5 min)-relaxing (0.5 min) in AnMBR. The optimum conditions were determined as 300 mg/L TiO2 and the corresponding to COD, Color, TOC and TN removal efficiencies were observed as 55 %, 23 %, 22 %, 30 %, respectively. The best membrane performance was observed at 300 mg/L TiO2 corresponding to membrane fouling rate as 0.01 mbar/min. TiO2 addition significantly mitigated membrane fouling (75 % decrease) for AnMBR. Bacteroidetes, Firmicutes and Proteobacteria have been observed to be the dominant species in LFL and MBRs. The bacterial species responsible for membrane fouling were determined as Alphaproteobacteria, Sphingobacteria and Flavobacteria. The addition of TiO2 was determined membrane fouling decreased in AnMBR. As a result of TiO2 NPs were observed to thin the cake layer and postpone membrane fouling and filtration.

In-situ generation of bifunctional reagents via Al/C microelectrolysis for efficient coagulation–Fenton oxidation treatment of leachate MBR effluent

Coagulation–Fenton oxidation stands as a prevalent method for organic pollutant removal from MBR effluent in landfill leachate. However, its dependence on intricate coagulant preparation and hazardous H2O2 handling presents challenges in logistics. Herein, a novel Al0/C–N, Cl composite was developed via high-energy ball milling and high-temperature sintering, which facilitates in situ generation of H2O2 and aluminum salt coagulant upon stirring in oxygen-containing aqueous solutions. Under conditions of 2 g/L Al0/C–N, Cl and initial pH 9, H2O2 production achieved 459 mg/L within 1 h, yielding an Al3+/H2O2 bifunctional reagent. Subsequent coagulation in MBR effluent and Fenton oxidation achieved removal efficiencies of 85.5 %, 76.4 %, and 99.3 % for UV254, total organic carbon, and chromaticity, respectively. The efficient degradation of refractory fulvic-like substances was obtained from this novel “coagulation–Fenton” hybrid process without additional coagulants and H2O2. These results illustrated that the hybrid process is a promising and efficient technology for the advanced treatment of landfill leachate.

Agricultural waste-based biochars for sustainable removal of heavy metals from stabilized landfill leachate.

In this work, biochars were used as adsorbents to remove Cu, Cd, and Zn ions in a real stabilized leachate from a controlled landfill. Oak fruit shells biochar (OFSBC) and date palm fibers biochar (DPFBC) were obtained by pyrolysis of oak fruit shells and date palm fibers at 700°C and 400°C, respectively. OFSBC and DPFBC showed well-developed structures and high specific surface areas (520.16 m2/g and 470.46 m2/g, respectively). Equilibrium adsorption of heavy metal ions on DPFBC and OFSBC occurred after 4h and 2h of stirring. The removal efficiencies of Cu, Cd, and Zn ions were 97.01%, 94.40%, and 80.59% with DPFBC and 90.10%, 88.33%, and 76.16% using OFSBC, respectively. The Avrami fractional order model was appropriate for describing kinetic adsorption. Increasing the dose of adsorbent improves heavy metal ion retention. Thermodynamic tests have proven the spontaneous and endothermic adsorption of these heavy metals. The electrostatic attraction, ion exchange, complexation, metal-π bending, and surface precipitation and pore filling were regarded as the most predominant heavy metal retention mechanisms from the landfill leachate onto the biochar surface. Separately, the DPFBC showed the best performance than OFSBC regarding the improvement of leachate quality. Chemical oxygen demand (COD), biological oxygen demand (BOD5), ammoniacal nitrogen (NH3-N), and phosphorus (P) were respectively removed at an efficiency of 53.57%, 29.17%, 36.07%, and 37.5%, respectively. Thus, the results allow highlighting that the adsorption on DPFBC and OFSBC can be an effective alternative in the practice of landfill leachate treatment.

Experimental investigation and Monte Carlo simulation of landfill leachate treatment using physicochemical method and a non-thermal plasma reactor

ABSTRACT Leachate treatment is one of the challenging subjects in the field of waste management. Leachate as a dumpling sites hazardous byproduct due to the high concentration of chemical oxygen demand (COD) and toxic compounds with dark colour is a potential pollutant of the environment, causing a lot of problems in the absence of treatment and direct discharge to the environment. In this study, the combinatory performance of sequential chemical flocculation and coagulation process and non-thermal plasma (NTP) technology on leachate from the Sarāvān city former controlled landfill, Iran, was investigated. The outcomes of Jar test illustrated that hydrated aluminium sulphate (PAC) was selected the best coagulant compared with hydrated aluminium sulphate (HAS) and ferric chloride (FC) to remove suspended solids and colour. The optimised parameters for 10% PAC pre-treatment were obtained 3 g lime and cationic 0.1 g polyelectrolyte per 1 litre of leachate. After pre-treatment by using jar test, NTP was used to remove turbidity, colour, COD and so forth. The sequential system-based all stages of pretreatment and NTP diminished the turbidity and colour removal to 98.6% and 99.2%, respectively. Furthermore, COD, BOD5, TSS, and TDS were also reduced. As a result, combination of pre-treatment and NTP technology are able to remove the landfill leachate effectively. Monte Carlo calculations exhibited that Al3+ and H2O2 had the most effects to decompose HA (Humic acid) compound in physicochemical pre-treatment and treatment stages.

Microbial community dynamics in different floc size aggregates during nitrogen removal process upgrading in a full-scale landfill leachate treatment plant

Upgrading processes to reduce biodegradable organic substance addition is crucial for treating landfill leachate with high pollutant concentrations, aiding carbon emission reduction. Aggregate size in activated sludge processes impacts pollutant removal and sludge/water separation. This study investigated microbial community succession and driving mechanisms in different floc-size aggregates during nitrogen removal progress upgrade from conventional to partial nitrification–denitrification in a full-scale landfill leachate treatment plant (LLTP) using 16S rRNA gene sequencing. The upgrade and floc sizes significantly influenced microbial diversity and composition. After upgrading, ammonia-oxidizing bacteria were enriched while nitrite-oxidizing bacteria suppressed in small flocs with homogeneity and high mass transfer efficiency. Larger flocs enriched Defluviicoccus, Thauera, and Truepera, while smaller flocs enriched Nitrosomonas, suggesting their potential as biomarkers. Multi-network analyses revealed microbial interactions. A deep learning model with convolutional neural networks predicted nitrogen removal efficiency. These findings guide optimizing LLTP processes and understanding microbial community dynamics based on floc size.

A comprehensive review of landfill leachate treatment technologies

The management of landfill leachate presents a significant environmental challenge, necessitating a comprehensive and dynamic treatment approach. This comprehensive review delves into the critical issue of landfill leachate treatment, exploring its environmental impact, treatment technologies, regulatory frameworks, and the path towards sustainable management practices. This review explores the complexities of landfill leachate, emphasizing the need for sustainable waste management practices to safeguard environmental health. Our analysis highlights the evolution of conventional and advanced treatment technologies designed to mitigate these risks, focusing on membrane technologies, advanced oxidation processes, and the promising potential of emerging techniques such as adsorption and biological nutrient removal. These technologies are evaluated for their efficiency, cost implications, and sustainability impacts, underscoring the challenges and opportunities within the current landscape of leachate treatment. The review aims to provide insights into designing efficient and effective treatment systems through a detailed analysis of conventional and advanced treatment methods. By examining a case study in Changsha City, the effectiveness of a comprehensive treatment system integrating various technologies is demonstrated. The review underscores the interconnectedness of human activities, environmental health, and waste management, emphasizing the importance of a holistic approach. It stresses the continuous improvement of leachate treatment technologies and the adoption of sustainable practices to reduce the environmental footprint of landfills. Ultimately, it calls for integrating multiple treatment processes, economic considerations, and readiness to address future challenges in landfill leachate treatment, contributing to the advancement of sustainable waste management practices.

Treatment and nutrient recovery from landfill leachate by sequential persulfate oxidation and struvite precipitation: An evaluation of technical feasibility.

The technical feasibility of advanced oxidation process, in particular persulfate (PS) oxidation followed by struvite precipitation for landfill leachate treatment and nutrient recovery has been depicted in the current study. Furthermore, the impact of activation of PS with thermal and ultraviolet (UV) irradiation techniques on COD removal efficiency is also investigated. A maximum COD removal efficiency of 96% is accomplished at 65°C together with supply of UV irradiation. The impact of persulfate dose, pH, and PS/65°C/UV system on COD and biodegradability is also illustrated in the current study. Additionally, decomposition rate constant values are also ascertained in the present study. Afterwards, nutrient recovery using struvite precipitation is carried out for sustainable utilization of resources. Preliminary treatment of leachate with PS/65°C/UV system is greatly conducive to recovering high quality struvite crystals. Besides, 94.9%, 83.5%, and 91.3% of PO43- -P, NH4+ -N, and Mg2+ recovery efficiency attained respectively at pH 9.5 and 1.2:1:1 molar ratio of Mg2+: NH4+-N: PO43--P. Additionally, all the nutrient recovery studies are validated using chemical equilibrium model Visual MINTEQ. Later, bioavailable fraction of PO43--P in the recovered struvite is also investigated for utilization as fertilizer. The presence of Cu and Zn in the recovered struvite precipitate enhanced its economic value as a fertilizer. Since Cu and Zn are vital micronutrients for growth of plants. The low soluble values of recovered struvite precipitate confirmed its utilization as slow releasing fertilizer.

Evaluation of greenhouse gas emission and reduction potential of high-food-waste-content municipal solid waste landfills: A case study of a landfill in the east of China

This study proposes a comprehensive evaluation method based on a two-stage model to assess greenhouse gas (GHG) emissions and reductions in high-food-waste-content (HFWC) municipal solid waste (MSW) landfills. The proposed method considers typical processes such as fugitive landfill gas (LFG), LFG collection, flaring, power generation, and leachate treatment. A case study of an HFWC MSW landfill in eastern China is considered to illustrate the evaluation. The findings revealed that the GHG emissions equivalent of the case landfill amounted to 21.23 million tons from 2007 to 2022, averaging 1.03 tons CO2-eq per ton of MSW. There was a potential underestimation of LFG generation at the landfill site during the initial stages, which led to delayed LFG collection and substantial fugitive LFG emissions. Additionally, the time distribution of GHG emissions from HFWC MSW was significantly different from that of low-food-waste-content (LFWC) MSW landfills, with peak emissions occurring much earlier. Owing to the rapid degradation characteristics of HFWC MSW, the cumulative LFG production of the landfill by 2022 (2 years after the final cover) was projected to reach 77 % of the total LFG potential. In contrast, it would take until 2030 for LFWC MSW landfills to reach this level. Furthermore, various scenarios were analyzed, in which if the rapid LFG generation characteristics of HFWC MSW are known in advance, and relevant facilities are constructed ahead of time, the collection efficiency can be improved from 31 % to over 78 %, resulting in less GHG emissions.

The effect of autochthonous metal ions and humic substances on landfill leachate ozonation: Reactive oxygen species and 3D fluorescence analysis

This study investigated the ozonation process for landfill leachate treatment, focusing on the impact of autochthonous metal ions (Fe3+, Cu2+, Mn2+, Mg2+) and humic substances on the degradation of pollutants. Our findings revealed that the presence of these metal ions significantly enhanced the generation of hydroxyl radicals (OH), especially for Fe3+, demonstrating the highest catalytic activity. However, the humic substance attenuated the signals of reactive oxygen species (ROS), particularly the superoxide radical (O2−) in the presence of Cu2+ and Mn2+. These suggested that metal ions could complex with humic substances and further inhibit ROS production. Despite this inhibition, Fe3+ maintained its ROS-generating capacity even in the presence of humic substances, indicating its potential as a robust catalyst in landfill leachate. Batch tests further demonstrated that Fe3+ had the most positive effect on the degradation of sodium humate, as evidenced by a significant reduction in fluorescence regional integration (FRI) values. An integrated membrane bioreactor (MBR) and ozonation system were conducted, which firstly processed activated sludge treatment in the MBR and then pumped into the ozonation system via a peristaltic pump. After ozonation, the leachate overflowed back into the MBR for further treatment, creating a closed-loop system. It was observed that there was a significant reduction in humic substances, with a decrease of 96.31% in the FRI. Parallel factor analysis (PARAFAC) results corroborated these findings, which indicated a marked reduction in the abundance of humic-like substances C-BO-1 and C-BO-4 during the 17 days treatment period. This study revealed the pivotal role of microorganisms, ROS, metal ions, and humic substances in the treatment of landfill leachate. The metal ions presented in the leachate were confirmed to produce ROS during the ozonation process. However, a significant quantity of humic-like substances reduced the reactive ROS through complexation and consumption reactions. Simultaneously, microorganisms in the MBR system consumed humic substances such as C-BO-1 and C-BO-4, which promoted the degradation of contaminants in the landfill leachate. These insights provided implications for optimizing ozonation processes in leachate management, potentially leading to more efficient and environmentally sustainable waste disposal practices.

Efficient hydrogen peroxide synthesis with Pluggable Capsule cathode for Electro-Fenton treating actual landfill leachate

Membrane concentrate of landfill leachate is the typical refractory wastewater with high contaminants concentration, high complexity, and high toxicity, posing a huge potential threat to the surface and subsurface water. Electro-Fenton (EF) based on in-situ synthesis of H2O2 is an effective method for the treatment of refractory organic pollutants. However, the low accumulative concentration of H2O2 and the poor scalability of the system remain major bottlenecks, limiting the practical application of EF. This study presented a modular air-breathing cathode, Pluggable Capsule Cathode (PCC), for efficient in-situ H2O2 synthesis through 2-electron oxygen reduction reaction (ORR). Based on PCC, corridor reactors (CR) were fabricated for in-situ H2O2 synthesis and actual landfill leachate treatment. Operated under the optimal conditions (dual-chamber, A/V=240 cm2 L−1, 2 M NaOH electrolytes and J=20 mA cm−2), the H2O2 concentration reached 28.1 g/L. In the EF system based on single-chamber CR equipped with PCCs, 81 % of COD and 89 % of NH3-N in landfill leachate were removed within 3 h. The total cost of landfill leachate treatment by the EF system based on CR-PCC was calculated as $ 5.06 m−3. The PCC based EF system was a promising process for the treatment of actual refractory wastewater, which provides a new insight for the structure design of cathode and reactor in the future.

Dielectric Barrier Discharge (DBD) enhanced Fenton process for landfill leachate nanofiltration: Organic matter removal and membrane fouling alleviation

This study investigated a sustainable approach through dielectric barrier discharge (DBD) enhanced Fenton technology coupling nanofiltration (NF) process for landfill leachate treatment. The DBD/Fe(II)/H2O2 system exhibited significant synergistic effects, removing 55.07 % of TOC and 53.79 % of UV254 within 60 min, respectively. Additionally, the DBD/Fe(II)/H2O2 system demonstrated exceptional performance in removing fluorescent substances and large molecular organic compounds, thereby reducing the formation of cake layer on the nanofiltration membrane. Moreover, membrane flux increased by 2.34 times, with reversible and irreversible resistances decreasing by 75.79 % and 81.55 %, respectively. Quenching experiments revealed ·OH as the primary active species for perfluorooctanoic acid (PFOA) degradation in the DBD/Fe(II)/H2O2 process. The degradation pathway of PFOA was also elucidated via capillary electrophoresis-quadrupole time-of-flight mass spectrometry analysis. Correlation analysis indicated that TOC and EEM were the primary fouling factors. Lastly, through an assessment of energy consumption, economic costs, and carbon dioxide emissions, the advantages and practical application potential of the DBD/Fe(II)/H2O2 system were demonstrated. In summary, the DBD/Fe(II)/H2O2 system emerges as a feasible strategy for NF pretreatment, holding immense potential for treating landfill leachate.

Multi-omics illuminates the functional significance of previously unknown species in a full-scale landfill leachate treatment plant

Landfill leachate treatment plants (LLTPs) harbor a vast reservoir of uncultured microbes, yet limited studies have systematically unraveled their functional potentials within LLTPs. Combining 36 metagenomic and 18 metatranscriptomic datasets from a full-scale LLTP, we unveiled a double-edged sword role of unknown species in leachate biotreatment and environmental implication. We identified 655 species-level genome bins (SGBs) spanning 47 bacterial and 3 archaeal phyla, with 75.9 % unassigned to any known species. Over 90 % of up-regulated functional genes in biotreatment units, compared to the leachate influent, were carried by unknown species and actively participated in carbon, nitrogen, and sulfur cycles. Approximately 79 % of the 37,366 carbohydrate active enzymes (CAZymes), with ∼90 % novelty and high expression, were encoded by unknown species, exhibiting great potential in biodegrading carbohydrate compounds linked to human meat-rich diets. Unknown species offered a valuable genetic resource of thousands of versatile, abundant, and actively expressed metabolic gene clusters (MGCs) and biosynthetic gene clusters (BGCs) for enhancing leachate treatment. However, unknown species may contribute to the emission of hazardous N2O/H2S and represented significant reservoirs for antibiotic-resistant pathogens that posed environmental safety risks. This study highlighted the significance of considering both positive and adverse effects of LLTP microbes to optimize LLTP performance.