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Landfill leachate is commonly heavily contaminated and consists of high amount of organic compounds, inorganic salts, toxic gases, halogenated hydrocarbons, and heavy metals that exerts a serious threat to public health and the environment. Thus, it requires treatments before direct release into receiving waters. Selecting the efficient method for leachate treatment is still a major challenge. While physicochemical treatment methods such as coagulation-flocculation, adsorption, membrane filtration, ozonation, air stripping, and advanced oxidation processes (AOP) are appropriate for mature leachate, young leachate requires biological treatments including membrane bioreactor (MBR), activated sludge (AS), upflow anaerobic sludge blanket (UASB), and rotational biological contactor (RBC). Recently, the integration of biological processes and physicochemical methods has been demonstrated to be very efficient. It is found that combined coagulation-flocculation/nanofiltration and activated sludge/reverse osmosis are more efficacious than other integrated physicochemical methods and combined physicochemical/biological methods, respectively.

Advanced oxidation processes (AOPs) were first proposed in the 1980s for drinking water treatment and later were widely studied for treatment of different wastewaters. During the AOP treatment of wastewater, hydroxyl radicals (OH·) or sulfate radicals (SO 4 ·− ) are generated in sufficient quantity to remove refractory organic matters, traceable organic contaminants, or certain inorganic pollutants, or to increase wastewater biodegradability as a pre-treatment prior to an ensuing biological treatment. In this paper, we review the fundamental mechanisms of radical generation in different AOPs and select landfill leachate and biologically treated municipal wastewater as model wastewaters to discuss wastewater treatment with different AOPs. Generally, the treatment efficiencies rely heavily upon the selected AOP type, physical and chemical properties of target pollutants, and operating conditions. It would be noted that other mechanisms, besides hydroxyl radical or sulfate radical-based oxidation, may occur during the AOP treatment and contribute to the reduction of target pollutants. Particularly, we summarize recent advances in the AOP treatment of landfill leachate, as well as advanced oxidation of effluent organic matters (EfOM) in biologically treated secondary effluent (BTSE) for water reuse.

Landfill leachate has been documented as a significant source of trace organic pollutants, comprising an expansive family of per- and polyfluoroalkyl substances (PFAS). This study presents the findings on the distribution of 13 perfluoroalkyl carboxylates (PFCAs) and 4 perfluoroalkyl sulfonates (PFSAs) in leachates from 6 municipal solid waste (MSW) landfills in western China. The total concentrations of 17 PFAS in sampled leachates ranged from 1805 to 43,310 ng/L, and 15 compounds were detected in all samples. The short-chain compounds perfluorobutane sulfonate (PFBS, mean mass fraction 23.1%) and perfluorobutyric acid (PFBA, mean mass fraction 20.6%) were dominant. There were higher PFAS concentrations in leachates from operating landfills (mean: 12,194 ng/L) compared to closed landfills (mean: 2747 ng/L), but there was no significant difference between young (< 10 years) and old landfills (> 10 years). Moderate to weak correlations were observed between PFAS concentrations and leachate properties, e.g., TN, NH 4 + -N, TOC, and pH. This is the first report on the distribution of PFAS in landfill leachates from western China. The results have identified landfill leachate as an underestimated source of PFAS in the environment and have contributed to a more comprehensive evaluation on PFAS presence across China. Graphical abstract

Sanitary landfilling is the predominant process for solid urban waste disposal, but it generates leachate that poses environmental, economic, and social concerns. Landfill leachate (LL) contains complex and refractory pollutants and toxic compounds that can vary depending on landfill maturity, age, and biochemical reactions, making its treatment challenging. Due to its unique characteristics and occurrence in remote locations, LL requires separate treatment from wastewater. Various conventional treatment processes involving biological, chemical, and physical processes have been used for LL treatment, but a single treatment process is insufficient to meet environmental standards. This review demonstrates that combined treatment processes are more effective and efficient for LL treatment compared to single processes. Among the various combinations, chemical–chemical and chemical–biological treatments are the most commonly used. Specifically, the integration of Fenton with adsorption and a membrane bioreactor (MBR) with nanofiltration (NF) processes shows promising results. The combined processes of MBR with NF, Fenton with adsorption, and PF with biological treatment show maximum removal efficiencies for COD, reaching 99 ± 1%, 99%, 98%, and 97%, respectively. Additionally, the combined Fenton with adsorption process and EC with SPF process enhance biodegradability as indicated by increased BOD5/COD ratios, from 0.084 to 0.82 and 0.35 to 0.75, respectively. The findings emphasize the importance of developing and implementing enhanced combined treatment processes for LL, with the aim of achieving efficient and comprehensive pollutant mineralization. Such processes have the potential to address the environmental concerns associated with LL and contribute to sustainable waste management practices.

More and more stringent requirements for pollution control and the implementation of the new discharge standard for landfill leachate make the development and application of landfill leachate treatment a research focus. The aim of the review is to determine appropriate technique for effective treatment of landfill leachate. In the paper, various leachate treatment technologies are presented and summarized, the key control parameters and some main problems are discussed from a technological point of view. It is proposed that the improvement of existing technical and the development and industrial application of a new treatment for landfill leachate are necessary. The development and application of integrated leachate treatment process of different physical, biological and chemical technologies could be a suitable option to reduce the contamination levels of leachate. Particularly, advanced oxidation technologies and an efficient integration between physical–chemical processes and biochemical processes are indicated as a significant research direction of new technology development.

Landfill leachate, which is a complicated organic sewage water, presents substantial dangers to human health and the environment if not properly handled. Electrochemical technology has arisen as a promising strategy for effectively mitigating contaminants in landfill leachate. In this comprehensive review, we explore various theoretical and practical aspects of methods for treating landfill leachate. This exploration includes examining their performance, mechanisms, applications, associated challenges, existing issues, and potential strategies for enhancement, particularly in terms of cost-effectiveness. In addition, this critique provides a comparative investigation between these treatment approaches and the utilization of diverse kinds of microbial fuel cells (MFCs) in terms of their effectiveness in treating landfill leachate and generating power. The examination of these technologies also extends to their use in diverse global contexts, providing insights into operational parameters and regional variations. This extensive assessment serves the primary goal of assisting researchers in understanding the optimal methods for treating landfill leachate and comparing them to different types of MFCs. It offers a valuable resource for the large-scale design and implementation of processes that ensure both the safe treatment of landfill leachate and the generation of electricity. The review not only provides an overview of the current state of landfill leachate treatment but also identifies key challenges and sets the stage for future research directions, ultimately contributing to more sustainable and effective solutions in the management of this critical environmental issue.

In order to investigate the photocatalytic degradation of dissolved organic matter (DOM) in landfill leachate, TiO 2 /ZnO heterostructural composite powders were fabricated combining with hydrothermal synthesis and solid-state reaction method. The prepared TiO 2 /ZnO composite powders consist of anatase TiO 2 nanoparticles distributing on the surface of wurtzite ZnO particles. The optical band gap of TiO 2 /ZnO powder is less than that of pure ZnO or TiO 2 powder. TiO 2 /ZnO catalyzers show high ultraviolet-degradation efficiency for methylene blue and dissolved organic matter. The degradation rate of TiO 2 /ZnO powder for fulvic acid–like substances in landfill leachate is 2.99 times that of pure ZnO powder, and is 1.30 times that of pure TiO 2 powder. The degradation of fulvic acid–like substances by TiO 2 /ZnO photocatalyst reduced some molecular weight of benzene ring structure substances in leachate. The effective separation of electron and hole in heterostructural TiO 2 /ZnO photocatalyst is the main reason for its high photocatalytic degradation efficiency of DOM in landfill leachate.

The leachate is a type of effluent from landfills containing high concentrations of ammonia, even after normal treatment procedures are applied. Due to its characteristic, the leachate can adversely impact the environment and public health. Leachate treatment seeks to remove a series of compounds with adverse characteristics present in this type of effluent. Ammonia nitrogen is the main problem, easily observed in concentrations near 2000 mg/L. The effluents with high concentrations of ammonia nitrogen can stimulate the growth of algae, reduce the dissolved oxygen in rivers, and cause toxicity on the aquatic biota, even in low concentrations. Many research for treatment methods aiming to remove this compound, specifically, have been increasingly deeper, mainly by physical-chemical processes. This study aimed to test the process of air stripping in a closed system and pilot scale, applied on leachate treatment of landfills, to remove the high concentrations of ammonia nitrogen and its recovery by the chemical absorption of ammonia on phosphoric acid, resulting in a product with potential application as agricultural fertilizer, the ammonia phosphate. The leachate flows used were 9, 18, 20, and 40 L/h, and the air flows were 1800 and 3600 L/h. Calcium carbonate (standard grade), commercial hydrated lime (CHL), and sodium hydroxide (standard grade) were used for pH adjustments. To the ammonia recovery, three flasks were used with 2.5 L of a phosphoric acid solution of 0.12 and 0.24 mol/L. The air stripping tower removed an average of 98% of ammoniacal nitrogen, with an operating time of 4 to 9 days. The volume of air consumed to remove 1 g of ammoniacal nitrogen varied from 9, 91, and 21.6 m 3 . The ammonia recovery was about 92% using a phosphoric acid solution, producing the ammonia phosphate.

Landfill leachate is a highly polluted wastewater resulting from the decomposition of organic waste in landfills. It contains high levels of organic matter, nitrogen, phosphorus, heavy metals, and other contaminants of environmental and health concerns, but landfill leachate could also be used to produce nutrient and energy. Here we review physical, chemical, and biological methods to treat landfill leachates. Methods include adsorption, membrane separation, coagulation and flocculation, ion exchange, air stripping, chemical precipitation, electrochemical oxidation, Fenton oxidation, ozonation, photocatalysis, activated sludge process, sequential batch reactor, rotating biological contactors, nitrification and denitrification, upflow anaerobic sludge blanket, phytoremediation, and bioremediation. We discuss the technical, social, economic and environmental benefits of removing contaminants, and of recovering nutrient and energy. Physicochemical methods remove 12–95% of chemical oxygen demand, 1–100% of ammonia nitrogen, 40–96% of metals, and 44–99% of color. Advanced oxidation processes remove 19–98% of the chemical oxygen demand, 12–85% of ammonia nitrogen, and 74–98% of total organic carbon. Biological methods remove 15–93% of the chemical oxygen demand, 43–97% of the biochemical oxygen demand, 14–100% of ammonia nitrogen, and 42–98% of phosphates. Optimized leachate treatment technology can recover 10–80% of nutrients and 0.1–7 kWh/m 3 of energy.

Plastic pollution poses a worldwide environmental challenge, affecting wildlife and human health. Assessing the biodegradation capabilities of natural microbiomes in environments contaminated with microplastics is crucial for mitigating the effects of plastic pollution. In this work, we evaluated the potential of landfill leachate (LL) and estuarine sediments (ES) to biodegrade polyethylene (PE), polyethylene terephthalate (PET), and polycaprolactone (PCL), under aerobic, anaerobic, thermophilic, and mesophilic conditions. PCL underwent extensive aerobic biodegradation with LL (99 ± 7%) and ES (78 ± 3%) within 50–60 days. Under anaerobic conditions, LL degraded 87 ± 19% of PCL in 60 days, whereas ES showed minimal biodegradation (3 ± 0.3%). PE and PET showed no notable degradation. Metataxonomics results (16S rRNA sequencing) revealed the presence of highly abundant thermophilic microorganisms assigned to Coprothermobacter sp. (6.8% and 28% relative abundance in anaerobic and aerobic incubations, respectively). Coprothermobacter spp. contain genes encoding two enzymes, an esterase and a thermostable monoacylglycerol lipase, that can potentially catalyze PCL hydrolysis. These results suggest that Coprothermobacter sp. may be pivotal in landfill leachate microbiomes for thermophilic PCL biodegradation across varying conditions. The anaerobic microbial community was dominated by hydrogenotrophic methanogens assigned to Methanothermobacter sp. (21%), pointing at possible syntrophic interactions with Coprothermobacter sp. (a H 2 -producer) during PCL biodegradation. In the aerobic experiments, fungi dominated the eukaryotic microbial community (e.g., Exophiala (41%), Penicillium (17%), and  Mucor (18%)), suggesting that aerobic PCL biodegradation by LL involves collaboration between fungi and bacteria. Our findings bring insights on the microbial communities and microbial interactions mediating plastic biodegradation, offering valuable perspectives for plastic pollution mitigation.