Comparison of different types of landfill leachate treatments by employment of nontarget screening to identify residual refractory organics and principal component analysis

Exploring the hidden chemical landscape: Non-target and suspect screening analysis for investigating solid waste-associated environments

Solid waste is an inevitable consequence of urbanization. It can be safely managed in municipal landfills and processing plants for volume reduction or material reuse, including organic solid waste. However, solid waste can also be discarded in (un-)authorized dumping sites or inadvertently released into the environment. Legacy and emerging contaminants have the potential to leach from solid waste, making it a significant pathway to the environment. Non-target screening (NTS) and suspect screening analysis (SSA) have become helpful tools in environmental science for the simultaneous analysis of a wide range of chemical compounds. However, the application of these analytical approaches to environmental samples related to Raw or Processed Solid Waste (RPSW) has been largely neglected so far. This perspective review examines the potential and policy relevance of NTS and SSA applied to waste-related samples (liquid, gaseous and solid). It addresses the hurdles associated with the chemical safety of solid waste accumulation, processing, and reuse, and the need for landfill traceability, as well as effectiveness of leachate treatments. We reviewed the current applications of NTS and SSA to environmental samples of RPSW, as well as the potential adaptation of NTS and SSA techniques from related fields, such as oilfield and metabolomics, to the solid waste domain. Despite the ongoing technical challenges, this review highlights the significant potential for the implementation of NTS and SSA approaches in solid waste management and related scientific fields and provides support and guidance to the regulatory authorities.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Non-targeted analysis for the screening and semi-quantitative estimates of per-and polyfluoroalkyl substances in water samples from South Florida environments

Per- and polyfluoroalkyl substances (PFAS) are a group of anthropogenic pollutants that are found ubiquitously in surface and drinking water supplies. Due to their persistent nature, bioaccumulative potential, and significant adverse health effects associated with low concentrations, they pose a concern for human and environmental exposure. With the advances in high-resolution mass spectrometry (HRMS) methods, there has been an increasing number of non-targeted analysis (NTA) approaches that allow for a more comprehensive characterization of total PFAS present in environmental samples. In this study, we have developed and compared NTA workflows based on an online solid phase extraction- liquid chromatography high resolution mass spectrometry (online SPE-LC-HRMS) method followed by data processing using Compound Discoverer and FluoroMatch for the screening of PFAS in drinking waters from populated counties in South Florida, as well as in surface waters from Biscayne Bay, Key west, and Everglades canals. Tap water showed the highest number of PFAS features, indicating a poor removal of these chemicals by water treatment or perhaps the breakdown of PFAS precursors. The high number of PFAS features identified only by CD and FluoroMatch emphasizes the complementary aspects of these data processing methods. A Semi-quantitation method for NTA (qNTA) was proposed using a global calibration curve based on existing native standards and internal standards, in which concentration estimates were determined by a regression-based model and internal standard (IS) response factors. NTA play a crucial role in the identification and prioritization of non-traditionally monitored PFAS, needed for the understanding of the toxicological and environmental impact, which are largely underestimated due to the lack of such information for many PFAS.

Advanced oxidation process based on hydroxyl and sulfate radicals to degrade refractory organic pollutants in landfill leachate

As a special type of wastewater produced in the landfill, leachate is mainly composed of organic pollutants, inorganic salts, ammonia nitrogen and heavy metals, and featured by high pollutants concentration, complex composition and large fluctuations in water quality and volume. Biological, chemical and physical methods have been proposed to treat landfill leachate, but much attention has been paid to the advanced oxidation processes (AOPs), due to their high adaptability and organic degradation efficiency. This paper summarizes the recent findings on the AOPs based on hydroxyl radical (OH) (e.g., ozonation and catalyzed ozone oxidations, Fenton and Fenton-like oxidations) and sulfate radical (SO₄^-) (e.g., activated and catalyzed persulfate oxidations), especially the production routes of free radicals and mechanisms of action. When dealing with some special landfill leachates, it is difficult for a single advanced oxidation technology to achieve the expected results, but the synergistic combination with biological or physical methods can produce satisfactory outcomes. Therefore, this paper has summarized the application of these combined treatment technologies on landfill leachate.

Comprehensive analysis and modeling of landfill leachate

Landfill leachate data compiled from 220 different landfills from 46 countries in Europe, Middle East, Asia, Africa, and America was analysed by multivariate statistical approaches. Data pre-treatment procedure such as handling of outliers, completion of missing data, and standardization of data was applied to prepare the raw data matrix for the complex statistical analyses including cluster and principal component analyses (PCA). Regression modeling was conducted to estimate leachate parameter values. Results show that usually inorganic parameters, if included in the PCA, dominated the first components indicating the highest correlations as well as accounting for majority of the variation in the data. Those highly correlated parameters in landfill leachate could be important in evaluation of their pathways into leachate in terms of transport and biodegradation mechanisms as well as their elimination potential from sampling and analytical procedures during monitoring activities at landfills. Some leachate parameters having significantly high concentrations, such as organics, salts, and some inorganics, impacted the formation of components in PCA. This in turn provides important information about the specific characteristics of leachate samples and the landfills to which they belong.

A versatile control strategy based on organic carbon flow analysis for effective treatment of incineration leachate using an anammox-based process

Anammox-based process provides an alternative for the sustainable treatment of incineration leachate that has high-load ammonium and high residual heat, but the high concentrations of organics in such leachates brought challenges for the process control. For the first time, a two-stage partial nitrification (PN)-anammox process coupled with a pre-enhanced anaerobic digestion (AD) was established to achieve efficient nitrogen removal from incineration leachate. Satisfactory nitrogen and chemical oxygen demand (COD) removal efficiencies were achieved-with the average values of 90% and 78%, respectively-despite fluctuating influent properties [1100-2000 mg-total nitrogen (TN)/L and 3800-15800 mg-COD/L]. A versatile control strategy was developed to create an optimum autotrophic environment for nitrifier and anammox bacteria: i) enhanced AD set before the PN-anammox process captured nearly 50% of the influent COD; ii) in the PN unit, ammonia-oxidizing bacteria were well adapted to COD concentrations of 1420-2400 mg/L, and dissolved oxygen (0.2-0.4 mg/L) controlling combined with a high free nitrous acid concentration (>0.08 mg/L) ensured a nitrite accumulation rate of >95%; and iii) in the anammox unit, a suitable influent NO₂^--N/NH₄⁺-N ratio (the average value of 1.27) was achieved by mixing AD effluent with PN effluent (1:1.78, v/v), contributing to a high TN removal of 78 ± 2.4%. Nevertheless, 980-1560 mg/L of COD remained in the influent of the anammox unit; biorefractory humic acids in this (245.6 ± 3 mg/L) might be the main component that caused the observed 66 ± 2% decrease in anammox activity. The proliferation of denitrifying bacteria and sulfate-reducing bacteria induced by the organic compounds may have led to the observed decline in the abundance of the anammox bacterium Candidatus Kuenenia. The proposed strategy guaranteed the robust operation of the PN-anammox process and provides a promising approach for the sustainable treatment of incineration leachate.

How does the pre-treatment of landfill leachate impact the performance of O3 and O3/UVC processes?

In this study, O₃ and O₃/UVC processes were evaluated for the treatment of landfill leachate after biological nitrification/denitrification, coagulation, or their combinations. The O₃-driven stage efficiency was assessed by the removal of color, organic matter (dissolved organic carbon (DOC) and chemical oxygen demand (COD)), and biodegradability increase (Zahn-Wellens test). Also, fluorescence excitation-emission matrix (EEM) and size exclusion chromatography coupled with OC detector (SEC-OCD) analysis were carried out for each strategy. The bio-nitrified-leachate (L_N) was not efficiently mineralized during the O₃-driven processes since the high nitrites content consumed ozone rapidly. In turn, carbonate/bicarbonate ions impaired the oxidation of the bio-denitrified-leachate (L_D), scavenging hydroxyl radicals (HO^•) and inhibiting the O₃ decomposition. For both bio-leachates, only O₃/UVC significantly enhanced the effluent biodegradability (>70%), but COD legal compliance was not reached. EEM and SEC-OCD results revealed differences in the organic matter composition between the nitrified-coagulated-leachate (L_NC) and denitrified-coagulated-leachate (L_DC). Nonetheless, the amount of DOC and COD removed per gram of ozone was similar for both. Cost estimation indicates the O₃-driven stage as the costliest among the treatment processes, while coagulation substantially reduced the cost of the following ozonation. Thus, the best treatment train strategy comprised L_DC (with methanol addition for denitrification and coagulated with 300 mg Al³⁺/L, without pH adjustment), followed by O₃/UVC (transferred ozone dose of 2.1 g O₃/L and 12.2 kJ_UVC/L) and final biological oxidation, allowed legal compliance for direct discharge (for organic and nitrogen parameters) with an estimated cost of 8.9 €/m³ (O₃/UVC stage counting for 6.9 €/m³).

Integrating hydrological, landscape ecological, and economic assessment during hydropower exploitation in the upper Yangtze River

Comprehensive investigation of hydrological processes associated with landscape ecology and economic development plays a key role in watershed management, and is less developed in watersheds with large-scale cascade dams. With the abundant hydropower resources and its unprecedented advantages, hydropower exploitation in the upper Yangtze River (Jinsha River) is critical to energy structure adjustment in China. Therefore, we integrated hydrological modeling, landscape ecology analysis, and economic analysis in the dammed Jinsha River. With climate variations in the Jinsha River Basin, the average flow near the uppermost dams in the mainstream grew from 796 m³ s^-1 (1990s), to 918 m³ s^-1 (2000s), and further to 1025 m³ s^-1 (2010s). During 1991 to 2017, the source power in the headwater region grew slightly, but varied little in the downstream area. In the lower dammed Jinsha River, analysis of landscape indicators showed that the landscape was enriched, while the landscape type distribution was more uniform. Moreover, hydropower exploitation brought benefits to regional economic development. Principal component analysis further highlighted the landscape ecological and economic variations with high loadings in the first principal component. With the non-significant temporal variations and normal spatial fluctuations in flow discharge, the landscape pattern was basically stable, and the utilization of hydropower can be sustainable in the Jinsha River. In addition, hydropower development drove local economic development. Based on the integrated analysis of hydrological, landscape ecological, and economic assessment at the watershed scale, our results stressed the significance of hydropower exploitation in the Jinsha River. However, more attention should be paid to the warming climate during hydropower exploitation. These findings are valuable for the scientific planning of hydropower bases in watersheds with large-scale cascade dams, and have substantial implications for sustainable hydropower development.

Advances in the characterization and monitoring of natural organic matter using spectroscopic approaches

Natural organic matter (NOM) is ubiquitous in environment and plays a fundamental role in the geochemical cycling of elements. It is involved in a wide range of environmental processes and can significantly affect the environmental fates of exogenous contaminants. Understanding the properties and environmental behaviors of NOM is critical to advance water treatment technologies and environmental remediation strategies. NOM is composed of characteristic light-absorbing/emitting functional groups, which are the "identification card" of NOM and susceptive to ambient physiochemical changes. These groups and their variations can be captured through optical sensing. Therefore, spectroscopic techniques are elegant tools to track the sources, features, and environmental behaviors of NOM. In this work, the most recent advances in molecular spectroscopic techniques, including UV-Vis, fluorescence, infrared, and Raman spectroscopy, for the characterization, measurement, and monitoring of NOM are reviewed, and the state-of-the-art innovations are highlighted. Furthermore, the limitations of current spectroscopic approaches for the exploration of NOM-related environmental processesand how these weaknesses/drawbacks can be addressed are explored. Finally, suggestions and directions are proposed to advance the development of spectroscopic methods in analyzing and elucidating the properties and behaviors of NOM in natural and engineered environments.

Monobutyl phthalate (MBP) induces energy metabolism disturbances in the gills of adult zebrafish (Danio rerio)

Monobutyl phthalate (MBP) is a primary metabolite of an environmental endocrine disruptor dibutyl phthalate (DBP), which poses a potential threat to living organisms. In this research, the acute toxicity of MBP on energy metabolism in zebrafish gills was studied. Transmission electron microscopy (TEM) results show that 10 mg L^-1 MBP can induce mitochondrial structural damage of chloride cells after 96 h of continuous exposure. The activity of ion ATPase and the expression level of oxidative phosphorylation-related genes suggest that MBP interferes with ATP synthesis and ion transport. Further leading to a decrease in mitochondrial membrane potential (MMP) and cell viability, thereby mediating early-stage cell apoptosis. Through a comprehensive analysis of principal component analysis (PCA) and integrated biomarker response (IBR) scores, atp5a1, a subunit of mitochondrial ATP synthase, is mainly inhibited by MBP, followed by genes encoding ion ATPase (atp1b2 and atp2b1). Importantly, MBP inhibits aerobic metabolism by inhibiting the key enzyme malate dehydrogenase (MDH) in the TCA cycle, forcing zebrafish to maintain ATP supply by enhancing anaerobic metabolism.

Operation strategies of n-DAMO and Anammox process based on microbial interactions for high rate nitrogen removal from landfill leachate

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) coupling to Anaerobic ammonium oxidation (Anammox) provides an opportunity for simultaneous nitrogen removal and methane emissions mitigation from wastewater. However, to achieve high nitrogen removal rate in such a process remains a critical challenge in practical application. This work investigated the interactions between n-DAMO and Anammox in membrane biofilm reactor (MBfR) and then developed operational strategies of MBfR for high rate nitrogen removal from landfill leachate. Initially, influent containing nitrate and ammonium facilitated the development of n-DAMO and Anammox microorganisms in MBfR, but nitrogen removal performance is hard to be further improved even deteriorated. Detailed investigations of interactions among n-DAMO and Anammox microorganisms confirmed that extra addition of nitrite into MBfR fed with nitrate and ammonium not only stimulated the activities of Anammox bacteria, but also enhanced the activities of n-DAMO archaea from 172.3 to 356.9 mg NO₃^--N L^-1 d^-1. Functional gene analysis also indicated that mcrA and hzsA genes increased after nitrite addition. Based on this finding, influent containing NO₃^-, NO₂^- and NH₄⁺ enabled nitrogen removal rates of MBfR increase from 224.9 to 888.2 mg N L^-1 d^-1. Finally, nitrate in the influent was gradually replaced with nitrite to mimic the effluent from partial nitriation of landfill leachate, but maintain the nitrate availability for n-DAMO archaea through increasing nitrate production from Anammox. These operation strategies enabled MBfR achieve the steady state with a nitrogen removal rate of 6.1 kg N m^-3 d^-1. Microbial community analysis revealed n-DAMO archaea, n-DAMO bacteria and Anammox bacteria jointly dominated the biofilm, and their relative abundance dynamically shifted with feeding regime. This work provides promising operational strategies for high rate of nitrogen removal from landfill leachate through integrating n-DAMO and Anammox process.

Assessing accuracy, precision and selectivity using quality controls for non-targeted analysis

The benchmarks to assess reproducibility are not well defined for non-target analysis. Parameters to evaluate analytical performance, such as accuracy, precision and selectivity, are well defined for target analysis, but remain elusive for non-target screening analysis. In this study, quality control (QC) guidelines are proposed to assure reliable data in non-target screening methodologies using a simple set of standards. Workflow reproducibility was assessed using an in-house QC mixture containing selected compounds with a wide range of polarity that can be detected either by electrospray ionization (ESI) in positive or negative mode. The analysis was performed by online solid phase extraction (SPE) liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS). Data processing was done by a commercially available software, Compound Discoverer v. 3.0 using an environmental working template, which searched a multitude of databases, including Chemspider, EPA Toxcast, MzCloud among others. We have specifically evaluated method specificity, precision, accuracy and reproducibility in terms of peak area and retention time variability, true positive identification rate, intraday (within days) and interday (consecutive days) variations and the use of QC samples to reduce false positives. The method showed a satisfactory accuracy with an identification rate of ≥70% for most of the QC compounds. Precision estimated based on peak area relative standard deviation (RSD) ranged between 30 and 50% for most of the compounds. Data normalization to a single internal standard did not improve peak area variability. Retention time precision showed great repeatability and reproducibility (RSD ≤ 5%). In addition, a simple model of RT vs log K_ow was designed based on our QC mixtures to efficiently reduced false positives by an average of 49.1%.

Mycoremediation of Old and Intermediate Landfill Leachates with an Ascomycete Fungal Isolate, Lambertella sp

In the present study, an Ascomycete fungal strain, Lambertella sp., isolated from environmental polluted matrices, was tested for the capacity to reduce the contamination and the toxicity of intermediate and old landfill leachates. Batch tests in flasks, under co-metabolic conditions, were performed with two different old leachates, with suspended and immobilized Lambertella sp. biomass, resulting in a soluble chemical oxygen demand depletion of 70% and 45%, after 13 and 30 days, respectively. An intermediate landfill leachate was treated in lab-scale reactors operating in continuous conditions for three months, inoculated with immobilized Lambertella sp. biomass, in absence of co-substrates. The Lambertella sp. depleted the corresponding total organic carbon by 90.2%. The exploitability of the Lambertella sp. strain was evaluated also in terms of reduction of phyto-, cyto-, and mutagenicity of the different Landfill Leachates at the end of the myco-based treatment, resulting in an efficient depletion of leachate clastogenicity.

Analysis of multiclass organic pollutant in municipal landfill leachate by dispersive liquid-liquid microextraction and comprehensive two-dimensional gas chromatography coupled with mass spectrometry

We propose a simple, fast, and inexpensive method for the analyses of 72 organic compounds in municipal landfill leachate, based on dispersive liquid-liquid microextraction and comprehensive two-dimensional gas chromatography coupled with mass spectrometry. Forty-one organic compounds belonging to several classes including hydrocarbons, mono- and polyaromatic hydrocarbons, carbonyl compounds, terpenes, terpenoids, phenols, amines, and phthalates, covering a wide range of physicochemical properties and linked to municipal landfill leachate, were quantitatively determined. Another 31 organic compounds such as indoles, pyrroles, glycols, organophosphate flame retardants, aromatic amines and amides, pharmaceuticals, and bisphenol A have been identified based on their mass spectra. The developed method provides good performances in terms of extraction recovery (63.8-127%), intra-day and inter-day precisions (< 7.7 and < 13.9 respectively), linearity (R² between 0.9669 and 0.9999), detection limit (1.01-69.30 μg L^-1), quantification limit (1.87-138.6 μg L^-1), and enrichment factor (69.6-138.5). Detailed information on the organic pollutants contained in municipal landfill leachate could be obtained with this method during a 40-min analysis of a 4-mL leachate sample, using only 75 μL of extraction solvent.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Treatment train for mature landfill leachates: Optimization studies

In the current study, a treatment train strategy for urban mature leachates, comprising biological and physicochemical processes, was tested for full legal compliance. The leachate presents a high organic and nitrogen content (1.1g C/L; 3.6g O₂/L; 2.0gN/L) and low biodegradability (BOD₅/COD=0.05). In the first stage, a sequential batch reactor (SBR), operated in a 24h-cycle mode (15h aeration +8.5h anoxic, with methanol as external carbon source +0.5h settling), was tested for total nitrogen (TN) removal. The maximum daily TN load that could be treated, reaching the legal limit (< 15mgN/L), increased by 50% with the rise in temperature from 20 to 30°C. For the following coagulation stage, the highest dissolved organic carbon (DOC) removal (64%) and lower final turbidity (33 NTU) were obtained with 240mg Fe³⁺/L, at pH3.0. The jar-tests, comparing nitrified (L_NIT.) and nitrified/denitrified (L_N/D.) leachate, stressed the effect of the leachate alkalinity, generated during the denitrification reaction, on process efficiency. For the coagulated L_N/D., with alkalinity of 1.1g CaCO₃/L, the final concentration of sulfate was only slightly below the legal limit (< 2g/L). A photo-Fenton (PF) oxidation process (pH range of 2.8-3.0, 60mg Fe²⁺/L), as third treatment step, promoted a significant enhancement on leachate biodegradability, consuming 75mM of H₂O₂ and 8.9 kJ/L of accumulated UV energy, to achieve an effluent that can be further biologically treated in compliance with the COD discharge limit (150mg O₂/L) into water bodies. Biological continuous mode tests using a conventional activated sludge process, with an hydraulic retention time (HRT) of 12h, allowed to obtain COD and TSS values (107±3 and 50±2mg/L, respectively) below the legal limit.

Landfill leachate treatment by sorption in magnetic particles: preliminary study

Leachates are still an open issue in environmental protection. Many of the applied methods for their treatment present low efficiency and thus need to be used collectively. In practice reverse osmosis is mostly used, as it is the most effective option, regardless of its cost. Magnetic methods to treat effluents have been used for water and wastewater treatment by the use of magnetic particles together with magnetic separation for the removal of contaminants. However, large-scale applications are few or even non-existent when we deal with complex contaminated media such as landfill leachates, for which not even research studies at laboratorial scale with real samples have been done yet. In this work, we apply for the first time magnetic sorption for the treatment of leachates, and close the full cycle by studying the regeneration and re-use of the magnetic particles; we also study the influence of the concentration of magnetic particles, the use of several pre-treatment methodologies and the type of particle used in the process, in real landfill samples from the waste treatment plant of Salamanca (Spain), for the removal of COD, NO₃^-, NO₂^-, NH₄⁺, Total-N, PO₄^3-, SO₄^2- and Cl^-. Regeneration of the magnetic particles after being used in the sorption stage is also studied, as well as their efficiency regarding their re-use. It is also determined the optimum number of batches for complete desorption and for regeneration of the particles, the effect of successive regeneration and re-use cycles, the use of two different regeneration methods, the efficiency of the desorption, the effect of the quantity of solvent and the influence of the time of sorption. Due to its innovative character and the complexity of the media, this work represents a first preliminary approach and, although some promising results have been obtained, further studies are required to completely understand and evaluate the proposed treatment process.