Investigating landfill leachate toxicity in vitro: A review of cell models and endpoints

Ecotoxicological impacts of landfill sites: Towards risk assessment, mitigation policies and the role of artificial intelligence

Waste disposal in landfills remains a global concern. Despite technological developments, landfill leachate poses a hazard to ecosystems and human health since it acts as a secondary reservoir for legacy and emerging pollutants. This study provides a systematic and scientometric review of the nature and toxicity of pollutants generated by landfills and means of assessing their potential risks. Regarding human health, unregulated waste disposal and pathogens in leachate are the leading causes of diseases reported in local populations. Both in vitro and in vivo approaches have been employed in the ecotoxicological risk assessment of landfill leachate, with model organisms ranging from bacteria to birds. These studies demonstrate a wide range of toxic effects that reflect the complex composition of leachate and geographical variations in climate, resource availability and management practices. Based on bioassay (and other) evidence, categories of persistent chemicals of most concern include brominated flame retardants, per- and polyfluorinated chemicals, pharmaceuticals and alkyl phenol ethoxylates. However, the emerging and more general literature on microplastic toxicity suggests that these particles might also be problematic in leachate. Various mitigation strategies have been identified, with most focussing on improving landfill design or leachate treatment, developing alternative disposal methods and reducing waste volume through recycling or using more sustainable materials. The success of these efforts will rely on policies and practices and their enforcement, which is seen as a particular challenge in developing nations and at the international (and transboundary) level. Artificial intelligence and machine learning afford a wide range of options for evaluating and reducing the risks associated with leachates and gaseous emissions from landfills, and various approaches tested or having potential are discussed. However, addressing the limitations in data collection, model accuracy, real-time monitoring and our understanding of environmental impacts will be critical for realising this potential.

The nematode Caenorhabditis elegans enhances tolerance to landfill leachate stress by increasing trehalose synthesis

The burgeoning issue of landfill leachate, exacerbated by urbanization, necessitates evaluating its biological impact, traditionally overshadowed by physical and chemical assessments. This study harnesses Caenorhabditis elegans, a model organism, to elucidate the physiological toxicity of landfill leachate subjected to different treatment processes: nanofiltration reverse osmosis tail water (NFRO), membrane bioreactor (MBR), and raw leachate (RAW). Our investigation focuses on the modulation of sugar metabolism, particularly trehalose-a disaccharide serving dual functions as an energy source and an anti-adversity molecule in invertebrates. Upon exposure, C. elegans showcased a 60-70% reduction in glucose and glycogen levels alongside a significant trehalose increase, highlighting an adaptive response to environmental stress by augmenting trehalose synthesis. Notably, trehalose-related genes in the NFRO group were up-regulated, contrasting with the MBR and RAW groups, where trehalose synthesis genes outpaced decomposition genes by 20-30 times. These findings suggest that C. elegans predominantly counters landfill leachate-induced stress through trehalose accumulation. This research not only provides insights into the differential impact of leachate treatment methods on C. elegans but also proposes a molecular framework for assessing the environmental repercussions of landfill leachate, contributing to the development of novel strategies for pollution mitigation and environmental preservation.

Identification of prevalent leachate percolation of municipal solid waste landfill: a case study in India

Landfill leachate forms when waste-inherent water and percolated rainfall transfer are highly toxic, corrosive, acidic, and full of environmental pollutants. The release of leachate from municipal solid waste (MSW) landfill sites poses a severe hazard to human health and aquatic life. This study examined the impact of leachate from Delhi's Ghazipur landfill on the nearby groundwater quality. Analysis of leachate samples was done to determine various parameters such as total dissolved solids (TDS), hardness, alkalinity, electrical conductivity, pH, BOD5, COD, nitrate, sulphate, chloride and iron, and presence of coliform bacteria. Significant dissolved elements (22,690-34,525 mg/L) were observed in the samples, indicated by the high conductivity value (1156-1405 mho/cm). However, a stable pH range (6.90-7.80) of leachate samples was observed due to high alkalinity concentrations between 2123 and 3256 mg/L. The inverse distance weighing (IDW) interpolation tool from QGIS 3.22.7 developed spatial interpolated models for each parameter across the Ghazipur area. The IDW interpolated graphs of various parameters over the whole study area confirmed these contaminations. In addition, leachate and groundwater samples were physio-chemically analyzed, and temporal fluctuation in landfill waste has also been studied. The temporal fluctuation results showed that when heat is produced, transmitted, and lost throughout the waste system, the maximum temperature position fluctuates over time. The findings of this study highlight the critical importance of landfill management in reducing groundwater contamination from MSW leachate.

A comprehensive overview on solid waste leachate effects on terrestrial organisms

Leachate is a highly complex waste with high toxicological potential that poses a significant threat to the terrestrial environment. Determining leachate physicochemical parameters and identifying xenobiotics alone is, however, not enough to determine the real environmental impacts. In this context, the use of terrestrial model organisms has been highlighted as a tool in ecotoxicological leachate assessments and as a guiding principle in risk assessments. In this context, this review aimed to present the most current state of knowledge concerning leachate toxicity and the bioassays employed in this evaluation concerning terrestrial plants and animals. To this end, a literature search on leachate effects on terrestrial organisms was carried out using ten search terms, in 32 different combinations, at the Web of Science and Scopus databases. A total of 74 eligible articles were selected. The retrieved studies analyzed 42 different plant and animal species and employed nine endpoints, namely phytotoxicity, genotoxicity, bioaccumulation, antioxidant system, cytotoxicity, reproduction, physiological changes, behavior and lethality. A frequent association of toxic leachate effects with metals was observed, mainly Pb, Cd, Cr, Mg, Zn and Cr, which can cause antioxidant system alterations and cyto- and genotoxicity. These elements have also been associated to reproductive effects in earthworms and mice. Specifically concerning plants, most of the retrieved studies employed Allium cepa in toxicity assays, reporting phytotoxic effects frequently associated to metals and soil parameter changes. Animal studies, on the other hand, mostly employed mice and evaluated genotoxicity and antioxidant system effects. Even with the description of toxic leachate effects in both plants and animals, a lack of knowledge is still noted concerning reproductive, physiological, cytotoxic, and behavioral effects in terrestrial species. We, thus, suggest that further studies be carried out on other animals, advancing our understanding on potential environmental leachate effects, also allowing for human health risk assessments.

Effect-based monitoring of two rivers under urban and agricultural influence reveals a range of biological activities in sediment and water extracts

Chemical contaminants, such as pesticides, pharmaceuticals and industrial compounds are ubiquitous in surface water and sediment in areas subject to human activity. While targeted chemical analysis is typically used for water and sediment quality monitoring, there is growing interest in applying effect-based methods with in vitro bioassays to capture the effects of all active contaminants in a sample. The current study evaluated the biological effects in surface water and sediment from two contrasting catchments in Aotearoa New Zealand, the highly urbanised Whau River catchment in Tāmaki Makaurau (Auckland) and the urban and mixed agricultural Koreti (New River) Estuary catchment. Two complementary passive sampling devices, Chemcatcher for polar chemicals and polyethylene (PED) for non-polar chemicals, were applied to capture a wide range of contaminants in water, while composite sediment samples were collected at each sampling site. Bioassays indicative of induction of xenobiotic metabolism, receptor-mediated effects, genotoxicity, cytotoxicity and apical effects were applied to the water and sediment extracts. Most sediment extracts induced moderate to strong estrogenic and aryl hydrocarbon (AhR) activity, along with moderate toxicity to bacteria. The water extracts showed similar patterns to the sediment extracts, but with lower activity. Generally, the polar Chemcatcher extracts showed greater estrogenic activity, photosynthesis inhibition and algal growth inhibition than the non-polar PED extracts, though the PED extracts showed greater AhR activity. The observed effects in the water extracts were compared to available ecological effect-based trigger values (EBT) to evaluate the potential risk. For the polar extracts, most sites in both catchments exceeded the EBT for estrogenicity, with many sites exceeding the EBTs for AhR activity and photosynthesis inhibition. Of the wide range of endpoints considered, estrogenic activity, AhR activity and herbicidal activity appear to be the primary risk drivers in both the Whau and Koreti Estuary catchments.

Numerical simulation of different pollutant control measures around an old landfill contaminated site: A field scale study

The remediation of contaminated soils is a great challenge for global environmental sciences and engineering. The landfill was a kind of infrastructure to deal with waste from different sources while it would also cause the threat to groundwater. Cut-off walls and pumping wells were usually applied in the landfill to prevent the spread of pollutants to wider areas. However, the combination of using both of methods was rarely analyzed, especially using field data for calibrating and fitting groundwater flow and pollutant transport. 7 monitoring wells were arranged in the study area to survey the subsurface seepage. The pollution monitoring was carried out for a period of 50 days, covering 31 types of inorganic and organic pollutants. The concentration of 2,4,6-trichlorophenol (TCP) was 556.7 times greater than the standard concentration. A coupled numerical model of groundwater flow and pollutant transport was developed to assess the effectiveness of various control methods. Three options were tested, including the implementation of a single cut-off wall as well as a combination of a cut-off wall and a pumping well, for preventing the discharge of pollutants from landfills. The combination of a cut-off wall and a pumping well is the best strategy for removal of TCP. The combination approaches lead to a reduction of pollution plumes by a factor of 11 compared to the case without pollution control measures. The research findings may provide a basis and reference for the application of cutoff walls and pumping well in landfill sites or contaminated groundwater.

The influence of combined treatment of municipal wastewater and landfill leachate on the spread of antibiotic resistance in the environment - A preliminary case study

Environmentally-friendly management of landfill leachate (LL) poses a challenge, and LL is usually co-treated with municipal wastewater in wastewater treatment plants (WWTPs). The extent to which the co-treatment of LL and municipal wastewater influences the spread of antibiotic resistance (AR) in the environment has not been examined to date. Two WWTPs with similar wastewater composition and technology were studied. Landfill leachate was co-treated with wastewater in one of the studied WWTPs. Landfill leachate, untreated and treated wastewater from both WWTPs, and river water sampled upstream and downstream from the wastewater discharge point were analyzed. Physicochemical parameters, microbial diversity, and antibiotic resistance genes (ARGs) abundance were investigated to determine the impact of LL co-treatment on chemical and microbiological contamination in the environment. Landfill leachate increased pollutant concentrations in untreated wastewater and river water. Cotreatment of LL and wastewater could affect the abundance and diversity of microbial communities and the interactions between microbial species. Co-treatment also decreased the stability of microbial co-occurrence networks in the examined samples. The mexF gene was identified as a potential marker of environmental pollution with LL. This is the first study to explore the impact of LL on the occurrence of AR determinants in wastewater and rivers receiving effluents.

Investigation on molecular characteristics of organic compounds during a full-scale landfill leachate treatment process based on non-targeted analysis

In this study, a new methodology for evaluating full-scale landfill leachate treatment processes by non-targeted analysis using comprehensive two-dimensional gas chromatography quadrupole time-of-flight mass spectrometry (GC × GC-QTOF-MS) was proposed. The method revealed the chemical complexity of organic compounds in landfill leachate samples at the molecular level and evaluated the removal efficiency of the anaerobic-anoxic-oxic (A2O) - membrane bioreactor (MBR) - nanofiltration (NF) treatment process in conjunction with multi-level classification of organic compounds. Results showed that the results of non-targeted analysis combined with multi-level classification of organic compounds had a significant correlation with the conventional water quality parameters and can be used to evaluate the treatment process. A total of 2508 organic compounds were detected in 6 samples. 17 emerging contaminants (ECs) with known potentially hazards were detected, including Diisobutyl Phthalate (DIBP), which is toxic to male reproduction and development, and 4-Tert-Butylphenol, which causes endocrine disruption in animals. The removal rate of organic compounds by this full-scale landfill leachate treatment processes reached 79.14%. The anaerobic tank played a crucial role with 64.98% contribution. For compounds, the removal rate of heterocyclics was as high as 94.67%, and the removal rate of aliphatics was poor, only 63.49%. This treatment process had almost perfect removal effect on the steroids in alicyclics and phenols in aromatics, but poor treatment effect on saturated alkanes in aliphatics and naphthenes in alicyclics. This study provides a methodology for accurate assessment of the molecular level of treatment processes, new insights for process optimization in waste treatment plants, and data support for the detection of emerging contaminants. The environmental hazards of landfill leachate can be further evaluated in the future in conjunction with ecotoxicity assessment studies.

Treatment of landfill leachate using photocatalytic based advanced oxidation process - a critical review

Landfill leachate is a discrete volumetric component of municipal solid waste; hence, researchers and professionals are more concerned about it because of its obscurity. Innovative treatment and emerging technologies are being scrutinized to address the treatment of landfill leachate challenges. The leading target of this review was to examine the possibility of removing recalcitrant organic pollutants from landfill leachate by photocatalytic-based advanced oxidation processes. A summary of the systematic applicability of conventional treatment for landfill leachate is provided, with a focus on physico-chemical and biological processes. The biological treatment, such as aerobic and anaerobic digestion, is an excellent technique for treating highly concentrated organic pollutants in the wastewater. However, Leachate can scarcely be treated using conventional techniques since it is enriched with refractory organics and inorganic ions. It is clear from the literature review that none of the available combinations of physico-chemical and biological treatments are entirely relevant for the removal of recalcitrant organic pollutants from leachate. Recently, the photo-assisted TiO2/ZnO oxidation has shown an excessively potential and feasible way to treat landfill leachate. TiO2/ZnO photocatalysis is currently developing to treat recalcitrant organic pollutants from landfill leachate. The effect of operating parameters reveals that pH and temperature affect the reaction rate. The addition of oxidant H2O2 to the TiO2/ZnO suspension suggests that TiO2 leads to an increase in the rate of reaction when compared to ZnO. Photocatalytic remediation technique of landfill leachate would support the goal of environmental sustainability by greatly enhancing the effectiveness of treated leachate reutilization. In this review, the selection of the best photocatalytic treatment for leachate based on its systematic relevance and potential conditions, characteristics, cost-effectiveness, essential controlling, discharge limit, long-term environmental effects, and its future study perspectives are emphasized and discussed.

Process of landfill leachate pretreatment using coagulation and hydrodynamic cavitation oxidation

Landfill leachate poses a threat to the environment and human health, and its complex composition made it difficult to treat. Among the methods for treating landfill leachate, the physicochemical combination method is considered to have significant effectiveness, low cost, and application potential. In this study, we propose a new method of coagulation and hydrodynamic cavitation/chlorine dioxide (HC/ClO2) for treating landfill leachate. The optimal conditions for coagulation and HC/ClO2 treatment were investigated experimentally. Under the optimal conditions for coagulation, the COD removal rate was 60.14%. Under the optimal HC/ClO2 treatment conditions, the COD removal rate was 58.82%. In the combined coagulation and HC/ClO2 process, the COD removal rate was 83.58%. Thus, the proposed method can significantly reduce the organic load before subsequent biological treatment processes, thereby reducing the operation cycles and cost of biological treatment.

Investigation with ESI FT-ICR MS on sorbent selectivity and comprehensive molecular composition of landfill leachate dissolved organic matter

Molecular characterization of landfill leachate dissolved organic matter (LDOM) is essential for developing effective processing techniques. However, the molecular selectivity of extraction method and ionization modes often leads to the bias of molecular characterization of LDOM. Here, seven representative sorbents were selected and electrospray ionization negative ion mode (ESI (-)) and positive ion mode (ESI (+)) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were used to investigate the molecular composition of different LDOM samples. Obvious sorbent selectivity during extraction procedure was observed, resulting in the underestimation of molecular diversity of LDOM from 32.7% to 69.3%. Totally, 14,000-18,000 unique molecules were obtained in a single sample, indicating the unprecedented molecular diversity of LDOM. Lignins, proteins and lipids are three major molecular groups in LDOM, and N or S containing molecules occupied 83%. Although much of total organic carbon was removed during biochemical treatment process, the molecular diversity of LDOM was not reduced because a considerable of bio-recalcitrant molecules was produced. The results uncover the sorbents selectivity and ionization modes selectivity in LDOM analysis and provided a comprehensive change of LDOM molecular composition during biochemical treatment, which benefits the development of accurate methods to remove organic carbon in landfill leachate.

PAHs remediation from hazardous waste landfill leachate using fenton, photo - fenton and electro - fenton oxidation processes - performance evaluation under optimized conditions using RSM and ANN

Polycyclic aromatic hydrocharbons (PAHs) are a class of highly toxic pollutants that are highly detrimental to the ecosystem. Landfill leechate emanated from municipal solid waste are reported to constitute significant PAHs. In the present investigation, three Fenton proceses, namely conventional Fenton, photo-fenton and electro-fenton methods have been employed to treat landfill leehcate for removing PAHs from a waste dumpig yard. Response surface methodology (RSM) and artificial neural network (ANN) methodologies were adopted to optimize and validate the conditions for optimum oxidative removal of COD and PAHs. The statistical analysis results showed that all independent variables chosen in the study are reported to have significant influence of the removal effects with P-values <0.05. Sensitivity analysis by the developed ANN model showed that the pH had the highest significance of 1.89 in PAH removal when compared to the other parameters. However for COD removal, H2O2 had the highest relative importance of 1.15, followed by Fe2+ and pH. Under optimal treatment conditions, the photo-fenton and electro-fenton processes showed better removal of COD and PAH compared to the Fenton process. The photo-fenton and electro-fenton treatment processes removed 85.32% and 74.64% of COD and 93.25% and 81.65% of PAHs, respectively. Also the investigations revelaed the presence of 16 distinct PAH compunds and the removal percentage of each of these PAHs are also reported. The PAH treatment research studies are generally limited to the assay of removal of PAH and COD levels. In the present investigation, in addition to the treatment of landfill leachate, particle size distribution analysis and elemental characterization of the resultant iron sludge by FESEM and EDX are reported. It was revealed that elemental oxygen is present in highest percentage, followed by iron, sulphur, sodium, chlorine, carbon and potassium. However, iron percentage can be reduced by treating the Fenton-treated sample with NaOH.

Potential toxicity of landfill leachate to zebrafish and mung beans

Landfill leachate has become a major public health concern due to its adverse health effects. However, its toxicological effects have not been thoroughly determined because of its complex composition. To address this issue, two model organisms were used in this study, including mung beans and zebrafish. Bean seedlings were exposed to different concentrations of landfill leachate (1%, 5%, 10%, 15%, and 20%, v/v, leachate/deionized water) for 7 days. Low concentrations (1%) of landfill leachate increased the growth of mung beans, whereas high concentrations (15% and 20%) of landfill leachate inhibited the growth and development of seedlings. Furthermore, landfill leachate reduced chlorophyll levels but increased malondialdehyde levels, leading to an increased rate of root-tip micronuclei. Zebrafish embryos were exposed to different concentrations of landfill leachate (0.5%, 1.0%, 1.2%, and 1.5%, v/v, leachate/E3 medium) for 120 h. The results showed that landfill leachate significantly decreased lower levels of hatching rate and heart rate but increased the mortality and malformation rates of embryos. Moreover, 1.0% landfill leachate reduced the frequency of spontaneous movement and the light stimulation reaction of embryos. Embryos exposed to leachate showed less exploratory behavior and fewer mirror attacks in the black and white areas. Our results suggest that exposure to landfill leachate could cause developmental toxicity and genotoxicity in plants and fish. The findings can improve our understanding of the environmental toxicity of landfill leachate and provide additional evidence for its risk assessment and management.

Nutrient recovery from municipal solid waste leachate in the scope of circular economy: Recent developments and future perspectives

Holistically considering the current situation of the commercial synthetic fertilizer (CSF) market, recent global developments, and future projection studies, dependency on CSFs in agricultural production born significant risks, especially to the food security of foreign-dependent countries. The foreign dependency of countries in terms of CSFs can be reduced by the concepts such as the circular economy and resource recovery. Recently, waste streams are considered as a source in order to produce recovery-based fertilizers (RBF). RBFs produced from different waste streams can be substituted with CSFs as input for agricultural applications. Municipal solid waste leachate (MSWL) is one of the waste streams that have a high potential for RBF production. Distribution of the published papers over the years shows that this potential was noticed by more researchers in the millennium. MSWL contains a remarkable amount of nitrogen and phosphorus which are the main nutrients required for agricultural production. These nutrients can be recovered with many different methods such as microalgae cultivation, chemical precipitation, ammonia stripping, membrane separation, etc. MSWL can be generated within the different phases of municipal solid waste (MSW) management. Although it is mainly composed of landfill leachate (LL), composting plant leachate (CPL), incineration plant leachate (IPL), and transfer station leachate (TSL) should be considered as potential sources to produce RBF. This study compiles studies conducted on MSWL from the perspective of nitrogen and phosphorus recovery. Moreover, recent developments and limitations of the subject were extensively discussed and future perspectives were introduced by considering the entire MSW management. Investigated studies in this review showed that the potential of MSWL to produce RBF is significant. The outcomes of this paper will serve the countries for ensuring their food security by implementing the resource recovery concept to produce RBF. Thus, the risks born with the recent global developments could be overcome in this way besides the positive environmental outcomes of resource recovery.

Inhalation bioaccessibility of inhaled triazole fungicides and health risk assessment during spraying

BACKGROUND

Ambient air pollution caused by pesticide drift has received great attention. To accurately evaluate the health risk of inhaled pesticides, bioaccessibility should be considered. However, methods to reliably assess pesticide residues remain limited, hindering the precise estimation of exposure assessment. We aimed to optimize an in vitro method for the inhalation bioaccessibility (IBA) measurement of triazole fungicides and to incorporate this into inhalation exposure assessment during pesticide spraying.

RESULTS

The IBA of triazole fungicides increased logarithmically with extraction duration, plateauing after 6 h. The frequency of agitation displayed a similar pattern, whereas the ratio of solid to liquid between 1/1500 and 1/250 was considerably negatively associated. The predicted values (35.9-53.5%) for IBA based on optimized methodological parameters determined using a response surface methodology showed an acceptable deviation from experimental values (30.7-50.8%), suggesting feasibility for in vitro IBA measurement. Incorporating IBA into calculations of inhalation exposure amount (IE) yielded a value of 8.5 × 10^-7 -2.1 × 10^-5  mg kg^-1  day^-1 , a 50-68% reduction compared to IE based on total amount. Additionally, the safety exposure threshold was determined for triazole fungicides using benchmark dose modelling of data from lung A549 cell proliferation toxicity assays, and in this context, margin of exposure (MOE) values were calculated to be within an acceptable level.

CONCLUSION

This in vitro method supplements bioaccessibility evaluation based on pesticide inhalation exposure, along with the risk to human health. © 2023 Society of Chemical Industry.

Interferences in the yeast estrogen screen (YES) assay for evaluation of estrogenicity in environmental samples, chemical mixtures, and individual substances

The Yeast Estrogen Screen (YES) has a specific mechanism of action that allows for the analysis of estrogenic EDC at low concentrations, and it has been broadly used to estimate the estrogenic potential of environmental samples. However, the experimental parameters of this assay still demand an investigation, such as cell density, incubation time, wavelength on the experimental outcome, cytotoxicity, and estrogenic activity adsorbed on suspended solids. We studied these interferences and applied the assay to single substances, mixtures, and environmental matrices from different sources. The increase in cell density amplifies the assay sensitivity only to a limited extent, while the reduction in incubation time decreased assay sensitivity - although it was not significant for surface water, no differences were observed between estradiol-equivalents derived of 48 h and 72 h measurements. The particulate phase was of utmost importance for the total estrogenic activity of the landfill leachate and surface water. Surface waters, landfill leachates and sediments also showed antiestrogenic activity and the integration of both estrogenic and antiestrogenic endpoints provided deeper insights into the potential risk associated with EDC. This study elucidated experimental interferences that may arise during the implementation and use of this assay, bringing more understanding to experimental parameters during the application of the assay for estrogenicity screening.

Integration of hydrochemical and induced polarization analysis for leachate localization in a municipal landfill

Landfills have been identified as a significant concern to the surrounding surface and groundwater ecosystem because of the discharge of leachate. To tackle the uncertain localization of the contamination plume due to low sampling densities, a combination of hydrochemical analysis and induced polarization survey (IP) is employed to characterize the leachate in a municipal landfill. The polarization effect in the contaminated area is significantly higher than expected for landfill sites, but relatively low chargeability zones (<100 mV/V) indicating the distribution of leachate are observed inside high conductivity (>600 mS/m) areas. With reliable geophysical results confirmed by similar formation factors from both field and laboratory data, the abnormal high polarization effect is influenced by installed steel sheet piles next to the survey cable. In addition, we successfully identify linear relationship between the geophysical responses and dominant inorganic conservative compounds (Cl^- and Na⁺) from the leachate plume. The gentle variations of borehole chemical parameters show that the plume is not affected by a continuous contamination source any more, indicating that the steel sheet pile effectively cut off the contamination from the leachate tanks. In conclusion, the integration of IP and hydrochemical data is an excellent way to locate contaminated zones and monitor the behaviors of leachate plume in the landfill.

The efficient treatment of mature landfill leachate using tower bipolar electrode flocculation-oxidation combined with electrochemical biofilm reactors

Mature landfill leachate contains high concentrations of organic and inorganic compounds that inhibit the performance of conventional biological treatment. Nowadays, few single treatment techniques could fulfill the requirements of cleaning mature landfill leachate. In this study, a tower bipolar electrode flocculation-oxidation (BEF-O) reactor and an electrochemical biofilm reactor (EBR) combine device was constructed to effectively treat mature landfill leachate. And the removal efficiency and mechanism of various pollutants using the BEF-O reactor were investigated. The BEF-O system with the current density of 100 mA/cm² shows excellent treatment efficiency, which can roundly remove most pollutants (NH₄⁺-N, COD and heavy metals, etc.), and increase the bioavailability of the effluent to facilitate subsequent EBR treatment. Benefiting from the metabolic stimulation and population selection effect of electric current on microorganisms, EBR has a denser biofilm, stronger anti-pollution load capacity, superior, and stable pollution treatment efficiency. More importantly, the combined device can reduce the concentrations of COD and NH₄⁺-N from 6410 to 338 mg/L and 4065 to 4 mg/L, respectively, and has an economical energy consumption of 32.02 kWh/(kg COD) and 54.04 kWh/ (kg NH₄⁺-N). To summarize, this research could provide an innovative and industrial application prospect technology for the mature landfill leachate treatment.

Enhanced treatment of landfill leachate by biochar-based aerobic denitrifying bacteria functional microbial materials: Preparation and performance

Objective

In this work, polyvinyl alcohol (PVA) and sodium alginate (SA) were used as entrapped carriers and Artemisia argyi stem biochar (ABC) was used as an absorption carrier to immobilize aerobic denitrifying bacteria screened from landfill leachate, thus a new carbon-based functional microbial material (PVA/SA/ABC@BS) was successfully prepared.

Methods

The structure and characteristics of the new material were revealed by using a scanning electron microscope and Fourier transform infrared spectroscopy, and the performance of the material for treating landfill leachate under different working conditions was studied.

Results

ABC had abundant pore structures and that the surface contained many oxygen-containing functional groups, carboxyl groups, and amide groups, etc. and it had good absorbing performance and strong acid and alkali buffering capacity, which was beneficial to the adhesion and proliferation of microorganisms. After adding ABC as a composite carrier, the damage rate of immobilized particles was decreased by 1.2%, and the acid stability, alkaline stability, and mass transfer performance were increased by 9.00, 7.00, and 56%, respectively. When the dosage of PVA/SA/ABC@BS was 0.017g/ml, the removal rates of nitrate nitrogen (NO₃ ^--N) and ammonia nitrogen (NH₄ ⁺-N) were the highest, which were 98.7 and 59.4%, respectively. When the pH values were 11, 7, 1, and 9, the removal rates of chemical oxygen demand (COD), NO₃ ^--N, nitrite nitrogen (NO₂ ^--N) and NH₄ ⁺-N reached the maximum values, which were 14.39, 98.38, 75.87, and 79.31%, respectively. After PVA/SA/ABC@BS was reused in 5 batches, the removal rates of NO₃ ^--N all reached 95.50%.

Conclusion

PVA, SA and ABC have excellent reusability for immobilization of microorganisms and degradation of nitrate nitrogen. This study can provide some guidance for the great application potential of immobilized gel spheres in the treatment of high concentration organic wastewater.

Abatement of the ecotoxicological risk of landfill leachate by heterogeneous Fenton-like oxidation

Landfill leachates are highly contaminated liquid waste, and their treatment and detoxification are a challenging task. The current system of ecotoxicological risk assessment is complex and time-consuming. It is of fundamental importance to develop simpler and faster tools for the evaluation of the treated liquid waste and for an easier preliminary screening of the most active catalytic formulation/reaction conditions of the Fenton-like process. Here, several analytical techniques have been used for the assessment of the reduction of toxicity of the landfill leachate after Fenton process over copper-zirconia catalyst (ZrCu). Ultraviolet-visible (UV-vis) spectroscopy and absorbable organic halogens (AOX) analysis have been coupled to achieve further insight into the degradation of contaminants. In addition, for the first time, the qualitative abatement of organic compounds is monitored through proton nuclear magnetic resonance (¹H NMR) analysis, providing a new method for evaluating the effectiveness of the treatment. Spectroscopic techniques reveal that the Fenton process induces a significant abatement of the aromatic and halogen compounds (51%) in the landfill leachate with a reduction of the toxicity that has been confirmed by ecotoxicological test with algae. These results validate the investigated tool for a simple rapid preliminary evaluation of the detoxification efficacy.

Enhanced leachate phytodetoxification test combined with plants and rhizobacteria bioaugmentation

Plant combination and rhizobacterial bioaugmentation are the modification of constructed wetlands (CWs) to promote the detoxification of leachate. In this study, characterization of leachate was carried out to ensure the maximum concentration of leachate that did not affect the plant's growth. Herein, the identification of leachate-resistant rhizobacteria is used to determine the type of bacteria that is resistant and has the potential for leachate processing in the next step. The phytodetoxification test is carried out by comparing the addition of rhizobacteria and without the addition of rhizobacteria to detox leachate parameter Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Suspended Solid (TSS), Total Nitrogen (TN), Cadmium (Cd), and Mercury (Hg). Results showed that used plants could still live in the largest leachate concentration of 100%. The rhizobacteria that were identified and bioaugmented in the reactor were Bacillus cereus, Nitrosomonas communis, and Pseudomonas aeruginosa. Phytodetoxification test by a single plant showed the efficiency ranged between 40% and 70%. The addition of rhizobacterial bioaugmentation and plant combination can improve the percentage of COD 80.47%, BOD 84.05%, TSS 80.05%, TN 75.58%, Cd 99.96%, and Hg 90%. These modifications are very influential for leachate detoxification through plant uptake and rhizodegradation processes.

(Anti)estrogenic activity impacted by complex environmental matrices: A DOM and multiphase distribution approach

The presence of estrogenic endocrine disruptors in aquatic environments has been a concern and bioassays are recommended tools for their monitoring. However, the physicochemical properties of contaminants and the environmental matrix features may influence the resultant response. This study aimed to assess this influence on the Yeast Estrogen Screen (YES) assay. Mixtures of 17β-estradiol (E2) and humic acid (HA) were evaluated through the Schild approach aiming to investigate the interactions between estrogens and dissolved organic matter (DOM). Moreover, environmental samples from municipal landfill leachate and wastewater treatment plant (WWTP) influents and effluents were screened for (anti)estrogenic activity at both dissolved and particulate phases. Finally, results were statistically confronted with physicochemical parameters through principal component analysis (PCA). The HA test concentrations strongly reduced the E2 response, even at low levels. Humic substances may not only reduce estrogen bioavailability, but also interfere with the assay mechanism through enzymatic inhibition thus masking the sample estrogenic potential. Landfill leachate had total E2-Eq in the range 1282-2591 ng L^-1, while WWTP influent and effluent were in the range 12.1-41.4 and <DL-2.3 ng L^-1, so estrogenicity was reduced 92% in average. Particulate phase was responsible for 33-100% of measured E2-Eq between matrices, though cytotoxicity occurred in some extracts. Antiestrogenic activity was observed in both phases and might also have masked the estrogenicity of samples. PCA did not resulted in positive correlations supporting a multiphase distribution pattern of estrogenic compounds. Nevertheless, the solids and organic matter characteristics supported the data interpretation. In conclusion, the in vitro YES assay is subjected to factors intrinsic to the environmental sample that can influence on the measured estrogenic response. Therefore, results interpretation should be performed together with organic matter characterization parameters, cytotoxicity and antiestrogenic activity evaluation.

A comprehensive assessment of leachate contamination at a non-operational open dumpsite: mycoflora screening, metal soil pollution indices, and ecotoxicological risks

The final disposal of municipal solid waste (MSW) in dumpsites is still a reality worldwide, especially in low- and middle-income countries, leading to leachate-contaminated zones. Therefore, the aim of this study was to carry out soil and leachate physicochemical, microbiological, and toxicological characterizations from a non-operational dumpsite. The L-01 pond samples presented the highest physicochemical parameters, especially chloride (Cl; 4101 ± 44.8 mg L^-1), electrical conductivity (EC; 10,452 ± 0.1 mS cm^-1), and chemical oxygen demand (COD; 760 ± 6.6 mg L^-1) indicating the presence of leachate, explained by its close proximity to the landfill cell. Pond L-03 presented higher parameters compared to pond L-02, except for N-ammoniacal and phosphorus levels, explained by the local geological configuration, configured as a slope from the landfill cell towards L-03. Seven filamentous and/or yeast fungi genera were identified, including the opportunistic pathogenic fungi Candida krusei (4 CFU) in an outcrop sample. Regarding soil samples, Br, Se, and I were present at high concentrations leading to high soil contamination (CF ≤ 6). Pond L-02 presented the highest CF for Br (18.14 ± 18.41 mg kg^-1) and I (10.63 ± 3.66 mg kg^-1), while pond L-03 presented the highest CF for Se (7.60 ± 1.33 mg kg^-1). The most severe lethal effect for Artemia salina was observed for L-03 samples (LC₅₀: 79.91%), while only samples from L-01 were toxic to Danio rerio (LC₅₀: 32.99%). The highest lethality for Eisenia andrei was observed for L-02 samples (LC₅₀: 50.30%). The applied risk characterization indicates high risk of all proposed scenarios for both aquatic (RQ 375-909) and terrestrial environments (RQ > 1.4 × 10⁵). These findings indicate that the investigated dumpsite is contaminated by both leachate and metals, high risks to living organisms and adjacent water resources, also potentially affecting human health.

Mitochondrial dysfunctions elicited by solid waste leachates provide insights into mechanisms of leachates induced cell death and pathophysiological disorders

Emissions (mainly leachates and landfill gases) from solid waste facilities are laden with mixtures of dangerous xenobiotics implicated with significant increase in various pathophysiological disorders including cancer, and eventual mortality of exposed wildlife and humans. However, the molecular mechanisms of solid waste leachates induce pathophysiological disorders and cell death are still largely unknown. Although, evolving evidence implicated generation of reactive oxygen species and oxidative stress as the possible mechanism. Recent scientific reports are linking reactive oxygen species and mitochondrial dysfunctions as the player mechanism in pathophysiological disorder and apoptosis induced by xenobiotics in solid waste leachates. This systematic review presents an explicit discussion of recent scientific findings on the structural and functional alterations in mitochondria induced by solid waste leachates as the molecular mechanisms plausibly responsible for the pathophysiological disorders, cancer and cell death reported in landfill toxicology and epidemiological studies. This review aims to increase scientific understanding on solid waste leachate induced mitochondria dysfunctions as the key player in molecular mechanisms of solid waste induced toxicity. The findings in this review were mainly from using primary cells, cell lines, Drosophila and fish. Whether the findings will similarly be observed in mammalian test systems in vivo and particularly in exposed humans, remained to be investigated. Improvement in technological advancements, enforcement of legislation and regulations, and creation of sophisticated health surveillance against exposure to solid waste leachates, will expectedly mitigate human exposure to solid waste emissions and contamination of the environment.

Accelerated PAH Transformation in the Presence of Dye Industry Landfill Leachate Combined with Fungal Membrane Lipid Changes

The ascomycete fungus Nectriella pironii, previously isolated from soil continuously contaminated by dye industry waste, was used for the biodegradation of phenanthrene (PHE), benz[a]anthracene (B[a]A), and benz[a]pyrene (B[a]P). The degradation of polycyclic aromatic hydrocarbons (PAHs) by N. pironii was accelerated in the presence of landfill leachate (LL) collected from the area of fungus isolation. The rate of cometabolic elimination of PHE and B[a]P in the presence of LL was, respectively, 75% and 94% higher than in its absence. LC-MS/MS analysis revealed that PAHs were converted to less-toxic derivatives. The parallel lipidomic study showed changes in membrane lipids, including a significant increase in the content of phosphatidylcholine (PC) (almost double) and saturated phospholipid fatty acids (PLFAs) and a simultaneous reduction (twofold) in the content of phosphatidylethanolamine (PE) and unsaturated PLFAs, which may have promoted the fungus to PHE + LL adaptation. In the presence of PHE, an intense lipid peroxidation (fivefold) was observed, confirming the stabilization of the cell membrane and its extended integrity. Determining the course of elimination and adaptation to harmful pollutants is essential for the design of efficient bioremediation systems in the future.

Leachate post-treatment by electrocoagulation process: Effect of polarity switching and anode-to-cathode surface area

In the electrocoagulation process, passivation or corrosion of the electrodes is one of the biggest challenges that cause a drop in treatment effectiveness. In this study, the effect of polarity switching was investigated, for the first time, in an attempt to enhance electrocoagulation treatment's ability to remove chemical oxygen demand (COD) and color from pretreated landfill leachate. Moreover, the ratio of the anode to cathode surface area and rotating electrode were examined in light of experimental results. The effect of different parameters, including the stirring speed, initial leachate pH, electrical current density, anode to cathode surface area ratio, and polarity switching time on system efficiency, was evaluated using the one-factor-at-a-time (OFAT) classical method. According to the results, polarity switching resulted in an almost 18% increase in COD removal, 14% increase in color removal, 13% decrease in electrical energy consumption (EEC), 51% decrease in the specific sludge production (TSS/COD), and improved electrode performance compared to non-polarity switching mode. The findings of this research showed the highest COD and color removal efficiencies, which were 34% and 67%, respectively, in a 120 min period, a stirring speed of 135 rpm, the initial leachate pH of 9, the current density of 14.4 mA/cm², the anode/cathode surface ratio of 0.35, and the polarity switching time of 300 s.

Ecotoxicological responses of Daphnia magna and Eisenia andrei in landfill leachate

Leachate toxicity using bioindicators such as microcrustaceans and earthworms has not been fully elucidated. These bioindicators are traditionally determined through physicochemical and microbiological analyses. The ecotoxicological assessment of leachate using indicator organisms from different environments is a technique to ensure the treatment and safe disposal of this effluent with minimum impact on human health and the environment. The current study aimed to evaluate the ecotoxicological responses of Daphnia magna and Eisenia andrei in landfill leachate, identifying which organism was more sensitive to this effluent. The leachate used in ecotoxicological tests was collected at the Campina Grande Sanitary Landfill (ASCG), Paraíba, Brazil. The leachate sample contained a high content of organic matter in the form of chemical oxygen demand (19496.86 mg.L^-1) and ammoniacal nitrogen (2198.00 mg.NL^-1), in addition to metals with carcinogenic potential, such as Cr (0.64 mg.L^-1) and Fe (1.16 mg.L^-1). The exposure of Daphnia magna to the leachate showed that the effluent is harmful to aquatic organisms, obtaining an EC 50, 48 h = 1.22%, FT of 128 and a TU of 81.96%. Among the contaminant concentrations tested in Eisenia andrei, 57% (59.28 mL.kg^-1) caused the highest lethality, causing the death of 21 earthworms within 72 hours of exposure. The avoidance test showed that exposure to leachate concentrations between 10.38 and 39.86 mL.kg^-1 led to the leakage of earthworms, and habitat loss was observed at a concentration of 55.80 mL.kg^-1, in which leak response (LR) ≥80% was obtained. This study demonstrates that the mentioned organisms are suitable for ecotoxicological tests in landfill leachate. Moreover, the microcrustacean Daphnia magna showed the most significant sensitivity, presenting a rapid ecotoxicological response to the leachate.

A comprehensive investigation of toxicity and pollution potential of municipal solid waste landfill leachate

It is evident from the literature that research on the treatment of leachate generated from municipal solid waste (MSW) landfills has been a focus area of environmental management. However, the available information is discrete because most studies have reported only one or a couple of aspects of either closed or active MSW landfill leachate treatment. Hence, this investigation has focused on comprehensive attributes of both closed landfill leachate (CLL) and active landfill leachate (ALL), including generation, characterisation, and toxicity assessment to quantify and establish their pollution potential. The results indicated that CLL generation is higher (188.59 m³/d) than ALL (49.53 m³/d). The concentrations of principal physical, chemical, and biological constituents and concomitant leachate pollution index were higher in CLL (33.20) than in ALL (26.65). Furthermore, the germination indices of CLL (57.48) and ALL (79.14) and tail DNA damage of CLL (56.49%) and ALL (23.8%) ratified greater phytotoxicity and genotoxicity potential, respectively of CLL over ALL. The reasons for the variations in the generation, characteristics, and toxicity of CLL and ALL were discussed in detail. Evaluation of the commonly used landfill leachate treatment methods through the analytical hierarchy process confirmed that the activated sludge process and Fenton oxidation process are the most and least preferred treatment methods. The comprehensive investigation of CLL and ALL have established their pollution potential and the inevitable necessity for their treatment. The findings of this investigation will serve as a ready reference for researchers from academia and industry who work on the monitoring, treatment, and management of landfill leachate.

Evaluation of disinfection byproducts for their ability to affect mitochondrial function

In the race to deliver clean water to communities through potable water reuse, disinfection and water quality assessment are and will continue to be fundamental factors. There are over 700 disinfection byproducts (DBPs) in water; evaluating each compound is practically impossible and very time consuming. A bioanalytical approach could be an answer to this challenge. In this work, the response of four major classes of DBPs toward mitochondrial membrane potential (ΔΨm) and cytoplasmic adenosine triphosphate (C-ATP) was investigated with human carcinoma (HepG2) cells. Within 90 min of cell exposure, only the haloacetic acid (HAA) mixture caused a cytotoxic response as measured by C-ATP. All four groups (haloacetonitriles (HANs), trihalomethanes (THMs), nitrosamines (NOAs), and HAAs) responded well to ΔΨm, R² > 0.70. Based on the half-maximum concentration that evoked a 50% response in ΔΨm, the response gradient was HANs >> HAAs ∼ THM > NOAs. The inhibition of the ΔΨm by HANs is driven by dibromoacetonitrile (DBAN), while dichloroacetonitrile (DCAN) did not cause a significant change in the ΔΨm at less than 2000 µM. A mixture of HANs exhibited an antagonistic behavior on the ΔΨm compared to individual compounds. If water samples are concentrated to increase HAN concentrations, especially DBAN, then ΔΨm could be used as a biomonitoring tool for DBP toxicity.

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.

Genome-centric metagenomics provides new insights into the microbial community and metabolic potential of landfill leachate microbiota

Landfills are important sources of microorganisms associated with anaerobic digestion. However, the knowledge on microbiota along with their functional potential in this special habitat are still lacking. In this study, we recovered 1168 non-redundant metagenome-assembled genomes (MAGs) from nine landfill leachate samples collected from eight cities across China, spanning 42 phyla, 73 classes, 114 orders, 189 families, and 267 genera. Totally, 74.1% of 1168 MAGs could not be classified to any known species and 5.9% of these MAGs belonged to microbial dark matter phyla. Two putative novel classes were discovered from landfill leachate samples. The identification of thousands of novel carbohydrate-active enzymes showed similar richness level compared to the cow rumen microbiota. The methylotrophic methanogenic pathway was speculated to contribute significantly to methane production in the landfill leachate because of its co-occurrence with the acetoclastic and hydrogenotrophic methanogenic pathways. The genetic potential of dissimilatory nitrate reduction to ammonium (DNRA) was observed, implying DNRA may play a role in ammonium generation in landfill leachate. These findings implied that landfill leachate might be a valuable microbial resource repository and filled the previous understanding gaps for both methanogenesis and nitrogen cycling in landfill leachate microbiota. Our study provides a comprehensive genomic catalog and substantially provides unprecedented taxonomic and functional profiles of the landfill leachate microbiota.

Exposure to Landfill Leachates Affects the Embryonic Development of Zebrafish, Danio rerio: A Case Study in Yucatan, Mexico

We report the chemical characterisation and toxic effects of municipal solid waste landfill leachates on the embryonic development of Danio rerio. The results of the Fourier transform infrared spectroscopy (FTIR) revealed the presence of nitrogen-containing groups and aromatic functional groups associated with highly toxic pollutants such as ammonia and heavy metal-humic complexes. Mortalities of up to 93 and 100% were observed in 1:64 and 1:32 landfill leachate dilutions, v/v, respectively. The hatching percentages of the fish were also severely affected, with very low percentages ranging from 0 to 33.3% for 1:32, 1:64 and 1:128 dilutions, v/v. Morphologically, a developmental arrest was evident for all treatments. This study reveals the high toxicity of landfill leachates that could contaminate the aquifer of the Yucatan Peninsula and threaten the health of living organisms.

Purposely Development of the Adaptive Potential of Activated Sludge from Municipal Wastewater Treatment Plant Focused on the Treatment of Landfill Leachate

Biological treatment is a key technology in landfill leachate treatment However, often its efficiency is not high enough due to the pollutants in concentrations above the critical ones. The present study aimed to investigate the adaptive responses that occur in activated sludge (AS) during landfill leachate purification. A model process with AS from a municipal wastewater treatment plant and landfill leachate in increasing concentrations was constructed. The data showed that when dilutions 25 and 50 times had been applied the structure of the AS was preserved, but the COD cannot be reduced below 209 mg O2/L. The feed of undiluted leachate destroyed the AS structure as SVI was reduced to 1 mL/g, biotic index to 1, floc size was greatly reduced and COD remained high (2526 mg O2/L). The dominant group of protozoa was changed from attached to free-swimming ciliates. An increase of the bacterial groups responsible for the xenobiotics elimination (aerobic heterotrophs, genera Pseudomonas, Acinetobacter, Azoarcus, Thauera, Alcaligenes) was registered. This was accompanied by a significant increase in free bacteria. The obtained data showed that for optimal treatment of this type of water it is necessary to include a combination of biological treatment with another non-biological method (membrane filtration, reverse osmosis, etc.).

Spatial Succession for Degradation of Solid Multicomponent Food Waste and Purification of Toxic Leachate with the Obtaining of Biohydrogen and Biomethane

A huge amount of organic waste is generated annually around the globe. The main sources of solid and liquid organic waste are municipalities and canning and food industries. Most of it is disposed of in an environmentally unfriendly way since none of the modern recycling technologies can cope with such immense volumes of waste. Microbiological and biotechnological approaches are extremely promising for solving this environmental problem. Moreover, organic waste can serve as the substrate to obtain alternative energy, such as biohydrogen (H2) and biomethane (CH4). This work aimed to design and test new technology for the degradation of food waste, coupled with biohydrogen and biomethane production, as well as liquid organic leachate purification. The effective treatment of waste was achieved due to the application of the specific granular microbial preparation. Microbiological and physicochemical methods were used to measure the fermentation parameters. As a result, a four-module direct flow installation efficiently couples spatial succession of anaerobic and aerobic bacteria with other micro- and macroorganisms to simultaneously recycle organic waste, remediate the resulting leachate, and generate biogas.

A sensitive electrochemical sensor for environmental toxicity monitoring based on tungsten disulfide nanosheets/hydroxylated carbon nanotubes nanocomposite

There has been growing concern about the toxic effects of pollutants in the aquatic environment. In this study, a novel cell-based electrochemical sensor was developed to detect the toxicity of contaminants in water samples. A screen-printed carbon electrode, which was low-cost, energy-efficient, and disposable, was modified with tungsten disulfide nanosheets/hydroxylated multi-walled carbon nanotubes (WS₂/MWCNTs-OH) to improve electrocatalytic performance and sensitivity. The surface morphology, structure, and electrochemical property of WS₂/MWCNTs-OH composite film were characterized by emission scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Raman spectroscopy, and electrochemical impedance spectroscopy. Grass carp kidney cell line was utilized as the sensor biorecognition element to determine the electrochemical signals and evaluate cell viability. The sensor was used to detect the toxicity of one typical contaminant (2,4,6-trichlorophenol) and two emerging contaminants (bisphenol AF and polystyrene nanoplastics). The 48 h half inhibitory concentration (IC₅₀) values were 169.96 μM, 21.88 μM, and 123.01 μg mL^-1, respectively, which were lower than those of conventional MTT assay, indicating the higher sensitivity of the proposed sensor. Furthermore, the practical application of the sensor was evaluated in chemical wastewater samples. This study provides an up-and-coming tool for environmental toxicity monitoring.

Landfill soil leachates from Nigeria and India induced DNA damage and alterations in genes associated with apoptosis in Jurkat cell

Landfill soil leachates, containing myriad of xenobiotics, increase genotoxic and cytotoxic stress-induced cell death. However, the underlying mechanism involved in the elimination of the damaged cells is yet to be fully elucidated. This study investigated the apoptotic processes induced in lymphoma (Jurkat) cells by landfill soil leachates from Olusosun (OSL, Nigeria) and Nagpur (NPL, India). Jurkat was incubated with sub-lethal concentrations of OSL and NPL for 24 h and analyzed for DNA fragmentation and apoptosis using agarose gel electrophoresis and Hoechst 33258-PI staining, respectively. Complementary DNA expression profiling of some pro-apoptotic and anti-apoptotic genes regulating apoptosis was also analyzed using real-time PCR (RT-PCR) method. Agarose gel electrophoresis revealed DNA fragmentations in OSL and NPL-treated cells. Hoecsht-33258 - Propidium Iodide (PI) based apoptotic analysis confirmed apoptotic cell death in exposed Jurkat. RT-PCR analysis revealed different fold changes in the pro- and anti-apoptotic genes in OSL and NPL-treated Jurkat. There was significant increase in fold change of the up-regulated genes; apoptosis inducing factor mitochondrion-associated 2 (AIFM2), Fas-associated death domain (FADD), Caspase-2, Caspase-6, BH3 interacting domain death agonist (BID), tumor suppressor (p53), and BCL2 associated agonist of cell death (BAD) and down-regulation of apoptosis inhibitor 5 (API5). Results suggest that OSL and NPL elicited genotoxic stress-related apoptosis in Jurkat. The dysregulation in the expression of genes involved in apoptotic processes in wildlife and human exposed to landfill emissions may increase aetiology of various pathological diseases including cancer.

A combined anaerobic digestion system for energetic brewery spent grain application in co-digestion with a sewage sludge

In the present study, a combined technology for energetic brewery spent grain (BSG) use in co-digestion with sewage sludge (SS) was presented. A holistic approach that includes the impact of co-substrates and their carriers on the anaerobic digestion (AD) process, and the energetic aspects, was involved. Prior to AD, BSG was pretreated involving the hydrodynamic cavitation (HC); two different carriers were applied: MPW (municipal pre-settled wastewater) and mature landfill leachate (MLL). An orifice plate with a conical concentric hole of 3/10 mm (inlet/outlet diameter) was applied as cavitation device. The initial pressure was 7 bar and the number of recirculation passes through the cavitation zone was 30. The AD experiments were performed in semi-flow reactors, under mesophilic conditions at HRT of 20 and 21 d. In both co-digestion series, the constant co-substrate dose of 6% v/v was adopted. In the presence of cavitated BSG and MPW, a significant increase in biogas/methane production was provided as compared to SS mono-digestion, with the related improvement in kinetic constant by 3.5%. The average biogas yield was 0.48 ± 0.03 m³ kg^-1 VS added, while in the control run 0.41 ± 0.03 m³ kg^-1 VS added. Using cavitated BSG and MLL, such a beneficial effect was not observed. In both co-digestion series, slightly lower VS removal (as for the control) and stable process performance occurred. Moreover, the improved energy balance was provided. Due to the technological aspects, only co-digestion of cavitated BSG and MPW with SS is recommended for implementation into a full-scale.

Long-term landfill leachate exposure modulates antioxidant responses and causes cyto-genotoxic effects in Eisenia andrei earthworms

It is estimated that approximately 0.4% of the total leachate produced in a landfill is destined for treatment plants, while the rest can reach the soil and groundwater. In this context, this study aimed to perform leachate toxicity evaluations through immune system cytotoxic assessments, genotoxic (comet assay) appraisals and antioxidant system (superoxide dismutase - SOD; catalase - CAT, glutathione-S-transferase - GST; reduced glutathione - GSH and metallothionein - MT) evaluations in Eisenia andrei earthworms exposed to a Brazilian leachate for 77 days. The leachate sample contained high organic matter (COD - 10,630 mg L^-1) and ammoniacal nitrogen (2398 mg L^-1), as well as several metals, including Ca, Cr, Fe, Mg, Ni and Zn. Leachate exposure resulted in SOD activity alterations and increased CAT activity and MT levels. Decreased GST activity and GSH levels were also observed. Antioxidant system alterations due to leachate exposure led to increased malondialdehyde levels as a result of lipid peroxidation after the 77 day-exposure. An inflammatory process was also observed in exposed earthworms, evidenced by increased amoebocyte density, and DNA damage was also noted. This study demonstrates for the first time that sublethal effect assessments in leachate-exposed earthworms comprise an important tool for solid waste management.

Characterization and treatment of landfill leachate: A review

Landfill leachate is a complicated organic wastewater generated in the sanitary landfilling process. Landfill leachate must be appropriately disposed to avoid ecotoxicity and environmental damage. An in depth understanding of the physiochemical characteristics and environmental behaviors of landfill leachate is essential for its effective treatment. In this study, recent advances on the properties of landfill leachate, its characterization methods and treatment techniques are critically reviewed. Specifically, the up-to-date spectroscopic techniques for landfill leachate characterization and advanced oxidation treatment techniques are highlighted. Moreover, the drawbacks and challenges of current techniques for landfill leachate characterization and treatment are discussed, along with the future perspectives in the development of characterization and treatment approaches for landfill leachate.

Potential toxicity of leachate from the municipal landfill in view of the possibility of their migration to the environment through infiltration into groundwater

Leachate from landfills is a product of complex biological and physicochemical processes occurring during waste storage. In the present study, the toxicity of landfill leachate (LL) to human and bacterial cells was investigated for better understanding of LL environmental toxicity. Studies regarding LL physicochemical properties and cytotoxicity analysis were conducted. In Escherichia coli, Pseudomonas fluorescens, Bacillus subtilis, fibroblasts and melanoma A-375 cells, cell viability assays were applied. For the determination of LL antibacterial activity, twofold dilution series of LL were prepared in the range from 50% to 0.1% (50%, 25%, 12.5%, 6.25%, 3.13%, 1.56%, 0.78%, 0.39%, 0.2%, 0.1%). Human cells viability was examined at LL concentrations of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 5%, 10%, 15%, 20% and 30%. ROS (reactive oxygen species) content and apoptosis level were also measured in bacterial and human cells under the influence of LL. Unexpectedly obtained results indicate stimulation of bacterial viability by LL. Fibroblasts under the influence of LL showed decrease in their viability and increase in apoptosis level and A-375 melanoma cells showed an increase in relative viability and decrease in apoptosis. ROS level in bacterial cells was elevated in higher LL concentrations and decreased in lower LL concentrations. In human cells, ROS content was rather high in both tested cell lines. Presented results indicate cytotoxic potential of analyzed LL and the necessity of LL monitoring because it may pose a health hazard for exposed human populations and the whole human environment.

Lethal and long-term effects of landfill leachate on Eisenia andrei earthworms: Behavior, reproduction and risk assessment

Leachate is difficult to biodegrade, and presents variable physical, chemical and biological characteristics, as well as high toxicological potential for soil, groundwater and water bodies. In this context, untreated leachate toxicity was evaluated through acute and chronic exposures in Eisenia andrei earthworms. Physico-chemical leachate characterizations indicate a complex composition, with high organic matter (COD - 10,634 mg L^-1) and ammoniacal nitrogen (2388 mg L^-1) concentrations. Metals with carcinogenic potential, such as Cr, As and Pb, were present at 0.60, 0.14 and 0.01 μg L^-1, respectively and endocrine disrupting compounds were detected in estradiol equivalents of 660 ± 50 ng L^-1. Acute tests with Eisenia andrei indicated an LC₅₀ (72 h) of 1.3 ± 0.1 μL cm^-2 in a filter paper contact test and 53.9 ± 1.3 mL kg^-1 in natural soil (14 days). The EC₅₀ in a behavioral test was estimated as 31.6 ± 6.8 mL kg^-1, indicating an escape effect for concentrations ranging from 35.0 to 70.0 mL kg^-1 and habitat loss from 87.5 mL kg^-1 of leachate exposure. Chronic exposure (56 days) led to reproduction effects, resulting in a 4-fold decreased cocoon production and 7-fold juvenile decrease. This effect was mainly attributed to the possible presence of endocrine disrupting compounds. An estimated NOAEL of 1.7 mL L^-1 and LOAEL of 3.5 mL L^-1 were estimated for earthworms exposed to the assessed effluent. Extremely high-risk quotients (RQ ≥ 1) were estimated based on leachate application in irrigation. Thus, adequate municipal solid waste management is paramount, especially with regard to generated by-products, which can result in high toxicological risks for terrestrial organisms.

Influence of seasonal temperature change on autotrophic nitrogen removal for mature landfill leachate treatment with high-ammonia by partial nitrification-Anammox process

In this study, a denitrification (DN)-partial nitritation (PN)-anaerobic ammonia oxidation (Anammox) system for the efficient nitrogen removal of mature landfill leachate was built with a zone-partitioning self-reflux biological reactor as the core device, and the effects of changes in seasonal temperature on the nitrogen removal in non-temperature-control environment were explored. The results showed that as the seasonal temperature decreased from 34°C to 11.3°C, the total nitrogen removal rate of the DN-PN-Anammox system gradually decreased from the peak value of 1.42 kg/(m³•day) to 0.49 kg/(m³•day). At low temperatures (<20°C), when the nitrogen load (NLR) of the system is not appropriate, the fluctuation of high NH₄⁺-N concentration in the landfill leachate greatly influenced the stability of the nitrogen removal. At temperatures of 11°C-15°C, the NLR of the system is controlled below 0.5 kg/(m³•day), which can achieve stable nitrogen removal and the nitrogen removal efficiency can reach above 96%. The abundance of Candidatus Brocadia gradually increased with the decrease of temperature. Nitrosomonas, Candidatus Brocadia and Candidatus Kuenenia as the main functional microorganisms in the low temperature.

Wild black rats (Rattus rattus Linnaeus, 1758) as zoomonitor of genotoxicity and systemic toxicity induced by hazardous emissions from Abule Egba unsanitary landfill, Lagos, Nigeria

Wild black rats (Rattus rattus) inhabiting Abule Egba landfill (AEL) were used as zoomonitor to assess health risk associated with exposure to hazardous chemicals from landfills. Twenty five R. rattus (16♂ and 9♀) captured within AEL and 15 (9♂ and 6♀) (control) caught from Iyano Ipaja (10 km away from AEL) were examined for bone marrow micronucleated polychromatic erythrocytes (MNPCE) and polychromatic erythrocytes/normochromatic erythrocytes (PCE/NCE) ratio, abnormal sperm morphology, alterations in hematological indices and erythrocyte morphology, and histopathology of the viscera using standard protocols. There was significant (p < 0.05) increase in MNPCE but decrease PCE/NCE ratio in bone marrow cells of exposed rats than the reference site. MNPCE was insignificantly higher in male than females. Cauda epididymal sperms from exposed rats showed significant high frequency of teratozoospermia. Erythrocyte count, hemoglobin concentrations, percentage hematocrits, mean corpuscular hemoglobin concentrations, leucocyte count, and lymphocytes decreased while mean corpuscular volume, neutrophils, and mean corpuscular hemoglobin increased in the exposed rats compared to the control. Also, abnormal erythrocyte morphology: acanthocytes, codocytes (target cells), schizocytes, and tear drops significantly increased in the exposed rats. Marginal sexual dimorphism was observed between males and females in the incidence of hematological indices. Histopathological lesions including interstitial edema, hemorrhage, lymphoid depletion, cellular infiltrations, proliferation of the alveolar pneumocytes, necrosis, tissue degeneration, and reduced germinal epithelium were observed in the testes, liver, lungs, heart, kidney, and spleen from the exposed rats compared to the control. Some physicochemicals and metals analyzed in leachates from the landfill are capable of inducing genome instability and systemic toxicity in the exposed rats. Rattus rattus exposed to hazardous chemicals from AEL harbored somatic and germ cell mutations, and tissue damage compared to the control rats. We suggest that R. rattus are useful sentinel for genotoxicity and system toxicity assessment of landfill-polluted sites.Graphical abstract.

Evaluation of the Phytotoxicity of Leachate from a Municipal Solid Waste Landfill: The Case Study of Bukov Landfill

Municipal solid waste landfilling, landfilling process and landfill reclamation result in leachate, which may be dangerous to the environment. Municipal solid waste leachate phytotoxicity tests were performed using the toxicity test and a subchronic toxicity pot experiment by direct application of leachate to reference soil in 5, 25, and 50% concentration for a period of 28 days. White mustard (Sinapis alba L.) seeds were exposed to different leachate dilution. Leachate were collected monthly in 2018 in the period from April to September. Furthermore, pH, conductivity, and dissolved oxygen were measured. The inhibition results on Sinapis alba L. seeds in the tested leachate samples ranged from −18.02 to 39.03%. Lower concentration of leachate showed a stimulating effect (only for Sample 1 and Sample 2 at 5% concentration). It was found out that leachate taken at the landfill is phytotoxic. The results of measurements are based on rainfall which affects the quantity and quality of the leachate. The values of germinated seeds/growing plants from the subchronic toxicity pot experiment ranged from 80 to 104%; therefore, the leachate is considered phytotoxic. However, it was confirmed that leachate may be used for landfill irrigation.

Effective treatment of high-salinity landfill leachate using ultraviolet/ultrasonication/ peroxymonosulfate system

Landfill leachate, as a complex medium with a high concentration of organic and mineral materials, is a serious problem for the environment. In the current study, the saline landfill leachate of Bushehr coastal city (Iran) was treated using ultraviolet/ultrasonic waves/peroxymonosulfate system. The initial TOC and TDS of the studied leachate was 915 mg/L and 7390 mg/L, respectively. The system had the maximum efficiency at conditions of pH 3, peroxymonosulfate (PMS) of 4 mM, and reaction time of 150 min. Based on the findings, the initial ratio of BOD₅/COD (0.66) was reduced to 0.38 using the developed system. After treatment of the landfill leachate at the optimal condition, the values of COD, BOD₅, and UV₂₅₄ were reached to 983 mg/L, 348 mg/L, and 10.16 cm^-1, respectively. The concentration of all studied elements (except Pb, As, and Ca) increased after purification. According to the GC-mass spectrometry, the molecular weight and concentration of organic matter in raw leachate were higher than that of the treated one. The studied system had an energy consumption value of 86 kW·h/m³ for the treatment of landfill leachate. The results confirm the effectiveness of the ultraviolet/ultrasonic waves/PMS system for the treatment of high saline landfill leachate.

Studying the mixture effects of brominated flame retardants and metal ions by comet assay

This study was designed to evaluate the sensitivities of diverse cell lines on DNA damage effects and genotoxic effects of three brominated flame retardants (BFRs) and three metal ions (Cu²⁺, Cd²⁺, Hg²⁺) by comet assay. First, THP-1 was identified as the most sensitive cell line in terms of DNA damage among 11 kinds of cells screened. Accordingly, the THP-1 cell line was used as a model in subsequent single/combined genotoxicity tests. Single exposure tests to BFRs or metal ions revealed that the DNA damage effects increased with increasing exposure concentration. In combined exposure tests, BFRs (at concentrations of 1/2 EC₅₀) were deployed in combination with different concentrations of Cu²⁺, Cd²⁺, or Hg²⁺. The results showed that the % tail DNA values were significantly increased by most mixtures. Our findings on combined toxic effects by comet assay provide valuable information for setting valid environmental safety evaluation standards.

UV-Fenton degradation of diclofenac, sulpiride, sulfamethoxazole and sulfisomidine: Degradation mechanisms, transformation products, toxicity evolution and effect of real water matrix

Four common refractory pharmaceuticals, diclofenac (DF), sulpiride (SP), sulfamethoxazole (SMX) and sulfisomidine (SIM) were detected in the Disc Tubular Reverse Osmosis (DTRO) concentrates with higher concentrations ranging from 0.85 to 11.57 μg/L from the local landfill. The effect of complex matrix of DTRO concentrates on the UV-Fenton degradation kinetics of DF, SP, SMX and SIM and their transformation products (TPs) were studied. All the four pharmaceuticals could be degraded more efficiently in the ultrapure water than that in the DTRO-concentrate matrix, which also had a significant negative effect on the kinetic constants of the degradation. Twenty-two out of forty-nine TPs were newly identified by HPLC-QTOF-MS and their peak-area evolution was presented. The main degradation pathways for four pharmaceuticals were identified. When assessing cytotoxicity by using HepG2 cells, there appeared to be an obvious toxicity-increase region for each of SP, SMX and SIM. Eleven TPs were identified as the potential toxicity-increase causing TPs by combination of the QSAR prediction, HepG2 cytotoxicity assessment and peak-area evolution of TPs. Therefore, UV-Fenton process was a promising method for the refractory pharmaceutical degradation even in the complex water matrix and choosing appropriate reaction parameters for the UV-Fenton could eliminate the cytotoxicity of the TPs.

Full-scale MBR applications for leachate treatment in China: Practical, technical, and economic features

Though having been applied for decades in the leachate treatment, membrane bioreactors (MBRs) have not attracted as much attention as their application in the municipal wastewater treatment. A timely survey for full-scale applications of MBRs treating leachate would be necessary to present a thorough knowledge and implication in this field. In this study, 175 full-scale MBRs treating leachate (with individual treatment capacity of ≥100 m³/d) in China were comprehensively analyzed. The accumulative treatment capacity exceeded 65,000 m³/d in 2018, and such projects were primarily distributed in areas with developed economy and large production of municipal solid waste. Sanitary landfill leachate owned 70 % of the leachate-treating MBRs' capacity, while the proportion for incineration plants increased gradually. Synchronously, leachate from incineration plants was more degradable than that from sanitary landfills. MBRs were advantageous to pollutant removal, fouling control, and successive energy mitigation of the whole treatment processes. The investment and footprint of processes adopting MBRs were medially ∼90,000 CNY/(m³/d) and ∼15 m²/(m³/d) respectively, and the energy consumption was 20-30 kW h/m³. The technical and economical applicability and environmental policy forces would strengthen a predictable increment of market share of MBRs in leachate treatment field in the future.