Household hazardous waste in municipal landfills: contaminants in leachate

Assessing the impacts and contamination potentials of landfill leachate on adjacent groundwater systems

Landfilling is a globally prevalent method for managing municipal solid waste disposal. Nonetheless, the potential for serious contamination and the significant regional disparities in the leachate produced pose varying degrees of risks to groundwater quality. Previous studies have focused on a single landfill or the same geo-climatic conditions, with a limited number of samples having resulted in a narrow distribution of landfill age and scale, which prevents the description of the pattern of change in landfill age and scale. As well as the effect of this change on the contaminants in the landfill leachate and surrounding groundwater is still unclear. Therefore, we sampled and analyzed leachate and surrounding groundwater from 62 landfills with different landfill ages, scales, and operating conditions in a region with dense and varied topography and climate. Aim to explore the effects of different landfill ages, scales, and operating conditions on contaminants in leachate and surrounding groundwater. Findings indicate that pollutant profiles in different media are influenced by the age, scale, and operational status of the landfill, and the impact of leachate on pollutant types and concentrations in groundwater is limited. A significant correlation exists between the concentration of contaminants in the groundwater affected by leaching from the impermeable layer and the age and scale of the landfill when compared to the leachate. The contamination potentials posed by different pollutants vary across environmental media. Total dissolved solids and NH4+-N in leachate presented high contamination potentials, whereas elemental metalloids (Mn, Al, Ba, and Fe) in the surrounding groundwater posed high environmental concerns. These insights furnish new avenues for monitoring, identification, and safeguarding against pollutants in landfills and proximate groundwater, which is imperative for the sustainable management of municipal waste.

Neurobehavioral deficits, histoarchitectural alterations, parvalbumin neuronal damage and glial activation in the brain of male Wistar rat exposed to Landfill leachate

Concerns about inappropriate disposal of waste into unsanitary municipal solid waste landfills around the world have been on the increase, and this poses a public health challenge due to leachate production. The neurotoxic effect of Gwagwalada landfill leachate (GLL) was investigated in male adult Wistar rats. Rats were exposed to a 10% concentration of GLL for 21 days. The control group received tap water for the same period of the experiment. Our results showed that neurobehavior, absolute body and brain weights and brain histomorphology as well as parvalbumin interneurons were severely altered, with consequent astrogliosis and microgliosis after 21 days of administrating GLL. Specifically, there was severe loss and shrinkage of Purkinje cells, with their nucleus, and severe diffused vacuolations of the white matter tract of GLL-exposed rat brains. There was severe cell loss in the granular layer of the cerebellum resulting in a reduced thickness of the layer. Also, there was severe loss of dendritic arborization of the Purkinje cells in GLL-exposed rat brains, and damage as well as reduced populations of parvalbumin-containing fast-spiking GABAergic interneurons in various regions of the brain. In conclusion, data from the present study demonstrated the detrimental effects of Gwagwalada landfill leachate on the brain which may be implicated in neuropsychological conditions.

Insights on volatile metals in landfill gas as determined from advanced treatment media

This study analyzed spent activated carbon (AC) from a landfill gas (LFG) treatment system for an expanded suite of lesser studied volatile metals, revealing elevated levels of As and Sb in the LFG, exceeding those previously reported, with minimum average concentrations of 640 µg m-3 and 590 µg m-3, respectively. The annual release of As and Sb through landfill gas was found to be significant, surpassing leachate emissions by an order of magnitude. Extrapolating these findings to all US landfills suggests that the release of As and Sb through landfill gas could be a major, previously overlooked source of these metals in global emission estimates, underscoring the need to include them when developing future inventories. The spent AC was further found to exceed US toxicity limits established for As, classifying it as hazardous waste under US regulations. However, findings suggest that the AC scrubber employed at the landfill effectively prevented substantial releases of As and Sb. This research emphasizes that landfill gas is a primary contributor to environmental release of As and Sb from landfills, even more so than leachate, highlighting the significance of implementing effective LFG treatment measures to mitigate the release of volatile metal emissions.

Utilization of microbial fuel cells as a dual approach for landfill leachate treatment and power production: a review

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

Environmental impacts of an unlined municipal solid waste landfill on groundwater and surface water quality in Ibadan, Nigeria

Environmental and public health concerns grow on the interaction of municipal solid waste (MSW) leachates from unlined waste disposal sites with aquifers in many developing countries. This study investigated the environmental pollution impacts of an unlined MSW landfill at Ajakanga area, Ibadan, southwest Nigeria. Analytical studies indicated that the concentrations of NO₃^-, SO₄^2-, PO₄^3-, NH₄^-, Cl^-, Na, Fe, Mn, Cr, and Mo in the leachate samples exceeded the WHO wastewater discharge limits. Hydrochemical parameters of the groundwater and surface water were within WHO allowable thresholds, except for EC, TDS, Fe, Mn, and Pb in the groundwater and Pb, Cd, and Cu in the surface water, indicating major geogenic and minor MSW leachate impacts on the groundwater and surface water chemistry. Bacteria found in the leachate include Enterobacter cloacae (16.67%), Pseudomonas spp. (14.28%) and Bacillus spp. (9.52%). The geoelectrical imaging data indicated substratum leachate infiltration greater than 10 m deep, which is consistent with the low resistivity values of the topsoil-weathered basement layers. The health risk assessment showed high hazardous index values, indicating health risks of Mn, Cd and Pb in the surface water for the residents around Ajakanga landfill. Hydrochemical data indicated greater impact of the MSW leachates on the surface water than the groundwater, while geophysical data showed greater propensity of the surrounding aquifer to leachate interaction through fractured basement zone with increasing abstraction. Waste site closure and hydrochemical monitoring are suggested measures to mitigate environmental pollution in the study area.

Impacts of garbage classification and disposal on the occurrence of pharmaceutical and personal care products in municipal solid waste leachates: A case study in Shanghai

Leachate generated during the treatment and disposal of municipal solid wastes (MSWs) can be an important source of pharmaceutical and personal care products (PPCPs) in the environment. With the implementation of garbage classification policy in China, the disposal methods of MSWs have changed, while its impacts on the occurrence of PPCPs in the generated leachate remain unknown. In this study, we investigated 49 target PPCPs in the leachates of classified MSWs, i.e. residual waste leachate (RWL) and food waste leachate (FWL), and revealed the influence of garbage classification implementation on the occurrence of PPCPs in leachates to be treated. The results showed the concentration and mass load of target PPCPs in the RWL samples (median values: 34.9 ng/L and 52.3 mg/d, respectively) were significantly higher than those in the FWL samples (median values: 19.3 ng/L and 14.5 mg/d, respectively). Macrolide (ML) antibiotics were the predominant PPCPs in the RWL samples, while in the FWL samples, quinolone (QL) antibiotics exhibited the highest concentration and mass load. The implementation of garbage classification policy led to the reduction of PPCP mass load (from 739 g/d to 262 g/d) in leachates to be treated. The findings are helpful for better designing or managing MSW treatment and disposal processes to minimize the emission of PPCPs from MSW leachates.

Volatile and semi-volatile organic compounds in landfill gas: Composition characteristics and health risks

Gas emitted from landfills contains a large quantity of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs), some of which are carcinogenic, teratogenic, and mutagenic, thereby posing a serious threat to the health of landfill workers and nearby residents. However, the global hazards of VOCs and SVOCs in landfill gas to human health remain unclear. To quantify the global risk distributions of these pollutants, we collected the composition and concentration data of VOCs and SVOCs from 72 landfills in 20 countries from the core database of Web of Science and assessed their human health risks as well as analyzed their influencing factors. Organic compounds in landfill gas were found to primarily result from the biodegradation of natural organic waste or the emissions and volatilization of chemical products, with the concentration range of 1 × 10^-1-1 × 10⁶ μg/m3. The respiratory system, in particular, lung was the major target organ of VOCs and SVOCs, with additional adverse health impacts ranging from headache and allergies to lung cancer. Aromatic and halogenated compounds were the primary sources of health risk, while ethyl acetate and acetone from the biodegradation of natural organic waste also exceeded the acceptable levels for human health. Overall, VOCs and SVOCs affected residents within 1,000 m of landfills. Air temperature, relative humidity, air pressure, wind direction, and wind speed were the major factors that influenced the health risks of VOCs and SVOCs. Currently, landfill risk assessments of VOCs and SVOCs are primarily based on respiratory inhalation, with health risks due to other exposure routes remaining poorly elucidated. In addition, potential health risks due to the transport and transformation of landfill gas emitted into the atmosphere should be further studied.

Machine-learning approaches in geo-environmental engineering: Exploring smart solid waste management

Over the past few decades, increased attention has been paid to domestic waste (DW) generation. DW comprises a large percentage of municipal solid waste (MSW), and its handling and processing involves serious technical issues while also consuming a major portion of municipal budgets. The accurate estimation, prediction, and characterization of DW is an ongoing challenge for many cities, municipalities, and local governments as they strive to implement sustainable strategies for MSW. The main objective of the present study is to estimate and correctly predict DW quantities using machine-learning (ML) algorithms. Several different ML algorithms are used in the research, including linear regression, regression trees, Gaussian process regression, support vector machine, and autoregressive integrated moving average methods for time series analysis. Two case studies are presented in this paper. In the first, domestic waste data covering the period from 2010 to 2021 were collected from the Saudi and Bahrain authorities, and in the second, the domestic waste-generating behavior of a family of eleven members was followed for one month. The results show that the biodegradable and non-biodegradable wastes generated by the family were in the range of 1.7-7.9 kg and 0.0-2.0 kg, respectively, and promising outcomes were obtained using an appropriate selection of input predictors in conjunction with time series analysis. The trained models are validated and tested using several types of evaluation metrics, including calculated residuals, mean square error, root mean square error, and coefficient determination (R²-Score). The latter values are in the range of 0.67-0.85 for the training and testing datasets for many of the predicted waste quantities. The results obtained from the study show that these algorithms can be used to reduce the environmental, economic, and societal impacts of waste by designing a smart waste management engineering system.

A critical review of the occurrence, fate and treatment of per- and polyfluoroalkyl substances (PFASs) in landfills

The aim of this critical review is i) to summarize the occurrence of Per- and polyfluoroalkyl substances (PFASs) in landfills; ii) to outline the environmental fate and transport of PFASs in landfills; iii) to compare the treatment technologies of PFASs in landfill leachate and remediation methods of PFASs in surrounding groundwater; iv) to identify the research gaps and suggest future research directions. In recent years, PFASs have been detected in landfills around the world, among which Perfluoroalkyl acids (PFAAs) especially Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonic acid (PFOS) are mostly studied due to their long-term stability. Short-chain PFASs (<8 carbons) are more common than long-chain PFASs (≧8 carbons) in landfill leachate. PFASs in landfill leachate are eventually transported to the surrounding groundwater, surface water and soil. Some PFASs evaporate from landfills to the ambient air. To avoid the environmental and health risks of PFASs in landfills, new technologies and combined use of existing technologies have been implemented to treat PFASs in landfill leachate. Integrated remediation methods are applied to control the diffusion of PFASs in groundwater surrounding landfills. In future, the mechanisms of PFAAs precursors degradation, the correlation among PFASs in different environmental media around landfills, as well as the environmental behavior and toxic effect of combined pollutants together with PFASs in landfill leachate and surrounding groundwater should be studied.

Efficient peroxymonosulfate activation by biochar-based nanohybrids for the degradation of pharmaceutical and personal care products in aquatic environments

Recently, pharmaceutical and personal care products (PPCPs) have been of wide concern due to their ecological toxicity, persistence, and ubiquity in aquatic environments. Peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) have shown great potential for eliminating PPCPs due to their superior oxidation ability and adaptability. Biochar-based nanohybrids have been employed as emerging catalysts for peroxymonosulfate (PMS) activation. Until now, few researchers have summarized PMS activation by biochar-based catalysts for PPCPs removal. In this review, the types, sources, fates, and ecological toxicities of PPCPs were first summarized. Furthermore, various preparation and modification methods of biochar-based catalysts were systematically introduced. Importantly, the application of activating PMS with biochar-based multifunctional nanocomposites for eliminating PPCPs was reviewed. The influencing factors, such as catalysts dosage, PMS dosage, solution pH, temperature, anions, natural organic matters (NOMs), and pollutants concentration were broadly discussed. Biochar-based catalysts can act as electron donors, electron acceptors, and electron shuttles to activate PMS for the removal of PPCPs through radical pathways or/and non-radical pathways. The degradation mechanisms of PPCPs are correlated with persistent free radicals (PFRs), metal species, defective sites, graphitized degree, functional groups, electronic attributes, and the hybridization modes of biochar-based catalysts. Finally, the current problems and further research directions on the industrial application of biochar-based nanocomposites were proposed. This study provides some enlightenment for the efficient removal of PPCPs with biochar-based catalysts in PMS-AOPs.

American oysters as bioindicators of emerging organic contaminants in Florida, United States

Per- and polyfluoroalkyl substances (PFAS) and phthalate esters (PAEs) are emerging contaminants of higher concern due to their wide industrial and commercial use, toxicity, and potential adverse health effects. In this study, we assessed PFAS and PAEs exposure in American oysters collected in three study sites in Florida, USA. Potential physiological effects of these contaminants were assessed by collecting oyster biometric data, calculating condition indices, and assessing oxidative stress levels in these individuals. Finally, a human health risk assessment was conducted based on the concentrations found in the consumable Tampa Bay (TB) oysters. All PFAS and PAEs compounds assessed in this study were detected in at least one oyster in all study sites. Among all locations, ΣPFAS concentration range was 0.611-134.78 ng·g^-1 and ΣPAEs <0.328-1021 ng·g^-1. Despite the smaller size of Biscayne Bay (BB) oysters, they displayed the highest concentrations of most of the PFAS and PAEs compounds, which is likely associated with population size, and other sources in the area. Condition index (CI) III was smaller in BB oysters, likely indicating a stressed population. Even though BB oysters were the most affected individuals, Marco Island (MI) oysters displayed the highest levels of lipid peroxidation, which can also be associated with environmental factors and decreased food availability. Conversely, TB oysters exhibited the highest levels of hydrogen peroxide, likely indicating a better defense mechanism in TB oysters compared to MI oysters. The human health risk assessment for TB oysters indicated low risk from PFAS and PAEs exposure, but there is no reference dose for other compounds and the human diet is wider than only oysters. Therefore, the risk of contaminant exposure is likely higher. This study demonstrates the value of integrating data on contaminant exposure and physiological responses of bioindicator specimens to better understand how emerging contaminants are affecting marine wildlife.

Evaluating the consequences of household hazardous waste diversion on public health and ecological risks of leachate exposure

Household hazardous waste (HHW) includes approximately 1% of municipal solid waste (MSW), which is related to the lack of efficient separate collection schemes co-disposed with MSW in many countries worldwide. In this research, the effect of HHW diversion on leachate quality and consequent reduction in risks to the environment and human health was investigated. In this regard, physicochemical parameters of MSW leachate samples with and without hazardous fraction were characterized. Next, leachate pollution index (LPI) and associated risks were assessed. The results showed that the source separation of HHW decreases the LPI value by 13.48% and improves the potential of leachate for biological treatment, leading to a reduction in leachate treatment costs and complexity. Based on risk assessment results, HHW diversion could lower cancer risks of organic compounds and heavy metals to acceptable levels for adults and children. Moreover, by the source-separating of HHW, hazard indices for aquatic and terrestrial bioassays reduced by 41.5 and 36%, respectively. Furthermore, despite the comparatively low generated amount of HHW, this fraction should be emphasized due to its unintended effects for public health and the environment.

Comparison between Aliivibrio fischeri and activated sludge microorganisms in the evaluation of the toxic pollutants of leachates from Brazilian landfills

Ecotoxicological assessment of landfill leachate has become a priority to determine its impacts on the ecosystem. Toxicity assays with microorganisms stand out due to their quick response, low cost and ease of testing. In this context, the present study evaluated the acute toxic effects of leachates from two landfills of different ages and modes of operation to bacterium Aliivibrio fischeri and activated sludge microorganisms and the ammonia nitrogen and humic substances (HS) sensitivity to these organisms. Reductions greater than 30% in leachate toxicity were observed after ammonia removal for A. fischeri and activated sludge microorganisms. After 97% removal of HS, the greater reductions in toxicity (44.28 to 79.82%) were verified for microbial species studied, indicating that the organic compounds (measured as chemical oxygen demand, total organic carbon and humic substances) were the primary pollutants responsible for the toxicity of the leachates. Concerning the organisms studied, A. fischeri showed greater sensitivity to the leachates' pollutants compared to the activated sludge microorganisms. Nevertheless, a strong correlation was observed between A. fischeri and activated sludge microorganisms' toxicity responses, suggesting that respirometry assay can be used to determine leachate toxicity.

An integrated approach for modeling uncertainty in human health risk assessment

A human health risk assessment (HHRA) will not remain simple and straightforward when it involves multiple uncertain input variables. Uncertainties in HHRA result from the unavailability and subjectivity of input variables. Though several studies have performed HHRA, the quantification of uncertainty in HHRA under a situation of data scarcity and the simultaneous application of random and non-random input variables have rarely been reported. The present study proposes an integrated hybrid health risk modeling framework involving the concurrent treatment of random and non-random input variables and estimating the uncertainties linked to the input variables in HHRA. The proposed framework presents the flexibility to classify the input variables into fuzzy and probabilistic categories, based on their data availability and provenience nature. The framework is demonstrated over the Turbhe sanitary landfill in Navi Mumbai, India, where the fate and transport of heavy metals in leachate are investigated through LandSim modeling. The present study considers the LandSim-simulated heavy metal concentration and body weight as a random variable and water intake, exposure duration, frequency, bioavailability, and average time as fuzzy variables. Further, the uncertainties in the non-carcinogenic human health risk have been quantified using Monte Carlo simulations, followed by a comprehensive multivariate sensitivity analysis of the proposed framework. High health risk at Turbhe is estimated for the male and female population. This study presents the first effort to quantify the non-carcinogenic human health risks from leachate-contaminated groundwater considering the health risk input variables as non-deterministic. The proposed framework is generic and applicable to any landfill site and will remain unaltered when integrated health risk assessment and uncertainty assessment are performed for the landfill.

Analysis of the possibility of conducting a comprehensive assessment of landfill leachate contamination using physicochemical indicators and toxicity test

The inevitable consequence of the operation of landfills is the emission of leachate, which is considered to be one of the main polluters of the ground and water environment. The leachate contains soluble organic compounds, inorganic contaminants, suspended solids, heavy metals and dangerous substances. The selection of the leachate disposal method requires a comprehensive assessment of its properties. Therefore, the physicochemical parameters and toxicity tests were chosen for a comprehensive assessment of the properties of leachate. Four municipal waste landfills (operational and non-operational) were selected for the study, for which multidimensional statistical analyses were carried out. The study was conducted between the period of April 2018 and December 2019. The comprehensive assessment showed that pollutants in leachate from the analyzed landfills remained at a level which did not allow them to be discharged to water or soil. The presence of substances particularly harmful to the aquatic environment (e.g AN, chromium, copper) may hinder their treatment together with household sewage, as it involves obtaining a permit required under laws. Toxicity of leachate may also be a problem, as it may persist after the treatment process is completed. The values of pH, EC and the concentrations of ON, TDS, TSS, chloride, iron and manganese had the strongest influence on the properties of leachate from all landfills. For operational landfills, these were also calcium concentrations, for non-operational ones COD, TU and the concentrations of TKN, AN, TS, sodium, potassium and magnesium. The mentioned parameters also showed strong correlation with other physicochemical properties of the leachate, which indicate their suitability for the monitoring of leachate and the aquatic environment in the vicinity of municipal waste landfills.

Limiting factors of heavy metals removal during anaerobic biological pretreatment of municipal solid waste landfill leachate

An anaerobic biofilm reactor was used to pretreat a typical municipal solid waste landfill leachate. It was challenging to remove Fe, Pb, and Ni to meet the discharge-to-sewer standards at a hydraulic retention time (HRT) typically used in previous studies. This work further systematically studied the factors that limited the metal removal. The HRT limited metal removal because the required metal sulfides precipitation time was more than 3.5 times of the HRT. Sulfide availability only slightly limited the metal removal since adding sulfate above the stoichiometric requirement improved the metal removal by only 5-11%. Via experiments combined with modeling, it was found that metal bisulfide was the dominant complex that limited Fe removal, but humic acids-metal complex was the dominant complex that limited the removal of Pb and Ni. When the total dissolved sulfide concentration is <18 mg/L, humic substances are more limiting the removal of the three metals than bisulfide. On the other hand, when the total dissolved sulfide concentration is >250 mg/L, bisulfide is more limiting than humic substances.

Household hazardous waste characterization and quantification at source in Thailand

Thailand is facing a management crisis of both urban and rural household hazardous waste (HHW). The collection and disposal of these wastes threaten both the environment and human health. The objective of the study was to investigate the characterization and quantification of household hazardous waste at source by all local administrations in Nakhon Nayok province, Thailand. The quantity of HHW in the household waste stream constitutes 2.53% of total household wastes (about 2.90 t/day). Most HHWs were generated in the local administration level (3.2%) followed by the subdistrict (2.9%) and municipality level (1.2%). The characterization of HHWs included paint products (20.1%), household batteries (17.4%), and unused medicines (14.1%). HHW characterization can be grouped as automobile products from municipalities (38.5%), paint and its containers from the subdistricts (43.08%), and pesticides from the more rural local administrations (24.73%). Albeit the amount of HHW waste found in the household waste stream is relatively small compared to the overall waste stream, it can still cause significant damage to human health and environment. This is because the elements and compounds that comprise hazard wastes are toxic at very low levels. Programs are needed to increase appropriate management of HHW to mitigate human health and environmental contamination risks. Reducing and separating HHW at source can minimize these problems during both normal and pandemic situations.Implications: The study of household hazardous waste (HHW) characterization and quantification is very importance for HHW management, especially study at source. In this study we found the smallest province in Thailand can produce HHW volume nearly three tons per day. The trend in consumption of household products may be increase. The government should therefore be more focused on HHW at source management in both normal and pandemic situations.

A nature-based solution to a landfill-leachate contamination of a confined aquifer

Remediation of groundwater from landfill contamination presents a serious challenge due to the complex mixture of contaminants discharged from landfills. Here, we show the significance of a nature-based solution to a landfill-contaminated aquifer in southeast Norway. Groundwater physicochemical parameters monitored for twenty-eight years were used as a proxy to infer natural remediation. Results show that concentrations of the major chemical variables decreased with time and distance until they tailed off. An exception to this was sulphate, which showed an increase, but apparently, exhibits a stationary phase. The water types were found to be most similar between samples from active landfill and post-closure stages, while samples from the stabilised stage showed a different water type. All the chemical parameters of samples from the stabilised stage were found to be within the Norwegian drinking water standards, except iron and manganese, which were only marginally above the limits, an indication of a possible recovery of this aquifer. The findings highlight the significance of natural attenuation processes in remediating contaminated aquifers and have significant consequences for future contamination management, where natural remediation can be viewed as an alternative worth exploring. This is promising in the wake of calls for sustainable remediation management strategies.

Identification of Groundwater Pollution Characteristics and Health Risk Assessment of a Landfill in a Low Permeability Area

The shallow weathering fissure groundwater in the red-bed area of Southwest China is usually the only drinking water source for most rural residents. In this study, a typical landfill with surrounding residents drinking unpurified groundwater in red-bed area was selected and water quality detection, groundwater numerical simulation and human health risk assessment were used to identify and assess groundwater pollution in the region. The chemical type evolved from HCO₃-SO₄-Ca-Mg and HCO₃-SO₄-Ca to Na-Ca-Cl-HCO₃ contaminated by the landfill. Na⁺ and Cl⁻ were selected as factors for rapid identification of groundwater pollution. Subsequent analyses using these factors showed that the leachate pollution plume boundary was 190 m downstream of the landfill. Analysis of the redox conditions revealed that the area from the landfill to 5 m downstream was the reduction zone, while the area beyond 5 m was the oxidation zone. The migration and attenuation patterns of inorganic salts (such as SO₄²⁻) and heavy metals (such as Fe and Mn) in the oxidation and reduction zones differed obviously. Meanwhile, the organic pollutants in the leachate were reduced and decomposed into organic acids, which caused the groundwater 80 m downstream of the landfill to become weakly acidic (pH ranged from 6.51 to 6.83), and promoted re-entry of adsorbed heavy metals (such as Pb) into the groundwater. The groundwater risk assessment based on human health revealed that lead, manganese, chlorobenzene, dichloroethane and chloroform constituted a major health threat to the residents. The rank of non-carcinogenic risk was lead >manganese, and the maximum area of non-carcinogenic risk was 15,485 m². The total carcinogenic risk caused by organic pollutants was 7.9 × 10⁻⁶, and the area of the carcinogenic risk zone was 11,414 m². Overall, the results of this study provide a scientific basis for management of drinking water and groundwater remediation in the red-bed area with low permeability.

Bioelimination of low methane concentrations emitted from wastewater treatment plants: a review

Sewage from residents and industries is collected and transported to wastewater treatment plants (WWTPs) with sewer networks. The operation of WWTPs results in emissions of greenhouse gases, such as methane (CH₄), mostly due to sludge anaerobic digestion. Amounts of emissions depend on the source of influent, i.e. municipal and industrial wastewater as well as sewer systems (gravity and rising). Wastewater is the fifth-largest source of anthropogenic CH₄ emissions in the world and represents 7-9% of total global CH₄ emissions into the atmosphere. Global wastewater CH₄ emission grew by approximately 20% from 2005 to 2020 and is expected to grow by 8% between 2020 and 2030, which makes wastewater an important CH₄ emitter worldwide. This review initially considers the emission of CH₄ from WWTPs and sewer networks. In the second part, biotechniques available for biodegradation of low CH₄ concentrations (<5% v/v) encountered in WWTPs have been studied. The paper reviews major bioreactor configurations for the treatment of polluted air, i.e. biotrickling filters, bioscrubbers, two-liquid phase bioreactors, biofilters, and hybrid reactor configurations, after which it focuses on CH₄ biofiltration systems. Biofiltration represents a simple and efficient approach to bio-oxidize CH₄ in waste gases from WWTPs. Major factors influencing a biofilter's performance along with knowledge gaps in relation to its application for treating gaseous emissions from WWTPs are discussed.

Removal of decidedly lethal metal arsenic from water using metal organic frameworks: a critical review

Water contamination is worldwide issue, undermining whole biosphere, influencing life of a large number of individuals all over the world. Water contamination is one of the chief worldwide danger issues for death, sickness, and constant decrease of accessible drinkable water around the world. Among the others, presence of arsenic, is considered as the most widely recognized lethal contaminant in water bodies and poses a serious threat not exclusively to humans but also towards aquatic lives. Hence, steps must be taken to decrease quantity of arsenic in water to permissible limits. Recently, metal-organic frameworks (MOFs) with outstanding stability, sorption capacities, and ecofriendly performance have empowered enormous improvements in capturing substantial metal particles. MOFs have been affirmed as good performance adsorbents for arsenic removal having extended surface area and displayed remarkable results as reported in literature. In this review we look at MOFs which have been recently produced and considered for potential applications in arsenic metal expulsion. We have delivered a summary of up-to-date abilities as well as significant characteristics of MOFs used for this removal. In this review conventional and advanced materials applied to treat water by adsorptive method are also discussed briefly.

Organic contaminants of emerging concern in leachate of historic municipal landfills

Many types of contaminants of emerging concern (CECs), including per- and poly-fluoroalkyl substances (PFAS), have been found in leachate of operating municipal landfills. However, there is only limited information on CECs presence in leachate of historic landfills (≥3 decades since closure, often lacking engineered liners or leachate collection systems) at concentrations that may pose a risk to nearby wells and surface water ecosystems. In this study, 48 samples of leachate-impacted groundwater were collected from 20 historic landfills in Ontario, Canada. The CECs measured included artificial sweeteners (ASs), PFAS, organophosphate esters (OPE), pharmaceuticals, bisphenols, sulfamic acid, perchlorate, and substituted phenols. The common presence of the AS saccharin, a known indicator of old landfill leachate, combined with mostly negligible levels of the AS acesulfame, an indicator of modern wastewater, revealed that most samples were strongly influenced by leachate and not cross-contaminated by wastewater (which can contain these same CECs). Several landfills, including ones closed in the 1960s, had total PFAS concentrations similar to those previously measured at modern landfills, with a maximum observed here of 12.7 μg/L. Notably elevated concentrations of several OPE, sulfamic acid, cotinine, and bisphenols A and S were found at many 30-60 year-old landfills. There was little indication of declining concentrations with landfill age, suggesting historic landfills can be long-term sources of CECs to groundwater and that certain CECs may be useful tracers for historic landfill leachate. These findings provide guidance on which CECs may require monitoring at historic landfill sites and wastewater treatment plants receiving their effluent.

Rainfall Influences Occurrence of Pharmaceutical and Personal Care Products in Landfill Leachates: Evidence from Seasonal Variations and Extreme Rainfall Episodes

Unused or expired pharmaceutical and personal care products (PPCPs) are usually discharged into municipal solid wastes, then travel to landfills, and eventually percolate into leachates. However, knowledge of their occurrence and temporal dynamics in leachates is limited, making landfill leachate an underappreciated emission source of PPCPs. Furthermore, the differences in PPCP variations in landfill leachates emphasize the necessity for identifying the influencing factors and elucidating the mechanisms for PPCP fluctuations. In this study, successive monthly monitoring of PPCPs in leachates throughout an entire year was performed to determine their seasonal variations and identify their influencing factors. Furthermore, five pairs of additional sampling campaigns were conducted before and after rainfall events during wet seasons to elucidate the influencing mechanisms. The results showed that there was a distinct seasonal variation in PPCPs in landfill leachates-elevated levels during the wet period (from April to September, with a mean concentration of 17.0 μg/L for total monitored PPCPs)-when compared to other months (mean concentration of 3.8 μg/L). Rainfall played a considerable role in mediating PPCP concentrations in leachates. The PPCP responses to five rainfall episodes further verified the influence of rainfall and demonstrated that the tendency to PPCP concentration increase was related to rainfall precipitation. Torrential rain events (i.e., 24 h cumulative precipitation of 50-99.9 mm) led to the most significant increases in PPCP concentrations in landfill leachates. In addition, the hydrophilicity of PPCPs contributed to the different fluctuations during the 1 year investigation and different responses to rainfall. To the best of our knowledge, this study provides the first direct evidence supporting the influence of rainfall on PPCPs in landfill leachates, which can help better understand the occurrence and behavior of emerging contaminants in this underappreciated emission source.

Characterizing Seasonal Variation in Landfill Leachate Using Leachate Pollution Index (LPI) at Nam Son Solid Waste Landfill in Hanoi, Vietnam

The improper treatment of landfill leachates is one of the major problems associated with waste landfilling and causes serious environmental pollution at waste landfill sites and their surroundings. To develop a suitable landfill leachate treatment system and to minimize the risk of environmental pollution, it is important to characterize seasonal and temporal variations of landfill leachates. This study investigated the leachate quality of the Nam Son waste landfill in Hanoi, Vietnam in 2017–2019 and characterized the potential risks of landfill leachate using a leachate pollution index (LPI). The results of this study showed that the seasonal and temporal variation of the overall LPI during the monitoring period was small and in the range of 20–25 (values 2.5 times higher than the maximum permissible limits of Vietnam National Technical Regulation on Industrial Wastewater). The LPI sub-indices attributed to organic and inorganic pollutants were major components of the LPI. Especially, the annually averaged values of LPI of inorganic pollutants were 7.7 times higher than the maximum permissible limits, suggesting that the treatment of inorganic pollutants, such as ammonium-nitrogen (NH4+–N) and total nitrogen (TN), is highly required at Nam Son landfill to prevent environmental pollution surrounding the landfill site.

Cyclodextrin-based adsorbents for the removal of pollutants from wastewater: a review

Water is a vital substance that constitutes biological structures and sustains life. However, water pollution is currently among the major environmental challenges and has attracted increasing study attention. How to handle contaminated water now mainly focuses on removing or reducing the pollutants from the wastewater. Cyclodextrin derivatives, possessing external hydrophilic and internal hydrophobic properties, have been recognized as new-generation adsorbents to exert positive effects on water pollution treatment. This article outlines recent contributions of cyclodextrin-based adsorbents on wastewater treatment, highlighting different adsorption mechanisms of cyclodextrin-based adsorbents under different influencing factors. The crosslinked and immobilized cyclodextrin-based adsorbents all displayed outstanding adsorption capacities. Particularly, according to specific pollutants including metal ions, organic chemicals, pesticides, and drugs in wastewater, this article has classified and organized various cyclodextrin-based adsorbents into tables, which could pave an intuitive shortcut for designing and developing efficient cyclodextrin-based adsorbents for targeted wastewater pollutants. Besides, this article specially discusses cost-effectiveness and regeneration performance of current cyclodextrin-based adsorbents. Finally, the challenges and future directions of cyclodextrin-based adsorbents are prospected in this article, which may shed substantial light on practical industrial applications of cyclodextrin-based adsorbents.

Trace gas emissions from municipal solid waste landfills: A review

Trace gas emissions from municipal solid waste (MSW) landfills have received increasing attention in recent years. This paper reviews literature published between 1983 and 2019, focusing on (i) the origin and fate of trace gas in MSW landfills, (ii) sampling and analytical techniques, (iii) quantitative emission measurement techniques, (iv) concentration and surface emission rates of common trace compounds at different landfill units and (v) the environmental and health concerns associated with trace gas emissions from MSW landfills. Trace gases can be produced from waste degradation, direct volatilisation of chemicals in waste products or from conversions/reactions between other compounds. Different chemical groups dominate the different waste decomposition stages. In general, organic sulphur compounds and oxygenated compounds are connected with fresh waste, while abundant hydrogen sulphide, aromatics and aliphatic hydrocarbons are usually found during the methane fermentation stage. Selection of different sampling, analytical and emission rate measurement techniques might generate different results when quantifying trace gas emission from landfills, and validation tests are needed to evaluate the reliability of current methods. The concentrations of trace gases and their surface emission rates vary largely from site to site, and fresh waste dumping areas and uncovered waste surfaces are the most important fugitive emission sources. The adverse effects of trace gas emission are not fully understood, and more emission data are required in future studies to assess quantitatively their environmental impacts as well as health risks.

A review of the treatment options for marine plastic waste in South Africa

Marine plastic is a major worldwide challenge, for which many solutions are being proposed. However, most of the solutions focus on the prevention and collection of the plastic, with little emphasis on the development of waste treatment options. This review seeks to propose areas where further studies could assist to close gaps in knowledge. Some identified gaps include a poor understanding of the quantities and composition of marine plastics, a lack of information about existing marine plastic treatment technologies, and the environmental impact of the available options. To better understand the capabilities of the current South African plastics recycling industry, data from the South African Waste Information Centre (SAWIC) are reported and discussed. While there is a lack of technology development for the treatment of marine plastic globally, the intention of this review is to drive research in this area by creating awareness and encouraging implementation of possible treatment technologies.

Leftover drug disposal: Customer behavior, pharmacist recommendations, and obstacles to drug take-back box implementation

Production and use of pharmaceuticals in the United States is high and continues to grow. This, combined with poor wastewater removal rates for drugs in excreted waste, and improper pharmaceutical disposal leads to the presence of pharmaceuticals in fresh- and marine waters and wildlife. In the United States, safe drug take-back boxes, or dropboxes, were established in pharmacies after federal legislation passed in 2014, allowing for year-round safe collection of leftover pharmaceuticals. The overarching objective of this work was to identify opportunities for improving access to proper pharmaceutical disposal. We assessed consumer behavior regarding drug disposal choices and knowledge of dropboxes at pharmacies, investigated pharmacist attitudes toward and recommendations about leftover drug disposal, and compared responses at locations with and without dropboxes. We also explored obstacles to dropbox adoption and usage. We found that customer awareness of dropboxes as well as knowledge about risks of improper disposal are low, however awareness was greater at pharmacies with dropboxes. Additionally, pharmacists at dropbox locations were more consistent in their messaging to customers, more likely to recommend proper disposal methods, and more supportive of drug take-back programs. Through a focus group, we learned that further consumer education would overwhelm the capacity of the existing dropboxes. Based on our findings, we recommend solutions to improper disposal focus on legislation mandating dropboxes at pharmacies and pressure on the pharmaceutical industry to fund proper disposal of unused pharmaceuticals.

Metagenomic Analysis of the Microbial Diversity in Solid Waste from Okhla Landfill, New Delhi, India

The Okhla landfill site is consistently in the news for having pollution levels higher than the city average. Here, we report the taxonomic characterization of the microbial diversity of Okhla landfill solid waste. The metagenome analyses revealed the microbial and metabolic diversity of the site.

Differences in the Composition of Leachate from Active and Non-Operational Municipal Waste Landfills in Poland

Leachate formation is one of the many environmental hazards associated with landfilling. The leachate may migrate from the landfill to surface water and groundwater, posing a potential threat to aquatic ecosystems. Moreover, its harmful effect on human health and life has been proven. Due to the risks that landfill leachates may pose, it is necessary to control the state of the environment in their surroundings. The paper presents an example of the application of selected statistical methods (basic statistics, statistical tests, principal component analysis) to assess the impact of individual pollution indicators on the quality of landfill leachates. The conducted analysis showed the existence of significant differences between the surveyed active (Legnica, Jawor) and non-operational (Wrocław, Bielawa) landfills in Poland. These differences were especially visible in the cases of the following: electric conductivity (EC) (non-operational landfills 1915–5075 μS/cm, active 5093–11,370 μS/cm), concentrations of total Kjeldahl nitrogen (TKN) (non-operational landfills 0.18–294.5 mg N/dm3, active 167.56–907.4 mg N/dm3), chemical oxygen demand (COD), organic nitrogen (ON), ammonium nitrogen (AN), total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), sulfates, chlorides, sodium, potassium, calcium, magnesium and nickel. Selected indicators should help to determine the progress of decomposition processes inside the landfill and the potential impact of leachate on the environment, and should be used in the mandatory monitoring of landfills.

Emerging contaminants removal from effluents with complex matrices by electrooxidation

The electrooxidation of methiocarb and bisphenol A was studied in complex matrices, namely, simulated and real sanitary landfill leachate samples, using a boron-doped diamond anode. With simulated sanitary landfill leachate samples, the influence of the type and ratio of carbon source (glucose/humic acid) and electrolyte (NaCl or Na₂SO₄) on the emerging contaminants removal was assessed. Using real sanitary landfill leachate, the influence of current density was evaluated. The experimental results showed that electrooxidation, using a boron-doped diamond anode, can be successfully utilized to degrade methiocarb and bisphenol A when present in complex matrices, such as sanitary landfill leachate, and that methiocarb is more easily oxidized than bisphenol A. Furthermore, it was found that the presence of chloride and high humic acid content increases emerging contaminants removal rate, showing that electrooxidation at boron-doped diamond is particularly adequate to solve the problems raised by sanitary landfill leachate, even when contaminated with emerging contaminants.

Concentrating Per- and Polyfluoroalkyl Substances (PFAS) in Municipal Solid Waste Landfill Leachate Using Foam Separation

Large volumes of per- and polyfluoroalkyl substances (PFAS)-contaminated wastewaters, such as municipal solid waste landfill leachates, pose a challenge for PFAS treatment technologies in practice today. In this study, the surfactant properties of PFAS were exploited to concentrate the compounds in foam produced via the bubble aeration of landfill leachate. The effectiveness of the foaming technique for concentrating PFAS varied by compound, with a mean removal percentage (the percent difference between PFAS in leachate before and after foam removal) of 69% and a median removal percentage of 92% among the 10 replicate foaming experiments. This technique appears to be similarly effective at sequestering sulfonates and carboxylate PFAS compounds and is less effective at concentrating the smallest and largest PFAS molecules. The results of this study suggest that for the pretreatment or preconcentration of landfill leachates, foaming to sequester PFAS may provide a practical approach that could be strategically coupled to high-energy PFAS-destructive treatment technologies. The process described herein is simple and could feasibly be applied at a relatively low cost at most landfills, where leachate aeration is already commonplace.

Groundwater contamination from a municipal landfill: Effect of age, landfill closure, and season on groundwater chemistry

Groundwater reservoirs continue to be threatened globally, mainly from anthropogenic activities. There is need to understand how remediation of groundwater can be influenced by site-specific factors. There are few studies, if any, that incorporate at least three site-specific factors in a single investigation of groundwater contamination from landfills. We report a study where waste age, landfill closure, and season were compared with changes in water quality, using a twenty-four-year groundwater chemistry dataset. Groundwater samples were extracted from monitoring wells and analysed for twenty-eight physicochemical parameters. Results showed discharge of both legacy pollutants and elevated inorganic pollutants into the groundwater. Among the site-specific factors, waste age was the most influential. At the landfill age of 21 years, concentrations of pollutants became close to the reference value. The result also indicated that closing the landfill caused significant decrease in concentrations of contaminants in the groundwater (P < 0.05). Season was the least influential, registering significant results only for dissolved oxygen, sulphate and chloride (P < 0.05). Lastly, the result showed strong attenuation of pollutants with distance, thereby demonstrating the feasibility of the aquifer acting as a natural treatment plant to the pollutants. This eliminates any serious environmental risk associated with the emanating leachate, but at a cost of prohibiting abstraction of the groundwater for human use, due to potential health risks.

Simultaneous Stripping of Ammonia from Leachate: Experimental Insights and Key Microbial Players

Air stripping is commonly used to remove the ammonia in multistage treatment systems for municipal landfill leachate (LFL). This paper proposes a novel approach combining the process of stripping with biological removal of ammonia, based on simultaneous nitrification and denitrification (SND) in a single hybrid sequencing batch reactor (HSBR). To avoid the accumulation of free ammonia (N-FAN), the shallow aeration system was used for the treatment of raw LFL with N-TAN level of 1520 mg/L and pH 9.24. The mean N-FAN removal efficiency of 69% with the reaction rate of 55 mg L−1 h−1 and mean ammonium (N-NH4+) removal efficiency of 84% with the reaction rate of 44 mg L−1 h−1 were achieved within a month in such an HSBR (R1). The comparative HSBR (R2), with conventional aeration system maintaining the same concentration of dissolved oxygen (DO ≤ 1 mg/L), was removing only trace amounts of N-FAN and 48% of N-NH4+. The quantitative analysis of 16S rRNA genes indicated that the number of total bacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Beta- and Gammaproteobacteria increased during the operation of both HSBRs, but was always higher in R1. Moreover, the bacterial community shift was observed since the beginning of the experiment; the relative abundance of Firmicutes, and Beta- and Gammaproteobacteria increased by 5.01, 3.25 and 9.67% respectively, whilst the abundance of Bacteroidetes and Actinobacteria decreased by 15.59 and 0.95%. All of the surveyed bacteria groups, except Gammaproteobacteria, correlated significantly negatively (p < 0.001) with the concentrations of N-NH4+ in the outflows from R1. The results allow us to suppose that simultaneous stripping and SND in a single reactor could be a promising, cost-effective and easy-to-operate solution for LFL treatment.

Municipal Solid Waste Landfills: An Underestimated Source of Pharmaceutical and Personal Care Products in the Water Environment

Pharmaceutical and personal care products (PPCPs) have been the focus of increasing concern in recent decades due to their ubiquity in the environment and potential risks. Out-of-date PPCPs are usually discharged into municipal solid wastes (MSWs), enter the leachates in MSW landfills, and have serious adverse effects on the surrounding water environment. However, the occurrence and removal of PPCPs from landfill leachates have rarely been examined to date. This lack of knowledge makes the landfill an underestimated source of PPCPs in the environment. In this review, we collected the relevant publications of PPCPs in landfill leachates, systematically summarized the occurrence of PPCPs in landfill leachates globally, evaluated the removal performances for various PPCPs by different types of on-site full-scale leachate treatment processes, and assessed the impacts of landfill leachates on PPCPs in the adjacent groundwater. In particular, influencing factors for PPCPs in landfill leachates, including the physicochemical properties of PPCPs, climate conditions, and characteristics of landfill sites (i.e., landfill ages) as well as sociological factors (i.e., economic development), were extensively discussed to understand their occurrence patterns. Future perspectives were also proposed in light of the identified knowledge gaps. To the best of our knowledge, this is the first review regarding the occurrence and removal of PPCPs from landfill leachates worldwide.

Optimization of reactive media for removing organic micro-pollutants in constructed wetland treating municipal landfill leachate

The removal of organic micro-pollutants (OMPs) from landfill leachate in constructed wetland (CW) media having different material mixtures of sand (S), clay (C), and iron powder (Fe) was investigated using experimental column study. The use of S:C:Fe media consisting of 60:30:10% (w/w) and cattail as vegetation was found optimum for the removals of 2,6-DTBP, BHT, DEP, DBP, and DEHP at 67.5-75.4% during long-term operation of 373 days. Adsorption and biodegradation were confirmed as predominant mechanisms for their removal in CW media but their contribution in total removal varied depending on chemical properties of OMPs. Adsorption kinetic could be well explained by pseudo-second-order whereas biodegradation kinetic followed first-order reaction. The adsorption affinity of OMPs to CW media was S:C:Fe > S:C > S in descending order. This study demonstrated high and sustainable removal of OMPs during long-term operation of CW with the optimized reactive media.

Effect of leachate effluent from activated sludge and membrane bioreactor systems with acclimatized sludge on plant seed germination

This research comparatively investigates the effect of landfill leachate effluent of two biological treatment schemes on germination of Lactuca sativa and Vigna radiata. The treatment schemes are two-stage activated sludge (AS) and two-stage membrane bioreactor (MBR) systems with acclimatized seed sludge. The AS and MBR are operated under two concentrations of landfill leachate influent: moderate (condition 1) and elevated (condition 2). The results show that, under condition 1, the AS and MBR efficiently remove 80-96% of organic compounds and nutrients and 81-100% of harmful micropollutants. Under condition 2 with elevated influent concentration, MBR is more effective in biodegrading micropollutants than the AS system. The germination rate (GR) and germination seed index (GSI) of L. sativa and V. radiata germinated with AS and MBR effluent from condition 1 are 100% and 1.29-1.56. Under condition 2, the GR and GSI with AS effluent are reduced to 80% and 0.65-0.77, while those with MBR effluent are 100% and 1.27-1.38. Quantitative real-time polymerase chain reaction (qPCR) analysis indicates that the bacterial community in the MBR is more abundant than in the AS, especially ammonia oxidizing bacteria, Nitrobacter, and Nitrospira, which aid heterotrophic bacteria in biodegradation of micropollutants and promote the growth of heterotrophs. The bacterial abundance and community composition render the MBR scheme more operationally suitable for elevated landfill-leachate influent concentrations. By comparison, the MBR system is more effective in removal of micropollutants than the AS, as evidenced by higher GR and GSI. The technology also could potentially be applied to water reclamation. A lack of technological and financial resources in many developing countries nevertheless precludes the adoption of MBR despite higher pollutant removal efficiency. An alternative solution is the use of acclimatized seed sludge in AS system to enhance treatment efficiency, especially in influent with low concentrations of micropollutants. In addition, the seed germination results suggest the possibility of water reuse in agriculture.

Comparison of mesophilic and thermophilic methane production potential of acids rich and high-strength landfill leachate at different initial organic loadings and food to inoculum ratios

Landfill leachate (LL), which can contaminate both ground and surface water is a major global environmental issue. The aim of the present study was to investigate the biomethane potential (BMP) of a high-strength LL with low pH (5.0), high solids concentration (16%), and high organic matter (170 g/L of chemical oxygen demand (COD); 55 g/L of volatile fatty acids (VFA)) with ammonia nitrogen (NH₃-N) (17 g/L). We investigated the BMP of LL at four different initial organic loadings (IOL) of 170 g/L, 85 g/L, 42.5 g/L and 21 g/L of COD and Food to inoculum (F/I) ratios of 0.5; 1; 2 and 3 at mesophilic (35 ± 2 °C) and thermophilic temperatures (55 ± 2 °C). We found that the highest cumulative CH₄ could be obtained at an IOL of 42.5 g/L of COD regardless of the F/I ratio and temperature. The highest methane content results in biogas at an IOL of 42.5 g/L were 72% and 74% at mesophilic and thermophilic temperatures respectively. About 80-100% of cumulative methane was produced within 15 days in thermophilic reactors, and 40-72% in mesophilic reactors. The kinetic study revealed a fourfold reduction of lag phase in thermophilic compared to mesophilic reactors. The methane yield and organic matter removal rate increased as the concentration of IOL in LL decreased from 170 g/L to 21 g/L regardless of temperature. There exists an inverse correlation between IOL and organic matter removal efficiency. About 80% COD reduction was obtained at mesophilic temperature, and 90% at thermophilic temperature, at an IOL of 42.5 g/L and 21 g/L of COD. The modified Gompertz model showed a good fit to the experimental data, with R² > 0.98 in all cases. Overall, the findings of this study conclude that treatment of acids rich and high-strength LL both at mesophilic and thermophilic temperature is feasible at an optimum IOL of 42.5 g/L of COD. However, treatment of LL at thermophilic temperature outperformed compared to mesophilic over the digestion time.

The way of microplastic through the environment - Application of the source-pathway-receptor model (review)

Microplastics in the environment is a highly relevant research topic. However, although more and more studies on environmental concentrations of microplastics are published, a profound risk assessment could not be carried out yet. This is mainly attributable to the fact that the current sampling and analysis methods do not provide a representative picture of the environmental pollution, as the fundamental knowledge about transport processes of microplastic is not present, and the ecotoxicological studies therefore cannot consider the relevant exposures of the organisms. To provide a methodological basis for further research and risk assessments, this paper applies the Source-Pathway-Receptor model to the context of microplastics, whereby the current state of knowledge can be compiled in a structured way and important knowledge gaps can be identified.

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.

Spinel-based ceramic membranes coupling solid sludge recycling with oily wastewater treatment

Highly efficient and economic treatment of wastewater sludges and wastewaters in one way is a challenging issue in the water treatment field. Herein we present a waste-to-resource strategy for rational fabrication of low-cost ceramic membranes, which simultaneously addresses the treatment of heavy metal-laden sludges and the separation of oil-in-water (O/W) emulsions. A thermal conversion mechanism is proposed for complicated reactions between simulated nickel-laden wastewater sludge and bauxite mineral. In addition to full stabilization and recycling of heavy metal wastewater sludges, rational tailoring of ceramic membrane structures can also be realized to achieve high water flux and favorable mechanical and surface properties. With rational structure design, the tailored spinel-based ceramic membranes exhibited high rejection and high flux (7473 LMH·bar^-1) simultaneously for separation of oily wastewater, outperforming other reported state-of-the-art ceramic membranes. The membrane fouling mechanism revealed the dominance of cake layer formation at low cross flow velocities, while a combined model of cake layer formation and pore blocking dominated membrane fouling at high cross-flow velocities. The proposed strategy can be potentially extended toward design of functional ceramic membranes derived from other heavy metal wastewater sludges and for other water treatment applications.

Assessment of groundwater pollution near Aba-Eku municipal solid waste dumpsite

Municipal solid waste (MSW) dumpsite constitutes a major anthropogenic point source of leachate contamination to the ambient groundwater and poses a significant threat to the geo-ecosystem. This study investigated the pollution of groundwater by leachate emanating from Aba-Eku MSW dumpsite in Ibadan, Nigeria, using bacteriological, hydrochemical, and geophysical techniques. There is a diversity of bacteria in the leachate and the dominant phyla being proteobacteria (83%) and firmicutes (17%). The mean concentrations (mg/L) of Mn, Fe, Al, Cu, Mo, and Cr in the leachate samples were above the World Health Organization wastewater discharge limits. The hydrochemical parameters of the groundwater samples around the dumpsite were generally within the permissible limits, except for K and Cl^-; which invariably indicate major inputs from water-rock interaction and minor contributions from the dumpsite. Three geoelectrical layers were indicated from the vertical electrical sounding data, which are the topsoil, the lateritic clay layer, and the weathered basement. Low resistivity values of 5-33 Ωm and 3-24 Ωm were obtained within 2 m and 5.5 m depths for the topsoil and the lateritic layer, respectively; while the 2-D subsurface model reveals leachate plume beyond 5 m. Although the MSW leachate is heterogeneous, the hydrochemical data show that the aquifer around the dumpsite has not been seriously polluted with the leachate, but there is a continuous percolation of leachate into the soil subsurface, based on the geophysical findings. Discontinuing waste dumping and groundwater extraction, which would over time reduce the leachate plume, are measures to enhance the groundwater quality in the area.

Zooremediation of leachates from municipal waste using Eisenia fetida (SAV.)

Leachates from municipal landfills are formed as infiltration waters flowing through the landfill. They contain toxic, dissolved products of biochemical reactions taking place in the deposit. They cause soil and groundwater pollution. It is necessary to take them out of the landfill cover and utilize toxins contained therein, in particular heavy metals. Such processes are conducted with the use of microorganisms. Due to the content of toxic compounds, introducing leachates into the process of biological purification poses a threat to the microorganisms used in these processes. An alternative to microbial co-treatment of sludge and leachate as well as soil contaminated with communal leachate is to use red hybrid of California (Eisenia fetida Sav.), an earthworm resistant to environmental toxins, in particular heavy metals. The aim of the conducted research is to demonstrate the possibility of using red hybrid of California in leachate bioutilization as a complementary or alternative method to the process of leachate utilization with the use of microorganisms. The obtained results led to the conclusion that Eisenia fetida accumulates environmental toxins well. By collecting and processing them in the tissues, it remedies the substrate and retains long life and fertility, and the ability to reproduce. The research demonstrated high dynamics of population growth (from 25 individuals in the initial deposit to 298 individuals after six months of research). These properties are related to the presence of enzyme proteins from the metallothionein group in the gastrointestinal tract cells. Packing heavy metals found in leachates into the metallothionein coat limits their toxic effect on earthworm tissues, which confirms the possibility of using earthworms in the processes of detoxification of municipal leachate.