Impact of the uncontrolled leakage of leachate from a municipal solid waste landfill on soil in a cultivated-calcareous environment

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.

Arthropods in landfills and their accumulation potential for toxic elements: A review

Landfills, as a source of potentially toxic elements (PTEs), pose a threat to the environment and human health. A literature review was conducted to explore the diversity of arthropods inhabiting solid waste landfills, as well as on the bioaccumulation of PTEs by arthropods. This review presents scientific papers over the last 20 years. Their importance in landfill ecosystems has been the subject of research; however, the issue of the accumulation of compounds such as toxic elements is emphasized only in a few studies. The bioaccumulation of PTEs was studied for 10 arthropod species that founded in landfills: Orthomorpha coarctata and Trigoniulus corallinus (class Diplopoda), Armadillidium vulgare and Trachelipus rathkii (class Malacostraca), the 6 species of the class Insecta - Zonocerus variegatus, Anacanthotermes ochraceus, Macrotermes bellicosus, Austroaeschna inermis, Calathus fuscipes and Harpalus rubripes.

Bioavailability and health risk of pollutants around a controlled landfill in Morocco: Synergistic effects of landfilling and intensive agriculture

Toxic contamination of agricultural soils by trace metal(oid)s can pose detrimental effects on human health and agroecological systems. In this view, the current research explored total and available metal(oid)s in surface soils and assessed the associated hazards using pollution indices, PMF modeling, PCA, and Montecarlo probabilistic human risk assessment with 10,000 repetitions. The mean concentrations of Cd, Pb, As, Cr, Ni, Cu, Zn, and Fe were 0.89, 24.86, 1.81, 19.10, 25.44, 7.98, 49.12 and 6183.32 mg kg-1 dry weight, respectively. These findings highlighted that the concentration of pollutants exceeded the values measured in the geochemical background. Soil enrichment by heavy metal (oid)s was confirmed by analyzing available fractions using DTPA ,CaCl2 and enrichment factor (EF). Additionally, pollution indicators (Igeo, PLI, and PERI) displayed significant contamination levels, with a higher ecological risk. Matrix Factorization (PMF) receptor and multivariate statistical analysis reflected that anthropogenic activities, particularly landfilling and agricultural practices were the main causes of the contamination. Furthermore, probabilistic and deterministic human risk assessments showed that carcinogenic risks exceeded the threshold values (10-4) set by the USEPA. Consequently, it is crucial to implement continuous monitoring and supervision of landfill sites to prevent additional pollution. These measures should be integrated into the management plans for waste management.

Landfill leachate has multiple negative impacts on soil health indicators in Hyrcanian forest, northern Iran

The storage of municipal solid wastes in unengineered landfills poses a severe threat to soil functions and health. Wastes seriously threaten human health and the terrestrial ecosystem, especially due to heavy metals. There is a general knowledge gap about the long-term impacts of storage wastes on the soil health indicators which are effective on soil functions. This investigation focuses on the examination of landfill leachate on soil health indicators from different years in the Hyrcanian forest region in northern Iran. For this purpose, soil sampling was done in the summer of 2012 and 2022 (from three depths of 0-10, 10-20, and 20-30 cm and on a surface of 30 cm × 30 cm). Soil samples were randomly collected from a polluted forest used as waste storage and a nearby unpolluted protected forest. In addition to the general soil physical, chemical and biological parameters, the amounts of cadmium (Cd) and lead (Pb) in the soil were also measured. Simultaneously with soil sampling, earthworms (from a depth of 0-30 cm) were collected and identified. Also, the concentration of Cd and Pb in the earthworm's biomass were measured in the laboratory. We found that unpolluted sites had maximum values of N, K, P, and Ca than the polluted sites. In addition, a decrease of soil aggregates stability, nutrient contents, microbial and enzyme activities, and also fauna and microflora abundance were found in the polluted sites in the period 2012-2022. Soil Cd and Pb contents were more in the polluted site in 2022 compared to the unpolluted site. Lumbricus rubellus and Lumbricus terrestris earthworms had significantly higher population in the polluted sites and higher accumulation of Cd and Pb in biomass. According to our results, soil health decreased in the order unpolluted site 2022 > unpolluted site 2012 > polluted site 2012 > polluted site 2022, which corresponds with the reduction of soil health during the release of landfill leachate. This investigation contributes to understand landfill pollution derived from leachate and its effects on soil physical, chemical and biological parameters to help managing landfill leachate. Therefore, the main issue is choosing a landfill system that minimizes the risk of pollution, installing a leachate collection system and constructing a landfill with engineering principles that can reduce the effects of urban waste pollution on soil health. We emphasize that landfilling is dangerous for the environment, so the government should implement sanitary landfilling to prevent further contamination of surface and underground waters, as well as soil in the precious Hyrcanian forest.

Effects of malic acid and EDTA on oxidative stress and antioxidant enzymes of okra (Abelmoschus esculentus L.) exposed to cadmium stress

Environmental stresses, including heavy metal pollution, are increasing at a growing rate and influencing arable lands. Chelators play an essential role in several biochemical pathways in the cells of plants treated with heavy metals. This research evaluated the modifying effect of malic acid (MA) and ethylenediaminetetraacetic acid (EDTA) on the physiological and biochemical parameters of okra plants exposed to Cd stress in which the okra plants were cultivated in hydroponic conditions. At the 4-leaf stage, they were applied with the treatments of cadmium nitrate at three levels (0, 50, and 100 mg/L), EDTA and MA at two levels (0.5 and 1 mM), and Cd + EDTA + MA at different rates for one month. The harvested plants were subjected to the measurement of the physico-biochemical factors. The results revealed that the application of Cd alone reduced leaf area (up to 21.57 %), and dissolved sugars (up to 40.51 % in the shoot and 45.19 % in the root) and increased MDA (up to 66.37 % and 76.43 % in the shoot and root, respectively), H₂O₂ (up to 67.14 % and 53.28 % in the shoot and root, respectively), proline (up to 52.04 % and 40.93 % in the shoot and root, respectively), and dissolved proteins (up to 14.59 % and 21.90 % in the shoot and root, respectively) contents in both shoots and roots whereas the application of MA and EDTA to the Cd-treated plants increased their leaf area and dissolved sugars and reduced MDA, H₂O₂, proline, and dissolved proteins content. The antioxidant enzymes, e.g., superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), were significantly higher in the plants treated with MA, EDTA, and Cd, but the application of MA and EDTA to the Cd-treated plants reduced the activity of all these antioxidant enzymes versus the plants only treated with Cd. MA and EDTA are likely to prevent the accumulation of Cd in the cytosol by binding to it and transferring it into vacuoles, thereby mitigating Cd toxicity in the okra plants.

Citizens' perception towards landfill exposure and its associated health effects: a PLS-SEM based modeling approach

Around 90% of municipal solid waste in India is treated improperly at open dumps and landfills, posing a severe threat to public health. Landfills are an annoyance whose presence causes uncertainty, stress, and dissatisfaction in neighboring residential areas. This research investigates the perceived impact of exposure to landfills on health in terms of environmental quality, general living status, and defensiveness. To meet the current study's objective, "Case of exposed population" to landfill, i.e., 384 participants dwelling near 1 km of the dump site in Siliguri municipality, West Bengal, India, were considered using a purposive sample approach. The present study adopted Partial Least Square-Structural Equation Modeling (PLS-SEM) approach to prove the hypothesis related to the residential perception of landfills and their impact on health. The findings reveal that all three constructs, namely environmental quality (β = .997, t = 19.607, and ρ < 0.001), general life status (β = .116, t = 2.475 and ρ < 0.05), and people's defensive attitude (β = .150, t = 2.526 and ρ < 0.001), significantly affect the health condition of those exposed to a landfill site. The results suggest that by understanding the impact of landfills on resident health, policymakers and bureaucrats can promote reliable and effective measures linked to sustainable solid waste disposal facilities. The administration must create a policy to protect citizens who live near landfills by improving the ambient environment, establishing health management facilities, and raising awareness through public participation.

Microbial mechanisms of refractory organics degradation in old landfill leachate by a combined process of UASB-A/O-USSB

A combined process of anaerobic digestion (UASB), shortcut nitrification-denitrification (A/O), and semi-anoxic co-metabolism (operated by an up-flow semi-anoxic sludge bed; USSB) was constructed for the treatment of old landfill leachate (>10 years). The performance and mechanism of refractory organics degradation by the combined process (UASB-A/O-USSB) were investigated. The results showed that the semi-anoxic co-metabolism contributes 57 % of the totally degraded refractory organics. Specific microorganisms and their corresponding metabolic functions drive the degradation of refractory organics in each unit of the UASB-A/O-USSB process. In detail, organics with simple molecular structures were preferentially degraded by anaerobic digestion and shortcut denitrification, whereas those with complex structures were subsequently degraded in the oxic tanks and USSB reactor by shortcut nitrification and semi-anoxic co-metabolism. The structural equation model showed that the combined process of shortcut nitrification and semi-anoxic co-metabolism had a better effect on the degradation of recalcitrant organics than the single process. These findings provide information on how refractory organics are metabolically degraded in a combined process.

Mechanical Strength, Water Seepage and Microstructure of a Novel Landfill Solidified Sludge Liner Material

In order to prepare a novel landfill liner material, we used industrial calcium-containing waste (slag, fly ash, and desulfurized gypsum) to solidify municipal sludge. The mechanical and permeability properties of the solidified sludge material (SSM) were evaluated using straight shear, uniaxial compression, and permeability tests. The hydration products, microscopic morphology, and elemental composition of the SSM after the wet and dry cycles were analyzed using a combination of scanning electron microscopy (SEM + EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The SSM has high strength and low hydraulic conductivity. The values of cohesion c and internal friction angle φ reached 0.45–3.31 MPa and 6.52–36.28°. The SSM exhibited a compressive strength of 0.93–11.67 MPa and hydraulic conductivity of 4.80 × 10−9–1.34 × 10−7 cm/s. Analysis shows that SiO2, Al2O3, and CaO in industrial calcium-containing solid wastes and sludges produce dense bulk and agglomerated C-S-H and C-A-S-H gels under alkali excitation. The optimum ratio of sludge, desulfurized gypsum, fly ash, and slag in the solidified sludge was 1:0.61:0.62:0.54, whereas the optimum exciter was Ca(OH)2. The SSM may be used as a good barrier material to prevent water seepage in landfills.

An overview of the environmental pollution and health effects associated with waste landfilling and open dumping

Landfilling is one of the most common waste management methods employed in all countries alike, irrespective of their developmental status. The most commonly used types of landfills are (a) municipal solid waste landfill, (b) industrial waste landfill, and (c) hazardous waste landfill. There is, also, an emerging landfill type called "green waste landfill" that is, occasionally, being used. Most landfills, including those discussed in this review article, are controlled and engineered establishments, wherein the waste ought to abide with certain regulations regarding their quality and quantity. However, illegal and uncontrolled "landfills" (mostly known as open dumpsites) are, unfortunately, prevalent in many developing countries. Due to the widespread use of landfilling, even as of today, it is imperative to examine any environmental- and/or health-related issues that have emerged. The present study seeks to determine the environmental pollution and health effects associated with waste landfilling by adopting a desk review design. It is revealed that landfilling is associated with various environmental pollution problems, namely, (a) underground water pollution due to the leaching of organic, inorganic, and various other substances of concern (SoC) contained in the waste, (b) air pollution due to suspension of particles, (c) odor pollution from the deposition of municipal solid waste (MSW), and (d) even marine pollution from any potential run-offs. Furthermore, health impacts may occur through the pollution of the underground water and the emissions of gases, leading to carcinogenic and non-carcinogenic effects of the exposed population living in their vicinity.

Quantitative water content estimation in landfills through joint inversion of seismic refraction and electrical resistivity data considering surface conduction

The disposal of municipal solid waste (MSW) in landfills is the prevalent method of waste management at the global scale. However, the production of landfill gases due to the methanogenic fermentation of wet MSW is a possible threat to human health and accounts for a substantial contribution to the global greenhouse gas emissions. Accordingly, information regarding water content is critical as it is an important factor triggering methane production in MSW landfills. In this study, we propose a petrophysical joint inversion scheme to quantitatively solve for the water content (WC) in landfills based on seismic refraction as well as electrical resistivity data collected at two different frequencies. In this way, we also take into account the contribution of the surface conductivity to the observed electrical response, which is crucial for a reliable quantification of the WC. Our results reveal a high water content within the MSW unit (WC > 20%) for areas characterized by a strong polarization response (normalized chargeability > 5 M_n mS/m). Such areas can be related to an increased biogeochemical activity as evidenced by the detected methane production. We observe consistent estimates between the water content resolved through the proposed joint inversion scheme and values measured in waste samples with a median percentage error of 17%. Our study demonstrates the possibility to obtain reliable estimates for the WC in MSW landfills through the petrophysical joint inversion of seismic and electrical data when surface conductivity is explicitly considered.

Urbanization influences the distribution, enrichment, and ecological health risk of heavy metals in croplands

The contamination of urban soils with heavy elements due to the rapid development of urbanization and urban services has become a major environmental and human health challenge. This study provides insight into the urbanization controls on combined pollution severity and health risk potential of heavy metals in corn-cultivated urban versus non-urban soils. A multifaceted assessment was conducted using enrichment factor (EF), ecological risk (ER), bioconcentration factor (BCF), transmission factor (TF), hazard index (HI), and carcinogenic risk (CR). The results indicate a significant increase in the concentration of all metals in urban farmlands. When compared to the non-urban soils, EF implies a significant increase of all metals in the urban soil, downgrading this index from minimal enrichment (EF < 2) in the control soils to moderate enrichment (2 ≤ EF < 5) in the urban soils. Likewise, the average ER value showed an increase in the urban soils than in the control soils in the order of Fluvisols (66.6%) > Regosols (66.1%) > Cambisols (59.8%) > Calcisols (47%). The BCF and TF values for different elements decreased in the order of Cd (0.41-0.92) > Cu (0.1-0.23) > Zn (0.1-0.18) > Ni (0.01-0.03) > Pb (0.005-0.011) and Zn (0.75-0.94) > Cu (0.72-0.85) > Pb (0.09-0.63) > Cd (0.17-0.22) > Ni (0.01-0.21), respectively, which indicates that certain metals were not mobilized to the extent that they had been accumulated in the plant roots. The total carcinogenic risk was ranged from 5.88E-05 to 1.17E-04 for children and from 1.17E-04 to 2.30E-04 for adults, which implies a greater associated health risk for children.

Emerging materials and technologies for landfill leachate treatment: A critical review

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Environmental and molecular approach to dye industry waste degradation by the ascomycete fungus Nectriella pironii

Textile industry effluents and landfill leachate contain chemicals such as dyes, heavy metals and aromatic amines characterized by their mutagenicity, cytotoxicity and carcinogenicity. The aim of the present study was investigation of the ascomycete fungus N. pironii isolated from urban postindustrial textile green space for its ability to grow and retain metabolic activity in the presence of the dye industry waste. Research focused mainly on dyes, heavy metals and aromatic amines, which had been detected in landfill leachate via HPLC-MS/MS analysis. Presence of all tested compounds as well as leachate in the growth medium clearly favored the growth of fungal biomass. Only slight growth limitation was observed in the presence of 50 mg L-1 o-tolidine. The fungus eliminated o-tolidine as well as dyes at all tested concentrations. The presence of metals slightly influenced the decolorization of the azo dyes; however, it was still similar to 90%. During fungal growth, o-tolidine was hydroxylated and/or converted to toluidine and its derivatives. Laccase and cytochrome P450 involvement in this process has been revealed. The results presented in the paper provide a valuable background for the development of a fungus-based system for the elimination of toxic pollutants generated by the textile industry.

Co-benefits of biochar-supported nanoscale zero-valent iron in simultaneously stabilizing soil heavy metals and reducing their bioaccessibility

We investigated the performance and encapsulation mechanisms of novel biochar-supported nanoscale zero-valent iron (nZVI-BC) used for the remediation of soil co-contaminated with arsenic (As), cadmium (Cd), and lead (Pb) via incubation and column experiments. Compared with the control, 0.50% of nZVI-BC significantly decreased the leakage of As, Cd, and Pb by 97.94-98.45%, 42.86-81.12%, and 82.14-92.49%, respectively. In addition, 0.50% of nZVI-BC could transform the fraction of unstable heavy metals into a stable form, which substantially decreased the availability, leachability, and bioaccessibility of the heavy metals and hence greatly reduced the human health exposure risk. Column experiments showed that 0.50% of nZVI-BC effectively restrained the leaching of As, Cd, and Pb by 95.60-99.84%, 70.82-84.18%, and 91.68-99.81%, respectively. The predominant encapsulation mechanisms of nZVI-BC included complexation, precipitation/co-precipitation, reduction, and the formation of ternary surface complexes. Based on these insights, we can devise new strategies for the remediation of soil co-contaminated with As, Cd, and Pb.

Degradation of soil quality by the waste leachate in a Mediterranean semi-arid ecosystem

The assessment of soil quality indices in waste leachate-affected soils is vital to understand the threats of land quality degradation and how to control it. In this respect, a study was conducted on the effects of uncontrolled landfill leachate on soil quality index (SQI) in calcareous agricultural lands using 28 soil variables. Using the total data set (TDS) and minimum data set (MDS) approaches, the SQI was compared between leachate-affected soils (LAS) and control soils by the integrated quality index (IQI) and nemoro quality index (NQI) methods. The results revealed that LAS were significantly enriched by soil salinity-sodicity indices including electrical conductivity (EC), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP), fertility indices including total N, available P and K, organic carbon, and cation exchange capacity (CEC), exchangeable cations (Ca, Mg, K, and Na), the available and total fractions of heavy metals (Zn, Cu, Cd, Pb, Ni). After the leachate got its way into the soil, the values of IQI and NQI were dropped ranging 5-16% and 6.5-13% for the TDS approach and 5-15.2% and 7.5-12.2 for the MDS approach, respectively. Clearly, the data showed that soil quality degradation was encouraged and stimulated by the leachate. Among the different models of SQI applied in the present study, IQI determined by MDS was the optimal model to estimate soil quality and predict crop yields given the analysis of the correlations among the SQI models, the correlations between the SQI models and wheat yield, and sensitivity index values.

Assessment of the environmental impact of sanitary and unsanitary parts of a municipal solid waste landfill

Only seven regional MSWLF in Serbia are considered sanitary, while about 3500 landfills operate without proper pollution control. This paper presents a unique opportunity to evaluate the impact of a closed landfill, and a new sanitary landfill, which are located next to each other. The following methodologies for the landfill impact assessment were applied, based on data from 2012 to 2017: Landfill water pollution index (LWPI) and Nemerow index (PI_GW) for groundwater, and the geo-accumulation (I_geo) and ecological risk (ERⁱ) indices and several PAH ratios for soil. The performance of the leachate control system was evaluated using two adapted pollution indices: LPI and the Nemerow index (PI_L). According to the obtained LWPI and PI_GW values, the quality of groundwater at the new landfill is improving (LWPI = 1.05-2.62; PI_GW = 0.52-1.29), while no significant changes were observed for the old landfill (LWPI = 3.06-5.13; PI_GW = 2.03-4.78). High concentrations of ammonia nitrogen (1.01-22.74 mg/l), Fe (0.76-57.11 mg/l), Ni (5.80-230.09 μg/l), Pb (4.2-202.4 μg/l) and ∑PAH₁₆ (150.93-189.55 ng/l) show the strong influence of the landfill on the groundwater quality at the old landfill, indicating the need for additional remediation action. High concentrations of Ni (21.9-133.0 mg/kg) and Cr (8.5-277.0 mg/kg) in the analyzed soil compared to other studies, as well as moderate I_geo values (I_geoNi = 0.36-1.88; I_geoCr = -1.20-1.52), raise concern and suggest the need for further monitoring. The high ERⁱ (158.6-295.0) and I_geo values (0.91-2.30) of Hg show significant potential ecological risk. LPI and PI_L values for early methanogenic phase leachate demonstrates the need to improve the leachate treatment system. The monitoring data and applied pollution indices indicate that Cr and As should be added to the EU Watch List of emerging substances, at least regarding EU potential candidate countries.

Assessment of Shallow Groundwater Contamination Resulting from a Municipal Solid Waste Landfill—A Case Study in Lianyungang, China

Groundwater contaminations based on the release and transportation of leachate from municipal solid waste (MSW) landfills are a potential hazard to the ecosystem and its inhabitants. In this study, nine chemical compositions of groundwater quality were collected and analysed from 16 monitoring wells and two ponds around the Diaoyushan MSW landfill in the north of Jiangsu Province, China. Multiple analyses were performed to assess the redox conditions and the groundwater environment. It was indicated that the landfill was in a low and stable biodegradability phase, and the most influential phase was the initial stage of the landfill site; the leachate leakage was the principal pollution source (49.18%) for the local groundwater environment. Artificial drainage of Dongdasha village expanded the contaminant plume scopes and deteriorated water quality further. The polluted groundwater area was provided with high concentrations of total hardness, Cl−, SO42−, total dissolved solids (TDS) and Pb.

Landfill Impacts on the Environment— Review

Waste management (WM) is a demanding undertaking in all countries, with important implications for human health, environmental preservation, sustainability and circular economy. The method of sanitary landfilling for final disposal of waste remains a generally accepted and used method but the available scientific evidence on the waste-related environmental and health effects is not conclusive. Comparative studies of various WM methods (landfilling, incineration, composting etc.) show that among the municipal solid waste (MSW) treatment and disposal technological options, sanitary landfilling or open dumping is popular in most countries because of the relative low cost and low-technical requirement. The European Union (EU) Directive on waste landfills has introduced specific goals for reducing the volume of disposed waste and very strict requirements for landfilling and landfill sites. Evaluation of the impact of landfills on the environment is a crucial topic in the literature and has received increased attention recently, given growing environmental concerns. The main goal of this survey was to conduct a comprehensive assessment of possible impacts of MSW landfills on the environment. The main conclusion of the overall assessment of the literature is that the disposal of MSW in landfills entails a number of environmental risks but with respect to the current situation and rich style of living adopted in industrially developed countries, the idea of WM systems functioning without landfilling—at least in the foreseeable future within one generation—seems to be somewhat unreal. The results also provided important information of landfills as a source of environmental risk. Results of this research may have an important impact on landfill management and the disposal of waste. From the literature review, it is evident that even if high levels of waste avoidance, reuse and recycling are achieved, some waste materials will always need to be forwarded for disposal.

Cadmium accumulation, translocation factor, and health risk potential in a wastewater-irrigated soil-wheat (Triticum aestivum L.) system

The accumulation of trace elements in wastewater-irrigated soils may introduce them to the food chain and therefore can threaten human health. The present study investigated the accumulation, translocation factor, and health risk potential of cadmium (Cd) in a soil-wheat system irrigated with treated wastewater compared with a reference soil (irrigated with fresh water). All treated wastewater-irrigated soils showed significantly higher levels of electrical conductivity (EC) than that of reference soil by 75-143%. Irrigation with treated wastewater increased both available and total Cd content in soil by 2-4 times. In all irrigated sites, Cd content was about twice as great as the maximum acceptable rate. Bioconcentration factor (BCF) and translocation factor (TF) indicated that Cd was mainly accumulated in the roots (BCF = 2.2-3.1), while little mobilization from roots to stems and grains was noted (TF_shoot/root = 0.07-0.21; TF_grain/root = 0.18-0.24). The average hazard quotient (HQ) for different age groups of the population varied in the range of 0.1-1.0, implying low non-carcinogenic health risk of Cd to local wheat-consuming residents. The risk of Cd to cause carcinogenic health risk (CR) was in the range of 1 × 10^-5 to 1 × 10^-4, indicating low to moderate potential risk. CR for different age groups was in the order: individuals above 18 years old > individuals 7-18 years old > individuals 0-6 years old. For reducing potential health risks to local people, it is imperative to continuously monitor heavy metal levels in the wheat-soil system and urgently adopt more efficient managerial strategies to reduce Cd contamination.

Enhanced Anaerobic Performances of Kitchen Wastes in a Semi-Continuous Reactor by EDTA Improving the Water-Soluble Fraction of Fe

The addition of Fe2+ is considered an effective method for increasing methane production, but the added Fe2+ may not be absorbed by anaerobic microorganisms due to complex chemical reactions. In this study, ethylenediaminetetraacetic acid (EDTA) was used as a ligand of Fe2+ (EDTA-Fe) to promote the dissolution of Fe, and the anaerobic performances of kitchen wastes (KWs) in a semi-continuous reactor were studied. The results indicated that the biogas yields and methane contents were enhanced to 594–613 mL·g−1VSadd·d−1 and 63.6–64.4% at an organic loading rate (OLR) of 2.5 gVSadd·L−1·d−1 due to EDTA-Fe addition. Simultaneously, the EDTA-Fe was more effective than Fe2+ in preventing the acidification of KWs with a high OLR (5.0 gVSadd·L−1·d−1). In addition, the sequential extraction results showed that the water-soluble fraction of Fe in the R3 (EDTA-Fe addition) was 1.49-fold of that in the R2 with Fe2+ addition. The contents of coenzymes F420 and F430 were also improved 1.09 and 1.11 times, respectively. Mechanism analysis confirmed that the EDTA enhanced methane production and operational stability by promoting the dissolution of Fe and maintaining a high content of water-soluble Fe.