Correction factors for large-scale greenhouse gas assessment from pulp and paper mill sludge landfill sites

Assessments of greenhouse gas (GHG) emissions in managed areas are facing various challenges. A non-flow-through, non-steady-state (NFT-NSS) chamber coupled to a frame permanently inserted into the landfilled substrates is a standard method for quantifying GHG emissions in managed areas, such as pulp and paper mill sludge (PPMS) landfill sites. Frequent measurements are needed to minimize uncertainties on GHG emission factors at the landfill site scale. However, maintaining a frame inserted into the substrates for a long time period is often impossible due to landfilling management operations. Therefore, GHG measurements using NFT-NSS chambers placed directly on substrates' surface could be an interesting option. Our objectives were to determine the relationships between CO2, CH4, and N2O fluxes measured with (F + ) and without (F-) a frame inserted in the substrates' surface and to develop correction factors for fluxes measured without a frame. Measurements were made at different PPMS landfill sites in the province of Québec, Canada. Stronger GHG flux relationships were observed at the provincial (across sites) than the specific site scale: the variance in GHG fluxes from F- chambers explained up to 80 % of variance in fluxes from F + chambers. The measured CO2, CH4, and N2O fluxes in F- chambers were on average 53, 78, and 63 % lower, respectively, than those estimated by the models at provincial scale. The correction factors developed with this approach could greatly extend the number of sites where in situ GHG measurements can be done and would help refining GHG inventories at the provincial and national levels.

Temporal variation in leachate composition of a newly constructed landfill site in Lahore in context to environmental pollution and risks

This study investigated the seasonal and temporal variations in the extent and source of physiochemical and toxic trace elements in the Lakhodair landfill site of Lahore, Pakistan. For this purpose, systematic composite samples were collected every month, consecutively for 1 year, and analyzed for different physiochemical parameters and trace elements. The results of TDS, TSS, COD, NH₃-N, BOD₅, sulfate, sulfides, phenolic compounds, and oil and grease were higher than the national environmental quality standard (NEQs). The concentrations of trace elements, especially Mn (1.7 mg/L) and Cd (0.05 mg/L), were above the MPL, while Fe (14 mg/L), Ni (1.6 mg/L), and Zn (6.7 mg/L) were also found higher than the NEQs in some samples. In Lakhodair leachates, the TDS, COD, NH₃-N, BOD₅, sulfides, and Cl^- have high concentration coefficient (i.e., CC 3 to > 6), which falls in the category of considerable to high contamination and risk level, while the remaining parameters were in the category of low to moderate contamination (CC 1 to ≤ 3) and moderate risk. The lower BOD₅/COD ratio (< 0.1) in spring and autumn seasons represents the active methanogenesis and anaerobic activities in the Lakhodair landfill site. The anaerobic and methanogenesis activities enhance the redox reaction as a result of CO₂ emission, which increases the pH, TDS, COD, Cl^-, BOD₅, NH₃-N, sulfides, and phenolic compounds in the leachate site. However, the lower concentrations of some trace elements in leachate may be because of an anaerobic process that may immobilize the trace elements. It is presumed that the trace elements in the Lakhodair landfill may be in a metastable state, which is difficult to leach out. It is hereby recommended that leachate produced in the Lakhodair landfill site should be handled carefully to limit the environmental and health implications.

Drivers and ecological consequences of arsenite detoxification in aged semi-aerobic landfill

Microbial populations responsible for arsenite [As(III)] detoxification were examined in aged refuse treated with 75 μM As(III) under semi-aerobic conditions. As(III) was rapidly oxidized to As(V) via microbial activity, and substantial As was fixed in the solid phase. The abundance of arsenite oxidase genes (aioA) was about four times higher in the moderate As(III) stressed treatment than in the untreated control. Network analysis of microbial community 16S rRNA genes based on MRT (random matrix theory) further illuminated details about microbe-microbe interactions, and showed six ecological clusters. A total of 166 "core" taxa were identified by within-module connectivity and among-module connectivity values. When compared with the control treatment without As(III), 12 putative keystone operational taxonomic units were positively correlated with As(III) oxidation, of which 10 of these were annotated to genera level. Eight genera were associated with As(III) detoxification: Pseudomonas, Paenalcaligenes, Proteiniphilum, Moheibacter, Mobilitalea, Anaerosporobacter, Syntrophomonas and Pusillimonas. Most of those putative keystone taxa were rare species in landfill, which suggests that low-abundance taxa might significantly contribute to As(III) oxidation.

Microbial aerosol particles in four seasons of sanitary landfill site: Molecular approaches, traceability and risk assessment

Landfill sites are regarded as prominent sources of bioaerosols for the surrounding atmosphere. The present study focused on the emission of airborne bacteria and fungi in four seasons of a sanitary landfill site. The main species found in bioaerosols were assayed using high-throughput sequencing. The SourceTracker method was utilized to identify the sources of the bioaerosols present at the boundary of the landfill site. Furthermore, the health consequences of the exposure to bioaerosols were evaluated based on the average daily dose rates. Results showed that the concentrations of airborne bacteria in the operation area (OPA) and the leakage treatment area (LTA) were in the range of (4684 ± 477)-(10883 ± 1395) CFU/m³ and (3179 ± 453)-(9051 ± 738) CFU/m³, respectively. The average emission levels of fungal aerosols were 4026 CFU/m³ for OPA and 1295 CFU/m³ for LTA. The landfill site received the maximum bioaerosol load during summer and the minimum during winter. Approximately 41.39%- 86.24% of the airborne bacteria had a particle size of 1.1 to 4.7 µm, whereas 48.27%- 66.45% of the airborne fungi had a particle size of more than 4.7 µm. Bacillus sp., Brevibacillus sp., and Paenibacillus sp. were abundant in the bacterial population, whereas Penicillium sp. and Aspergillus sp. dominated the fungal population. Bioaerosols released from the working area and treatment of leachate were the two main sources that emerged in the surrounding air of the landfill site boundary. The exposure risks during summer and autumn were higher than those in spring and winter.

Investigation and modeling of odors release from membrane holes on daily overlay in a landfill and its impact on landfill odor control

In the present work, we studied the NH₃ and H₂S odor fluxes between the exposed working area and the HDPE covering film holes of the daily overlay in an actual landfill site with a daily operating area of 1600 m² in Hangzhou, China. We showed that the odors were released from the membrane pores and the average concentrations of NH3 and H2S release reached 109.6 ± 56.6 and 86.0 ± 31.1 mg/m²/s, respectively. These concentrations are 43.8 and 57.3 times the exposed working surface. Furthermore, mathematical modeling based on the total amount of odor release revealed that there was a linear positive correlation between the total odor amount and the landfill operation area. However, the maximum number of film holes allowed on the covering layer has nothing to do with the working area and exposed working time, which is mainly determined by the HDPE film width in terms of ensuring the deodorizing effect of the covering operation. If the HDPE film with a width of more than 4 m is used, the number of film holes allowed within 100 m is more than 8. Therefore, in order to reduce the odor, the appropriate film width should be selected according to the actual operating conditions such as the mechanical operation level at the time of welding, the design of the landfill site, and the operational norms. This study explores the effect of film hole quantity of the daily cover in the landfill on the odor release from the landfill, which can provide an important reference for the design, operation, and decision-making of the daily cover operation of the sanitary landfill.

Bioaerosols in the landfill environment: an overview of microbial diversity and potential health hazards

Landfilling is one of the indispensable parts of solid waste management in various countries. Solid waste disposed of in landfill sites provides nutrients for the proliferation of pathogenic microbes which are aerosolized into the atmosphere due to the local meteorology and various waste disposal activities. Bioaerosols released from landfill sites can create health issues for employees and adjoining public. The present study offers an overview of the microbial diversity reported in the air samples collected from various landfill sites worldwide. This paper also discusses other aspects, including effect of meteorological conditions on the bioaerosol concentrations, sampling techniques, bioaerosol exposure and potential health impacts. Analysis of literature concluded that landfill air is dominated by microbial dust or various pathogenic microbes like Enterobacteriaceae, Staphylococcus aureus, Clostridium perfringens, Acinetobacter calcoaceticus and Aspergillus fumigatus. The bioaerosols present in the landfill environment are of respirable sizes and can penetrate deep into lower respiratory systems and trigger respiratory symptoms and chronic pulmonary diseases. Most studies reported higher bioaerosol concentrations in spring and summer as higher temperature and relative humidity provide a favourable environment for survival and multiplication of microbes. Landfill workers involved in solid waste disposal activities are at the highest risk of exposure to these bioaerosols due to their proximity to solid waste and as they practise minimum personal safety and hygiene measures during working hours. Workers are recommended to use personal protective equipment and practise hygiene to reduce the impact of occupational exposure to bioaerosols.

Evaluation of landfill sites using GIS-based MCDA with hesitant fuzzy linguistic term sets

There are many criteria to be considered in environmental, social, and economic issues for the landfill site selection (LSS). Multi-criteria decision analysis (MCDA) methods are often used to solve complex decision-making problems such as LSS. However, decision-makers (DMs) may hesitate during the evaluation of the landfill sites with possible incorrect evaluation concerns. Therefore, the inclusion of the hesitant fuzzy linguistic term sets (HFLTS), which considers the hesitations in the preferences of DMs, is suitable for the solution of the problem. On the other hand, geographic information systems (GIS) is an important decision support tool that can analyze different types of spatial data. The aim of this study is to evaluate landfill sites. To do so, the applied approach includes the processes of identifying appropriate alternative sites for landfills by combining HFLTS-based MCDA method and GIS and evaluation of alternative sites with Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The applicability of the proposed approach is tested on Samsun city, Turkey. As a result, scenario analysis, which is dominated by environmental criteria, provides better results dominated by social-economic criteria. Consequently, 12 alternative locations are selected and evaluated for the LSS. Atakum and Canik districts of Samsun city are determined as very suitable locations for landfill sites.

Seasonal CH4 and CO2 effluxes in a final covered landfill site in Beijing, China

As the main solid waste disposal method in China, landfill sites are considerable sources of methane (CH₄) and carbon dioxide (CO₂). This study characterized the seasonal variation of CH₄ and CO₂ effluxes at a large and well-managed final covered landfill site in China. A three-year monitoring program was conducted. There were two different seasonal variation patterns for hotspot and non-hotspot' CH₄ and CO₂ effluxes. For non-hotspots, the CH₄ and CO₂ effluxes' seasonal variations were mainly affected by the seasonal change of the landfill's cover soil respiration activity, particularly the CH₄ oxidation capability. CH₄ had a higher efflux in winter; in other seasons, the CH₄ efflux fluctuated around 0; the CO₂ effluxes were (1) increased in spring and peaked in summer or early autumn; (2) then, they decreased to a minimum value in late autumn or early winter; and (3) fluctuated with the CH₄ efflux in winter. The CH₄ emissions in winter account for 60.4-84.4% of the all year outputs. For the hotspots', the CH₄ and CO₂ effluxes seasonal variations were mainly determined by the seasonal change of the landfill cover's soil gas permeability. The ratio of CH₄ emissions in winter to the all year outputs range from 17.4 to 68.7%.

Fate and partitioning of heavy metals in soils from landfill sites in Cape Town, South Africa: a health risk approach to data interpretation

The fate and persistence of trace metals in soils and sludge from landfill sites are crucial in determining the hazard posed by landfill, techniques for their restoration and potential reuse purposes of landfill sites after closure and restoration. A modified European Community Bureau of Reference's (BCR) sequential extraction procedure was applied for partitioning and evaluating the mobility and persistence of trace metals (As, Cd, Cr, Cu, Ni, Pb, Sb, Se, Zn) in soils from three landfill sites and sludge sample from Cape Town, South Africa. Inductively coupled plasma optical emission spectroscopy was used to analyze BCR extracts. The mobility sequence based on the BCR mobile fraction showed that Cu (74-87%), Pb (65-80%), Zn (59-82%) and Cd (55-66%) constituted the mobile metals in the soils from the three sites. The mobility of Cu, Zn and Ni (> 95%) was particularly high in the sludge sample, which showed significant enrichment compared to the soil samples. Geo-accumulation index (I_geo) and risk assessment code were used to further assess the environmental risk of the metals in the soils. Exposure to the soils and sludge did not pose any non-cancer risks to adult and children as the hazard quotient and hazard index values were all below the safe level of 1. The cancer risks from Cd, Cr and Ni require that remedial action be considered during closure and restoration of the landfill sites.

Impact of small municipal solid waste landfill on groundwater quality

The aim of this paper is to analyse changes in the physicochemical elements in groundwater in the vicinity of a small municipal solid waste landfill site located within the territory of the European Union on the basis of 7-year hydrochemical research. Samples of groundwater and leachate near the examined landfill were collected four times a year during two periods, between 2008 and 2012 during the use of the landfill and between 2013 and 2014 at the stage of its closure. The research results were analysed on the basis of general physicochemical properties: pH; total organic carbon (TOC); electrical conductivity (EC); inorganic elements: Cr, Zn, Cd, Cu, Pb, Hg; and one organic element-polycyclic aromatic hydrocarbon (PAH). The analysis was carried out in accordance with the EU and national legislation requirements regarding landfill monitoring. The assessment of the groundwater and analysis indicators of the leachate pollution allowed interpretation of the impact of the municipal solid waste landfill on the state of the water environment in the immediate vicinity. The results show that the increased values of Cd, EC, and TOC turned out to be the determinants of the negative impact of leachate on the groundwater quality below the landfill. The integrated water threat model determined the potential negative impact of a landfill site. The extent depended on local environmental conditions and the self-cleaning process. Deterioration of the chemical status in the quality of the groundwater within the landfill area was a consequence of the lack of efficiency of the existing drainage system, which may result from the 19-year period of its use. The applied correlation relationship between physicochemical elements between leachate and groundwater with a time shift due to the extended time of migration of contaminants or mass transfer in waterlogged ground can be an important tool to identify the threat of groundwater pollution in the area of landfill sites.

Sulfate and organic matter concentration in relation to hydrogen sulfide generation at inert solid waste landfill site - Limit value for gypsum

In order to suggest a limit value for gypsum (CaSO4) for the suppression of hydrogen sulfide (H2S) generation at an inert solid waste landfill site, the relationship between raw material (SO4 and organic matter) for H2S generation and generated H2S concentration, and the balance of raw material (SO4) and product (H2S) considering generation and outflow were investigated. SO4 concentration should be less than approximately 100mg-SO4/L in order to suppress H2S generation to below 2000ppm. Total organic carbon (TOC) concentration should be less than approximately 200mg-C/L assuming a high SO4 concentration. The limit value for SO4 in the ground is 60mg-SO4/kg with 0.011wt% as gypsum dihydrate, i.e., approximately 1/10 of the limit value in inert waste as defined by the EU Council Decision (560mg-SO4/kg-waste). The limit value for SO4 in inert waste as defined by the EU Council Decision is high and TOC is strictly excluded. The cumulative amount of SO4 outflow through the liquid phase is much larger than that through the gas phase. SO4 concentration in pore water decreases with time, reaching half the initial concentration around day 100. SO4 reduction by rainfall can be expected in the long term.

An integrated Markov chain Monte Carlo algorithm for upscaling hydrological and geochemical parameters from column to field scale

Predicting and controlling the concentrations of redox-sensitive elements are primary concerns for environmental remediation of contaminated sites. These predictions are complicated by dynamic flow processes as hydrologic variability is a governing control on conservative and reactive chemical concentrations. Subsurface heterogeneity in the form of layers and lenses further complicates the flow dynamics of the system impacting chemical concentrations including redox-sensitive elements. In response to these complexities, this study investigates the role of heterogeneity and hydrologic processes in an effective parameter upscaling scheme from the column to the landfill scale. We used a Markov chain Monte Carlo (MCMC) algorithm to derive upscaling coefficients for hydrological and geochemical parameters, which were tested for variations across heterogeneous systems (layers and lenses) and interaction of flow processes based on the output uncertainty of dominant biogeochemical concentrations at the Norman Landfill site, a closed municipal landfill with prevalent organic and trace metal contamination. The results from MCMC analysis indicated that geochemical upscaling coefficients based on effective concentration ratios incorporating local heterogeneity across layered and lensed systems produced better estimates of redox-sensitive biogeochemistry at the field scale. MCMC analysis also suggested that inclusion of hydrological parameters in the upscaling scheme reduced the output uncertainty of effective mean geochemical concentrations by orders of magnitude at the Norman Landfill site. This was further confirmed by posterior density plots of the scaling coefficients that revealed unimodal characteristics when only geochemical processes were involved, but produced multimodal distributions when hydrological parameters were included. The multimodality again suggests the effect of heterogeneity and lithologic variability on the distribution of redox-sensitive elements at the Norman Landfill site.