Temporal and spatial variation of greenhouse gas emissions from a limited-controlled landfill site

Climatic zone effects of non-native plant invasion on CH4 and N2O emissions from natural wetland ecosystems

Plant invasion can significantly alter the carbon and nitrogen cycles of wetlands, which potentially affects the emission of greenhouse gases (GHGs). The extent of these effects can vary depending on several factors, including the species of invasive plants, their growth patterns, and the climatic conditions prevailing in the wetland. Understanding the global effects of plant invasion on the emission of methane (CH4) and nitrous oxide (N2O) is crucial for the climate-smart management of wetlands. Here, we performed a global meta-analysis of 207 paired case studies that quantified the effect of non-native plant invasion on CH4 and N2O emissions in tropical/sub-tropical (TS) and temperate (TE) wetlands. The average emission rate of CH4 from the TS wetlands increased significantly from 337 to 577 kg CH4 ha-1 yr-1 in areas where native plants had been displaced by invasive plants. Similarly, in TE wetlands, the emission rates increased from 211 to 299 kg CH4 ha-1 yr-1 following the invasion of alien plant species. The increase in CH4 emissions at invaded sites was attributed to the increase in plant biomass, soil organic carbon (SOC), and soil moisture (SM). The effects of plant invasion on N2O emissions differed between TS and TE wetlands in that there was no significant effect in TS wetlands, whereas the N2O emissions reduced in TE wetlands. This difference in N2O emissions between climate zones was attributed to the depletion of NH4+ and NO3- in soils and the lower soil temperature in temperate regions. Overall, plant invasion increased the global net CH4 emissions from natural wetlands by 10.54 Tg CH4 yr-1. However, there were variations in CH4 emissions across different climatic zones, indicated by a net increase in CH4 emissions, of 9.97 and 0.57 Tg CH4 yr-1 in TS and TE wetlands, respectively. These findings highlight that plant invasion not only strongly stimulates the emission of CH4 from TS wetlands, but also suppresses N2O emissions from TE wetlands. These novel insights immensely improve our current understanding of the effects of climatic zones on biogeochemical controlling factors that influence the production of greenhouse gases (GHGs) from wetlands following plant invasion. By analyzing the specific mechanisms by which invasive plants affect GHG emissions in different climatic zones, effective strategies can be devised to reduce GHG emissions and preserve wetland ecosystems.

Flare exhaust: An underestimated pollution source in municipal solid waste landfills

Flares are commonly used in municipal solid waste landfills, and the pollution from flare exhaust is usually underestimated. This study aimed to reveal the odorants, hazardous pollutants, and greenhouse gas emission characteristics of the flare exhaust. Odorants, hazardous pollutants, and greenhouse gases emitted from air-assisted flares and a diffusion flare were analyzed, the priority monitoring pollutants were identified, and the combustion and odorant removal efficiencies of the flares were estimated. The concentrations of most odorants and the sum of odor activity values decreased significantly after combustion, but the odor concentration could still exceed 2,000. The odorants in the flare exhaust were dominated by oxygenated volatile organic compounds (OVOCs), while the major odor contributors were OVOCs and sulfur compounds. Hazardous pollutants, including carcinogens, acute toxic pollutants, endocrine disrupting chemicals, and ozone precursors with the total ozone formation potential up to 75 ppm_v, as well as greenhouse gases (methane and nitrous oxide with maximum concentrations of 4,000 and 1.9 ppm_v, respectively) were emitted from the flares. Additionally, secondary pollutants, such as acetaldehyde and benzene, were formed during combustion. The combustion performance of the flares varied with landfill gas composition and flare design. The combustion and pollutant removal efficiencies could be lower than 90%, especially for the diffusion flare. Acetaldehyde, benzene, toluene, p-cymene, limonene, hydrogen sulfide, and methane could be priority monitoring pollutants for flare emissions in landfills. Flares are useful for odor and greenhouse gas control in landfills, but they are also potential sources of odor, hazardous pollutants, and greenhouse gases.

Odor emission rate of a municipal solid waste sanitary landfill during different operation stages before final closure

This study investigated the odor emission rate from different areas of a municipal solid waste landfill. The surface odor emission rate (SOER) of eight odorous compound groups were determined by flux chamber method. The SOER of working face, seams of daily cover, membrane surface of daily cover, seams of temporary cover, membrane surface of temporary cover, seams of intermediate cover, membrane surface of intermediate cover were 138.34, 49.83, 13.56, 90.35, 14.48, 4.05, and 8.14 μg/(m²·s), respectively. Therefore, odor emission hotspots were at seams of daily and temporary cover areas. Converting the odor emissions at emission hotspots to the entire membrane cover surface, the average SOER of working face, daily cover area, temporary cover area and intermediate cover area were 138.34, 17.95, 22.43, and 6.24 μg/(m²·s), respectively. Combined with the size of each landfill area, the total odor emissions of the four above areas of a landfill zone were 830, 108, 1346, and 5175 mg/s, respectively, suggesting the necessity to control the odor emission of membrane cover stages especially for large-scale landfills. In terms of odor components, alcohols (38.7 %), sulfur compounds (22.9 %) and aldehydes (15.7 %) were major odorous groups.

Numerical model for static chamber measurement of multi-component landfill gas emissions and its application

The quantitative assessment of landfill gas emissions is essential to assess the performance of the landfill cover and gas collection system. The relative error of the measured surface emission of landfill gas may be induced by the static flux chamber technique. This study aims to quantify effects of the size of the chamber, the insertion depth, pressure differential on the relative errors by using an integrated approach of in situ tests, and numerical modeling. A field experiment study of landfill gas emission is conducted by using a static chamber at one landfill site in Xi'an, Northwest China. Additionally, a two-dimensional axisymmetric numerical model for multi-component gas transport in the soil and the static chamber is developed based on the dusty-gas model (DGM). The proposed model is validated by the field data obtained in this study and a set of experimental data in the literature. The results show that DGM model has a better capacity to predict gas transport under a wider range of permeability compared to Blanc's method. This is due to the fact that DGM model can explain the interaction among gases (e.g., CH4, CO2, O2, and N2) and the Knudsen diffusion process while these mechanisms are not included in Blanc's model. Increasing the size and the insertion depth of static chambers can reduce the relative error for the flux of CH4 and CO2. For example, increasing the height of chambers from 0.55 to 1.1 m can decrease relative errors of CH4 and CO2 flux by 17% and 18%, respectively. Moreover, we find that gas emission fluxes for the case with positive pressure differential (∆Pin-out) are greater than that of the case without considering pressure fluctuations. The Monte Carlo method was adopted to carry out the statistical analysis for quantifying the range of relative errors. The agreement of the measured field data and predicted results demonstrated that the proposed model has the capacity to quantify the emission of landfill gas from the landfill cover systems.

Semen quality and sperm DNA methylation in relation to long-term exposure to air pollution in fertile men: A cross-sectional study

Some studies have examined the association between air pollution and semen quality. While it is less of evidence on the sperm quality after long-term air pollution exposure, especially the co-exposure of different air pollution components. Additionally, the role of DNA methylation in it hasn't been confirmed. This study aimed to investigate whether long-term exposure to air pollution was associated with semen quality, as well as to explore the effect of sperm DNA methylation in such association. From 2014 to 2016, 1607 fertile men were enrolled to evaluate 14 parameters of semen quality. Exposure window was defined as one-year before semen sampling. Multivariable linear regression and weighted quantile sum (WQS) regression model were used to investigate the association between six air pollutants co-exposure and semen quality. Sensitivity analysis regarding at the normal semen quality group was also conducted. Semen samples were randomly selected from 200 participants to detect the genomic 5-methylcytosine (5 mC) and 5-hydroxymethylcytosine (5-hmC) levels in sperm. In the total population, PM₁₀, PM_2.5, SO₂, and NO₂ were negatively associated with sperm total motility (PM₁₀: β = -2.67, P = 0.009; PM_2.5: β = -2.86, P = 0.004; SO₂: β = -2.32, P = 0.011; NO₂: β = -2.21, P = 0.012). Results of the normal semen quality group were consistent with those from the whole population. WQS regression results indicated significant decreasing sperm total motility after the co-exposure of the six air pollutants (β = -1.64, P = 0.003) in whole participants. Wherein, PM₁₀ accounted for largest proportion (43.4%). The 5-hmC level was positively associated with PM₁₀ exposure (β = 0.002, P < 0.001). Long-term exposure to PM₁₀, PM_2.5, SO₂, and NO₂, as well as co-exposure to six air pollutants, reduced semen quality in fertile men. As the most significant contributor of air pollutant, PM₁₀ exposure decreased sperm DNA methylation.

Evolution of sulfate reduction behavior in leachate saturated zones in landfills

The sulfate reduction behavior of the landfill leachate saturated zone under different temperatures was investigated. The results showed that temperature had significant effects on sulfate reduction behavior. The sulfate reduction efficiency was the highest at high temperatures (55 °C and 45 °C), followed by mesophilic temperature (35 °C). Normal temperature 25 °C was far less effective than 55 °C, 45 °C and 35 °C. High abundances of aprA and dsrA genes were distributed under high temperatures. Through indicator species analysis and functional comparison, some key taxa were identified as putative key genera for sulfate reduction. Under high temperature, Paenibacillus could effectively degrade dimethyl sulfide. DsrAB is present in the genome of Tissierella. Gordonia, Syntrophomonas, and Lysinibacillus under mesophilic temperature indicates the potential of these organisms to degrade heterogenous biomass, environmental pollutants or other natural polymers with slow biodegradation. This microbial function is similar to that of the putative key genera under normal (25 °C) temperature. Most of the putative key genera belong to Firmicutes, Proteobacteria and Myxococcota. This study provides theoretical support for the control of hydrogen sulfide release from landfills.

Quantification and control of gaseous emissions from solid waste landfill surfaces

Landfilling is the most common option for solid waste disposal worldwide. Landfill sites can emit significant quantities of greenhouse gases (GHGs; e.g., methane, carbon dioxide, and nitrous oxide) and release toxic and odorous compounds (e.g., sulfides). Due to the complex composition and characteristics of landfill surface gas emissions, the quantification and control of landfill emissions are challenging. This review attempts to comprehensively understand landfill emission quantification and control options by primarily focusing on GHGs and odor compounds. Landfill emission quantification was highlighted by combining different emissions monitoring approaches to improve the quality of landfill emission data. Also, landfill emission control requires a specific approach that targets emission compounds or a systematic approach that reduces overall emissions by combining different control methods since the diverse factors dominate the emissions of various compounds and their transformation. This integrated knowledge of emission quantification and control options for GHGs and odor compounds is beneficial for establishing field monitoring campaigns and incorporating mitigation strategies to quantify and control multiple landfill emissions.

Quantification of landfill gas emissions and energy production potential in Tirupati Municipal solid waste disposal site by LandGEM mathematical model

The present key challenges the world is currently facing are the environmental pollution, climate change and energy crisis. The anthropogenic emissions of carbon dioxide due to burning of fossil fuels for energy production and other greenhouse gas emissions are considered unsustainable, and whole world is having a paradigm shift towards the renewable energy. The one of the major contributor of the greenhouse gases like methane, carbon dioxide are the municipal solid waste landfill sites. The landfill sites contains nearly 50–60% of organic contents, and they undergo anaerobic decomposition with a help microbes in the waste dumps contribute to the higher percent of methane emissions. There is now enhanced public awareness on sustainable products, and commodities usage in their daily needs, hence the global warming can be slowed down and devise an environmentally sound sustainable society. The present study aimed to provide a methodology to quantify the amount of methane and carbon-di-oxide emitted from the Tirupati municipal solid waste dumpsite using LandGEM3.02 model and empirical equation to estimate the renewable energy potential. The method provided was simple and more accurate having higher efficiency in predicting the landfill emissions and subsequently the energy potential. The study shows that the energy emission potential are maximum to the waste with a higher fraction of biodegradable organic content. Therefore, the method can be implemented in all the landfills by the policy makers to predict the methane emissions and control the greenhouse gas emissions by sequestering the methane and carbon dioxide optimally for energy production.•

Landfill gases are a primary constituent in greenhouse gases and has potential for energy production.

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The results from this study showed an abundant quantity of methane and carbon dioxide are emitted from tripathi landfill site.

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The study concludes that methane can be extracted and used as alternative source of sustainable energy.

Assessment of GHG Interactions in the Vicinity of the Municipal Waste Landfill Site—Case Study

Landfills have been identified as one of the major sources of greenhouse gas (GHG) emissions and as a contributor to climate change. Landfill facilities exhibit considerable spatial and temporal variability of both methane (CH4) and carbon dioxide (CO2) rates. The present work aimed to evaluate the spatial distribution of CH4 and CO2 and their δ13C isotopic composition originating from a municipal landfill site, to identify its contribution to the local GHG budget and the potential impact on the air quality of the immediate surroundings in a short-term response to environmental conditions. The objective was met by performing direct measurements of atmospheric CO2 and CH4 at the selected monitoring points on the surface and applying a binary mixing model for the determination of carbon isotopic ratios in the vicinity of the municipal waste landfill site. Air samples were collected and analysed for isotopic composition using flask sampling with a Picarro G2201-I Cavity Ring-Down Spectroscopy (CRDS) technique. Kriging and Inverse distance weighting (IDW) methods were used to evaluate the values at unsampled locations and to map the excess of GHGs emitted from the landfill surface. The large off-site dispersion of methane from the landfill site at a 500 m distance was identified during field measurements using isotopic data. The mean δ13C of the landfill biogas emitted to the surrounded atmosphere was −53.9 ± 2.2‰, which corresponded well to the microbial degradation processes during acetate fermentation in the waste deposits. The calculated isotopic compositions of CO2 (δ13C = −18.64 ± 1.75‰) indicate the domination of biogenic carbon reduction by vegetation surrounding the landfill. Finally, amounts of methane escaping into the air can be limited by the appropriate landfill management practices (faster covers active quarter through separation layer), and CH4 reduction can be achieved by sealing the cover on the leachate tank.

A critical review of environmental and public health impacts from the activities of evaporation ponds

Evaporation ponds (EVPs) are among the most cost-effective, and simple wastewater treatment technologies used in many regions/countries with high solar radiation levels. However, its operational limitations, which include the overflow of wastewater, leakages via liners, and large surface area of the EVP that is exposed to atmosphere, creates a negative feedback to the environment. Therefore, the main aim of this review study of more than a hundred works published a little all over the continents is to provide a summary of various contaminations that are associated with EVPs activities through different environmental compartments. In addition, the impacts of EVP on fauna, human health including the current on-site sustainable mitigation strategies were also reviewed. The first conclusion from this study shows that the most commonly contaminants released into surface waters, groundwater, soil and sediments were heavy metals, pesticides, herbicides, selenium, including several major anions and cations. Non-methane hydrocarbons (NMHCs), volatile organic compounds (VOCs), and particulate matters (PMs) were the main air pollutants emitted from the surfaces of an EVP. Limited data is available about the emissions of atmospheric greenhouse gas (GHGs) especially carbon dioxide (CO₂) and methane (CH₄) from EVP surfaces. Migratory birds and aquatic organisms are the most vulnerable fauna as EVP wastewaters can cause obstruction of movements, affect diversity, and causes mortalities following the exposure to the toxic wastewater. The study revealed limited data about the potential health risk associated with occupational and environmental exposure to radiological hazards and contaminated drinking water from EVP activities. On-site EVP treatment strategies using bioremediation and electrochemical treatment technologies have shown to be a promising sustainable mitigation approach. Knowledge gaps in areas of GHGs monitoring/modeling, pollution exposure estimation and health risk assessments are urgently required to gain deeper understanding about the impact of EVP activities, and incorporate them into future EVP designs.

Global warming potential of typical rural domestic waste treatment modes in China: a case study in Ankang

The global problem of domestic waste management increases with rapid population growth and with economic and urban development. In developing countries, treatment of rural domestic waste (RDW) is distinguished from urban waste. Quantitative assessment of greenhouse gas emissions from RDW disposal treatment is needed to achieve carbon neutrality. Reliable global warming potential (GWP) assessments of RDW are not differentiated in the widely accepted "urban-rural integration" centralized disposal model. We considered five different scenarios for RDW management. Scenario 1 (S1), unsanitary landfill (open-air dump); scenario 2 (S2), sanitary landfill; scenario 3 (S3), incineration; scenario 4 (S4), biological + incineration; and scenario 5 (S5), classification + composting + sanitary landfill + recycling. Life cycle assessment was used for GWP, and sensitivity analysis was calculated to point out the sensitive parameter. We found that the mean GWP ranged from 5.14 × 10⁴ to 2.31 × 10⁵ kg CO₂-equivalents. Pollution from untreated RDW with landfill gas emissions led to large contributions under all scenarios. The collection and transportation ratio was sensitive to all scenarios, and we found that, if the recyclable materials separated at source were not used efficiently, the impact on GWP would be greater than under the unclassified waste scenarios. A "new urban-rural integration" mode (S5) that included household classification, village collection, town transfer, and county and urban disposal was introduced for RDW management. These quantitative results have a great potential for promoting effective RDW management in China and other developing countries.

Trace volatile compounds in the air of domestic waste landfill site: Identification, olfactory effect and cancer risk

Landfill sites are regarded as sources of volatile compounds (VOCs) and odors emitted to the atmosphere. Surface emissions of VOCs and odors were investigated in a rural domestic waste landfill site located in southwest China. A total of 76 chemical compounds belonging to 3 chemical families were identified and quantified. The total number of VOCs (TVOC) detected ranged from 18.1 to 806.3 mg/m³, while odorous gases and greenhouse gases ranged from 0.4 to 21.2 and 0-100.5 mg/m³, respectively. High emissions were found in the air surrounding the leachate storage pool (LSP) and dumping area (DPA). The dominant species of VOCs were hexaldehyde, m-xylene, propylene oxide, acetophenone, and 2-butanone. The traceability analysis showed that the odors and VOCs diffused to the downwind boundary mainly came from the DPA and LSP. According to the olfactory effect analysis and cancer risk assessment, the main odor-causing gaseous pollutants were hydrogen sulfide, propionic acid, styrene, and 2-pentanone, while benzene, trichlorethylene, and 1,3-butadiene were the dominant carcinogens. This study provides new insights into the emission characteristics, olfactory effects, and cancer risks of VOCs and odors emitted from rural domestic solid waste landfill sites.

Methane and nitrous oxide emissions from shallow windrow piles for biostabilisation of municipal solid waste

Shallow windrow piles were applied as a low-cost option for biostabilisation of municipal solid wastes (MSW) prior to their utilization as refuse-derived fuel (RDF). A considerable amount of greenhouse gas (GHG) emissions can be emitted during the biostabilisation of MSW, especially when in operation under high moisture conditions such as there are in tropical Asia. This study investigated the emission of methane (CH₄) and nitrous oxide (N₂O) from shallow windrow piles - with heights of 0.5-1.0 m - for the stabilization of MSW at a full-scale facility in Thailand. Measurements of CH₄, CO₂, and N₂O emissions using the static-chamber method revealed high spatial heterogeneity characteristics in all zones with different waste ages. Peak methane emissions were observed after four months of biostabilisation. The average spatial methane emissions from the waste piles ranged from 7.33 to 26.88 g m^-2 d^-1 (14.86 g m^-2 d^-1, on average). The CH₄ generation-rate constant was within the range of 3.3 to 4.0 yr^-1, which is higher than that reported - about 2.20-3.50 yr^-1 - from a deep windrow pile (3.5-4.0 m height). The spatial distribution of N₂O emissions was in the range of 4.51-199.14 mg N₂O t^-1dry wt.d^-1 (6.6-111.7 mg N₂O m^-2 d^-1), similar to those previously studied from landfill operations. This shallow windrow pile technique can be applied as low-cost technology for biostabilisation of MSW in developing countries, where land area is available.Implications: Shallow windrow pile was applied as a low-cost option for biological treatment of municipal solid waste in developing countries where land area is available. This study evaluated the greenhouse gas emission characteristics during the operation of windrow pile. The findings suggest that the emission rates were varied spatially with waste ages in different zones. Higher methane generation rate constant was derived from shallow window pile as compared to deep windrow pile. The methane and nitrous oxide emission factors were derived.

Time-resolved characteristics and production pathways of simulated landfilling N2O emission under different oxygen concentrations

Nitrous oxide (N₂O), an important greenhouse gas, is emitted from landfill reservoirs, especially in the working face, where nitrification and denitrification occur under different O₂ concentrations. In order to explore the effects of O₂ concentration on N₂O emissions and production pathways, the production of N₂O from simulated fresh waste landfilling under 0%, 5%, 10%, and 21% (vol/vol) O₂ concentrations were examined, and ¹⁵N isotopes were used as tracers to determine the contributions of nitrification (NF), heterotrophic denitrification (HD), and nitrification-coupled denitrification (NCD) to N₂O production over a 72-h incubation period. Equal amounts of total nitrogen consumption occurred for all studied O₂ concentration and the simulated waste tended to release more N₂O under 0% and 21% O₂. Heterotrophic denitrification was the main source of N₂O release at the studied oxygen concentrations, contributing 90.51%, 69.04%, 80.75%, and 57.51% of N₂O under O₂ concentrations of 0%, 5%, 10%, and 21%, respectively. Only denitrification was observed in the simulated fresh waste when the oxygen concentration of the bulk atmosphere was 0%. The nitrate reductase (nirS)-encoding denitrifiers in the simulated landfill were also studied and significant differences were observed in the richness and diversity of the denitrifying community at different taxonomic levels. It was determined that optimising the O₂ content is a crucial factor in N₂O production that may allow greenhouse gas emissions and N turnover during landfill aeration to be minimised.

Greenhouse gas emissions from semi-aerobic bioreactor landfills with different vent-pipe diameters

The emission patterns of three greenhouse gasses (GHGs), viz. CH₄, CO₂, and N₂O from landfills, were examined on a lab scale. Three simulated semi-aerobic bioreactor landfills (SABL1, SABL2, SABL3), with respective vent-pipe inner diameters (φ) of 25, 50, and 75 mm, were used to investigate their effect on the greenhouse effect (GHE) during the municipal solid waste (MSW) stabilization process. We found that the vent-pipe φ influenced both MSW degradation and GHG emissions, increasing the vent-pipe φ which improved the removal of carbon and nitrogen-based pollutants. The GHG emissions were 364, 356, and 309 kg CO₂ equivalents per ton of MSW from the SABL2, SABL1, and SABL3, respectively, during the operation of 465 days. Of the three GHGs, CH₄ influenced the GHE the most, contributing 72.53%, 79.17%, and 71.42% in SABL1, SABL2, and SABL3, respectively. In the same sequence, CO₂ (14.87%, 14.06%, and 21.9%) and N₂O (12.6%, 6.77%, and 6.69%) were the second and third contributors to the GHE, respectively. Considering the rapidly MSW stabilization and the mitigation of GHG emissions, a vent pipe with φ of 75 mm in the SABL column (φ of 800 mm) was suggested. Moreover, the GHG mitigation in the SABL should be implemented by prioritizing CH₄ collection and oxidation. The results provided a technical guidance for GHG mitigation in MSW management.

Municipal Solid Waste Characterization and Landfill Gas Generation in Kakia Landfill, Makkah

In many countries, open dumping is considered the simplest, cheapest, and most cost-effective way of managing solid wastes. Thus, in underdeveloped economies, Municipal Solid Wastes (MSW) are openly dumped. Improper waste disposal causes air, water, and soil pollution, impairing soil permeability and blockage of the drainage system. Solid Waste Management (SWM) can be enhanced by operating a well-engineered site with the capacity to reduce, reuse, and recover MSW. Makkah city is one of the holiest cities in the world. It harbors a dozen of holy places. Millions of people across the globe visit the place every year to perform Hajj, Umrah, and tourism. In the present study, MSW characterization and energy recovery from MSW of Makkah was determined. The average composition of solid waste in Makkah city is organic matter (48%), plastics (25%), paper and cardboard (20%), metals (4%), glass (2%), textiles (1%), and wood (1%). In order to evaluate energy recovery potential from solid waste in Kakia open dumpsite landfill, the Gas Generation Model (LandGEM) was used. According to LandGEM results, landfill gas (methane and carbon dioxide) generation potential and capacity were determined. Kakia open dump has a methane potential of 83.52 m3 per ton of waste.

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

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

Mapping biogeochemically active zones in landfills with induced polarization imaging: The Heferlbach landfill

In this study, we investigate the applicability of the Induced Polarization (IP) imaging method to discriminate between biogeochemically active and inactive areas of a landfill. The elevated amount of degradable organic carbon in landfills results in the development of biogeochemical hot-spots associated with high rates of microbial activity and the generation of landfill gas and leachate as metabolic products. Our results demonstrate that the electrical conductivity is mainly sensitive to the increase in the fluid conductivity associated to leachate production and migration. Whereas images of the polarization effect, expressed in terms of the imaginary component (σ″) or the phase of the complex conductivity (ϕ), reveal the potential to characterize variations in the architecture and biogeochemical activity of the landfill. Correspondingly, biogeochemically active zones (leachable TOC contents above 1500 mg/kg dry waste) are related to high polarization values (σ″ > 10 mS/m, ϕ > 40 mrads), whereas low leachable TOC contents (<300 mg/kg dry waste) in the inactive areas are characterized by low polarization values (σ″ < 1 mS/m, 10 < ϕ < 25). Additionally, landfill sections corresponding to construction and demolition waste (CDW), associated to negligible TOC content, exhibit the lowest polarization response (σ″ < 0.1 mS/m, ϕ < 15). We prove that IP imaging is a well-suited method for landfill investigations that permits an improved characterization of landfill geometry, variation in waste composition, and the discrimination between biogeochemically active and inactive zones.

Mobile genetic elements in potential host microorganisms are the key hindrance for the removal of antibiotic resistance genes in industrial-scale composting with municipal solid waste

During the municipal solid waste (MSW) composting, antibiotic resistance genes (ARGs) could be one of the concerns to hinder the application of MSW composting. However, the understanding of enrichment and dissemination of ARGs during the industrial-scale composting is still not clear. Hence, this study aimed to investigate the ARG distributions at different stages in an industrial-scale MSW composting plant. Seven target ARGs and four target mobile genetic elements (MGEs) and bacterial communities were investigated. The abundances of ARGs and MGEs increased during two aerobic thermophilic stages, but they decreased in most ARGs and MGEs after composting. Network analysis showed that potential host bacteria of ARGs were mainly Firmicutes and Actinobacteria. The reduction of potential host bacteria was important to remove ARGs. MGEs were an important factor hindering ARG removal. Water-extractable S and pH were two main physicochemical factors in the changes of microbial community and the abundance of ARGs.