Consuming un-captured methane from landfill using aged refuse bio-cover

Methane Emission Reduction and Biological Characteristics of Landfill Cover Soil Amended With Hydrophobic Biochar

Biochar-amended landfill cover soil (BLCS) can promote CH₄ and O₂ diffusion, but it increases rainwater entry in the rainy season, which is not conducive to CH₄ emission reduction. Hydrophobic biochar–amended landfill cover soil (HLCS) was prepared to investigate the changes in CH₄ emission reduction and biological characteristics, and BLCS was prepared as control. Results showed that rainwater retention time in HLCS was reduced by half. HLCS had a higher CH₄ reduction potential, achieving 100% CH₄ removal at 25% CH₄ content of landfill gas, and its main contributors to CH₄ reduction were found to be at depths of 10–30 cm (upper layer) and 50–60 cm (lower layer). The relative abundances of methane-oxidizing bacteria (MOB) in the upper and lower layers of HLCS were 55.93% and 46.93%, respectively, higher than those of BLCS (50.80% and 31.40%, respectively). Hydrophobic biochar amended to the landfill cover soil can realize waterproofing, ventilation, MOB growth promotion, and efficient CH₄ reduction.

Enhanced Methane Oxidation Potential of Landfill Cover Soil Modified with Aged Refuse

Aged refuse with a landfill age of 1.5 years was collected from a municipal solid waste landfill with high kitchen waste content and mixed with soil as biocover material for landfill. A series of laboratory batch tests was performed to determine the methane oxidation potential and optimal mixing ratio of landfill cover soil modified with aged refuse, and the effects of water content, temperature, CO2/CH4, and O2/CH4 ratios on its methane oxidation capacity were analyzed. The microbial community analysis of aged refuse showed that the proportions of type I and type II methane-oxidizing bacteria were 56.27% and 43.73%, respectively. Aged refuse could significantly enhance the methane oxidation potential of cover soil, and the optimal mixing ratio was approximately 1:1. The optimal temperature and water content were about 25 °C and 30%, respectively. Under the conditions of an initial methane concentration of 15% and an O2/CH4 ratio of 0.8–1.2, the measured methane oxidation rate was negatively correlated with the O2/CH4 ratio. The maximum methane oxidation capacity measured in the test reached 308.5 (μg CH4/g)/h, indicating that the low-age refuse in the landfill with high kitchen waste content is a biocover material with great application potential.

Assessment of municipal solid waste management system in Lae City, Papua New Guinea in the context of sustainable development

ABSTRACT

Lae City (LC) of Morobe Province is the second-largest city in Papua New Guinea. Due to the abundant natural resources it inherits, the resultant urbanization has led to an influx of the human population. This increase in population as a result of industrialization has led to increased municipal solid waste (MSW) accumulation. To address this exigent issue, which affects the nation's carbon footprint, it is imperative to review socio-economic and geographic factors to establish a feasible approach for managing MSW efficiently and sustainably. In the quest to achieve the same, the present assessment focuses on the 3 core waste management hierarchy systems to support sustainable development for LC by reviewing existing opportunities and challenges associated with the current MSW management system and the associated policies. The result shows that as a sustainable approach to MSW management of LC, a zero-waste campaign for resource recovery engaging all stakeholders can be implemented since the organic content of MSW generated in LC is as high as 70%. Moreover, the dumping of MSW at the dedicated dumpsite site can be minimized if policies are strengthened and the proposed waste avoidance pathway is implemented strictly. In addition to this, to avoid the contamination of groundwater and recovery of methane, the use of the Fukuoka approach in the existing landfills has been suggested to capture leachate without any huge expenditure.

Biochar-Mediated Anaerobic Oxidation of Methane

Biochar was recently identified as an effective soil amendment for CH₄ capture. Corresponding mechanisms are currently recognized to be from physical properties of biochar, providing a favorable growth environment for aerobic methanotrophs which perform aerobic methane (CH₄) oxidation. However, our study shows that the chemical reactivity of biochar can also stimulate anaerobic oxidation of CH₄ (AOM) by anaerobic methanotrophic archaea (ANME) of ANME-2d, which proposes another plausible mechanism for CH₄ mitigation by biochar amendment in anaerobic environments. It was found that, by adding biochar as the sole electron acceptor in an anaerobic environment, CH₄ was biologically oxidized, with CO₂ production of 106.3 ± 5.1 μmol g^-1 biochar. In contrast, limited CO₂ production was observed with chemically reduced biochar amendment. This biological nature of the process was confirmed by mcr gene transcript abundance as well as sustained dominance of ANME-2d in the microbial community during microbial incubations with active biochar amendment. Combined FTIR and XPS analyses demonstrated that the redox activity of biochar is related to its oxygen-based functional groups. On the basis of microbial community evolution as well as intermediate production during incubation, different pathways in terms of direct or indirect interactions between ANME-2d and biochar were proposed for biochar-mediated AOM.

Impact of leachate recirculation frequency on the conversion of carbon and nitrogen in a semi-aerobic bioreactor landfill

To study the impact of leachate recirculation frequency on the transformation of carbon and nitrogen pollutants in a semi-aerobic bioreactor landfill (SABL), three laboratory-scale SABLs were investigated, each using a different leachate recirculation frequency (daily, once each 3 days, and once each 5 days). Results showed that degradation of total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), chemical oxygen demand (COD), and total organic carbon (TOC) could be described using a quadratic polynomial-compound index model. Degradation rates of TN, NH₄⁺-N, COD, and TOC slightly increased from 0.01795, 0.01814, 0.01451, and 0.01166 day^-1 to 0.02054, 0.01903, 0.01488, and 0.01203 day^-1, respectively, when the recirculation frequency increased from once per 5 days to once per 3 days. When recirculation frequency was increased to daily, degradation rates of TN, NH₄⁺-N, COD, and TOC significantly increased to 0.03698, 0.02718, 0.02479, and 0.02872 day^-1, respectively. Moreover, when recirculation frequency increased from once per 5 days to once per 3 days, the gasification rate of nitrogenous and carbonaceous pollutants was enhanced between 20.38 and 8.17%, respectively. When the leachate recirculation rate further increased to daily, only a small amount of carbonaceous and nitrogenous pollutants was transformed to the liquid phase. Thus, increasing the leachate recirculation frequency in an SABL benefits the removal of carbonaceous and nitrogenous pollutants from the reactor. In addition, the greater is the recirculation frequency, the lower is the residual carbon and nitrogen in the solid phase, and the higher is the gasification rate. A proper recirculation frequency promotes the stabilization of landfill leachate. This study provides a theoretical reference and experimental evidence for accelerating the stabilization of MSW and contributes to the macro-control of landfills.

CH4 mitigation potentials from China landfills and related environmental co-benefits

China's CH₄ emissions from 1955 existing (old) and 495 planned (new) landfills are estimated and projected by adopting a bottom-up method, targeting a 2012 baseline year and a 2030 projected target year. Nine key CH₄ mitigation measures are proposed for the CH₄ mitigation assessment from landfills. Approximately 0.66 million metric tons (Mt) of CH₄ and 1.14 Mt of CH₄ will be released, respectively, from new and existing landfills under a 2030 business-as-usual (BAU) scenario, which is 23.5% lower than a U.S. Environmental Protection Agency estimation. It is estimated that 0.60 and 0.97 Mt of CH₄ can be reduced under new policies (NP) and low-carbon (LC) policy scenarios, respectively. The combined biocover and landfill gas collection and flaring system is the most promising mitigation measure, while mechanical biological treatment and mineral landfill also contribute substantially to CH₄ reduction. The odor-affected population under NP and LC scenarios will decrease by 39.5 and 64.2%, respectively, when compared to the 2030 BAU scenario. The LC scenario is a recommended policy for meeting China's nationally determined contribution targets and reducing the not-in-my-backyard impact due to this policy's significant reduction of CH₄ emissions.

Seasonal characteristics of odor and methane mitigation and the bacterial community dynamics in an on-site biocover at a sanitary landfill

Landfills are key anthropogenic emission sources for odors and methane. For simultaneous mitigation of odors and methane emitted from landfills, a pilot-scale biocover (soil:perlite:earthworm cast:compost, 6:2:1:1, v/v) was constructed at a sanitary landfill in South Korea, and the biocover performance and its bacterial community dynamics were monitored for 240 days. The removal efficiencies of odor and methane were evaluated to compare the odor dilution ratios or methane concentrations at the biocover surface and landfill soil cover surface where the biocover was not installed. The odor removal efficiency was maintained above 85% in all seasons. The odor dilution ratios ranged from 300 to 3000 at the biocover surface, but they were 6694-20,801 at the landfill soil cover surface. Additionally, the methane removal efficiency was influenced by the ambient temperature; the methane removal efficiency in winter was 35-43%, while the methane removability was enhanced to 85%, 86%, and 96% in spring, early summer, and late summer, respectively. The ratio of methanotrophs to total bacterial community increased with increasing ambient temperature from 5.4% (in winter) to 12.8-14.8% (in summer). In winter, non-methanotrophs, such as Acinetobacter (8.8%), Rhodanobacter (7.5%), Pedobacter (7.5%), and Arthrobacter (5.7%), were abundant. However, in late summer, Methylobacter (8.8%), Methylocaldum (3.4%), Mycobacterium (1.1%), and Desulviicoccus (0.9%) were the dominant bacteria. Methylobacter was the dominant methanotroph in all seasons. These seasonal characteristics of the on-site biocover performance and its bacterial community are useful for designing a full-scale biocover for the simultaneous mitigation of odors and methane at landfills.

Effect of landfill cover layer modification on methane oxidation

Levels of methane (CH₄) oxidation in materials used for landfill cover attained in the laboratory are not often replicated in the field due to effects from the surrounding environment. This study investigates the three dominant factors affecting CH₄ oxidation in the cover layer, namely, the thickness of cover layer, the methanotroph spraying manner, and the osmotic coefficient of the cover material. Results show that improved CH₄ emission performance of the cover layer can be realized if methanotroph are introduced, meaning that a thinner cover layer is required. The highest CH₄ emission reduction can be realized by spraying methanotroph into the top, middle, and bottom layers of a 30-cm thick cover layer with an osmotic coefficient of 7.76 × 10^-5 cm s^-1. Comparing results on cover layer thickness, methane monooxygenase (MMO) activity was much lower with increasing thickness meaning that the thicker cover could reduce O₂ availability, thus inhibiting MMO activity. This suggests that MMO may be responsible for differences in CH₄ emission reduction and/or oxidation making the osmotic coefficient an important factor for cover layer material.

Effects of ammonia on methane oxidation in landfill cover materials

The effects of ammonia (NH3) on CH4 attenuation in landfill cover materials consisting of landfill cover soil (LCS) and aged municipal solid waste (AMSW), at different CH4 concentrations, were investigated. The CH4 oxidation capacities of LCS and AMSW were found to be significantly affected by the CH4 concentration. The maximum oxidation rates for LCS and AMSW were obtained at CH4 concentrations of 5% and 20%(v/v), respectively, within 20 days. CH4 biological oxidation in AMSW was significantly inhibited by NH3 at low CH4 concentrations (5%, v/v) but highly stimulated at high levels (20% and 50%, v/v). Oxidation in LCS was stimulated by NH3 at all CH4 concentrations due to the higher conversion of the nitrogen in NH3 in AMSW than in LCS. NH3 increases CH4 oxidation in landfill cover materials.

Effects of nitrogen conversion and environmental factors on landfill CH4 oxidation and N2O emissions in aged refuse

We determined the effects of nitrification capacity and environmental factors on landfill methane oxidation potential (MOP) using an aged refuse in laboratory batch assays and compared it with two different types of soils. The nitrogen conversion in the three experimental materials after 120 h incubation yielded first-order reaction kinetics at an initial concentration of 200 mg kg(-1) NH4(+)-N. The net nitrification rate for the aged refuse was 1.50 (p < 0.05) and 2.08 (p < 0.05) times that of the clay soil and the sandy soil, respectively. The net NO3(-)-N generation rate by the aged refuse was 1.93 (p < 0.05) and 2.57 (p < 0.05) times that of the clay soil and the sandy soil, respectively. When facilitated by ammonia-oxidizing bacteria during CH4 co-oxidation, the average value of the MOP in the aged refuse at a temperature range of 4-45 °C was 2.34 (p < 0.01) and 4.71 (p < 0.05) times greater than that of the clay soil and the sandy soil, respectively. When the moisture content ranged from 8 to 32% by mass, the average values for the MOP in the aged refuse were 2.08 (p < 0.01) and 3.15 (p < 0.01) times greater than that of the clay soil and the sandy soil, respectively. The N2O fluxes in the aged refuse at 32% moisture content were 5.33 (p < 0.05) and 12.00 (p < 0.05) times more than in the clay and the sandy soil, respectively. The increase in N2O emissions from a municipal solid waste landfill can be neglected after applying an aged refuse bio-cover because of the much higher MOP in the aged refuse. The calculated maximum MOP value in the aged refuse was 12.45 μmol g(-1) d.w. h(-1), which was much higher than the documented data.

Utilization of stabilized wastes for reducing methane emission from municipal solid waste disposal

Stabilized solid wastes were utilized to mitigate methane emission from the landfill. Loose texture of plastic wastes encouraged air diffusion from the soil surface whereas fine organic fraction has good water holding capacity and nutrients to stimulate methane oxidation reaction. Biological methane oxidation capacity in stabilized waste layer was found to be up to 34.1 g/m(3)d. Microbial activity test revealed methanotrophic activities of plastic and degraded organic wastes were in the same order. The mixture of plastic and fine degraded organic waste matrix provided sufficient porosity for oxygen transfer and supported the growth of methanotrophs throughout 0.8m depth of waste layer. Fluorescent in situ hybridization (FISH) analysis confirmed the presence of methanotrophs and their population was found varied along waste depth.

Phosphorus removal from aqueous solutions using a synthesized adsorbent prepared from mineralized refuse and sewage sludge

Mineralized refuse and sewage sludge generated from solid waste from municipal landfills and sewage treatment plants were sintered as a cost-effective adsorbent for the removal of phosphorus. Compared with the Freundlich model, phosphorus adsorption on the synthesized adsorbent, zeolite and ironstone was best described by the Langmuir model. Based on the Langmuir model, the maximum adsorption capacity of the synthesized adsorbent (9718 mg kg(-1)) was 13.7 and 25.4 times greater than those of zeolite and ironstone, respectively. The desorbability of phosphorus from the synthesized adsorbent was significantly lower than that of zeolite. Moreover, phosphorus removal using the synthesized adsorbent was more tolerant to pH fluctuations than zeolite and ironstone for the removal of phosphorus from aqueous solutions. The immobilization of phosphorus onto the synthesized adsorbent was attributed to the formation of insoluble calcium, aluminium and iron phosphorus. The heavy metal ion concentrations of the leachate of the synthesized adsorbent were negligible. The synthesized adsorbent prepared from mineralized refuse and sewage sludge was cost-effective and possessed a high adsorptive capacity for phosphorus removal from aqueous solutions.

Characterization of Methylocystis strain JTA1 isolated from aged refuse and its tolerance to chloroform

To accelerate the efficiency of methane biodegradation in landfills, a Gram-negative, rod-shaped, non-motile, non-spore-forming bacterium, JTA1, which can utilize methane as well as acetate, was isolated from the Laogang MSW landfills, Shanghai, China. Strain JTA1 was a member of genus Methylocystis on the basis of 16S rRNA and pmoA gene sequence similarity. The maximum specific cell growth rates (micro(max) = 0.042 hr(-1), R2 = 0.995) was derived through Boltzmann simulation, and the apparent half-saturation constants (K(m(app)) = 7.08 mmol/L, R2 = 0.982) was calculated according to Michaelis-Menton hyperbolic model, indicating that Methylocystis strain JTA1 had higher-affinity potential for methane oxidation than other reported methanotrophs. By way of adding the strain JTA1 culture, the methane consumption of aged refuse reached 115 mL, almost two times of control experiment. In addition, high tolerance of Methylocystis strain JTA1 to chloroform could facilitate the methane oxidation of aged refuse bio-covers. At the chloroform concentration of 50 mg/L, the methane-oxidation rate of bio-cover reached 0.114 mL/(day x g), much higher than the highest rate, 0.0135 mL/(day x g), of reported bio-covers. In conclusion, strain JTA1 opens up a new possibility for environmental biotechnology, such as soil or landfills bioremediation and wastewater decontamination.

Landfill CH4 oxidation by mineralized refuse: effects of NH4(+)-N incubation, water content and temperature

Mineralized refuse, excavated from a municipal solid waste (MSW) landfill that had been closed for more than 10 years, was incubated in livestock wastewater for 150 d to accumulate ammonia-oxidizing bacteria and also co-oxidize methane (CH(4)). The extent of CH(4) oxidation and carbon dioxide (CO(2)) emissions from the incubated mineralized refuse (IMR) were investigated to assess its applicability as a bio-cover material at landfill sites for minimizing total greenhouse gas emission equivalents. From the initial 200 mg nitrogen (N) kg(-1) incubated for 120 h, the nitrate-N content produced in the IMR was twice (P<0.05) that of the untreated original mineralized refuse (OMR) and 3.81 (P<0.05) times that of soil. For an initial CH(4) concentration of approximately 10% by volume in the headspace, CH(4) consumption and net emission of CO(2) from the soil, IMR and OMR all agreed well with first-order and zero-order kinetics models for a 120-h incubation (R(2)=0.667 and R(2)=0.995, respectively). Similar to N turnover, the rate of consumption of CH(4) by the mineralized refuse was some 50.0% higher than for soil (P<0.05). Based on the net rate of CO(2) generation, the CH(4) oxidation rate by IMR was 14.2% (P>0.05) greater than for OMR and 56.1% (P>0.05) higher than for soil. Variation of water content and temperature produced substantially higher CH(4) consumption rates by IMR than by either OMR or soil. After treatment by livestock wastewater, the CH(4) oxidation capacity of mineralized refuse was moderately improved, due to the enhancement of CH(4) adsorption by retained suspended solids and the subsequent co-oxidation by the accumulated ammonia-oxidizing bacteria. By correlation analysis for the three experimental materials, CH(4) oxidation rate was significantly correlated with specific surface area and organic matter content (P<0.05), and was positively correlated with CO(2) generation, NH(4)(+)N nitrification and NO(3)(-)N generation rate (P>0.05).