An official website of the United States government
Fugitive methane (CH4) and carbon dioxide (CO2) emissions at municipal solid waste (MSW) landfills constitute one of the major anthropogenic sources of greenhouse gas (GHG) emissions to the atmosphere. In recent years, biocovers involving the addition of organic-rich amendments to landfill cover soils is proposed to promote microbial oxidation of CH4 to CO2. However, most of the organic amendments used have limitations. Biochar, a solid byproduct obtained from gasification of biomass under anoxic or low oxygen conditions, has characteristics that are favorable for enhanced microbial oxidation in landfill covers. Recent investigations have shown the significant potential of biochar-amended cover soils in mitigating the CH4 emissions from MSW landfills. Although the CH4 emissions are mitigated, there is still considerable amount of CO2 that is emitted to the atmosphere as a result of microbial oxidation of CH4 in landfill covers as well as the CO2 derived from MSW decomposition. Basic oxygen furnace (BOF) slag is a product of steel making has great potential for CO2 sequestration due to its strong alkaline buffering and high carbonation capacity. In an ongoing project, funded by the U.S. National Science Foundation, the potential use of BOF slag in landfill covers along with biochar-amended soils to mitigate both CH4 and CO2 emissions is being investigated. This paper presents the initial results from this study and it includes detailed physical and chemical and leachability characteristics of BOF slag, and a series of batch tests conducted on BOF slag to determine its CH4 and CO2 uptake capacity. The effect of moisture content on the carbonation capacity of BOF slag was also evaluated by conducting batch tests at different moisture contents. In addition, small column experiments were conducted to evaluate the gas migration, transport parameters and the CO2 sequestration potential of BOF slag under simulated landfill gas conditions. The result from the batch and column tests show a significant uptake of CO2 by BOF slag for the tested conditions and demonstrates excellent potential for its use in a landfill cover system.
more »
« less
Effect of basic oxygen furnace slag particle size on sequestration of carbon dioxide from landfill gas
The mineral carbon sequestration capacity of basic oxygen furnace (BOF) slag offers great potential to absorb carbon dioxide (CO2) from landfill emissions. The BOF slag is highly alkaline and rich in calcium (Ca) containing minerals that can react with the CO2to form stable carbonates. This property of BOF slag makes it appealing for use in CO2sequestration from landfill gas. In a previous study, CO2and CH4removal from the landfill gas was investigated by performing batch and column experiments with BOF slag under different moisture and synthetic landfill gas exposure conditions. The study showed two stage CO2removal mechanism: (1) initial rapid CO2removal, which was attributed to the carbonation of free lime (CaO) and portlandite [(Ca(OH)2)], and (2) long-term relatively slower CO2removal, which was attributed to be the gradual leaching of Ca2+from minerals (calcium-silicates) present in the BOF slag. Realising that the particle size could be an important factor affecting total CO2sequestration capacity, this study investigates the effect of gradation on the CO2sequestration capacity of the BOF slag under simulated landfill gas conditions. Batch and column experiments were performed with BOF slag using three gradations: (1) coarse (D50 = 3.05 mm), (2) original (D50 = 0.47 mm), and (3) fine (D50 = 0.094 mm). The respective CO2sequestration potentials attained were 255 mg g−1, 155 mg g−1, and 66 mg g−1. The highest CO2sequestration capacity of fine BOF slag was attributed to the availability of calcium containing minerals on the slag particle surface owing to the highest surface area and shortest leaching path for the Ca2+from the inner core of the slag particles.
more »
« less
- Award ID(s):
- 1724773
- PAR ID:
- 10547643
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- Waste Management & Research: The Journal for a Sustainable Circular Economy
- Volume:
- 37
- Issue:
- 5
- ISSN:
- 0734-242X
- Format(s):
- Medium: X Size: p. 469-477
- Size(s):
- p. 469-477
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Among many anthropogenic sources of greenhouse gases (GHG), landfill emissions, consisting of methane (CH4) and carbon dioxide (CO2), are one of the major contributors of anthropogenic GHG. In recent years, various innovative landfill biocovers have been investigated and developed to mitigate the emissions of methane (CH4) from municipal solid waste (MSW) landfills. However, the problem of CO2 emissions [which constitute about 40% of landfill gas (LFG)] from MSW landfills still remains unresolved. An innovative cover system which consists of basic oxygen furnace (BOF) slag with biochar amended soil is being developed to mitigate CH4 and CO2 emissions from landfills. The biochar amended soil is effective in mitigating CH4 emissions by microbial methane oxidation, while BOF slag could be effective in sequestering CO2 emissions by carbonation mechanisms. However, the properties of BOF slag vary based on several factors such as mineralogical composition of slag, particle size, moisture content, and temperature. In this study, CO2 sequestration potential of BOF slag was evaluated under synthetic LFG condition. The performance of the BOF slag in sequestering CO2 under different moisture condition was also examined. The results showed that BOF slag can sequester substantial amount of CO2 under LFG condition. The study also enlightened the importance of moisture for initiating carbonation reaction; however, the moisture alone was not the controlling parameter for CO2 sequestration. The mineralogy of the BOF slag plays an important role in determining CO2 sequestration capacity of the slag.more » « less
-
Slag and Al/Mg oxide modified Douglas fir biochar (AMOB) were compared for their phosphate adsorbing abilities for use individually or in combination for simulated agriculture run-off remediation in wetlands. Aqueous batch and column sorption experiments were performed for both low-cost materials. AMOB was prepared in bulk using a novel green method. Material analyses included XRD, elemental analysis, SEM, EDX, and BET. Biochar and slag have different phosphate removal mechanisms. In short residence times (≤2 h), adsorption phenomena dominate for both adsorbents. Surface area likely plays a role in adsorption performance; slag was measured to be 4.1 m2/g while biochar’s surface area was 364.1 m2/g. In longer residence times (>2 h), the slow leaching of metals (Ca, Al, and Mg) from slag continue to remove phosphate through the precipitation of metal phosphates. In 24 h, slag removed more free phosphate from the solution than AMOB. Preliminary fixed bed column adsorption of slag or AMOB alone and in tandem was performed adopting a scaled-up model that can be used to remediate agricultural runoff with high phosphate content. Additionally, a desorption study was performed to analyze the efficiency of material regeneration. While AMOB does not release any adsorbed phosphates, slag slowly releases 5.7% adsorbed phosphate over seven days.more » « less
-
Municipal solid waste (MSW) landfills are regarded as one of the major sources of greenhouse gas (GHG) emissions across the world. In order to control these emissions, an innovative and sustainable biogeochemical cover system that consists of soil, biochar and basic oxygen furnace (BOF) slag is being developed to completely eliminate fugitive methane (CH4) and carbon dioxide (CO2) emissions from the landfills. The effectiveness of such cover systems is highly dependent on the survival and activity of methanotrophs under highly alkaline conditions induced by the presence of slag. In this study, a series of microcosm batch tests on landfill cover materials in different proportions were investigated to study the effect of cover materials on microbial CH4 oxidation in the mixed as well isolated systems. Results demonstrated negligible CH4 oxidation and substantial CO2 sequestration when the BOF slag was integrated/mixed with soil (pH~7) and biochar-amended soil (pH~11). However, layered or separated cover material conditions (biochar-amended soil overlain by slag and soil overlain by slag) demonstrated promising CH4 oxidation potential, thus concluding that extreme alkaline conditions inhibit the CH4 oxidation. Overall, this study showed that a layered system consisting of the soil or biochar-amended soil layer overlain by BOF slag layer is optimal for CH4 oxidation and subsequent CO2 sequestration. Large column experiments and field test plots are being performed to evaluate the long-term performance of the proposed geochemical cover system under dynamic environmental (moisture and temperature) conditions.more » « less
-
The municipal solid waste (MSW) in landfills undergoes anaerobic decomposition to produce landfill gas (LFG), which predominantly consists of methane (CH4) and carbon dioxide (CO2). Fugitive LFG emissions which are otherwise not targeted by gas collection system escape into the atmosphere, forming one of the largest anthropogenic sources of CH4 and CO2 emissions in the United States. The landfill cover soil plays an important role in mitigating the LFG emissions by microbial oxidation of CH4 to CO2 thereby reducing the CH4 emissions to atmosphere. Several researchers have investigated the addition of organic amendments to the cover soils in order to enhance microbial oxidation of CH4 in landfill covers. In recent years, biochar as an organic amendment has shown promise in enhanced microbial oxidation due to its inert/stable chemical nature to degradation, high surface area, high internal porosity, and high moisture holding capacity. However, in all these efforts there is no regard given to the CO2 that still escapes into the atmosphere in undesirable amounts. Steel slag, a product from steel making industry, due to its high alkaline buffering capacity, high carbonation potential, and its unique cementitious properties has found numerous applications in civil and environmental engineering. But, until now there has been no study on the potential use of steel slag in landfill covers to sequester the CO2 emissions. Ongoing research study, funded by the U.S. National Science Foundation, explores the use of BOF steel slag in conjunction with biochar amended cover soil so as to first convert CH4 to CO2 by microbial oxidation and thereafter sequester the resulting CO2 from CH4 oxidation and the prevailing CO2 from anaerobic decomposition together by steel slag, thereby significantly mitigating the LFG emissions from landfills. In this paper, a review on the current applications and carbon sequestration mechanisms of BOF steel slag is presented. Finally, the proposed concept of the biogeochemical soil cover for mitigation of LFG emissions and some of the results from a preliminary investigation indicating the CO2 sequestration potential by steel slag are discussed.more » « less
