When these wastes are improperly managed, they pose a significant risk to the environment and public health. Pathogens, chemicals, antibiotics, and nutrients present in wastes can contaminate surface and ground waters through runoff or by leaching into soils. Excess nutrients cause algal blooms, harm wildlife, and infect drinking water. Drinking water with high levels of nitrates is linked to hyperthyroidism and blue-baby syndrome.
Municipal water utilities treat drinking water to remove nitrates, but it is costly to do so. Organic wastes also generate large amounts of methane as they decompose. Methane is a powerful greenhouse gas that traps heat in the atmosphere more efficiently than carbon dioxide. Given equal amounts of methane and carbon dioxide, methane will absorb 86 times more heat in 20 years than carbon dioxide.
To reduce greenhouse gas emissions and the risk of pollution to waterways, organic waste can be removed and used to produce biogas, a renewable source of energy. When displacing fossil fuels, biogas creates further emission reductions, sometimes resulting in carbon negative systems.
Despite the numerous potential benefits of organic waste utilization, including environmental protection, investment and job creation, the United States currently only has 2, operating biogas systems, representing less than 20 percent of the total potential. Biogas is produced after organic materials plant and animal products are broken down by bacteria in an oxygen-free environment, a process called anaerobic digestion. Biogas systems use anaerobic digestion to recycle these organic materials, turning them into biogas, which contains both energy gas , and valuable soil products liquids and solids.
Anaerobic digestion already occurs in nature, landfills, and some livestock manure management systems, but can be optimized, controlled, and contained using an anaerobic digester. Biogas contains roughly percent methane, percent carbon dioxide, and trace amounts of other gases. The liquid and solid digested material, called digestate, is frequently used as a soil amendment. Some organic wastes are more difficult to break down in a digester than others.
Food waste, fats, oils, and greases are the easiest organic wastes to break down, while livestock waste tends to be the most difficult.
Mixing multiple wastes in the same digester, referred to as co-digestion, can help increase biogas yields. Warmer digesters, typically kept between 30 to 38 degrees Celsius Fahrenheit , can also help wastes break down more quickly. After biogas is captured, it can produce heat and electricity for use in engines, microturbines, and fuel cells.
Biogas can also be upgraded into biomethane, also called renewable natural gas or RNG, and injected into natural gas pipelines or used as a vehicle fuel. The United States currently has 2, operating biogas systems across all 50 states, and has the potential to add over 13, new systems. Stored biogas can provide a clean, renewable, and reliable source of baseload power in place of coal or natural gas. Baseload power is consistently produced to meet minimum power demands; renewable baseload power can complement more intermittent renewables.
Similar to natural gas, biogas can also be used as a source of peak power that can be rapidly ramped up. Using stored biogas limits the amount of methane released into the atmosphere and reduces dependence on fossil fuels.
The reduction of methane emissions derived from tapping all the potential biogas in the United States would be equal to the annual emissions of , to 11 million passenger vehicles. Based on a waste-to-wheels assessment, compressed natural gas derived from biogas reduces greenhouse gas emissions by up to 91 percent relative to petroleum gasoline.
Diverting that waste to anaerobic digestion would turn a cost into an opportunity, generating revenue from energy production and co-products. Source: New York Times , June 2, In addition to climate benefits, anaerobic digestion can lower costs associated with waste remediation as well as benefit local economies. Building the 13, potential biogas systems in the United States could add over , temporary construction jobs and 23, permanent jobs.
Anaerobic digestion also reduces odors, pathogens, and the risk of water pollution from livestock waste. Digestate, the material remaining after the digestion process, can be used or sold as fertilizer, reducing the need for chemical fertilizers.
Digestate also can provide additional revenue when sold as livestock bedding or soil amendments. Around 30 percent of the global food supply is lost or wasted each year.
LFG capture prevents the release of methane into the atmosphere as a GHG methane is 21 times as powerful as CO 2 and the electricity subsequently produced by LFG combustion produces less CO 2 emission than conventional fossil fuel combustion. However, since LFG partly originates from biomass in the landfills, part of this CO 2 had already been sequestered earlier in the biomass cycle and will be sequestered again in plants, trees, etc.
This methodology helps to determine a baseline for GHG emissions in the absence of landfill gas capture. In addition, for the part of delivering the electricity production with the captured methane to the grid, greenhouse gas emission reductions can be calculated using the Approved Consolidated Methodology ACM which helps to calculate an average grid-based emission factor in the absence of the landfill gas capture project: Consolidated methodology for grid-connected electricity generation from renewable sources Version In , the World Bank published an assessment of the capital costs of investments in LFG capture for electric power production World Bank, One plant assessed was a hypothetical 5-MW electric power station in the USA, with the following performance assumptions.
For this LFG recovery plant, the following capital cost assumptions were made based on experience with municipal solid waste plants :. Based on these assumptions the capital cost, operation and management costs, and other costs associated were annualised to estimate generation costs as follows:.
For the calculations, it has been assumed that the feedstock would be provided free of charge. However, a provision for royalties to an assumed municipal corporation from the sale of electricity and manure was included under variable costs. This estimation was then refined including future cost projections and uncertainty analysis. Based on this capital cost projection, the electricity generation costs for the plant would vary between USD 0. These figures provide insight in the financial aspects of LFG capture and use projects, although the order of magnitude of the cost items may be different across countries and between industrialised and developing countries.
As explained above, LFG capture and use projects have been established under the CDM, where they generally strongly benefit from the value of the Certified Emissions Reductions to be generated through the projects. For example, the Landfill Gas to Energy Facility project at the Nejapa Landfill Site in El Salvador has presented the following overview of how the internal rate of return of the project changes with on changes in revenues and costs, and the market value of greenhouse gas emission reduction.
Connecting countries to climate technology solutions. Toggle navigation. Breadcrumb Home. Methane Capture at Landfills for Electricity and Heat. Waste management. Opportunities enabled:. Reduce GHG emissions. Technology group:. Waste Management. Enteric fermentation. Integrated solid waste management. Community based. PFCs reduction. The fuel cell produced no electricity.
They added humic acids—a non-living electron shuttle—and the fuel cells worked. Bacteria from the sludge are better shuttles than humic acids because they are self-sustaining. The researchers have filed provisional patents on this process.
Source: Penn State. Search for:. Science Health Culture Environment. Share this Article. You are free to share this article under the Attribution 4. Deep biosphere holds secrets to evolutionary history. Mutant microbe produces carbon-neutral biofuel.
0コメント