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Airspace/Bioreactor
The single most valuable component of landfill design and operation is conservation of airspace. Airspace is what is being sold by landfill owners and operators. Most landfills are permitted to a certain volume or height limit. The more tonnage of waste or revenue generating materials that can be place in a cubic yard, the more the life of a landfill can be extended. There are several methods that can be used to increase the life of the landfill by increasing the amount of waste that can be disposed of in the permitted volume as shown below
- Use the future (predicted) density in existing landfill workbooks that is achievable at a landfill based on the design, operations, and existing estimates on the life of a landfill. AE has methods available that can use the starting or existing measured density of a landfill and accurately determine the final density based on the design height of the landfill (mechanical or primary settlement) and based on estimates of biodegradation (biological or secondary settlement). The prediction of final density also may show that existing estimates are conservative and shorter than the true life of the landfill. Secondary settlement can be predicted based on leachate and gas production factors and also by measuring statistical trends with existing cumulative density measurements over time. Increases over existing density estimates can be as high as 40 percent.
- Increase moisture content of MSW at the working face. Use leachate, groundwater, surface water, stormwater, or other non-hazardous liquids to increase the moisture content of MSW. Similar to soils, the ideal per cent moisture or proctor of MSW for the best immediate compaction is between 34-36% according to literature. Most MSW only contains between 15-25% moisture. Most state regulations only allow leachate to be applied to the working face but some have allowed groundwater and stormwater. USEPA, however, has promulgated the Research, Development, and Demonstration regulation in March 22, 2004 and allows states that adopt it to provide research permits that could allow non-hazardous liquid wastes [also a new source of revenue $$] to be disposed of in landfills to enhance stabilization. The special permits are for a 3 year term renewable up to 4 times. Alan Environmental (AE) is uniquely qualified to assist the waste industry in justifying and selecting the appropriate liquid waste streams that will increase immediate landfill density (as no volume is consumed), increase immediate compaction at the working face and provide long-term stabilization or degradation rates in the landfill.
- New revenue [$$] sources are also available thru participating in the RDD regulation and/or at States willing to accept applications presently to allow special permits for a landfill to receive and manage liquid wastes as amendments or “fertilizer” for landfill degradation. Liquid wastes can immediately improve the bottom line and increase densities since they do no take up any air space, in fact liquid waste increase air space by increasing degradation and settlement. Liquid waste can be injected in interim closed or final closed Subtitle D landfills as they do not increase the volume or height of the landfill. A company can still make revenue in portions of the landfill that were closed to new receipt of MSW.
- Other new revenue increases could be realized at sites where gas to energy projects are viable and leachate recirculation and addition of other liquids could increase gas production from 50% to up to 5 times compared to the “dry” Subtitle D landfill. AE has innovative landfill gas system conceptual designs that can help remove gas very effectively from “wet” landfills.
- Leachate recirculation,(LR) which could include the addition of other liquid waste as well, is also recommended for injection into the landfill in fixed infrastructure such as trenches, wells, or other cost-effetive means in order to distribute nutrients, moisture, bacteria, enzymes, and movement of fine particles that can all increase landfill settlement. Leachate recirculation in the same area of the landfill many times over will allow the landfill to increase moisture content to field capacity (40-50% moisture,recommended by bioreactor experts) that will help optimize degradation rates. [Note: It is impractical to achieve moisture content to field capacity at the working face as compaction will be reduced and machinery will be bogged down] Settlement from 25- 40% has been reported over a period of several years at sites that have achieved this moisture content. Since settlement is the inverse of density, this means that increases in initial landfill density can be from 33% to over 67%.
- For those facilities already have permits for leachate recirculation and are implementing the technology and not satisfied with results, AE can peer review the operational and design of the system to optimize performance. Many sites may not be applying sufficient volume and pressure of leachate into injection systems or evenly applying moisture to the working face to optimize settlement and airspace gains.
- AE had used methods (using statistical and geotechnical models, for example) to evaluate landfill airspace utilization (e.g., waste density) and can accurately predict future airspace. Using the right method can show how good density measurements can increase landfill life as well as optimize compaction methods.
- AE also has unique design concepts, by teaming with design engineers and hydrogeologists to create more airspace from original conceptual designs by excavating deeper into the subsurface. Such landfills are “inward-gradient” designs.
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