Designing a landfill cell with gas collection in mind from the start, is the best way to maximize production over time. While all cells take time to stabilize in decomposition, considering everything from seasonal temperatures to rainfall levels will pay off in the long run. Well-built and managed landfill cells can produce profitable volumes of landfill gas (LFG) for over a decade, so it’s worth the effort to put a little more work into design and installation. Without the concept of LFG production guiding the installation, it’s all too easy for daily practices like compaction or cover to interrupt the steady flow of methane later. Make sure you’re building your landfill cells with optimal gas production in mind with these five tips.
Balancing Moisture Levels
For the landfill cell where gas is incidental, it’s often the goal to keep moisture levels through the pile as low as possible. This reduces the total volume of leachate produced over time, dropping maintenance requirements as well. However, landfill cells designated for optimized gas production need a higher level of moisture instead. Good moisture content distributed throughout the mass of waste encourages steady bacterial decomposition, producing the greatest possible levels of methane in throughout the lifespan of the capped cell. When there’s too much water in the LFG producing cell, the wells become swamped and can’t be properly pressurized anymore to extract the gases. Leachate systems built with impermeable geomembranes are essential for directing excess moisture away from the gas collection system.
Accepting Special Waste Products
It’s essential to set waste policies for various cells before a single piece of trash enters each part of the system. Many landfills combine hazardous waste with standard waste storage areas. However, it is best to keep the materials in separate cells so that they can be handled based on the specific type of gas they usually produce. Waste materials that can interfere with the effective production of LFG include:
- Construction and demolition waste, which is often either reactive when mixed with other waste or too finely compacted to allow for steady gas flow
- Sludges and fine silts from river and lake dredging projects, materials that settle too tightly together to let gas flow easily and which tend to form laminated layers in the midst of the mound
- Ash from power plants or industrial processes,
- Liquid waste in any form, from general sewage to specific chemicals or runoff.
Choosing a Daily Cover
Daily covers play a large role in ensuring good air flow throughout a trash mound. The wrong cover material stops air flow and inhibits good moisture levels, but no cover material will also allow for improper settling and compaction that also leads to gas production issues. Soil is the best daily cover material for landfill cells intended for gas production, but it’s not always available in the volumes necessary for this process. In these cases, sand or gravel may work well, instead, without affecting gas transfer rates. Impermeable covers can be used for daily cover if they’re removed after the addition of each layer of trash, but they can’t stay in place in most landfill designs without affecting the gas flow rate.
Predicting Temperature Fluctuations
Changes in daily temperature affect gas rates, so it’s important to track maximum gas levels for both winter and summer peaks rather than just an average of all daily temperatures. Aside from planning the volume and capacity of the gas collection system based on both temperature highs and lows, it’s important to consider freeze resistance. Many parts of the gas collection system at a landfill site are particularly prone to frost damage due to the materials used to construct them. Even iron and steel can become brittle and snap off when you combine the extreme cold of gas flowing through the inside with nearly equal cold from the exterior. Burying equipment under the surface of the final cap may interfere with maintenance, but it’s usually less expensive than paying to build structures just to insulate this sensitive equipment for a few months out of the year.
Grading for Runoff Control
Grading the ground is essential. It encourages gas to flow out of the trash pile and into the horizontal or vertical wells and is also the best technique for managing how much rainfall runs off into the cell or out of the area. In most cases, the cell needs grading to direct water away from the cell rather than into it. Most landfill cells produce more than enough moisture for steady gas production in the years to come just from the organic waste mixed into the trash stream. If a cell could benefit from the addition of extra runoff, it’s easy enough to set up part of the runoff system to direct it into the pile at an even rate for maximum distribution.
Designing your newest landfill cells with gas production in mind is always possible; even when older cells weren’t built for it. Gas producing cells begin with durable liners and end with equally impermeable cover materials. Find both of the geomembranes you need to accomplish this task here at BTL Liners. Our products make it easy to optimize your entire gas collection system, not to mention working for leachate collection as well.
