While landfill systems designed for gas collection and control may be primarily focused on gases, liquids also play important roles and can’t be overlooked. Landfill systems built for gas collection tend to collect both leachate and condensate; two different but related liquids that are usually handled separately. Identifying whether a particular liquid is a leachate or condensate when there’s a leak or other issue will ensure only the necessary treatments are applied to solve the problem. Leachate and condensate can become valuable byproducts in their own right with careful handling and processing, but there’s no need to over-treat condensate if it’s not as concentrated or hazardous like the leachate.
Why Some Liquid is Necessary
Keeping a completely dry environment inside of a sealed municipal waste landfill cell isn’t just unfeasible, it’s also not ideal for good gas production. The more moisture inside a landfill cell in general, the higher the level of gas produced over time. Of course, there is a tipping point for this effect as well, at which too high of a liquid level in the waste will result in reduced decomposition and gas production. That’s why it’s essential to manage leachate levels and control them over time by covering the cell both on a daily basis and when it’s completed and finished. Without the right cover material, water will continue to fill the landfill cell and create more leachate. The continual refilling of the landfill cell can also increase condensate. Thus, making it into the gas collection system as the sealed facility heats up in the summer and water evaporates. Balancing sufficient liquid levels with rainfall control is a delicate process, but the result is maximized gas production with minimal issues with cell stability and long-term control.
Leachate vs Condensate
Leachate is the liquid that drips through and from the pile of trash contained in a landfill cell. It’s generated from a combination of both rainfall that seeps down through the pile and water created by the decomposition of organic material. Even with daily cover and an impermeable final cover material, it’s inevitable that every pile will generate some amount of leachate. It’s a highly concentrated waste product that contains bacteria, dissolved and suspended waste, heavy metals, and other contaminants.
Condensate is water generated during the collection and processing of landfill gas. While it will contain a wide mix of chemical compounds like nitrogen and ammonia, it’s generally far lower in contamination than leachate. It’s also easier to process into water that is safe to release into the environment, but it’s generally less valuable and lower in total volume than leachate. In some systems, with a high volume of leachate, condensate may be added to the system and processed along with it due to the relatively low volume.
Leachate is generally produced in far larger volumes than condensate. A 100-acre landfill may produce over a million gallons of leachate per year, while condensate is usually around 500,000 gallons or less for the same size of facility. Exceptionally wet municipal waste mixtures may produce more condensate than usual because of extra evaporation through the system.
Leachate Management Systems
Leachate collection uses similar equipment to gas collection to condense and direct the liquid where it can be safely stored. Perforated pipes are used for both types of collection systems, but leachate is generally collected with gravity alone rather than pressure as with gas. There’s no need for active control in these systems since careful placement of the pipes is enough to control the flow of the liquid. Leachate is generally stored in open ponds after collection since it’s relatively stable and releases few gases during evaporation. In contrast, condensate is usually best kept contained to keep gas loss to a minimum unless it’s been mixed into the leachate to dilute it.
Seepage and Leakage
Both leachate and condensate can escape into the surrounding environment and cause substantial risk. The chemicals mixed into these liquids, including heavy metals and nutrients like nitrogen, tend to be damaging to both ground and surface water in particular. If liquids full of contaminants that are hazardous to human health seep down through the soil, they can eventually mix into drinking water supplies for nearby residences and businesses. Soil health is also negatively impacted by most of these chemicals and compounds. Seepage is the slow movement of water through the pores of soil, but leaks can also occur when larger openings allow water to rush through. Impermeable liner materials are essential to control both causes of environmental damage from condensate and leachate.
Condensate Concerns for LFG Production
The greatest concern with LFG condensate is odor. Since these liquids tend to be particularly high in volatile forms of ammonia and nitrogen, there tends to be a more detectable smell from this waste product than even more concentrated and hazardous forms of leachate. Condensate can be highly valuable, but it requires special handling to keep from evaporating and form the same gases that were being controlled in the first place. Polishing and treating condensate allows for it to be used directly on the landfill site, while keeping it untreated may make it more valuable as an agricultural product.
On-Site Uses for Both Leachate and Condensate
Depending on the composition of the leachate and condensate liquids, it may be possible to directly reuse it on the landfill site with minimal to no processing. Condensate is commonly used with only minor treatment as a road application to keep dust under control; especially on a landfill that still has open cells being packed on a daily basis. Drainage, cleaning, sewage treatment, and even cooling are other common uses for treated wastewater on the landfill site. Combined wastewater is less likely to be reused on site than separated leachate and condensate unless there’s a complex water treatment system in place.
With the combination of liners and covers from BTL Liners, it’s possible to keep both leachate and condensate under control for the life of the landfill. Each cell needs it’s own control system for these waste liquids since they can be dangerous to the environment if allowed to escape, just like the gases collected in these facilities.
