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Landfill Gas and Leachate from Sanitary Landfills

Statten Island landfill gas wellIt didn’t always used to be the case that landfills produced landfill gas and the very strong and potentially polluting leachate that modern controlled sanitary landfills produce today. Until the 1970s most landfills around the world were truly what are correctly called “dumps”, or “tips” nowadays. Pre-1970 there were far more dumps than there are now and consequently they were smaller. Because most people even in the developed nations had fires in their homes, and had grates on which they could burn combustible organic materials, much of it was burnt for the warmth it gave out, or simply because the householder found it more convenient to throw it on the fire than take it out to the rubbish bin.

The old tips of those days, being smaller less deep than modern landfills, and having less organic/ compostible matter didn’t produce nay appreciable amount of landfill gas, and remained aerobic (full of air or naturally aerated), so although there was leachate produced it was much weaker in its pollution potential after even just a few weeks of decomposition in air than modern leachate. There were problems with the leachate contaminating underground water in sands, gravels and rocks and some of that polluted groundwater did get into drinking water supplies on occasions but the scale of the problem was quite localized around the landfills and generally not have much influence further afield than 50 to 150 metres.

That all changed when governments started to bring in stricter regulations at about that time. At first the dumps which were not provided with a lined base, and leaked their leachate out into the ground were simply covered with soil, but that did not last for long especially when the landfill gas that then resulted migrated and exploded. This new gas and stronger (longer lasting) leachate problem arose because no longer could enough air get into the landfill, and the landfills became “anaerobic” or lacking in air/ sufficient oxygen, for these places to compost their organic matter. Instead, all landfills became huge anaerobic digesters, and started to produce large volumes of “biogas”, and were lined at the bottom resulting in a much stronger leachate, which was the result of anaerobic digestion and is called “digestate” when it comes out of an anaerobic digestion plant.

Clearly, landfill gas and leachate both had to be collected and managed from the new “supertips”. We have discussed leachate in other articles already on this website, so from now on we will concentrate on the part that landfill gas now plays within landfills, and how that can be used as a renewable energy resource.

Landfill gas (LFG ), which is produced when anaerobic bacteria decomposes natural/ organic waste, is pumped out under negative pressure using a series of wells or a vacuum system, is collected in a central area for processing. The gas may be made use of to create electrical energy on-site, or it may be upgraded to pipeline-quality gas. Incorporated with natural gas, it can provide the fuel for conventional combustion turbines or used to sustain anything from space-heaters for factories and offices, up to large combined cycle turbines.

A wide variety of factors influence the quantity of gas that a supertip or “MSW garbage dump” produces and the range of elements within that gas. These aspects consist of, but are not restricted to, the types and age of the waste buried in the land fill, the quantity and types of organic compounds in the waste, and the wetness of the material and temperature level of the waste. Temperature level and moisture levels are heavily influenced by the surrounding climatic environment.

However, it can be said that by volume, LFG has on the average about 50 percent methane and 50 percent carbon dioxide and water vapor. It also consists of small amounts of nitrogen, oxygen, and hydrogen, less than 1 percent non-methane natural materials (NMOCs), and trace amounts of inorganic materials. Only a few of these substances have strong, poignant smells (as an example, hydrogen sulfide), but that is enough to make it extremely odorous at times. NMOCs include particular hazardous air pollutants (HAPs) and volatile organic substances (VOCs), and these can react with sunshine to form ground level ozone (a gas) if unrestrained.

Worryingly, almost 30 organic dangerous air contaminants have been identified in uncontrolled LFG, consisting of benzene, toluene, ethyl benzene, and vinyl chloride. Direct exposure to these pollutants can cause unfavorable health effects. Thermal treatment of NMOCs (consisting of HAPs and VOCs) and methane through flaring or combustion in an engine, turbine, boiler, or other gadget significantly lowers the discharge of these materials and should be enforced, but isn’t in some localities.

However, garbage dump gas is a readily used, local energy source that can be used by the communities around the landfill in many different ways to offset the requirement for the use of non-renewable resources such as oil, coal and gas.

Land fill gas is a kind of biomass energy classified as “waste energy.” The process of decomposition, which occurs when organic product is broken down by bacteria without air being present creates this methane gas. Methane from landfill gas, if it allowed to leak out into the atmosphere as most of it does, is a significant factor adding to global warming and can be unsafe as it can explode or cause fires. Many landfills merely burn this gas, however with innovative initiatives, this clean, renewable energy can be easily utilized to generate electrical energy.

To produce power, gas wells slowly draw methane from the garbage dump and pipe it to a facility where it’s burned to turn engines or turbines and produce valuable electricity. Subject to the land fill design and its management complying with current landfill regulations, the waste composition, compaction, moisture and a number of other factors ensures that LFG is produced. That means that, countless land fills are readily available worldwide to collect and utilize this useful renewable resource source for power generation. If the gas is not collected and used for a power source and land fill gas is allowed to run away to environment, the methane within it is a powerful greenhouse gas, 21 times more so than carbon dioxide. Therefore, its prevention of escape to atmosphere and its exercise as a renewable fuel source is both a win-win situation for the landfill operator, and a “must do” for us all globally.

For a garbage dump restoration that avoids greenhouse gas from migrating into the atmosphere while preventing offensive smells and smouldering fires, the gas has to be continuously extracted under controlled conditions. Perforated tubes are drilled into the landfill body and interconnected by a pipework system. Using a blower, the gas is drawn from the garbage dump. A well-designed gas collection system will flexibly capture the gas from numerous areas and high temperatures, plus leachate, condensates and remaining air content.This can be done in a cost-efficient gas and leachate collection system, along with producing a steady gas quality. Several engineering companies are specialists in this field and offer their design and installation services on an around-the-world basis.

Landfill gas is an emotive subject that can give rise to certain public issues associating with risks of explosion and asphyxiation from gas migration in the ground, and the wellness and environmental dangers postured by discharges to air. Land fill gas consists of primarily methane and CO2 together with trace components. It is an asphyxiant as well as odorous and very hazardous to health.

When most people think about renewable energy resources, they consider wind, solar and hydroelectric, and often not a lot else. That is unfortunate because there is another source of energy that is developed every day across the globe, and that is landfill gas from all our municipal trash and the sooner it is collected from all landfill sites the better, due to the damage it is doing to our planet as part of the climate change problem.

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What is Leachate?

Introduction to leachateLandfill leachate is liquid (mostly rainfall in all modern sanitary landfills) that moves through, or drains from, a landfill. This liquid in its passage through the waste materials in the landfill, dissolves soluble contaminants.

It  is mostly just a strongly organically (vegetable matter) contaminated effluent comprising which although more strongly contaminated than almost any other industrial effluent, still consists almost entirely of water.

The risk that leachate poses is that it will damage the environment if it escapes. Modern landfills are always designed to prevent liquid from leaching out and entering the environment. However, if they are not properly managed, the leachate is at risk for mixing with groundwater near the site, which can have polluting effects on surface water and groundwater. It has sometimes polluted wells, making it unfit to drink.

Leachate Characteristics

Leachate characteristics are determined by the waste disposed in the site, the landfill design, and the mode of operation at the landfill, as well as the age of the landfill itself. Young landfills (<5 years) tend to have an acetogenic leachate with a low pH as well as the highest levels of COD, BOD and heavy metals. In contrast older leachate leachate which is said to be a methanogenic will usually have slightly higher ammonia but less of the other contaminants seen in younger leachate. Ammonia is hard to treat in leachate, and at times (especially in arid climates) the salinity can also be a factor, no matter the age of the landfill.

In many landfills the leachate is collected at the base of the landfill and instead of being sent away for treatment at first, it is recirculated back through the landfill. This normally increases the rate at which the waste material decomposes, improves landfill gas production, and the leachate itself becomes older and easier to treat after recirculation.

Leachate Plant Operation

Landfill operators must always carefully monitor the groundwater and local streams to be sure that, the landfill remains fully sealed to the original design.

There are many landfills which have their own leachate treatment plants, and the best are designed so that their operation is automated. The operating condition of the plant is displayed at all times on a flow chart and instrumentation diagram, and the system is equipped with alarms to ensure that the operational staff can react quickly in the event of a malfunction.

Even without staff intervention the best leachate treatment plants are set up so that any operational faults stop the plant and the specific cause of the fault is displayed to the staff in charge to remedy before any pollution can occur.

Leachate information pages you may find interesting on other websites:

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