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5 Stages of Biodegredation in Landfills  Each cell contains the waste deposited in one day  Landfills are constructed one cell at a time.

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Presentation on theme: "5 Stages of Biodegredation in Landfills  Each cell contains the waste deposited in one day  Landfills are constructed one cell at a time."— Presentation transcript:

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8 5 Stages of Biodegredation in Landfills  Each cell contains the waste deposited in one day  Landfills are constructed one cell at a time over a period of 20 to 30 years  A the end of the day, each cell is capped with a layer of sand or soil  At any given time, different parts of the same landfill are in different stages of decomposition  The time frame for decomposition is variable, depending on the nature of the waste, the landfill conditions, and the local climate

9 Stage 1: Initial Adjustment  Waste absorbs moisture, compacts, and settles slowly  Oxygen is present as microbes and animals begin to consume and digest organic matter  When the oxygen supply is exhausted, aerobic organisms die off and anaerobic microbes take over as principal decomposers  This aerobic to anaerobic transition occurs 6 to 18 months after waste is placed in cell

10 Stage 2: Transition  Carbon dioxide completely replaces oxygen as the primary landfill gas  Anaerobic bacteria convert the substances created by aerobic bacteria to acetic, lactic, and formic acids and to alcohols, including methanol and ethanol  The acids produced during this stage percolate through the waste as highly acidic leachate  “Transition” stage lasts for several months

11 Stage 3: Acid Formation  Anaerobic decomposition continues to produce leachate with its high concentrations of organic acids  As pH drops, waste metals such as chromium, iron, and magnesium to dissolve in the leachate  Nitrogen & phosphorous slowly become available to anaerobic bacteria, which facilitates population growth  Over time fermenting bacteria convert organic acids, alcohols, hydrogen and carbon dioxide to acetate  Landfill settles unevenly

12 Stage 4: Methane Fermentation  Methane-producing bacteria transform the acetate, methanol, and other chemical to methane, carbon dioxide and water  The methanogenic bacteria produce significant amounts of methane and carbon dioxide (landfills account for about 20% of human-generated methane emissions)  Landfill continues to settle  This stage lasts from 15 to 60 years

13 Stage 5: Final Maturation  There is little scientific data on the details of this phase & its long-term characteristics are uncertain  Bacterial populations decline  Gas and leachate production eventually ends  Landfill topography stabilizes

14 Problems and Questions  Does the threat to human health end when biological activity ends?  The regulations requiring capping and lining effectively prevent air and water from entering the landfill, slowing down decomposition processes.  In the absence of decomposition, waste remains “mummified”  Groundwater contamination is a continual threat


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