Waste Decomposition: The Main Stages of waste decomposition, or the waste degradation process
An understanding of the Main Stages of waste decomposition, or the waste degradation process is essential to understand how a landfill will gradually change over many years.
We are often asked how many years will it take before a particular landfill can be built upon, or will no longer require leachate treatment, and the inability of landfill professionals to provide a quick question often surprises questioners.
We hope that this article will help provide an understanding of the difficulties in the prediction of landfill degradation rates, let alone the forecasting when all the processes involved will have run their paths and degradation completed. Furthermore, even after degradation processes have significantly ceased, many landfills will still need further flushing with water before the leachate produced becomes innocuous and harmless to the environment.
In the past thirty years the increasing size and containment/capping of landfills has gradually extended the degradation periods of landfills.
At the start of this period most landfills were small and shallow, would remain uncapped and aerobic throughout, did not contain significant plastics, and would be quite rapidly degraded and rendered harmless; if not in 10 years, within a few tens of years.
Large current landfills, capped and kept dry by leachate management procedures which seek to minimise landfill costs during the active life of the landfill, and hazardous waste landfills - all will take thousands of years to neutralise.
The Aerobic, Anaerobic and Back to Aerobic Sequence
The first point to note about the decomposition of landfills is that the characteristics of a landfill are primarily governed by the presence or otherwise of aerobic or anaerobic conditions.
Clearly, on day one all landfills will be aerobic (there will be a surplus of air), however, fairly soon all landfills become anaerobic in parts of the landfill, as the ability of oxygen to diffuse into the waste mass is lost within the body of the wastes.
The reactions within the landfill are very much governed by the presence or otherwise of anaerobic conditions. All landfills will eventually return to the aerobic state when all significant oxygen demanding reactions have ceased, but this will take from tens of years, to one or more thousands.
The diagram below should provide a broad overview of the complexity of the stages of biological decomposition in a landfill.
Printable version for those with Microsoft PowerPoint (Tm).
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