Physical chemical and biological processes that take place in the body of landfill

As the wastes are stored and remain at the polygon for a long time, this ecological system is dynamic. The main kinds of chemical reactions that occur at the polygon are oxidation-reduction and pH-dependant reactions. The scope of oxidation-reduction reactions at the polygon depends on the level of oxygen in the body of polygon. The dissolution of ??2 in the water and presence of organic acids in the substrate reduces pH, making many metals dissoluble, and the active mobilization of a significant amount of wastes at the polygon that is the source for environmental pollution takes place. The indicators for migration of chemical substances outside the polygon are the higher levels of Ca, Mg, Cl, specific conductivity, total organic oxygen, biological oxygen demand and chemical oxygen demand, etc.

In general, the biological decomposition may occur under aerobic and anaerobic conditions. The aerobic decomposition continues until all oxygen (O2), containing in the body of polygon is spent and the dissolved oxygen in leaky deposits is used up. The adverse products of aerobic reaction are the heat, ?O2, ?2? and inorganic material with available great number of oxygen for completion of reaction. In practice, the duration of aerobic phase is relatively short and depends on design solution and operating conditions of polygon, including the degree of wastes density and moisture content (the moisture replaces the air from the space between wastes particles). Microbes, being active during this phase, are mainly obligate and facultative ? aerobic. During aerobic phase the temperature inside the polygon may reach 45 - 55 °?. The negative impacts on the environment during aerobic phase are minimal as the final main products of biological decomposition are inert inorganic solid substances, ??2 and ?2O. Although the intermediate products of decomposition may be discharged during aerobic phase, their amount and relative contribution into environmental pollution are insignificant.

Although both phases are important, the anaerobic decomposition makes stronger and longer impact in terms of polygon characteristics. The larger part of biodegradable organic substances at the polygon undergoes to anaerobic biological processes. Microorganisms, responsible for anaerobic decomposition, include both facultative and obligate anaerobes. Among other properties, the main difference between aerobic and anaerobic phases is the absence of noticeable heat formation by the latter phase. Thus, during anaerobic phase the temperature of wastes at the polygon gradually drops from high values, characteristic for aerobic phase, practically to the temperature of environment. In general, we can distinguish two groups of adverse products at anaerobic phase:
1) volatile organic acids; 2) gases.

The main factors that influence on biological decomposition of wastes at the modern polygon are the humidity, nutritional medium and degree of wastes resistance to impact of microorganisms. Among abovementioned factors the humidity is the most important variable in relation to the rate and degree of wastes decomposition at the polygon. Under anaerobic conditions, the higher the content of moisture in wastes is, the more actively the biological processes take place. If the content of moisture in biodegradable wastes is less than 20%, the activity of anaerobic processes is significantly reduced.

Organic substances in HSW are the living environment for disease-inducing microorganisms, helminthes eggs, maggots and thus are the source for sanitary hygienic hazard. This hazard of polygon is decreased in proportion to biological stabilization and decomposition of organic components in HSW.

One of the important indices for degradation of wastes at the polygon is the rate and value of sedimentation (i.e. reduction in the level of polygon surface). The sedimentation is as a rule the main limiting factor at use of polygon. This process continues until completion of wastes biological decomposition.

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