Biochemical and Microbiological Changes in Landfill

Waste decomposition in a landfill is typically an anaerobic process involving the coordinated activity of several groups of micro-organisms. Based on laboratory scale experiments, the microbiological processes that occur in a landfill have been delineated into four phases viz.: (1) aerobic phase; during which both oxygen and nitrates are consumed using sugars and organics. (2) anaerobic acid phase; (3) accelerated methanogenic phase; and (4) decelerated methanogenic phase. In the anaerobic acid phase, carboxylic acids accumulate, the pH drops and degradation of complex polymers sets in. However, the level of methane remains low. In phase three, methane production is extensive, and rapid consumption of acids leads to a rise in pH, while degradation of polymers, like cellulose, also increases. In the deceleration phase, methane production remains at levels similar to, or less than in phase three, while degradation of cellulose and hemicellulose increases again (Erses et al., 2008; Kulikowska and Klimiuk 2008; O'Sullivan et al., 2008).

It is not known whether this is a cyclic process in which phases 2-4 repeat until waste mineralisation is complete, as none has been monitored scientifically, long enough for waste to be completely stabilised (Barlaz, 1997), and the boundaries between the phases are also not clearly defined. Biochemical changes associated with the different phasesmay take place simultaneously. The processes involved in phases 1-4 take several years to occur, and complete stabilisation of the waste, even longer and may only be slightly improved by the inoculation of the landfill with select microbial innoculant (O'Sullivan et al., 2008).

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