What are the stages of biodegradation in a landfill environment?
Aerobic Phase (first few days) – This is the phase when aerobic microbes are becoming established and moisture is building up in the refuse. While standard plastic absorption capability is relatively small, the additive causes further swelling, weakening the polymer bonds and creating molecular spaces where moisture and microbial growth can rapidly begin the aerobic degradation process. Oxygen is replaced with CO2.
Anaerobic, Non-Methanogenic Phase (roughly 2 weeks to 6 months) – After oxygen concentrations have declined sufficiently the anaerobic processes begin. During the initial stage (hydrolysis), the microbe colonies eat the particulates, and through an enzymatic process, reduce large polymers into simpler monomers. The secreted monomers mix with the organic additive, causing additional swelling and opening of the polymer chain and increased quorum sensing. This further excites the microbes to increase their colonization and consumption of the polymer chain. As time progresses, acidogenesis occurs where the simple monomers are converted into fatty acids. CO2 production occurs rapidly at this stage.
Anaerobic, Methanogenic Unsteady Phase (6 to 18 months) – The microbe colonies continue to grow, eating away at the polymer chain and creating increasingly larger molecular spaces. During this phase acetogenesis occurs, converting fatty acids into acetic acid, carbon dioxide, and hydrogen. As this process continues, CO2 rates decline and hydrogen production eventually ceases.
Anaerobic, Methanogenic Steady Phase (1 year to 5 years) The final stage of decomposition involves methanogenesis. As colonies of microbes continue to eat away at the remaining surface of the polymer, acetates are converted into methane and carbon dioxide, and hydrogen is consumed. The process continues until the only remaining element is the humus. This highly nutritional soil creates an improved environment for the microbes and enhances the final stage of decomposition.