Q-204. Microbial Function and Resilience during Shock Loading of Highly Degradable Substrates into Solid Waste

B. F. Staley, J. S. So, F. L. de los Reyes III, M. A. Barlaz;
North Carolina State Univ., Raleigh, NC.

Microbial communities in landfills and landfill bioreactors are exposed to wide variations in substrate availability. Under certain situations, large quantities of highly degradable substrates are placed in the landfill over a short period of time. This can result in a sharp increase in volatile fatty acids and a decrease in pH, causing inhibition of key microbial groups such as methanogenic Archaea. Previous work suggests that higher microbial diversity in anaerobic systems results in greater stability, indicating that functional redundancy may result in better resilience during shock loading events. The objective of this work was to 1) evaluate the resilience and diversity of the microbial community in decomposing refuse under shock loading conditions, and 2) formulate landfill management strategies that minimize the potential for inhibition. In separate treatments, one-time and successive spikes of a highly degradable substrate were made to laboratory scale reactors. Unspiked reactors were also operated as controls. DNA and RNA were extracted from samples collected before, during and after spiking. Terminal restriction fragment length polymorphism (T-RFLP) and clone libraries were used to evaluate the impact on microbial community structure and obtain phylogeny. After spiking, RNA/DNA ratios increased sharply; however, a lag time of 1-5 days was observed at higher spike levels. This trend was highly correlated with methane production. Results thus far indicate that unspiked and low level spike conditions selected for Methanosaeta over Methanosarcina. Methanosaeta have slower growth rates than Methanosarcina at high acetate concentrations. Under high concentrations of acetate, as occurs during a large spike event, a methanogen population dominated by slower growing species that grow on a limited number of substrates may prove less resilient or experience longer recovery. This implies that the landfill management strategies employed and the waste types accepted for disposal affect both the rate of methane production and extent of refuse degradation via alterations in methanogen community structure.