Q-203. The Effect of Environmental Selection Mechanisms on Microbial Ecological Succession During Refuse Decomposition

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

Landfilled refuse is one of the largest sources of anthropogenic methane (CH4) in the U.S. Since CH4 is both a source of energy and a greenhouse gas, the rate and extent of waste decomposition has important implications for enhancing CH4 recovery and minimizing its atmospheric release. Given the syntrophic relationship between anaerobic bacteria and methanogenic Archaea, microbial diversity is a critical component of the refuse decomposition process. Previous work has suggested cellulolytic, acetogenic and methanogenic groups experience population increases as refuse degrades. However, the impact of ecological succession on the anaerobic microbial food web has not been studied. The objectives of this study were to: 1) identify dominant Bacteria and Archaea in refuse during decomposition and 2) evaluate the importance of environmental parameters on microbial ecological succession. Fresh refuse was placed in laboratory scale reactors and decomposed under anaerobic conditions for roughly 140 days. Bacterial and archaeal community structure was evaluated on extracted DNA and RNA from 10 samples of refuse solids and leachate using terminal restriction fragment length polymporphism (T-RFLP) and clone libraries. Results showed that DNA levels, which are indicative of population, were relatively constant throughout refuse decomposition. Total RNA levels, on the other hand, were highly correlated with CH4 and CO2 production. T-RFLP results showed that >80% of dominant T-RFs were replaced by new dominant T-RFs, indicating substantial ecological succession occurred. Low T-RF richness was observed when levels of soluble substrates were high, suggesting that excess substrates maximize competitive selection of only a few dominant organisms. These results suggest environmental paramaters such as VFA level can be used as selectors to maintain distinct population demographics. It may be possible to exploit this finding to enhance refuse decomposition and improve CH4 production.