Investigating the relationships between anaerobic digestion processes and microbial populations within bioreactors treating municipal solid waste

The purpose of this research was to study the impact processes of a two-phase bioreactor has on the microbiological stabilization of municipal solid waste. In addition, we compared various inocula, and their effects on seven bench-scale reactors to determine which microbial groups were not important.; In the large scale bioreactor study (Chapter 2), the second phase methanogen MPN was 105 cells/ml (near the end of the incubation period at day 205), which correlated with 73% methane gas headspace production. At the same time, the second phase had an increase in volatile fatty acid levels (VFA) such as acetate (3,804 mg/L), and paralleled an increase in methane, (up to 95%, v/v) with an optimal pH of 7.; Additional research was conducted (Chapter 3) to determine which of the inocula limited the single-phase system (0.250 L serum bottles) when placed with a MSW component (food, yard, or paper waste). Methane and volatile fatty acids were monitored to examine metabolism which represented bacterial activity. Native sludge inocula produced the highest amount of methane with any component, but yielded only 1.5% methane when mixed with serum bottles that contained a combination of food, yard, and paper waste.; In the final part of the study (Chapter 4), seven small-scale two-phase bioreactors were inoculated with simulated-MSW (SMSW) and a known cellulose-degrading acetate-producing organism in the first phase and anaerobic treatment plant sludge and a known aceticlastic methanogen in the second phase. Throughout Chapter 4 reactor treatments will be described as "inocula in first phase: inocula in second phase." By comparing all seven small-scale reactors (plus the sterile control) we observed that after 34 days reactor 4 produced more methane than reactor 1. This was surprising since reactor 1 was also considered a positive control standard. After 40 days reactor 4 did not produce additional methane, but reactor 1 increased up to 77% methane production at day 48. Also of interest, reactor 7 produced the highest levels of acetate producing 3.5mM/day at day 10. By tracking the end-products of both trophic groups (acetogens and methanogens), and quantifying these bacterial populations we have obtained data on limiting factors in two-phase digestion.