| In the first part of the study, a bioreactor landfill cell was operated aerobically for six months to quantify the extent of aerobic degradation and mechanisms limiting aerobic activity during air injection and liquid addition. From an analysis of in situ aerobic respiration and gas tracer data, it was found that a large fraction of the gas filled pore space was in immobile zones where it was difficult to maintain aerobic conditions, even at relatively moderate landfill cell-average moisture contents of 33--36%. Even with the intentional injection of air, anaerobic activity was never less than 13%, and sometimes exceeded 65%. Analyses of gas tracer and respiration data were used to quantify rates of respiration and rates of mass transfer to immobile gas zones. The similarity of these rates indicated that waste degradation was influenced significantly by rates of oxygen transfer to immobile gas zones, which comprised 32--92% of the gas-filled pore space.;In the second part of the study, a landfilled-based two-stage (anaerobic/aerobic) batch digester cell was constructed, operated, and monitored for treatment of source separated green waste while recovering energy and compost. The performance was evaluated in terms of cell operating temperature, leachate quality, methane generation rate, air emissions, waste decomposition indicators, energy production, and compost quality. The overall average temperatures of the cell during the anaerobic and aerobic phases were desirably high, in the thermophilic range. Although concentration of ammonia reached a high value of 2,400 mg/L, the volatile fatty acids concentrations and pH values were consistent with a healthy digester with no inhibition of methane production throughout the operating period. The decay rate observed in the landfill digester (k=0.82/yr) thus represents about a 20-fold acceleration of methane generation compared to the U.S. EPA default for solid waste. The biofilter's removal of volatile organic compounds and total gaseous non-methane organic compounds varied from 99 to 96% and 99 to 68%, respectively. The biochemical methane potential decreased by 83% during the entire operation, indicating compost feedstock contents were well decomposed. Compost removed and tested passed all of the U.S. Composting Council's Seal of Testing Approval Standards. |
