Comparison of refuse decomposition in the presence and absence of leachate recirculation at the Yolo County, California test cells

by 1975- Mehta, Rinav C.

MEHTA, RINAV C. Comparison of Refuse Decomposition in the Presence and Absence of Leachate Recirculation at the Yolo County, California Test Cells. (Under the direction of Morton A. Barlaz.) A side by side comparison of two 8,000-metric ton test cells, one operated with (enhanced) and one without (control) leachate recirculation, was performed to evaluate the effects of leachate recirculation on refuse decomposition at Yolo County, CA. After about three years of operation, refuse was excavated in three borings of the enhanced cell (E1, E2 and E3) and two borings in the control cell (C1 and C2). The objective of this study was to present a comparison of test cell performance with respect to moisture content, settlement, methane production and solids decomposition. Refuse moisture content data show that leachate recirculation resulted in an increase in refuse moisture content, but also show that the refuse in the enhanced cell was not uniformly wet. The average moisture content in E1, E2 and E3 was 38.8, 31.7 and 34.8%, respectively, while the average moisture content in C1 and C2 was 14.6 and 19.2%, respectively. The extent of decomposition was determined by the biochemical methane potential (BMP) and the ratio of cellulose plus hemicellulose to lignin ((C+H)/L). BMP analysis showed the average methane potential in the enhanced and control cells to be 24.0 and 30.9 mL CH4/dry-gm, respectively, and the (C+H)/L of 1.09 and 1.44. These data correlates well with the measured methane production in the enhanced and control cell of 54 and 26 L CH4/wet-kg, respectively. Thus, laboratory and field data shows more decomposition in the enhanced cell relative to the control cell. While the overall averages may not appear significantly different, a closer look at the performance of E1 shows a difference in both moisture content and solids decomposition when compared to the control cell. Hence, the extent of decomposition varies within the enhanced cell. The sampling program conducted for the Yolo County test cells, in concert with data on settlement, methane production and the volume of liquid actually recycled, represents perhaps the most complete set of data available to date on a field-scale leachate recirculation landfill. ii