Refuse decomposition in the presence and absence of leachate recirculation

A side by side comparison of two 8,000 metric ton test cells was performed to evaluate the effects of leachate recirculation on refuse decomposition at Yolo County, CA. After about 3 years of operation, refuse was excavated in three borings from the enhanced cell (E1, E2, and E3) and two borings from the control cell (C1 and C2). 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. Leachate recirculation resulted in both higher methane yields, (63.1 versus 27.9 L CH4/wet-kg over 1231 days) and increased settlement (15.5% versus 3% of the waste thickness). The extent of decomposition of excavated refuse samples was determined by the biochemical methane potential (BMP) and the ratio of cellulose plus hemicellulose to lignin [(C+H)/Li]. Solids analyses showed the average BMP in the enhanced and control cells to be 24.0 and 30.9 mL CH4/dry-g, respectively. The corresponding (C+H)/Li ratios were 1.09 and 1.44, respectively. These data correlate well with the increased methane production in the enhanced cell. Thus laboratory and field data show more decomposition in the enhanced cell relative to the control cell. The refuse 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.