[Impacts of initial moisture content of MSW waste on leachate generation and modified formula for predicting leachate generation].

The amount of leachate generation rate in MSW landfills is often underestimated during design phase in China. A water balance model of a valley landfill, whose size is 400 m long, 500 m wide and 50 m thick, is created to investigate the influences of initial moisture content of waste on source and production of leachate. The 50 m thick waste mass is assumed to be 5 layers. Each layer is 10 m thick with a filling period of 2 years. The leachate mainly comes from precipitation and from squeezed pore water of waste. It is found that higher initial moisture content of waste leads to higher amounts of squeezed leachate and total leachate generation rate, and also results in a high ratio of squeezed leachate to total leachate generation rate. For the cases that the initial moisture contents of waste are 27%, 40%, 50%, and 60%, the amounts of total leachate generation rate are 272, 583, 823 and 1 063 m3 x d(-1), respectively, and the amounts of squeezed leachate are--144, 168, 408, and 647 m3 x d(-1), respectively. It is also found that when the initial moisture content of waste is greater than 50%, the squeezed leachate becomes the primary source of total leachate generation rate. However, the formula for predicting leachate generation rate used in the national code could not consider the contribution of squeezed leachate, this may cause a significant underestimation of leachate generation rate for the case having a high initial moisture content of waste. Based on the water balance analyses, a modified formula for predicting leachate generation rate, which includes the contribution of squeezed leachate is proposed. It is verified by consideration of the operational practices of two large-scale landfills in southern China.