Effect of Waste Depth on Leachate Quality from Laboratory Construction and Demolition Debris Landfills

Abstract

Landfill leachate quality varies as a function of many factors including waste type, waste depth, time, weather, and landfill operations. A laboratory study was conducted to examine the effect of waste depth on construction and demolition (C&D) debris leachate quality over a period of 365 days. Both single and serial lysimeters were used to simulate leachate from two different C&D debris landfill waste depths. For the serial lysimeter, five individual lysimeters were connected in series; leachate produced from the first lysimeter was pumped into the top of the next lysimeter and so on. The leachate serially flowed through a 6-m depth of C&D debris. An additional single lysimeter with a 1.2-m waste depth was operated by itself. Leachate samples were collected from both lysimeter sets and analyzed for a number of chemical constituents. Although waste depth was demonstrated to play an important role in the chemical composition of leachate from simulated C&D debris landfills, factors such as biological activity and chemical precipitation may also play a major role. Soluble ions (e.g., sodium) increased in concentration at the greater waste depth as the liquid to solid ratio decreased. Some metals (e.g., copper) showed little difference in leachate concentrations between the two different waste depths; concentrations of these metals decreased to below detection limit when reducing conditions became established. The results suggested that sulfate reducing bacteria converted dissolved sulfate from gypsum drywall to sulfide species; many metals are known to precipitate as metal sulfides. The responses of various chemical constituents to increasing waste depth vary as a function of the nature of the contaminants in the leachate as well as chemical and biological conditions in the waste.