02 April 2010
Posted in Center Information
This report contains two separate experiments. The first experiment revolves around lead and its impact on disposed electronic devices. Lead is the element most likely to cause discarded electronic devices to be characterized as hazardous waste. To examine the fate of lead from discarded electronics in landfills, five lysimeters were filled with synthetic municipal solid waste (MSW). A mix of electronic devices was added to three lysimeters (6% by weight), while two lysimeters served as controls. A sixth lysimeter contained waste excavated from an existing MSW landfill. Leachate quality was monitored for 440 days. In lysimeters with the synthetic waste, leachate pH indicated that the simulated landfill environment was characteristic of the acid phase of waste decomposition; lead leachability should be greater in the acid phase of landfill degradation as compared to the methanogenic phase. Lead concentrations ranged from 7μg/L to 66μg/L in the lysimeters containing electronic waste ranged and from < 2μg/L to 54μg/L in the control lysimeters. Although the mean lead concentrations in the lysimeters containing electronic devices were greater than the controls, the difference was not found to be statistically significant when comparing the data sets over the entire monitoring period. Lead results from the excavated waste lysimeter suggest that lead concentrations in all lysimeters will decrease as the pH increases toward more neutral methanogenic conditions.
The second experiment revolves around pressure-treated wood. Pressure-treated wood is often disposed of in landfills in the US, very frequently in construction and demolition (C&D) debris landfills. C&D debris landfills in many states are not equipped with liner systems to protect groundwater. With the voluntary withdrawal of chromated copper arsenate (CCA) treated wood for most residential applications in January 2004, copper-based wood preservatives, including alkaline copper quaternary (ACQ), are more widely used. To evaluate the impact of metal losses from ACQ-treated wood disposed in C&D debris landfills and compare to those of CCA-treated wood under similar conditions, leachates from three simulated C&D debris landfills (lysimeters) were collected and analyzed for over a period of one year. The wood component in one lysimeter (the control lysimeter) contained pallet wood; the second lysimeter contained CCA-treated wood, and the third contained ACQ-treated wood. Each lysimeter was buried in an active landfill for temperature control. Several batch leaching tests (including the standardized toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP)) were also conducted for comparison purposes. Although the two lysimeters containing treated wood had vii elevated copper concentrations within the waste matrix, the concentration in the leachate samples from these lysimeters was below detection for Cu (<4μg/L) throughout the duration of the experiment, likely a result of precipitation as copper sulfide mineral in the reducing conditions of the simulated C&D landfills. As expected, the lysimeter containing CCA-treated wood showed elevated concentrations of arsenic and chromium, with maximum concentrations of 1.16 mg/L and 0.2 mg/L respectively. Greater amounts of boron (B) leached from ACQ-treated wood than CCA-treated wood or pallet wood debris. The results suggest that copper leaching will not be a major concern upon the disposal of ACQ-treated wood in C&D debris landfills. Arsenic leaching from CCA-treated wood remains a concern for unlined C&D debris landfills.