Fate of Selected Metals In a Compost System with Used Wallboard Additives.

Twenty percent of all the material delivered to Construction and Demolition (C&D) sites in the province of Nova Scotia is gypsum wallboard. This can be in the form of residential or business demolition, as well as new wallboard from construction activities. Currently in Nova Scotia, there are no recycling programs for this material therefore it ends up in landfill sites. There are four objectives to this study. First, was to determine the inherent variability in heavy metal concentrations in waste gypsum wallboard from across Nova Scotia. This was accomplished by collecting wallboard samples at a C&D site. An extraction for total heavy metals was done (nitric acid/hydrogen peroxide) and extracts analyzed using atomic absorption spectrometry. Second, was to investigate the potential to compost waste gypsum in a mechanical in-vessel composter. Two composts were prepared, with and without wallboard. Weekly samples were collected and analyzed for total heavy metals and bio-available (DTPA extraction) heavy metals. The third objective will be to investigate the mobility of heavy metals through compost and soil through the use of concrete leaching cells. The compost placed in these cells will be exposed to ambient conditions and water that flows through the compost and underlying soil will be collected. Three treatments will be used for this study; without wallboard, with wallboard and with de-papered wallboard. The periodically collected samples of compost, soil and leached water will be tested for total and bio-available heavy metals concentrations. Finally, a full scale windrow testing will be established to investigate the feasibility of large scale composting of waste gypsum wallboard. This final study will bring together all the knowledge gained in the previous three studies with a real world example of what a compost operation could expect when using waste gypsum wallboard.