Evaluation of Waste Gypsum Wallboard as a Compost Additive

Abstract

Twenty percent of all the material delivered to construction and demolition (C&D) disposal sites in the Province of Nova Scotia, Canada, is waste gypsum wallboard (WGW) (Dillon Consulting Ltd., 2006). This is typically in the form of residential or business demolition waste, which includes WGW from new construction activities. This study looked at the use of papered and de-papered waste gypsum wallboard in compost to evaluate its impact on the process, total heavy metal concentration, bioavailable metal concentration, and movement of heavy metals. The study consisted of three components: a short term mechanical in-vessel compost sub-study to assess the impact of composting WGW; a lysimeter cell sub-study to evaluate potential movement of compost constituents from compost to soil and water under a static compost system open to the ambient environmental conditions; and, a final sub-study to determine the performance of waste gypsum wallboard in compost under controlled composting conditions. The study found that the inclusion of up to 34% (by mass) WGW had no negative effects on the degradation of carbon, final pH, and final electrical conductivity in the compost product, however, WGW-containing composts did increase concentrations of total sulphur. There was the potential for elevated levels of total lead and cadmium but the compost produced was within the CCME Class A guidelines for heavy metal concentration. Waste gypsum wallboard containing composts also had increased levels of bioavailable cadmium compared to non-WGW composts.