Effects of Using Waste Gypsum Wallboard On Composting Dynamics and Chemical Parameters.

Waste Gypsum Wallboard was added to a horse bedding/straw compost to evaluate the effect on chemical composting parameters. The completely randomized design study consisted of two treatments, compost with and without waste gypsum wallboard addition, and four replicates. The waste gypsum wallboard was sourced from a construction and demolition debris disposal site and consisted of new construction scraps and material received from renovation/demolition projects. The wallboard was crushed using a disc grinder and further size reduced with a tremmel screen to less than 0.5 inch in size. Waste gypsum wallboard was added at a rate of 18% on a dry weight basis.  Samples were collected at initial compost preparation and after mixing at 43, 121, 340, and 353 days. The compost was evaluated for pH, electrical conductivity, chloride ion concentration, total carbon, total nitrogen, and total sulphur. It was found that both treatments had similar reductions in total carbon to nitrogen ratios over the length of the study even though the waste gypsum wallboard treatment had significantly lower total carbon and total nitrogen contents. An increase was measured in pH for both treatments over the length of study from. The total sulphur content of the waste gypsum wallboard treatment was nine times greater than the control treatment (2.7% vs. 0.3%) by the end of the study. The waste gypsum wallboard treatment had a lower overall dry mass loss at 38% compared to 50% for the control treatment. Overall, in this study the addition of waste gypsum wallboard to compost was not found to have a negative effect on composting dynamics.