Simulation of Construction and Demolition Waste Leachate

Abstract

Solid waste produced from construction and demolition (C&D) activities is typically disposed of in unlined landfills. Knowledge of C&D debris landfill leachate is limited in comparison to other types of wastes. A laboratory study was performed to examine leachate resulting from simulated rainfall infiltrating a mixed C&D waste stream consisting of common construction materials (e.g., concrete, wood, drywall). Lysimeters (leaching columns) filled with the mixed C&D waste were operated under flooded and unsaturated conditions. Leachate constituent concentrations in the leachate from specific waste components were also examined. Leachate samples were collected and analyzed for a number of conventional water quality parameters including pH, alkalinity, total organic carbon, total dissolved solids, and sulfate. In experiments with the mixed C&D waste, high concentrations of total dissolved solids (TDS) and sulfate were detected in the leachate. C&D leachates produced as a result of unsaturated conditions exhibited TDS concentrations in the range of 570–2,200 mg/L. The major contributor to the TDS was sulfate, which ranged in concentration between 280 and 930 mg/L. The concentrations of sulfate in the leachate exceeded the sulfate secondary drinking water standard of 250 mg/L. The leachate produced from lysimeters exposed to conditions of constant flooding possessed a greater concentration of dissolved constituents than leachate from the unsaturated lysimeters. The sulfate concentration ranged from 950 to 1100 mg/L. In both scenarios, the primary ions contributing to the dissolved solids were sulfate and calcium, both a result of gypsum drywall. The flooded lysimeters remained at a constant pH of 11 throughout the experiment, whereas the pH dropped to neutral conditions (pH 6–7) in the unsaturated columns after 1 month of the leaching experiment. The high pH of leachate from the flooded columns was attributed to concrete. Based on leaching tests on individual waste components, wood and cardboard were the primary materials contributing to dissolved organic carbon. The organic carbon concentrations in the leachate were generally lower than typical municipal waste leachate. The biological conversion of sulfate to sulfide was evident in many columns, and was most pronounced in the unsaturated, mixed-waste columns.