Design and performance of a pilot-scale equipment for CCA-treated wood remediation

Increasingly stringent regulations regarding waste disposal encourage the development of options for reuse, recycling and revalorisation of waste. Metals-bearing treated wood wastes are no exception. Previous studies identified a possible treatment technology for chromated copper arsenate (CCA) preservative-treated wood waste based on sulphuric acid leaching. In this study, the scale-up of this technology was extended from 200 ml flask to 80 l working volume stirred-tank reactor. The study involved three leaching steps of 2 h each, at 75 °C with 0.2 N H2SO4 and 15% solids content followed by three rinsing steps. This procedure led to removal of 99.5% of the arsenic, 95.7% of the chromium and 99.6% of the copper from the wood chips on average. The effluents generated by the leaching steps were then treated by precipitation. This technology allowed 99% removal of As, Cr and Cu from the leachate, leading to effluents satisfying the regulations for effluent discharge in municipal sewers. The mass balance was assessed for the whole process (leaching, rinsing and precipitation of the leachate) and the output to input ratio was between 80% and 100%. Furthermore, the economic analysis concluded that the operating cost of the process (leaching, rinsing and precipitation of the leachate) was about 250 $/ton of treated wood (t.t.w.) with the conditions employed in this study. However, the cost could be reduced at least to 89 $/t.t.w. by using a counter current leaching process as developed in a previous study.