Electrodialytic remediation of CCA treated waste wood in pilot scale

When CCA (Chromated Copper Arsenate) treated wood is removed from service and turns into waste, the contents of Cu, Cr and As is still high due to the strong fixation of CCA in the wood. This high content of toxic compounds presents a disposal challenge. Incineration of CCA treated waste wood is not allowed in Denmark, instead the wood is to be land filled until new methods for handling the wood are available.

Since the amounts of CCA treated wood being removed from service is expected to increase in the years to come, the need of finding alternative handling methods is very relevant. In this present study the utility of the method Electrodialytic Remediation was demonstrated for handling of CCA treated waste wood in pilot scale.

The electrodialytic remediation method, which uses a low level DC current as the cleaning agent, combines elektrokinetic movement of ions in the wood matrix with the princi-ples of electrodialysis. It has previously been shown that it is possible to remove Cu, Cr and As from CCA treated wood using electrodialytic remediation in laboratory scale (Ribeiro et al., 2000; Kristensen et al., 2003), but until now, the method had not been studied in larger scale.

The pilot scale plant used in this study was designed to contain up to 2 m3 wood chips. Six remediation experiments were carried out. In these experiments, the process was up-scaled stepwise by increasing the distance between the electrodes from initially 60 cm to fi-nally 150 cm. The remediation time was varied between 11 and 21 days, and phosphoric acid and/or oxalic acid was used to facilitate the desorption of CCA from the wood.

In the most successful of the experiments carried out, the concentration of CCA in the wood was reduced by up to 82 % for Cr, 88 % for Cu and at least 96 % for As.