Combustion Ash As a Potential Electrode Material: Modifying Surface Structures Via Electrical Treatment

Ash, a byproduct of waste to energy plants, typically has a relatively high heavy metal content and as such safe means for its disposal or reutilization are under investigation. It is intrinsically hydrophobic and highly oxidized, which leads to high melting points and, in general, very low conductivities. The research presented here seeks to explore the potential of combustion ash to be used as an electrode material for a microbial fuel cell (MFC). This application requires an increase in conductivity, hydrophilicity, and, ideally, low toxicity.

Three bottom ash samples were investigated, namely Essex-2, Essex-6, and HP3-BA. By applying an electrical potential across the ash in the presence of deionized water, several key property changes can be achieved. Using a variety of analytical techniques including SEM, XRD, TGA/DSC, and tensiometry, we find that not only is the melting point lowered for all three ash samples, a color change indicative of chemical reactions occurs within the ash upon application of the potential. SEM analysis provides evidence of changes in crystal structure and water-ash contact angles are altered from hydrophobic to completely wetting. Unlike in electrowetting, these changes are found to last even after the electric potential is removed. The color change of the ash could be indicative of a change in oxidation state, which may assist in metal recovery processes and in other disposal methods. The ability to alter these key characteristics of the ash opens up an array of possibilities for its safe reuse, including applicability as an electrode in a MFC.