What do you mean by "improve?" Do you want to raise the dielectric constant, lower the dielectric constant, increase the loss, lower the loss, or some combination? By solid waste are you talking about sewage? What are you trying to do?
when organic solid waste were subjected to microwave irradiation, they were converted into carbon, during carbonation ash content obtained was more at high temperature and exposure time. To withstand that situation normally we can use activated carbon (ie Activated carbon is mixed with solid waste). The addition of Activated carbon improved both quantity and quality of carbon. Similarly what are the other ways to improve carbon yield?