The present invention provides a rough surface scattering method and solver for efficiently computing electromagnetic scattered fields resulting from an incident wave being reflected from a surface slowly varying on the scale of the wavelength. The voice outputs of different systems can be differentiated by way of voice characteristics. Methods of making the adsorbent composition comprise providing a liquid stream; dispersing iron salts in the liquid stream to form an iron salt solution; adding a carrier to the iron salt solution to form a prepared stream; adding a tannin extract to the prepared stream to form a reaction stream; and forming the adsorbent composition in the reaction stream.