Solid waste disposal is a serious problem in the United States and other developed countries. Solid waste can constitute valuable raw materials for commercial and industrial operations, however, and one of the challenges facing scientists is to develop an economically efficient method for utilizing it.

Although the concept of bacterial waste conversion is simple, achieving an efficient method for putting the technique into practice is difficult. The main problem is that efficiency of conversion requires increasing the ratio of solids to water in the mixture, and this makes mixing more difficult mechanically. The high-solids reactor was designed by scientists at the Solar Energy Research Institute (SERI) to solve this problem. It consists of a cylindrical tube on a horizontal axis, and an agitator shaft running through the middle of it, which contains a number of Teflon-coated paddles oriented at 90 degrees to each other. The pilot reactors...