DEVELOPMENTS IN THE THERMAL DRYING OF SEWAGE-SLUDGE

The application of heat to dried sewage sludge has been practised by t he water industry for many years. Early technologies were effective bu t their utilization of energy was not so efficient. Other industries h ave faced up to this problem and, as a result, have developed thermal- drying techniques which are more efficient and therefore more cost eff ective. In recent years, the transfer of this technology to sewage-slu dge drying has been taking place, and some companies have designed dry ers specifically for this purpose. Commercial and legal pressures have also focused attention on the final product and its use in agricultur e, horticulture, land reclamation, landfill, incineration, and as a su bstitute for fuel. This paper reviews the work which has been undertak en to determine the changes which occur as sewage sludge is dried, and discusses the technology which is available at present. Factors influ encing capital and operating costs and product choice are also include d.