EVALUATION OF THE DUAL DIGESTION SYSTEM .1. OVERVIEW OF THE MILNERTONEXPERIENCE

A number of advantages are claimed for dual digestion as a system for sewage sludge pasteurisation and stabilisation. In this paper, the fir st of a series of 4, an overview of a 4-year full-scale (45 m3 aerobic reactor and 500 m3 anaerobic digester) dual digestion research projec t is presented. The project was undertaken at Milnerton (Cape, South A frica) and its principal objective was to evaluate the claims made for the dual digestion system. In this paper the claims are stated; the l ayout and operation of the dual digestion system described; the main r esults obtained briefly discussed; and the claims evaluated with the a id of the results. It is concluded that most of the claims are valid, inter alia, the mesophilic anaerobic digester performance is not adver sely affected by the first stage autothermal thermophilic aerobic reac tor compared to conventional digestion. The 3 sequel papers focus atte ntion on the aerobic reactor; its operation, performance, control, des ign and simulation of the temperature profile for both air and pure ox ygen systems.