AEROBIC THERMOPHILIC TREATMENT OF SEWAGE-SLUDGE AT PILOT-PLANT SCALE .2. TECHNICAL SOLUTIONS AND PROCESS DESIGN

The performance of the ATS process depends essentially on the oxygen t ransfer efficiency. Improvement of the mass transfer capacity of a bio reactor allowed to reduce the incubation time necessary to attain slud ge stabilization. It is important to use equipment with a high aeratio n efficiency such as an injector aeration system. The ratio between th e total oxygen consumption and the organic matter degradation (Delta C OD) ranged between 0.4 and 0.8 in the pilot plant, whereas 1.23 was fo und in completely mixed bioreactors (Bomio, 1990). No significant impr ovement of the bacterial degradation efficiency was attained with a sp ecific power input exceeding 6-8 kW m(-3). A mean residence time of le ss than 1 d allowed organic matter removals up to 40% with specific po wer consumption of 10 kWh kg(-1) COD oxidized. The sludge hygienizatio n is one of the objectives and benefits of the thermophilic treatment: not only temperature but also the total solids content were important factors affecting inactivation of pathogens. The inactivation rate wa s promoted by the increase of temperature, while the residual colony f orming units decreased with reducing the total solids content of sewag e sludge. It is concluded that continuous operation mode would not aff ect the quality of the hygienization but could display the high degrad ation potential of the aerobic system.