Effect of Atuothermal Thermophilic Aerobic Digestion Operation on Reactor Temperatures

A pilot scale facilities of Autothermal Thermophilic Aerobic Digestion (ATAD) was designed for stabilization of sewage sludge. The operating parameters that influence reactor temperature change were studied such as volatile solids (VS) concentration of feed sludge, hydraulic retention time (HRT), aeration rate, and mixing mechanical energy. The effect of reactor temperature on the destruction pathogens was also determined. This study found that: 1) the optimal initial VS concentration and HRT of the sludge were 30~40g/L and 10~15d respectively; 2) aeration rate has relevance to VS concentration and has important effect on reactor temperature rise and VS reduction. An excessive air flowrate resulted in a drop in temperature; 3) reactor can keep normal temperature in condition of circular flowrates at 12~14 m³/h and mixing power density at 280~330W/m³; 4) ORP values demonstrated that the ATAD process was an anaerobic environment first, and then microaerophilic. This study demonstrates that the ATAD process was not completely autothermal, but required a heat component from mechanical mixing energy to maintain reactor temperature. The temperature in ATAD tank was likely, the most important factor influencing the rate of pathogen inactivation.