Operation scheduling of batch autothermal thermophilic aerobic digestion processes

Abstract

The autothermal thermophilic aerobic digestion (ATAD) is an exothermic batchwise operated sludge treatment process, in which sludge undergoes heating and pasteurization as temperature attains values about 50-60ºC. Based on detailed process models, different approaches have been suggested (Rojas and Zhelev, 2009) to minimize the specific energy requirement of existing ATAD designs by altering the operating conditions, but less attention has been paid to process optimization by means of operation planning and timing. This work aims at minimizing the specific energy requirement of existing ATAD processes considering simultaneously operational conditions, planning and timing. Hence, a scheduling formulation including process model variables and a flexible recipe is proposed. Energy savings are reported for a case study of a simplified treatment plant. The proposed approach results in energy consumption reduction by optimizing batch sizes and operating conditions.