Full-scale evaluation of heat balance for autothermal thermophilic aerobic treatment of food processing wastewater

A full-scale autothermal thermophilic aerobic treatment (ATAT) of food-processing wastewater was evaluated in this study. The wastewater was rich in oil and grease at concentrations of 1,500-2,000 mg/L. The system has been operated for more than one and a half years since the startup. Under steady state conditions, the ATAT process was capable of spontaneous reaction at temperatures of 45-55°C without the addition of external heat. Treatment efficiency was as high as 95% in COD reduction at a volumetric COD loading of 4.1 kg/m³-d. A mathematical heat balance model was developed based on the theoretical considerations of heat sources and losses for the ATAT process. A computer algorithm was established to evaluate specific heat potential (Hs) of the wastewater under steady state conditions. Six months of steady-state data were used for the evaluation. The result shows that on average the wastewater had a specific heat potential (Hs) of 4,720 kcal/kg-COD removed and the biological heat contributed 41.4% of the total heat input. A net heat flux of 4,270 kcal/min and volumetric heat intensity (Hv) of 38.0 kcal/L was necessary to maintain reaction temperature at 48.2°C for the ATAT process. The full-scale ATAT process showed the typical characteristics of high removal rate, low sludge yield, and poor solids settleability for thermophilic aerobic treatment reported in the literature.