Comparison of Activated Sludge Processes at Different Temperatures: 35°C, 27–55°C, and 55°C

The performance of mesophilic (35°C; referred to as R1) and thermophilic (55°C; R3) laboratory activated sludge processes (ASPs) as well as ASP with a fluctuating temperature (27-56°C; R2) was compared. During the 124-day runs, in R1 and R3 hydraulic retention time was gradually reduced from 18 h to 3 h, corresponding to an increase in volumetric loading rate from 2 to 10 kg soluble COD m−3d−1; in R2 hydraulic retention time was gradually reduced from 18 to 4.5 h, corresponding to an increase in volumetric loading rate from 2 to 7.5 kg soluble COD m−3d−1. R1 removed on average 85% of soluble COD (GF50-filtered) that was approximately 10% more than R3. In R2 SCOD removal was dependent on the operating temperature, being comparable to R1 and R3 at respective temperature. However, the COD for 0.45 µm-filtered (bacteria-free) effluent samples was lower for R3 than for R1, indicating the role of free bacteria on effluent quality. Furthermore, 24 h post-aeration of R3 effluent at 35°C decreased SCOD (GF50-filtr...