Thermophilic Aerobic Wastewater Treatment in Continuous-Flow Bioreactors

Thermophilic aerobic biological wastewater treatment was investigated at 55°C in continuous-flow bioreactors using a synthetic wastewater containing gelatin and (alpha)-lactose as principal organic constituents. By operating multiple continuous-flow bioreactors at different hydraulic residence times (HRTs), the maintenance constant (kd) was calculated to be 0.046 day-1, a value approximately 10-fold lower than that previously reported for thermophilic processes but similar to that for mesophilic treatment. Investigation into the bacterial community structure by denaturing gradient gel electrophoresis of polymerase chain reaction-amplified 16S ribosomal RNA genes revealed that the dominant phylotypes in the bioreactors changed as a function of HRT. Cell reactivity, measured as the specific content of protein and RNA, declined as HRT increased. Catabolic enzyme activities specific to the principal organics in the synthetic wastewater, however, increased at higher HRTs. In conclusion, the performance of thermophilic aerobic biological wastewater treatment processes was similar to that of conventional mesophilic processes with respect to maintenance requirements (i.e., cell yields) as well as bacterial community shifts, cell reactivity, and cell activity.