Two-Phase, Two-Stage, and Single-Stage Anaerobic Process Comparison

In this research, three anaerobic process configurations-namely, two-phase dual sludge (TPDS), two-stage single sludge (TSSS), and single-stage-were evaluated for effluent COD concentration. The same temperature, SRT, and glucose substrate were used in all experiments. In every case, TPDS and TSSS configurations significantly outperformed the single stage. All experiments were carried out at a temperature of 35°C, and all reactors were operated as daily fill-and-draw with HRT = SRT. The following ranges for each design parameter were studied: pH (4.5, 5.5, and 6.5); first stage HRT (3, 8, and 24 h); and floc load (3, 9, and 27 gCOD/gVSS). The overall HRT/SRT of all systems was 30 days, and a pH-Stat system was used to control the pH in the acidification reactors at the desired value. Statistical evaluation of the results indicated that a floc load of 3 in the first reactor of TPDS yielded the lowest effluent COD concentrations under the studied range of parameters, while for the TSSS reactor configuration the staging of the system itself was the controlling phenomena responsible for reduced effluent COD.