The conventional single-stage anaerobic digestion system employed in korea has been limited in an effective stabilization and sewage sludge. This indicates relatively higher management cost for the sewage sludge treatment. Temperature-phased anaerobic bioreactor system could be an alternative technology to circumvent these problems. This system includes a thermophilic (55℃) reactor and a mesophilic (35℃) reactor in sequence. The temperature-phased system employs a thermophilic process where consumption of organics at higher concentration can be performed. This system can be remove pathogen more efficiently and cause little scuming or foaming that has been typical in the conventional sludge treatment system.
The purpose of this study was to compare the performance of the temperature-phased (thermophilic/mesolphilic) sludge treatment system with the conventional single-stage system in treating mixtures of primary sludge and waste activated sludge in terms of sludge stabilization methane production and hydraulic retention time.
For this study, TPAD system comprised a two-stage reactor system which gas composed of a thermophilic anaerobic digestion system (12.6L) and a mesophilic reactor (34.8L) in sequential order while the conventional single-stage system had a working volume of 51L. Both reactor systems were run in various range of hydraulic retention time to comparatively analyze an optimal retention time for each system.
The experimental results were summarized as follows. Little foaming was observed in TPAD system after 18 days of operation while the foaming was significant in the conventional system from the beginning. In terms of volatile solids (VS) removal the TPAD system showed a maximum rate at the HRT of 10 days. However, the conventional system gave a similar effect as in TPAD system after 28 days, indicating TPAD system was almost 3 times as effective as the conventional system in terms of treatment time. COD, VS removal efficiency in the thermophilic reactor of TPAD system was inversely proportional to HRT but this was compensated in the mesophilic reactor in the system. The conventional system, however, needed longer HRT to reach the equivalent removal efficency. pH and VFA/alkalinity ratio in both systems a were generally maintained in a stable range regardless of HRT.
From the above results, it was generally concluded that the TPAD system was more efficient in stabilization of sludge, organics reduction, methane production, and decreased HRT, hence reduced volume in sludge digester.
This study showed contribute to an understanding of TPAD system in view of sludge treatment compared with the convintional system and to development of a TPAD system applicable to a field situation.