Hydrodynamic behavior and start-up performance in a periodic anaerobic baffled reactor treating traditional Chinese medicine wastewater for different operation patterns

In order to explore the effect of operation pattern on performance, hydrodynamic behavior and start-up performance including molecular weight distribution (MWD) of soluble organic compounds in a periodic anaerobic baffled reactor (PABR) handling traditional Chinese medicine (TCM) wastewater. Residence time distribution test with tap water in the clean PABR was carried out at a certain hydraulic residence time of 48 h in experiments and in computational fluid dynamics (CFD) simulations, both of which were in good agreement for the 'every second' (switching period T = 48 h), the 'clockwise sequential' (T = 96 h), and the 'no switching' (T = infinity) operation pattern. The CFD model output visualized the hydrodynamic-mass transport, which heavily influenced by operation pattern, successfully inside a PABR. The PABRs run in those three operation patterns were subjected to three successive step changes in average organic loading rate at about 1, 2, 4 and 6 kg COD m- 3 d-1 for 12, 24, 24 and 6 d, respectively. Pollutants in the TCM wastewater had the longest time to be digested and degraded within PABR run in the 'every second' operation pattern, resulting in a most stable performance among the three. Performance of PABR was consistent with the variation in MWD of soluble organic compounds no matter what the operation pattern was. High-MW species (93-130 kDa) broke down into simpler intermediate-MW solutes (7-56 kDa) by the metabolism of anaerobic flocs sludge mostly in the compartment which contributed most to the total COD removal of PABR. Then, intermediate-MW solutes were mineralized step by step into low-MW solutes (100 Da) and biogas in the follow-up compartments in the sequence of flow pattern.