Comparative analyses of hydraulic characteristics between the different structures of two anaerobic baffled reactors (ABRs)

•An opposite folded plate reactor (OFPR) was proposed.•Hydraulic characteristics on the different structures of two ABRs was presented.•A useful method to evaluate the mixing pattern and the dead space was studied.•The special design of the OFPR could increase COD removal rate effectively.•The construction of the OFPR could provide a larger effective volume.

The plane folded plate reactor (PFPR) and opposite folded plate reactor (OFPR) are two types of anaerobic baffled reactor (ABR) with similar design concepts and principles. Residence time distribution (RTD) analysis on the PFPR and OFPR under clean and working conditions at the same hydraulic residence time (HRT) of 4, 6, 8 and 10 h were performed to investigate mixing patterns and dead space. The results under all test conditions showed that the mixing pattern for both reactors fell within the “intermediate state”, that was, between plug flow and completely mixed. The mixing pattern of the OFPR, however, was closer to plug flow. Thus, the dead space of the OFPR was less than that of PFPR, regardless of whether the reactors were inoculated, and the chemical oxygen demand (COD) removal of the OFPR was better compared with that of the PFPR under the same HRT. The experimental results revealed that the OFPR was a potential reactor for wastewater treatment.