The two-stage cyclic anaerobic filter system involves operation of two equal-volume reactors in series. After a given period of operation, the flow regime is reversed so that the follow reactor becomes the lead reactor and vice versa. The basic concept behind the two-stage, cyclic
(TSC) process is that active biological solids remaining in the follow reactor from the previous lead position continue to remove soluble organic constituents to lower concentrations than would be achieved by a single-stage unit. A study was conducted by the authors to develop a procedure
for optimizing the time between flow reversals. Six laboratory-scale anaerobic filters were operated at organic loading rates varying from 0.5 to 20 g soluble COD/L/day and at system hydraulic retention times ranging from 6 to 10.5 days. Two sets of reactors in series were operated
in the cyclic mode. Wastewater from a brewery was used as feed throughout the study. The COD of this wastewater ranged from 1,500 to 2,500 mg/L. All systems were operated at 35°C. The authors' study has shown that the performance of the two-stage cyclic anaerobic filter system
was closely related to the cycle time. The optimum cyclic time could be determined by using an operational index [Soτc/M], which includes influent wastewater, COD (So), cycle time (τc), hydraulic retention
time (), and biomass inventory (M). This optimum cycle time also corresponded to the time when the gas production in the second (follow) stage became less than 10 % of the total gas production. The hydraulic pattern of the upflow hybrid anaerobic filter under normal operating
conditions demonstrated performance similar to that of a plug flow reactor with strong dispersion. Compared with the clean bed condition with gas mixing, the dirty beds displayed more short-circuiting. These results suggest that, under normal operating conditions, biogas mixing and biomass
accumulation had a significant effect on reactor hydraulics, thereby causing short-circuiting.
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