BATCH AND CONTINUOUS FLOW-REGIME SYSTEM COMPARISON PERFORMING BPR

A laboratory bench-scale sequencing batch reactor (SBR) and a continuous flow activated sludge (CFAS) systems were compared performing biological phosphorus removal (BPR). Both systems followed the Anaerobic/Oxic configuration, were fed with the same synthetic wastewater, inoculated with the same biological seed, and operated under similar conditions.The results of this investigation show two main advantages of the SBR system over the CFAS system. The advantages were greater phosphorus removal efficiencies and better sludge settling characteristics. The average total phosphorus removal efficiency in the SBR system was nearly complete, while the average phosphorus removal efficiency of the CFAS system was 60 percent. Both systems however presented similar average carbon and nitrogen removal efficiencies of 92 and 60 percent respectively. The sludge settling characteristics developed in both systems are described by their average total suspended solids (TSS) concentration in the effluent and their average sludge volume index (SVI). Their average TSS and SVI values were 10 and 3 mg/L and 187 and 52 mL/mg for CFAS and SBR systems respectively.Once both systems reached steady-state conditions, their biomasses were exchanged in order to observe the behavior of biomass in each reactor regime. Exchanging their biomasses resulted in inverting the characteristics of both activated sludges. The well-developed SBR biomass promptly deteriorated its BPR and sludge settling properties once it was exchanged into the continuous flow-regime. Contrary, the poor-developed CFAS biomass considerably improved its BPR and settling properties when exchanged into the batch system. Microscopic examinations of the biomass structures suggested that both systems developed similar microorganisms, but the presence of phosphate accumulating organisms was more robust in the SBR system. Observations found that filamentous organisms were equally present in both systems, however their presence in the CFAS system resulted in bulking sludge, which was successfully controlled by chlorination.Based on the results of this investigation it is concluded that the SBR system offers more stable and efficient BPR performance than the CFAS system. In addition, it is clearly concluded that the SBR configuration greatly helps controlling the sludge bulking.