Various operational strategies in Sequencing Batch Reactors (SBR's) were developed and compared in this study for their effectiveness in achieving simultaneous and complete carbon, nitrogen and phosphorus removal. In addition to investigating the removal efficiencies of each system and their practical control, microbial studies with PCR (Polymerase Chain Reaction) specific-targeted primers and PCR-DGGE (Denaturing Gradient Gel Electrophoresis) were also performed....[ Read more ]

Various operational strategies in Sequencing Batch Reactors (SBR's) were developed and compared in this study for their effectiveness in achieving simultaneous and complete carbon, nitrogen and phosphorus removal. In addition to investigating the removal efficiencies of each system and their practical control, microbial studies with PCR (Polymerase Chain Reaction) specific-targeted primers and PCR-DGGE (Denaturing Gradient Gel Electrophoresis) were also performed.

Fast denitrification frequently observed in a time-based SBR 8 h operation was further investigated in 12-h SBR batch experiments with postdenitrification. Glucose addition was found to be more useful in the postdenitrification process with relatively fast denitrification without triggering phosphate release to the effluent. However, phosphorus may be released, even with limited glucose. Hence, a faster and reliable control instrument is needed to prevent this phosphate release into the final SBR effluent. A phosphate biosensor proved to be a reliable and fast measure which should enable control this release, with the SBR cycle being terminated once the denitrification is completed and at the detection of any secondary phosphate release. A two-sludge system performing enhanced biological phosphate removal (EBPR) and nitrification was also used in an attempt to investigate the stability of EBPR. However, the distribution of organic carbon in the influent to both SBR's made the system worse than the single system. This situation may be improved by further modifications to the operational strategies such as lengthening the nitrification period, and adjusting the cycle times to optimize the carbon distribution between the two SBR's. The dual system, however, suggested that nitrate may have a previously underestimated effect on long term phosphorus removal. To investigate the effect of nitrate on EBPR, two single SBRs were investigated. One was fed with the usual components at their usual concentration, while the other SBR was fed with nitrate without changing COD (Chemical Oxygen Demand) over N (nitrogen) and COD over P (phosphate) ratio. The nitrate-fed SBR was not able to sustain EBPR compared with the 'normal-fed SBR'. Normal-fed sludge could maintain its EBPR for much longer time. When the influents of the two SBRs were swapped, similar EBPR trends were observed.

Several DNA isolates from all SBRs were studied. The results showed that even though each system had different DGGE patterns, there are however no exclusive differences in the DGGE patterns when successful and failed EBPR was performed in one reactor. All PCR specific-targeted primers (e.g: for Rhodocyclus, Acinetobacter, Accumulibacter phosphatis) reactions showed that all of those micro-organisms were present in the SBRs in the 'good' and 'bad' EBPR.

Thus unlike other studies, which suggested that some changes in microbial community were the cause of different capability in phosphorus removal, our work suggests nitrate may be one of the primary causes of the deterioration of phosphorus removal in this transient period, before any changes in microbial community takes place. It also suggests that the role of nitrate in phosphorus removal has been underestimated in previous studies. In practical terms, the combination of existing BOD (Biological Oxygen Demand) and phosphorus sensors with nitrate sensors, which is under development, offers the possibility of developing a practical operational strategy for simultaneous and complete carbon, nitrogen and phosphorus removal.