| Summary: | Compared to conventional nitrification and denitrification, anaerobic ammonium oxidation (anammox) is a more energy saving and cost effective process for biological nitrogen removal (BNR). To date, the anammox process has been applied widely and designed mainly to treat sidestream wastewaters. However, only 15%-20% of the influent domestic sewage nitrogen loading is present in the sidestream, while the bulk of it still needs to be removed from the mainstream. Research efforts thus have shifted from sidestream to mainstream applications of anammox, including the application of anammox bioreactors at low temperature, low influent ammonium strength, and under the presence of organic carbon (characteristic of municipal mainstream wastewaters). In this dissertation research, the applicability of anammox process in lab-scale and full-scale mainstream systems have been studied. The overall goals of this dissertation research were (1) to develop an effective strategy to enrich an anammox moving bed biofilm reactor (MBBR) under low influent nitrogenous substrate concentration and ambient temperature (23 Cº), and link microbial ecology to the process performance of the enriched anammox MBBR; (2) to explore the catabolism and anabolism of anammox bacteria in a mainstream MBBR before and after dosing of organic carbon; (3) to extend the strategy of mainstream anammox enrichment under ambient temperature (23 Cº) to low temperature (15 Cº) , and link microbial ecology to the process performance; (4) to evaluate the microbial community structure, kinetics and performance during startup and long-term operation of a full-scale mainstream anammox process; (5) to investigate the reliability of the new enriched mainstream anammox MBBR under the imposition of additional wet weather flow; (6) to develop a reliable and sensitive mothed of hydrazine determination in anammox reactor.
First, an anammox MBBR was successfully enriched under low nitrogenous substrate and ambient temperature. It needs to be addressed that, even with the limited fraction of Candidatus “Kuenenia stuttgartiensis” in the coming inoculum from the sidestream MBBR, Candidatus “Kuenenia stuttgartiensis” was effectively enriched in the biofilm biomass of the mainstream MBBR. Moreover, the enhanced activity of Candidatus “Kuenenia stuttgartiensis” was demonstrated through this whole time series experiments, and achieved the most competitive level among all functional groups. Therefore, the importance and necessity of bioaugmentation are addressed during the enrichment of mainstream anammox process.
Second, successful enrichment of a mainstream anammox moving bed biofilm reactor was accomplished at low nitrogenous substrate and low temperature. 16S amplicon sequencing was employed to investigate the microbial ecology of the biomass in the biofilm and suspension. Results showed the dominance of Candidatus "Kuenenia" related anammox bacteria in the biofilm of mainstream reactor, though Nitrospira spp. related nitrite oxidizing bacteria were still detected in a limited fraction. These results are crucial to show the effective enrichment of anammox reactor by bioaugmentation even under low temperature, especially in a practical way.
Third, the performance, kinetics and microbial ecology were studied before, during and after the imposition of additional organic carbon. The dosing of organic carbon resulted in a reversible negative impact on both the activity of AMX and the reactor performance. Stable isotope probe and 16S amplicon sequencing were applied to investigate the metabolism of functional groups. The results showed anammox bacteria are not capable of assimilating acetate, while the community assimilating 13C-labeled acetate was mainly assigned to denitrifiers. Presence of denitrifiers were observed in the mainstream MBBR and stayed inactive without sufficient organic carbon. In sum, these results demonstrate that the mainstream anammox process as tested was resilient to a short period imposition of organic carbon.
Fourth, the performance and microbial ecology of the ambient-temperature mainstream anammox were investigated under wet weather condition. Based on the full recovery of reactor performance as well as the stable microbial ecology, the applicability of the mainstream MBBR under wet weather conditions was demonstrated.
Fifth, real-time polymerase chain reaction was applied to evaluate the startup and operation of two parallel sidestream DEMONTM systems as well as the initiation of the mainstream anammox process through bioaugmentation. Results provided the evidence that anammox bacteria was the most abundant functional group in two parallel DEMONTM systems, showing the successful startup in the sidestream. Furthermore, anammox bacteria were selectively retained in the mainstream with high bioaugmentation rates from the sidestream. These results are critical to demonstrate the significance of bioaugmentation in the startup of mainstream anammox system even in full-scale wastewater water treatment plant.
Finally, a sensitive and reliable spectrophotometric method was proposed to measure hydrazine concentration in anammox reactor. The concentration of hydrazine could be precisely determined in the presence of nitrite, when a certain amount of sulfamic acid is introduced.
In sum, the application and characterization of anaerobic ammonium oxidation (anammox) process to treat sidestream and mainstream wastewaters in both lab-scale and full-scale was investigated in detail. From a practical perspective, the knowledge gained can lead to a better design and operation of engineered nitrogen removal process.
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