Partial Nitrification Processes for Ammonium Rich Sludge Thickening Lagoon Supernatant Treatment

  • Author / Creator
    Shao, Yanxi
  • In wastewater treatment, nitrogen removal is becoming increasingly challenging to meet the more stringent standards and regulations. At local wastewater treatment plant, nitrogen removal is challenging when the plant was experiencing shock loadings. Thus, improving the nitrogen removal is urgently needed at the wastewater treatment plant. It is found that more than 30% of the total nitrogen loading to the plant is contributed by returning the high ammonia strength lagoon supernatant separating from the anaerobically digested sludge. Technology improvement facilitates the nitrogen removal efficiency. Nitrogen is conventionally removed through complete nitrification processes. However, the processes may consume a large amount of oxygen to treat high ammonia strength wastewater. In this case, a more sustainable treatment using partial nitrification is preferred. The first part of this thesis was testing the applicability of integrated fixed film activated sludge (IFAS) technology to handle the shock loading conditions. The second part of this thesis focused on investigating the applicability of the IFAS technology in treating the high ammonia strength supernatant. Complete nitrification was employed for low strength wastewater treatment. The complete nitrification oxidized ammonium to nitrite by ammonia oxidizing bacteria (AOB), and further to nitrate by nitrite oxidizing bacteria (NOB). For the partial nitrification, the process oxidized the ammonium to nitrite, instead of nitrate. The partial nitrification process saved 25% of the oxygen requirement, as compared to the complete nitrification process. If combining the partial nitrification with the denitritation process, the combined processes can even save 40% of carbon sources requirement for the denitritation. In the first part of this thesis study, a bench top IFAS reactor was operated to investigate the ammonium removal efficiency and the stability of IFAS reactor in response to sudden operational condition changes. Suspended flocs and attached biofilm were the two major biomass aggregates in the IFAS reactors, the differences of the microbial structure and biodegradation kinetics of these two aggregates were explained in detail. The second part of this study investigated the impact of ammonium concentration on the establishment of partial nitrification microbial community in an integrated fixed-film activated sludge (IFAS) reactor. Partial nitrification was achieved successfully under room temperature when the NH4+-N concentration in the feeding was greater than 400 mg/L. The ammonium nitrogen concentration in the digested sludge supernatant determined the free ammonia concentration, which was identified as the key controlling factor for the partial nitrification process. Molecular analysis confirmed that AOB abundance increased and NOB number reduced at high ammonium loading conditions. Compared with biofilm, suspended sludge played a major role in ammonium removal, which contributed to 66% total ammonium conversion. The impacts of feed water characteristics, including the ammonium concentration and the percentage of raw digested sludge liquor supernatant in the feed, on microbial population dynamics and nitritation kinetics were elucidated. It was observed that increased ammonium concentration in the reactor feed led to the enhanced specific ammonium conversion and nitrite accumulation rates but reduced microbial community diversity. The increased raw supernatant percentage reduced specific ammonium conversion and nitrite accumulation rates and led to an increased microbial community diversity. Microbial community structures varied significantly in suspended flocs and in attached biofilm. The production and composition of extracellular polymeric substances (EPS) were important parameters of bioreactor performance. The characteristics of EPS from nitritation- and nitrification- dominant processes in the IFAS reactors were compared. The results showed that the loosely bound EPS (LB-EPS) mainly consisted of polysaccharides, while tightly bound EPS (TB-EPS) were composed of polysaccharides and protein in variable ratios. The quantitative polymerase chain reaction and EPS composition analysis (X-ray photoelectron spectroscopy and three-dimensional excitation and emission matrix fluorescence) demonstrated that the microbial community structure determined the TB-EPS composition. Higher abundance of AOB was related to higher amide or amine like substances content and more aromatic and tryptophan protein like substances in TB-EPS. The decrease of heterotrophic bacteria and nitrite oxidizing bacteria correlated to a decreased hydrocarbon-like substance and humic acid like substances in the TB-EPS. Quartz crystal microbalance with dissipation studies demonstrated that the adsorption of TB-EPS to solid surface was stronger and less reversible as compared to the LB-EPS, which emphasized the importance of protein in cell adhesion.

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  • Degree
    Doctor of Philosophy
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