|Ph.D Student||Dawas Anwar|
|Subject||Investigation of the Partial Nitritation/Anammox Process in|
a Fixed Bed-Biofilm Reactor at Main-Stream
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Carlos Dosoretz|
|Dr. Isam Sabbah|
|Full Thesis text|
Biological autotrophic nitrogen removal from wastewater proceeds via aerobic partial nitritation (PN) followed by anammox-anaerobic ammonium oxidation (PN/A). The key factor for stable PN/A is limited dissolved oxygen (DO) supply. Application of PN/A for main -stream municipal wastewater treatment, characterized by low ammonium concentration-high C/N ratio and low temperatures, is therefore challenging.
The general objective of this research was to investigate PN/A at main-stream conditions. To achieve the objectives, the research was performed in four steps. First, the ubiquity and distribution of anammox bacteria in a conventional municipal wastewater treatment plant (WWTP) was characterized. Second, PN at main-stream conditions was studied in a fixed bed-up flow reactor using split feed/external recirculation taking advantage of the inherent oxygen and substrate gradients. A numerical model for process optimization was developed and the microbial ecology characterized. Third, a major emphasis was placed on coupling process performance with the microbial ecology to understand the effect of the operational conditions on the microbial dynamics of the system. Finally, the concept of process stability suitable for main-stream conditions was examined through coupled entrapment of PN/A biomass with ammonium and nitrite adsorbents (zeolite and resin) in a polyurethane foam matrix (PUF).
Anammox bacteria were detected in all stages of the WWTP tested and activity demonstrated by 15N-isotopic tracing, depicting their propensity to proliferate at main-stream. Managing aeration by split feed-external recirculation in a fixed-bed bioreactor resulted a reliable tool for effectively controlling PN at main-stream conditions. Optimal ratio with minimal accumulation was achieved at recirculation rates of 4-6 at well-developed plug-flow regime. A significant change was observed in the abundance of the bacterial communities along the reactor in comparison to the seed. The DO profile/substrate availability affected the distribution of N-transforming bacteria along the reactor. Ammonia oxidizing bacteria were dominant in the bottom layers, anammox bacteria growth was enhanced in the middle layers, and nitrite oxidizing bacteria in the upper layers. The low DO concentration promoted growth of Nitrospira defluvii which has extremely high oxygen affinity. The numerical model successfully predicted the experimental results and displayed good sensitivity to intrinsic oxygen uptake parameters. The combination of zeolite and resin in the same PUF matrix proved effective in minimizing nitrite oxidizing bacteria activity and PN stability, while protecting anammox bacteria from DO inhibition. Concluding, the main outcomes of this research provide an evidence for the possible integration of anammox process in main-stream under appropriate partial nitrification conditions.