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Title: Effect of microbubble on the performance of the partial nitrification and Anammox process
Author: Zhu, Xia
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2013
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Nitrogen pollution is an increasingly important global concern because it has multiple impacts on terrestrial, aquatic and atmospheric environments. Nitrogen is usually present in wastewater as ammonium. Ammonium can be removed from wastewater by a variety of physicochemical and biological processes, but biological processes are preferred because they are usually more efficient and environmentally friendly. Conventional biological nitrogen removal is carried out by autotrophic nitrification and heterotrophic denitrification via nitrate, which use biodegradable organic matter as electron donor. However there are some kinds of wastewater with low concentrations of biodegradable organic matter such as landfill leachate and anaerobic digester supernatant. In these cases an external organic carbon source is necessary in order to obtain a complete denitrification, which implies higher economic cost. Partial nitrification- Anammox process as a promising and novel biological technology of removing nitrogen from high-strength ammonium wastewater with a low C/N ratio has attracted increasing attention due to its higher efficiency and cost-effectiveness compared with the conventional nitrification-denitrification nitrogen removal process. However, many challenges were faced during the development of stable and high-efficiency partial nitrification-Anammox performance, such as NOB activity, the effort to save energy, strict conditions and influent with favourable composition for Anammox. In order to improve the efficiency of Partial nitrification- Anammox process as much as possible whereas using the least energy, the microbubble generation system was firstly applied into the partial nitrification-Anammox process. The steady microbubble cloud produced by fluidic oscillator was verified size ranging from 60 μm to 600 μm which provides higher mass transfer rates and gas hold-up in gas-liquid phase bioreactor due to the fact that the microbubble was characterized by higher surface area to volume ratio and slower rising velocity. The simulation of the inner motion of the airlift loop reactor with COMSOL offered a visual difference between microbubble aeration and fine bubble aeration. In the partial nitrification process dissolved oxygen is a key factor for the growth of ammonia oxidizing bacteria (AOB). Two contrasting experiments in sequencing batch airlift loop reactors (SBAB) with and without fluidic oscillator were conducted over 200 days to investigate the effect of microbubble aeration system on the long term partial nitrification process. The results showed the microbubble aeration system can significantly enhance the activity of AOB to speed up the biological treatment with fewer oxygen requirements and effectively prevent the production of nitrate. The performance of the partial nitrification in an airlift loop bioreactor with fluidic oscillator was greatly improved in terms of treatment capacity and stability compared to the one without fluidic oscillator. Thereafter different operational parameters such as temperature and pH were examined to optimize the operational strategies for the partial nitrification process. The microbial communities that catalyse partial nitrification were analysed by molecular biotechnology. The morphology of bacteria at different growth stages was observed by SEM and TEM. Real-time PCR was used to quantify populations of ammonia-oxidizing bacteria and nitrite oxidizing bacteria. For the Anammox process, a strict anaerobic condition is required to operate successfully. As we all know, the stack gas is usually consists of depleted oxygen but mostly nitrogen (typically more than two-thirds) derived from the combustion, carbon dioxide (CO2), and water vapour, among which CO2 is considered as a greenhouse gas contributing to global warming. Bubbling the synthetic power station stack gas into the Anammox reactor by means of the microbubble generation system not only obtain this circumstance but also provide the heat required by good activity of anammox bacteria. In addition to maintaining desirable conditions, the dissolved CO2 can provide a carbon source for the growth of anammox bacteria and adjust the value of pH in the reactor which is able to save substantial operational cost caused by pH control. Two contrasting experiments in round sequencing batch gas lift loop bioreactors (SBGB) with and without fluidic oscillator were carried out nearly 100 days. The performance of Anammox process in the SBGB with fluidic oscillator was noticeably improved comparing to the one without fluidic oscillator. The size distribution of granular Anammox sludge was analysed by ImageJ to investigate the effect of microbubble on the granulation. The batch assays were conducted to measure the maximum specific Anammox activity in different gas lift loop bioreactors. The morphology of Anammox bacteria at different growth stages was observed by SEM and TEM. Real-time PCR was used to quantify populations of Anammox bacteria in different stage and different bioreactors. The kinetic model for laboratory-scale partial nitrification and Anammox (anaerobic ammonium oxidation) process with sequencing batch gas lift loop bioreactors (SBGB) with and without fluidic oscillator were investigated. According to Monod model and Stover-Kincannon model the kinetic parameters of the model including maximum specific rates and half-maximum rate concentrations for partial nitrification and Anammox were estimated respectively from the results obtained from a laboratory-scale SBGB fed with synthetic wastewater.
Supervisor: Zimmerman, William Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available