Wastewater nitrogen removal using mixed microbial culture under oxygen-limited conditions | |
| Author | Than Khin |
| Call Number | AIT Diss. no.EV-04-04 |
| Subject(s) | Sewage--Purification--Nitrogen removal Denitrification Mixed culture (Microbiology) |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-04-04 |
| Abstract | Performance of mixed microbial culture for nitrogen removal was investigated under oxygen-limited conditions. Methane was used as a sole carbon source for nitrate nitrogen removal. The overall objectives of this research were to investigate simultaneous removal of ammonium and nitrate nitrogen in a fluidized bed bioreactor by using mixed microbial culture under oxygen-limited conditions and to evaluate the optimum removal rate of total nitrogen removal at various bulk dissolved oxygen concentrations. To obtain meaningful results, proper methodology of experimentation was developed and improvisation of the experimental procedures. The seed sludge was taken from "Y annawa" Domestic Wastewater Treatment Plant, Bangkok, Thailand, and a landfill cover soil. The mixed microbial culture sludge was prepared before experiments were carried out. Initially after setup of the reactor, the recirculation rate was maintained at about 38 times the influent flow rate to achieve complete-mix conditions. Experiments were carried out to confirm the complete mix regime. A completely mixed fluidized bed bioreactor was operated in the continuous flow mode for nitrogen removal. Synthetic wastewater containing NH4N, N03N, NaHC03 and nutrients was used in this research. The bulk dissolved oxygen (DO) concentrations were varied by varying gas dissolution flow rates (GDFR). The experiments were performed at different gas dissolution flow rates of 90 ml/min (DO= 0.5-0.9 mg/L), 400 ml/min (DO= 1.1-1.6 mg/L), and 650 ml/min (DO= 1.8-2.0 mg/L). There were three main experiments carried out for biological nitrogen removal using mixed culture sludge under oxygen-limited conditions in a fluidized bed bioreactor namely: (i) determination of the optimal NH4N removal rate at each GDFR at constant N03N loading rate (ii) determination of the optimal N03N removal rate at each GDFR at constant NH4N loading rate (iii) determination of the optimal simultaneous NH4N and N03N removal rate at each GDFR. Simultaneous ammonium and nitrate nitrogen removal were obtained. Total optimal nitrogen removal rates of 15-mg N/g VSS. d, 21-mg N/g VSS. d and 26.4-mg N/g VSS. d were obtained at bulk dissolved oxygen concentrations 0.5-0.9 mg/L, 1.1-1.6 mg/Land 1.8-2.0 mg/L, respectively in a fluidized bed bioreactor. No significant accumulation of nitrite was found in this experiment. Possible mechanisms of nitrogen removal under oxygen-limited conditions were 1) partial oxidation of NH4N to N02N by aerobic ammonia oxidizers and subsequent conversion of N02N to dinitrogen gas with remaining NH4N as electron donor by anaerobic ammonia oxidizers and 2) removal of N03N using methane as sole carbon source by association of methanotrophic and heterotrophic denitrifiers. Batch experiments were conducted to investigate the mixed microbial culture activity involving nitrogen removal at different substrates at different conditions. There were five batch experiments setup for nitrogen removal; (i) Ammonia removal under oxygen-limited conditions suitable for aerobic and anaerobic ammonia oxidizers; (ii) Ammonia and nitrate removal under oxygen-limited conditions suitable for aerobic and anaerobic ammonia oxidizers; (iii) Nitrate removal using methane as a carbon source under oxygen-limited conditions suitable for methanotrophs and denitrifiers; (iv) Anaerobic ammonia removal using nitrite as an electron acceptor suitable for anaerobic ammonia oxidizers; and (v) Ammonia and nitrate removal using methane as a carbon source under oxygen-limited conditions suitable for aerobic and anaerobic ammonia oxidizers, methanotrophs and denitrifiers. Expressed in another way, the batch experiments confirmed that the mixed microbial culture contained aerobic and anaerobic ammonia oxidizers, methanotrophs and denitrifiers. They could contribute to the novel biochemistry of nitrogen removal under different operational conditions. Moreover, the methane oxidation activity test was carried out for determination of the rate of methane oxidation under different oxygen/methane ratios (wt/wt). This activity test confirmed that the mixed microbial culture contained methanotrophs that can oxidize methane and produced carbon dioxide under aerobic condition. The experimental procedure developed in this study can be applied for simultaneous ammonia and nitrate nitrogen removal in a fluidized bed reactor using mixed microbial culture under oxygen-limited conditions. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-04-04 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Annachhatre, Ajit P.; |
| Examination Committee(s) | Chongrak Polprasert; Athapol Noornhorm;Henze, Mogens ; |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2004 |