Partially Aerated Biofilter (PAB) for simultaneous removal of SS, COD, and nitrogen using immobilized bacteria | |
| Author | Thapa, Phatta Bahadur |
| Call Number | AIT Thesis no. EV-98-9 |
| Subject(s) | Sewage--Purification--Nitrogen removal Sewage--Purification--Biological treatment |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Regulations requiring nitrogen removal is gradually increasing in order to avoid oxygen depletion, toxicity to aquatic life, and eutrophication in receiving waters. Biological nitrogen removal can be an attractive method for nitrogen removal from wastewater. This research describes the operational aspects for the start-up of high-rate nitrogen removal reactor using immobilized bacteria through a laboratory scale reactor. This study was conducted to identify the most important factors to be considered for the start-up of high performance reactors designed for simultaneous nitrogen, COD, and SS removal. Firstly, simultaneous immobilization of nitrifiers together with heterotrophs was attempted but nitrifiers could not be established firmly because they were embedded in the heterotrophic bacteria, which were easily sloughed off from the pellets while backwashing. Secondly, only nitrifiers were grown and immobilized by supplying ammonium nitrogen as a sole substrate. Once organic substrate, as well as nitrogen, was fed into the reactors, heterotrophs made a yellow-whit€'. band by covering nitrifiers in the middle part of the reactor columns. Backwashing on every alternate day was found to be necessary to remove excessive heterotrophs from the outer layer of biofilm although headloss did not develop to any significant level within that time span. Even then, the reactors did not achieve steady state in terms of nitrification unless average bulk liquid dissolved oxygen concentration was raised well above 3 mg/L. This was achieved by stepwise increase of oxygen flow rate to 0.3 Umin together with enhanced oxygen mass transfer by improving diffuser system. High purity oxygen was used as oxygen source to simultaneously fulfill the demand of high dissolved oxygen concentration and the need to minimize intermixing of the pellets. Steady state, in terms of nitrification and COD removal, was achieved after adopting above-mentioned measures of high DO concentration and backwashing but denitrification remained low because of higher DO concentration in the anoxic zone. Reduced oxygen flow rate to lower DO concentration in the anoxic zone, resulted in incomplete nitrification. Extension of anoxic zone by raising aeration point from 40 cm to 60 cm, however, yielded complete nitrification and above 77% denitrification. Partially Aerated Biofilter (P AB) developed in this study can be operated at a COD loading rate of 2.57 kg/m3 -d (88% average removal), total nitrogen loading rate of 0.47 kg/m3 -d (60% average removal), suspended solid loading rate of 0.86 kg/m3 -d (77% average removal) with an empty bed HRT of 1.3 hours. |
| Year | 1998 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Takizawa, Satoshi; |
| Examination Committee(s) | Ozaki, Hiroaki ;Preeda Parkpian; |
| Scholarship Donor(s) | Government of Japan; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1998 |