| Author | Tuan, Vu Anh |
| Call Number | AIT Diss. no. EV-80-1 |
| Subject(s) | Sewage--Purification--Activated sludge process
|
| 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 |
| Abstract | Better treatment of wastewater in terms of effluent quality produced and reliability against system failure has always been sought. Experimental data collected in this study reveals that by changing the mixing regime in an aeration tank toward plug flow condition, an improved performance of activated sludge process can be achieved. The biodegradable
COD remaining in the process effluent reduces remarkably when the aeration tank is divided into a series of stirred tanks. Bulking sludge is
also less likely to occur than in complete mixing. Where available data in literature conflicted with the present findings and conclusion of theoretical analyses concerning the role of the mixing refilled, it was found that misinterpretation of collected data or misconduct of experilllents accounted for the conflict. The activated sludge process with the mixing regime in an aeration tank modelled by a number of tanks in series is referred to as the partially mixed activated sludge (PMAS) process. The term partially mixed includes completely mixed as one extreme and plug flow as another. A mathematical model based on knowledge of microbial kinetics was developed to depict the performance of the PMAS process. Performance at the steady state of the PMAS process could be depicted
well by the proposed model. In the extreme case of completely mixed the model predicted similar results as those which are currently accepted by
the profession. The concept of viability and loss of non-viable cells by decay was incorporated, this allowing the proposed model to offer a plausible explanation of the variable biomass decay rate constant and total oxidation. With respect to the mixing regime in an aeration tank, the proposed model predicts a better effluent quality when the regime
tends to plug flow. Generally there is a good agreement between the prediction and laboratory data. In dynamic operation, the growth rate hysteresis, which has been
known when the biological treatment system is subjected to changes in substrate concentration, was observed in the laboratory completely mixed
unit. The proposed model, in which the biomass growth rate is controlled by quantity of incorporated substrate available to biomass, successfully depicts the phenomena. The application of the proposed model to a sludge recycle system will require a better modelling of the secondary settling tank. Simulation based on the proposed model shows that 'the PMAS process responds better when the aeration tank is divided into a number of tanks.
Results are surprising since it is traditionally believed that the completely mixed condition would offer the best dilution and thus the best shock loading handle capability. Data available in literature, does not disprove the results of the simulation since it was collected when the
plug flow system was operated under extremely unfavorable anoxic conditions and there was serious short circuiting in its aeration tank. Under such conditions, the plug flow condition could however respond as well as the completely mixed did when percentage removals were used as basis of comparison. |
| Year | 1980 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development |
| 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) | N.C. Thanh ; Lohani, Bindu N.
|
| Examination Committee(s) | Chongrak Polprasert ; Selvalingam, Selvadore ; Jr. Grady, C.P.L.
|
| Scholarship Donor(s) | Canadian Government |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1980 |