| Author | Nguyen Phuoc Dan |
| Call Number | AIT Diss no.EV-02-01 |
| Subject(s) | Sewage--Purification--Biological treatment
|
| 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 | This study aimed to compare the performance of aerobic treatment using wild mixed
yeast and bacterial culture for high salinity wastewater. The operating conditions of yeast
treatment under high salinity such as pH, sludge retention time (SRT) and dissolved
oxygen (DO) were examined. The comparative evaluation is based on determination of
biokinetic coefficients using the respirometric method and treatment efficiency of longterm
operation of two laboratory-scale membrane bioreactor systems.
The biokinetic experiments reveal that yeast culture has a lower observed maximum
specific grow rate (μobs) at low salt content (20g/L) than that of bacteria. But μobs of yeasts
at higher salt contents (above 30 g/L) did not decline dramatically and had higher value
than that of bacteria. The osmotolerant yeast mixture was able to tolerate a wider pH range
than bacterial culture. The chemical oxygen demand (COD) removal rate of the yeast
mixture was highest at pH values 5.0-5.5.
Two laboratory-scale membrane bioreactor systems were investigated to treat high
salinity wastewater containing high organic (5,000 mg/L COD) and salt content (32 g/L
NaCl), namely: the Yeast Membrane Bioreactor (YMBR), and Yeast pretreatment
followed by Bacterial Membrane Bioreactor (BMBR). In the YMBR system, experimental
runs were conducted with a mean biomass concentration of 12 g MLSS/L. Here, the
maximum COD removal rate of 0.93 g COD/g MLSS.day was obtained at F/M of 1.5 g
COD lg MLSS.d, whereas the BMBR system was operated with a biomass concentration
of up to 25 g MLSS/L, resulting in maximum COD removal rate of 0.32 kg COD /kg
MLSS.day at F/M ratio of 0.4. In comparison the BMBR, the YMBR could obtain higher
COD removal rate at higher organic loading, indicating the potential of the yeast reactor
system to treat high salinity wastewater containing high organic concentration.
Transmembrane pressure in the BMBR was progressively increased from 2 to 60 kPa
after 12d, 6 d and 2 d at hydraulic retention time (HRT) of 14h, 9 hand 4h, with average
biomass concentration of 6.1, 15 and 20 g MLSS/L respectively. By contrast, the
transmembrane pressure in YMBR was only increased from 2 to 60 kPa only after 76 days
of operation, with an average biomass concentration of 12 MLSS/L and an operating HRT
range of 5 - 32 h.
The comparative evaluation of treatment performance of both YMBR and BMBR
with the low organic-feed wastewater (1,000 mg/L COD and 32 g/L NaCl) was examined.
COD removal of both processes were above 90% at HRT of 5 h. Under the same operating
conditions, the YMBR could run under transmembrane pressure 10 times lower than the
BMBR with a significantly reduced membrane fouling rate. This may be due to low
production of adhesive extracellular polymers (ECP) and the secondary filtration layer
formed from large free yeast cells. ECP production of bacterial sludge was increased
considerably at high salt contents and high sludge retention time (SRT). For the bacterial
sludge, the increase salinity led to increase in ECP value, whereas the ECP content of the
yeast sludge was relatively very small. |
| Year | 2002 |
| Type | Dissertation |
| 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 (EV) |
| Chairperson(s) | Visvanathan, C.; |
| Examination Committee(s) | Chongrak Polprasert;Nguyen Cong Thanh;
Trankler, Josef;Rakshit, Sudip K.;Simard, Ronald E. ; |
| Scholarship Donor(s) | Swiss Development Cooperation (SDC); |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology |