| Author | Supawat Chaikasem |
| Note | A dissertation submitted in partial fulfillment of the requirements for the
degree of Doctor of Engineering in
Environmental Engineering and Management, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | A two stage thermophillic anaerobic membrane bioreactor (TAnMBR) was used for treating
high strength particulate wastewater (tapioca starch) with enhanced biodegradation rates and
low biomass generation. Operating the reactor under thermophillic condition offers benefit
like higher organic removal rate with higher growth rate and better biodegradation
efficiency. Thus leading to shorter hydraulic retention time (HRT). It also provides a more
complete pathogenic microorganism destruction, lower biomass yield, elimination of
cooling needs for wastewater discharge at high temperature. On the contrary, thermophillic
condition causes poor sludge granulation and sludge settleability due to high sludge
deflocculation and deterioration of settling properties. This negatively affects the biomass to
produce extracellular polymeric substances (EPS) which promotes dense and firm sludge
granulation. Therefore, resulting in sludge washout due to highly sludge degranulation and
dispersed sludge formation which subsequently deteriorated the quality of effluent.
In this study, two stage TAnMBR which consists of a hydrolytic reactor followed by a
methanogenic reactor and a microfilter (0.1 μm) was operated under external semi dead-end
mode at thermophillic condition (55°C). This assured complete biomass retention;
consequently ensure handling high loading conditions. Two stage TAnMBR ensures the
optimum growth conditions for hydrolytic/acidogenic bacteria and methanogenic archaea.
This enhances the biological activity, consequently increases methane production. Initially,
anaerobic seed sludge enrichment and acclimatization was done in sequencing batch reactor
(SBR). After that a two stage TAnMBR was operated at three different loading conditions.
The reactor was first operated at loading rate 6 kgCOD/m3.d, and then PVA-gel was added
to compare the performance of hydrolytic reactor. Similar performance evaluations were
conducted at loading rate 8 and 12 kgCOD/m3.d, respectively.
At loading rate 6 kgCOD/m3.d, hydrolytic reactor operated at 9.6±0.5 g/L of volatile
suspended solid (VSS) concentration in order to study the performance of hydrolytic reactor
with and without PVA-gel addition on volatile fatty acid (VFA) concentration. The results
showed that hydrolytic reactor with PVA-gel addition significantly increased VFA
concentration and enhances methane productivity at loading rate of 6 kgCOD/m3.d (p <
0.05). The VFA production in hydrolytic reactor significantly increased from 4.0±0.2 to
4.6±0.5 g/L with PVA-gel addition at OLR 6 kgCOD/m3.d (p < 0.05). Once the loading rate
was increased to 8 and 12 kgCOD/m3.d, VFA production also significantly increased to
4.9±0.2 and 6.0±0.1 g/L (p < 0.05), respectively. The increase in VFA concentration could
be attributed to an increase in biological activity with PVA-gel addition. Furthermore,
methane productivity had also significantly increased from 1.4 to 1.7 Lmethane/Lreactor.d (p <
0.05). This was due to an increasing in VFA concentration in hydrolytic effluent. Similarly
with an increase in loading rate to 8 and 12 kgCOD/m3.d methane productivity further
significantly increased to 1.9 and 2.4 Lmethane/Lreactor.d (p < 0.05), respectively. Two stage
TAnMBR achieved organic removal rate (ORR) of 5.3 to 10.1 kgCOD/m3.d with organic
removal efficiency of 84-92%. However, membrane fouling was one of the limiting factors
in membrane application. Membrane fouling investigations indicated that the predominant
fouling in TAnMBR was organic reversible fouling caused by bound extracellular polymeric
substances (EPS). Bound EPS was observed to be increased at loading rate 12 kgCOD/m3.d
as compared to 8 kgCOD/m3.d. Furthermore, fouling investigation at both loading conditions
showed that filtration resistance was due to the presence of higher bound EPS at higher
loading rate, which lead to sticky sludge and thus favor to develop cake/gel formation on
membrane surface or inside the pore of membrane. |
| Year | 2015 |
| 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 and Management (EV) |
| Chairperson(s) | Chettiyappan Visvanathan; |
| Examination Committee(s) | Nguyen Thi Kim Oanh;Anal, Anil Kumar ;Khanal, Samir Kumar; |
| Scholarship Donor(s) | Royal Thai Government – AIT Fellowship; |