Effect of PVA-gel on performance improvement of a two stage thermophilic anaerobic membrane bioreactor | |
| Author | Supawat Chaikasem |
| Call Number | AIT Diss no.EV-15-02 |
| Subject(s) | Anaerobic Treatment Sewage Purification Wastewater--Treatment |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy 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) | Visvanathan, Chettiyappan; |
| Examination Committee(s) | Nguyen Thi Kim Oanh;Anal, Anil Kumar; |
| Scholarship Donor(s) | Royal Thai Government; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2015 |