Rapid biogas production by methane-producing bacteria encased in polymeric membranes | |
| Author | Supansa Youngsukkasem |
| Call Number | AIT Diss. no.FB-12-07 |
| Subject(s) | Biogas Methane |
| Note | A dissertation submitted in partial fulfillment of the requirement for the degree of Doctor of Philosophy in Food Engineering and Bioprocess Technology, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. FB-12-07 |
| Abstract | The aim of this study was to apply encapsulation an d cell containment technology for rapid biogas production. Three methods of encapsulation o r cell containment of methane producing bacteria that were investigated in this research pr oject, were attempted to increase the cell density in the reactors for this purpose. First, encapsulation with a one-step liquid-droplet -forming technique was investigated. Spherical capsules were produced with an average di ameter and membrane thickness of 4.3 and 0.2 mm, respectively. The capsules were made fr om alginate, using chitosan or Ca 2+ as counter-ions and with the addition of different var iants of carboxymethylcellulose (CMC), to study its effect on the performance of the encapsul ated bacteria. The results showed that higher methane production rates were obtained with digesting bacteria encapsulated in capsules produced using CMC with a higher degree of substitution (0.9 DS) compared to lower values (0.7 DS). This may be attributed to th e higher stability of these capsules. The anaerobic digestion by bacteria encapsulated in chi tosan-alginate capsules was in contrast not as successful. The failure of these bacteria to pro duce substantial amounts of methane may be explained by the inhibitory effect that the chitosa n may have on the bacteria.The highest daily methane production of the natural capsules with 1.3 %, 2.6% and 5.2% CaCl 2 , were 41.90, 43.76 and 35.32 mL/g COD, respectively on the 5 th day of digestion. The results from this experiment showed that the CaCl 2 concentration had an effect on the membrane struct ure, and consequently on the methane production by the encap sulated bacteria.The encasing bacterial cells in sachets (3×3 and 3× 6 cm 2 ) made of Durapore ® membrane (hydrophilic PVDF) with a pore size of 0.1 μ m was a lso investigated. During the digestion process, the dissolved substrates penetrated throug h the capsule membrane and biogas was produced inside the sachets and diffused out of the m. In a batch digestion system, the results showed that the maximum daily volume of methane was produced by bacteria encased in sachets of size 3×6 cm 2 on the 6 th day of digestion. The maximum daily volume (78 mL/ g COD) was larger than what was produced by the same amount of bacteria in sachets of the smaller size that day (50, 4 and 2 mL/g COD for 3x3 , 3x3 blank and 3x6 blank, respectively). The protective effect arising from the encasing of the methane-producing bacteria was also investigated. Free and encased cells were grown in synthetic medium with limonene, a potent hydrophobic toxic compound present in citrus wastes , at concentrations of 0%, 1%, 2% and 3% (v/v).The protective effect of the sachets becam e clear for higher concentrations of limonene. The free cells were clearly affected by 2 and 3% limonene with methane productions on the 5 th day of 6.56 and 8.43 mL compared to 31.22, 27.53 f or 0 and 1% respectively. Bacteria encased in sachets, on the o ther, showed similar production volumes of 23.65, 20.03, 23.06 and 19.00 mLfor 0, 1, 2 and 3%, respectively. The biological digestion performance of the encased methane producing bacteria compared to free cells in a long term semi-continuous process w as also studied. The results showed that a maximum organic loading rate (OLR) of 20 gCOD/L.day was reached by encased bacteria while the free cells could only reach an OLR of 5 g COD/L.day due to loss of bacterial cells during the continuous process. The largest methane volume produced in one day by the encased cells was 8,305 mL on the 37 th day, while the maximum biogas production by free cells was 1,271 mL on the 12 th day. Moreover, the encased bacteria were found to have a better volatile fatty acids (including acetate, pro pionate and butyrate) conversion capacity to biogas. In the encased bacterial system, the result s showed that acetate, propionate and butyrate concentrations decreased to low levels eve n as the daily organic loading was raised continuously, from 2.5 to 10.0 g COD/L.day. With a higher OLR of 15 or 20 g COD/L.day, volatile fatty acids however started to accumulate in the reactor. Finally, a multi-layer membrane bioreactor with mem brane compartments for retaining the bacterial cells was developed, which showed better biogas production performance than a free cell bioreactor system. Functionalization of the sy nthetic membranes used in the multi-layer membrane process was found to be an important facto r. In this experiment, a Polyamide 46 membrane, called a passive membrane, was made since the structure contains no group with polarity. Functionalization of the polyamide 46 int o a homogenous hydroxylated derivative, creating the hydrophilic hydroxylated polyamide 46 (HPA), improved the capillary effect and reduced the fouling. The commercial Durapore membra ne filter (PVDF) membrane had similar hydrophilic properties, and was used to com pare with the prepared polyamide membranes. All results showed that hydrophilic memb ranes, (PVDF and HPA), had better performances in biogas production compared to the h ydrophobic membrane (PA). This can be explained by noting that PA membranes resulted in a decreasing cross-flow velocity because of biological foulant films. HPA and PVDF, however, exhibited a high flow rate of nutrients because hydroxyl groups tend to form hydrogen bonds with polar solvents. The accumulated VFA concentration in the reactor with free cells te nded to increase as the OLR was increased, indicating that the cells remaining inside the reac tor were not able to digest all of the nutrients.The total VFA accumulation in the reactor with the PA membrane was higher than the others. It decreased only slightly at an OLR of 3.08 g COD / L.day, and then from 6.16 to 8.16 g COD / L.day, considerable amounts of VFA wer e found to accumulate. The total VFA concentration in the reactor with HPA membrane decr eased with increasing OLR, from 3.08 to 6.16 g COD / L.day, and started to accumulate at an OLR of 8.16 g COD / L.day from the 18 th day, accompanied by a decrease in the produced bio gas. It can be concluded that encapsulation and containm ent of methane producing bacterial cells using natural and synthetic polymeric membranes as well as a multilayer membrane bioreactor are promising methods for increasing the biogas production rate due to their ability to retain and protect the cells inside the bioreact ors. |
| Year | 2012 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. FB-12-07 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Rakshit, Sudip Kumar |
| Examination Committee(s) | Tahezadeh, Mohammad J.;Athapol Noomhorm;Anal, Anil Kumar;Gallardo, Wenresti G. |
| Scholarship Donor(s) | Rajamangala University of Technology Isan EM EuroAsia schorlarship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2012 |