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A comparative study of two high cell density methanogenic bioreactors
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Dr Zia Shaikh
Z Ahammad Sk, Gomes J, Sreekrishnan TR
Asia-Pacific Journal of Chemical Engineering
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Methanogenesis is usually the rate-limiting step in the anaerobic digestion process. The slow growth rates of methanogens make the overall treatment processes slow. Use of anaerobic high cell density reactors is a promising option for increasing the overall rate of conversion. Anaerobic fluidized bed reactors (AFBRs) work on the principle of high cell density. Although better mixing is achieved in AFBR, entrainment of bio-granules and higher pumping cost are some of the major drawbacks of the reactor. A hybrid anaerobic reactor (HAR) incorporates the positive aspects of the AFBR while eliminating most of its shortcomings. The performance of a HAR was studied and compared with the performance of an AFBR for the treatment of the same simulated waste water. The AFBR had equal amount of activated charcoal/pumice stone as the carrier material. After 240 days of operation, 38.1%, 32.3% and 29.6% acetate conversions were obtained in the HAR, AFBR with activated charcoal and AFBR with pumice stone, respectively. The gas was found to have 59.2%, 45.7% and 50.2% methane content in the case of HAR, AFBR with pumice stone and AFBR with activated charcoal, respectively. HAR showed consistently better performance when compared with either of the AFBR. Surface charge difference between methanogens and support material also showed that the methanogens preferred activated charcoal over pumice stone. Scanning electron microscope (SEM) studies showed that the self-immobilized bio-granules from the HAR were more compact (and stable). Granules from the AFBR did not have a dense bio-film like the ones from the HAR.
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