A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 2005

Granular activated sludge was formed in two laboratory scale Sequencing Batch Airlift Reactors (SBAR) using two types of support media. One reactor was cultivated with bivalve shell carrier media (CR) and the other with anaerobic granules media (AR). First, these reactors were operated at loading rate of 2.5 kg COD/m3.day for granular sludge formation and characterization with glucose as sole carbon source. Second, applied loading rate could be increased for estimating maximum and optimum loading rate of granules and contemporarily carrying out more granule characterization. Organic loading rate was varied from 2.5 to 30 kg COD/m3.day. The optimum loading rate was found to be 10 kg COD/m3.day and bivalve shell carrier was identified to be a good media for granule formation due to more compact (settled biomass concentration of 21-49 mg/Lgranule), higher settability (mostly SVI of less than 26 mL/g, settling velocity of 21-103 m/h), and shock loading suffering ability. Granule size was in range of 0.5-4 mm at all loading rates. CR granules were smoother than AR one with smaller cavities. At each loading rate, supernatant of both reactors was also analyzed for its fouling potential and compared with that of conventional sequencing batch reactor. It was found that supernatant of carrier reactor was least fouling with MFI of 1.9x103 and 130.7x103 s/L2 at loading rate of 2.5 and 5 kg COD/m3.day, respectively. Fouling potential was identified due to cake layer formation on membrane surface and soluble polysaccharides of supernatant. Finally, two treatment sequences, internal (continuous mode) and external (batch mode) membrane modules were coupled with SBARs to find out suitable application of aerobic granules for membrane bioreactor. The internal one which was totally as same configuration as conventional submerged membrane bioreactor made granules worn after two days of operation and granules characteristics became like conventional activated sludge. In addition, maximum fouling rate of internal system was 79.7 kPa/day that was three fold more than the external one of 24.8 kPa/day with permeate flux of 8.7 L/m2.h for both systems. Fouling time was 1 and 7 days for internal and external membrane module, respectively. However, the external system was much more suitable with granule membrane bioreactor. It produced high effluent quality with low turbidity of 0.8 NTU, COD of less than 20 mg/L at loading rate of 10 kg COD/m3.day. Moreover, unsettled biomass of supernatant was also biodegraded as substrate in membrane reactor and this could reduce sludge production and prolong operating duration of membrane.