Control of Fouling Substances in Membrane Bioreactors with Intermittent Aeration

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The performance of the submerged membrane separation activated sludge process with intermittent aeration was investigated in a laboratory scale experiment changing organic loading rate and intermittent aeration cycle. A rectangular PVC tank was used as an aeration tank, in which a flat-sheet type Micro-Filtration membrane made of poly-olefin with the pore size of 0.2μm was submerged. Organic loading rate to the reactor was set at 0.3 and 0.8 g-TOC/L/day. C/N ration in the feed was set at around 5.0 for every condition. Aeration cycle was changed from 10min-10min (aeration - stop) to 120min-120min in different organic loading conditions. Flux through the membrane was set at 0.25m/day. Membrane fouling proceeded rapidly in 0.8 g-TOC/L/day conditions. However, when organic loading rate was 0.3 g-TOC/L/day, bacterial metabolic substances were degraded rapidly compared to the production thereby decreasing viscosity in mixed liquor. Nitrogen removal rate was between 60% and 80% for 0.8 g-TOC/L/day loading, and between 50% and 65% for 0.3 g-TOC/L/day loading. And the nitrogen removal was highest in 40min to 60min aeration cycle conditions. Too short aeration cycle did not result in sufficiently long anoxic periods for denitrification while too long cycle resulted in unnecessary anaerobic periods after depletion of nitrate. Intermittent aeration was effective also for decreasing viscosity in mixed liquor.