[Preliminary study on characteristics of volumetric oxygen transfer coefficient in granular sludge systems]

The volumetric oxygen transfer coefficient (k(L)a) was tested with mature aerobic granules in the same aeration measurement device and under the same aeration conditions. The k(L)a (min(-1)) was 0.586 1 +/- 0.009 5, 0.586 1 +/- 0.0272, 0.555 6 +/- 0.016 8, 0.5338 +/- 0.0268 for floc sludge, and 0.645 5 +/- 0.027 6, 0.632 0 +/- 0.0755, 0.618 5 +/- 0.062 5, 0.640 6 +/- 0.055 5 for aerobic granules, when the sludge concentration MLSS (mg x L(-1)) was controlled at 2 000, 4 000, 6 000, 8 000, respectively. This indicated that granular sludge exhibited higher k(L)a values than the flocs, and the k(L)a value of floc sludge decreased with the increase of the sludge concentration; however, insignificant decease was found for granular sludge. After screening of granules with different diameter, the k(L)a values of the aerobic granular sludge with different sizes which had the same MLSS, volume, surface area and particle number were compared, and insignificant difference was found, suggesting that the effects of these factors on the k(L)a of granular sludge were negligible. The findings of this work may have significance for the energy-saving operation of wastewater treatment plants.