High organic loading influences the physical characteristics of aerobic sludge granules |
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Authors: | Moy B Y-P Tay J-H Toh S-K Liu Y Tay S T-L |
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Affiliation: | Environmental Engineering Research Centre, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore |
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Abstract: | Aims: The effect of high organic loading rate (OLR) on the physical characteristics of aerobic granules was studied. Methods and Results: Two column-type sequential aerobic sludge blanket reactors were fed with either glucose or acetate as the main carbon source, and the OLR was gradually raised from 6 to 9, 12 and 15 kg chemical oxygen demand (COD) m−3 d−1. Glucose-fed granules could sustain the maximum OLR tested. At a low OLR, these granules exhibited a loose fluffy morphology dominated by filamentous bacteria. At higher OLRs, these granules became irregularly shaped, with folds, crevices and depressions. In contrast, acetate-fed granules had a compact spherical morphology at OLRs of 6 and 9 kg COD m−3 d−1, with better settling and strength characteristics than glucose-fed granules at similar OLRs. However, acetate-fed granules could not sustain high OLRs and disintegrated when the OLR reached 9 kg COD m−3 d−1. Conclusions: The compact regular microstructure of the acetate-fed granules appeared to limit mass transfer of nutrients at an OLR of 9 kg COD m−3 d−1. The looser filamentous microstructure of the glucose-fed granules and the subsequent irregular morphology delayed the onset of diffusion limitation and allowed significantly higher OLRs to be attained. Significance and Impact of the Study: High organic loading rates are possible with aerobic granules. This research would be helpful in the development of aerobic granule-based systems for high-strength wastewaters. |
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