Performance and Surface Characteristics of Sludge Operated at Increasing Organic Loads After Aerobic Granulation

The applied OLR and SLR are among the important parameters to govern bioreactor performance and the sludge characteristics. After successful aerobic granulation in a SBR, the OLR was increased stepwise from 4 to 12 g/(L-d) until the aerobic granules disintegrated into flocculent sludge. Effects of these loading rates on bioreactor performance and sludge surface characteristics such as exocellular protein, polysaccharide and hydrophobicity, were investigated. For a high-efficiency aerobic granule system, OLR and SLR should be in the range of 4-6 g/(L-d) and 0.43-0.66g- COD/(g-MLVSSd), respectively. Proper operational parameters such as, SRTs up to 46.2-49.1 days and MLVSS up to 8.8-10.4 g/L, could be achieved under these loading rates. After granulation, the SDS-PAGE banding changes of exocellular protein indicated that the secreted protein tended to reduce with the increase of applied OLRs, while the secreted polysaccharide in EPS showed an opposite trend, thus leading to a decrease of PN/PS ratio from 4.9 to 0.9. The cell surface hydrophobicity decreased from 75.8% at OLR of 4g/(L-d) to 38.5% at OLR of 12 g/(L-d). A less hydrophobicity of sludge surface was associated with the changes in the EPS. The reduction in surface hydrophobicity was associated with the disintegration of aerobic granule into bioflocs at a high OLR. This might explain why the disintegration of granules would occur at the high influent COD loads employed [10 and 12 g/(L-d)]from a point of bacterial surface properties.