(207b) Structural Analysis and Dewatering Characteristics of Waste Sludge from WWTP MBR

A pilot-scale UF membrane bioreactor (MBR) of designed capacity 1 m3/day was set in an industrial wastewater treatment plant to evaluate the performance. The membrane is hollow-fiber configuration with surface area 0.93 m2 and pore size 0.036 ìm. This study mainly focused on the testing results of waste sludge, including dewaterability improvement and structural analysis. Comparing with biological sludge discharged from the current WWTP process, MBR sludge required 20% less cationic polyelectrolyte dose to reach similar specific filtration resistance (~ 1e+12 m/kg). This could significantly reduce the cost for running dewatering facilities and final disposal. Meanwhile the chemical and morphological analyses showed that MBR sludge exhibited lower EPS (exocellular polymeric substances) content, slightly smaller flocs, and more compact morphology (2-D box-counting fractal dimension). The porous floc structure might be reconstructed to relatively compact one in the environment of long sludge retention time and abundant aeration of MBR tank, and this conversion then improved solid-liquid separation efficiency. Additionally, to estimate the appropriate polyelectrolyte dose in prior to dewatering, we applied the algorithm of Yen et al. (2002) by measuring the hysteresis loop area of the sludge rheogram (shear stress vs. shear rate) using co-axial cylinder viscometer. For both sludges, the area dramatically increased at some critical polyelectrolyte dosage and then kept a plateau. The critical dosage, though not the optimal determined in CST and SRF tests, still led to an acceptable dewatering performance for the sludge.