Insights into dewatering and characterization of the waste activated sludge

Abstract

Abstract On-site filtration experiments were carried out at the local Common Effluent Treatment Plant (CETP) to measure the properties of the waste activated sludge (WAS). The consequences of several operational parameters such as effect of pressure, filtration media, coagulant addition, etc. were studied. To better understand the role of hydrodynamics as well as the biological content, a comparison was made between the activated sludge (AS) and WAS cake and its properties. In our findings, the cake obtained in case of WAS filtration was denser as compared to the cake from AS. In the former, it was found to be in the range of 2–2.5% w/v of WAS as compared to 0.25–0.5% w/v of AS. The addition of coagulant accelerated settling and in turn reduced the WAS filtration time by 10 fold. Important filtration parameters obtained for WAS were: cake resistance (α) = 1.5 × 1011 m/kg, cake porosity (e) = 0.86, cake compressibility (η) = 0.41, effective mean particle size (x) = 0.5 µm, capillary number (Nc) = 2.7 × 10–3, irreducible saturation (S∞) = 0.155 and threshold pressure (Pb) = 1 × 105 N/m2.