Factors Affecting Capillary Suction Time of Sludge Using Wet Front Distance and Filtrate Flow Rate Methods

Sludge generated during wastewater treatment is difficult to handle due to their high water content, hence a need for dewatering. The factors that affect the outcome of capillary suction time (CST) were studied using piggery and domestic sludge samples conditioned with ferric chloride. Effects of conditioner concentration, hydrostatic pressure and mixing time were investigated. Filtrate flow rate studies were also carried out as an alternative to wet front progression to determine CST. Ferric chloride was varied from 0.002 to 0.008 g/ml, hydrostatic height was varied from 20 to 40 mm while mixing time ranged from 0 to 120 sec. The optimum conditioner concentration was observed to be 0.0055 and 0.0035 g/ml for piggery sludge and domestic sludge respectively. At 5 % level of significance, hydrostatic height was observed to have no significant effect on the CST for the range of hydrostatic heights chosen. The optimum mixing time observed for 90 g/l and 30 g/l piggery sludge was 50 and 25 sec respectively. While the optimum mixing time for 28 g/l and 14 g/l domestic sludge was 10 and 5 sec respectively. Flow rate was discovered to have an inverse relationship with CST, with the optimum conditioner concentration corresponding to the peak flow rate and minimum CST for both test samples. Hence, in other to eliminate the difficulty presented by the anisotropic property of the capillary suction apparatus (CSA) filter paper, filtrate flow method can be used instead of wet front progression method.