Impact of Temperature on Sludge Dewatering Properties Assessed by the Capillary Suction Time

Highlights of the novel dewaterability estimation test (DET) device

Many industries, which are producing sludge in large quantities, depend on sludge dewatering technology to reduce the corresponding water content. A key design parameter for dewatering equipment is the capillary suction time (CST) test, which has, however, several scientific flaws, despite that the test is practical and easy-to-perform. The standard CST test has a few considerable drawbacks: its lack of reliability and difficulties in obtaining results for heavy sludge types. Furthermore, it is not designed for long experiments (e.g. >30 min), and has only two measurement points (its two electrodes). In comparison, the novel dewaterability estimation test (DET) test is almost as simple as the CST, but considerably more reliable, faster, flexible and informative in terms of the wealth of visual measurement data collected with modern image analysis software. The standard deviations associated with repeated measurements for the same sludge is lower for the DET than for the CST test. In contrast to the CST device, capillary suction in the DET test is linear and not radial, allowing for a straightforward interpretation of findings. The new DET device may replace the CST test in the sludge-producing industries in the future.

Influence of calcium compounds as a compression framework on activated sludge dewaterability and calorific value

Calcium compounds have been known to be important for enhancing aggregation and dewaterability of activated sludge. In this study, the effect of calcium compounds (CaO, Ca(OH)₂, CaCl₂, CaSO₄ and CaCO₃, respectively) on sludge dewaterability and calorific value was investigated. Upon addition of CaO, Ca(OH)₂, CaCl₂, CaSO₄ and CaCO₃ (112 mg/g dry sludge) into activated sludge, after compressed filtration the moisture content of sludge was found to be 49.7%, 55.7%, 57.1%, 65.3% and 56.5%, respectively. The addition of calcium compounds altered the structure of sludge by CaCO₃ and Ca(OH)₂ production, which improved sludge filterability and provided frameworks and water passages during compression. Furthermore, sludge conditioned by CaO addition had better dewaterability than other calcium compounds. The heat generated from the CaO hydration and high pH might damage flocs' structure and improve dewaterability of sludge. Moreover, it was found that excess addition of calcium compounds led to low calorific value in combustion process. The study concluded that CaO is the optimal additive for sludge further dewatering by compressed filtration.