Enhancement of thickening and dewatering characteristics of sewage sludge using cement kiln dust

Sewage sludge conditioning with chemicals has been employed widely to improve thickening and dewatering processes. Although it is a good alternative for process improvement, its cost is high. It is important to find effective and cheap conditioners. Large quantities of cement kiln dust (CKD), which proved to be a good chemical stabilizer of sewage sludge, are emitted from cement factories. In this study, the effect of using CKD on the thickening and dewatering performance of sewage sludge were investigated by zone settling test, free gravity drainage test, specific resistance to filtration (SRF) and natural drying tests. The results indicated that adding CKD to sewage sludge by 60% of total solid could improve the sludge thickening, dewatering as well as stabilization. The settleability of sludge was improved as follows: the zone settling velocity increased from 43.2 to 98.4 m/d, the SRF decreased from 5.93 (10(3)m/kg) to 0.76 (10(3)m/kg) and the actual dewatering time required to achieve sludge with solid content more than 20% reduced from 5 to 2 d, while the pH value remained in the required range for stabilization.