Abstract

In this study, the effects of lime addition on the sludge digestion by sodium hydroxide were investigated. The optimum dosage and time required for sludge digestion using only NaOH were found to be 1.6 g/L and 3 hours, respectively. At the optimised condition, lime was added at varying concentration (0.3 g/L to 1.6 g/L). As a result, soluble COD was increased when increasing lime dosage upto 0,7g/L. However when lime dosage was higher than 0,7g/L, a part of soluble COD was precipitated. Similarly, at lime dosage of 0,7g/L the phosphorus precipitation efficiency was approximately 61%. The capillary suction time of the digested sludge was reduced from 1360 s to 350 s as compared with the control sample. In conclusion, the combined alkali digestion not only prevent the TP increase in the effluent but also decreased the time to filter thus makes the digested sludge more easy to manage.