Experimental Research on Lime Drying Process of Mechanical Dewatered Sludge from a Wastewater Treatment Plant in Beijing

This paper studied the effects of lime treatment on the pre-dewatered sludge from a wastewater treatment plant in Beijing. The moisture, leaching solution's pH, heavy metals and organic matter content have been analyzed before and after lime treatment on the sludge. The results showed that: the moisture of the original sludge significantly impacted by the lime treatment. 25% of lime dosage by weight was needed in the process of treating sludge moisture from 86.60% to 60%, while only 20% is needed in the process from 80.62% to 60%; The mixed materials’ pH has no significant difference after dosing more than 10% lime, all samples’ pH values were around 13 after lime treated 30 min, the pH trend basic on 120d monitoring shows the pH was slightly declined but still above 12; Lime treatment on sludge has effects on immobilization of heavy metals. After dosing 10% of lime, the leaching solution's Ni, Cu, Zn contents dropped from 0.55 mg/L, 2.42 mg/L and 1.09 mg/L to 0.13 mg/L, 1.54 mg/L and 0.01 mg/L; Lime treatment on sludge has a promoted stabilization of organic matter. After dosing 10% and 20% of lime, the mixtures leaching solution's COD reduces sharply, from 1950 mg/L to 298 mg/L and 152 mg/L respectively. These indicate that lime treatment has obvious effect on sewage sludge stabilization.