Abstract
A sludge solubilization system with the combination of alkaline treatment and high speed mixer was practically operated in a petroleum refinery, however , solubilization rate was reduced vigorously by the abundant metal ions from the change of wastewater composition. Therefore, effects of metal ions on solubilization rate were investigated. With the increase of Ca and Mg ions reduced solubilization from 40％ to 25％. This phenomenon might be caused mainly by Ca ion increase in the sludge derived from wastewater containing abundant metals （Na, Ca, Mg, K and so on）. Furthermore, by the addition of polyaluminium chloride （PAC） in solubilizing process could reduced Ca in the sludge and resulted the increase of solubilizing rate. 150 mg/l of PAC addition continuously increased solubilization rate from 20％ to 45％ and this effect of PAC addition kept more than 25 days.
