Improvement of acidification on dewaterability of oily sludge from flotation

This paper presents the improvement of acidification on the dewaterability of oily sludge from a flotation process. Various parameters, including the volume of supernatant water, capillary suction time (CST), and specific resistance to filtration (SRF) were used to evaluate the dewaterability of oily sludge. In addition, floc size distribution and release rates of Al(III) were used to explain skeleton breakage as a result of the acidification treatment. Results show that dewaterability increased obviously as the sludge pH decreased. After 120 min of settling, the volume of supernatant water reached 77% at pH 4.0. Maximum reductions in CST and SRF were 93.1% and 89.2%, respectively. Following acidification, the flocs in the oily sludge achieved a broader particle size distribution and a smaller median diameter [d (0.5)] of 36.0 μm (cf. 74.4 μm for the raw sample). In addition, lower pH led to a greater rate of release of Al(III). This study verifies that the floc skeleton of oily sludge can be broken through the dissolution of aluminum hydroxide; i.e., acidification enhances the dewaterability of oily sludge by changing the floc structure. All results indicate that acidification is advisable as a pretreatment of oily sludge.