Development of New Excess Sludge Reduction System with Combination of Alkaline Solubilization and High Speed Mixing

Abstract

To develop a compact and low cost excess sludge reduction system, alkaline treatments were carried out using sludge from a petroleum refinery. Alkaline treatment with a concentration of 0.025-0.05 mol/L solubilized about 30% of the sludge after 1 h. Alkaline wastes from petroleum refinery such as sodium sulfide, sodium hydrosulfide, and diisopropanol amine could be used to solubilize about 10-30% of the sludge. Combination of alkaline solubilization (0.05 mol/L NaOH) and high speed mixing achieved about 50% solubilization rate after 1 h at 25°C. Application of this system in a petroleum refinery (600 m3 aeration vessel and 450 m3 sedimentation vessel, 3 m3 solubilization vessel) resulted in average solubilization rate of 44% and reduction rate of sludge of 47% during 64 days operation. Return of alkaline solubilized broth into the aeration vessel did not affect the treatment. In 40 L bench scale experiments, solubilization rate of 59% and sludge reduction rate of 94% were obtained when the amount of sludge solubilization was increased up to 2-3 times of excess sludge produced under the standard activated sludge treatment without the solubilization process.