Optimization and mechanism of oily sludge treatment by a novel combined surfactants with activated-persulfate method

Highlights: • A novel combined surfactant and activated persulfate treatment method was proposed. • The oil removal rate of the oily sludge achieved 94.6 ± 2.8% after treatment. • The residual oil content was less than 1%, which has reached the discharge standard. • The main contributing free radicals in the oxidation process were HO– and SO₄^–. • The complex organics were degraded into small molecules in the oxidation process. Recently, the extensive discharge of oily sludge, due to excessive use of fossil oil, has become a serious worldwide concern, as it leads to serious environmental pollution and even threat human health. However, the complex properties and compositions of oily sludge make it difficult for the treatment of oily sludge. This study proposed a novel method of combined degradation of oily sludge by surfactants with activated-persulfate, and analyzed the degradation efficiency and degradation pathway. The organics in oil sludge were eluted by surfactant, and the residual oil difficult to be eluted was further oxidized by activated persulfate. The combined method significantly improved the degradation efficiency of oily sludge, and the removal rate reached 94.6 ± 2.8%, and the oil content of the residual oily sludge was 0.57%, which had reached the discharge standard. The mechanism analysis indicated that surfactant could increase the solubility of oil by reducing the surface tension, and the hydroxyl radical and sulfate radical generated by activated persulfate could degrade the complex organic matters into small molecule matters, achieving efficient degradation of oil sludge. This work demonstrated a new avenue for the efficient and cost-effective treatment of oily sludge, opening an environmentally friendly treatment concept.