Modification of aged oily sludge (AOS) through pressure filtration and electro-dewatering methods under citric acid...

Aged oily sludge (AOS) exhibits more challenging properties compared to ordinary oily sludge, making modification treatments essential for improving dewatering efficiency. This study innovatively employs citric acid (CA) as a pretreatment agent for AOS and combines pressure filtration (PF) and electro-dewatering (EDW) to conduct volume reduction experiments, while investigating the dewatering mechanism of CA pretreatment. Under a pressure of 75 kPa, the AOS moisture content decreased slightly from 80.12 % to 78.00 %, while the addition of 0.02 g CA/g AOS further reduced it to 71.69 %. Under conditions of 25 kPa and 25 V/cm, EDW lowered the moisture content to 47.36 %, achieving faster average dewatering rate of 0.086 g/s. This study investigated the oil and water distribution within sludge cake layers, analyzed their migration during EDW, and explained the anodic drying phenomenon. Engineering applicability was assessed through energy consumption and calorific value analyses. Mechanistic insights revealed oil component changes, highlighting the roles of surfactants, electric field forces, pH, and temperature. Formula-based calculations were also conducted for field-driven processes. This study presents an innovative deep dewatering technology for AOS, investigating the dewatering mechanism from various perspectives, including demulsification, electric field, pH, and thermal effects. Additionally, it evaluates the energy consumption and economic cost, providing a theoretical foundation for its engineering applicability and offering new perspectives for the treatment and disposal of AOS.