Settling and filtration experiments for the removal of flocs produced by a hybrid sono-electrochemical process

Choosing the right method for floc separation after electrochemical treatment seemed to be a problem in a number of previous research papers. Therefore, ultrasonic and electrochemical (sono-EC) processes in circulating flow mode were combined with settling and filtration to treat the oily wastewater and to remove the produced flocs. Experimental results showed that the inclined settling, which represented lamellar settling, was not recommended for the low-density flocs, as it did not accelerate the settling process. Overall settling time was 45 min with the final mineral oil concentrations up to 25 mg/l. On the other hand, mineral oil removal efficiency was about 57 % using the combination of settling and filtration. Achieved mineral oil concentrations (8.76 mg/l and 28.63 mg/l) were in accordance with the European standards for discharge into the sewerage system or direct discharge into the water body. It was recommended that all three filter pore sizes are used together to achieve the complete removal of mineral oil, turbidity and safety, as the filter with the smallest pores would often clog due to the floc residue in the treated wastewater.