PURPOSE: To maintain BOD(Bio-chemical oxygen demand) of the quality of treated water to ≤10mg/l by aerating with the suspended particle biological membrane method of the relevant treated water obtained after electrolysis of the organic waste water and floating the suspended matter.

CONSTITUTION: By adopting the electrolytic flotation method as a preliminary treatment, oil and suspended solid SS are floated and removed and also after removing soluble BOD by using flocculant, BOD value of treated water is reduced by the suspended particle biological membrane method to digest organic matter in the presence of a large amount of microoraganizm. The electrolytic flotation is a method differed from pressure flotation and executing floating separation by adhering bubbles of hydrogen and oxygen generated by the electrolysis onto the suspended matter. Practically, after miscellaneous dusts are removed in the treating process, pH is adjusted by addition of the inorganic flocculant and high molecular flocculant and floatingly separated by the air flotation. Additionally, residual BOD is treated by the suspended particle biological membrane method.