A new sewage treatment system which is composed of a fluidized pellet bed separator, aerobic biological filter and micro–membrane filter was studied.
In the newly proposed system, at the first stage, higher molecular weight organic substances and suspended matter are removed by way of chemical coagulation and flocculation. For the operation, a new fluidized pellet bed separator with high separation rate of 200-300 m/day is introduced to improve the treatment rate. A large percentage of organ ic substances are removed by the new coagulation/flocculation process. Hence, the total BOD load to be applied to the following biological treatment becomes very low. In addition to this, the organic substances in the effluent from the fluidized pellet bed separator are on lylower molecular weight substances which are easily biologically decomposed. Therefore easily decomposing and lower concentration pollutants enable use of a simple biological treatment p rocess such as aerobic biological filter with as short a detention time as 1 hour. Finally, effluent from the biological filter is treated by a micro-membrane filter. By the membrane process, suspended matte rs in the biologically treated water can be removed completely. Phosphate concentration of the treated water is very low, which is caused by aluminum coagulation in the first step and biological intake of the nutrient in the second step followed by complete sol id liquid separation in the third step.