A NEW SEWAGE-TREATMENT SYSTEM WITH FLUIDIZED PELLET BED SEPARATOR

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 mol ecular weight organic substances and suspended matter are removed by w ay 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 organic substances are removed by the new coagulation/flocculation pr ocess. Hence, the total BOD load to be applied to the following biolog ical treatment becomes very low. In addition to this, the organic subs tances in the effluent from the fluidized pellet bed separator are onl y lower molecular weight substances which are easily biologically deco mposed. Therefore easily decomposing and lower concentration pollutant s enable use of a simple biological treatment process such as aerobic biological filter with as short a detention time as 1 hour. Finally, e ffluent from the biological filter is treated by a micro-membrane filt er. By the membrane process, suspended matters in the biologically tre ated water can be removed completely. Phosphate concentration of the t reated water is very low, which is caused by aluminum coagulation in t he first step and biological intake of the nutrient in the second step followed by complete solid liquid separation in the third step.