NOVELTY - A waste-water-treatment apparatus comprises first microorganisms processing tank (11) in which wastewater from pumping unit (22) is pumped through wastewater path, second microorganisms processing tank (12), first and second flow paths which connect two microorganisms processing tanks, first filter (15) and second filter which are interposed in middle of first flow path and second flow path, first and second pressure chambers (21) which face pressure surface at side of second microorganisms processing tank of first filter and of second filter, and two valve apparatuses.    USE - Wastewater treatment apparatus for purifying carbon compound and nitrogen compound.    ADVANTAGE - The apparatus has favorable purification performance for a long time and easy maintenance of filter.    DETAILED DESCRIPTION - A waste-water-treatment apparatus comprises first microorganisms processing tank (11) in which wastewater from pumping unit (22) is pumped through wastewater path, second microorganisms processing tank (12) which is arranged on first microorganisms processing tank, first and second flow paths which connect two microorganisms processing tanks, first filter which is interposed in middle of first flow path, second filter (15) which is interposed in middle of second flow path, first pressure chamber (21) which faces pressure surface at side of second microorganisms processing tank of first filter, second pressure chamber which faces pressure surface at side of second microorganisms processing tank of second filter, first valve apparatus which selectively connects first pressure chamber to second microorganisms processing tank or wastewater path, and second valve apparatus which selectively connects second pressure chamber to second microorganisms processing tank or wastewater path. An INDEPENDENT CLAIM is included for a control process of waste-water treatment apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of the waste-water-treatment apparatus.    First microorganisms processing tank (11)    Second microorganisms processing tank (12)    Filter (15)    Pressure chambers (21)    Pumping unit (22)