TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Casing: The casing has a taking out port for the treated water above the inflow port. The outflow port connects with a circuit which connects by means of a pump with a circulating water supply port which is open within the casing between levels of the inflow and taking out ports. The taking out port passes in the casing through orifices which are perforated radially above the taking out port through a circular wall coaxially installed in the casing.Preferred Carrier Assembly: A part of the circuit is to be an outflow passage formed on the axial line of the carrier assembly, an opening at the lower end of the outflow passage is to be the outflow port. The outflow passage is a continuation of the axial hole of a central spacer which is fitted to form a space between two carrier discs, in a hole perforated on the axial line of the carrier disc. The outflow port passes in an alternative way by a changeover valve to a drain and the circuit. The carrier assembly comprises support frames and carrier discs and outer spacers. The support frames and carrier discs are provided with holes for bolts on the same vertical lines and the assembly is assembled by piling carrier discs on support frames by means of the outer spacers, by passing the bolts through the holes and axial holes of the outer spacers by fastening nuts onto the bolts. The assembly is settled by fixing the support frames to arms of the casing. The carrier disc is formed by connecting outer units circularly around an outer circumference of a regular hexagonal object with H-shaped rails and corner spacers. The outer units are of shape enclosed with lines of regular hexagonal object, radiative lines from the center to each end of the line of the hexagonal body and a circular arc of the casing cut off by the radiative lines. The hexagonal body is formed by connecting regular hexagonal units in a honeycomb fashion with each other and also in the empty portions in the outer circumference rhombic segments with neighboring hexagonal units by means of H-shaped rails, corner spacers and intermediate spacers.Preferred Corner Spacer: The corner spacer comprises space forming portions, a protrusion beneath the corner spacer, a protrusion receiver which protrudes coaxially from the upside of the protrusion and a pair of rail receivers which protrude at an angle of 120 deg. at right angle with the axial line of the protrusion. From the protrusion a hole for the bolt passing through the protrusion receiver and the H-shaped rails are connected with each other, supported by the pair of rail receivers. The liquid passage is the shape of a cone with its head cut off. A bore of the liquid passage in the raw water inflow side is smaller than that of the outflow side.Preferred Central Spacer: The central spacer comprises, with respect to large diameter portion at one end of the axial hole, an inner step for regulating fitting extent of another central spacer and an outer step for regulating fitting extent of the carrier disc. The dimension from the outer step to the end face of the large diameter portion regulates the space. The dimension between the end face of the central spacer is so settled as to suit with the thickness of the carrier disc when another central spacer comes in contact with the inner step.Preferred Outer Spacer: The outer spacer comprises by stages from one end to the other on its axial line a base, an axial portion and a fit-in portion. The axial length of the base regulates the space. The axial length of the axial portion fits with the thickness of the carrier disc. The axial length of the fit-in portion fits with thickness of the carrier disc. The axial length of the fit-in portion fits with the axial length of the enlarged portion which is formed to set the fit-in portion of an outer spacer of a similar construction to the outer spacer, in an end portion on the base side of the axial hole.Preferred Intermediate Spacer: The intermediate spacer comprises a space forming portion, a protrusion beneath the space forming portion, a protrusion receiver which protrudes coaxially from the upside of the protrusion and a pair of rail receivers which protrude at an angle of 180 deg at right angle with the axial line of the protrusion. A rail receiver protrudes between the rail receivers at 60 deg with one or other side, a hole for the bolt passing from the protrusion through the protrusion receiver. The H-shaped rails are connected with each other supported by the pair of rail receivers.Preferred Apparatus: The support frame comprises a boss, arms, frames and a central support ring. The boss has a hole fitting with the axial hole of the central spacer. The arms protrude radially from the boss and the frames are spanned between the end portions of the arms and perforated with the holes. The central support ring has an inner diameter larger than the hole, fitting with an outer diameter of the central spacer and is set to the arms at one end of the boss concentrically with it. The frames have at one end of the hole an outer support ring for closely receiving the outer spacer.