Recovery of clay by microfiltration

Pretreatment of dilute suspensions leads to separation of water and solids. Reuse of both water and flushed solids can be smart both economically and environmentally. Many industries produce effluents with mixtures of water and solid particles. Traditionally, the effluent is discharged via a sewer to a receiving watercourse. Separation by microfiltration (MF) is a well suited method for recovery of production materials in dilute suspensions. Micromembranes typically have pore sizes of 0.2 mu m. Larger particles are therefore retained and the permeate is free of suspended solids. Bacteria, for example, are larger than 0.2 mu m. Removal of bacteria by MF therefore, may be defined as a physical "disinfection" process. The china producer Figgjo AS is big its Norway. The company produces cups and plates for restaurants, cruise-vessels and individual homes. The production of china results in effluents rich in clay and glaze particles. Traditionally, clay is difficult to separate without space-consuming and chemical-intensive processes such as coagulation, flocculation and sedimentation. After installing clay separation by MF, Figgjo AS has nearly eliminated clay in the effluent. The membrane plant efficiently concentrates and recovers clay for reuse in the production of china. The factory recovers 35 tons of clay annually by :MF. The savings in clay equates to a payback of the investment in MF equipment in 5 years. Compared to chemical coagulation for clay separation, the payback time is less than a year for a MF plant. There is no reuse of clay after chemical precipitation, and there is a sludge handling cost; transportation and sludge deposit. The operation of the MF plant is automatic. The permeate flux is around 50 l/m(2)/h (lmh) at a cross-flow velocity of 2 m/s and an operational pressure of maximum 2 kg/cm(2). The plant is flushed once a day with clean water. No chemical cleaning of the membranes is necessary.