| 摘要 |
PURPOSE:To reduce membrane cost by enabling the reutilization of a membrane having become impossible in the recovery of a transmitted water amount even if washing is performed, in a multistage type membrane separation apparatus, by using a membrane, of which the transmitted water amount after washing reached a reference value set so as to be lower than an initial transmitted water amount or less, as the membrane of a post-stage side. CONSTITUTION:The ultrafiltration membranes of ultrafiltration membrane separation apparatuses 1, 2 of respective stages are respectively same in a fractional MW at the time of a new article and the second stage apparatus 2 uses a membrane advance in clogging. The second stage apparatus 2 uses the membrane which was used in the first stage apparatus 1 to generate clogging and of which the transmitted water amount was not recovered up to a preset transmitted water amount as the membrane of the first stage even if washing is performed. By this method, treatment can be performed in the same way as an apparatus wherein membranes gradually reduced in a fractional MW apparently are arranged in a multistage fashion.
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