METHOD FOR REUSING WASTE WATER FROM ACID TREATMENT STEP IN PRODUCTION PROCESS OF KRAFT PULP WHICH HAS ACID TREATMENT STEP BEFORE BLEACHING STEP

摘要

PROBLEM TO BE SOLVED: To provide a method for reusing waste water discharged from an acid treatment step and efficiently carrying out reduction of chromaticity of waste water discharged to the environment in addition to saving of an acid treatment chemical and reduction of amount of water used or discharged, in a process for producing kraft pulp having the acid treatment step before bleaching step.;SOLUTION: In production process of craft pulp having an acid treatment step S5 before bleaching steps S7-S13, waste water treated in the acid treatment step is recovered and the recovered waste water is subjected to oxidation treatment S20 and the waste water is added to at least either of a washing machine S6, a dehydration machine S6 before or after the acid treating step and the acid treatment step S5 to recycle the waste water in the acid treatment process. On this occasion, it is recommended that oxidation treatment of waste water treated in the acid treatment step is carried out by using a gas containing at least ozone. In this case, it is preferable on efficient utilization of ozone to utilize discharged ozone-containing gas for oxidation of acid treatment waste water when using ozone in bleaching step.;COPYRIGHT: (C)2008,JPO&INPIT