Study On The Treatment And Recycling Of Wastewater From The Twin-screw Extrusion Pupling

Pre-immerging raw materials by NaOH solution and then extruding them by twin-screw extrusion to produce pulp fibers is a clean and novel high yield pulping method. In such cases, the wastewater produced is not only far less than other pulping processes, but also can be reused in the pulping process. However, there are many fiber fragments and low temperature alkaline extractable materials left in the pulping liquor. They can be accumulated to very high concentration with the continuous reuse of the wastewater. On the one hand, the extracting of the alkaline extractable materials may be stopped to some extent; on the other hand, the new alkaline may be consumed by alkaline extractable materials. Therefore, the alkline charge must be increased to ensure the intensity of paper. In the end, the alkline extractable materils in the wastewater and taken by the slurry become balanceable. So it is necessary to treat the wastewater.Firstly, the changes of the solid content, the COD_cr, the total reducing, sugar content and the chroma of the wastewater in the circulation were studied, and the physical properties of the handsheets were also determined.Secondly, the paper introduced three flocculation systems, PAC-CPAM, acid extraction, and polyaluminum chloride sulfate (PACS)-CPAM in treating the wastewater from twin-screw extrusion pulping respectively. It was found that the PAC-CPAM system removed only less than 20% COD_Cr The efficiency of acid extracting system was better, when the pH value was less than 3.5, the COD_Cr reduction was 43.31%. The PACS-CPAM system was much more effective than either of the above, 58% removal of COD_Cr was achieved when treating pH was about 9.Thirdly, through the anaerobic - aerobic combined treatment, the COD_Cr of the exiting wastewater of aerobic is 1200—1300 mg/L when the COD_Cr of the entering wastewater of anaerobic is about 10000mg/L. The treated wastewater can be used in pulping or washing.In the end, the KOH instead of NaOH in the pulping process was studied. The pulping wastewater could be used for irrigating.