| Wheat straw is one of the most important papermaking materials in our country, which is very plentiful and cheap. However, wheat straw pulping pollution is quite serious. The aims of this thesis are mainly optimizing pulping technology with wheat straw as raw material, and treating with water pollution produced in course of pulping and papermaking. Through research on craft of the wheat straw P-RC APMP, the optimum pre-treatment conditions were discussed, and wheat straw pulp fiber quality was analyzed by FQA and electron microscope. The final effluent of the middle-stages wastewater treated with deep treatment method which was composed of flocculation pretreatment, IC anaerobic treatment, BAF aerobic treatment and micro flocculation, achieved a good water quality. The influence of the deep treated water reusing for pulping stages (for example washing grass, cooking, refining, etc) on brightness and physical strength index was studied and the optimum reuse ratio and the number were ascertained.The pre-treatment conditions of wheat straw P-RC APMP pulping including stock preparation type, temperature of the soaking water and squeezing extrusion were investigated. The results showed that higher temperature of the soaking water can improve the brightness and strength properties. The performance of the pulp with squeezing extrusion was better than the pulp without squeezing extrusion. FQA and ESEM analysis found that the hot water soaking and squeezing treatment can increased the Ln, Lw, Lww of fiber, decreased fines content and debris, made fiber surface depressed, soft, slack, increased the specific surface area and promote fiber bonding and fiber by itself was not subjected to undue degradation and fracture.Effluent from the P-RC APMP pulping was treated with different inorganic flocculants, including Al2(SO4)3, FeSO4, Fe2(SO4)3, PAC, AlCl3, FeCl3. The results showed that Fe2(SO4)3 had the best effection,and its cost is relatively lower. Under the condition of the adding of Fe2(SO4)3 is 150～200 mg·L-1, the pH in effluent is 6.51,COD is 2000 mg·L-1,BOD5 is 590 mg·L-1,SS is 308 mg·L-1,chroma is 300 times.The wastewater after flocculation pretreatment was treated by imitating IC anaerobic reactor. The results showed that IC anaerobic reactor had a high removal rate of the wastewater. The pH of the final effluent was 6.5, COD was 580 mg·L-1, BOD5 was 175 mg·L-1, chroma was 200 times, SS was 153 mg·L-1. The effluent subjected by IC anaerobic treatment was treated by BAF aerobic reactor. The results showed that BAF had a very good efficiency of anaerobic effluent removal, COD can reach up to 150 mg·L-1, SS was 34 mg·L-1, chroma was 50 times, pH was 7.4.The effluent from BAF was treated to decolorize and further to reduce the COD. The results showed that, Al2(SO4)3 used in conjunctions with the PAM can significantly speed up the flocculation settling velocity and improve water quality. Reaction time shortened to 5 min. Water quality of effluent can be achieved: pH was 6.5, COD was 50 mg·L-1, chroma was 12 times, SS was 8 mg·L-1, turbidity was 10 NTU. Application of PAM combination with the Al2(SO4)3 in advanced treatment of wastewater from wheat straw pulping was feasible, which had merit of strong adaptability, low investment, easy operation and management, simple operation, good effect. The treated water can meet the current water quality of the national wastewater discharge standard.Reusing of the advanced treated water to different pulping section including washing, pre-treatment, extrusion, refining and pulp washing and the best recycling proportion were investigated. The results showed that the whiteness and intensity had little or no impact when the advanced treated wastewater recycling for washing. However, the wastewater after treatment can not be all reused. This is because entire reusing will cause reduction of the whiteness and the strength index, accumulation of salinity, increase of the indicators of water pollution. It is acknowledged that that the proportion of recycling water can only account for 60% has not distinct bad impact on quality of pulp.
|
PDF Full Text Request