Oblique - Coagulation And Sedimentation - Sec A / O Combined Process Of Papermaking Wastewater

The paper-making industry produces a large amount of wastewater with highlyconcentrated pollutants, which brings serious pollution to environment and mustbe treated effectively. This thesis aims to establish the technology of slopescreen-flocculation sedimentation- combined two-stage A/O process on the basisof 40000m³·d^-1 wastewater treatment demonstration project in Jiangsu Lee & ManPaper Manufacturing Co. Ltd. A large-scale engineering has been designed,constructed and run. The results show that it is feasible to apply slopescreen-flocculation sedimentation-two-stage A/O process for paper-makingwastewater treatment.1. The process can remove the pollutants from the wastewater efficiently. Itsaverage removal percentage is 97.9% and 99.1% for COD_Cr and SS respectively.The performance is stable, and the effluent reaches the requirement by＜Discharge Standard of Water Pollutants for Paper Industry＞(GB3544-2001).2. The slope screen in the process can reclaim fiber from wastewaster efficiently.The SS in paper-making wastewater is as high as 3500 mg·L^-1 with 50%recyclable fiber. When the 100-mesh slope screen with 35°-oblique-angle isapplied to reclaim the fiber, the superficial loading rate is set at 5～12 m³·m^-2·h^-1,the removal percentage of COD_Cr and SS of 52.8% and 53.7% respectively isacchieved. The income from fiber reclamation is about 33 Yuan per ton of paper,which is 2.5% of the total cost for paper manufacture.3. The flocculation sedimentation tank in the process can remove the majority ofunrecyclable SS and insoluble organic compounds, raise the ratio of BOD/CODwhich is favorable to the following biological treatement. The average influentCOD_Cr and SS are 1740mg·L^-1 and 1766mg·L^-1, with the average removalpercentage of COD_Cr and SS up to 53.8% and 94.8% respectively. The effluent SSis lower than 100mg·L^-1. 4. The process can remove pollutants by using wastes. The excessive activatedsludge is recycled to flocculation sedimentation and thereby cuts down thechemical dosage. On the basis of SS less than 100mg·L^-1, PAC and PAM dosagewas about 30ppm and 1ppm when excessive activated sludge is recycled toflocculation sedimentation. Otherwise, PAC and PAM dosage was about 83ppmand 3ppm. Comparing the two cases, the recycling of excessive activated sludgesaves running cost by 25% and obviously improve the dehydration of excessiveactivated sludge at the same time.5. The two-stage A/O process has the potential to make the wastewater reach thedischarge standard. The two-stage A/O process can remove soluble organiccompounds with COD_Cr volumetric loading rate of 0.9～2.1 kg·m^-3 d^-1, averageCOD_Cr removal percentage of 89.7% and average effluent COD_Cr of 77mg·L^-1.Judged from the biological phases, the first-stage A/O process works at highloading rate and the microbial population is relatively simple. On the contrary,the second-stage A/O process works at low loading rate and the microbialpopulation is relatively complicated. The kinetic model for COD_Cr degradationhas been established and the relation between COD removal and tank number hasbeen determined. The model indicates that the optimal tank number is 3.