عنوان مقاله [English]
Background and objectives: The effluent of paper machines contains high amounts of COD, suspended solids, color and turbidity. These pollutants have sever effects on environment. Also there are high amounts of water in the sludge structure. Therefore the dewatering of sludge is the main mission in an optimal sludge treatment. The polymeric flocculation has more advantages than coagulation like the production of large, compact and compressed flocs with good sedimentation properties and also lower dependence on PH. Also the absorption of high contents of aluminum causes dangerous effects on human body, therefore the application of natural components in sludge preparation for coagulation and flocculation shows an increasing trend. Papermakers tend to decrease water consumption with closed systems, but the accumulation of the suspended solid in white water is one of the limitations for this goal. In this research alum and chitosan were used as a wet end additive for decreasing the suspended solids in white water and increasing the NSSC strength properties. Due to the fact that the preparation of sludge with natural components is preferred to chemical components, the efficiency of chitosan with alum was studied in this research.
Material and methods: The NSSC pulp with freeness of 400±10 Ml was taken from mazandran wood and paper industries. The pulp consistency was 3% and the pH adjusted around 7 after the defibration of pulp. Then the pulps were treated with alum (in two levels of 1% and 1.5%), chitosan (0.8 % and 1%) and also the composition of alum+chitosan (0.8%-1% and 1%-1.5%) and finally handsheets were made. The strength properties of handsheets and the white water properties were measured.
Results: The results showed that the best treatment for the decreasing of the white water’s color was with 1% chitosan. For the reduction of COD and turbidity, the best treatment was the composition of alum+chitosan (1%-1.5%). The decreasing amounts of color, COD and turbidity was 24, 77 and 76 percent respectively. The strength properties like burst, tensile and tear were increased by 10, 16 and 25 percent respectively with 1% chitosan compared with control samples. The RCT and CMT of samples treated with alum+chitosan (1%-1.5%) increased by 41 and 23 percent respectively compared with control samples.
Conclusion: The chitosan has the most effect on COD, turbidity and color while the alum+ chitosan composition has the best effect on turbidity and COD. The strength properties of papers treated with 1% chitosan and alum+ chitosan( 1%-0.8%) was better than the papers which were treated with alum+ chitosan( 1%-1.5%) and chitosan(0.8%). The RCT and CMT of samples treated with alum+chitosan (1%-1.5%) and chitosan (0.8%) were better than other treatments.