ENZYME DEINKING TECHNOLOGY ON OLD NEWSPAPERS AND THE CHARACTERISTICS OF ITS WASTEWATER

摘要

In order to find the low pollution deinking technology of old newspaper (ONP),enzyme was used for ONP deinking.Orthogonal experiments were carried out to analyze the enzyme deinking efficiency,and the characteristics of enzyme deinking wastewater was compared to those of chemical deinking wastewater.The results showed that the effective residual ink concentration (ERIC) increased with the increase of emzyme when the enzyme was in the range from 0.08% to 0.4%.Excessive enzyme resulted in the decrease of ink removal and pulp brightness,and the appropriate amount of enzyme was 0.1%.Flotation time had certain influence on ink removal.ERIC value changed a little when the flotation time was in 6 to 8 min,but it decreased sharply when flotation time exceeded 8 min.ERIC value was lower when the consistency of pulp was below 10%,but it increased with the increase of pulp consistency and reached the maximum when the pulp consistency was 15%.Enzyme had higher activity in the range of 50-70 °C,accordingly it also had good deinking effect in this range.The optimal enzyme deinking conditions for ONP are: enzyme: 0.1%; deinking temperature: 50 °C; repulping concentration: 10%; flotation time: 10min.Under these conditions,the ERIC value was the lowest,the brightness was the highest,and the tensile index and tear index of the paper made from the deinked pulp (DIP) were higher than that of the paper made from pulp without deinking.To obtain deinked pulp with similar ERIC value,enzyme deinking wastewater was nearly neutral,which had lower pH value than that of chemical deinking wastewater,the turbidity and CODcr of enzyme deinking wastewater were about 50% and 76% of that of chemical deinking wastewater,respectively.The pollution load of enzyme deinking wastewater was far below that of chemical deinking wastewater.