Homework(111607)
- 1. Homework : Focus week By : Joanna Je, 08S2
- 2. How to recycle paper Adding water and applying mechanical action to separate fibers from each other. Using screens to remove contaminants that are larger than pulp fibers. Spinning the pulp slurry in a cleaner causes materials that are more dense than pulp fibers to move outward and be rejected. Passing air bubbles through the pulp slurry causes ink particles to collect with the foam on the surface. By removing foam, pulp is made brighter. Mechanical action is applied to fragment contaminant particles. Small particles are removed. The fiber is made into a new paper product in the same way that virgin paper is made. Process water is cleaned for reuse. The unusable material left, sludge, is buried in a landfill, burned at the paper mill, or used as a fertilizer.
- 3. Standards Paper fibers cannot be recycled indefinitely because fiber length and strength are degraded with each use. Individual fibers can only be recycled 4-6 times. When fibers become too short, they are not retained in the pulp or paper and end up in the sludge. New fibers are usually added to recycled pulp when new paper products are made. Consequently, most recycled paper will still contain some pulp. There is no universal standard for the maximum percentage of virgin pulp in recycled paper. 'Recycled' paper is available that includes anywhere from 10~100% "post-consumer" paper. The EPA mandated the use of 50% post-consumer recycled paper by the federal government, state governments that receive federal funding, and many companies that receive money from the federal government. The EPA does not regulate recycled paper used outside of the government; it only sets a minimum guideline. The UK also does not have any legal standards, only non-mandatory guidelines instituted by a variety of different organizations.
- 4. Forest preservation Today, 90% of paper pulp is made of wood. Paper production accounts for 43% of harvested wood, and represents 1.2% of the world's total economic output . Recycling of newsprint saves about 1 metric ton of wood while recycling 1.1 ton of printing or copier paper saves slightly more than 2 metric tons of wood. This is because kraft pulping requires twice as much wood since it removes lignin to produce higher quality fibers than mechanical pulping processes. Relating metric tons of paper recycled to the number of trees not cut is meaningless, since tree size varies tremendously and is the major factor in how much paper can be made from how many trees. Trees raised specifically for pulp production account for 16% of world pulp production, old growth forests 9% and second- and third- and more generation forests account for the balance. Most pulp mill operators practice reforestation to ensure a continuing supply of trees. The Forest Stewardship Council (FSC) certifies paper made from trees harvested according to guidelines meant to ensure good forestry practices. It has been estimated that recycling half the world's paper would avoid the harvesting of 80,000 km² of forestland.
- 5. Water and air pollution The U.S. EPA has found that recycling causes 35% less water pollution and 74% less air pollution. Pulp mills can be sources of both air and water pollution, especially if they are producing bleached pulp. Modern mills produce considerably less pollution than those of a few decades ago. Recycling paper decreases the demand for virgin pulp and thus reduces the overall amount of air and water pollution associated with paper manufacture. Recycled pulp can be bleached with the same chemicals used to bleach virgin pulp, but hydrogen peroxide and sodium hydrosulfite are the most common bleaching agents. Recycled pulp, or paper made from it, is known as PCF (process chlorine free) if no chlorine-containing compounds were used in the recycling process. However it should be noted that recycling mills may have polluting by-products, such as sludge. Deinking at Cross Pointe's Miami, Ohio mill results in sludge weighing 22% of the weight of wastepaper recycled.