Waste Engineering

Information about PET and appearing problems from the viewpoint of waste technology

Use of PET worldwide
Use of PET worldwide

PET products are worldwide, growing in popularity. In 2008, were worldwide about 24 million tons of PET, used in the form of fibers and about 12 million tons of PET packaging. Even more than 1 million tons of films and other technical applications of PET were 2008 worldwide deployment difficulty (see Table 1).

Products made from PET are easily recyclable and can be a versatile recycling center. When PET is however discarded, many problems arise. PET has a very long shelf life in the environment and is very resistant to the influences of the environment. Today, many plastic products are stored in landfills over long periods. When PET is added to a thermal utilization in the combustion process, there are also toxic byproducts caused.

The discipline of Environmental Engineering is located in this issue of the waste treatment situation. A genetically modified microorganism, which has the ability to degrade plastics into its components and to metabolize these ingredients and produce high-quality and useful products of it, would be an ideal solution to the disposal problem of PET.

Use of PET and Material Flow Analysis

Over the past few years the percentage of use of PET in Europe rose significantly. Using the example of Germany, you can clearly see how the consumption of PET bottles has developed. The market share of PET bottles for soft drinks in Germany has risen from about 40% in 2002 to almost 80% in 2008.

Moreover, it is possible to see, from the packaging of soft drinks also, that the trend towards increased use of PET packaging, in recent years, also very significantly related to the decrease in the use of other types of packaging such as glass, cardboard and cans.

If you look at the percentage values ​​in quantities (t), PET is consumed often in which order of magnitude PET in Europe. Consumption increased by approximately 1.400Mio. tons in 1998, to almost 2,500 million tons in the year 2006.

The PET bottles are collected after use and then sorted by colors, and processed to granulate. These granules are processed and new bottles made ​​from it that are after a quality control back into circulation. In this way, through a long product life cycle, commodities spared. PET packaging can be reused in various forms. The PET cycle (PET recycling loop) shows the cycle of PET packaging. Before a PET bottle leaves the circuit and will supplie a different utilization, it may be filled again 17-20 times.

In 2009 statistics have been created by the Society for Packaging Market Research, that show the amount of plastic waste and its recycling methods. With the material flow analysis software STAN these material flows are presented vividly.

The recycling rate of plastic waste is 48.4%, the energy recovery rate is higher.

If a PET bottle leaves the circuit, it will initially be available as granules, flakes, or in bales on the market. Rates vary daily and will vary depending on the form offered.

The PET will be bought for further processing and it is either processed into fibers, which will then turn into textile products or it is processed as a packaging material, such as egg cartons or even used for car parts or computer parts. If these products have reached the end of its product life, they end up for disposal and this is mainly burned in incinerators. Through the good calorific value, PET waste can be used for the generation of energy.

PET bottles can be incinerated at high temperatures, without producing toxic substances. When combustion takes place, with insufficient temperature, it produces toxic byproducts.

Actual situation of the disposal of PET

By the requirements of the EU legislation (WFD) and in Germany (new Recycling Act), the producers of products have to be include into the responsibility for the disposal. There is, by this product stewardship, a redemption penalty. Since PET can be used for a long time and is also the recycling returned to the circuit, the disposal is in accordance with the life cycle not in the foreground. Nevertheless, PET may eventually need to be disposed of, and then there is, for the producers in Germany and Europe, the opportunity to sell the PET on the commodities exchange.

The withdrawal of the no longer usable PET bottles (returnable) is first in the beverage market. Here ends the responsibility of the consumer. Mortgage drink bottles should be disposed by the consumer, via the Dual System Germany (DSD "The Green Dot”) in the yellow recycling sacks or bins. The bottles of both collections are then transported to a local disposal company and treated there.

The bottles are crushed either in a shredding machine or in a scroll compressor. This process simultaneously devalued the PET beverage bottles. Thereafter, the material is brought in sorting.

Of these facilities, PET is automatic sorted in foreign materials and recyclable PET. PET separated in colored PET and clear PET. The material is then baled and either returned to the circulation or marketed under the Ordinance.

PET has a relatively high calorific value. That makes it interesting for combustion. The cement industry uses material like plastics for the firing of cement kilns. If the industries that use PET to fire, do not or no longer have access to the same extent to PET, it could lead to controversy.

Alternative ways oft he recycling of PET (-bottles)

The calorific value of PET is about the calorific value of paper, wood or lignite. But with a calorific value of 4 to 7 kWh / kg there are higher calorific alternatives.

In addition to the main recycling routes of PET, there are now also smaller alternatives. These alternatives exploitations make no significant contribution to the total amount and are mentioned only briefly. China is a large consumer of PET, which is traded on commodity exchanges. There are textiles produced from the PET fibers. This is the most common way for PET fibers, which are no longer returned to the circuit.

A group of students from Switzerland has developed a project that brings to aid acquisition of PET bottles, light in the “slums” of poorer Asian cities. Here is a PET bottle is filled with water and a little bleach and the lid sealed. This bottle is then passed through a hole in the ceiling of the hut, attached to the half. By the reflection of light striking on the outside of the bottle, this design brightens the room, how could a 55-watt light bulb.

Disposal of PET, using the iGEM project oft he TU-Darmstadt

The microorganism, which is developed in the iGEM project could be made at different points of the PET circuit:

The microorganism may be initially recognized by the collection of PET bottles. Here the percentage of the PET which is no longer used for recycling, is discarded. For this proportion, there are usually fibers produced, which can be used for textiles and other manufactured packaging, such as egg cartons or other plastic parts such as computer parts can be made ​​from this discarded plastic.

From this percentage, a part of this amount could be used for the disposal by the microorganism.

The second approach would be for the disposal of the products, which were produced from the discarded PET bottles. After the using phase of the products made from PET bottles, they will be disposed, mainly supplied by combustion.

At this point, to keep the proportion of harmful combustion less, it is possible to offer the microorganism as a further disposal way and in the future it may replace the complete combustion.