Team:TU Darmstadt/Project/Ecology



Environmental Science

Environmental Engineering is a interdisciplinary field ranging from waste water treatment to disposal of hazmat. The project of the iGEM team of TU Darmstadt specifically addresses the area of waste management and waste water technology. The present information on waste management was provided by Kathrin Jager and the wastewater engineering content by Carolin Groß. Their evaluation is primarily focussed on Germany and Europe. This is due to the fact that there is hardly any detailed information available on global PET distribution.

Waste Management

General information about PET and introduction to the problems from the viewpoint of waste technology

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 problem (see picture 1).

Picture 1: Global use of PET (Source:

Products made from PET are easily recyclable and its regycled parts can be rused in many further applications. When PET is however discarded, many problems arise because PET has a high shelf life in the environment and is very resistant to the influences of uv light or heat. 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 emerging toxic byproducts. 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. In Germany occures an increasing consumption of PET bottles during the last few yeras. The market share of PET bottles for soft drinks in Germany increased from about 40% in 2002 to almost 80% in 2008.

Picture 2: Development of the market share of the PET bottle for soft drinks (in%; Germany) (Source:

There is a significantly coherence between the growing usage of PET packaging and the decreasing utilization of glass, carton or can. This coherence is probably based on the initiation of the tin pawn throughout Germany.

2004 2005 2006 2007 2008
PET 50.5 59.3 67.0 73.0 77.5
Glas 31.5 24.2 19.1 15.6 13.3
Carton 17.4 16.1 13.5 11.0 8.8
Can & others 0.5 0.4 0.4 0.4 0.4
Total 100 100 100 100 100

Figure 3: Packaging structures for soft drinks (in%, Germany) (Resource:

The consumption of PET beverage bottles in Europe increased by approximately 1,4 Mio. tons in 1998 to almost 2,5 Mio. tons in 2006.

Picture 4: PET beverage bottles consumed in Europe in million tons (Source:

The PET bottles are collected after usage and were separated by color and shred into granulates. These granulates can be reused for new bottles. After a quality control the new bottles return into circulation. With this procedure resources and energy could be spared.

In 2009 statistics of the Society for Packaging Market Research shown the amount of plastic waste and its recycling methods. The software STAN can visualize the material flow of waste and was used for this statistic.

Picture 5: Representation of the recycling of plastic waste (Data: environmental data bank)

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 depends on the respective form (e.g. flakes or granulates).

Form Amount (t) Average Amount per Offer Minimum Price Maximum Price Average
PET Residue 19.2 6.4 0.45 0.65 0.55
PET Re-granulate 422 70.3 0.8 0.9 0.85
PET Grist 2624.5 87.5 0.15 0.96 0.59
PET Bales 5908 203.7 0.02 0.52 0.29

Figure 6: Prices for PET at the market (Data:

For further processing the PET is bought and processed into fibers. The fibers can be used for textile production and packaging material, such as egg cartons or even used for car or computer parts. Once these products have reached the end of its product life, they end up for disposal being mainly burned in incinerators, at high temperatures without producing toxic substances. When combustion takes place with insufficient temperature, it produces toxic byproducts. Due to the high energy value and low toxicity, PET can be used as an energy source.

Content Damage
Vaporization (H2O) Not toxic
Carbondioxid (CO2) Harmfull
Carbonmonoxid (CO) Toxic
Soot / Carbon© Toxic
Aromate (Benzol, Naphtalen, Biphenyl, PAK) Harmful for Health, cancerous, long-term harmfull

Figure 7: Substances which can be caused by combustion

The 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.

Polymers Combustible Heating value
ABS, ASA, EVA Olefin rubber, Polyolefin, PS Gasoline, fuel oil, domestic gas >10kWh/kg
A/MMA, LCP, PA, PBT, PC, PEC, PEEST, PEI, PPS, PPSU, PPT, PVAL Hard coal, (light) fuel oil >7...10 kWh/kg
CSF, PBI, PES, PET, PUR, PVC, Starch, Cellulose Paper, timber, brown coal >4...7 kWh/kg
E/TFE, PVC-C, MF, UF, VDC/VC, VF Cannel, sawdust >1,5...4 kWh/kg
FEP, PCTFE, PFA none <1,5 kWh/kg

Figure 8: Sorts of plastic, Comparison fuels and heating values 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.

Alternative ways of the recycling of PET (-bottles)

In addition to the main recycling routes of PET, there are also other alternatives now. 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, employing the iGEM project of the TU Darmstadt

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

Picture 9: PET Recycling, exploitation and disposal with

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.

Wastewater Engineering

The General Aspects of Wastewater Engineering

The term wastewater engineering covers all the technologies associated with wastewater, wastewater collection, wastewater discharge and wastewater treatment. The two largest areas of wastewater engineering are related to the water quality and the wastewater and drainage technology.

Treatment plant construction and its purification stages

In a sewage treatment plant, there are various purification steps, which can be in turn to be subdivided into smaller stations. The various stages are generic. Each treatment plant, however, has a special structure. Example:

Wastewater plant

Purification steps:

Rain relief: If rain and waste water fed into one channel of the wastewater treatment plant (mixed system), then the sewer system usually be relieved by a rain-relief system, through a storm water and / or by an overflow basins.


  • Wastewater is passed through a screen or sieve drum
  • Coarse dirt stuck
  • Distinguishes are in fine and coarse screens

Sand / grease trap:

  • The sand and grease trap is a sedimentation tank, with the task of removing coarse settleable contaminants from wastewater.

Primary clarifier:

  • Suspended solids (faeces, paper, etc.) settles
  • Approximately 30 percent of the organic matter can be removed.

Aeration tanks:

  • Is in the so-called activated sludge tank by venting the activated sludge (mass of flaky aggregate bacteria) offset the reduced effluent wastewater constituents of the fresh sewage biotically oxidatively.


  • process forms a unit with the aeration tank
  • separated by settling of the activated sludge from wastewater

Focus of the wastewater technology at iGEM

Based on the iGEM project we have decided to focus on cleaning techniques in wastewater treatment plants. Among the techniques of wastewater treatment in recent years, in addition to mechanical (rake, sand trap and sedimentation) and biological processes (activated sludge) also chemical processes (precipitation and phosphate) and the use of membrane filters replaced. Through the project, we asked ourselves how we can use the micro-organism in a water treatment plant in the future

Possible application of in the Aeration tank

Since the microorganism works only aerobic would be the best possible use to the aeration tank. For the future, an additional test basin at the example of the treatment plant in Gross-Gerau would be to test the dose, in which you can add the tribes, in which tolerability they stand with other organisms, how they could be dangerous to humans and whether any improvement in water quality occurs.

Additional data WWTP Gross-Gerau

To give a little insight into the actual situation of the treatment plant Gross-Gerau, I run here on a few key figures:

Dry weather feed:

  • 5000 m³

Rainy weather feed:

  • Up to 15,000 m³

Biological oxygen demand (BOD)

  • 550 mg

Chemical oxygen demand (COD)

  • 800 mg

C: N: P ratio: The molar ratio of the three elements carbon, nitrogen and phosphorus to one another in an aqueous medium.

  • C = carbon
  • N = nitrogen
  • P = phosphorus

Is the relation of this ratio not held, there is no nitrification.

Based on these data, it may be possible to test the microorganism PETer, in cooperation with the treatment plant Gross-Gerau, in an experiment.


[1] Umweltbundesamt: Aufkommen und Verwertung von Verpackungsabfällen in Deutschland im Jahr 2009, 2012

[2] Veolia Umweltservice: Disposal of PET, [14.5.2012]

[3] Liter of Light Switzerland: [12.5.2012]

[4] Welt Online: [12.5.2012]

[5] Plasticker: [12.5.2012]

[6] Studiofroh: [12.05.2012]

[7] Forum PET: [12.05.2012]

[8] Kalaweit, A. et al.: Handbuch für technisches Produktdesign, Springer 2011

[9] [11.07.2012]

[10] [11.07.2012]

[11] [16.07.2012]

[12] [14.06.2012]