From the beginning of the 1980's communal waste water treatment plants have become increasingly equipped with denitrification stages.

The simple rules of dimensioning for plants that are solely for nitrificating aeration use that had previously been used needed to be extensively revised and expanded. A number of different attempts at dimensioning have been applied in Germany, which have been developed and spread by various universities.

In order to create a unitary dimensioning system an academic group including members of different institutes of environmental engineering, was founded in 1988. In September 1989 this group published an approach of dimensioning that gained a large distribution over the following years. The approach that was taken was due to the systems complexity not applicable by manual dimensioning and therefore forming the basis for the development of the waste water treatment design tool design2treat at the Institute of Environmental Engineering at the RWTH Aachen University.

Today the design2treat software is especially in North-Rhine-Westphalia a wide spread design tool and is an official test program used by the public authorities. The development of the software has been financially supported by the "Oswald-Schulze-Foundation" and the ministry of the environment NRW and the program has been gradually improved and extended by the institute of environmental engineering in cooperation with the Office for the Environment NRW. During the course of this development thetoday most widely spread design approach of the DWA work sheet A 131 has been implemented into the design2treat software.

Furthermore the software has been continuously expanded by possible additional treatment components, for example the dimensioning of reactors for the biological phosphor elimination, the dimensioning of cascade denitrification plants and also the design of plants using sequencing batch reactors.