With the increasing demand for renewable energy, electrical companies have been able to tap into a new and more attractive market. It is therefore becoming more and more worthwhile to certify already existing plants and those production devices that produce electricity based on renewable energy. For this reason the "Stadtische Werke Winterthur", Winterthur's electrical company, questioned if electricity produced with gas from the sewage works could be classified as renewable energy, and if so, under which certification it would then be declared as ecological energy.

Out of this resulted the major question of this diploma essay, whether or not the electricity produced with sewage gas could be certified with an ecological label.

The necessary information was collected through discussions with experts, in literature and on the Internet. The task required a thorough analysis of various processes at the sewage plant as well as familiarity with the ecological labels in use. With the criteria from the VUE and by using a "Kennwertmodell", or "coding table", based on the essay "Okobilanz zur Klargasverstromung", one was able to check whether or not the electricity of the ARA Hard fulfilled the demands and could be certified with the ecological label "Naturemade Star". The results showed that the electricity produced by the ARA Hard should be capable of receiving the established and demanding label "Naturemade Star".