Zehnder also was director of the Swiss Federal Institute of Aquatic Science and Technology during this latter period.
Zehnder subsequently moved to Rabat, Morocco, where he worked as a consultant for the World Health Organization until 1973.
[1][2] During his PhD work Zehnder managed to discover and isolate Methanothrix soehngenii, which fellow microbiologist Willem Meindert de Vos described as a major discovery.
[3] He subsequently spent two years in the United States as a research associate in the bacteriology department at the University of Wisconsin–Madison.
[1][2] Zehnder then moved to Stanford University where he was employed as assistant professor in the department of civil engineering.
[3] In 1992 he became both director of the Swiss Federal Institute of Aquatic Science and Technology and professor of environmental biotechnology at ETH Zurich.