Academic Appointments
| 2005-present | CEE Dept. Chair | Rice University, Houston, TX |
| 2004-present | G.R. Brown Professor | Rice University, Houston, TX |
| 2001-2003 | Professor | The University of Iowa, Iowa City |
| 1999 | Visiting Professor | EAWAG, Switzerland |
| 1998-2003 | Associate Director | Center for Biocatalysis & Bioprocessing |
| 1997-2001 | Associate Professor | The University of Iowa, Iowa City |
| 1993-1997 | Assistant Professor | The University of Iowa, Iowa City |
| 1985-1988 | Environ. Engineer | Tetratech Inc., San Bernardino, CA |