1 Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, Netherlands. m.c.m.vanLoosdrecht@tudelft.nl.
2 Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, Netherlands. UNESCO-IHE Institute for Water Education, Westvest 7, 2611 AX Delft, Netherlands.