How to deactivate all the desktop effects of KDE permanently?

Head to

System Settings > Hardware > Display and Monitor > Compositor

Remove ✔ mark from Enable compositor on startup

When this is done, make reboot.

EDIT: this answer is for KDE 4 - not 5

This can be done from:

System Settings > Workspace Appearance and Behaviour > Desktop Effects > General > Activation

A screenshot to show the menu:

enter image description here

And a lot of options in there to selectively block the effects so you don't miss out on all of the fun :)

In openSUSE Leap 42.2 , to turn off desktop effect. click settings > configure desktop> scroll down to display and monitor> compositor...un-click enable compositor on start up.