Hello Blender community! 
Could someone help me out and tell what sort of effect is used here - something like small particles floating here and there on 7th sec or 20th sec of the video. And how can I recreate this effect in Blender.
just use a particle system with very few particles, little/no gravity, a high amount of damping, and then need some VERY weak forces to make the particles move a little. add some randomness to the particle size, maybe some Brownian movement too. and set up your materials or nodes to get the look you want.
Thank you very much! Sorry for the late answer too… I will try to use it, just not real good with physics part of Blender yet. I will see, if I make it right…