The primary treatment of waste water involves the removal of:

During the primary treatment of waste water the removal of particles are carried out physically through the process of filtration and sedimentation. This process involves removal of stable particles.

Therefore, from the above options, only stable particles are removed during the processes involved in the primary treatment of waste water. The other options are incorrect as they are not removed during primary treatment of waste water. So, option b. stable particles is the correct answer.