The role of ballast specific gravity and velocity gradient in ballasted flocculation.

•The water quality challenge premeditated the high rate clarification process.•The concealed role of G value and ballast characteristics was unraveled.•G value optimization respective to ballast can lead to superficial floc settling.•Ballast specific G-value design can lead to material and energy efficient system.•This study can help design compact system with shorter hydraulic retention time.