Separation of colloidal minerals from water by oscillating flows and grouping

One of the major challenge in water treatment is the removal of mineral colloids of sub-micron to micron size that, virtually unaffected by gravity, cannot be easily settled out of solution. To aid in the removal of these particles, the coagulation/flocculation process is typically used, which involves the addition of chemicals to neutralize the repulsive electrical forces of the colloids and then mixing to enhance particle aggregation and promote the formation of flocs. The current study proposes an innovative technique for colloid removal based on physical flow manipulation by an oscillating device whose action causes intermittent velocity gradients over time, space and direction. This unique manipulation causes the suspended particles to aggregate and rearrange in separate groups that are amenable to sedimentation. The proposed technique was tested under various operational conditions, including oscillation frequencies, alum doses and with/without rapid mixing. In addition, it was compared to the traditional coagulation/flocculation process in the treatment of similar suspensions. The results indicate that gentle oscillation can promote simultaneous flocculation and sedimentation in the same reactor over short periods of time. This technique, whose implementation can result in reductions to reactor sizes and process times, has a strong potential to improve conventional processes.