Reasons for the overly fast flocculation speed of PAM and PAC and solutions
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I’ve read articles stating that if particles aggregate and grow too rapidly during flocculation, two problems arise: (1) as the flocs grow too fast, their strength decreases; when subjected to high shear forces during flow, the adsorption bridges that hold them together are broken. It is difficult for these broken bridges to re-form, so the flocculation process is also one where speed needs to be controlled. As the flocs grow, the flow velocity should be reduced continuously to prevent the already formed flocs from breaking apart. (2) The rapid growth of some flocs leads to a sharp decrease in their specific surface area in water; small particles that have not undergone complete reactions lose the conditions necessary for such reactions. The probability of collisions between these small particles and larger particles decreases significantly, making it difficult for them to grow any further. Such particles cannot be retained by sedimentation tanks, nor are they easily captured by filter beds. I tried using PAM and PAC on a small scale, and their sedimentation effect was good; however, during operation the flocs were relatively small and numerous, and very fine suspended particles could still be seen in the settled water. I don’t know what’s causing it. Is there any way to fix it?
There are many factors that affect the use of flocculants, such as temperature, pH, and the properties of ions. Based on what you’ve described, I think it’s not that too much flocculant was used, but rather too little. If the temperature is high, try adding some water to see if the sedimentation speeds up.
Add another filter at the outlet to capture small flocs.