SUN Zhi-tao,LI Jun,WANG Xiu-jie,et al.Multi?stage Flocculation Efficiency of APAM Led by Adsorption and Bridging Mechanism[J].China Water & Wastewater,2022,38(2022 1 1):31-39.
Multi?stage Flocculation Efficiency of APAM Led by Adsorption and Bridging Mechanism
China Water & Wastewater[ISSN:1000-4062/CN:12-1073/TU]
volume:
第38卷
Number:
2022 1 1
Page:
31-39
Column:
Date of publication:
2022-01-01
- Keywords:
- multi-stage flocculation; anionic polyacrylamide; adsorption and bridging; floccharacteristics; re-flocculation; sludge dewatering
- Abstract:
- Flocculation process of anionic polyacrylamide (APAM) led by adsorption and bridging mechanism was explored. The differences between conventional flocculation and multi-stage flocculation in pollutants removal, flocculation performance, flocculation growth kinetics and sludge conditioning energy consumption were compared and analyzed by changing flocculant dosing conditions. Under the same dosage, the effluent turbidity of the two-stage flocculation was the lowest, followed by the three-stage flocculation and the conventional flocculation. The two-stage flocculation achieved the lowest turbidity of 19.53 NTU in the effluent at the minimum dosage of APAM (2 mg/L). Compared with conventional flocculation, the growth rate of floc, average particle size and sedimentation velocity of two-stage flocculation increased by 12.67%, 30 μm and 36.74%, respectively. The best flocculation performance of the two-stage flocculation was obtained under the condition of dosing interval of 240 s and dosage ratio of 1∶1, and the effluent turbidity was 15.34 NTU, the floc sedimentation velocity was 1.1 NTU/s and the floc density reached 1.123 4 g/cm3. In the process of floc breakage and re?growth, both the two-stage flocculation and the conventional flocculation could recover to the level before breakage. However, irreversible damage of the floc structure occurred after breakage. Proportion of flocs with sizes of 0-100 μm increased, and proportion of flocs with sizes more than 400 μm decreased. In addition, the strength factor of the two-stage flocculation (68.15%) after breaking was higher than that of the conventional flocculation (41.63%), and flocs produced by the two-stage flocculation had higher strength and stronger shear resistance. In terms of excess sludge conditioning, the lowest water content of filter cake (75.5%) could be achieved by only adding 40 mg/L APAM for the sludge produced by two?stage flocculation. Therefore, two?stage flocculation can significantly improve the turbidity removal efficiency and flocculation performance, which is a promising direction of enhanced flocculation.
Last Update:
2022-01-01