[Particle entrapment mechanism in deep bed filtration]

Theoretical analysis was carried out in this paper to study the interaction in the bed filtration process, and the physico-chemical forces between the filter media and suspended particles in water were presented. Pilot study of the micro-flocculation deep bed filtration was carried out in the No. 9 Potable Water Treatment Plant of Beijing, the interception of particles of 1-10 microns diameter in the 500 cm deep filter bed was analyzed, and the head loss variation during 65 h was monitored. The shear force of 1-10 microns diameter-particle under 24 m/h filtration velocity was calculated. The theoretical physico-chemical forces between the filter bed and suspended particle of 1-10 microns diameter under the condition of -25 mV and -125 mV surface potential was also presented. The theoretical results are reasonably consistent with the experimental data, from which it can be concluded that the operation principles of micro-flocculation deep bed filtration could be analyzed by the physico-chemical interaction between the particles and filter media.