Transient stage deposition of submicron particles in deep bed filtration under unfavorable conditions

Deterioration in the filter removal efficiency of submicron particles (λ/λ0) under unfavorable surface conditions is affected by the number of deposited particles per filter grain. In the case of above micron particles, the deterioration of filter removal efficiency has been mainly due to the blocking effect of deposited particles and not by the number of deposited particles. Deposition of large numbers of submicron particles changed the surface characteristics of collectors (filter grain associated with deposited particles) and enhanced unfavorable surface conditions. Filtration experiments were conducted with monodispersed suspensions of known sizes of submicron latex particles at different ionic strengths, using glass beads as filter grains. The filtration performance was predicted using a mathematical model assuming a linear relationship between λ/λ0 and σ (i.e. λ/λ0=1−kσ). For both particles, k was found to decrease and λ0 was found to increase with the increase in the ionic strength. Charge accumulation on the filter grain for deposition of submicron particles was calculated and was found significant at all the ionic strengths studied. For monodispersed suspensions of 0.816 μm particles, charge accumulation was found to decrease with the increase in the ionic strength of the suspensions. A comparison was made on the relative importance of blocking effect and charge accumulation for the filtration of submicron particles.