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

Deterioration in the filter removal efficiency of submicron particles (lamb da/lambda(0)) under unfavorable surface conditions is affected by the numbe r of deposited particles per filter grain. In the case of above micron part icles, the deterioration of filter removal efficiency has been mainly due t o the blocking effect of deposited particles and not by the number of depos ited particles. Deposition of large numbers of submicron particles changed the surface characteristics of collectors (filter grain associated with dep osited particles) and enhanced unfavorable surface conditions. Filtration e xperiments were conducted with monodispersed suspensions of known sizes of submicron latex particles at different ionic strengths, using glass beads a s filter grains. The filtration performance was predicted using a mathemati cal model assuming a linear relationship between lambda/lambda(0) and sigma (i.e, lambda/lambda(0) = 1-k sigma). For both particles, k was found to de crease and lambda(0) was found to increase with the increase in the ionic s trength. Charge accumulation on the filter grain for deposition of submicro n particles was calculated and was found significant at all the ionic stren gths studied. For monodispersed suspensions of 0.816 mu m 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 bl ocking effect and charge accumulation for the filtration of submicron parti cles. (C) 2000 Elsevier Science Ltd. All rights reserved.