Measurement of Biocolloid Collision Efficiencies for Granular Activated Carbon by Use of a Two-Layer Filtration Model

Abstract

Point-of-use filters containing granular activated carbon (GAC) are an effective method for removing certain chemicals from water, but their ability to remove bacteria and viruses has been relatively untested. Collision efficiencies (␣) were determined using clean-bed filtration theory for two bacteria (Raoutella terrigena 33257 and Escherichia coli 25922), a bacteriophage (MS2), and latex microspheres for four GAC samples. These GAC samples had particle size distributions that were bimodal, but only a single particle diameter can be used in the filtration equation. Therefore, consistent with previous reports, we used a particle diameter based on the smallest diameter of the particles (derived from the projected areas of 10% of the smallest particles). The bacterial collision efficiencies calculated using the filtration model were high (0.8 < ␣ < 4.9), indicating that GAC was an effective capture material. Collision efficiencies greater than unity reflect an underestimation of the collision frequency, likely as a result of particle roughness and wide GAC size distributions. The collision efficiencies for microspheres (0.7 < ␣ < 3.5) were similar to those obtained for bacteria, suggesting that the microspheres were a reasonable surrogate for the bacteria. The bacteriophage collision efficiencies ranged from >0.2 to <0.4. The predicted levels of removal for 1-cm-thick carbon beds ranged from 0.8 to 3 log for the bacteria and from 0.3 to 1.0 log for the phage. These tests demonstrated that GAC can be an effective material for removal of bacteria and phage and that GAC particle size is a more important factor than relative stickiness for effective particle removal.Microbial contamination of drinking water is a major health problem in many areas around the world (8, 9). Because conventional water treatment technologies are often not available in places with the greatest water contamination problems, the World Health Organization has proposed that point-of-use (POU) water treatment devices are the most efficient solution to the problem (33). Many POU devices rely on adsorption onto granular activated carbon (GAC) as a mechanism for removal of contaminants. In order for POU water treatment to be successful, the GAC must be effective in removing both chemical and microbial contaminants from the water. While GAC is widely known to be effective for decolorization, dechlorination, and chemical removal (14, 15, 17, 31), the efficiency of this material for removal of bacteria and viruses is relatively unknown.The methods used to characterize the relative adhesion of bacteria and viruses to GAC range from batch adsorption tests to column tests. Batch adsorption tests have confirmed that microorganisms adsorb exclusively to the exterior surface of GAC due to pore size exclusion (24, 25, 27), but they do not provide information that is sufficient to predict removal rates in columns. Mass transfer models can be used to characterize chemical removal with GAC in packed beds, but they do not provide detailed information concerning ...

Biotin- and Glycoprotein-Coated Microspheres as Surrogates for Studying Filtration Removal of Cryptosporidium parvum in a Granular Limestone Aquifer Medium

“…Presumably, when they were injected together, the less negatively charged gly- coprotein-coated CPMs attached to the more negatively charged unmodified CPMs and were carried along. The ␣ values calculated were Ͼ1 and similar to those found for granular activated carbon (38), showing that the material is very effective at removing colloids. Low ␣ values represent low levels of removal, and conversely, high ␣ values represent high levels of removal.…”

Transport of multiple Escherichia coli strains in saturated porous media

“…In such case, the single collector contact efficiency might be under estimated, giving rise to attachment efficiencies in excess of unity. Others (Shellenberger and Logan, 2002;Morrow et al, 2005;Paramonova et al, 2006;Yang et al, 2006;Lutterodt et al, 2009a) have also reported on attachment efficiencies above 1. For the remaining three strains (2041, 1514, and 2049), it was difficult to find an explanation for their very high attachment efficiencies of 1.42, 1.61 and 2.10, other than to assume that the bacteria size that was used in calculating the single collector contact efficiency had been wrong, most likely due to the presence of surface structures sticking out of the surface of these strains, thereby actually acting as a bigger colloidal particle than used in the TE correlation equation.…”

“…In addition, in some cases, L α values greater than 1 were found. The latter is not very strange (Shellenberger et al, 2002;Morrow et al 2005;Paramonova et al 2006), due to the presence of cell surface organelles like flagella and pili that extend beyond the cell surface. In such case, the aspect ratio used in the computation of the single-collector contact efficiency might be under estimated.…”

“…We did not consider sticking efficiency values in excess of 1 to be very strange. The presence of cell surface organelles like flagella and pili that extend beyond the cell surface may cause underestimation of the aspect ratio used in the computation of the singlecollector contact efficiency (Shellenberger and Logan, 2002;Morrow et al 2005;Paramonova et al 2006). For many strains (UCFL-131, UCFL-167, UCFL-263, and UCFL-348), in AGW removal of E. coli was complete before the final sampling port was reached.…”

Influence of adhesion to activated carbon particles on the viability of waterborne pathogenic bacteria under flow

“…For interaction controlled assays, sufficient transport of bacteria toward a collector surface is required. Packed bead reactors constitute such a system and indeed packed bed reactors have been applied in bacterial removal by carbon particles (Paramonova et al, 2006), but reproducible packing of the reactor system is difficult. Moreover, the bacterial fate in terms of growth and reproduction upon adhesion to a carbon particle cannot be determined, as generally only breakthrough curves of bacteria passing the system are measured.…”