Removal of virus to protozoan sized particles in point-of-use ceramic water filters Angela R. Bielefeldt*, Kate Kowalski, Cherylynn Schilling, Simon Schreier, Amanda Kohler, R. Scott Summers Department of Civil, Environmental, & Architectural Engineering, University of Colorado at Boulder; 428 UCB, Boulder, CO 80309-0428, USA article info Article history: Received 5 August 2009 Received in revised form 28 September 2009 Accepted 29 October 2009 Available online 10 November 2009 Keywords: Ceramic water filter Virus Bacteria Protozoan Particle removal abstract The particle removal performance of point-of-use ceramic water filters (CWFs) was char- acterized in the size range of 0.02–100 mm using carboxylate-coated polystyrene fluorescent microspheres, natural particles and clay. Particles were spiked into dechlorinated tap water, and three successive water batches treated in each of six different CWFs. Particle removal generally increased with increasing size. The removal of virus-sized 0.02 and 0.1 mm spheres were highly variable between the six filters, ranging from 63 to 99.6%. For the 0.5 mm spheres removal was less variable and in the range of 95.1–99.6%, while for the 1, 2, 4.5, and 10 mm spheres removal was >99.6%. Recoating four of the CWFs with colloidal silver solution improved removal of the 0.02 mm spheres, but had no significant effects on the other particle sizes. Log removals of 1.8–3.2 were found for natural turbidity and spiked kaolin clay particles; however, particles as large as 95 mm were detected in filtered water. ª 2009 Elsevier Ltd. All rights reserved. 1. Introduction Ceramic water filters (CWFs) are used for point-of-use water treatment around the world. CWFs are a low-cost technology that can be locally produced using naturally available clay soil and fine organic materials such as sawdust or rice hulls. The material is fired in a kiln burning away the organic material and leaving behind small pores. The pore sizes and surface charge of the ceramic determine the ability of the filter to remove particles and pathogens from the water. CWFs are typically coated with silver to provide an additional disinfec- tion mechanism. However, because this silver leaches out of the filters over time, the long-term pathogen removal may be based primarily on the filtration characteristics. The reported measured pore sizes in CWFs from the Potters for Peace (PFP) factory in Nicaragua, used in our study, range from 0.6 to 3 mm in areas of the filters without cracks (which have lengths up to 500 mm) (Lantagne, 2001); and 0.02–200 mm with 14 mm the predominant size (Van Halem, 2006). The pore sizes in ceramic disks produced in the lab from flour, grog, and clay were primarily 0.02–15 mm, with a few 100–490 mm(Oya- nedel-Craver and Smith, 2008). These results indicate that filtration-based removal of viruses (<0.1 mm), should be poor, particularly since the bulk of the water is likely to flow through the cracks or larger pores. Previous studies have measured the removal of proto- zoans, bacteria, and viruses by CWFs. In studies on CWFs without silver the microorganism removal can be attributed to filtration. Brown (2007) found 1.8–2.4 log removal and 1.3–1.9 log removal of Escherichia coli and MS2 bacteriophage, respectively, in laboratory studies. The removal of MS2 was not significantly different in filters with silver applied, * Corresponding author. Tel.: þ1 303 492 8433; fax: þ1 303 492 7317. E-mail addresses: angela.bielefeldt@colorado.edu (A.R. Bielefeldt), kakowals@hotmail.com (K. Kowalski), s_chillin_g@hotmail.com (C. Schilling), simonsch@brandeis.edu (S. Schreier), amkohler@gmail.com (A. Kohler), r.summers@colorado.edu (R. Scott Summers). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 44 (2010) 1482–1488 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.10.043