Removal of Cryptosporidium and polystyrene microspheres from swimming pool water with sand, cartridge, and precoat filters

Abstract

Cryptosporidium has caused the majority of waterborne disease outbreaks in treated recreational water venues in the USA for many years running. This research project evaluated some common US swimming pool filters for removing Cryptosporidium oocysts, 5-µm diameter polystyrene microspheres, and 1-µm diameter polystyrene microspheres. A 946 L hot tub with interchangeable sand, cartridge, and precoat filters was used at room temperature for this research. Simulated pool water for each experiment was created from Charlotte, NC (USA) tap water supplemented with alkalinity, hardness, chlorine, and a mixture of artificial sweat and urine. Precoat (i.e., diatomaceous earth and perlite) filters demonstrated pathogen removal efficiencies of 2.3 to 4.4 log (or 99.4-99.996%). However, sand and cartridge filters had average Cryptosporidium removals of 0.19 log (36%) or less. The combined low filter removal efficiencies of sand and cartridge filters along with the chlorine-resistant properties of Cryptosporidium oocysts could indicate a regulatory gap warranting further attention and having significant implications on the protection of public health in recreational water facilities. The 5-µm microspheres were a good surrogate for Cryptosporidium oocysts in this study and hold promise for use in future research projects, field trials, and/or product testing on swimming pool filters.

Attachment behavior of latex microspheres on a fibrous media

“…Similarly, use of fabric material in colloid filtration through aqueous media is relatively new and very little is known in the literature. Most of the reported studies are on a collector media wherein a huge path length of the bed is required (e.g., glass beads [9,10,17], quartz/ Yes Yes ottawa sand [5,6,8,12,13,19,20], silica [11,18,20], goethite [7], goethite coated sand [14]) for colloid removal whereas higher colloid removal efficiencies can be obtained by using fabric as a filtration media at lower path lengths. The current work is a systematic study to investigate the attachment of latex microspheres (oocyst surrogates) on a fibrous substrate in presence of divalent cations and dissolved organics when present in water, on fibrous substrates, and both (on fabric surface and in water).…”

“…Lowering of attachment of oocysts and microspheres on various granular substrates was reported to be due to more negative surface charge of oocysts and microspheres. The removal trends of microspheres and oocysts were similar, suggesting that microspheres can be used to provide a conservative estimate of oocysts removal through filtration [3,[6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Characterization and chlorine reactivity of particulate matter released by bathers in indoor swimming pools

“…Combining sand filtration with granular activated carbon filtration has been proven to be the most effective treatment for reducing DBPs and their precursors; however, conventional water treatment techniques combining (or not combining) coagulation and sand filtration remain the most widely utilized methods (Lee et Blatchley, 2022). Nonetheless, during the filtration step, dissolved and undissolved compounds are retained on the filter media (Amburgey et al, 2012), where they are exposed to chlorinated water and can form new or additional DBPs, until the backwashing process is initiated (Skibinski et al, 2016). The reactivity between chlorine and DOM brought by bathers has been the subject of numerous studies, and a solution simulating DOM brought by bathers has been formulated (body fluid analogs (BFA)) (Borgmann-Strahsen., 2003;Goeres et al, 2004;Judd and Black., 2000;Judd and Bullock., 2003).…”

Preventing and controlling spp. in aquatic facilities: environmental health practitioners’ experiences in Victoria, Australia

“…For example, pool water treatment is ineffective as Cryptosporidium spp. is highly resistant to chlorine 29 and common filtration systems used in aquatic facilities have limited effectiveness in physically removing the pathogen from water 30 . Numerous studies investigating cryptosporidiosis outbreaks associated with aquatic facilities have highlighted several important factors for the prevention and control of the disease.…”