Removal of parasitic protozoa from water using a mobile water filtration apparatus intended for field use by military or emergency personnel

Military Medicine, Jan 2003 by Robertson, Lucy J

Various water treatment equipment is available for use in the field by military and emergency personnel to obtain safe potable water from contaminated, or potentially contaminated, sources. Because the importance of waterborne transmission of parasitic protozoa has only been recognized in the past 25 years, most of this equipment has been designed with elimination/inactivation of bacterial contaminants as a priority. Less attention has been given to other potentially waterborne pathogens, including parasites. Although some of the portable water filtration equipment commercially available provides marketing information data on removals of different pathogens including, in some instances, Cryptosporidium and Giarda, there is very little independently generated data published in the scientific literature. Although some of the data available in marketing information may be accurate and reliable, some may not. Most of the information published in the scientific literature concerned with pathogen removal in drinking water treatment focuses upon municipal-- size treatment plants. Whereas we were unable to find any publications investigating small-scale water filtration units suitable for military use, a few publications have investigated portable, point-of-use filters; these small filters are intended for use by individuals/small numbers of people and are designed for recreational use, e.g., for campers, etc. They would not be suitable for providing drinking water for relatively large numbers of people such as troops in action or personnel and civilians in disaster situations. Ongerth et al.9 tested four such point-of-- use filters for removal of Giardia cysts and found variable efficiencies with only one being more than 95% effective. Gerba and Naranjo10 tested a "structured matrix"-type filter against a range of pathogens, including bacteria, viruses, and Cryptosporidium and found it effective. Another publication11 compares the bacterial removal/inactivation efficiency of 10 different portable water treatment systems and reports that they demonstrated a range of efficiencies.

In this project, the ability of a water filtration system, currently used in the field by the Norwegian army, was assessed for its ability to remove Cryptosporidium oocysts and Giardia cysts that had been inoculated into a water supply. Background data on the efficiency of this system in removal of bacteria, turbidity, particulate matter, or parasites were not available to these authors, despite extensive searching and enquiries. However, promotional material indicated that water treated by this system should conform to World Health Organization and German drinking water standards.

Materials and Methods

Water Filtration Equipment

The water filtration equipment being tested was a Berkefeld Filter (drinking water purifier), type TWA 3. Berkefeld drinking water purifiers operate by a precoat filtration process. Prior to filtration, the raw water can be treated in holding tanks by following a standard dosing plan (SDP). In the SDP, the water is heavily chlorinated and then a flocculation/sedimentation procedure follows, using ferric chloride and calcium hydroxide. At the start of filtration, filter material (Berkesil KE, a mixture of diatomaceous earth and activated carbon) is fed to the precoat filter, which then forms a filtering layer in the 19 Berkefeld filter candles through which the water is pumped. Following filtration, chlorination adjustments of the filtered water can be performed.