Introduction

Cryptosporidium, a genus of apicomplexan protozoans, is a protozoan parasite that causes a gastrointestinal illness called Cryptosporidiosis, an infection that affects both humans and cattle (Public Health England, 2011). Both the illness and the parasite are often referred to as “Crypto”. It occurs in many species, all of which are infectious. They come with an external shell that acts as protection against most factors that affect them, including disinfection by chlorine. This makes them very tolerant, hence heightening their chances of surviving outside their hosts immensely. As such, the parasite is able to stay active for a long period as it awaits transmission into the host, the most common of which is through water (Centers for Disease Control and Infection, 2013). This can be either drinking water or recreational water, such as swimming, which is among the most common places to get infection. Other avenues include surfaces that have been contaminated by feces from an animal or human beings, soil and food. Transmission by blood is not possible.

Direct Filtration

The most common method used to disinfect water that contains Cryptosporidium is direct filtration. This is because it incurs lower costs to set up considering the sedimentation, and occasionally the flocculation tanks are never required. Moreover, it has low running costs in terms of the lower coagulant dosages it uses, as well as significantly reduced maintenance costs, which result from the lack of need to power both the sedimentation and flocculation tanks. The process generally involves the addition of coagulant, a rapid mix, flocculation and filtration, all the while excluding such separation processes as floatation or sedimentation (U.S. Environmental Protection Agency, 2014). Direct filtration is also a process that can run concurrently with others within the same purification system. This makes it an optimal choice.

Previous Research into the Area

Eva Nieminski and Jerry Ongerth documented the earliest studies that can be made on the attempts to remove the Cryptosporidium parasite through direct filtration back in 1995. The two conducted a two-year Cryptosporidium oocyst and Giardia cyst removal evaluation on a large scale of a water treatment plant that was 900-gpm and another pilot plant that was 0.5-gpm (Nieminski & Ongerth, 1995). Both plants operated the direct filtration and conventional treatment regimes. The treatment effectiveness in removing turbidity, as well as the raw water quality in terms of algal content, acted as control mechanisms in the removal of seeded cysts, surpassing the mode of treatment used by the process. The result was the identification of high correlation between the removal of respective size particles and the cyst removal rates. Turbidity removal and cysts reflected poor correlation, whereas none was noted between heterotrophic bacteria and cysts.

With the pilot plant operating in conventional mode, Cryptosporidium removal were at an average of 2.98 logs, while they averaged 2.97 in the direct filtration mode. The large scale water treatment plant, on the other hand, recorded an average Cryptosporidium removal of 2.25 logs and 2.79 logs for the conventional treatment mode and the direct filtration mode respectively. This went to show that Cryptosporidium oocysts are particles that are efficiently removable by appropriate pretreatment, clarification and proper operation of filters (Lingireddy, 2002).

Eva Nieminski conducted a similar study later on in 1997 towards identifying the removal of Cryptosporidium and Giardia through both direct filtration and conventional water treatment. This time, however, the study was conducted at 8 full scale cyst seeding trials and 20 pilot-scale trials. The results from these trials were that the source water quality, which included algal content and turbidity, ensured control of the seeded Cryptosporidium’s removal. The observations highlighted high correlation rates between the removal of the respective size particles and cyst removal rates, low correlations between the removal of turbidity and cysts, and no significant correlation between the hydroscopic bacteria and cysts removals (Nieminski, 1997). Two versions of the immune-fluorescence staining method were applied for their efficiencies in identifying Cryptosporidium cysts that were seeded at known concentrations. This was to assure that the best available enumeration method was in place for accuracy purposes in the trials.

References

Centers for Disease Control and Infection, (2013) Parasites – Cryptosporidium (also known as

“Crypto”). Retrieved March 22, 2014, from http://www.cdc.gov/parasites/crypto/

Centers for Disease Control and Infection, (2013) Parasites – Cryptosporidium (also known as

“Crypto”). Retrieved March 22, 2014, from http://www.cdc.gov/parasites/crypto/gen_info/infect.html

Lingireddy, (2002) Control of Microorganisms in Drinking Water. Virginia: ASCE Publications

Nieminski, E. & Ongerth, J. (1995) Removing Giardia and Cryptosporidium by Conventional

Treatment and Direct Filtration. American Water Works Association. 87(9):96-106

Nieminski, E. (1997) Removal of Cryptosporidium and Giardia through Conventional Water

Treatment and Direct Filtration. United States Environmental Protection Agency & The National Risk Management.

Public Health England, (2011) Cryptosporidium. Retrieved March 22, 2014, from

http://www.hpa.org.uk/topics/infectiousdiseases/infectionsaz/cryptosporidium/

U.S. Environmental Protection Agency, (2014) Direct Filtration. Retrieved March 22, 2014,

from http://iaspub.epa.gov/tdb/pages/treatment/treatmentOverview.do?treatmentProcessId=1667135053

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