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Potable Water Biotechnology, Membrane Filtration and Biofiltration 481
Giardia and Cryptosporidium have been the principal organisms controlling disinfection
regulations in the US over the last decade.
Giardia is a protozoan parasite that occurs in a trophozoite and an oval-shaped cyst form.
Cysts excreted in the feces of an infected host move passively through the environment (18).
If cysts are ingested, infection may be transmitted to another vertebrate host. Giardia is
distributed worldwide in lakes, ponds, rivers, and streams. Reported Giardia levels have
ranged from 10,000 to 100,000 cysts/L in untreated sewage, 10 to 100 cysts/L in treated
sewage, and ten or fewer cysts/L in surface water sources and tap water (18). According to the
US EPA’s Surface Water Treatment Rule (SWTR), the public water systems filter, except in
rare circumstances, and disinfect surface water and groundwater that is directly impacted by
surface water; 99.9% of Giardia should be removed or killed. Commonly used water
disinfectants can effectively inactivate Giardia cysts depending on the disinfectant concentration
and contact time. Cysts are relatively more resistant to disinfectants than bacteria and
viruses, and high doses and lengthy contact times may be needed. This may result in high
levels of DBPs that are regulated by the US EPA (18). The appropriate technology for
removal of cysts is filtration, especially by using membranes. Microfiltration and ultrafiltration
can also effectively remove Giardia cysts from water.
Cryptosporidium is a parasite that can live inside the intestines of humans, farm and wild
animals, and pets. The source of Cryptosporidium is animal or human fecal waste. Cryptosporidium
can form a protective shell, allowing it to survive under harsh conditions. As a
result, Cryptosporidium has been found in water, soil, and food, after contamination with
fecal waste. It is reported that the conventional filtration process used by treatment plants may
not remove all Cryptosporidium from the drinking water supply. These unfiltered organisms
may also survive chlorine treatment. Cryptosporidium can be effectively removed from
drinking water by reverse osmosis, or filtration using 1 mm or smaller filter.
The SWTR and Groundwater Disinfection Rule have led to the investigation of ultrafiltration
and microfiltration for microbial removal. Many membrane filtration methods have been
developed and used to detect the presence of both Cryptosporidium and Giardia in surface
and treated water samples. Through examination of the sizes of the target organisms and the
range of membrane pore sizes, it is apparent that removal of these organisms is specific to the
particular membrane and its pore size distribution (4). The selection of membrane type with
the appropriate pore size is a crucial consideration for the removal of all microorganisms
especially Cryptosporidium and Giardia from drinking water.
2.5. Nitrate Removal from Drinking Water
Nitrate (NO3 ) removal in drinking water is one promising area in application of membrane
biotechnology. Contamination of drinking water sources with NO 3 originates from over
fertilization (both artificial fertilizer and animal manure) in agriculture, human and animal
waste disposal, disposal of wastewater from food processing operations, and anthropogenic
sources (19). Nowadays, NO3 – contamination of groundwater is becoming a worldwide
problem. A significant fraction of groundwater used for drinking water exceeds the MCL
for NO3 – in many regions of the world (20). In the United States, 10–25% of the water from