Scientific data on levels of micro-organisms indicate that the concentration of coliform bacteria (i.e. e.coli), commonly found in surface waters, ranges from 10⁵ (also expressed as log 5) per 100 ml for polluted stream water to 10⁹ / 100 ml in raw sewage. Considering infectious levels of 10³ for immune compromised people, the target effluent concentration after treatment should be less than 1/100 ml or a reduction of at least 8 log.

Cysts (i.e cryptosporidium and giardia) are the largest waterborne micro-organisms (3 - 6 micron) and occur in surface waters in a concentration of 10/L. They are highly infectious and the target effluent after treatment should contain less than 1/100L, equivalent to a 3 log reduction.

Since 1976 we know that not only ingested bacteria can have serious health effects, but also if inhaled Legionella Pneumophilia bacteria can cause a severe form of lung infection.

Conventional methods as RO, UV treatment or chemical disinfectants only partly and inadequately inactivate micro-organisms, as water temperature, pH, turbidity and other external factors, as well as the relative resistance of micro-organisms to disinfectants, influence effectivity.

The Ster-O-Tap^® low pressure membrane technology offers a consistent and efficacious solution to biological control. Ster-O-Tap^® membranes remove in excess of 1 million ( 10⁶) times more organisms or particulate matter than the highest rated carbon blocks, ceramic filters or UV sterilizers.

  Micro-Organisms

Bacillus subtilis	Cryptosporidium Oocysts	Escherichia coli (ecoli)
Giardia lamblia	Salmonella Typhi	Shigella Sonii
Enterococcus faecalis	Pseudomonas Aeruginosa	Vibrio Cholera
Information regarding approximate infectious doses and size may be gathered by selecting the desired image. Each of the bacteria is compared in size to a cut off pore size of ± 0.15 µm.