Biological Water Purification Methods

Water Purifying Methods That Work on Some Biological Toxins

Boiling Water

Boiling water for 20 minutes is an acceptable method of water purification, but this is only reasonable for small quantities of water. While boiling will kill many pathogens, the boiling process vaporizes water so you have a lot less water left after the boiling process.

While the standard method of water purification was and is chlorine -- and more and more water processing plants additionally use chloramines and fluoride -- sometimes these harmful chemicals simply won't kill everything, as evidenced by the table below. This is the time for a filter.

Certain viral organisms are beyond minute, smaller than bacteria. The smallest bacteria is about the size of the largest virus. They range from 0.002 micron - 0.3 micron. About the only things less in size are herbicides, pesticides, synthetic dyes, metals and salts. So viruses require correspondingly minute filtering. The drawback is that filters for these extremely small particles quickly clog. To remove every type of virus, you would need a filter that could remove down to .002 microns, however, that filter size is very expensive and would need to replaced frequently.

Prefilters are used to extend the life of sub-micron filters -- one that removes particles larger than bacteria. This puts the largest load on the less refined filter, allowing the sub-micron filter to remove anything that slips through. One-micron Absolute filters remove bacteria, including giardia cysts and cryptosporidium.

Although many water purifiers on the market can eliminate 99.9999+% bacteria, 99.9+% protozoan parasites and 99.9% waterborne viruses, this does not address small viruses. Even more high-end water purifiers removes bacteria, protozoa, cysts and chemicals, but not viruses.

Reverse Osmosis Filtration

According to Osmonics, Inc. "RO can meet most water standards with a single-pass system and the highest standards with a double-pass system. RO rejects 99.9+% of viruses, bacteria and pyrogens. Pressure, on the order of 200 to 1,000 psig (13.8 to 68.9 bar), is the driving force of the RO purification process. It is much more energy efficient compared to heat-driven purification (distillation) and more efficient than the strong chemicals required for ion exchange. No energy-intensive phase change is required. 

However, there are many drawbacks to Reverse Osmosis system, making it an inefficient and ineffective means of purifying drinking water. The small pores in the membrane block particles of large molecular structure like salt, but more dangerous chemicals like pesticides, herbicides, and chlorine are molecularly smaller than water (Binnie et al, 2002). These chemicals can freely pass through the porous membrane. For this reason, a carbon filter must be used as a complimentary measure to provide safe drinking water from the reverse osmosis process. Such chemicals are the major contaminants of drinking water after municipal treatment.

Another downside to reverse osmosis is the removal of healthy, naturally occurring minerals in water. The membrane of a reverse osmosis system is impermeable to natural trace minerals. These minerals not only provide a good taste to water, but they also serve a vital function in the bodys system. Water, when stripped of these trace minerals, can actually be unhealthy for the body.

Reverse osmosis also wastes a large portion of the water that runs through its system. It generally wastes two to three gallons of water for every gallon of purified water it produces. Reverse osmosis is also an incredibly slow process when compared to other water treatment alternatives. And, it uses a holding tank for water that must be kept scruplously clean so as not be become a breeding ground for mold, slime and other microbials.

Ultraviolet (UV) Light

The way UV water purification works is that water enters the purifier’s chamber. Once inside, it is exposed to UV light. The UV lamp used for this type of germicidal disinfection produces light at a wavelength of 253.7 nanometers (2,537 Angstrom units). At this wavelength, UV light destroys up to 99.9% of all bacteria, protozoa, viruses, molds, algae and other microbes. This includes such waterborne diseases as: E.coli, hepatitis, cholera, dysentery, typhoid fever as well as many others. UV purifiers work best when the water temperature is between 35oF - 110oF. Extreme cold or heat interferes with the purifier’s performance. Other factors that impact the ability of the UV to penetrate the water to kill the bacteriainte include:

  • Turbidity higher than 5 NTU
  • TDS (total dissolved solids) higher than 10 mgl
  • Iron higher than .3 ppm (parts per million)
  • Hardness greater than 6 grains
  • pH lower than 6.5 or higher than 9

Assuming your water meets the above conditions, UV works on the following microorganisms:

(Ultraviolet energy at 253.7 nm wavelength required for 99.9% destruction
of various microorganisms - in wsec/cm squared)

Bacillus anthracis 8,700 Shigella dysentariae (dysentery) 4,200
Corynebacterium diphtheriae 6,500 Shigell flexneri (dysentery) 3,400
Dysentery bacilli (diarrhea) 4,200 Staphylococcus epidermidis 5,800
Escherichia coli (diarrhea) 7,000 Streptococcus faecaelis 10,000
Legionella pneumophilia 3,800 Vibro commo (cholera) 6,500
Mycobacterium tuberculosis 10,000 Bacteriophage (E. Coli) 6,500
Pseudomonas aeruginosa 3,900 Hepatitis 8,000
Salmonella (food poisoning) 10,000 Influenza 6,600
Salmonella paratyphi (enteric fever) 6,100 Poliovirus (poliomyelitis) 7,000
Salmonella typhosa (typhoid fever) 7,000 Baker's yeast 8,800


Ozone is another option for water treatment, but residential systems are expensive. Look over this table of doses and reactions times for various organisms.

Typical Dosage

Reaction Times

Aspergillus Niger (black Mount) Destroyed by 1.5 to 2 mg/1
Bacillus Bacteria Destroyed by 0.2 mg/1 within 30 seconds
Bacillus Anthracis Ozone susceptible
Clostridium Bacteria Ozone susceptible
Clostridium Botulinum 0.4 to 0.5 mg/1
Diphtheria Destroyed by 1.5 to 2 mg/1
Eberth Bacillus (Typhus abdominalis) Destroyed by 1.5 to 2 mg/1
Echo Virus 29 After a contact time of 1 minute at 1 mg/1 of ozone, 99.999% killed.
Escheriachia Coli Destroyed by 0.2 mg/1 within 30 seconds
Encephalomyocarditis Virus Destroyed to zero level in less than 30 seconds with 0.1 to 0.8 mg/1
Enterovirus Virus Destroyed to zero level in less than 30 seconds with 0.1 to 0.8 mg/1
GDVII Virus Destroyed to zero level in less than 30 seconds with 0.1 to 0.8 mg/1
Herpes Virus Destroyed to zero level in less than 30 seconds with 0.1 to 0.8 mg/1
Influenza 0.4 to 0.5 mg/1
Klebs-Loffler Virus Destroyed by 1.5 to 2 mg/1
Poliomyelitis Virus Kills 99.999% with 0.3 to 0.4 mg/1 in 3 to 4 minutes
Proteus Bacteria Very Susceptible
Pseudomonal Bacteria Very Susceptible
Rhabdovirus Virus Destroyed to zero level in less than 30 seconds
Salmonella Bacteria Very Susceptible
Staphylococci Destroyed by 1.5 to 2 mg/1
Stomatitis Virus Destroyed to zero level in less than 30 seconds with 0.1 to 0.8 mg/1
Streptococcus Bacteria Destroyed by 0.2 mg/1 within 30 seconds

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