Water Purification

Water Purification

by Robert D. Spencer

The simple ideas of water purification (which are so often presented on the internet and in literature) assume, that one is starting with a reasonably clean source of water. Such is not always the case. If one finds oneself “out in the wild” in “not the best of circumstances”, such simple thinking and unreasonable assumptions can be fatal. Having spent my career in water purification and possessing a strong interest in emergency preparedness; I have considered the potential problems to be faced in an emergency. Being the analytical sort, I quite naturally try to contemplate a worst-case scenario. I want to present a workable plan for water purification, which may save lives. 

Potential Contaminants

  • Suspended Solids – Consists of plant matter, soil, clay, sand, chalk, insoluble minerals, etc. (These are larger than 1 micron) 
  • Algae – This annoying microscopic plant life is found wherever there is water. These are larger than 1 micron. 
  • Protozoa – Such as amoeba, paramecium, ciliates, rotifers, etc. These are larger than 1 micron.
  • Parasites – Cryptosporidium, Giardia lamblia, schistosomes, etc. These are larger than 1 micron. 
  • Bacteria – Such as escherichia coli, anthrax, etc. These are larger than 0.1 micron
  • Viruses – Such as polio, hepatitis, etc. These are around 0.0000001 micron. ·
  • Prions – These are mutated nucleic acid fractions, which cause diseases. These are around 0.0000001 micron
  • Volatile Organic Compounds (VOCs) – low molecular weight organics (e.g. methyl ethyl ketone (MEK))  
  • Semivolatile Organic Compounds (SOCs) – medium molecular weight organics
  • Polyaromatic hydrocarbons (PAHs) – Petroleum compounds such as compose gasoline, diesel, benzene, etc. These are non-polar, oily characteristic organics.
  • Pesticides · Herbicides ·
  • Polychlorinated biphenyls (PCBs) – Used widely as an electrical insulating fluid under government and insurance industry mandates since the 1930s. Then banned by the EPA in 1978. 
  • Dioxin – a byproduct of bleaching paper. One of the most toxic substances known. Dubbed “Agent Orange” during the Viet Nam War. 
  • Halogenated solvents – trichloroethane, methylene chloride, chloroform, carbon tetrachloride, etc. (These are non-polar organics.) 
  • Organic acids – tannic acid (from plants), fulvic acid (from soil), humic acid (from soil), acetic acid (from decaying vegetation), etc. These are slightly polar organics. 
  • Pharmaceuticals and their metabolites
  • Heavy metals – Such as cadmium, cobalt, lead, mercury, arsenic, etc. 
  • Soluble inorganics – Salt, sulfuric acid, hydrochloric acid, cyanides, chromates, nitrates, chlorides, etc. These are non-polar ionic compounds.
  • Radioactive isotopes – particularly important after nuclear war or a terrorist “dirty bomb”.

Water Purification Methods

  • Precipitation – chemicals bind to contaminants to create large masses, which can be filtered. Typically, calcium oxide (lime) or aluminum sulfate (alum) is used. (These chemicals may not be available or economical in an emergency.) ·
  • Flocculation – polymers bind to contaminants to create large masses, which can be filtered. (These chemicals may not be available or economical in an emergency.)  
  • Filtration – physically removes particles down to the pore size of the filter. The smaller the filter, the more pressure must be applied to force the water through the filter. This force must be applied to separate the water from the particles. This includes coarse filtration methods down to 1-micron pore size, as well as molecular separation methods (e.g. membrane filtration, reverse osmosis, nano-filtration, and ultra-filtration), with pore sizes just above the molecular diameter of water. Filters may be manufactured from sand, glass, porcelain, plastic, activated charcoal, paper, cloth, or other solids. Coarse filters should be placed in line before finer filters, inasmuch as coarse filters are inexpensive and can prevent the finer filters from being overloaded. Filters may be replaced or back washed as needed. ·
  • Adsorption – media (such as charcoal or clay) holds chemicals to its surface by attraction to its electronic structure. · 
  • Disinfection – chemicals, which kill microorganisms, denature prions, oxidize cyanides and other toxins, etc. Typically, these are reactive poisonous chemicals (e.g. chlorine, chloramine, ozone, hydrogen peroxide, permanganate, etc.). Typically, these are oxidizing compounds. The disinfectant may leave a slowly decomposing residual (e.g. chlorine, chloramine, hydrogen peroxide, permanganate, etc.), or may decompose rapidly (e.g. ozone). Those leaving a residual offer extended protection against infiltration of pathogens. Ozone breaks down into oxygen, whereas hydrogen peroxide breaks down into oxygen and water. ·
  • Distillation – is the separation of compounds by taking advantage of the differences of their boiling points. This is effective against salt, alkaline cyanides, many radioactive isotopes, etc. 

The Economy of Water Purification

For this plan, it is assumed, that in an emergency situation, there will be limited resources. This plan must fit within a family budget and must be comprehensible to the average adult. Consequently, the more technological and expensive methods are ruled out. (If you can use those methods, you don’t have an emergency.)

Water Purification Process Strategy 

  1. Gross filtration at 100 microns to remove larger solids using fiberglass screen material or polyester cloth as a filtering media. 
  2. Medium filtration at 10 microns to remove suspended solids such as clay, rust, and chalk using fine sand as a filtering media. 
  3. Fine filtration at 0.2 microns using a ceramic filter or powdered-sugar-fine sand to remove any bacteria. 
  4. Adsorption of non-polar organics onto activated charcoal filter. 
  5. Disinfection to kill ultra-small water borne pathogenic organisms (e.g. such as polio virus), which may have escaped filtration. 
  6. Distillation to remove ionic contaminants. 
Activated Charcoal

Activated charcoal is produced by placing a dense wood (e.g. hardwood or coconut shells) into a metal container (e.g. capped steel pipe) having a small hole in one end. This hole is needed to vent the steam and other gases (e.g. methanol, acetic acid, and other products) produced as the wood decomposes by destructive distillation. What is left inside the pipe is charcoal. This charcoal may be used after washing with water to remove the trace ash minerals, or it may be enhanced to be activated charcoal by treatment with steam at 1100°F. 

Another means of producing activated charcoal is to blend hardwood sawdust with zinc chloride, roast the mixture in the metal container as stated above, then removing the ash minerals and zinc chloride by dissolving them in water. Recycle the zinc chloride by boiling away the water, in which it is dissolved. 

Solar distillation

Distillation is a very energy intrinsic process. Water requires 80 calories to raise one gram of it from room temperature to boiling, and another 540 calories to boil it. This would consume close to half its weight of carbonaceous fuel to distill the water. In other words, for every gallon of water distilled, one would consume half a gallon of precious fuel. This issue has troubled me for years, as I have sought for a way to produce safe drinking water in a survival scenario. Recently, I looked at some videos on solar cooking. I then realized, that we could capture this free energy and put it to use. (from http://solarcooking.wikia.com/wiki/Scheffler_Community_Kitchen)   

Filtration procedure

  • To a 3 or 4 inch diameter PVC pipe secure a PVC pipe cap, to which a hose barb has been attached. 
  • Add 1 inch of pea size gravel. 
  • Add 1 inch of fiberglass or inert synthetic fabric. (This is to maintain separation of the layers.) 
  • Add 2 inches of sand. (Powder the sand for finer filtration, if desired.) 
  • Add 1 inch of fiberglass or inert synthetic fabric. 
  • Add two feet or more of activated charcoal. 
  • Add 1 inch of fiberglass or inert synthetic fabric. 
  • Add 2 inches of sand. (Powder the sand for finer filtration, if desired.) 
  • Add 1 inch of fiberglass or inert synthetic fabric. 
  • Add 1 inch of pea size gravel. 
The pipe should be filled with this media or cut to length, so that there is no room for the media to be pushed aside by the flowing water. If the water pushes the media aside, the water will not be filtered.

  • Secure a PVC pipe cap, to which a hose barb has been attached. This is your combined activated charcoal filter. This is held in a vertical position with the water being introduced at the bottom end of the filter. The water flow rate should be no more than 1/2 of the pipe volume per minute, in order to prevent the water from pushing the media aside. The pipe caps should be secured with silicone glue rather than PVC cement, so that they are leak-proof, but so that the caps may be removed for changing the filter media as needed. This cartridge is reusable. The filtration media (except for the charcoal) may be washed, bleached and reused. The charcoal may be recycled by roasting it in the metal pipe as described previously. This burns off the contaminants, except for metals.
  •  A 0.2 micron ceramic filter should be placed after this combined activated charcoal filter. The water should form a sufficiently tall column to produce the pressure to force the water through this ceramic filter. It may be desirable to use an entire 8 foot PVC pipe to form this column, in order to produce enough pressure for rapid filtration. Experience will show, if this is needed. As the filters become clogged with material, the flow rate at a given pressure will decrease.
  •  Another way of determining clogging is an increase of head pressure being needed to maintain a given flow rate. A pressure meter positioned in the pipe immediately before the ceramic filter and an in-line flow meter after the ceramic filter would be helpful in making the determination regarding when the filter media is in need of cleaning. These are helpful, but not necessary. After these two stages of filtration, the disinfection should be performed with a chlorine product, ozone, hydrogen peroxide, or potassium permanganate. Finally, the solar distillation is done to provide safe drinking water.