Feature

What's good in space is good on the ground - water purification

Clean water is as important to an astronaut circling the Earth in a space station as it is to a child at a mud walled school in remotest Africa. And both the astronaut and the child have the same problem - if their clean water is made using a hi-tech filter system that breaks, they will have to drink dirty water and will probably get sick as it is too expensive to send a technician over to repair the filter. Hence, a well designed water system for cleaning water in a space station is as relevant to rural Africa as it is to those that live in space. As long as the price is right of course.

Water purification uses many different approaches. Essentially the harmful things in water can be divided into categories such as living organisms that are dangerous (eg Cholera and other bacterial pathogens, various viruses, worms, fungi), things that make the water look bad (dirt, algae, tannins), and pollutants such as pesticides, heavy metals and ions.

To remove living organisms from water, chemical dosing is highly effective - chlorine or iodine can be added to the water killing the pathogens. But, chemicals such as iodine and chlorine are in themselves quite toxic, so they must be removed. The following article looks at a relevant technology which can do this.

Water is one of the most basic necessities of mankind. Over one billion people, worldwide, lack access to sufficient quantities of water to survive. As a result, ten million people die each year from water-borne diseases and two million of those people are young children. The problem is not a new one, but it has been a particularly difficult one to solve by traditional means.

The Major Source of the Problem: Bacteria, Viruses and Cysts
These pathogenic organisms breed in unprotected water and unsanitary conditions. Even efforts to help the needy are often thwarted by re-contamination of treated water during transportation and storage prior to use.

The Traditional Means of Treatment:

Centralized Plants and Expensive Infrastructure

The traditional water treatment approach has been to build multi-million rand centralized treatment plants and install costly underground piping systems to deliver it to users.

That approach has worked well for hundreds of years in densely populated areas, where sufficient capital is available for such projects.
However many of the billion people who lack access to sufficient safe drinking water to survive live in sparsely populated areas and/or they lack the funds necessary to build the plants and distribution systems needed for central processing.

Point of Entry/Use

Point-of-Entry (POE) and Point-of-Use (POU) Treatment Alternatives
Alternatives to centralized treatment exist in either point-of-entry or point-of-use configurations. These designs can use either more local water supplies, saving on the expense of placing pipes between the central treatment plant and the user or they can be used as additional treatment measures or safeguards at the user end of centralized systems.

What is wanted then is a technology that Is foolproof, easy to maintain, with no electricity requirement and no moving parts.

An example of a technological solution

Water Systems International and the U.S. based Water Security Corporation, are water treatment technology companies dedicated to providing solutions to the world's most challenging water quality problems. Having resident expertise in organic chemistry and most forms of point-of-entry and point-of-use (POE/POU) water filtration and purification, the company is well-positioned to identify, qualify and advance leading-edge technologies.

The system pictured produces 18 litres per minute, sufficient for a small rural village.

Components developed by these companies were used by NASA to provide clean drinking water in the manned space programme. Now the technology is being made available to the rest of us (in the case of Africa, through the technology agents Khayalami Africa Pty(Ltd).

The system pictured produces 18 litres per minute, sufficient for a small rural village. Systems include a sediment filter, 1 micron carbon pre-filter, MCV & Iodosorb cartridges for disinfection and a 0.5 micron cyst/polishing filter as well as a FILTER WATCH flow monitor which alerts the user when 130,000 litres have passed through the system indicating it is time for a filter replacement. Additional configurations and ganged systems to provide higher throughput are also available.

How it works

The water purification technology set includes two proprietary technologies, MCV® Iodinated resin and our iodine scrubber, Iodosorb®.
a. MCV® Iodinated resin is a slow release resin, capable of sustaining a predictable release of iodine into incoming water over a long period of time (release versus time is called Elution).

The long, predictable elution curve of this product makes it perfect for cartridge-based water treatment systems. It is truly a "fire and forget" technology, with simple spin-on cartridge replacement at prescribed total treated water volumes. And, the spent cartridges are completely landfill safe.

b. Iodosorb® Scrubber is also a resin-based product. It has an affinity for all species of iodine (iodine changes species when used). Because its architecture is such that it works when water is passed over it, it too is ideal for cartridge-based water treatment systems. Like MCV®, Iodosorb® is also a technology that is safe for landfill disposal after use.

c. Finally, the technology package can be engineered to leave a small residual of iodine disinfectant in the product water, to guard against re-growth of pathogenic organisms during shipment and storage prior to use. The chart below compares MCV® Iodinated resin and the Iodosorb® Scrubber to competing technologies Comparison to Current Technologies.

Editors summary - essentially water is first filtered of big solid things by a prefilter (this removes odds and ends in the water such as sticks, snails, fish scales, stones, small pieces of sand and so on). The carbon prefilter will also remove certain bad tastes from the water. Next, the iodine cartridge releases iodine into the water killing living things, and then the next cartridge removes the chemicals that were made in this step, as iodine would have reacted with bits of the organisms, tearing them apart and killing them, and producing all sorts of spectacularly complicated iodine compounds, so of which would be unhealthy. The system then has as a final check- a neat little finishing filter which removes any cysts that made it through so far.

Filtration gurus talk about log kill factors of filters - this has nothing to do with the timber industry but in fact refers to logarithmic, hence a 2 lot kill rate would see the number of bacteria reduced from 100 to 1, and a 4 log kill rate from 10 000 to 1 and in the case of these technologies described from a million to one for bacteria and from 10 000 to one for viruses - not the sort of odds one would wish to bet on to win money, but I would bet on it to save lives!

More information:

garth@scienceinafrica.co.za 

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