Monday, September 22, 2008

Raw Innovation

Before I go on to discuss the actual design process, lab tests, results,
applications and such, you must be wondering to yourself "why concrete for a
water filter"? Well, this is what I was wondering myself when I first began thinking about how
such a filter would work, but also what the advantages and disadvantages of
using such a filter would be. And after reading the previous post, you can all come to the conclusion that I made it a "mission" of sorts to come up with a cheap water filter made of a
universal material available to everyone.

Think about this. Concrete has been used in one form or another since the
Sphinx and the Pyramids were built. The Great Wall, elements of ancient
western hemisphere civilizations as well. Portland cement as we know it today
was developed by the Romans who mixed quick lime into their mix to allow the
concrete for their roads, aquaducts and other structures to cure and become
usable in a shorter amount of time and even in wet conditions.

And over time, concrete became and has remained the global standard for
building materials. This means that around the world, there are skilled people
who know how to engineer and work concrete for their local needs, even in the
poorest countries. I've met people who have traveled to small villages where the
locals mix concrete on prepared dirt surfaces and place it for basic structures.
So this is not so much a case of re-inventing the wheel as it is teaching an old
dog a new trick.

I brought this idea to Dr. Stephan Durham, a faculty member at CU Denver who
specializes in concrete. It should be of no surprise he was a bit skeptical at first,
but he did give me some literature on something called "pervious concrete".
Pervious concrete has been around for about 30 years, but recently it has
become more "vogue" for lack of a better term as local and state governments
become increasingly aware of the need to improve surface water quality and
take a look at non-traditional sources of pollution like construction sites,
parking lots, building runoff, gas station surfaces and sidewalks.
Pervious concrete, which is basically standard concrete with most or all of the
fine grains not included in the mix, resembles a grey rice krispie treat in appearance.

The mechanism for improved water quality begins with surface water containing
a variety of organic and inorganic pollutants. The water runs over the surface
of pervious concrete and trickles through the pores. During this process larger
diameter pollutants such as drops of autmobile fluid, brake material, dust, etc are
removed (though not completely). When the water meets the much less
pervious bed of small diamater gravel or prepared soil on which the concrete
sits, the water velocity slows and the pollutants settle onto the surface of the
bed while the water slowly percolates though the bed thanks to hydraulic

The pervious concrete filter relies on filter length to remove pollutants via a
variety of mechanisms (I'll go into that in later posts). The big difference
between this filter and the use of pervious concrete for a parking lot is that the
parking lot design revolves around strutural integrity while the filter has no
structural requirement and yet is much longer vertically than a section of
parking lot pervious concrete.

So with that in mind, here is a list of potential uses for a pervious concrete filter
(including the Moon and Mars since they have many of the same materials used
for concrete manufacturing).

I. Acid Mine Drainage Remediation
a. Acid Mine Drainage (AMD) contributes to surface water pollution.
b. Global demand from large developing countries has increased mining
activities as well as the use of alternative sources such as scrap metal.
c. AMD waters may be another potential source of metals.
d. This is highlighted by a Pennsylvania Department of Environmental
Protection study stating [Rathbun, 2004]:
e. “the annual cost to state taxpayers for AMD remediation to be $23
million dollars a year and the estimated state wide value of sludge from these
systems to contain millions of dollars in metals, yet it is handled as waste.”
f. Experimental results have shown that:
1. The filter increased the pH by an average factor of 3.3.
2. The average percent concentration of iron in the filtrate was 15% of
the original concentration.
3. The average percent concentration of sodium in the filtrate was 39%
of the original concentration.
4. The average percent concentration of zinc in the filtrate was 26% of
the original concentration.
5. The average percent concentration of sulfate in the filtrate was 37%
of the original concentration.
g. From a Sustainability perspective:
1. The per unit cost and lifespan of the filter may be attractive for
developing countries for both AMD and improved drinking water quality
2. Any country with existing ready mixed concrete infrastructure can
produce the filter.
3. Filters may have a long storage life and can be easily transported for
use in remote areas and disaster relief.
4. The filter is not designed to be load bearing.
5. Recycled concrete to be used as a source of aggregate, requiring the
fines to be removed by sieve.
6. The filter can be easily produced by manual or automated processes.

II. Poverty Relief
a. local, low tech concrete plants or factories can make filters from
separately pre-packaged ultra fine particles, gravel and Portland cement.
Concrete companies at the regional or national level can prepare, package and
sell these supplies at local prices.
b. Containers can be assembled on site from other local/regional
suppliers or bought by the concrete companies, and given to subcontractors for
final assembly before shipment, or all components can be collected and taken to
the local area for final, on-site assembly.
c. Concrete materials are available almost everywhere, and ultra fine
material should be easy to process and fairly readily available.
d. “Expired” cartridges can be swapped out by trained local people and
sent back to the local concrete factory for recycling. The same local people can
be trained to test the water using simple testing kits to determine when the
cartridge is no longer effective.

II. Military applications
a. Field hospitals can assemble these filters and swap out “expired”
cartridges as needed. They will also be able to test the water as needed for
specific needs and add additional treatment as needed.
b. All of these filters can be recycled by military construction units or
contractors using prepared ultra fine particles, portland cement and pebbles.

III. Underserved Communities
a. Communities in underserved areas of developed countries can utilize
these filters in the same manner as impoverished communities, so those who do
not choose or are unable to live in areas with formal water treatment plants can
use the pervious concrete water filter to process surface and subsurface water
for consumption.
b. These pervious concrete filters are also recycled by sending them
back to concrete plants.
c. The filters can be sold as individual units for individual households
or as larger units for small, multi-family communities.

IV. Other commercial applications
a. Water treatment kits for outdoors enthusiasts, national guard or civil
protection units and as emergency treatment kits for ranchers and farmers.
b. The final stage of gray water systems, to remove all impurities from
gray water after the water has been used for irrigation and before it is consumed.
c. Pretreatment for industrial or laboratory use.
d. Treating brackish water in tailings ponds where oil sand or oil shale
mining is taking place (not yet experimentally proven).
e. Pre-treatment of salt water. This filter will not desalinate water to the
point of making the water consumable, but it could remove significant amounts
of salt (and chemical pollutants) which could prolong the life of filtration
membranes and potentially reduce the amount of energy needed to desalinate

V. Lunar exploration
a. (soil composition)
b. Portland cement composition: calcium silicate cement made with a
combination of calcium, silicon, aluminum, and iron.
c. Similar soil composition means concrete could be produced on the
moon, which means concrete filters can be produced.
d. A gray water system mixing human waste with artificially produced
water would utilize the concrete filter as the last step to filter water for reuse in
irrigation and other non-potable uses..

VI. Martian exploration
a. Iron ore mining
b. Rock composition
c. Portland cement composition: calcium silicate cement made with a
combination of calcium, silicon, aluminum, and iron.
d. Similar soil composition means concrete could be produced on the
Mars, which means concrete filters can be produced.
e. A gray water system mixing human waste with artificially produced
water would utilize the concrete filter as the last step to filter water for reuse for
irrigation and other non-potable uses.

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