Porous Concrete Bottle Filter

You may download my latest draft on 'Making Porous Concrete Bottle
Filters' by clicking HERE. 

In March, (2011) I began in earnest to develop a recipe for porous concrete
that could be set into plastic bottles and other water-tight containers to filter
turbid water.  I differentiate porous concrete (made from sand) that I use
to purify water for people from pervious concrete (made from aggregates)
that is used to make parking lots for cars.  The recipes are similar, but the
materials are different.  Figures 1 shows a 5-gallon turbid water treatment
setup using a 1-liter porous concrete bottle filter.  The idea is to make an
affordable filter that will remove sediment and pathogens much the way
more expensive ceramic filters do.  Also,  I'm trying to make an efficient
tool that has nearly the volume and capacity of larger biosand filters.  The
main advantages of porous concrete are that it is made from affordable,
abundant and sustainable materials including sand, water and Portland
cement that are available worldwide.  Moreover, the technology is simple
and easy to transfer. 

However, a big obstacle to using Portland cement is that it is very caustic.
Concrete made from Portland cement and sand has a high ph (~13) and
high alkalinity due to ingredients like sodium oxide in the cement and the
formation of calcium hydroxide that is an outcome of the hydration process
that forms concrete.  Alkalines are being formed in concrete even after many
weeks and months of cure time.  The first thing I had to do was to develop
a low-alkaline cement.  I found straight Portland cement too caustic and
raised the ph of filtered water to uncomfortable levels.  Too many alkalines
were being washed out with the water.  The main symptoms (for me) of
high ph/alkalinity is a mild sore throat that lasts for hours.  On the other
hand, there is evidence to suggest high ph water can kill and inhibit the
growth of bacteria including e. coli.  (So, this may be a blessing in disguise?)

After experimenting with different proportions of fine sand, water, and
an admixture of (food grade) diatomaceous earth with Portland cement,
I found a low-alkaline recipe that worked.  I learned that diatomaceous earth
is a natural prozzolan and reduces alkalinity by reducing the amount of
Portland cement needed to form the porous concrete by 30%.  I further
reduce alkalines in the water by adding a post-treatment filter of fine sand
or (better) granulated active carbon (GAC).  Finally, I found that as the filter
is used and the concrete continues to cure, alkalinity decreases to palatable
levels. 

To date, my best results come from a binary concrete-carbon filter made
with GAC that is added after the concrete filter in the bottle.  You make this
filter with 2/3 concrete and 1/3 GAC.  The carbon filter removes most of the
alkalines in the concrete treated water.  However,  if GAC is not affordable
or available, then clean fine sand will do the job - you just need to replace it
more often.

Even with the addition of GAC, the cost of the filter is about $2.  The
flow-rate of a 1-liter bottle filter inside a 5-gallon water bucket is about
1.5-gallons an hour.  I expect the concrete-carbon filter to treat about
400-gallons of turbid water before being replaced by another $2 filter. 
Without the carbon, a 1-liter concrete-sand filter should treat 200-gallons
- at a cost of about 30-cents.

Figure 2 shows other kinds of filters I developed from the basic model. These
include the concrete-carbon filter, bottle-to-bottle filter,  personal filter, and
1/2-gallon pitcher filter. 

In addition to small point-of-use filters, I am developing a larger modular
porous concrete pipeline section that may be added to any simple water
distribution pipeline system. The idea is to filter surface water that comes
directly from lakes, ponds, rivers and streams so it is fit for human and/or
animal consumption. 

Again, you may download instructions for making Porous Concrete Bottle
Filters by clicking HERE.

You can follow the 'Porous Concrete Filter' topic on the
Water|Sanitation|Hygiene forum.

                        ______________________________

The idea for using porous concrete (above) came from my earlier development
of a sand bottle filter.  I discuss this tool below.  I believe it is still a good tool
for turbid water pre-treatment, but not as good as porous concrete or ceramic
filters.  Nonetheless, it is the most affordable pre-treatment filter I know.

Sand Bottle Filter

In January,  (2011)  I began development of small homemade bottle filters
that I set in my ceramic gravity feed configuration.  At that time, I  discovered
the potential of homemade bottle filters, but did not realize a stable configuration
until I began testing the Doulton ceramic filter.  I married the two ideas to create
affordable DIY sand bottle filters.

Figure 3 shows my first attempt using a recycled 1-liter PET water bottle
with a 1/4-inch hole at the base that acts as an inlet.  The bottle cap includes a
pull-out nozzle that serves as an outlet.   To make the filter, my first step was
to temporarily removed the bottle cap and place it aside.  Next, I cut away the
plastic ring beneath the bottle cap.  Next, I filled the bottle with tightly packed
fine sand, sandwiched between pea gravel to make the filter.  The trick is to
pack the media tightly to create as solid a filter block as possible to reduce
water channeling.  Next,  I took a 5-gallon (number 2) plastic bucket and drilled
a 1-1/8-inch hole near the base even with the bottle nozzle.  Then, I improvised
a gasket by shaping a piece of non-toxic adhesive putty.  Finally,  I slipped the
filter through the drilled hole and replaced the bottle cap - screwing it down to
make a water-tight seal.  I used a 6-inch piece of 1-inch diameter vinyl tubing
to help direct the flow of water from the filter outlet.  The DIY process took
about 20-minutes. 

I found this simple filter was able to significantly improve the turbidity of dirty
water for the cost of a few pennies.  The turbidity is so improved that this
water is ready for disinfection using SODIS or chlorine.  With a flow-rate of
2-gallons per hour, this filter is a useful tool for hazardous water pre-treatment. 
I am still testing the tools capacity, but I estimate that 100-gallons of moderately
turbid water can be pre-treated before the filter needs to be recharged with clean
sand.