A biological pond filter

For the past 4 years, we have been working with a biological sand water filter applied to filtering water that is used in a pond. The  preceding link takes you to one of our other websites where the assembly of the filter is shown in detail, along with some photos of the pond. The filter has continued to work flawlessly since August of 2010. As of today (December 23, 2014) the filter is still working and keeping the water crystal clear. Birds, and squirrels use the pond continuously. The water stays absolutely clear 24/7, with the exception of the times when it is frozen. Every year so far, the pond has frozen along with the filter. There has been no damage with the exception of the water level falling considerably when the pond freezes over. There are no fish in the pond, but there is an abundance of organic material constantly falling into the pond. We clean out the bottom once a year. That is all we have to do with the exception of adding some harvested roof water during the summer months. 

All that is used in the filter is sand and gravel. The sand does not need to be changed. The only filter maintenance needed involves taking the top off of the barrel and gently agitating the surface of the sand inside to break loose the heavy layer of active organisms in the biolayer. That’s it. Very simple. Organisms in the water grow on the surface of the sand and literally eat the organic material in the water leaving only purified water to flow down through the rest of the sand and back into the pond. The filter has an overflow that directs back into the pond so no output flow regulator is necessary. Gravity does all that work on its own.

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Rain water harvesting

We are now approaching our 8th year of slow sand filter operation here. The first filter we started back in 2007, filter 1, is still running, and producing clean clear water. It filters rain water run off from a composition roof. It removes 99.99 percent of bacteria from the input water, and also removes petroleum contamination (see the 9th 10th reports down from the top at the link page shown) that is present in the water from contack with the roof surface, and air pollution.

The 5 gallon filters we tried last winter for the most part failed. The remaining two 5 gallon filters out of the 4 we started with, are running in series. We hope to test these in late February.

All of the pond filters are running, including the first one we put together four years ago.

There are two filters that have continued to run through two 20 degree (F) weather events which lasted 10 days each. They kept running because the input water is taken from a well that has a 100 watt incandescent light bulb heating the water before it goes into the filters. The water is kept running 24 hours a day at a very slow rate – about 20 to 30 gallons per hour. We have shown here, that it is possible to keep slow sand water filters outdoors and keep them running where there are not severe winters.

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Slow sand filters frozen in November 2014

It is now November 21, 2014, and all of the filters that were frozen have thawed out and are running again. All of the filters here, with the exception of filter 2 and filter 3, were frozen for 10 days. The temps were below freezing for 8 nights in a row. Filter 2 and 3 filter water from a surface well that has a pump that runs water heated by a 100 watt light bulb. This was enough to keep the filters from freezing up at temps of 23 degrees F at night and 33 degrees F during the day for 8 days. The water runs 24/7 through the filters at a very slow rate of 20 gallons per hour. Nothing has been done on the 5 gallon filter. All but 2 of the 5 gallon filters were removed from service because they did not work. The two remaining filters run in series with the coarse sand filter first, and the fine sand filter second. No tests have been possible because of freezing weather. Now the 2 5 gallon filters will need to run for at least 2 weeks before a test is possible. The weather may not hold. It may be well into next year before any tests are possible.

A wind storm came through, early this month,  with very strong winds from the north northEast and wind chills of 10 degrees. (That is really, really cold for this area). We very seldom get strong winds from the east or Northeast.  In 65 years I do not remember another time we have had strong winds from the north east here. The storm blew down a huge tree on one of our buildings and that has taken all of my spare time to clean up. Much damage and much repair and clean up yet to do.

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Emergency water supply

Water can be taken for granted if it is conveniently available. That is a huge mistake. Without water, a person cannot survive much longer than 4 or 5 days at the very best. Lots of things can happen that will interrupt access to water. One such situation nearly happened in 2012, but it was not a catastrophe thanks to a near miss. Quote from the NASA website: “Two years ago, Earth experienced a close shave . . .” “but most newspapers didn’t mention it. The “impactor” was an extreme solar storm, the most powerful in as much as 150+ years.”

Read that article closely. Then read this: http://en.wikipedia.org/wiki/Solar_storm_of_1859

Now, what on earth does this have to do with water. If you read both articles carefully, you will find that a geomagnetic solar storm (sometimes referred to as a coronal mass ejection) of significant strength is capable of shutting down electrical power to nearly everyone on earth. This means no gps, no electricity, no internet, no electric heat . . .  .   The one in 1859 caused arcing on telegraph lines, and caused fires in the telegraph offices. In this day and age, a storm as strong as that one (like the one that missed us by about a week in 2012) would shut down the internet, and the electrical power that brings water to most people everywhere. There would be no usual public water anywhere, at the worst, at best it would be very difficult to find.

Please, don’t take my word for it, read what the scientists say. At the wikipedia site, there are referenced 41 (some scholarly) articles on this type of occurrence.

This does not mean panic, and get paranoid. Things would be back to normal all over within several years or less, and there should be disaster plans in effect all over that would be able to handle this type of event in a few weeks or so. But, in the mean time, finding water will be a real pain, to say the least.

Set up a couple (maybe more than a couple) of rain barrels and a water filter; you may be really glad you did.


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Slow sand filtration information

For the past eight years we have been building, testing, and operating small slow sand filters. What we have discovered here coincides very closely to some of what is covered in this document published by the State of Washington in 2003.  If you are interested in finding out more about slow sand filtration, this document is excellent. There is more information for larger filters in the pdf at the link to the 2003 document, but the theory of operation is basically the same for the smaller filters we describe here at this location.

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slow sand filter field tests

It is now October 2, 2014. Filter 1, and filter 4 have output water with no (0) coliform and no (0) e coli bacteria present. The cistern water that flows through filter 2, and filter 3, has 4 cfu’s of coliform per 100ml and 20 cfu’s of e coli per 100 ml.  See the images below:

These images are of filter 1, filter 4, and the cistern output water tests.

These images are of filter 1, filter 4, and the cistern output water tests.

Tests on filter 2, filter 3 and filter 5 will be done in the next couple of weeks.

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Five gallon slow sand filter

On September 27 2014,  after 6 months of continuous operation since this winter’s extended below freezing weather, a field test was done on the 5 gallon filters 10a and 10b. The tests indicate that filter 10a did not work satisfactorily. In fact, the output of the five gallon filter 10a was hundreds of times worse than its input water, which came from the source which is water collected from the first flush diverter/settling barrel array. Filter 10b, which filters the output water from filter 10a, did show some additional removal of ecoli and coliform bacteria as compared to the output of filter 10a which appeared to actually add bacteria. But both filters’ output was far worse than the input from the source water. These results indicate that .25 mm sand is just too coarse to work in a shallow filter such as these 5 gallon subjects, and that .15 mm effective size sand just barely works, and may not work at all. These results also indicate that having more than one shallow filter is absolutely necessary for even marginal results, and that the water from the first must be fed into the second. This testing is after 6 months of operation. I will post images of the test results sometime today or tomorrow. The 55 gallon filter (filter 1) that has been running here for 8 years has output that is tens of thousands of times better than either one of these 5 gallon filters.  It uses the same source water as the 5 gallon filters.

It is important to note that these tests are only valid for this water here at this location. Water in a different area, such as a climate where the temperature is always way above freezing, will have different characteristics, and may very well be filterable by a 5 gallon filter. 


These are the test results for filter 10a and 10b. The “source” water is from the diverter output (water taken from the house roof)

Water comes from the “source” goes into filter 10a, flows out (supposedly filtered) and then goes into filter 10b. The water out from 10b, the source water, and the water out from 10a are what was tested. The water out from 10b, is better than its input, so that filter is working somewhat.  Filter 10a is not working, it is adding huge amounts of bacteria to the water. The red dots are coliform, and the blue dot in the filter 10a dish is e coli.

The water coming from this filter, filter 10a, is highly toxic and not safe. The filter has been removed from any more testing and is no longer active. The sand has been discarded and the bucket and the sand have been sterilized. The bucket will be reused in a different setup.

What might this test result indicate?

1. A 5 gallon filter using sand with an effective size of larger that .15 mm won’t adequately filter water at this location.

2. Water run through two 5 gallon filters (first one, then out of that and then into the next one ) is filtered better than just going through 1 filter.

3. Filter 10a obviously adds bacteria to the water. It is totally not working and is supplying toxic water output. That is the .25 mm effective size sand. It does not work.

4. Filter 10b filters that bad water from 10a and makes it better, but not good enough.

5.  Contaminated water is slipping through the area between the sand and the inside of the bucket where the surface of the bucket was not adequately roughed up with sandpaper.

6.  The sand in the bucket is not deep enough to catch all of the bacteria possibly because bacteria predation typically occurs deeper than just a few centimeters down from the top surface of the sand. As this happens over a long time period, in this case 6 months, the escaped bacteria simply build up in the lower regions of the sand. Know that there is only about 10 inches of sand in one  of these filters.

7.  Filter 10a uses an overflow pipe to allow the excess water added to the top bucket to flow into a reservoir bucket. That water is, occasionally, then poured back into the filter 10a  input. It could be that bacteria is multiplying in that reservoir, and then overwhelming the 5 gallon filter.

9.  The bucket used to transfer water to filter 10b could be inadvertently adding bacteria to the water. It could be that filter 10b is actually working quite well.

Filter 10b uses .15 mm effective size sand. The flow rate is very, very, very slow. It may be that another filter with .15 mm effective size sand would adequately filter the water. In other words 3 filters in series may work. But, the sand size must be no larger than .15 mm effective size. That will mean an extremely slow flow rate.

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Rain water harvesting and slow sand filter update

All the filters are still functional with the exception of one. The filter connected to the largest pond has been inactivated by damage due to the wildlife present here.  We are reasonably sure the damage was caused by raccoons. The output pipes were disrupted and as a result all the water was pumped out into the ground. Re-activation will have to wait until there is enough rain to refill pond. In the mean time the filter remains inactive. This will be an interesting test of the pond filter to determine what happens if the filter stays inactive for over 2 weeks.  This has been a warm dry summer with several periods of heavy rainfall, and extended periods of warm dry, sunny weather.

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How safe is your water?

To harvest rain water or use water from the public water supply – what to do? According to a recent article in the New York Times, which mentions the trouble with the Silver Lake reservoir near Los Angeles California, public water is becoming more and more polluted as time goes on. We covered the problem with the Silver Lake reservoir already – bromates were found in the water. These bromates were due to other pollutants mixing and then being chemically altered by sunlight.

Pollutants are all over the place now. Reservoirs that fill using river water, or surface runoff can have up to 60, 000 different chemicals present in the water, yet only 91 are tested for by law. The above mentioned article states (from a citation using EPA records) that there are more than 60,000 chemicals used in the U.S.

We have already shown, on this blog, and our three other websites,  that way less contamination exists in rain water than in surface water, or runoff that comes in contact with areas that have been contaminated by urban development, industry, or agricultural activities. The first few hundred gallons of water that runs off of your roof washes away most of the pollution that has settled from the air. All that is left is the petroleum residue from composition roofing. In the case of non-toxic roofing, such as galvalume, little pollution remains after the initial washing from the first few minutes of a moderate rain shower.

It is important to know that some contaminants need only be present in very small amounts to be hightly toxic over long periods of time (years). Trihalomethanes, Haloacetic Acid, Bromate, and Chlorite and microcystins are some examples.


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Microcystin removal by slow sand water filtration

Will a slow sand filter take out microcystin toxins more effectively than conventional water filtration (rapid sand filtration) ? It appears as though the answer is yes:

http://www.ncbi.nlm.nih.gov/pubmed/12203961  (information is in the abstract; access to the entire document requires a log in.)

http://www.who.int/water_sanitation_health/dwq/chemicals/microcystin_sections.pdf   (its a 3 page document; read the entire document)

http://www.ibg.uu.se/digitalAssets/164/164676_3bojcevska-hristina-jergil-erik.pdf   (page 19 and read the entire document)

Removal of Algae and Cyanobacterial Toxins during Slow Sand and Bank Filtration  (page 53 “schmutzdecke”)

Biodegradation of the cyanobacterial toxin microcystin LR in natural water and biologically active slow sand filters     (page 1300)

www.terrapub.co.jp/onlineproceedings/ec/02/pdf/ERA33.pdf   (page 280)

Biological treatment options for cyanobacteria metabolite removal A review  (page 1543)

Slow sand filtration is not used in most water treatment facilities in the U.S. , even though it is more efficient, more sustainable, and less expensive than rapid sand filtration. Slow sand water filtration has been around for hundreds of years and has been shown to work. The city of Salem, Oregon is one of the few cities in the U.S. that uses slow sand filtration. 



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