I have relevant experience in this field. I have sent you an email; feel free to contact me at any time.

Count me in too. Also, I have a few engineering friends that potentially have relavent experience. Where are you working in Honduras.

Hello: Really appreciate the contacts. We are working toward installation of the 70,000 GPD filter for the Barrio of Cristales, in Trujillo, Colon. Their water committee is excellent and very dedicated. We provide the material and they do all the work. They have cleaned out an old dam on the Cristales River in the mountains, and have completed a primary water storage tank of 26,000 gallons this year. Next year we plan to build the two filter tanks and another 26,000 gallon tank for clean water. The whole system including distribution will be gravity driven. This will feed pure water to 750 homes and 2050 souls. Our Rotarian focus is to prevent deaths of children age 5 and under from drinking contaminated water - statistics show the world is losing 6,000 PER DAY of preventable deaths. You can see a lot more about this global initiative at www.rotary.org

I agree. The use of a sodium hypochlorite generator is likely ideal for this application.

Also, another alternative if the turbidity of the water after filtration is low enough is to utilize UV disinfection. Recent advances in this technology have resulted in very cost effective disinfection for villages of the size mentioned. If the flow and head of water from the source is sufficient, microhydropower can be used to provide the electrical power for such purifiers if electrical power is not directly available.

You two have given me plenty to think about. I promise to do that. In the meantime all I need is to finish seiving the sand from Trujillo and I will have all the parameters needed to confirm or reject the production potential of the filters we have postulated. I will post this within the next two days, and then we can go from there. The reason I am very dedicated to slow sand is that it is essentially independent of outside factors, and highly sustainable. It is also noted that it is extremely effective against parasites where chlorination is less effective. The two technologies tend to be mutually reinforcing. Really great to have colleagues. Thanks.

You are right about that. Slow sand filtration will develop a beneficial microbial layer over time that will aid in trapping and killing pathogens. Following sand filtration, passing the water through activated carbon will remove organic impurities before sterilization. If you have access to UV, use it first before chlorination so as to reduce your sodium hypochlorite consumption.

The main advantage of chlorination over other forms of sterilization is that it provides residual protection, something even ozonation, the most effective form of sterilization, does not provide. All the best to you and your team my friend.

Hi Dvader1000,

I believe by pathogens you mean germs (bacteria & virus) which cause disease. There are many bacteria & virus which are harmless to humans and believe what you meant by beneficial microbes are these.

But how do you guarantee that in a slow sand filter only beneficial microbes will develop? How about contamination from an animal..then E-coli developing in the sand layers?

I understand total coliform above a certain level is bad for humans and cause diarrhoea?

my question in essence is can a slow sand filter become a breeding ground for deadly bacteria & virus such as Vibrio cholera bacteria, Clostridium botulinum bacteria ,Salmonella typhi bacteria,Hepatitis A virus?

I believe most of the filtration methods slow sand or pressure sand or other are mostly either cosmetic or to to assist in down stream sterilization techniques such as UV

Unfortunately UV-c (note not UV-a or UV-b) and Ozone are expensive technologies for 3rd world. Much better can be done with that money by having a Pressure Sand Filter coupled with Chlorination, which is probably the most cost effective method available for sterilization.

Going for pressure sand filter will reduce the capitol cost involved in building a slow sand filter. again I am assuming that electricity is available and if not slow sand filtration probably is the only solution.

You are correct on this basically. That's why I recommended disinfection after filtration. I know chlorination may be a bit costly for a Third World nation. That is why I suggested building a sodium hypochlorite generator. Once constructed, the only material it needs to operate are fairly low cost: filtered water and sodium chloride.

I hope this clears things up.

YOU ARE DEFINITELY ON THE RIGHT TRACK WITH SAND FILTRATION.

I RECOMMEND THAT YOU GO TO GOOGLE AND OPEN THE FOLLOWING SITES:

THESE SITES ARE BASIC REFERENCES FOR PROFESSIONAL WATER TREATING CHEMISTS, MICROBIOLOGISTS AND ENGINEERS BUT THEY WILL GIVE YOU A GOOD COMPREHENSIVE IDEA OF HOW TO ENGINEER YOUR SYSTEM TO COMBAT PATHOGENS.

THE MAJOR STEP IS IN THE REMOVAL OF TURBITY AND SAND FILTRATION IS BY FAR YOUR BEST WAY. YOU NEED TO PAY PARTICULAR ATTENTION TO REMOVING TURBIDITY DOWN TO VERY,VERY LOW LEVELS BECAUSE ORGANISMS LIKE CRYPTOSPORIDIUM ARE CARRIERS OF PATHOGENIC MICROORGANISMS.GOOD FLOCCULATION CHEMISTRY FOLLOWED BY SAND FILTRATION WILL REMOVE MOST HOSTS. I SUGGEST THAT YOU TAKE A GOOD LOOK AT AVAILABLE FLOCCULANTS LIKE ALUM OR IRON SULFATE AND POSSIBLY ORGANIC POLYMERS . (I DID A LOT OF THE BASIC RESEARCH WITH POLYMERS IN 1970).

GO TO GOOGLE:

OPEN:

WORLD HEALTH ORGANIZATION FIRST ADDENDUM TO THIRD EDITION-- AN ENORMOUS AMOUNT OF GOOD INFORMATION THAY YOU CAN USE BUT LOOK PARTICULARLY AT PAGES 140-141 and read about the use of ozone and UV light. I suggest that you think of using ozone because there are many suppliers from which to choose,but remember that you must have ozone exposure to organisms no less than ten minutes after filtration and remember that at the end of the first 15-18 minutes the concentration will drop by 50% (half life depends on water chemistry and temperature)

I recommend that you expose pathogenic organisms at an initial concentration of 2ppm (mg/L)or as much as an ORP (Oxidization Reduction Potential) value of 800.

ORP sensors are available from many sources.

NEXT OPEN: EPA PREVENTING WATERBORNE DISEASE

Wow, I thought this was third world. Sand Filter is a cheap and relatively simple classic treatment apparatus, which is relatively insensitive to handling. Flocculation with alum or polymers; disinfection through electolytic reaction of salt , chlorine, hypochlorite, etc; and GAC are all expensive, require repeated purchases of treatment materials, need continuous management and sensitive to handling. You need to consider how you handle any other treatment stages based on what the local population is capable of supporting and managing. If they will not purchase the necessary treatment materials regularly as needed, or allow them to run well after breakthrough just to cut costs, it might not be worth it to install. Work within budget.

Hello: You have it right! In order to install anything in the third world we have to consider what is going to happen later. Honduras has a chlorination standard that has to apply to all water provided for human consumption. Yet, on our last trip down there we took a sample at a "typical" user home and the e. coli tested 18 at the local hospital. Specifying something and actually DOING it consistently, and repeatedly over the years is absolutely another thing. We simply have to take that into account and MUST provide solutions that don't depend on whims or on short term lack of $. Hopefully slow sand filtration, low-tech though it is, will save lives. It did in London in the early 1800's and is still valid today. Maybe because it uses a process that was invented by GOD!

Re my comment No 10, I found a link which you all may find interesting.

http://www.mwra.state.ma.us/germs/germ7.htm

Dean,

I too am looking at ways to help people in third world countries find safe drinking water with minimum investment and long term sustainability. My search of the internet has found many organizations that are on the same mission; mostly religious affliated orgnaizations. There is a web site that you should look into that provides low cost chlorination systems for just such applications. (www.waterforlife.com) According to their web site they have successfully installed many of their chlorination systems into Honduras, as well as, elsewhere in the world. Anyway, sustainability, complexity and cost are always trade-offs in developing these water treatment systems in low technology areas of the world. Its not just clean water at the central village water tap but clean water at the peoples' homes, which require them to carry buckets of water in open, contaminated containers, that needs to be addressed. Chlorination seems to be the initial, easiest and least-costly approach, once turbidity is adequately reduced (hopefully via the slow sand filtration)

3BAYSFULL: Nice to hear from you and your interest in my favorite subject. You are absolutely correct. One of the big challenges has been to take care of the widely scattered houses that are nowhere near piped water. There are many approaches such as SODIS (putting water in pop bottles and putting them in sunshine), drinking straws that are really little filters, ceramic filters, but probably the most widely used and successful are intermittent slow sand filters. These are just small slow sand filters about the size of a water cooler into which the homeowner pours raw water and then out comes purified water. One of the most aggressive NGO's that has been working this in Central America is Pure Water for the World our of Vermont http://www.purewaterforthewowrld.org Carolyn Meub founded this group and is also a Director in Rotary's action group http://www.wasrag.org. This is a very good site for information on water and sanitation. They have an excellent movie on the subject. Another very active and effective group is http://www.handstohonduras.org. This is a group founded by Tom Plumb from the Port Isabel Rotary Club, who is my partner in the Trujillo work. He brings down typically 50 or 60 volunteers every year to work alongside their Honduran colleagues building schools, latrines, water projects, electrification, computers, etc. He is literally a "legend in his own time" and is also a character - his comment "It may be just a legend in his own mind" Sorry for posting a book - I do get a little carried away on the subject of protecting babies (maybe because I am a great grand-father). (I will be 84 tomorrow).

Dean

Hi all,

I was briefly browsing through the website and saw this thread... couldn't help but offer some assistance.

I have worked with sand filters for quite some time, and they come with a great deal of problems like, loss of filter media, high back-wash water volumes etc... but for the purpose mentioned, it may be an economical solution. I do suggest you also check out Pall Cooperation, who has a Municipal Water Treatment Package program for small communities.

Thanks and regards.

Hello Dean,

My name is Linda Gilbert and I am one of the organizers of the Vermont-Hands to Honduras-Tela program. We travel to Tela with about 80 volunteers, mostly from Vermont, to do construction (school classrooms), medical clinics, water projects support our rehab therapies clinic, ambulance training, etc.

On your notice # 15, you refer to Tom Plumb's website (but you have our web site listed).

Tom Plumb, Hands to Honduras, website is handstohonduras.com

Our VT-Hands to Honduras-Tela, website is handstohonduras.org

I just wanted to bring this to your attention so that you readers could see Tom's information.

Thank you so much. And I enjoy reading your site. It is very pertinent and helpful.

Linda Gilbert

Linda: Of course I knew of your group, and have in fact followed your progress for almost a year. I also knew that your two web sites are only different by the .com and .org distinction. We drove through Tela on our October visit and Tom was constantly pointing out places where schools were built. Both of you are to be highly commended for what you have accomplished - together and independently. I look forward to meeting you in the future as we strive to save lives in that beautiful and hospitable country.

Yours in Service

Dean

DVader1000: I now have some detailed questions regarding design of the slow sand filter that I think would be better done via email. I am so new on the forum that I don't know how to get back to you. If you can help get me straightened out I will send you an email that goes into some detail..

Best Regards,

Dean Woodward

I have beeen quietly watching this thread on the sidelines with interest. What details are you looking for?

Hello All: On further consideration I will post here the preliminary details of our slow sand filter that we are planning for Barrio Cristales at Trujillo, Colon Honduras. This will be a Rotary Matching Grant that will supply funds for materials only; all labor to be supplied by the community. They have already built a 26,000 gallon brick and concrete mountain-side tank under an earlier Matching Grant, and that tank is under service. They did a superb job on this, including carrying all material up the mountain on the backs of men and women. These are highly motivated Garifuna (black Carib) people. In their complete history they have never had dependable and pure water (no water at all except that carried in during the dry seasons). Their community is approx. 750 households and 2050 souls.

The filter will be two cells, each cell described as follows:

Construction brick and concrete tank 18' in diameter and height 11' (inside dimensions).

Collection network (perforated) in bottom of tank.

Gravel (graduated in three layers, top layer pea gravel) 18" total depth.

Sand very fine and washed d10 = .13mm, d60= .35mm. UC 2.54 36" deep

Influent through manifold near top of tank through multiple perforations to make sure that influent does not disturb surface of sand.

Control valves and meters on both influent and effluent.

Sight glasses on both input level and output levels with calibration so that hydraulic differentials can be recorded.

Test kits to observe e. coli, turbidity and chlorination levels.

Sand will be cleaned by "wet harrowing".

Existing 26,000 gallon tank comprises effectively an input source that can be purged to remove fines as needed.

New 26,000 gallon tank to contain clean water and chlorination contact tank.

All water movement including distribution down mountain by gravity only (no electricity on the mountain).

I would appreciate as many people as feel capable of calculation of the range of expected daily clean water production to do so. It would offer me welcome reassurance that I have neither over-sized or under-sized the two filters.

This is a perfect example of what Rotary International can do all over the world (just a tiny fraction of all that we do - including purging the planet of polio - toward which we are applying $200M at present - $100M of which is a grant from Gates Foundation - the largest single grant in history). These are in no way brags - just facts.

I am a full-time Rotarian for Life

Dean Woodward

I'll need to look up some numbers.

Your filter area is around 250 sq feet. Flow rate through the filter will be dependant on pressure drop, which will be low due to gravity feed.

For population of 2000 +/-, in third world conditions (no flush toilets, dishwahers, washing machines, long showers, etc) I would guess 5-10 gallons of water usage per day per person, so total water demand is on the order of 1300-2600 cubic feet of water per day. (10,000gal/7.5 gal/cu ft). From what I understand, US water consumption is on the order of 100 gallons per day by comparison.

My initial feel is you might want a second 26,000 gal tank as a backup sand filter becuse you will be operating at capacity with limited oppurtunities for maintenance. However, I may be completely off the mark, and welcome other comments to my initial assumptions.

For even water distribution through the filter, consider the use of slotted trays. This may be easier to fabricated at a remote site and easier for the local population to maintain.

Mr. Reid: Very perceptive comments. We can easily add an addiional clean water tank in subsequent years. Our involvement with this community is long term - probably for the rest of my life (I just turned 84).

My main concern is that we have included enough clean water throughput as a start because it is a little hard to expand that (of course we could provide expansion room for a third tank (which would be a good idea).

One point is that the head is just the head - the tanks will be atmospheric.

Col. Dean

A bit of reading and research for you:

http://www.ask.com/web?q=water+flow+rate+through+sand+filter&qsrc=0&o=0&l=dir

http://en.wikipedia.org/wiki/Slow_sand_filter

http://www.who.int/water_sanitation_health/publications/ssf/en/index.html

Third link has a good book for your reading pleasure which is a PDF download.

Given a trickle rate of 2.5 to 10 gal/hour/SF area, daily flow could be anywhere from 15,000 to 60,000 gallons per day. Being conservative, I vote for more tank area.

Again this is free advice, so check it carefully!

Sorry for the late reply. I've been involved in several different projects simultaneously. Okay, the basic situation is that slow sand filters will tend to clog after a while, so a backwash unit is required. Periodic raking and releveling of the sand will also help to keep the sand pores open. Also, if the filter is in the open air, algae may grow on the sand; this again will tend to clog the sand. It may also impart an unpleasant smell and taste to the water. Some species, particularly the cyanobacteria, can cause illnesses as well, but if the water has very low organic content, this shouldn't really be an issue. Just to be on the safe side, you may want to consider covering the filter with a tarpaulin sheet. If nothing else, it will protect the filter from bird droppings.

Regarding your question to the pressure head. I would suggest using a water tower maybe 10 meters in height. This will give you a head of about 1 bar. If you don't have enough electrical power for a pump, I would suggest using hydraulic rams if you have access to flowing water. Use a battery of them to transfer water to the tower quickly.

I hope the above is helpful.