Basic disinfection of potable water in 3rd world 1

[brianslater]

Help
I'm not a water expert, just a humble engineer working on the borders of Laos/cambodia. We have a simple rain water harvesting system collecting into 5000l cement jars - a long established practice. However we do get outbreaks of jungle belly which I believe is due to poor management of the jars (I smelled and tasted the water). They dont practice roof flushing of first run off (for 10 mins say). we have a lot of birds and worse, the jungle chickens. they dont have effective covers over the jars, they dont flush out the gutters (not easy), we have a lot of trees and leaves.

It seemed to me that 4 drops of household bleach (sodium hypochlorite 5%vv) per litre would help sanitise the water but I cant find anywhere on the net that admits this as an ok practice. Do you see any problem with this?
Once the water is disinfected it should stay that way (assuming the covers are in place and no new rain arrives. After a week or so the chlorin will have gone anyway.

If this is ok, why dont they use this in Bangladesh, say?
Its cheap and cheerful. All this pious advice about boiling water for 15mins is of no use when you dont have firewood.

Secondly I was proposing to use a simple form of sand filter for the local pond/river water which is sometimes available, mainly to remove turbidity and vegetable matter, then dose with bleach. Any comments on this

Please excuse my ignorance if I am stating the obvious here. Its very frustrating to read the learned dissertations from 3rd World water.org to find they have told you nothing useful

Your guidance may reduce the incidence of child jungle belly, which I also get sometimes.

 

[dhdoyle]

So Brianslater sez:
> You say Im trying too hard, but in fact, calcium deficiency is a problem here because everyone drinks
> rainwater and its not so clever for growing kids who get bone problems in some areas.
> Hardened water would solve the problem.

OOps! I didn't mean that calcium deficiency wasn't worth the effort! I meant that I thought you didn't have to resort to inorganic chemistry (adding calcium bicarbonate) in order to do the job.

I understand the red earth - rain forest soil is generally low in nutrients due to leaching, right?

Cheers!
Dave

 

[semo]

If you want to filter, you could use sand with or without charcoal in a barrel or a capped pipe (8"-12" diameter).

I would think you could perforate the bottom of the barrel/pipe cap, add a 6"-9" pea gravel layer, 12"-18" sand layer, and 12" charcoal layer (optional). The pea gravel would help keep the sand from falling through the perforations (make sure the perforations are smaller than the pea gravel).

Clean the sand/charcoal/pea gravel thoroughly and disinfect it and the barrel/pipe with bleach before you assemble the filter.

Don't know how much water you put through the unit; but, instead of backwashing like a water plant does, every so often you would need to disassemble it rewash and/or replace the media and reassemble it. This along with the disinfection will help remove most of the viruses and cysts.

 

[hydrae]

Countryham says
" A FREE CHLORINE RESIDUAL SHOULD BE REALIZED ONLY AFTER TWENTY (20) MINUTES OF CONTACT....FURTHERMORE, YOU DON't NEED A TEST KIT BECAUSE WHEN YOU CAN SMELL THE CHLORINE AFTER TWENTY MINUTES YOU HAVE ADDED ENOUGH AND- IF YOU HAVE ADDED TOO MUCH,- JUST HEAT THE WATER AND DRIVE THE CHLORINE OFF AS A GAS...Regards, Countryham "

one problem with the above quote.


Chlorine stinks the most when there is not enough in there.

The biological material contain ammonia, when chlorine starts to work on ammonia but is not done yet, it smells the worst! chlorine combines with the ammonia to form monochlormine (a passive slow acting disinfectant) then it forms dichoromine then trichoromine. It is only when there is more than enough chlorine for the ammonia reactions that free chlorine is present, at that time the odor drasticly drops.
The chlorine that is combined with the ammonia in the form of dichloromine and trichloromine are not available for disinfection but that is the stuff that realy stinks.
The rule of thumb for operators of drinking water plants and swimming pools, if it stinks of chlorine, then add more...


Hydrae

 

[brianslater]

Hi Hydrae
Thanks for that titbit, most useful. In fact its these custom and practice things that are the most valuable. I am not at all skilled in the arts of chemistry but that paradoxical smell is a good tip. Of course the ammonia thing comes from human bodies I suspect (in swimming pools).

Its unlikely to be present in rainwater collected from a clean roof.?

Would it be likely in well water unless the well water was contaminated from a cess pit?

I heard there was a rule of thumb for the separation of a well from a cess pit

ie the well should be at least 20ft deep with a leak proof lining pipe. The pipe must only draw water from the bottom . No water should seep from the earth layers higher up around the pipe. No surface water should run into the well.

The well should be at least 10 meters away from any simple cess pit.

Do you agree with this?

Of course it varies according to the soil and whether there is un underground impermeable rock or clay, but here its mostly laterite, iron oxide mud and sand for a considerable depth. the water table is normally 3 meters down rising to 1 meter in the rainy season.

rgds

Brian

 

[hydrae]

Brianslater

Well water can contain ammonia, even wells that test coliform free, I am working with a water provider that started chlorinating their well water for other reasons and found out they have .15 mg/l of ammonia in the well water. So they are increasing the dose above the minimum target.

As for your rain water situation, any biologic (including leaves) that gets into the cistern can be a source of ammonia or other items (such as iron) that will combine with the chlorine and reduce the effectiveness of the disinfectant. As long as the nets you mentioned earlier are in place that should keep it under control

As for drilling shallow wells in areas of high and variable ground water levels, this is risky to find a clean source because the time the water has been underground would be very short.

In US wells need to be at least 50 ft from sewer drain systems (drain fields or cess pits), increase that to 100 ft if the well serves the public.

It sounds like the local solution of cisterns on rain gutters is the most reliable for the long term when maintainted. Using sand filters and bleach on this stored water is also an excelent idea to add to the multibarrier approach.

low life pond dweller ;-}

 

[brianslater]

Hi Semo
Our local pond water storage systems use a backwash sand filter.
We can make simple sand filters quite readily as river sand is plentiful. Now about charcoal?

I have conflicting info on the use of this. Ive heard that using ordinary crushed lumpwood charcoal(ie not farbricated charcoal as used on BBQs)has no real effect. It has to be activated. This involves heating it in a closed vessel to around 500C drive drive off any oils and impurities. Its then available to act as a de-odouriser and taint remover.

Any comment here?

BTW
Ive also heard that these BBQ nuts are fabricated by compressing crushed charcoal with common cement (as a binder) and waste oil to help with lighting the fire. The waste oil bothers me as I believe it can hold high levels of Vanadium. I wouldnt want that on my Tee bone.

Any comment?

 

[brianslater]

Hi Hydrae
What is your definition of a shallow well as opposed to a deep well?

The traditional way here is to use pre-cast concrete rings about 1 metre dia and to dig inside so that the ring gradually fall into the well hole. Very tiring, takes 3 man 3-4 days and its hazardous. the depth is 15 to 20 feet max

 

[redgreen]

I apologize if I am repeating what others have stated, but this post has had several responses and I haven't gone through them all in detail.

I would suggest you think in terms of the multi-barrier approach and deal with all aspects of water supply from collection, treatment, supply/delivery, and ongoing monitoring. Do whatever you can to ensure a clean source. Is there a way to "keep the birds away" from the rooftops? Can you have the roofs gutters cleaned out frequently enough to reduce the organic deposits? That would be a starting point. The cleaner the source, the easier it will be to treat and end up with a safe water supply.

Bleach is used all of the time in small communities for disinfection of drinking water. I have designed some small systems in Canada that use it as the only source of disinfection. Be aware that the concentration of the bleach does change over time as it is stored (decreases) so you should be carefull if you are dosing it on a volume basis only. Also, chlorine beach and organics can be a bad thing and can lead to formation of THMs. Again, try to reduce the organics in the water before you add the bleach.

It is important that the water being fed to the piping network have free chlorine residual, otherwise you are facing the real possibility that by the time the water gets to the user it will be contaminated once again.

A low tech, lo-cost residual test kit sounds like a must to me. It will be easy to teach the local people on how to use it.

Keep at the good work.

Red

 

[semo]

Hi brianslater

I agree with hydrae on the chlorine smell means add more. I don't know what testing equipment you can get; but, a simple color wheel type of chlorine test (anyone with a pool has one) will probably suffice. You can get ones where you dip a litmus paper in the water and compare it to the chart (very simple and foolproof).

I also noted that your original post said you only disinfected once. Like redgreen said I think that a residual needs to be maintained. That means you would test on a regular basis and add bleach as needed to keep the chlorine level up (if water is constantly added and/or removed from the storage) or redisinfect the water prior to usage. If everything is not disinfected (jars, caps, etc.) or they are touched prior to sealing, the water can become contaminated again.

As for the charcoal. To the best of my knowledge, plain charcoal will provide some adsorption like activated charcoal does; but, the charcoal is activated to make the material more porous so that it adsorbs more. I've not tried it; but, I think plain charcoal will have some effect; but, with a lot lower effect and shorter lifespan than activated. As far as BBQ briquettes, I don't think I would use them. I'm not sure how they are made; but, whenever I use them to grill, they smell like something is in them that I wouldn't want in my water.

I'm not sure you really need charcoal though if you have a clean water that does not contain odors or other volatiles.

On surface water treatment plants in the states, a CT time must be calculated to ensure adequate removal of Giardia cysts and viruses. Sand filtration accounts for 99.68% removal of Giardia and 99% removal of cysts. That does not meet the gov't requirements; but, disinfection with adequate contact time accounts for the remaining requirements. That said, the filtration will provide as much or more removal than the disinfection and provide you with a safer water without a large cost.

 

[hydrae]

A deep well is deep enough so short term weather effects are not seen in the level of water in the well.
for safety there should be a least one impermable layer before the water bearing zone (such as clay). If the soil is permable all the way down it is still just irregularaly filtered surface water.

Hydrae

 

[brianslater]

Hi Hydrae
Yes I get the idea. A deep well is one that taps below an impermeable layer. I dont think we have any soil like that here, just laterite

Hi Semo
Its interesting about charcoal and its effectiveness when unactivated. I might try some kind of test. Of course swimming pool water has a much higher concentrtation of chlorine and you dont normally drink the stuff. Whether litmus paper or colour wheels are effective on 5ppm Cl in potable water is questionable. Do you have any rule of thumb for the amount of sand filtration required for a small system of say 10,000 gals per year

Hi Redgreen
We have developed quite an enthusiatic thread here, more to the question than meets the eye.
I cant keep wild birds away from roofs but they dont normally perch or roost on corrugated iron roofing

The gutter problem is interesting becuase these are often high up, 20 metres or more and therefore difficult to clean. I am looking at a ground level design (yes put the gutters near ground level). These can be constructed from galvanised sheeting (used as roofing hips) folded into a vee shape with a 30degree angle. They are mounted on trestles 1.5m high and feed into the standard cement storage jars. Roofs here are typically constructed with large overhanging eves at least 1 metre. Although we get heavy downpours the pitch angle of the roof is shallow around 20 degrees and the water pours off quite slowly sufficiently to be captured in the gutter troughs below.

They are easy to keep clean and a simple filter mesh at the end traps any leaves. The only problem is jungle chickens and stopping them perching on the troughs. Im working on this
Of course the disadvantage is that it doesnt look very elegant but in a farmhouse situation, nothing does anyway.

Perhaps I could put a layer of sand in the trough?

 

[WaterWizard]

Wow lots of good ideas amd observations.
I think the basic thing in your situation is,"do what you can".
Filtration, if possible, is most important, many of those nasties love to live on the particles and removing the particles will remove many of them. Is it now save? No but safer!
Clorination via household bleach? If that's all you have use it. Is it possible you will form some THMs organo-metalic compounds etc? Yes but which is worse that or the water in its non disinfected state.
Can't be sure you are keeping adequate free residual chlorine? A little chlorine is better than none, the buggies may grow back, but at least you knocked some of them down for a while.
If you can mannage it it is always best to have perfectly safe drinking water by controlling all these parameters, but if not possible, then as I said, "do what you can". Any improvement is better than no improvement.

Edd

 

[semo]

The litmus paper just shows what the chlorine concentration is. Ranges vary by individual manufacturers or kits; but, they usually go from 0 to 4 or 10 mg/l. You are looking to have 1 mg/l residual after a 20-30 minute reaction time.

Your situation is kind of different than meeting standards on a large scale like we have to; but, the basics should be the same. As far as filtration is concerned, most of the filtration occurs in the top 4 inches of media. We typically use 12-inches of sand. We also use 18-inches of antracite coal on top of this; but, the antracite is an optional layer that is primarily used to extend the filter life. Older sand only filter designs used 24 to 30 inches of sand. All of this is above the support media (larger sand/gravel which keeps the sand from washing through the discharge). As water wizard said, anything is better than nothing.

Sand filters are also typically designed for a flow rate of approximately 2 gpm/sf of surface area. I don't know how your water arrives. You may have nothing then a sudden surge of water during a storm. If that is the case, you may want a holding tank before the filter with a small opening in it acting as an orifice to keep the flow rate relatively constant. You may have slow consistent storms which deliver water on a constant flow where you can size a filter for that delivery rate. With this in mind, you can size the surface area of the filter for the flow rate that suits your system.

You will have to clean the filter media by washing it every so often. A lot of that also has to do with your water quality and the sand size so making a statement on how often will just be a guess. The dirtier the water, the more often you will have to wash it. Also, the smaller the sand particles, the more quickly the particles get trapped and the more often you wash it; but, the larger the particles, the deeper the penetration of the dirt.

Typically, as the filter media becomes dirty, the water level above the media will continue to rise until enough pressure is generated to cause breakthrough. At this point, the filter no longer works. We typically backwash on a daily or bi-daily basis unless 3-feet of head is reached above the normal water level; however, that is with the plant in operation from 12-24 hours each day. We typically see filter run volumes of 1000-2000 gallons per square foot between runs.

If your water is clean coming into the filter, I will guess that you will want to wash every few weeks. You will have to watch the filter to see how it acts. You also need to keep the filter media submerged to prevent it from drying and shrinking (forming voids for the water to run without filtration occurring). If you see cracking in the media, media pulling away from the sides, or clogging (evidenced by high ridges in the sand), you've went past the backwash time. If you're water is clean, you probably won't see this and will just need to set up a routine to backwash on a regular basis.

I hope this helps.

I also thought of something you mentioned in an earlier post about needing more calcium in the water. I don't know what you have access to in your location; but, with bleach as a disinfectant, you are using Sodium Hypochlorite which is in a liquid form. Swimming pool people typically use a white granular disinfectant which is Calcium Hypochlorite. The use of it as a disinfectant will add some (be it small) calcium to the water. There are some disinfection systems here that use this chemical (in pressed tablets) where the water flows through it and over a specific number of tablets to get the chlorine concentration needed. If you had access, you could place these tablets in the flow to constantly disinfect the water as it flowed through the filter into your holding tank. Just a thought.

 

[brianslater]

Hi Semo

Thanks for the tips there , will "digest" the filter info. Water is something we all take for granted. I wish some 15 years ago I had migrated into the water industry along with many others who came across from the Petrochem industry (when it went through a drastic price crash). There is something rather satisfying about producing a clean water supply not like petrochem products where I got stuck.

FYI the main differences between the industries are

a) 5 year project timeframe (instead of 9-18 months of frantic pressure
b) Non hazardous process (instead of an often highly dangerous environment)
c) stable market (instead of the resource often being controlled in a politically volatile country)