Fifteen communities at my field site rely on a central water treatment system. The system's intake draws water from a river. The river water has high levels of clayey sediment. We are told that this results in the intake becoming jammed.
The system needs to produce 5 million litres of clean water per day.
A secondary filter should be set to less than one micron (nanofiltration or ultrafiltration). And should be checked to determine if it is cloudy when the colloidal clay has been removed. In addition, it should be placed a series of parallel nanofilters to improve efficiency and reduce the need for filter changes.
There are other economic experiments with homemade ceramic filters.
You can use alum in the storage tank to reduce suspended particulate matter . pH should be adjusted with alkali dosing. Then it can be passed through nano-filters. The process will improve life span of nano-filters.
You can use different size of sand filter to reduce the clayey sediment then next level span and activated carbon filters
Get the water sample analyzed to determine the level of turbidity. This can be done by taking the sample to a nearby laboratory. Then one can decide the type of filtration process that will be efficient. On the other hand hand on instrument may be taken to site to check the levels.
Using a coagulant you can remove fine clay particles. Since this is a rural area we can use low cost sand filters or charcoal filters to improve the water quality.
You first need to decide what you budget is. Membranes (UF) work well in small/remote locations but will clog quickly without pretreatment of some sort, and end up with high operational costs. Ferric chloride is the best and cheapest coagulant for settling out clayey particulates, then follow sedimentation with sand or membrane filtration. There could also be issues with manganese in the water which could require chlorine or permanganate to precipitate.
Dear Shun Deng Fam,
You can look at the model implemented by Grameen Veolia in Bangladesh. This firm is doing the job with efficiency and least production cost.
Clay particles carry negative charge. Addition of any trivalent coagulants Like Alum can attract the clay particles and convert it into flocs.There is a need of tank to reduce flow velocity ,so that flocculation process occurs in proper way
First, how many people are there in 15 communities. In some places, a community will consist of 20 - 30 families, while in other a single community may consist of 200 families. Next, if we keep the water in settling tank, will the clay in the river water settle down? Some will settle down. By constructing a settling tank, and abstracting the water from the settling tank , you may be able to prevent the addition of chemicals or reduce the amount of chemicals that you add to precipitate the clay particles. The choice of the method is going to depend on the physical and properties of the clay and the size of the community you are going serve.
It is necessary to use slow sand filtration with filtration velocity about 1 m/h.
Slow sand filtration is an option. if the turbidity of water is high then coagulant and sedimentation is the proper solution. It is possible that if other impurities along with clay is present, then sedimentation and filtration is one the best solution and it is conventional treatment process
Your budget is $/cubic meter?
OK. lets suppose a a very low one, but can not escape from at least doing removal of particulate matter (done this) you could use sand bed (sand from the same river could be). OK at this point you need to remove bacteria using any oxidant agent (chlorine, ozone, H peroxide). All said, assuming you do not have excess concentration of grease, metals, pesticides, etc. Do you any chemical and microbiological characterization of the river water?. Regards.
You can use coagulant like Alum/Ferric Chloride to remove suspended particulate matter. Some alkali dosing is required to maintain ph of water. Then can be passed through activated charcoal to absorb colour and order. Finally some chlorine treatment is required to remove bacteria. Residual chlorine must be less than 15ppm.
For a rural community, design for a simple system where you avoid mechanical parts, mixing, chemicals and the need for well trained technicians.
I would think of a settling tank (to save on construction cost a high rate settling system - i.e., inclined plates or tube settler) would be suitable, the next step I would be a rough (coarse) bed filter (Horizontal gravel or pebble filter) where three sections of coarse-medium-small size gravel are laid in series to remove the fine solids (flocculation would take place to some extent). The third part in this rural water filtration plant is the slow sand filter which is reliable and does not need much maintenance.
The settling tank needs de-sludging probably one a week. The gravel filter needs cleaning (by a jet of water from a hose) once every 4 to 6 month. The slow sane filter needs the removal of the top few cm`s once a year.
Such a system works with whatever budget. Selection of the construction materials is flexible with the size; if large go for concrete and masonry. If small (family size), metal or plastic tanks would work.
Operation is simple and design to have the flow by gravity, except probably for a pump for the headwork (takes water from source and pump it to the settling basin).
Design of inclined plate or tube settling is simple and some literature is available through the internet. There is a manual for designing slow sand filter (published back in the 1980`s by AWWA). Gravel filter design is quite simple and some papers are available on the web.
Some helpful literature to start with:
http://web.mit.edu/watsan/Docs/Student%20Theses/Ghana/Thesis_Losleben_Final_5-20-08.pdf.
Process Analysis and Optimization of Direct Horizontal-Flow Roughing Filtration
Manual of Design for Slow Sand Filtration
http://www.who.int/water_sanitation_health/publications/ssf9241540370.pdf.
Practical experiences at 5 slow sand filtration plants in South Africa
An Introduction To Slow Sand Filtration
design and construction of a domestic slow sand filter using the ...
Dear Shun Deng Fam,
because we are working on this topic for some years now. I can tell you that all the technologies suggested could be efficient. All depends on the extent of contamination (e.g. concentration, nature) and the affinity of filter material.
Where ncessary iron/sand filters will complete the job, see the attached article (and related, all available at my RG).
I hope this would be helpful!
Depend on the amount of water for your community in the peak time. Sand filter will be a choice. We developed new cellulosic membrane also can be used for your application. cellulosic material is biodegradable material and cheaper than other polymer material.
I suggest to build retention pond in order to settle suspended load at intake point.
Sandfiltration is not bad, but that seems to be in use already, backflushing every once in a while might help. Another option might be to use a reedbed filter in which the plants take care for the particles do not dominate the systems too much. good luck.
You can use simple fileration system with fiber filter or membrane filter for clalification of high concentation clay water
A slow sand filtration system is recommended. No need of electrical or mechanical parts. However you have to wait for sometime before the water become drinkable. This gestation period is to allow the top film (skumdecke) to form and the water will become bacteria free. Also little maintenance is required.
River bank filtration (RBF) could be another option, i.e. placing groundwater wells at the banks of the river and withdrawing the water from production wells. This is often an economic and easy managed way of providing water of improved quality compared to direct surface water abstraction. Hydraulic connection between wells and river is necessary. See attachment for further information. RBF is increasingly used in several countries, i.e. India: http://www.saphpani.eu/glossary/bank-filtration.html
http://pubs.acs.org/doi/pdf/10.1021/es022441j
You need 15 nm filtration system to purify the filthy water from the clayey sediment...
Normally a sand filter is a good choice. depending on type of solution you might need to have different layers of sand sizes. this is the easiest way requiring minimum maintenance and training
Dr Biswajit is on target. There is a long history of success with slow sand filters in low tech low cost applications. Robert Koch-father of microbiology -demonstrated success in 1880's. Passive operation and minimal O& M . No chemicals.
The multi-stage filtration technique is mostly preferred especially for river water treatment. A gravel filter followed by slow sand filtration will definitely work. this method is cheap to operate especially if the treatment plant is constructed to flow via gravity. It is cheap and easy to maintain with relatively unskilled labour.
While most of the procedures suggested would work well at a reasonable cost (I would recommend slow tangential sand filtration or RBF followed by activated carbon if possible), nano-filtration would require either expensive materials or pressure application, with the possibility of filter clogging by clay.
It is useful to you this video presentation, please watch it.
This is the link: http://www.youtube.com/watch?v=ZiFPMssxqW4
I recommend these Sawyer Filtration system. It's economic, long lasting and of high filtration rate. Many institutions are using it during emergencies and also for remote areas in Africa
Here is the link http://sawyer.com/international/
I suggest sand filtration basins, they are very effective and cheaper for clay particles.
A sand or pervious concrete filter followed by chlorination or ozonation
Hansa,
I would not/never use chlorination just because a bigger problem than diarrhea might be the result: cancer!
Additionally, there should be lack of skills (and chemical stocks) for both chlorination and ozonation in those rural communities.
Regards,
Hansa, Why pervious concrete instead of sand or RBF previously suggested?
I'm afraid ozonation is out of reach in most rural communities and I agree with Chicgoua on long-term dangers of chlorination due to the formation of chlorinated organics..
By utilizing RBF, the content of organic matter in water is normally considerably reduced; thus, the formation of disinfection byproducts (DBPs) when using chlorine for disinfection may also be reduced. Formation of the different DBPs depends on what fractions of natural organic matter (NOM) that are present in water. After RBF, normally the larger fractions of NOM are removed from the water phase, whereas smaller (and less biodegradable) fractions may remain (the change in the composition of NOM after RBF depends on the prevailing vegetation and climate conditions).
At low turbidity/particle content of water, UV could be an alternative disinfection method to chlorine. UV is often used in rural municipialities in Norway, where water supply is often based on small bank filtration/groundwater systems with little treatment and where there is often a lack of personel to manage complex water treatment. UV maintainance is usually operated from the UV supplier company.
Right, Hanne, but dont forget that even low concentratios of chlorinated byproducts can be harmful in the long term.
Right, Juan, we should also consider that the rural water quality (thus, the NOM level) (in the deloping wolrd) is not known as a rule [even 'treated' water is not chemically/biologically analyzed]. Whenever possible we should avoid chemicals (the clorine taste has also been a problem).
Re Dr Kvitsand' s comment, UV is not a good disinfection choice in a rural environment. The usual situation is that there is significant potential for contamination during distribution. Having a chlorine residual provides at least some protection.
Re Dr Casado's comment. DBPs are undesirable but the jury is still out as to whether there is a chronic risk. What is well established is that inadequate treatment including inadequate disinfection is a significant cause of waterborne disease and deaths in those environments. WHO makes it very clear that DBP concerns should never ever cause water suppliers to compromise on disinfection.
We must be realistic and protect against known serious risks, rather than dwell on hypothetical small risks.
Dr Noubabactep is also wrong on this water safety issue. Please read the many WHO discussions on this matter and the tallys of the millions of annual deaths mostly children due to poor sanitation.
需要做一个前置过滤器，用购买的净水器外套自己做一个就可以，很简单，而且很好用。使用时间长。直接购买的前置过滤器只是一层筛网，使用时间太短。
怎么中国人都不讲中国话呢？我们说汉语，让老外学去吧。哈哈。
Dr. Cotruvo, good morning!
I can not understand what is wrong in telling members of academia that the quality of water should be assessed and not just assumed. Was it not the origin of As disaster?
My point is that the quality of water should be controlled, analytically controlled EVERYWHERE. That is what I teach to my students. Nothing against bridging solutions, but a bridge remains a bridge, the destination is the goal and this goal is achievable. That was already stated in a WHO report from 1959.
[A big problem of chlorine in the field is that non-skilled people are introducing wrong quality of 'chlorine' in wells of unknown water volumes. And in a country as developed as South Africa (SA) there was permanently lack of chemicals for water treatment until 2009 as reported by researchers of the University of Petroria. I hope that things have changed during the past five years, but there are countries that need some decades to come where SA where in 2009.]
Please again don't get me wrong I'm advocating for better solutions. Nothing against pragmatic solutions that have been helping for decades (let improve and change potential harmful operations).
Best regards,
CN
Mr. Tianlong Qiu .Please translate it into English language so we can understand your valuable opinions.
Water treatment in rural communities in Brazil still has many shortcomings, since there isn't a standard for the selection of the water treatment methodology that fits the raw water quality. In view of this problem, we developed a simplified selection model of water treatment technologies for small rural communities. This decision making process has as criteria raw water physico - chemical parameters and water flow, which is a reflection of the size of the community .
We tried to keep the process as simple as possible so it could be used by any professional with basic training. For the model to run, it is necessary to determine the parameters color , pH , turbidity , iron , manganese , fluoride , hardness , chloride , nitrate, nitrite , ammonia and algae density. Due to the difficulty of removing fluoride and chloride from water with simple technologies, they were considered as exclusion criteria. The other parameters were used as selection criteria. The technologies chosen as the model solutions have the ability to treat raw water with iron and manganese , eutrophic waters and even river water with high turbidity. The water treatment technologies adopted were the full cycle , ascendant direct filtration, dual filtration and oxidation followed by rapid ascending filtration in three different sizes.
We developed cellulose material based Membrane and MBR system. It should be very good for your application. As membrane material is cheaper and biodegradable. system is simply.
Dear Tianlog Qiu:
I wish I could read your answers. But unfortunately, I do not read Chinese. Will you could not write them in English or Spanish as other investigators. I know it's 'boring' not able to converse in the original language. But ...
The use of sea water purified like a drinking water is true or not from view of health?
Dr. Cotruvo,
Just to correct you, warning on the dangers of chlorinated DBPs is not the equivalent to avoid disinfection. There are other disinfection methods other than chlorination.
Erkan, sea water can not be converted to drinking water the same way fresh water can be. You need specific processes such as inverse osmosis.
In Cameroon, drinking water in rural communities is purified by filtration through sand for turbidity, filtration through activated carbon and clay for ions and exposition to the solar energy for bacterias.
Dr. Laminsi provides another available way for disinfection. Use of hydrogen peroxide instead of chlorine would be another alternative.
Coagulation-sedimentation is probably the best option for the removal of suspended materials such as clay and even microalgae. This should be the cheapest option. If further treatments are needed these will depend on the quality of the feed water. Potentially you will need a few filtration and sterilisation steps.
See this solution:
http://www.virginia.edu/jpc/docs/WaterPurificationSouthAfrica2010.pdf
How much drinking water is needed and what treatment steps are available today ? Do you have access to land areas to expand the production facility ? Is there an opertunity to provide some of the communties locally with water i.e. ground water or are they totally dependent on the central water works ?
The source of raw water are very important to decide the process of water treatment for drink.
Based on your information: raw water pre-treatment to remove clay, particle and others------traditional bio-treatment to remove chemicals --UF or NF- than UV or Chlorine --- drink water. In most case, membrane system could be a good choice.
Dr. Feng, you are describing a quite general process to obtain drinking water. It would work, of course, but I'm afraid that most rural communities would need simplified and less expensive solutions, such as some already suggested.
When discussing this topic, it is important to keep in mind the different traditions that exist amongst different countires regarding application of water treatment methods, combined with the intitial raw water qualities and the achieved removal of unwanted subsituents during the applied treatment method.
Re. Dr. Casado, Noubactep, and Cotruvo; UV disinfection is increasingly beeing used in Norway, also at the larger waterworks, due to the ability of disinfecting parasites, in addition to bacteria and most viruses, compared to chlorine. Chlorine residuals when drinking water leaves Norwegian waterworks are usually low (0.5 mg/l), since the aim is to disnfect the water at the DWTP and not on having residuals at the distribution system (which used to be a second aim). Today there is little emphasis on having redisual chlorine at the distribution system since the biofouling layer at the distribution system is considered to "protect" microorganisms which are often adsorbed into this layer.
It would be interesting to have any comments from Dr. Fam, who initially posted the question, regarding the discussion that has evolved, and what options that would be useful and realitsic for the particular case.
From my assessment of the question, the problem highlighted was high levels of clay in the abstraction source. River bank filtration can work well in a rural setup with careful design of abstraction wells.
Hi Dr. Fam,
How long has the system (the intake) been in operation? Do you have a treatment system now? What does it entail?
Have there been any changes in the environment conditions (e.g deforestation) in the area that feed the river?
If the system is young and the clayey sediments are not been increased by excess sediment transport due to erosion- then RBF may be an option as many have suggested..
Dr Casado is right. Let's be practical. Go to Google and look for work by Gerardo Galvis on slow sand in rural low tech environments. It works and it is rugged, low cost and it does not require external equipment.
well-constructed sedimentation with biofilter can prevent it and is cheap. information at [email protected]
Before filtration first step sedimentation, then pass through sand and cocoanut husk. Membrane filtration is very good fior small scale filtration.
I would suggest you to have a centralized sedimentation tank. First pump water into the sedimentation tank allow it to settle. Pump water from middle of the tank to the purification system. However, this also depends on the volume of water you treat every day. This work for small scale systems. Pl. tell the exact volume and we can decide on the system
We have tested pervious concrete filter for rural water filtration. It is the best option as there would not be any need to change the sand. Moreover the rates achieved are that for slow sand filtration. The basic treatment train would be intake tower followed by a pervious concrete filter and a disinfection tank after the same.
Alum may be one of the choices to remove suspended solids from water followed by passing the water through any agri - biomass.
Dear Shun Deng Fam, a lot of valid things have been said before. However my question is what do you want/need to achieve?
Just remove the clay-> bank filtration or rapid sandfiltration (residence times 1h) with backwashes should do (and is probably cheapest).
If the cay sediments rapidly (which would be uncommon sedimentation can work and would also be a cheap solution.
need to remove other contaminants (pesticides)-> underground passage with slow infiltration (usually with residence times of 20 d). This would also be a rather cheap one but needs some carefull groundwater hydraulic designing.
If Your ambition level/need is higher than it might be time for UF.
welcome to discus further [email protected]
We developed an MBR system that may meet your requirement. Its flux is much higher than the current MBR membrane.
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