In my project area, we use bore wells as a water source, but recently the water is contaminated by nitrates.
Could you please let me know which low-cost technology can be used to removes nitrates in borehole water in rural areas of a developing country?
Conventional processes for nitrate removal - ion exchange, reverse osmosis and electro dialysis - are quite expensive and pose a question of subsequent disposal of generated nitrate waste brine.
By the Zambian Drinking Water Standard (ZDWS), recommended nitrate levels are 10 mg/l NO3-N equaling 44.3 mg/l NO3. We would like to reach these levels so any advice is helpful.
I agree that minimum cost segregates the end users. Make a small bottled water plant for mothers of young infants and find a way to fund this minimum cost approach. Minimum cost technology for this minimum flow can be designed if you define the flowrate and water quality parameters fully / completely. Purpose driven funding might be available for the identified target group.
@ David,, that can be a great idea,, but communities may receive that message with mixed feelings where others (pregnant mothers) who will be asked not to drink from the same water (high nitrate)..also setting-up a bottled water treatment may be a big challenge more especially that the Government is still struggling to provide 100% conventional water treatment to its people..!
I agree that minimum cost segregates the end users. Make a small bottled water plant for mothers of young infants and find a way to fund this minimum cost approach. Minimum cost technology for this minimum flow can be designed if you define the flowrate and water quality parameters fully / completely. Purpose driven funding might be available for the identified target group.
I agree that minimum cost segregates the end users. Make a small bottled water plant for mothers of young infants and find a way to fund this minimum cost approach. Minimum cost technology for this minimum flow can be designed if you define the flowrate and water quality parameters fully / completely. Purpose driven funding might be available for the identified target group.
Depending on the volume of water to treat, you could possibly use biofiltration. Under anoxic conditions, bacteria can remove, "digest" the nitrates. You would need enough residence time to do the appropriate removal.
Usually another vessel is added after the sediment filter and used as the biofilter. The biocidal treatment is done after the biofiltration. To determine how much removal can be done, you would need to do preliminary bench work.This is, by far, the least expensive way to treat water.
There arenot quiteexpensivewater treatmenttechnology-if interested-please sendthe amount andcomposition of the water-will send thecost of the equipment.
Sergey,, the flow rate is 20 litres/minute borehore and 70 mg-N/l,,, the alloweable limit in drinking water is normally 10 mg-N/l..via envaros@yahoo.com
There arenot quiteexpensivewater treatmenttechnology-if interested-please sendthe amount andcomposition of the water-will send thecost of the equipment.
If no low nitrate well water sources would be available to replace or blend the nitrate rich well water, then nitrate shall best be reduced to inert nitrogen gas as applied at full scale over at least 30 years. This nitrate reduction can be achieved in various ways but - as always - the most sustainable and cost-effective solution for a specific case depends on the design flow rate (m³/h) and on the nitrate concentration (mg/l). Also the raw well water composition, pH and temperature would be important. Please specify as to advise more specifically for your case.
The cheapest option is by blending but this relies on an alternative source of low nitrate water and a vessel where blending can occur. Dependent on the nitrate levels, the amount of low nitrate source may be minimal. Targeting the water for consumption against any used for washing may also reduce the volume of quantity of water you need to treat.
A key concept is as follows: "The current EPA standard of 10 ppm nitrate-nitrogen for drinking water is specifically set to protect infants" i.e. to protect bottle-fed infants under 6 months. So in rural Zambia, if mothers habitually breast feed their infants beyond 6 months then it is fairly safe to allow other humans to consume the non-standard water. Where bottle-feeding is unavoidable you should advise mothers to seek other sources that have lower nitrate content, e.g. rainwater harvesting for babies' bottles. (Admittedly it is not easy in rural Zambia to harvest, store and keep clean.)
The other issue is the source of the nitrates. In Europe and USA it comes mostly from widespread use of fertilizers. In Rural Africa it is more likely from nearby pit latrines, cattle kraals etc. So, in general do not allow householders to site their pit latrines close to the borehole, or site boreholes near to latrines and kraals. Alternatively, if there are many such latrines and the borehole is surrounded by them, you may need to propose a borehole further away from habitation. Not ideal but may be a solution. Also users can learn to differentiate between sources and the specific source for a particular activity. Hope this helps. Barry M. Jackson
@ Barry,, well said and thank you for the in-depth search and advise,,,the problem is that Nitrate concentrations in drinking water are not only increasing in rural but also in peri-urban areas where we have working mothers who may not breast feed their babies for the full 6 months,,, hence now the search for a low cost treatment technology..!!
Barry's comments are correct. There is is increasing risk to infants as the concentrations exceed the WHO Guideline values for nitrate and nitrite. Nitrite is the greatest concern because it is the proximate toxic agent. The greatest risks are for infants who have a GI infection, and that is often a matter of microbial contamination of the source water, because the bacteria may be pathogens, and the water will also be under reducing conditions converting nitrate to nitrite. So the first thing to do is to assure that the source is safe and disinfected with chlorine. There is some leeway in the exceedance of the WHO guideline--be sure to read the short discussion in the 4th edition. If you are exceeding nitrate and the water is disinfected, you should both notify consumers (mothers) to be alert for the symptoms, and probably temporally use alternate low nitrate water. Methaemoglobinaemia is detectable and reversible.
A trickling filter followed by flash aeration may do the trick. Though this may require some electrical energy and tanks to be constructed, the water post this treatment will definitely have acceptable levels of nitrates. Just need to initiate a nitrification denitrification cycle. Also, if the water requirement is 20 - 40000 liters, the RO units cost quite less. In India, we provide an RO of that capacity for approximately 5 - 6 lakh rupees. It comes to around $10000 USD. And its worthwhile if you want to use the water for drinking.
Is it possible for you to build a tank / pond to store the water from the borewell for a few days before use. If so treating the water in the tank / pond would be possible. We have a solution to grow Diatom Algae in such tanks / ponds. Diatoms would consume the Nitrate and some of it would escape into air as N2 gas.
Depending on the aquifer, bore water may also cause scaling issues. Take a look at our website for a maintenance free, chemical and salt free water conditioner that does not require electricity. www.softerwatercondioners.com
I suggest your try a chemical process in which aluminum powder reduces nitrate to ammonia, nitrogen and nitrite. [Consequent Control of pH and concentrations of dissolved aluminum, nitrite and ammonia might be possible at a realistic cost]
Can design a low cost 2 stage bio filter. Need flowrate, full water analysis, seasonal change / ranges. System would require one low head pump or utilise existing pumping head. Is power supply available? Options can be considered to tailor. Is there more than one system / How Many? d_marioni@yahoo.ca
It is tricky to remove nitrates as they are so stable, and I expect that management of water quality in a borehole will bring with it many other challenges! Depending on the amount of water needed daily, you could consider looking into an algal turf scrubber where water is abstracted and passed through conditions optimised for algal growth (i.e. lots of sunlight) to remove nutrients and various pollutants. Algal productivity essentially strips nitrates from the water, and you simply have to harvest the algae at times to maintain healthy continuous growth. There is quite a lot of literature on this method, but I have only used this approach for my marine fish tank at home. It is scalable though. However, the best (and most direct strategy) perhaps would be to identify the direction of groundwater flow to the borehole, and trace this back to the source of the nitrates (overuse of artificial fertilisers? septic tanks? agricultural practices?). You will then need to work with the various stakeholders to put in place some measures to reduce input of nitrates to the groundwater. Good luck!