What are nitrates?
Nitrate is a naturally occurring substance found in ground water and surface water supplies (levels are generally higher in well water). The agricultural industry produces higher levels of nitrate in groundwater due to the presence of animal manure and fertilizer run-off.
Why do nitrates need to be removed from water?
When nitrate is consumed above safe levels it affects oxygen transport in the body and causes dizziness, fatigue, and weakness. Nitrates are especially dangerous for children younger than 3 months of age. Long-term consumption of drinking water containing high levels of nitrate can lead to birth defects and certain cancers. Elevated levels of nitrate in freshwater can also create harmful algal blooms that can kill fish stocks and create by-products that are toxic to humans and livestock.
What are the limits of nitrate in water?
The World Health Organization limits the safe level of nitrates to 50 mg/L. The Australian Drinking Water Guidelines limit nitrates to 100 mg/L for adults and children over 3 months of age and 50 mg/L for children under 3 months of age.
How are nitrates removed?
There are four main methods for removing nitrates from water:
- Membrane filtration (particularly reverse osmosis)
- Biological denitrification (uses bacteria to convert nitrates into nitrogen gas)
- Electrodialysis (removes nitrates using electrical charge and specialty membranes)
- Ion exchange (uses resins to exchange nitrate and sulfate for chloride)
Why we use reverse osmosis to remove nitrates
Each process has its advantages and disadvantages. As the ion exchange process preferentially absorbs sulfates, saturated resins release nitrates in the presence of additional sulfates. The resins must be periodically recharged using either concentrated sodium chloride or bicarbonate. Additionally, backwash brines will be high in nitrates so care must be taken with the disposal. Electrodialysis works well with low salt concentrations but removal efficiencies reduce with increasing salt concentration. Biological denitrification requires careful temperature control to ensure the health of the bacteria. The product water also requires aeration as the denitrification process strips oxygen from the water.
Reverse osmosis removes 80-95% of the nitrate depending on the membrane chosen and the configuration of the RO unit. High levels of nitrate can require a two-pass system. Nanofiltration can also be used to remove nitrate but this level can be as low as 60%. To achieve sufficient nitrate removal when the levels are high, enough salt may need to be removed that the product water may require remineralization. Moerk Water preferentially uses reverse osmosis for nitrate removal as it is the most mature and adaptable of all of the nitrate removal technologies.
Your Next Step
Enquire now with Moerk Water Solutions to discuss your nitrate removal needs.