Just for fun, let's explore how implausible are the claims of Brightwell for Nitratr
The nature of this implausibility is that seawater is mostly sodium chloride and yet they claim it can be regenerated in sodium chloride solutions. It says nothing about the ability to work in freshwater (where the scientific literature supports the ability to bind nitrate).
http://brightwellaquatics.com/products/nitratrt.php
"To initially lower excessive nitrate, each 500ml of NitratR will remove 20ppm nitrate in 100 US-gallons of water (or 10ppm per 200 US-gallons)"
OK, so that claim suggests that the 500 mL of NitratR is binding 20 ppm (mg/L) out of 100 gallons (378.5 liters), or 20 mg/L x 378.5 L = 7,570 mg or 7.6 grams of nitrate.
Sounds great so far!
They them claim that:
"
To regenerate: Dissolve 4 cups table salt in 1 US-gallon of room-temperature water per 250-ml NitratR to be regenerated in a clean pail; place resin into pail and stir; allow beads to soak overnight; strain and rinse beads thoroughly in fresh water before re-using. "
OK, let's think it through. That 250 mL of polymer has 3.8 grams of nitrate on it (since Brightwell says 500 ml can bind 7.6 grams of nitrate). The more effective it is at binding nitrate relative to the competing ion, chloride, the more nitrate will remain bound in the regeneration solution. Let's take the case that regeneration means you get back 50% of the original capacity. Any less is, IMO, stretching the definition of being able to "regenerate" hundreds of times, and any more retained will make their product look even poorer in the analysis that follows.
So, that regeneration solution contains 4 cups of table salt. Four cups of sodium chloride weighs about 1170 grams of sodium chloride, and hence 710 grams of chloride.
If we think the regeneration is 50% complete, that means that the solution then contains half of the nitrate originally bound to the polymer, or half of 3.8 grams or 1.9 grams of nitrate (with 1.9 grams remaining on the polymer).
Since nitrate was coming off of the polymer, and chloride going on, and the process stopped at 1.9 grams of nitrate in the solution which also contains 710 grams of chloride (actually 709 g since 1 gram went onto the polymer), then the binding of nitrate stopped when the chloride to nitrate ratio in the regeneration solution was 709/1.9 = 373.
NOTE: This result means that nitrate is coming off the polymer, not on, when the level of the chloride in solution is higher than 373 times the nitrate concentration.
In seawater, the chloride concentration is about 19,000 ppm. This analysis would suggest that at any nitrate concentration below 1/373 times this level, or 51 ppm, nitrate would come off the polymer, not bind to it.
If we had assumed the regeneration procedure was even more effective (lets say 90%), then the numbers change so that the nitrate in solution at equilibrium is 3.42 grams and the chloride is about 708 g., so at any chloride to nitrate ratio above 708/3.42 = 207, nitrate is coming off rather than binding. This means that at nitrate concentrations below 19,000/207 = 92 ppm, no nitrate is binding.
Of course, we could keep pushing down on the actual ability to regenerate the polymer as claimed. Suppose only 10% is able to be regenerated in the method they claim (really not meeting the criteria for regeneration, IMO, but let's explore it). At 10% released, the nitrate in the regeneration fluid is 0.38 grams, and chloride is 710 grams, for a ratio of 710/0.38 = 1868. Thus, at any nitrate concentration below 19,000 ppm/1868 = 10 ppm, none will be binding.
Thus I conclude, as we already know from other basis, such as the scientific literature of the relative binding affinity of "nitrate specific resins" relative to chloride, that the claims of Brightwell do not survive a simplistic analysis.
