Calcium Polysulfide to remove nitrates

[fredE]

I have a waste stream containing 400ppm NO3 from rinse tanks in a nitric acid pickling facility. A contractor has suggested using calcium polysulfide to remove nitrates before sending the water to a collection area for pH adjustment which will then go to the POTW for disposal. Is this a common treatment option? What is the price for the calcium polysulfide?

 

[Muggle]

Sorry - can't anwser your question. You may want to look at electrolytic treatment. We just performed tests on wastewater from a phosphate mine - pH of the water approx. 1.2..Water going for certified analysis to lab for client (AWS Consultants in florida). We removed all nitrogen from the water, even breaking nitrogen from dispergent added to the wastewater from cooling tower blow down. Simple process - no chemicals required. If want more info - you ahve to contact Art Suma at AWS Consultants - they are the customer we ran the tests for - up to them to pass the information on. He can be reached at DCHPPAGE@aol.com.

Does this sound like a solicit - can't help it - ther is no literature or sites I can recommend you too to investigate.

regards -
Dave/Aquatic Technologies

 

[kenvlach]

I believe Muggle is referring to ‘electrocoagulation.’ In this technique, the wastewater is passed through a reactor consisting of parallel plate electrodes of alternatingly positive and negative charge to generate H⁺ and OH^-. The pollutant species are reduced or oxidized to their most stable form. E.g., organics are oxidized, hexavalent chromium is reduced, chelated complexes are broken down, etc. The pH is also moderated. No chemicals are used, although if steel or aluminum plates are use, Fe⁺³ or Al⁺³ enter the wastestream and act as coagulants for metal hydroxides. A nice clean process. Works best for dilute wastes like yours.

Plenty of websites: do a search for electrocoagulation. Get a sales rep to bring a demo unit to test on your wastestream(s).

 

[moltenmetal]

kenvlach- how would electrocoagulation remove nitrate? By reducing it to nitrite? And if so, would that be doing anyone a favour, since nitrite is readily re-oxidized to nitrate?

 

[kenvlach]

Good question. I had noticed that a vendor site showing electrocoagulation reduces both nitrate and nitrite concentrations:

http://www.powellwater.com/treat-potable.htm,

but I'm not sure of the exact chemistry. Metal surfaces can catalyze the reduction of nitrate, so there may be breakdown occurring on the plates. A study below reports on treatment of nitrate, but [the abstract] doesn't mention nitrite.

Journal of Hazardous Materials
Volume 89, Issue 1 , 4 January 2002, Pages 83-94
Removal of nitrate from water by electroreduction and electrocoagulation
"The aim of this work was to investigate the feasibility of the removal of nitrate from water by applying electrochemical methods such as electroreduction and electrocoagulation. In electroreduction, removal of nitrate to an allowable concentration has been accomplished at the pH range of 5–7 with energy consumption value of 1×10^-3 kWh/g. In electrocoagulation, an allowable concentration of nitrate has been achieved at the pH range of 9–11 with energy consumption value of 0.5×10^-4 kWh/g. Full removal of nitrate was also possible but with higher energy consumptions for these two methods."

 

[moltenmetal]

kenvlach: the references you've given suggest that the removal mechanism is direct electrochemical reduction of nitrate sequentially to nitrite then nitrogen. Impressive!

The claims in the paper above sound quite promising (i.e. 0.001 kWh/g of nitrate would represent a very low energy input per unit volume). However, I would doubt the energy input requirement is constant with mass removal and independent of influent concentration. If you have the complete paper and can e-mail it to me at martinsmoltenmetal@hotmail.com I'd be very interested!