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Case Study: Nitrates Remediation

Challenge

GRAFTA Nanotech Inc was engaged by a copper-molybdenum mine, located in south-central British Columbia, to provide a sustainable solution for reducing concentrations of nitrate, currently exceeding the regulatory limits.

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The mining site is facing challenges regarding the discharge of the high nitrate water currently accumulated onsite at an extensively large volume. Nitrate concentration in this water is about 12 mg/L and there is only a nine-month window of time annually to discharge the water meeting the strict guideline of 10 mg/L.

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Given the high annual volume of water subject to discharge, a few water treatment technologies have been proposed for the mine including reverse osmosis (RO) and biochemical reactors (BCRs). The main challenge with regards to these technologies have been the high capital and operational cost as well as their efficiency, sensitivity to cold weather and producing highly concentrated reject.

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BCRs that have been limitedly experienced in similar sites, use biological reduction of nitrate at a relatively slow rate which requires a significantly large volume of reactor. Meanwhile, BCRs generate ammonium which in turn needs to be removed from the “treated” water. This feature is not provided within the BCRs and an additional treatment system would be required.

Key Project Requirements

  • Meeting strict nitrate removal guidelines to discharge into receiving surface water bodies;

  • Small footprint of treatment system and minimal reliance on electromechanical requirements;

  • Short retention times and reasonable longevity;

  • Cost effectiveness of the treatment system;

  • No additional treatment required for removing ammonium

  • Long-term sustainability.

Solution

GRAFTA™ 2.0 is an engineered graphene-based nanotechnology developed to target specific contaminants such as nitrate.

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Removal of nitrate is achieved through chemical reduction of nitrate followed by adsorption of the generated ammonium on graphene oxide nanosheets within the same reactor.

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The graphene and graphene oxide provide the most efficient platform for an end result water quality that lowers the concentration of target contaminants not only below discharge standards, but in most cases to nondetectable concentrations.

Results

Performance of GRAFTA™2.0 was tested through permeating the contaminated water with a nitrate concentration of 12 mg/L.

 

GRAFTA™2.0 lowered the concentration of nitrate to less than 1 mg/L through three sequential columns each with a retention time of about 30 minutes.

 

Through over 56 passes, concentrations remained consistently low, and no breakthrough was achieved. In fact, the concentration of nitrate was reduced following a simplified first-order reaction, indicating persistent removal of nitrate over time.

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A significant portion of the ammonium generated as a result of the chemical reduction of nitrate was adsorbed by graphenic structure of GRAFTA™2.0 leading to an end concentration of less than 1 mg/L.

 

Significant longevity is anticipated, promising long-term feasibility of using GRAFTA™2.0 to remove nitrate from the target water with reasonable replacement frequency.

 

GRAFTA™2.0 consistently maintained the concentration of nitrate below the strict guidelines that would allow the site to discharge the treated water into receiving surface bodies to reuse the treated water in the mining process in compliance with quality and quantity aspects of water conservation.

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