Improved brine recycling during nitrate removal using ion exchange.

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Wastewater Management

Background:

• Ion exchange is effective for nitrate removal from drinking water.
• Disposal of spent brine from ion exchange regeneration poses economic and environmental challenges, limiting wider application.
• Small communities face particular difficulties with the cost and logistics of spent brine disposal.

Purpose of the Study:

• To develop a novel spent brine recycling system for ion exchange processes.
• To improve the economic viability and widespread application of ion exchange for nitrate removal.
• To reduce salt consumption and wastewater discharge associated with ion exchange regeneration.

Main Methods:

• A combined biological denitrification and sulfate reduction system using two upflow sludge blanket reactors (USBRs) in series.
• Integration of a granular activated carbon (GAC) adsorption column to treat bio-reactor effluent.
• Repeated operation of ion exchange columns (A520E resins) over 25 cycles using virgin and recycled brines.

Main Results:

• Denitrification reactor achieved 96% nitrate removal efficiency.
• Sulfate reduction reactor achieved 62% sulfate reduction efficiency.
• Granular activated carbon treatment prevented throughput decrease in ion exchange resins caused by bio-polymers and dissolved organics.
• Recycled brine with sulfate reduction enhanced bicarbonate concentration, acting as a co-regenerant, leading to reduced salt usage and discharge.

Conclusions:

• The novel spent brine recycling system effectively reuses brine for ion exchange regeneration.
• The combined biological treatment and GAC filtration is crucial for maintaining ion exchange efficiency.
• This integrated approach offers a sustainable and economical solution for nitrate removal, particularly for small communities.