Forward Osmosis to Recycle Dye Wastewater

Carpet and textile dyeing mills use copious amounts of water in their operations. In many areas, the shortage of fresh water is hampering operations. Conventional nanofiltration and/or reverse osmosis membrane equipment requires very high levels of chemical pre-treatment of the wastewater to remove the synthetic and natural oils that foul membranes, creating a chemical-laden concentrated waste stream after the water is removed.

According to a Jan. 26 press release, the Catalyx TWO system can treat the water streams without chemicals, enabling the concentrated wastewater that is rich in organics to be incinerated in a boiler or anaerobically digested to produce biogas.

Nature uses forward osmosis to transport water throughout living organisms such as plants and animals. Commercial reverse osmosis membrane systems do the opposite -- deriving pure water from saltwater. Reverse osmosis applies very high hydraulic pressure on the saltwater to extract pure water -- against the water's natural tendency. These membranes cannot operate in the forward osmosis mode because they have to be built to withstand such pressures.

Reverse osmosis pressure pushes the fouling contaminants against the membranes and degrades performance and increases operating costs. Thus state-of-the-art membranes have largely been excluded when it comes to high organic, fouling content wastewater.

Juzer Jangbarwala, Catalyx, Inc. inventor and founder stated, "Our vision is to practice 'subtraction' while treating water, instead of 'addition' of chemicals, as is typically done in the treatment of high organic waste. By concentrating the waste through simple water subtraction, it opens up new possibilities, such as reclaiming the process chemicals and generating biogas from the organics."

Jangbarwala noted, "While the eventual goal at Catalyx is to design a system which can utilize this unique membrane for desalination of seawater, we are currently only focused on the system's ability to dewater very difficult-to-treat wastewater."

Catalyx has successfully tested the TWO system for other applications, including concentration of ion exchange waste by 50 percent at a coal bed methane produced water treatment plant, recycling tannery wastewater, and concentrating animal farm wash water and landfill leachate water to enhance biogas production.

Jangbarwala added, "Osmotic pressure is a source of energy, and the differential can be used to either convert that energy to electricity or as a tool for energy storage. An exciting possibility with our unique membrane is to build an 'energy storage' system for offshore windmills. High winds are not always synchronized with the grid requirements. During the high wind periods, we could desalinate seawater using the excess electricity, and during low winds, allow the osmotic pressure differential between seawater and the desalinated water to generate electricity and feed the grid."

For more information, visit under technology/wastewater treatment.