Enabling Water Reuse by Treatment of Reverse Osmosis Concentrate: The Promise of Constructed Wetlands

Abstract

As more cities experience water stress, the use of reverse osmosis (RO) membranes for wastewater treatment and reuse will expand. The concentrated waste stream resulting from RO treatment can pose chronic ecotoxicity risks if discharged to surface waters or shallow coastal ecosystems. Most existing RO concentrate treatment technologies are cost prohibitive, but constructed wetlands hold promise as a viable multibenefit solution because they have the potential to provide simultaneous treatment of nutrients, metals, and trace organic contaminants at a relatively low cost. They also are popular with the public. A handful of water-stressed cities have already begun experimenting with constructed wetlands for RO concentrate treatment. However, further research is needed to reduce the land area needed for treatment and increase the reliability of constructed wetland systems.

The frontiers of water and sanitation

“…Furthermore, the discharge of Ro concentrate could contribute to hypoxia, ocean acidification and compromise the health of aquatic organisms. For these reasons, it may become necessary to treat concentrates from wastewater recycling projects prior to discharge or avoid the discharges altogether 30 . For Ro plants lacking coastal access, the current generation of brine and concentrate management technologies, such as deep well injection, evaporation ponds, zero liquid discharge (ZLD) or near zero-liquid discharge (NZLD) greatly increase the overall cost of water purification.…”

Constructed Wetlands: A Sustainable Solution for Concentrate Management

“…Recent articles (e.g., Scholes et al 2021) document progress in the use of CWs for ROC management. Two examples of the CW approach implemented by the authors illustrate its benefits and requirements.…”

Inverse Design of Pore Wall Chemistry To Control Solute Transport and Selectivity

“…Energy security is intimately linked to the sustainability of current water resources, and thus, efficient water treatment processes are crucial for employing alternative lower quality water sources. The maturity of membrane technologies for low-energy, reliable treatment of seawater through reverse osmosis has led to their widespread adoption for desalination , and utility for water reuse and other advanced water treatment systems . However, membranes are not yet capable of economically treating highly impaired waters, such as oilfield-produced water, currently an enormous wastewater stream on the order of 2 billion gallons per day .…”

“…The maturity of membrane technologies for low-energy, reliable treatment of seawater through reverse osmosis has led to their widespread adoption for desalination 11,12 and utility for water reuse and other advanced water treatment systems. 13 However, membranes are not yet capable of economically treating highly impaired waters, such as oilfield-produced water, currently an enormous wastewater stream on the order of 2 billion gallons per day. 14 The development of membrane separation processes providing energy-efficient routes to converting such highly contaminated sources into "fit-for-purpose" water 15 (e.g., for irrigation, streamflow augmentation, power) as well as recovering valuable resources from these waste streams remains a grand goal 16−19 but is hindered by key challenges associated with the concentration and broad chemical variety of contaminants.…”