As described by the premier publisher in the desalination industry, the standard paradigm of membrane treatment is reaching the limits of its efficiency.  DXV Water Technologies has invented a process that represents an extraordinary leap in efficiency by breaking the standard paradigm of membrane systems.   

Overview

The Depth Exposed Membranes for Water Extraction or DEMWAX™ system maximizes the use of natural forces to drive membrane based water treatment processes. Natural pressure and water movement at depth in a water body provides a free, sustainable way to displace current energy intensive processes.  The DEMWAX™ system has numerous advantages over these existing water treatment systems, including:

Traditional reverse osmosis involves an on-shore plant that uses energy-intensive high pressure systems to push water through tightly configured spiral wound membranes. This membrane configuration, designed for on-shore processes, effectively treats water. However, its high-recovery paradigm requires vast pressure resulting in an energy intensive system, significant operating costs and environmental impact.

A typical seawater reverse osmosis (SWRO) plant has many components that are eliminated in the DEMWAX™ plant. Some of these are shown below.

Coastal Footprint of an SWRO Plant	Pre-treatment Systems
Pressure Vessels & Piping	Exotic Materials & Energy Recovery

There have been prior attempts to use the natural pressure of a water body for reverse osmosis. While technically successful, locating complex systems with many moving parts in an underwater environment has proven highly impractical.

To practically harness natural pressure, DXV has invented an elegantly simple system designed around a unique membrane configuration that allows the elimination of most of the complexity of a desalination plant.

The DEMWAX™ technology utilizes flat-sheets of membrane that are aligned vertically in a series such as in a heat exchanger. Each membrane sheet is comprised of two opposing membranes sealed around a permeate carrier sheet similar to the flaps on a spiral element.

The DEMWAX™ system utilizes a different configuration than spiral membrane elements. In contrast to tightly wound spiral elements, the DEMWAX™ elements are spaced sufficiently to allow a large amount of source water relative to the product water penetrating the membrane to flow past the membrane unimpeded. This allows for operation at an extremely low recovery (ratio of product to feed water) resulting in extremely low energy use (near theoretical limits). A breathing tube conveys atmospheric pressure, creating a pressure differential that allows source water to penetrate the membrane as treated water. The level of treatment depends on the type of membrane used (RO, NF, UF, MF, etc.) and the submerged depth.

A perpendicular collection channel collects the treated water from the membrane.

The cartridges are submerged into a body of water to a depth where there is sufficient natural pressure to drive the process, efficiently pushing water molecules through the membrane and leaving out bacteria, viruses, salt and other contaminants. The depth requirement is proportional to the amount of dissolved solids in the source water (approximately 850 feet/260m for seawater and 40 feet/15m for a typical fresh water source). Clean water is then pumped back to shore by a standard submersible pump.

The traditional water treatment plant paradigm includes a controlled setting on shore; however the typical problems with offshore systems are mitigated with the DEMWAX™. Salt and storms are the two destructive forces associated with in situ ocean technologies such as wave power generation systems. However, the DEMWAX™ has no moving parts in the salt water and is located far below the effects of even the largest hurricanes.

 

DEMWAX™ has numerous benefits over traditional SWRO and membrane fresh water treatment, including reduced energy use (and resulting carbon emissions) and operating cost. The DEMWAX™ technology mitigates the brine disposal issue and eliminates process chemical use.

 

*An acre-foot (AF) is equal to approximately 326,000 gallons or 1,200 cubic meters.

This dramatic improvement in efficiency allows the DEMWAX™ desalinaton system to compete on a cost basis with existing conveyance projects settting this technology apart from other desalination technologies.  For example, Southern California water supplies do not yet include seawater desalination, but those planned for the future will benefit greatly from the DEMWAX™.

State Water Project	Colorado River Aqueduct	Seawater Reverse Osmosis

 

Project	kWh/1,000g
California State Water Project	9.2
Colorado River Aqueduct	6.1
Traditional SWRO	15
DEMWAX™	4.5

Lifecycle cost analysis shows that the DEMWAX™ will save substantial cost versus the most efficient, modern membrane processes today.