Using Effective Liquid Analysis for Affordable Reverse Osmosis (RO) Desalination

When you know that 94 percent of the earth’s surface is saltwater and only a tiny percentage is potable water, the need to desalinate seawater becomes logical. It doesn’t become economical or efficient, however, unless you understand liquid analysis. In a recent article in Water & Wastewater Asia, Emerson experts Ryo Hashimoto and Vishal Thakkar talk about the application of liquid measurements in desalination plants.

While there are two types of desalination (distillation and reverse osmosis), most major markets use RO because distillation is so energy intensive. RO, however, requires very careful attention to the health of the costly RO membrane, which can be fouled by solids in the seawater. Fouled membranes can be cleaned – unless it’s permanent fouling and that’s when the expensive replacement of the membrane becomes a factor.

 To prevent fouling and degradation of the membrane, all desalination plants pretreat, which removes harmful chemicals, filters out suspended solids, and controls scale formation. RO membranes are highly sensitive to feedwater pH and degrade rapidly in an alkaline environment, so the primary liquid measurements required in pretreatment are pH and oxidation reduction potential (ORP). Depending on the nature of the feedwater, some plants may also use free chlorine and turbidity measurements. Learn more about how pH is applied in pretreatment.

The measurement most associated with the actual separation process is conductivity, which provides a cost-effective way of measuring both the seawater and permeate. This article discusses two types of conductivity measurement and the ideal type to use for the application.

Generally, plants use chlorine as a secondary disinfection step in post treatment just to assure that no contaminant have made it through the membrane. Either free chlorine or monochloramine sensors are required for post-treatment analysis, as is turbidity, since lime is often introduced to improve water quality.

The use of wireless analyzers is a cost-saving strategy for desalination plants, providing an easy way to integrate needed measurements into the system without the need for costly wires and infrastructure.

Read more about the effective use of liquid analysis in desalination >

How do you use liquid analysis in your application?