Seawater Desalination: How To Ensure Your Membranes’ Quality

Seawater desalination is a big industry for countries which do not have the luxury of high numbers of gushing springs with drinking water quality. Water is essential for us to stay alive. The need for drinking water increases with the continuously growing population. To use seawater as a source of drinking water requires high-tech processes to ensure proper drinking water quality.

Seawater desalination

Reverse osmosis membranes are increasingly important for the final stage of seawater desalination. The membrane lifetime and the maintenance costs of a desalination plant are determined by the interaction of seawater components with the membrane surface.

These interactions between seawater and the reverse osmosis membrane are based on adsorption processes occurring at the solid/liquid interface. They play a major role in the technological separation process used to gain drinking water.

Simply put, adsorption is the accumulation of simple or complex ions and molecules or particles on solid surfaces, like a reverse osmosis membrane.

The affinity of the salts contained in seawater to the solid membrane and the rates of adsorption and desorption of these salts determine the applicability and the lifetime of the used material. That’s why the membranes used for desalination have to be checked regularly to ensure always the same quality of the resulting drinking water.

A direct method allowing investigation on real material surfaces to follow the changes in the membrane properties is definitely preferred.

The SurPASS electrokinetic analyzer focuses on the chemical analysis of solid surfaces and makes it possible to follow adsorption and desorption rates directly.

Adsorption processes under real-life conditions

Semi-automated analysis of the depletion of ions and particles in solution is laborious. Such analysis requires equilibrium conditions, which makes it impossible to study the time dependence of adsorption processes, i.e. kinetics.
Available automated measuring instruments for adsorption studies require the use of model surfaces to simulate material properties. However, there remains the uncertainty whether a model surface is representative.

SurPASS breaks through the restrictions of current adsorption measuring techniques. The adsorption processes can be studied under real-life conditions.

SurPASS makes use of the changes in the surface charge. This analysis makes it feasible to investigate the interaction between the solid membrane surface and compounds dissolved in seawater.

Upon contact with water, the solid membrane surface exhibits a specific charge, which is described by the zeta potential – the primary information provided by SurPASS.

The SurPASS principle

The surface charge at the solid/water interface determines the electrostatic interaction between the solid surface and dissolved components in the aqueous phase.

Surface charge is related to the electrokinetic or zeta potential at the solid/liquid interface. For macroscopic solids the zeta potential is determined by the measurement of streaming potential or streaming current. Both are electrokinetic effects that arise from the motion of the liquid phase relative to the solid surface.

electrolyte-flow

The zeta potential value is directly dependent on the concentration of adsorbed ions and particles.

zeta-potential-adsorption

So you know under real conditions whether your reverse osmosis membranes need maintenance or exchange to guarantee the same high quality of drinking water gained from seawater treatment.

As a membrane producer you can study the properties of reverse osmosis membranes under real-life conditions and optimize them for use in separation processes as required for seawater desalination.

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