Membrane Based

Water is one of the world's most valuable resources. Yet it is under constant threat due to climate change and resulting drought, explosive population growth, and waste. One of the most promising efforts to stem the global water crisis is industrial and municipal water reclamation and reuse. Water reuse can be defined as reused, recycled or reclaimed water as water that is used more than one time before it passes back into the natural water cycle. Thus, water recycling is the reuse of treated wastewater for beneficial purposes such as agricultural and landscape irrigation, industrial processes, toilet flushing, or replenishing a groundwater.

Utilizing proven, reliable technologies from Dew, forward-thinking industrial leaders are saving money, generating new revenue sources, and helping the environment by reclaiming and reusing wastewater. Leading industries are leveraging Dew experience and expertise to safely recover wastewater and generate new incomes by using this reclaimed water for agricultural and industrial applications.

The growing significance of using membranes in recycling and reuse of water treatment process is due to various factors. Foremost of it is for water recycling and reuse.

In recent years other factors have helped to extend the use of membrane techniques in all areas of water and wastewater treatment.

Stricter government regulations on water quality: a process that physically removes pathogens, membrane makes it possible for disinfection to occur without producing any undesirable by-products.

  • Water reuse: wastewater has now become a resource in cities as well as in water deficient areas. Membranes are an ideal tool for recycling water due to their extensive abatement range.
  • Membrane technology has been proven in last 50 years for difficult water and waste water processes.

Basic Principles

Membranes are semi-permeable thin barrier sheets. Synthetic membranes are used to remove different solutions and particles in the water recycling process.

Nanofiltration (NF) and reverse osmosis (RO) as well as microfiltration (MF) and ultrafiltration (UF) are often described as being pressure processes.

MF is a direct continuation of conventional filtration that makes it possible to remove particles smaller than a micron such as colloids and bacteria.

UF goes even further. Thanks to this process viruses and heavy molecular organic compounds can be removed.

These two processes use a straining technique and therefore separation depends on the size of the pores and which species are chosen, while in NF and RO the pores are not visible.

The retention level for inorganic and organic solutions depends on their solubility and their diffusivity in the membrane. Retention also depends to a large extent on the net charge on the membrane surface.

Reverse osmosis (RO)

RO can only occur at higher pressures than those of the osmotic pressures of feed water.While the osmotic pressure of brackish water is relatively low (1.4 and 3.4 bars for 4.0 g/l of calcium sulphate and sodium chloride solution), that of seawater is relatively high (27 bars for 35 g/l of sodium chloride).

Electro dialysis (EDI)

EDI is a fundamentally different process. Rather than have the water pass through the membrane, the ions are transported through the membrane under the influence of an electric potential. Micro-porous positive and negative membranes are alternatively filled with electrodes in order to specify which columns will be enriched with or depleted of salts. ED's role is limited to the removal of ionic species.

There is also a modified version of ED, called "electrodialysis reversal" which consists of reversing the polarity of the electrodes at various frequencies in order to minimize scaling and clogging.

Recycling and Reuse

The conversion rate is a concept that applies to all membrane processes. This is the fraction of feed water converted into treated water. Nowadays it is common to have several stages membrane based plant to recycle 90% of water and zero liquid discharge systems.