Guide to forward osmosis applications

A general introduction to forward osmosis applications

We realize that navigating any portal can be challenging at times. To make life easier for you – our readers – we have therefore decided to summarize all our forward osmosis application related knowledge on a single page with the aim of creating a more accessible entry point to the ForwardOsmosisTech portal. We hope we have succeeded in doing so below. As always, send us a mail at forwardosmosistechportal@gmail.com if you have suggestions for improvements or simply have something on your mind you want to share with us.

Concentration, dilution, water production, and energy production

As the title suggests there are essentially 4 ways for forward osmosis systems to provide value in end user applications:

  1. Concentration, where water is extracted by forward osmosis processes from specific feed streams. Continuous extraction of clean water from said feed solutions will result in volume reduction, which in effect concentrates solutes and any other components. This process is also known as dewatering.
  2. Dilution (indirect water production), where water is extracted from feed streams by forward osmosis processes into a given draw solution. Continuous extraction of clean water into the draw solution will result in volume increase, which in effect dilutes solutes and any other components. Dilution can be seen as an indirect way of producing water.
  3. Direct water production, where the clean water extracted from feed streams into draw solutions is separated from the draw solutes by means of complementary separation processes (e.g. reverse osmosis, nanofiltration, ultrafiltration, membrane distillation, thermal separation etc.).
  4. Energy production, where the clean water extracted from feed streams into draw solutions is used to generate hydraulic pressure on the draw side, which in turn can be used to generate electrical energy via turbines. This process is known as pressure retarded osmosis.

The table below summarizes a few examples of real-life applications, where the 4 value generators described above are put to use. Notice that some applications utilize more than one value generator and thus provide value to end users on several levels.

Application Utilized value generator

Industrial wastewater treatment – example 1

Dewatering of industrial wastewater

Some industrial waste-waters are inherently difficult to treat with conventional pressure-driven water treatment technologies due to a high content of fouling agents (TDS & TSS) and/or a high salt content. Examples include – but are in no means limited to – wastewater from the oil and gas industry, wastewater from wet scrubbers used to remove contaminants from sources of air pollution, and wastewater from the textile dying industry. In all the aforementioned applications, forward osmosis systems are a good low-energy alternative to installing expensive pre-treatment systems or using evaporators. Since disposal costs for industrial wastewater are mostly volume-based, the primary role of the forward osmosis system is to de-water the industrial wastewater to a point where disposal costs have been reduced to an acceptable level. In a continuous water treatment system, the water extracted through forward osmosis must be separated from the draw solutes in order to regenerate the osmotic strength of the draw solution. This process of water separation can be carried out by traditional pressure-driven membrane technologies, which are now operating directly on a diluted forward osmosis draw solution with greatly reduced fouling propensity. An important driver for designing forward osmosis based wastewater treatment systems with continuous draw solution generation is the simultaneous production of reusable water.

  • Concentration
  • Direct water production

Industrial wastewater treatment – example 2

fertigation by means of fertilizer driven forward osmosisIn some industrial applications, the value of the wastewater treatment system lies in its ability to produce a dilutate without consumption of precious fresh water resources. One good example of such applications is fertigation,  an agricultural process where a forward osmosis system is used to extract clean water from impaired water sources into a concentrated liquid fertilizer solution. In the process, the liquid fertilizer solution becomes diluted to a point where substantially less fresh water resources are needed to produce the final fertilizer-containing irrigation water.

  • Dilution (indirect water production)

Industrial wastewater treatment – example 3

Stand-alone FO system for feed stream concentration and draw stream dilution

One of the best application areas for forward osmosis systems can be found within the field of industrial process optimization. Imagine a factory/plant with two separate aqueous streams: one needs to be concentrated and another needs to be diluted. Traditionally these streams are treated separately but a forward osmosis system is able to utilize the osmotic pressure in the concentrated stream to extract water in a low energy fashion from the diluted stream. Thus, forward osmosis systems offer the possibility to replace two costly treatment processes with a single-step, low energy process. In our article about stand-alone forward osmosis systems we give an example of how forward osmosis technologies can be used for industrial process optimization in traditional RO-based desalination plants.

  • Concentration
  • Dilution (indirect water production)

Osmotic power generation – example 1

Pressure retarded osmosisOsmotic power generation plants generate electricity from the osmotic pressure difference of two aqueous streams via the principle of pressure retarded osmosis (PRO). Briefly, PRO is a forward osmosis process where the  water extracted into the draw solution is used to generate hydraulic pressure, which in turn can run a turbine. Traditionally, osmotic power generation plants have been envisioned to utilize the osmotic pressure difference between river water and seawater.

  • Energy production

Osmotic power generation – example 2

Pressure retarded osmosisForward osmosis systems capable of running in PRO mode could potentially also be used for combined osmotic power generation and industrial process optimization. The idea is to co-localize desalination plants and wastewater treatment plants and utilize the brine waste from the desalination plant to both dewater wastewater streams and at the same time generate electricity through pressure retarded osmosis. In the process, the brine waste becomes diluted to seawater salinity levels, thus, greatly reducing the cost of brine discharge.

  • Energy production
  • Dilution (indirect water production)
  • Concentration