project

Remineralisation of RO permeate

Expert(s):
Erwin Beerendonk BSc

  • Start date
    01 Aug 2016
  • End date
    01 Aug 2018
  • collaborating partners
    Royal Haskoning DHV, Oasen N.V.

Oasen is working on the full-stream treatment of, among others, river-bank filtrate using RO, which entails the complete removal of practically all substances, including minerals, from the water. A crucial aspect of this development is the conditioning of the RO permeate through the addition of appropriate minerals, i.e., the remineralisation. This step is necessary to ensure that the water that reaches the customer has no problems, that is, that it has an optimal composition and minimal interaction with the pipes. The remineralisation in effect determines the ultimate quality of the drinking water. The technique can be applied to water from various other sources besides river-bank filtrate, for instance, groundwater, surface water and seepage water, following their RO treatment.

Technology

First, we identify the most suitable process and equipment options for the remineralisation of RO permeate at Oasen. We then study the best option on a pilot scale, and research the use of a soft sensor to control the water quality. A soft sensor is an innovative solution, which combines existing knowledge and the use of data fusion to close knowledge gaps.

Second, we determine the most suitable innovative remineralisation (partial softening – RO – remineralisation) of RO permeate at Oasen. We then develop and test, on lab and pilot scales, the most promising innovative combination of partial softening – RO – remineralisation.

Third, we conduct research to gain insight into the chances of innovative remineralisation and into those elements that, internationally, play a role in the remineralisation of drinking water following desalination, particularly in cool-climate countries.

Initial results

Oasen has connected a calcite filter to the RO step on a pilot scale, as the most suitable option for remineralisation in the short term. The initial tests with the calcite filter were used to optimise the filter’s operation and to test the practicality of a model for the soft sensor. A survey showed that the calcite filtration process is set up in such a way that the development of a soft sensor for RO permeate remineralisation, on the basis of conductivity measurements, does not outweigh the associated (development and implementation) costs. The period ahead will be used to further improve the model to increase understanding and improve the design of the calcite filtration process.

The most suitable innovative option for the application of remineralisation in the medium term is to soften the water by applying ion exchange before the RO. Various laboratory experiments were conducted and the best ion-exchange resin was selected so as to remove the right minerals from the groundwater. Using an innovative regeneration method, these minerals can potentially be discharged separately from the ion exchange resin and be used for the remineralisation of the RO permeate.

Challenge

To achieve the goals for the implementation of remineralisation in the short term, we have opted for calcite filtration together with magnesium dosing to remineralise the RO permeate. This process is being studied on a pilot-installation scale at Kamerik; we will also be analysing and modelling water quality with a view to developing a soft sensor.

The innovative option selected for the application of remineralisation involves softening the water through ion exchange before the RO. The possibility is being studied of subsequently using the ion exchange regenerant to remineralise the RO permeate. Elements of this concept – such as resin selection, exchange cations and anions, and an innovative regeneration process – are being researched on a lab scale. The concept is being studied on a pilot-installation scale, with a focus on the separate discharge of minerals during an innovative regeneration.

Solution

  1. Define the desirable composition of the drinking water.
  2. Review conventional and innovative remineralisation options; completed.
  3. Assess costs and select options on the basis of: (1) partial softening before the RO, (2) RO with enhanced yield, (3) reuse of softening salts generated in (1). As a result, option (3) was selected for
  4. Conduct pilot tests for innovative remineralisation after the partial softening with cation IEX, with a focus on innovative regeneration.
  5. Conduct pilot and supplementary research on a model and the application of a soft sensor for calcite filtration.
  6. Estimate the technical/economic applicability of the variants in item (3) at Oasen and on the international market.
  7. Reports and publication.