project

Remineralisation of RO permeate

Expert(s):
Erwin Beerendonk BSc

  • Start date
    01 Aug 2016
  • End date
    01 Aug 2018
  • collaborating partners
    HaskoningDHV Nederland B.V., 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., remineralisation. This step is necessary to avoid any problems during the transport of the water to the customer (water composition and 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 develop 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 a literature and market study to gain insight 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, on a pilot scale, connected a filter to the RO step, as the most suitable option. This filter is filled with calcite pellets and is fed by the RO permeate. 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. Over the coming three months, further work will be done on the soft sensor and the behaviour of the particles, both in and after the calcite filter, will be tested.

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.

One innovative remineralisation application option involves softening the water through ion exchange before the RO. The ion exchange regenerant can then be used to remineralise the RO permeate. This concept will first be researched on a lab scale (resin selection, exchange cations and anions, etc.), and subsequently on a pilot-installation scale.

Solution

  1. Define the desirable composition of the drinking water.
  2. Review conventional and innovative remineralisation options.
  3. Elaborate the options (cost considerations and selection) on the basis of: (1) partial softening prior to RO, (2) RO with enhanced yield, (3) reuse of softening salts generated in (1).
  4. Conduct pilot tests for innovative remineralisation (regarding partial softening: think of IEX cation, pellet softening, nanofiltration).
  5. Pilot research with proof-of-principle of the application of modelled soft sensor for calcite filtration.
  6. Estimate the technical/economic applicability of the variants in item (3) at Oasen and on the international market (see ‘Other observations’ below).
  7. Reports.