Multi-Source, Single-Stage, Full-Stream RO

The objective is a tested Multi-Source, Full-Stream RO concept, with minimal pre- and post-treatment (single stage), which uses flexible water sources and produces water of impeccable quality. The concept is researched in partnership with Oasen and the Schieland and de Krimpenerwaard Water Authority, and the collaboration of WE-Consult.


The Multi-Source, Single-Stage, Full-Stream RO concept was launched by Prof. W.G.J. van der Meer in his inaugural lecture at TU Delft (February 2013). ‘Multi-Source, Single-Stage, Full-Stream RO’ is the working name of a conceptual innovation in drinking water treatment, based on single stage membrane filtration, in particular reverse osmosis (RO). The main technical characteristics of the concept are: (i) the extensive removal of dissolved and undissolved particles from the water; (ii) the production of demineralised water that is subsequently remineralised; (iii) a flexible use of local sources [fresh and brackish groundwater and surface water, bank filtrate, rainwater, (pre-treated) wastewater and seawater]; and (iv) (the possibility of) a decentralised, local and small-scale production and supply of drinking water.

The application of the Multi-Source, Single-Stage, Full-Stream RO concept should result in a number of special performance characteristics, such as: (i) the production of securely-supplied drinking water of impeccable quality; (ii) an optimal preparedness for future developments (climate change, salinisation, customer desires, quantity and quantity of available sources); (iii) high sustainability (reduced use of energy and chemicals, fewer residuals, less contamination in the distribution network and indoor installations); and (iv) lower overall costs.


To achieve the objective two paths are at first explored for the application of RO to the most difficult source, that is, surface water:

  1. Optimal design and operational management using commercially-available RO systems, with the least amount of pre-treatment possible.
  2. Optimal design and operational management using innovative RO systems without pre-treatment.

The following is done, partly in parallel to paths 1 and 2:

  • Appraisals made to arrive at an optimal choice for the re-mineralisation of RO permeate. This part is elaborated in a parallel TKI project: ‘Re-mineralisation of RO permeate’.
  • Researched the extent to which the integrity of the  Multi-Source Single-Stage concept can be guaranteed and safeguarded (especially regarding disinfection capacity).
  • Researched whether the micropollutants present are sufficiently removed by the Multi-Source Single-Stage concept. This part is elaborated in a parallel UvA/Oasen/KWR research project:  ‘Efficiency of small contaminant removal by Reversed Osmosis (ECROS)’.
  • Gained insight into the biological stability of Multi-Source Single-Stage RO. This part is no longer a component of the TKI Multi-Source Single-Stage RO project.

Research is carried out on surface water using commercially available RO membranes with (1) ultrafiltration pre-treatment as state of the art method and (2) minimal pre-treatment using screens. An innovative RO system has been developed that is being tested in parallel on surface water. At the same time, the most suitable approach to guaranteeing the integrity of the Multi-Source Single-Step RO concept is being sought.

In the final phase of the project, one selected system is examined for its robustness and implementability in practice; the impact of switching water sources on membrane fouling is also studied.


Installations have been designed and built for research work on the application of RO with commercially-available RO, including minimal pre-treatment, and with innovative RO without pre-treatment. Field studies have been carried out at two locations (pond water at KWR and surface water at Oasen’s Kamerik site) with locally available surface water which generated extensive membrane-system fouling, which can be controlled through a package of measures. The measures include (i) pre-treatment with screens, (ii) periodic air/water cleaning, (iii) low flux operational rates and (iv) pre-treatment with cation exchange. At the same time, a study is underway on an innovative spacerless system which controls fouling in an innovative fashion. Different monitoring systems have been evaluated to safeguard membrane integrity and disinfection capacity of the Multi-Source 1-step RO system, and a novel innovative membrane integrity monitor will be investigated and developed in a parallel project (TKI Natural Viruses). In a follow-up study performed in 2019, membrane fouling could be successfully controlled using a periodic automated cleaning-in-place (CIP) strategy in RO systems using minimal pre-treatment.