Micro- and ultrafiltration in surface water treatment

Surface water utilities in the Netherlands often directly intake river water, which has sometimes passed through a reserve or reservoir. This water needs to be treated in a process which, in the classical approach, begins with micro-screening. This is followed by coagulation and (sand) filtration, which removes undesirable materials, especially particles, natural organic matter (NOM) and biomass. An alternative means of removing particles is membrane filtration (micro- or ultrafiltration, or MF/UF), in which surface water, following the micro-screening, can be directly filtered using porous membranes. This project involves a desk study, supplemented with experiments, to research the degree to which MF/UF, possibly in combination with iron and powdered carbon, offers a suitable alternative to drinking water utilities.

Alternative to coagulation and filtration

The classical approach to surface water treatment with coagulation and filtration has a number of drawbacks:

  • use of chemicals as coagulant (ca. 10 mg/L FeCl3);
  • sludge production;
  • changes in pH;
  • large plant-surface requirements;
  • (often) insufficient removal of particles, organic matter and biomass (limited disinfection).

In contrast, MF/UF has a variety of advantages:

  • little or less use of chemicals;
  • no sludge production;
  • stable pH;
  • compact and modular plant;
  • complete removal of particles.

For these reasons MF/UF can also be used in pre-treatment for (deep) infiltration in the dunes, conventional post-treatment and reverse osmosis membranes. This makes it an attractive alternative for DPWE utilities at various drinking water production sites.

Despite all its advantages, MF/UF is susceptible to membrane fouling, and it only removes a very limited amount of NOM. Membrane fouling causes operational problems that often result in an undesirable capacity loss. To address this problem, low iron (sometimes aluminium) dosing is applied to the feed stream to the MF/UF. Moreover the NOM, and possibly also organic micropollutants, can be reduced through the use of an additional ‘filter aid’, such as powdered activated carbon (PAC).

Desk study and exploratory experimental tests

This project involves a desk study that will establish the state-of-the-art regarding the technique and the application possibilities for pre-treatment of surface water with MF/UF, supplemented with a possible iron dosing and/or ‘filter aid’. In a second project phase, for a (limited) number of promising combinations generated by the desk study, a laboratory MF/UF set-up will be used to further study the process, including, inasmuch as possible, a calculation of the associated costs.