Application of membrane fractionation for better understanding of biological stability of water

The selection of the water source and the subsequent water treatment processes have different impacts on the biological stability of the water. In the Netherlands and Flanders, the biological stability in the drinking water treatment is improved as much as possible through intelligent source selection and water treatment. Extensive research into biological stability has shown that both particles and dissolved organic matter influence the biological stability. To gain a better understanding of this question, in the present study we are applying a new version of the previously developed membrane fractionation tool.

Investigating the role of particles and organic matter with the membrane fractionation tool

The project’s central question concerns which particles and dissolved matter need to be removed, and to what extent, in order to obtain biologically stable water. A proper answer to this question requires a better understanding of the composition of these particles and dissolved matter. Which nutrients are bound to particles, and which measurement methods and analyses can be used to determine them?

In the previous Joint Research Programme project, ‘Particle composition and biological stability – Isolation and identification of organic and particle fractions related to biological stability (2019-2020)’, we focused on understanding the composition of particles and organic matter in the feedwater. We worked on the isolation in fractions according to molecular weight with membrane fractionation, the identification of these obtained physical organic and particle fractions, and the determination of their biological stability. A protocol was developed for the fractionation of feedwater using a series of membranes (micro-, ultra- and nanofiltration membranes). The membrane fractionation was carried out on a single type of surface water (lake IJsselmeer water), combined with biological stability measurements.

The objective of the present follow-up research is to gain further understanding of the composition of particles and organic matter in relation to biological stability. To this end, we use the previously developed membrane fractionation tool and focus on different water types (surface water, groundwater), seasonal influences on surface water, and the impact of selected treatment stages.

Testing different water types throughout the year

In consultation with the project supervisory group, and in collaboration with the biological safety theme group, a number of water types and analytical techniques are selected for the membrane fractionation experiments. We develop a membrane fractionation installation which is suited for on-site use, so that samples can be taken continuously. The installation is fed with the selected water types, with sampling of four different particle and organic matter fractions and the selected starting water. Several fractionation experiments are involved, and sampling is conducted throughout the year. It is therefore done in different seasons, because of the differences in temperature and composition. The characterisation and identification of the different fractions is done using LC-OCD (liquid chromatography, followed by organic carbon detection). The influence of the different fractions on the biological stability is determined using different measurement methods.

Managing biological stability with the right treatment

With knowledge about biological stability in relation to the composition of particles and organic fractions in different water types, the functioning of the relevant treatment process – e.g., rapid and ultra-filtration – will be better understood and organised. This will contribute to the optimisation of treatment processes capable of managing biological stability problems in the distribution network.