Reuse of process water in dairy ingredient production – and food processing in general – opens the possibility for sustainable water regimes. Membrane filtration processes are an attractive source of process water recovery since the technology is already utilized in the dairy industry, and its use is expected to grow considerably in the coming time. At Arla Foods Ingredients, permeate from a reverse osmosis polisher (ROP) filtration unit is sought to be reused as process water, replacing the intake of potable water. Although reuse of process water is an attractive option, chemical and microbiological safety is of major importance in the food and dairy industry and must thus be guaranteed at all time. To ensure this, (i) statistical characterization in combination with (ii) real-time, on-line monitoring of relevant parameters need to be in place. Process analytical technology provides the principles for real-time, on-line monitoring, but first the relevant target molecules and concentration ranges should be identified.

We present the results of chemical characterization by gas chromatography coupled with mass spectrometry detection and inductively coupled plasma with optical emission spectroscopy showing the organic and elemental composition, respectively. Results indicate that smaller molecules and elements (such as urea, phosphate and boron) pass the ROP membrane but also larger molecules (long chain fatty acids, 1H-indole, glycerol-phosphate, glutamic acid and corresponding alpha-keto acid) are occasionally found, although in very small concentrations. Urea has been identified as the main organic compound permeating the ROP membranes in this process and near-infrared spectroscopy has been investigated for real-time quantification using chemometrics (PLS regression) with prediction uncertainty estimation.