The MULTI-ReUse project is a project funded by the Ministry of Education and Research. It deals with the reuse of treated wastewater for industrial process waters.

For the utilization of treated wastewater as industrial process water, the re-germination potential is an important factor, as biofilm formation and biocorrosion are undesirable. A low substrate content is crucial for the biological stability of process water. The assimilable organic carbon (AOC) is part of the dissolved organic carbon (DOC) and in principle represents the substrate for microorganisms in the water. A low DOC/AOC ratio corresponds to a low re-germination potential.

Methods for the estimation of the AOC are currently based on the measurement of the increase of culturable bacteria. This usually takes a long time.

An alternative to this is reversed isotope labelling. Mineralization processes of organic compounds can be investigated in degradation experiments by adding a ¹³C-labelled carbonate buffer to the system. The isotopic composition of the background DIC changes as substrate derived CO₂ is formed, which mainly consists of ¹²C-CO₂. This change can be measured to calculate the mineralization of the AOC.