Collaborative tests were performed with partners at various research institutions to standardize an experimental procedure. The results were statistically evaluated. The assessment certified high-quality data as an outcome of the standardized method. A process design optimization for membrane cascades was carried out with the statistical data. It showed that small differences affect a possible process configuration. Subsequently, five optimization scenarios were used to investigate the design of an OSN cascade. As a unique condition, at least one of the solutes had a negative retention value. This condition means that the membrane did not retain this substance. The solute instead accumulated in the permeate. The achievable selectivity is dependent on the mutual distance of the respective retentions. Also, their position on the retention scale is significant. The experiments were continued in the field of Solvent tolerant nanofiltration (STNF). The polymeric membranes used were developed for the OSN or aq. NF. Water was successively added to the organic solvent to create an appropriate process medium. The dominant effects changed in solvent mixtures with an ethanol content of between 60 wt% and 80 wt%. This result applied for charged and uncharged solutes. Similar, a ceramic membrane type was used, which was coated with polyelectrolytes in water. This membrane type had previously only been used in the aq. NF. The retention and flux results were explained by the cononsolvency effect combined with the polarity effect of the solution. Cononsolvency were traced back to the disturbing of hydrogen bonds.