Nanofiltration of wastewaters from olive oil production: Study of operating conditions and analysis of fouling by 2D fluorescence and FTIR spectroscopy

The presented work tries to solve the problem of the large volumes of oil mill wastewater (OMW). For this, nanofiltration is presented as a possible second stage of treatment. Different membranes were tested under different operating conditions, varying cross flow velocity (CFV) and transmembrane pressure (TMP), in order to obtain a concentrate rich in phenolic compounds and also an adequate permeate able to be returned to the process as machinery cleaning water. The NF270 membrane under the conditions of 1 ms(-1) CFV and 10 bar of TMP was observed to be the best to concentrate the phenolic compounds, with high permeate flux and low fouling. Different types of tests were performed: membrane adsorption tests with different compounds, nanofiltration tests with a model solution (MS) to analyse fouling and check the effectiveness of the cleaning protocol and, finally, the selected NF270 membrane was tested with OMW. Also, for the first time, 2D fluorescence spectroscopy and Fourier-transform infrared spectroscopy (FTIR) were used together as tools to study membrane fouling. From the adsorption tests it was observed that all the considered compounds had an effect on the membrane surfaces, which was also confirmed from the nanofiltration tests (with the DM900 membrane the most affected). After cleaning, the membranes fouled with MS and OMW did not recover the spectra of the pristine membranes but, instead, matched the spectra presented by the new membranes subjected to the cleaning protocol. Finally, the following a suitable membrane for this purpose is selected In addition, it has been proved that the used spectroscopic techniques are a feasible option for the study of both fouling and efficiency of cleaning protocols.

Automated summary

This study aims to address the issue of large volumes of oil mill wastewater (OMW) by using nanofiltration as a potential secondary treatment. Different membranes were tested under various operating conditions to concentrate phenolic compounds and produce permeate suitable for machinery cleaning water. The NF270 membrane showed the best performance in terms of phenolic compound concentration, permeate flux, and fouling. In addition, 2D fluorescence spectroscopy and FTIR were used to study membrane fouling.