NOM characterization by LC-OCD in a SWRO desalination line

摘要

The quantification and characterization of natural organic matter (NOM) in seawater reverse osmosis desalination (SWRO) is of great importance to improve our understanding of NOM role and to evaluate the performance of the different units involved in desalination facilities. In this study, we compared the effectiveness of two pre-treatment methods, operated in a pilot facility fed with Mediterranean seawater, in terms of determining NOM composition and NOM removal using liquid chromatography coupled with organic carbon detection (LC-OCD). LC-OCD was also used to assess the SWRO operation. Conventional pre-treatment using a flotation unit followed by dual-media filtration achieved 12% of dissolved organic carbon (DOC) removal. The same level of DOC removal was achieved by coupling flotation and ultrafiltration. In both pre-treatment methods, low-molecular-weight (LMW) neutrals and biopolymers were reduced by 33-40% and 18-19%, respectively. Reverse osmosis (RO) membranes acted as almost a complete barrier for humics, building blocks, and LMW neutrals, which had a rejection rate of over 97%. Despite this, 31μgCL~(-1) of LMW acids and 48μgCL~(-1) of biopolymers were found in the RO permeate. LMW acids could also be found in the RO permeate due to the affinity these compounds have with the membrane material. However, biopolymers should be more effectively rejected due to their structure and molecular weight (>20 kDa). The hypothesis proposed to explain the presence of biopolymers in permeate is a possible biofilm growth in the permeate side of the membrane module.