tannins and 3-hydroxybenzoic-acid

The removal of small trihalomethane precursors (THMPs) from aqueous solution by two commercial nanofiltration membranes (NF70 and NF270) was investigated. Resorcinol, phloroglucinol, and 3-hydroxybenzoic acid were selected as model compounds of small THMPs, while tannic acid was chosen as a medium molecular disinfection by-product (DBP) precursor for comparison. The performance of nanofiltration membranes were evaluated by introducing polyethylene glycol (PEG) solutions and uncharged saccharides to estimate molecular weight cut-off (MWCO) and membrane pore radii, respectively. The streaming potential was measured to estimate the membrane surface charge at different pH values, which reveals that the NF270 membrane is more pH-sensitive than the NF70 membrane. The rejections of the above selected THMPs were assessed under various pH values, and the removal efficiencies of THMPs for both membranes at high pH values are reasonably well. Charge exclusion is the prevailing mechanism for the selected small model compounds retended by the negatively charged nanofiltration membranes, while size exclusion and adsorption are controlled mechanisms but not sufficient for the rejection of unionized small organic molecules. In general, the NF270 membrane exhibits the superior permeation rate value, which takes an advantage over the NF70 membrane from the aspect of energy conservation.

Topics: Filtration; Hydrogen-Ion Concentration; Hydroxybenzoates; Membranes, Artificial; Nanotechnology; Nylons; Phloroglucinol; Resorcinols; Solutions; Tannins; Trihalomethanes; Water Pollutants, Chemical; Water Purification

This research is dedicated to determine the rejection ratios of disinfection by-products (DBPs) precursors including resorcinol, phloroglucinol, 3-hydroxybenzoic acid, and tannic acid solution in the presence of calcium by nanofiltration with NF70 membrane. The rejections of these model compounds also were studied at various compositions of a feed solution by changing pH and concentrations of model compounds. It was found that the model compound rejection and membrane permeability increase with pH due to the conformational transformation of ionizable molecules and electric interaction between the model compounds and NF70 membrane. The interactions of model compounds with calcium have no significant effect on model compounds retentions. Because of the complexation of calcium with model compounds, calcium rejection rises with the presence of model compounds and with an increase of pH.

Topics: Calcium; Disinfection; Equipment Design; Filtration; Hydrogen-Ion Concentration; Hydroxybenzoates; Ions; Models, Chemical; Nanotechnology; Phloroglucinol; Resorcinols; Tannins; Temperature; Waste Disposal, Fluid; Water Purification