Removal of organic pollutants in model water and thermal wastewater using clay minerals

Abstract

Water treatment method was developed for the removal of different anionic dyes such as methyl orange and indigo carmine, and also for thymol applying sodium bentonite and cationic surfactant - hexadecyltrimethylammonium bromide (HTAB) - or polyelectrolytes (polydiallyldimethylammonium chloride, poly-DADMAC and poly-amines). The removal efficiency of these model substrates was examined in model water using UV-Vis spectrophotometry, HPLC and TOC analysis. The clay mineral and HTAB were added in one step to the polluted model water in Jar-test experiments. The influence of the cation exchange capacity (CEC) of the applied clay mineral and the presence of polyaluminium chloride coagulant (BOPAC) were also tested for the water treatment process. The structures of the in situ produced and pre-prepared organoclay composites were compared by XRD analysis. The rapid formation of organoclay adsorbents provided very efficient removal of the dyes (65–90 % in 3–10 mg/L TOC₀ range) with 200 mg/L sodium bentonite dose, however thymol was less efficiently separated. Adsorption efficiencies of the composites were compared at different levels of ion exchange such as at 40, 60 and 100 %. In the case of thymol, the elimination of inorganic carbon from the model water before the TOC analysis resulted in some loss of the analysed volatile compound therefore the HPLC analysis was found to be the most suitable tool for the evaluation of the process. This one-step adsorption method using in situ formed organoclay was better performing than the conventional process in which the montmorillonite-surfactant composite is pre-preapared and subsequently added to the polluted water. The purification performance of this method was also evaluated on raw and artificially polluted thermal wastewater samples containing added thymol.

Keywords:

• Wastewater purification
• thermal water
• organic pollutants
• montmorillonite
• organoclay
• cationic polyelectrolytes
• adsorption

Acknowledgments

This work was financially supported by grants from the Hungarian Research Foundation (OTKA CK80193 and PD78378) and by the Hungarian National Office of Research and Technology (NKFP DA_THERM TECH_08_A4). KM also thanks the support of the Hungarian Academy of Sciences (Bolyai János Research Fellowship). AMCOL Specialty Minerals is thanked for providing free SPV 200 sodium bentonite sample. Kunipia-F sodium bentonite as a free gift of Kunimine Industries Co., Ltd. is also highly appreciated. Authors would like to acknowledge the sodium bentonite (SBS) provided by the research group of the Department of Physical Chemistry and Material Science at the University of Szeged, led by Professor Imre Dékány.