Sorption of organic compounds of varying hydrophobicities from water and industrial wastewater by long- and short-chain organoclays

It is generally assumed that short-chain organoclays are better sorbents for non-ionic organic compounds than are the long-chain organoclays. We believe that the above statement is correct only for relatively hydrophilic or slightly hydrophobic compounds and that the opposite should be true for highly hydrophobic compounds, namely, that long-chain organoclays are expected to be superior to the short-chain analogs for sorption of highly hydrophobic materials. To verify our hypothesis, the sorption of six compounds with a range of log Kow values from 2.5 to 6 was studied on tetramethyltriammonium-(TMA) and octadecyltrimethylammonium-(ODTMA) bentonite, representing short- and long-chain organoclays, respectively. Compounds with low or medium hydrophobicities (log Kow 2.5–3.8) were more strongly sorbed on the short-chain organoclay, whereas the more hydrophobic compounds (log Kow 5.2–6.1) were better sorbed on the long-chain organoclay, in agreement with our hypothesis. The efficacy of organoclays in removing organic pollutants from the effluent of a pesticide producing plant was evaluated. Pesticide sorption from the wastewater was studied on both types of organoclays. It was found that both organoclays were able to remove organic pollutants from industrial wastewater, but solute uptake by short-chain organoclays was strongly depressed by competition, while long-chain organoclays were only slightly affected, if at all, by the presence of competing solutes in the industrial wastewater.