Adsorptive characteristics of ionogenic aromatic pesticides in water on powdered activated carbon

The adsorptive characteristics of ionogenic pesticides on powdered activated carbon were described. The effects of pH on the adsorbabilities of MCPB (an acidic pesticide) and imazalil (a basic pesticide) onto-powdered activated carbon (PAC) were evaluated by correlating I-octanol-water partition coefficients (log P-ow) with the Freundlich adsorption constants over a pH range of 3 similar to 9. After being corrected with pH, the Values of log P-ow were found to be linearly related to the logarithm of k (i.e. log k). For MCPB, log k as well as log P-ow decreased with the increase of pH in the range of pH > pK(a) and became constant in the range of pH < pK(a) and vise versa for imazalil. Adsorption of ionic species ante PAC became negligible at an ionic strength of similar to 10(-3) M when pH-pK(a) was lower than 4 for MCPB and pH-pK(a) higher than -4 for imazalil. Similar relationship between log k and log - P-ow was obtained for other four acidic pesticides (bentazone, :pentachlorophenol, denoseb and MCPP) and two neutral pesticides (imidacloprid and linuron), which suggested that the log P-ow values mainly determined the adsorbabilities of these pesticides onto PAC. The calculation results showed that the activated carbon amount needed (ACAN) for lowering pesticide concentration from 500 to 50 mu g/l was also linearly related to log P-ow, and the ACAN for bentazone(log P-ow, 0.11 at pH = 7) Was 51.9 mg/l, while that for imazalil (log P-ow, 3.80 at pH = 8.0)was 3.1 mg/l. (C) 1998 Elsevier Science Ltd. All rights reserved.