Removal of Dissolved Hydrophobic and Hydrophilic Organic Substances during Coagulation/Flocculation of Surface Waters

Abstract

Dissolved organic carbon (DOC) from raw and coagulated surface waters was fractionated at acidic pH using two superposed XAD 8 and XAD 4 resin columns, into three fractions : hydrophobic substances (i.e. humic substances) adsorbed on XAD 8, hydrophilic acids adsorbed on XAD 4 and “non-acid” hydrophilics which represent the organics contained in the final effluent. DOC of untreated waters was evenly split between the hydrophobic and hydrophilic fractions. The “non-acid” hydrophilics were generally as or slightly more abundant than the corresponding hydrophilic acids. For three of the six waters studied, DOC distribution was not modified after coagulation/clarification treatment. These waters also exhibited a low reduction in THMFP and TOXFP per unit of DOC after treatment. One water showed moderate change and two a significant change in DOC distribution. With the latter, a large decrease of their THMFP/DOC and/or TOXFP/DOC ratios was observed. As expected, the apparent molecular weight distributions(1000 daltons nominal membrane cutoff) have been shifted toward the low molecular weight fraction. Aluminum coagulation experiments were carried out on isolated humic, fulvic and hydrophilic acids. Humic acids were identified as the most reactive fraction, with a dramatical reduction of their THMFP/DOC and TOXFP/DOC ratios after coagulation. Fulvic and hydrophilic acids were found to react to the same extent with the coagulant, and showed comparable THMFP and TOXFP perunit of DOC before and/or after coagulation.