DOM removal from Lake Kinneret by adsorption columns and biodegradation: a pilot study and modeling

Abstract

A year-long removal of dissolved organic matter (DOM) from Lake Kinneret water, the main reservoir of surface drinking water in Israel, was studied by adsorption pilot plant columns with media which included new (virgin) granular activated carbon (GAC), regenerated GAC (rGAC), a clay–polymer nanocomposite (PD–MMT), and a combined media (COMB) of PD–MMT composite followed by rGAC at the same volumes. Lake Kinneret water is characterized by low specific absorption of UV at 254 nm (SUVA₂₅₄), high ionic strength and high bromide content. We studied DOM removal mechanisms by each adsorbent and their combination, via monitoring their emerging concentrations through the columns. The effect of DOM removal on trihalomethanes formation (THMF) was also elucidated. Simulated and predicted DOM adsorption in GAC columns by developing an extended model including adsorption and biodegradation is presented. The best yield of DOM removal results (expressed as UV₂₅₄ and DOC) was by the COMB and GAC columns. The COMB presents a synergistic result by the combination of two removal mechanisms, electrostatic by PD–MMT and hydrophobic by rGAC. The analysis along the columns shows that whereas the removal by GAC and rGAC was carried out through all layers, the removal by PD–MMT was preferentially by the upper and middle layers. Emerging SUVA₂₅₄ values decreased for all media throughout the pilot run. The humic matter (HM) compounds comprising hydrophobic characteristics were more efficiently removed than the non-absorbing fractions at 254 nm (NABS₂₅₄) with more hydrophilic characteristics. THM precursors' removal by COMB as well as GAC satisfied the THM regulations. The removal of hydrophilic matter in the presence of bromide should improve the reduction of THM formation in treated water. Modeling of DOM removal at the laboratory and pilot plant, which focused on removal by GAC column, could fit the data only by considering DOM biodegradation. When a steady state during pilot operation was reached, biodegradation yields, the main contribution to DOM removal, improved the overall capacity of GAC removal beyond the adsorption process.