Enhanced softening: factors influencing DBP precursor removal

Abstract

Bench‐scale tests demonstrate the importance of magnesium hydroxide precipitation and NOM characteristics on precursor removal by softening. Relationships of hardness removal, natural organic matter (NOM) removal, and selected chemical characteristics of NOM were explored, and the implications of the enhanced softening portion of the proposed Disinfectants/Disinfection By‐products Rule were assessed. For most of the nine raw water sources examined, the amount of dissolved organic carbon (DOC) removed (both on an absolute and a percentage basis) correlated strongly with the amount of magnesium precipitated. A semilogarithmic model provided a good fit to the data for six of the nine waters (R2 values >0.8). Greater absolute removal of DOC was achieved for raw waters with higher initial DOC concentrations. DOC removal by softening was most effective for the raw water sources with the highest percentage of hydrophobic organic carbon. Greater specific ultraviolet absorbance values also corresponded to greater DOC removal.

Effect of polyaluminum chloride on enhanced softening for the typical organic-polluted high hardness North-China surface waters

“…While considering the two source waters from the Luan River, higher content of hydrophobic DOM in LW Sum compared with LW Win , the UV 254 is removed more efficiently by coagulation at natural pH and coagulation under softening condition. Which is agreed with the results from Thompson et al [12] that magnesium precipitation effectively remove the hydrophobic fraction of the organic carbon.…”

“…It is found that a small increase in magnesium precipitation results in a significant NOM removal [12]. Systems that remove at least 10 mg/L Mg hardness as CaCO 3 are proposed to exempt from the enhanced softening requirements by the USEPA [1].…”

Characterization of precursors to trihalomethanes formation in Bangkok source water

“…Interestingly, these two base fractions also provided relatively high SUVA values (greater than 2 L/mg m). High SUVA was reported to imply high aromatic character [18,19] and therefore this result implied that the aromatic organic compounds were the active precursors of THMs. The HPON fraction, however, also exhibited high level of SUVA but its specific THMFP was rather low.…”

FTIR evaluation of functional groups involved in the formation of haloacetic acids during the chlorination of raw water

“…High SUVA values were known to indicate high molecular weight, hydrophobic and aromatic character components [10][11][12][13]. This simply meant that SUVA was used to suggest the possibility of organic matters to form potentially harmful disinfection byproducts if presented in adequate quantity, and therefore it could be treated as a possible indicator for the formation of disinfection by-products [14].…”