Abstract:
A rapid natural organic matter (NOM) fractionation tool was developed to enable
NOM to be classified by hydrophobicity at the water treatment works and in the
catchment. This fractionation method uses XAD adsorption resins to remove
hydrophobic (HPO) NOM from solution in 6 minutes. A review of fractionation
literature identified the need for this tool, as the information provided by onsite UV254
monitors does not identify the seasonal changes in NOM type. This is needed to
enhance effluent quality whilst optimising chemical dosage. The rapid tool was used
to fractionate model compounds and natural waters, with the fractions produced
compared against the traditional column fractionation procedure.
Both fractionation tools recognised the hydrophobicity of the model compounds to be
tannic acid>1,3 acetonedicarboxylic acid>d-xylose which agreed with their log KOW
values. However, the rapid tool isolated a greater proportion of the model compound
with intermediate hydrophobicity due to a higher resin concentration than in the
traditional method. Both tools identified the same seasonal trend in the
hydrophobicity of Butterley Reservoir, but rapid fractionations produced a lower
average % HPO fraction (measured as dissolved organic carbon (DOC) removal from
the solution). This was investigated by comparing the relationship between DOC and
UV254 for control tannic acid solutions and solutions after prolonged mixing with
resin. DOC leaching from the resin was confirmed by DOC concentrations of over
9mgC/L when 10mL resin was mixed with 1L ultra pure water for 72 hours. Resin
leaching caused the HPO and transphilic (TPH) fractions to be overestimated in
column fractionation with back elution but underestimated in rapid fractionation with
mass analysis.
