Abstract:
Seasonal periods of high rainfall have led to difficulties in removing sufficient natural
organic matter (NOM) to meet trihalomethane (THM) standards, and hence better or
alternative treatments are required. Typically bulk water parameters such as dissolved
organic carbon (DOC) and UV absorbance at 254nm (UV254) are used to optimise
treatment processes. Here the isolated fraction character and molecular weight (MW)
distribution was used in conjunction with bulk water parameters to tailor process
options for the treatment of humic rich waters. Three options for the removal of NOM
were proposed. A staged coagulation based on the optimisation of isolated fractions.
The results showed that although no significant reduction in DOC or UV254 was
observed filter breakthrough was significantly reduced. Secondly a novel magnetic ion
exchange process (MIEX®) for the removal of NOM was evaluated. The results
showed that a combination of MIEX® and ferric reduced the THM formation potential
(THMFP) by more than 50% and lower MW compounds that are known to be untreated
by conventional coagulation were reduced. This option was also shown to be the most
robust option for the treatment of waters with differing quality caused by seasonal
changes and different catchments. Finally the addition of a range of adsorbents
including carbons, hydroxides and clays to both the raw water and the isolated low MW
fractions showed that an increase in DOC and UV254 removal was achievable. This was
proposed as a post coagulation option during times of high organic loading. All
processes provide viable options for the treatment of humic rich waters during times
when current processes are being challenged and having difficulty meeting THM
standards.
