Abstract:
Natural organic matter (NOM) is found ubiquitously in raw water and is known to react
with the chlorine used in water treatment to produce disinfection by-products (DBPs),
some of which are potentially harmful to human health due to their links with cancers.
Trihalomethanes (THMs) and haloacetic (HAAs) acids are the two types of
carbonaceous DBPs widely regulated. The THMs and HAAs are widely regarded as
being good indicators of the presence of the more than 500 other DBPs that have been
found in treated drinking water. At large and medium sites in Scotland, the coagulation-
flocculation process has long been the main control barrier for removal of the precursors
for DBPs. At small sites, ultra and nano filtration membrane filtration processes have
been considered a good solution due to their small footprint requirement and large
volume of water output. In addition, granular activated carbon (GAC) filtration has long
been employed for removal of organic matter. However, increases in the organic content
of raw waters, stricter regulatory requirements and concerns over coagulant cost and
availability have driven the reconsideration of how NOM laden water sources in
Scotland are treated. This thesis investigated the approaches required to increase the
robustness of drinking water supply to mitigate against these factors.
A stronger correlation was found between commonly measured water quality
parameters and DBPs in raw water sources compared to treated water, which was as a
result of the lower hydrophobic content of the latter. However, the DBP removal as a
function of DOC reduction was calculated and revealed coagulation using ferric sulfate
in the pH 4-5-5-5 range as the most feasible solution at large and medium sites. The use
of GAC media with high pore uniformity would be appropriate at large or medium sited
where up to 50% DOC reduction would be sufficient to control DBPs. At small sites,
the tighter pore size membranes showed improved THM precursor removal, whilst most
of these maintained a throughput of within 90% of the current membranes.
