Abstract
M.Sc.
The disinfection of drinking water is an important step in the water treatment
process. However, toxic (unwanted) disinfection by-products (DBPs) are often
produced during the disinfection of drinking water. One such group of DBPs are
the nitrosamines such as N-Nitrosodimethylamine (NDMA). Nitrosamines,
particularly NDMA, are highly carcinogenic, mutagenic and teratogenic. The US
Environmental Protection Agency (USEPA) placed these compounds into the
group B2, which indicates compounds of probable human carcinogens. The
USEPA integrated risk information system (IRIS) database lists an estimated 10-6
lifetime cancer risk level for NDMA in drinking water of 0.7 ng/L.
The formation of NDMA during drinking water disinfection, particularly
chloramination, has been linked to the formation of NDMA through a reaction
between monochloramine and organic nitrogen precursors via unsymmetrical
dialkylhydrazine intermediates, such as unsymmetrical dimethylhydrazine
(UDMH). UDMH is oxidized by dissolved oxygen to form NDMA. Therefore, it is
also crucial to remove NDMA precursors (UDMH and dimethylamine (DMA)),
before disinfection is carried out. Also, the chlorination of secondary wastewater
can result in the formation of NDMA.
In this research project, determination of nitrosamines, especially NDMA was done
at four different water treatment plants in South Africa. Water samples collected
from Midvaal, Sedibeng, Magalies (Vaalkop and Klipdrift) and Rand Water
treatment plants were qualitatively analysed for the presence of NDMA. Also, the
determination of possible NDMA precursors such as dimethylamine and UDMH
was investigated in water samples collected from Sedibeng water treatment plant.
The water samples were collected before and after each drinking water treatment
process (coagulation, sedimentation, filtration, chlorination and chloramination or
ozonation). Solid phase microextraction (SPME) was employed in the extraction of
the water samples. Polydimethylsiloxane/divinylbenzene (PDMS/DVB) proved to
be the most efficient fibre for the SPME extraction procedure. The water samples
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were then qualitatively analysed using gas chromatography-mass spectrometry
(GC-MS).
Very small amounts of NDMA were detected in water samples collected from
Sedibeng water treatment plant. There was no detectable presence of NDMA or
other nitrosamines in water samples collected from the other treatment plants.
Water-insoluble cyclodextrin (CD) polyurethanes were then used to ascertain how
much of the NDMA they would remove. The CD polymers showed capacity to
remove NDMA and dimethylamine (which is a known NDMA precursor) in the
water samples with 80% removal efficiency for NDMA (when comparing peak area
before and after treatment with CD polymers) and approximately 98% removal rate
for DMA.