One of the greatest public health achievements in the early twentieth century was
the introduction of chlorine as disinfectant in drinking water treatment plants. However it is
known that chlorine is not totally effective in inactivating spores, cysts, oocysts or virus. In
addition, since 1974 it has been proved is known that the chlorine added as a disinfectant
reacts with the organic matter present in water to give rise to chlorinated compounds among
which the ones that have attracted more attention are the trihalomethanes (THMs). Currently
THMs are considered potentially carcinogenic, genotoxic and mutagenic compounds. The
maximum concentration of THMs in water is regulated in Spain through the RD 140/2003 to
a maximum of 100 µg L-1. For these reasons currently some drinking water treatment plants
work with alternative disinfectants different to chlorine (mainly ClO2 or O3) that have greater
disinfection power and reduce THM formation.
Due to the interaction of chlorine added as disinfectant with dissolved organic
matter and the formation of disinfection byproducts, there have been numerous studies
aimed at the characterization of these organic precursors present in hydric resources. In
general dissolved organic matter consists on a hydrophobic fraction (humic and fulvic acids
and/or lignin derivatives) and a hydrophilic fraction (polysaccharides, proteins, compounds
with medium/high polarity with carbonyl and/or carboxylic groups). Humic and fulvic acids
derived from the humification process of organic matter from plants and soils are
macromolecules formed by high molecular weight compounds consisting of aromatic
substructures substituted with functional groups, mainly-OH and -COOH groups, and to a
lesser extent by saccharide and aliphatic structures. These compounds, usually represented
by phenolic units (mainly 1,3-dihydroxybenzene derivatives) have been widely accepted as
the main responsible for the formation of the disinfection by-products (DBPs). Currently,
other compounds that have gained importance in the formation of DBPs are -dicarbonyl
compounds.
Besides the natural dissolved organic matter, many compounds derived from
human activity are increasingly being detected in water supplies or drinking water. Some of
these compounds have been regulated (i.e. the presence of pesticides) but there is now a
group of emerging pollutants consisting in pharmaceutical compounds and their metabolites.
Furthermore, the presence of these compounds raises large concern on the effectiveness of
water treatment systems for the efficient removal of such and related compounds.
Given these precedents in the present study we have focused on the water quality
parameters related to dissolved organic matter and microorganisms resistant to chlorination.
Initially we proceeded to the characterization of dissolved organic matter from the
Turia river (Chapter 3). This natural water resource is one of the main sources of drinking
water to Valencia and its metropolitan area (1,500,000 consumers). Among the various
conclusions drawn from the study it is remarkable the abundance of compounds with
polysaccharides structure as well as fatty acids. It is also remarkable that unexpectedly we
did not observe the presence of humic and fulvic acids in Turia river. Humic and fulvic acids
are easily detectable by the spectroscopic techniques employed. In contrast, our study has
detected the presence of acetaminophen, a compound considered as emerging pollutant in
water supplies. Given the high content of polysaccharides in the Turia river water, we have
evaluated the behavior of carbohydrates as THM precursors by interaction with chlorine
(Chapter 4). The results indicate that although THM values generated in the reaction of
chlorine with carbohydrates are minor compared to traditional models of humic and fulvic
acids, in systems where there are high concentrations of these carbohydrates, they can
contribute significantly to the formation of THMs.
Previous studies have provide a few examples showing that metal cations (i.e.
Cu2+) can act as promoters in the formation of THMs. Based on these precedents and taking
into account the high concentration of other metal cations in natural waters we studied the
influence of the presence of ions Ca2+ and Mg2+ in the formation of THMs, of selected model
compounds and a sample from the Turia river water (Chapter 5). The results of this study
indicate that the presence of these alkali-earth ions during the chlorination process greatly
enhances the THMs formation.
Given the presence of emerging pollutants and the increasing use of alternative
disinfectants we assessed the reactivity of -lactam antibiotics (penicillin, amoxicillin and
cefadroxil, Chapter 6) and amino acids (tryptophan, tyrosine and histidine, Chapter 7)
against ClO2. The conclusion of the study is that ClO2 is effective for the elimination of
amoxicillin and cefadroxil treatment under typical conditions (pH 8, room temperature,
diluted aqueous conditions) and inefficient to degrade penicillin under these conditions.
Moreover, reaction product study under various conditions has allowed proposing a
mechanism for the reaction of ClO2 with selected antibiotics and amino acids, which agrees
with the available data and reactivity of ClO2. Finally, it was found that ClO2 pretreatment
prior to chlorination is effective for THM reduction in solutions containing these types of
compounds.
Finally, we have evaluated the disinfection effectiveness of a system based on a
photocatalytic TiO2 fiber for the disinfection of water contaminated with microorganisms
resistant to chlorination (Cryptosporidium Parvum and Giardia Lamblia, Chapter 8). The
results show that the UV/TiO2 system is effective to achieve complete disinfection of these
protozoa working in real conditions of treatment. Chlorine plays a synergistic role in the
system significantly reducing the exposure times needed to carry out the effective
disinfection.