► NOM has to be removed from drinking water for practical and hygienic reasons. ► To improve NOM removal, characterisation and quantification of NOM is important. ► Several different methods are used ...in NOM characterisation. ► This review highlights most of these used methods.
Natural organic matter (NOM) is found in all surface, ground and soil waters. During recent decades, reports worldwide show a continuing increase in the color and NOM of the surface water, which has an adverse affect on drinking water purification. For several practical and hygienic reasons, the presence of NOM is undesirable in drinking water. Various technologies have been proposed for NOM removal with varying degrees of success. The properties and amount of NOM, however, can significantly affect the process efficiency. In order to improve and optimise these processes, the characterisation and quantification of NOM at different purification and treatment processes stages is important. It is also important to be able to understand and predict the reactivity of NOM or its fractions in different steps of the treatment. Methods used in the characterisation of NOM include resin adsorption, size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, and fluorescence spectroscopy. The amount of NOM in water has been predicted with parameters including UV–Vis, total organic carbon (TOC), and specific UV-absorbance (SUVA). Recently, methods by which NOM structures can be more precisely determined have been developed; pyrolysis gas chromatography-mass spectrometry (Py-GC–MS), multidimensional NMR techniques, and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The present review focuses on the methods used for characterisation and quantification of NOM in relation to drinking water treatment.
The Tibetan Plateau covers an area of about one fourth of Europe, has an average elevation over 4000
m above sea level, and is the water sources for about 40% of world's population. In order to ...foresee future changes in water quality, it is important to understand what pressures are governing the spatial variation in water chemistry. In this paper the chemistry including major ions and trace elements in the headwaters of four major Asian rivers (i.e. the Salween, Mekong, Yangtze River and Yarlung Tsangpo) in the Tibetan Plateau was studied. The results showed that the content of dissolved salts in these Tibetan rivers was relatively high compared to waters from other parts of the world. The chemical composition of the four rivers were rather similar, with Ca
2+ and HCO
3
− being the dominating ions. The exception was the Yangtze River on the Plateau, which was enriched in Na
+, Cl
−, SO
4
2− and Li due to silicate weathering followed by strong evaporation caused by a negative water balance, dissolution of evaporites in the catchment and some drainage from saline lakes. The concentrations of heavy metals (Cu, Co, Cr, Ni, Cd, Pb, and Hg) and As, NH
4
+ were generally low in all the rivers. Anthropogenic impacts on the quality of the rivers were identified at a few locations in the Mekong River and Yarlung Tsangpo basins. Generally, the main spatial variation in chemical compositions of these under studied rivers was found to be governed mainly by difference in geological variation and regional climatic-environment. Climate change is, therefore, one of main determining factors on the water chemical characteristics of these headwaters of Asian major rivers in the Tibetan Plateau.
Nearly 20
years of industrial scale metal mining operations in Tibet have caused an impact on the region's surface water quality. However, no information with respect to the pollution has been ...provided to the public. The aim of this work was to evaluate the chemical quality of the stream water and to assess the present and future potential risks of acid mine drainage to the regional and downstream environments.
This study, based on data collected in 2006, 2007 and 2008 in the Gyama valley, using the Environmental Risk Index (
I
ER) documents that elevated concentrations of Cu, Pb, Zn, Mn, Fe and Al in the surface water and streambed at the upper/middle part of the valley pose a considerably high risk to the local environment. In contrast, the risk level at the stream source area is zero and only minor risk at the lower reaches. The iron and copper contamination of the upper/middle part of the river appears to be both natural and accelerated by the mining activities. The level of dissolved contaminants in the water decreases within short distance downstream due to precipitation and sorption to the streambed and strong dilution by a tributary stream and eventually by the Lhasa River.
A high content of heavy metals in the stream sediments as well as in a number of tailings with gangue and material from the ore processing, poses a great potential threat to the downstream water users. Environmental changes such as global warming or increased mining activity may increase the mobility of these pools of heavy metals.
The water used by 85% of the Asian population originates in Tibetan Plateau. During April and May of 2006, water samples were collected from four major Asian rivers in the Plateau (i.e. the Salween, ...Mekong, Yangtze River and Yarlung Tsangpo) and analyzed for Cu, Pb, Zn, Ag, Mo, Cd, Co, Cr, Ni, Li, Mn, Al, Fe, Mg and Hg. The results showed that elements such as Mg were rather high in Tibetan rivers, giving a mean electrical conductance of 36
mS/m. In a few locations, the results also showed relatively high concentrations of Al and Fe (>1
mg/L). However, the concentrations of Cu, Zn, Ag, Cd, and Cr were generally low. Contamination with Pb was identified at a few locations in the Salween and Ni at a few sites in the Yangtze River.
For the first time, total dissolved metal contents in source water of four major Asian rivers were evaluated at the same time.
UV-induced transformation of dissolved organic matter (DOC) is often accompanied by reduction of molecular weight and aromaticity and an increase of low-molecular weight (LMW) matter that can be ...utilized as a substrate by heterotrophic bacteria. Moreover, the generation of reactive transients and mineralization of DOC occurs. For a better understanding of the modification that starts after irradiation and to distinguish between possible chemical and biological modifications, we selected different natural organic matter (NOM) from Norway and Germany. The aqueous solutions were treated by UV irradiation and divided into two aliquot samples. NaN
3
anti-bacterial treatment was applied to one sample, and high-pressure size-exclusion chromatography (HPSEC) analysis was used for both. In all samples, we found typical modifications of NOM after UV irradiation. Incubation (>7 days) of UV-irradiated NOM samples resulted in lower levels of LMW matter and increased aromaticity. Parallel to these changes of carbon fractions, an increase in bacterial cell numbers was observed. Addition of NaN
3
to NOM, however, inhibited the reduction of LMW matter, indicating that microbial activity accounted for the observed changes in NOM. Analysis of the bacterial community composition by denaturing gradient gel electrophoresis (DGGE) of the amplified 16S rRNA genes revealed that bacterial communities of non-irradiated and UV-irradiated NOM were different and that UV selected for specific members of α-proteobacteria, β-proteobacteria, and Bacteriodetes. Our results imply that after UV-irradiation of NOM, specific bacterial members are well adapted to low pH, high LMW DOC concentrations, and oxidative stress, and therefore thrive well on UV-irradiated humic matter.
It has been generally accepted, during the last few decades, that the dissolved natural organic matter in water DNOM appearing as yellow brownish color, has become more and more “polluted” by ...inorganic and organic micro-pollutants. Due to the complexing properties of NOM, lipophilic organic micro-pollutants, such as, PCBs will be mobilized into water together with the DNOM.
A mixture of eight PCBs, with Cl-content from tri-Cl to hepta-Cl, was added to solutions of ten different DNOMs. The DNOMs were aqua’s solutions of RO-(reverse osmosis)-isolated material, having approximately the same concentration of carbon. After a contact time of three days, standard analytical PCB-method was used to determine the recovery of the added PCBs.
The results show that the analytical availability of the added PCB was significantly reduced in the presence DNOM, compared to distilled water. The percentage loss in recovery of PCB increased with the content of Cl, in mean, from 3%/mg C for tri-Cl to 9%/mg C for hepta-Cl. The results also suggest that the analytical recovery of PCB was affected by the quality and the nature of the organic matter. For example the longer the DNOMs had been in the aquatic phase, the less efficient they are attached to the PCBs.
In a "large-scale-catchment-manipulation-research-project", a dystrophic lake was divided into two halves by means of a plastic curtain, from the middle of the natural outlet to the opposite shore. ...Since fall 1990, one lake half and the corresponding catchment has been sprinkled with artificial acid precipitation, while the other was left untouched. The catchment acidification experiment took place in an area of Norway receiving little acid rain. During a few day period in October 1994, after four years of acidification, the natural organic matter (NOM) from 2270 l of water was isolated from each of the two sides of the lake, using the following sequential technique: coarse filtration; exchange of cations with Na super(+); concentrate organic solutes from 2270 l of water to 70 l by means of reverse osmosis membranes; filtration of the 70 l through 0.45 mu m membranes; concentration to 4-5 l by evaporation at low pressure and at 30 degree C; freeze drying (yield 70-75 g). Small portions of both isolates (100-200 mg) were distributed to a number of different laboratories in Europe and North America for analyses. Characteristic data, such as distribution of ions, proton- and copper binding capacity, content of metals, content of organic S, organic N, free- and hydrolysable amino acids are reported here. A number of analytical techniques were used, including UV-VIS, IR and fluorescence spectrophotometry, C-13 NMR; pyrolysis, GC/MS and HPLC. Studies on adsorption- and flocculation abilities of the two "water qualities" and formation of trihalomethanes (THM) upon chlorination, is also included. The results from 10 different laboratories are presented and similarities and differences between the two semi-identical samples are discussed. Some studies of the consequence of the isolation step on the quality of the NOM, are also discussed.
The chemistry of a limed lake and its main tributaries were studied for 3 years (1992–94) with an emphasis on natural organic matter (NOM). Increased transparency and decreased water colour indicated ...a general reduction of NOM in the lake. Increased A
254
nm
/A
410
nm
ratios in the epilimnion during summer and early autumn suggested degradation of higher molecular size organic matter into low molecular size NOM. Increase in ammonium and dissolved inorganic carbon concentrations in the lake was possibly due to the NOM degradation. Using budget calculations and the literature values, photodegradation and microbial activity were estimated to be the main mechanisms of the NOM removal. These mechanisms accounted for about 30–35% and 60–65% of the total loss of organic matter, respectively, in the summer and early autumn period. Low sedimentation rates indicate that co-precipitation of organic matter with calcium, aluminium and/or iron was of minor importance in these seasons.
Relationships among different spectroscopic, chemical, and biological properties of dissolved natural organic matter (NOM) were investigated. NOM samples were isolated by means of reverse osmosis ...from eight Norwegian lakes. Elemental composition, absorption spectra (UV, VIS, IR), the influence on algal growth, and accumulation rates of metals by mussels in the presence of NOM were measured. Linear regression and principal components analyses were utilised to assess relationships between the biological and chemical properties. It was concluded that the content of organic matter in the isolates and the aromaticity of NOM, as characterised by UV and VIS spectra, are best correlated with the biological properties.
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