Natural organic matter in water characterization and treatment methods pdf
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- Natural Organic Matter in Water
- Natural Organic Matter in Water
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Approximately 77 percent of the freshwater used in the United States comes from surface-water sources and is subject to natural organic matter contamination according to the United States Geological Survey.
Natural Organic Matter in Water
Natural organic matter in aquatic systems - a South African perspective. Natural organic matter NOM is a complex heterogeneous mixture of humic HS and non-humic substances which are widespread in the aquatic environment. Other constituents are amino acids, aliphatic and aromatic hydrocarbons containing oxygen, nitrogen and hydroxyl groups.
It is the combination and proportions of these motifs which give NOM its overall polarity and reactivity. Its main origins include soils, residues of fauna and flora, microbial excrements and anthropogenic faecal loads, agriculture activities and urban landscapes. Due to the different origins of the precursor material and the extent of transformation it undergoes, the composition of NOM in different water bodies varies.
Characterization methods for NOM can be divided into three broad categories namely: i direct measuring methods, which measure the amount of organic matter in the sample; ii spectrometric methods, which measure the amount of radiation absorbed and or released by chromophores; and iii fractionation methods, which separate NOM according to size and polarity.
South Africa has 6 distinct water quality regions, and each region has a unique NOM character and quantity. Existing water treatment plants do not remove NOM to levels low enough to inhibit the formation of disinfection by-products DBPs. Currently, research is focusing more on the use of alternative techniques for NOM removal; these include advanced oxidation processes AOPs , nanomaterials, and ceramic membranes.
While NOM is well studied in other parts of the world, to the best of our knowledge, there is no state-of-the-art investigation of the occurrence and removal of NOM in South African source waters.
This review aims at i synthesizing literature on the nature, occurrence and ecological impact of NOM, ii evaluating the removal of NOM in the six different water quality regions of South Africa, and iii suggesting novel approaches that can be used to remove NOM in South Africa.
Keywords : advanced oxidation, ceramic membranes, disinfection byproducts, treatability, water treatment. The rapid growth of the human population and the emergence of rapid industrialization and agricultural activities have brought about an increase in organic and other pollutants in drinking water systems.
Organic pollutants are broadly classified as man-made organics and natural organics. These are the product of the degradation of animal, plant and microorganism remains, including microbial excretions Lavonen, Pedogenic refractory organic matter refers to fulvic acid components found in soil. NOM can be derived from both the sources within the aquatic environment autochtonous and from external sources allochthonous Wershaw et al. Basically, the allochtonous NOM is dependent on the type of plant and animal remains that finds its way to the water sources.
In plants, for instance, the soluble compounds that can easily leach from the plant tissue are the main components of NOM Wershaw et al. Previous studies have shown that allochthonous NOM is typically enriched in fulvic acids and is highly aromatic and coloured, while autochthonous NOM is characterised by a lower fulvic acid content and C:N ratio Lee, ; Rostad et al.
Thus NOM is composed of different organic compounds, from highly aliphatic to highly coloured aromatic compounds Matilainen et al. It consists of lignin, cutin, proteins, polyphenols and other polymers as its main building blocks Wu et al.
Because of the negatively charged carboxylic groups found on its surface, NOM carries an overall negative charge with a range of molecular sizes and chemical compositions Anderson, For this reason, NOM has hydrophilic, hydrophobic, and transphilic components Matilainen et al. The hydrophobic component consists of fulvic and humic acids, is made up of phenolic structures, aromatic carbon and conjugated double bonds, and is responsible for the brownish colour observed in most surface water sources Goslan et al.
In addition to aesthetic problems such as colour, taste and odour, NOM also contributes to the fouling of filtration membranes, serves as a precursor for disinfection by-products DBPs. The major difference between the humic and fulvic acids is based on their solubility, with humic acids soluble only at higher pH levels and fulvics soluble at all pH levels Chen et al.
Research has shown that humic acids and humin are recalcitrant to microbial degradation Grinhut et al. The charge density of both humic and non-humic substances is not uniform, with the humics having higher charge density compared to the non-humics.
Because of this, humic substances can be easily removed in water using techniques such as coagulation Rostad et al. The other differences between humic acid and fluvic acid are based on the molecular weight, numbers of functional groups carboxyl, phenolic OH and extent of polymerisation Lee, The molecular weight distributions for aquatic fulvic acid and humic acid are reported to be from to 2 Da and 2 to 5 Da, respectively Lee, Overall, NOM is mainly composed of carbon, oxygen, hydrogen and nitrogen elements Lee, , with humic acids having the lower content of oxygen but being higher in carbon Lee, Conversely, the hydrophilic component has a high content of aliphatic carbons and nitrogenous compounds, such as amino acids, carbohydrates and sugars Matilainen et al.
The transphilic component is made up of a mixture of hydrocarbon and carboxyl compounds, aliphatic amides, alcohols, aldehydes, esters, polysaccharides, and ketones with less than 5 carbons. The characteristics and amount of NOM depend on the climate, topography and geology, and the type of agricultural and industrial activities practised at a certain location Nkambule et al. PdO species appeared on the surface of the TiO 2.
While upland and agricultural locations with dense vegetation have very turbid runoff with a high content of humic substances, lowland areas are generally high in non-humic substances Rostad et al. Moreover, due to climate change, changes in soil acidity and land use variations over the years, the quantity of NOM has increased in water sources Rostad et al.
While NOM is fairly well researched in other parts of the world e. Taiwan - Lee et al. This review therefore aims at i synthesizing literature on the nature, occurrence and ecological impact of natural organic matter, ii evaluating the removal of natural organic matter in the 6 different water quality regions of South Africa, and iii suggesting novel approaches that can be used to remove natural organic matter in South Africa.
Ecological impacts of natural organic matter. Although NOM in natural waters poses no known harm, its occurrence in raw water poses a challenge to water treatment plants WTPs Haarhoff et al. Such challenges include: i the presence of NOM imparts repulsive organoleptic properties to water; ii NOM combines with pollutants and also provides a shielding surface for microorganisms, this leads to increased coagulant dosage, oxidants and disinfectants required for drinking water treatment; iii NOM reacts with disinfectants e.
Water disinfection is one of the fundamental developments in the past century for improving human health Latifoglu, ; Bond et al. Disinfecting water is important because it kills micro-organisms that can cause waterborne diseases such as cholera, with chlorine being the preferred disinfectant because of its high oxidising potential Latifoglu, ; Gopal et al.
The presence of NOM in water results in the formation of disinfection by-products DBPs during the disinfection step chlorination of the water treatment plant Nkambule et al. More than DBP compounds have been identified and their formation in drinking water is based on various factors such as pH, temperature, contact time, dose, inorganic compounds, the type of NOM present in water, and the treatment processes being used Gopal et al. Previous studies have shown that the highest contributor of DBP precursors is the hydrophilic fraction of NOM; however, even the hydrophobic fraction contributes to the disinfection by-product formation DBPF if it is not effectively removed after coagulation Matilainen and Sillanpaa, ; Li et al.
Thus, understanding the composition of both the hydrophilic and hydrophobic fractions of NOM will have a positive impact towards the choice of remediation approach to remove DBPs from water. THMs are volatile and can be categorised into chlororform, bromoform dichlorobromomethane and dibromochloromethane Cedergren et al. Various alternative approaches have been suggested and tested to be effective in one way or the other compared to the use of chlorine as a disinfectant Gopal et al.
Other researchers prefer the use of chloramine as a disinfectant instead of chlorine Pifer and Fairey, However, switching to chloramine disinfectant has some disadvantages such as corrosion in the distribution system and also increased occurrence of nitrification Pifer and Fairey, Moreover, it is less effective compared to chlorine due to the fact that it requires longer contact time and produces volatile by-products that are responsible for bad taste and malodour in water Gopal et al.
In addition, the use of iodine and bromine can result in the formation of more hazardous DBPs compared to the chlorinated precursors because they are highly reactive to the hydrophilic fraction of NOM Matilainen and Sillanpaa, ; Li et al. Characterisation of natural organic matter.
Direct measuring methods. While DOC is the organic carbon present in water after it has been filtered through a 0.
The evolved CO 2 is then subsequently measured using infra-red spectroscopy Matilainen et al. Spectrometric methods. Ultraviolet-visible spectroscopy. Research has shown that any wavelength within the range nm is suitable for NOM measurement Matilainen et al.
However, due to the range of chromophores present in NOM, the molar absorptivity values vary. Matilainen et al. Fluorescence excitation-emission matrix spectroscopy. Up to the mids, synchronous fluorescence spectroscopy was commonly used for monitoring NOM in drinking water plants. The disadvantage, however, is this technique does not measure the entire EEM, but only one or two characteristic peaks.
Generally, fluorescence is used to determine the presence of biodegradable NOM in water Matilainen et al. The development of FEEM spectroscopy enabled more rapid qualitative determination of NOM components, and, when coupled to modelling techniques, can quantify these components.
FEEM spectroscopy is used to determine various forms of humic substances by collecting all the emission spectra at different excitation wavelengths Baghoth, The location and size of the resulting peaks depend on the composition of NOM present in water.
This method is particularly important because of its ability to detect changes in properties of the species of interest. It models FEEM data into individual components of fluorophores, and can segregate components into protein-like and humic-like forms Nkambule et al. While rudimentary peak-picking methods were previously used to identify the fluorescence components of a sample, PARAFAC is more robust because it permits individual components of NOM to be extracted for further analysis Pifer and Fairey, Fractionation methods.
One of the transformations NOM undergoes along the treatment train is changes in polarity Rosario-Ortiz et al. This transformation can be simulated at laboratory scale using the polarity rapid assessment PRAM methodallowing an accurate representation of its polarity as it exists in the environment. Additionally, analysis only requires mL of sample and can be performed in 2 h.
In this paper, the underlying theory of the method is presented, followed by its optimization, with emphasis on the development of conditions for the analysis of NOM in natural waters. A series of organic probe compounds showed that the most important physicochemical property describing the interaction between the NOM and the SPE sorbents was the hydrophobic surface area, allowing for the estimation of the hydrophobic character under ambient conditions.
Evaluation of the effects of chemical concentration, pH, and ionic strength show that 1, which relies on the preferential adsorption of NOM fractions on solid phase extraction SPE sorbents Table 1. This method produces 9 fractions of NOM, namely: hydrophobic acid, base and neutral; hydrophilic acid, base and neutral, and transphilic acid, base and neutral. This method was further modified to produce 3 fractions, namely, hydrophobic, hydrophilic and transphilic Nkambule et al.
These fractions give the same information as the original PRAM method. Once the fractions making up the bulk NOM are isolated, they can then be individually characterized in order to gain more insight, in order to remove the prevalent NOM.
Each of these techniques yields specific information, and each method employed individually does not give conclusive data on the character of NOM.
Thus, a series of characterization techniques is employed to give detailed information. It is important to firstly identify NOM character, as the type of organics present will affect both the choice of treatment process and its performance Jefferson and Goslan, Most of these techniques are expensive, time consuming, and involve a lot of chemical procedures to produce clean resins and for regeneration, and hence cannot be used for routine water quality monitoring.
Natural organic matter removal approaches. Research has shown that water availability problems are expected to increase in the coming years even in those regions that are currently recognized as water rich Nkambule et al.
This challenge requires intensive research to identify effective and robust new methods for water treatment at low cost using less energy, while minimizing the use of chemicals which could have negative impacts on the environment.
To remove organic pollutants, most WTPs include some of the following processes: i coagulation; ii adsorption using granular activated carbon GAC and ion exchangers; iii filtration using micro-filtration membranes MF , ultra-filtration UF , nano-filtration NF , reverse osmosis RO , and ceramic membranes; and iv bioremediation.
Coagulation has been used to reduce colour, turbidity and to eliminate pathogens during the water treatment process Anderson, However, the conditions used for colour removal and turbidity are not exactly the same for those for NOM removal, thus, enhanced coagulation is used.
Nevertheless, increasing the coagulant dosage will increase production of sludge , the disposal of which is problematic due to the high content of metal ions Murray and Parsons,
Natural Organic Matter in Water
Organic matter , organic material , or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial and aquatic environments. It is matter composed of organic compounds that have come from the remains of organisms such as plants and animals and their waste products in the environment. Organic matter is very important in the movement of nutrients in the environment and plays a role in water retention on the surface of the planet. Living organisms are composed of organic compounds. In life they secrete or excrete organic materials into their environment, shed body parts such as leaves and roots and after organisms die, their bodies are broken down by bacterial and fungal action.
Such variability is posing a serious challenge to most water treatment technologies, especially the ones designed to treat drinking water … 3. No natural cutoff exists between these two fractions and the distinction is arbitrary, based on the filtration of the sample. Availability of drinking water is essential for all living organisms on the planet. One is water containing humic acid, which is commercially available. These reference NOM sam ples contain not only the hydrophobic and hydrophilic acids but also other soluble organic solutes that are 2. NOM can cause major problems as it is converted into disin-fection by-products DBPs when chlorine is used during water treatment Krasner et al.
These metrics are regularly updated to reflect usage leading up to the last few days. Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts. The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric. Find more information on the Altmetric Attention Score and how the score is calculated. High performance size exclusion chromatography HPSEC was used to obtain the molecular weight distributions of natural organic matter NOM from two South Australian drinking water sources.
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Natural organic matter in aquatic systems - a South African perspective. Natural organic matter NOM is a complex heterogeneous mixture of humic HS and non-humic substances which are widespread in the aquatic environment. Other constituents are amino acids, aliphatic and aromatic hydrocarbons containing oxygen, nitrogen and hydroxyl groups. It is the combination and proportions of these motifs which give NOM its overall polarity and reactivity.
Please purchase via www. Author s : Mika Sillanpaa. Binding: Paperback. An essential resource containing the latest breakthroughs in the characterization, treatment and removal of Natural Organic Matter NOM from drinking water, Natural Organic Matter in Waters: Characterization and Treatment Methods focuses on advance filtration and treatment options, and processes for reducing disinfection by-products. Based on the author's years of research and field experience, this book begins with the characterization of NOM including: general parameters, isolation and concentration, fractionation, composition and structural analysis and biological testing.
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