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Research Methodology / Research Methodology (BNE)
Module Code: MHK220882 / MHH124269
CRITICAL EVALUATION OF JOURNAL PAPER
Student Number:
Programme:
Title of Journal Paper:
Author(s) :
Journal / Conference:
Volume / Issue:
Critical Evaluation done by:
Pages:
Student Name
DISSECTION OF PAPER
Section 1. Abstract (read the abstract and answer the following questions)
1. What is the objective of the paper?
The objective is to in light the people of the effects of the wastage done by the industrial water.
2. What are the contributions from the authors?
The damage and the solutions.
3. What are the main results mentioned in the abstract?
The use of organic polymer.
4. Does the abstract serve as a summary of the paper, presenting the objective, scope and results?
Yes it does, it is pointing out the issues and the treatment for it.
Section 2: Introduction (read this section and answers the following questions)
1. What ‘research problem’ is discussed in the paper?
2. What rationale is given by the authors, attributing importance to the research problem?
3. How many earlier works are cited by the authors and what are the perceived drawbacks of these
earlier works?
4. How and why the authors claim to have a better technique or approach?
Section 3: Methodology
1. What methodology is used by the authors to address the research problem?
2. In what way the methodology used by the authors is relevant to the methodology you proposed to
adopt?
Section 4: Results and Conclusions
1. List the results obtained by the authors.
2. What are the conclusions drawn by the authors from the study.
Research Methodology / Research Methodology (BNE)
Module Code: MHK220882 / MHH124269
Write a critical analysis of the paper (about 200 words)
WA T E R R ESEA RCH 41
(20 0 7 ) 23 01 – 2 32 4
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/watres
Review
Organic polyelectrolytes in water treatment
Brian Boltoa,×, John Gregoryb
CSIRO Manufacturing and Materials Technology, Private Bag 33, Clayton South, Vic 3169, Australia
Department of Civil and Environmental Engineering, University College London, Gower Street, London, WC1E 6BT, UK
a
b
a r t icleinfo
abs tr a c t
Article history:
The use of polymers in the production of drinking water is reviewed, with emphasis on the
Received 22 December 2006
nature of the impurities to be removed, the mechanisms of coagulation and flocculation,
Received in revised form
and the types of polymers commonly available. There is a focus on polymers for primary
8 March 2007
coagulation, their use as coagulant aids, in the recycling of filter backwash waters, and in
Accepted 9 March 2007
sludge thickening. Practicalities of polymer use are discussed, with particular attention to
Available online 25 April 2007
polymer toxicity, and the presence of residual polymer in the final drinking water. The
Keywords:
questions of polymer degradation and the formation of disinfection by-products are also
Water treatment
addressed.
Coagulation
Crown Copyright & 2007 Published by Elsevier Ltd. All rights reserved.
Flocculation
Residual polymer
Disinfection by-products
Contents
1.
2.
3.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2302
Natural impurities in water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2302
Polymer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2303
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2303
3.2. Characterisation of polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2303
3.3. Cationic polyelectrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2304
3.3.1. Poly(diallyldimethyl ammonium chloride). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2305
3.3.2. Epichlorohydrin/dimethylamine polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2305
3.3.3. Cationic polyacrylamides (PAMs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2305
3.3.4. Natural cationic polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2305
3.3.5. Charge densities of cationic polyelectrolytes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2306
3.4. Anionic polyelectrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2306
3.4.1. Anionic PAMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2306
3.4.2. Natural anionic polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2306
3.5. Non-ionic polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2306
3.5.1. Polyacrylamide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2307
×Corresponding author. Tel.: +61 3 9252 6489; fax: +61 3 9252 6288.
E-mail addresses: brian.bolto@csiro.au (B. Bolto), j.gregory@ucl.ac.uk (J. Gregory).
0043-1354/$ – see front matter Crown Copyright & 2007 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.watres.2007.03.012
2302
4.
5.
6.
7.
8.
1.
WA TER R ES EARCH
41 (20 07) 2 3 0 1 – 2 32 4
3.5.2. Natural non-ionic polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2307
Mechanisms of action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2307
4.1. Polymer adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2307
4.2. Polymer bridging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2308
4.3. Charge neutralisation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2309
4.4. Kinetic aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2310
4.5. Interaction with dissolved organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2311
Applications in potable water treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2312
5.1. Primary coagulation in drinking water treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2312
5.1.1. Conventional sedimentation and filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2312
5.1.2. Direct filtration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2312
5.1.3. Dissolved air flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2313
5.2. Polymers as coagulant aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2313
5.3. Recycling of filter backwash waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2313
5.4. Sludge thickening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2314
Practical aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2315
6.1. Polymer selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2315
6.2. Monitoring systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2315
6.3. Polymer toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2316
6.4. Residual polymer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2316
6.5. Polymer degradation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2317
6.6. Disinfection by-products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2317
Costs of using polyelectrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2318
Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2319
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2319
Introduction
The main applications of organic polyelectrolytes in potable
water production are in coagulation and flocculation, and in
the dewatering of treatment plant sludges. The water
production processes are usually followed by sedimentation
and filtration, although with only slightly contaminated
waters the sedimentation step may be omitted. Flotation is
an option instead of sedimentation, especially for algae-laden
waters. The sludges obtained from the various separation
processes have very high water contents and must be further
concentrated to minimise transportation costs; polymers
have a role in this sludge conditioning.
Polymers have been utilised in coagulation/flocculation
processes for water purification for at least four decades
(Kawamura, 1976). In comparison with alum, some of the
advantages flowing from the use of polymers in water
treatment are:
●
●
●
●
●
lower coagulant dose requirements,
a smaller volume of sludge,
a smaller increase in the ionic load of the treated water,
reduced level of aluminium in treated water,
cost savings of up to 25–30% (Rout et al., 1999; Nozaic et al.,
2001).
Polymers are especially beneficial in coping with the
problems of slow-settling flocs in low-temperature coagulation or in treating soft coloured waters, where they improve
settleability and increase the toughness of flocs (Faust and
Aly, 1983). The capacity of a treatment facility may be more
than doubled with the formation of larger and stronger flocs,
the rate of solid and water phase separation can be
significantly increased, and the dosage of other chemicals
lowered. Also, the range of waters that can be treated is wider.
There are disadvantages of course, with higher costs in
particular situations and environmental factors being the
main concern. There is a greater sensitivity to incorrect
dosage, with turbidity and natural organics removal less
efficient in some instances (Nozaic et al., 2001).
With a few notable exceptions (Leu and Ghosh, 1988), there
is not a great deal of published information on the relationship between polymer structure and treatment performance
in drinking water production; that is, on the influence of
molecular structure on coagulation/flocculation, on the rates
of both precipitation and sedimentation, on product water
quality and on the solids content of the final sludge. Raw
water processing normally involves physicochemical procedures, based on coagulation and flocculation of suspended
solids and colloids, and the adsorption of soluble material on
solid substrates such as metal hydroxide flocs. The focus in
this review is on the use of soluble polymers in coagulation
and flocculation processes.
2.
Natural impurities in water
The impurities present in the source water can be in the form
of dissolved and colloidal natural organic matter (NOM), as
dissolved salts, and as suspended material such as clays,
silica, microbial cells or algae. Some of the more commonly
found natural components containing organic material are, in
decreasing size order, zooplankton, phytoplankton, bacteria,
viruses, clay-humic acid complexes, humic acids, proteins,
polysaccharides, fulvic acids, and very small species such as
WATER R ESEA R CH
41 (2007) 2301 – 2324
fatty acids, carbohydrates, amino acids, and hydrocarbons. They
are formed by the biological degradation of organic life
substances (Thurman, 1985), and include highly coloured
compounds. Inorganic salts of natural origin are also present to
some degree.
Dissolved organic compounds, defined as those which will
pass through a membrane having pores of 0.45 mm size, when
measured as dissolved organic carbon (DOC), have levels in
the range 0.1–115 mg/l, with 5.75 mg/l being reported as a
global average for streams (Boggs et al., 1985). DOC poses a
problem for the water treatment industry for a number of
reasons. Apart from the aesthetic problems of colour, taste
and odour, its presence poses a health hazard because of the
formation of potentially carcinogenic chlorinated hydrocarbons when the water is disinfected with chlorine—the wellknown problem of disinfection by-products (DBPs). Furthermore, DOC exacerbates the deterioration of the microbiological water quality in distribution systems, fouls membranes
and ion-exchange resins, interferes with the oxidation of
dissolved iron and manganese to insoluble easily removed
forms, and can encourage corrosion, especially of copper, but
not always of iron (Huang and Yeh, 1993; Broo et al., 1999). It
can also block the pores of activated carbon filters, hindering
adsorption of trace organic contaminants such as taste and
odour compounds (Ding et al., 2006). Humic substances are
troublesome materials in that they have quite variable
properties, in terms of acidity (pKa 3–5), molecular weight
(MW) (several hundred to tens of thousands) and molecular
structure (mostly phenolic and carboxylic acid functionalities, but also alcohol, quinone, ether, ester, and ketone
groups). They behave as negatively charged colloids or
anionic polyelectrolytes at natural pH levels and have surface-active properties, but can interact via their hydrophobic
aromatic and aliphatic regions with non-polar pollutants
such as pesticides and polychlorinated biphenyls. Humic
substances are often present as stable complexes with metal
ions. These variable properties influence reactivity, which as
mentioned changes spatially and temporally. If the smaller
charged organic molecules are first removed from raw water
by ion exchange, as proposed in one full-scale plant (Bourke
and Slunjski, 1999), a subsequent alum clarification stage is
greatly facilitated: larger flocs are formed that settle three
times more rapidly, far less organics are left in the product
water, and only 25% of the original alum dose is required in a
conventional clarification process (Bursill et al., 1985).
Suspended particulate matter is an important component of
all natural waters. Particles can range from 10 mm or more
down to sub-micron colloidal size (Thurman, 1985). Such
material needs to be removed from potable supplies because it
supplies a surface onto which microbes can adsorb and be
protected from disinfection chemicals by a coating of slime, or
the particles themselves may be actual bacteria or oocysts of
protozoa such as Cryptosporidium. Typical suspended solids
levels are 2–200 mg/L, although they can be higher than
50,000 mg/L in flooding rivers. The particles have a substantial
organic and biological content, typically 1–20%, but are mainly
inorganic materials like silica, aluminosilicates and iron and
manganese oxides. The charge on the particles is controlled by
an adsorbed layer of NOM, as well as by the salinity and the
concentration of divalent cations in the water (Beckett and Le,
2303
1990). Humic substances can adsorb onto the particles via
surface metal cations. The surface potential of the particles is
an important parameter influencing coagulation and adsorption behaviour. It can be monitored via particle microelectrophoresis, and in natural systems is invariably negative,
irrespective of the nature of the primary particle (Beckett and
Le, 1990). The coating of organics has a strong impact on the
amount of coagulant required and the rate of coagulation,
slowing the rate markedly at low salinities, but having less of
an effect as the salinity increases (Gibbs, 1983).
3.
Polymer types
3.1.
General
Polymers used in water treatment are water soluble and
mainly synthetic in nature, although a few natural products
may be of interest. Polymers are broadly characterised by
their ionic nature: cationic, anionic and non-ionic. These will be
described separately below, after a brief discussion of polymer
properties and characterisation. Strictly, ionic polymers
should be called polyelectrolytes, although this terminology is
not always followed.
3.2.
Characterisation of polymers
The most important characteristics of polymeric flocculants are
MW and, in the case of polyelectrolytes, charge density (CD).
MW values range from a few thousand up to tens of millions.
Conventionally, polymers are regarded as having, low, medium
or high MW, corresponding to MW values in the ranges: o105,
105–106 and 4106, respectively. CD will be discussed later.
All polymers used as flocculants in water treatment, must be
water soluble. In aqueous solution polymers very often adopt a
random coil configuration, shown schematically in Fig. 1. For very
high MW polymers, the size of the coil is typically of the order of
a hundred nm, with the size being proportional to the square
root of the MW. A convenient measure of the ‘‘diameter’’ of a
polymer molecule is the root mean square (rms) value of the endto-end distance, r (see Fig. 1). For many common non-ionic
polymers, this is given (in nm) roughly by 0.06M1/2, where M is
the MW (Napper, 1983). For M ¼ 1 million this gives the rms endto-end distance as about 60 nm. Note that if a polymer chain
were fully stretched, the end-to-end distance could be up to
10 mm or more, but this is a highly unlikely arrangement. The
random coil represents the most probable configuration. The
extent of the random coil depends on the interaction between
polymer segments. If there is appreciable repulsion between
segments, then the coil expands somewhat. The most obvious
examples are polyelectrolytes, where the segments are charged.
In this case, the polymer coil can be significantly expanded and
there are important ionic strength effects. At quite high ion …
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