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NOM removal from drinking water by chitosan coagulation and filtration through lightweight expanded clay aggregate filters

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Recent innovations in Norway regarding coagulation-contact filtration for the removal of natural organic matter (NOM) include chitosan as a natural and biodegradable coagulant, and filter media based on lightweight expanded clay aggregates (Filtralite). The main advantages associated with chitosan are: reduced solids production compared with conventional coagulants; and treatment and disposal of natural, biodegradable sludge, which does not contain metal hydroxides from metal-based coagulants. Filtralite can be produced with an inverse relationship between grain size and density, thus allowing an approximation to the ideal situation of decreasing grain size in the direction of flow. Traditionally, this important property of a filter bed is utilised in up-flow filters, or in dual or multimedia down-flow filters with combinations of two or more filter media. This paper presents experimental results from pilot-scale treatment of NOM-containing raw waters using chitosan for coagulation and expanded clay aggregates as filter media. A dual media anthracite-sand filter and alum coagulant was used as a reference for comparison with conventional process configurations.
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NOM removal from drinking water by chitosan
coagulation and filtration through lightweight expanded
clay aggregate filters
Bjo¨ rnar Eikebrokk and Torgeir Saltnes
Bjo¨ rnar Eikebrokk (corresponding author)
SINTEF Applied Chemistry,
Dept of Water and Wastewater,
N-7465 Trondheim,
Torgeir Saltnes
NTNU-Norwegian University of Science and
Department of Hydraulic and Environmental
N-7491 Trondheim,
Recent innovations in Norway regarding coagulation-contact filtration for the removal of natural
organic matter (NOM) include chitosan as a natural and biodegradable coagulant, and filter media
based on lightweight expanded clay aggregates (Filtralite). The main advantages associated with
chitosan are: reduced solids production compared with conventional coagulants; and treatment and
disposal of natural, biodegradable sludge, which does not contain metal hydroxides from
metal-based coagulants. Filtralite can be produced with an inverse relationship between grain size
and density, thus allowing an approximation to the ideal situation of decreasing grain size in the
direction of flow.Traditionally, this important property of a filter bed is utilised in up-flow filters, or in
dual or multimedia down-flow filters with combinations of two or more filter media. This paper
presents experimental results from pilot-scale treatment of NOM-containing raw waters using
chitosan for coagulation and expanded clay aggregates as filter media. A dual media anthracite-sand
filter and alum coagulant was used as a reference for comparison with conventional process
Key words |chitosan, coagulation, direct filtration, expanded clay aggregates, NOM removal
Natural organic matter (NOM) in drinking water has
gained a lot of attention in many countries in recent years.
The main reasons for this are concerns regarding colour,
taste and odour, known and unknown disinfection
by-products (DBP), formation of biofilms in distribution
systems, and increased availability of micro-pollutants
associated with NOM. In 1998, the applied NOM removal
technologies in Norwegian treatment plants included
coagulation and filtration (74 plants), macro-porous
anion exchange (12), nanofiltration (63), and ozonation-
biofiltration (1).
Most coagulation filtration plants apply aluminium-
based coagulants and dual media anthracite-sand filters.
Recently, some plants have shifted to iron-based coagu-
lants and calcium carbonate (CaCO
) as a filter medium in
up-flow single medium alkaline filters, or in down-flow
triple media filters with anthracite, sand and CaCO
. The
main goal is to obtain NOM-removal and corrosion con-
trol, i.e. increased levels of calcium, alkalinity and pH. A
typical scheme of a coagulation-contact filtration plant for
NOM removal and corrosion control is shown in Figure 1.
Metal-based coagulants are used with conventional dual
media anthracite-sand filters, with lime and carbon diox-
ide for pH and corrosion control purposes. Due to the
loose nature of the metal–NOM coagulation products and
the high solids production from elevated coagulant doses
required for NOM control, the filter run lengths are short
compared with those achieved in turbidity removal. In
addition, some plants have problems complying with the
admissible residual metal concentration levels. Against
this background, optimisation of coagulation and filtra-
tion design and operation are important issues, including
testing and evaluation of alternative coagulants and types
of filter media.
323 © IWA Publishing 2002 Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
In order to maintain low concentrations of DBP, water
quality standards normally regulate the maximum admis-
sible concentration levels of NOM before chlorination. In
general, the Norwegian water quality standard has set the
maximum colour and organic carbon levels to 20 mg Pt
and 5 mg TOC l
, respectively. The maximum levels
of aluminium and iron are 0.2 mg l
. However, when
used as coagulants in water treatment the maximum
admissible level is 0.1 mg l
. In contrast to the maximum
colour and TOC levels established in Norway, the US
regulations on disinfectants and DBPs (USEPA 1998)
require 0–50% removal of TOC depending on raw water
TOC and alkalinity levels. In addition, many countries
also regulate the maximum admissible level of DBP, i.e.
trihalomethanes (THM) and haloacetic acids (HAA).
In the US the term ‘enhanced coagulation’ has evolved to
describe a coagulation process optimised for NOM-
removal, which was initially designed for turbidity
removal. Enhanced coagulation normally implies the use
of elevated coagulant doses and stricter pH control to
obtain the required 0–50% reduction in TOC. In high
alkalinity waters an inorganic acid or coagulant overdos-
ing is used to reduce the pH to optimum levels, normally
in the range of 5–6. In low alkalinity raw waters, however,
a base is normally required to prevent the pH from drop-
ping below the optimum level due to the acid reaction
of the metal coagulants. The elevated coagulant dose
requirements and sludge production rates normally
associated with increased NOM removal result in rela-
tively short filter runs due to early breakthroughs, more
rapid headloss development, increased backwash water
consumption, and the need for increased sludge process-
ing and disposal capacity. The importance of these factors
is even more pronounced in direct or contact filtration
systems. In this context it is important to evaluate alterna-
tive types of coagulants with respect to the potentials for
obtaining reduced coagulant doses and sludge production
rates, as well as a more easily disposable sludge. In
addition, new types of filter media need to be considered
that may be more adapted to or tailor-made for
coagulation-contact filtration processes primarily
designed for NOM removal. In Norway there is consider-
able interest in chitosan as a natural and non-toxic
Figure 1 |Schematic of a coagulation-contact filtration process with metal-based coagulants, dual media anthracite-sand filters, and lime and carbon dioxide for pH- and corrosion
control (Ødegaard et al. 1999).
324 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
alternative to metal-based coagulants, and in lightweight
expanded clay aggregates (Filtralite) as an alternative filter
Chitosan as a coagulant
Chitosan (Figure 2) is a natural cationic biopolymer
obtained from full or partial deacetylation of chitin, the
structural polymer of the outer skeleton of insects and
crustaceans (shrimp and crab shells). The production pro-
cess involves processing of the shells, deacetylation, dry-
ing and milling. The degree of acetylation of the product
used here (Primex ChitoClear 90) is more than 90%. The
cationic charge stems from protonation of the amino
groups. In the experiments reported here the coagulant
was dissolved in hydrochloric acid, with a concentration
of the dosing solution of 10 g l
. The coagulation abilities
have been known for a long time and, as it is virtually
non-toxic, this coagulant has undoubtedly a potential also
for the coagulation of NOM (Eikebrokk 1999). The disad-
vantage is that the current price level of chitosan makes
competition with metal-based coagulants and synthetic
polymers difficult. However, few results have been pre-
sented regarding important aspects of NOM-coagulation
and filtration performance with chitosan.
Expanded clay aggregates as filter media
Lightweight expanded clay aggregates (Filtralite) are pro-
duced by burning clay at high temperatures (1100°C).
Filtralite can be produced with different porosity, i.e. dry
density. In the experiments presented here, the qualities of
Filtralite used were high density crushed (F-HC) and
normal density crushed (F-NC), with approximate wet
densities of about 1,800 and 1,200 kg m
, respectively.
Pictures of Filtralite and anthracite grains are presented in
Figure 3, illustrating well the difference in porosity for the
anthracite and Filtralite NC grains. The settling velocity of
the filter grains following bed expansion during backwash
determines the stratification and the layer structure of a
filter bed. Thus, a correct combination of grain size and
filter material (i.e. density) in the different layers is essen-
tial to obtain the required decrease in grain size and
increase in grain settling rates with depth in a down-flow
filter bed (Ives 1979). As presented in Figure 4, initial
calculations on the settling rates at transient hydraulic
conditions (Newton) of the initially produced 0.5–1.6 mm
Filtralite HC and 1.6–2.5 mm NC grains showed a risk of
intermixing of the F-HC grains below 0.8 mm with the
largest F-NC grains (above 2.3 mm). Therefore, F-NC
grains below 0.8 mm in size were removed before the start
Figure 2 |Characterisation of chitin (top) and chitosan (Smidsrød & Moe 1995).
Figure 3 |Grains of anthracite (left) and Filtralite NC (right).
Figure 4 |Calculated settling rates of Filtralite HC and NC grains at transient hydraulic
conditions (5 and 10°C). Assumed wet densities: 1,850 and 1,240 kg m−3,
325 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
of the experiments. In these calculations, the anticipated
wet densities were set to 1240 and 1850 kg m
for F-NC
and F-HC.
In order to characterise the grains by settling velocity,
30 grains covering the given size range of the two Filtralite
fractions were measured and compared with anthracite
and sand grains (Figure 5). The settling velocities of the
grains were measured in a column of water as a function of
grain storage time in water. When soaked in water, grain
density and settling rates may increase because water is
penetrating the pores. Figure 5 shows that this is true for
the high porosity grains of F-NC where settling rates
appear to increase for a period of several weeks. However,
the settling rates of grains of F-HC, anthracite and sand
are constant during storage in water. The measured set-
tling rates are lower than those calculated in Figure 4, for
F-HC grains in particular, indicating that the actual wet
densities are lower than those used for the calculations.
However, no significant overlap in settling rates between
the grains of the different fractions was detected, and the
given Filtralite fractions were applied in pilot-scale
coagulation-contact filtration experiments.
The range of raw waters tested was considered to cover
most Norwegian humic waters commonly treated by
coagulation and filtration. The raw waters had typical
colour levels from 15 (RW15) to 50 mgPt l
(RW50). The
corresponding typical organic carbon levels were 2.3 and
5 mgNPOC l
, respectively, and the range of specific
UV-absorption (SUVA) was 3.8–5 l m
Turbidity levels were in the range of 0.1–0.2 NTU. The
coagulants tested with this raw water included:
alum (ALG)
poly aluminium chloride (PAX14), and PAX with
high calcium content (Ca- PAX)
ferric chloride sulphate (JKL)
chitosan (Chi), a natural cationic biopolymer.
As an example of the performance of metal-based coagu-
lants, Figure 6 shows the minimum specific ALG-doses
required to comply with a residual aluminium standard of
0.1 mg Al l
(< 0.1 res. Al). Also shown in Figure 6 are
the doses required to obtain 70–90% colour removal and
50–60% removal of organic carbon. Dose requirements
are related to the specific UV-absorption (SUVA) of the
tested raw waters.
It can be concluded from Figure 6 that residual alu-
minium controls the minimum dose requirement for raw
waters with SUVAs of 4.3 or higher unless the required
colour or organic carbon removal exceeds 90% or 60%,
respectively. As raw water SUVA decreases below 4.3,
indicating a shift towards lower molecular weight NOM,
colour and organic carbon in particular become more
important relative to residual aluminium with respect to
Figure 5 |Average settling rates (30 grains) and sieve size analysis for grains of Filtralite NC and HC, anthracite and sand.
326 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
controlling the coagulant dose requirements. Even in that
case, removal requirements of more than about 65% and
50% with respect to colour and NPOC are needed
before NOM removal (i.e. colour or NPOC) controls the
minimum coagulant dose requirement.
The experiments were run in a pilot-scale coagulation
filtration plant shown in Figure 7, described in more detail
elsewhere (Østerhus & Eikebrokk 1994; Eikebrokk 1996).
The identical and parallel filter columns used in this
study, i.e. the anthracite-sand reference filter (F1) and the
Filtralite filter (F2) are shown in Figure 8. The Filtralite
NC and HC used in F2 had an effective size (d
and 0.84 mm, and uniformity coefficient (d
and 1.54, respectively. Dried and sieved samples taken
from the middle sections of the anthracite and sand layers
in the dual media filter (F1), showed effective sizes (d
0.82 and 0.50 mm, and uniformity coefficients (d
1.44 and 1.32, respectively.
By splitting the flow after coagulation and pH control,
possible differences in inlet water quality to the filters is
minimised. A direct comparison of the performance of the
two filters is then possible. The data from the flow meter,
on-line pH and turbidimeters (Hach Low Range 1720)
were continuously presented graphically on a PC-screen
and stored electronically.
The water sampling points (as shown in Figure 7)
were: (1) raw water (RW), (2) coagulated water (CW), and
(3) filter effluent water (FW). The raw water and filter
effluent water were characterised by:
– turbidity
true colour
Figure 6 |Specific dose requirements as function of raw water SUVA when using ALG for coagulation of the tested raw waters (Eikebrokk and Saltnes 2000).
Figure 7 |Scheme of the pilot plant used in the coagulation-filtration experiments.
Figure 8 |Scheme of the parallel anthracite-sand reference (F1) and Filtralite (F2)
327 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
total organic carbon as non-purgeable carbon,
NPOC (Dohrman DC-190)
metal coagulant residues (according to the applied
Coagulated water samples were analysed with respect to:
suspended solids (SS)
zeta potential (Coulter Delsa 440 SX).
Water samples were stored at 4°C before analysis accord-
ing to the Norwegian Standard for Water and Wastewater
analysis. In addition, samples of raw water and filter
effluent water were analysed by Aquateam a.s with respect
to molecular weight fractionation (HPLC Sigmachrome
GFC-100) and biodegradable dissolved organic carbon
(BDOC) according to procedures described by Charnock
&Kjo¨ nno¨(2000).
Evaluation criteria
Coagulation and filtration performance was evaluated on
the basis of filter effluent quality and headloss data. From
the linear relationship between headloss and time, the
slope of the line is kC
v(McEwen 1998):
vt (1)
= headloss after filtration time t
= initial head loss at time 0 (‘clean’ bed)
k = constant
= concentration of particles in filter influent
Figure 9 |Obtained colour and organic carbon removal efficiencies when using chitosan
for coagulation of the raw waters RW15 and RW50. Water temperature:
6–11°C (Eikebrokk and Saltnes 2000).
Figure 10 |A typical example of process performance with chitosan coagulation and
filtration in the parallel anthracite-sand (A-S) and Filtralite (FMM) filters
(RW50, 7.5 mg Chi l−1, 10°C, 10 m h−1, pH 5.7–5.9).
328 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
v= rate of filtration (m h
t= time of filtration (h)
In a particular case of filtration with constant conditions
regarding inlet water quality, type and dose of coagulant,
rate of filtration, etc., the equation can be simplified:
where K is a ‘constant’ depending on the type of particles
to be removed and properties of the filter bed. In the
experiments presented here comparing two filter beds that
are tested in parallel and receiving the same water, differ-
ent K-values illustrate differences in filter bed properties
and different distribution patterns of deposited particles
within the beds.
Table 1 |Process performance and filtration characteristics when using chitosan or ALG in anthracite-sand (F1) or Filtralite (F2) filter beds. (Raw water 50 (RW50) indicates a raw water
colour level of 50 mg Pt l−1)
(mg l−1)
rate (m h−1)
(gSS m−3)
Anthracite-sand (F1) Filtralite (F2)
k= K/vC0
(gSS m−2))
k= K/vC0
(gSS m−2))
201 50 Chi 7.5 10 9 0.45 0.232 0.26 0.08 0.056 0.06
205 50 Chi 5 10 6 0.34 0.144 0.23 0.09 0.031 0.05
206 50 Chi 5 7.5 7 0.30 0.114 0.22 0.06 0.028 0.05
Avg Chi 5.8 9.2 7 0.36 0.163 0.24 0.08 0.038 0.05
204 50 ALG 3.1 7.5 15 0.38 0.070 0.06 0.06 0.019 0.02
208 50 ALG 3.1 12.5 16 0.59 0.160 0.08 0.13 0.041 0.02
211 50 ALG 3.1 7.5 16 0.30 0.061 0.05 0.07 0.019 0.02
Avg ALG 3.1 10.0 16 0.42 0.097 0.06 0.09 0.026 0.02
Table 2 |Average effluent water quality data from filters F1 and F2 with ALG and Chi as coagulants (RW 50, three runs with every coagulant as shown in Table 1)
Filtr. rate
(m h−1)pH
(mgPt l−1)
Org. carbon
(mgNPOC l−1)
Removed fractions
gSS m−2)Colour
ALG-F1 10 6.5 0.42 3 1.7 0.94 0.65 0.42 0.097 0.06
ALG-F2 10 6.5 0.93 3 1.9 0.95 0.62 0.09 0.026 0.02
Chi-F1 9.2 6.5 0.09 9 3.1 0.80 0.36 0.36 0.163 0.24
Chi-F2 9.2 6.6 0.10 9 3.2 0.79 0.34 0.08 0.038 0.05
329 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
The relationship between chitosan dose and removal effi-
ciencies with respect to colour and TOC is shown in
Figure 9 (Eikebrokk 2000). It was demonstrated before
that Filtralite may serve as an efficient substitute for
anthracite in dual media filters when ALG, JKL and chi-
tosan are used for coagulation (Eikebrokk & Saltnes 2000;
Eikebrokk 2000).
A typical example of the performance of chitosan
coagulation and filtration in anthracite-sand and Filtralite
filters is presented in Figure 10. Data on process perform-
ance and filter effluent quality obtained in the experimen-
tal runs with chitosan and Filtralite are summarised in
Table 1. Table 2 presents the average values obtained with
ALG and chitosan in filters F1 and F2. Removal efficien-
cies with respect to colour and TOC are in the range of
79–80% and 34–36%, respectively. Corresponding effi-
ciencies with ALG are 94–95%, and 62–65%. The solids
production with Chi is in the range of 6–9 mg SS l
15–16 mg l
with ALG at the given dose levels of
5–7.5 mg Chi l
and 3.1 mg Al l
. The benefits of the
Filtralite filter (F2) are obvious in terms of lower initial
headloss and rate of headloss increase compared with
anthracite-sand (F1). This is true regardless of the coagu-
lant used. The typical range of optimum pH values is
5.8–6.6 with ALG and 5.0–6.5 with Chi, with typical
optimum zeta potentials of − 10 to + 20 mV. The increase
in zeta potential with increasing coagulant dosage seems
more consistent with chitosan. The filter run lengths
obtained until the occurrence of breakthrough or headloss
termination are considerably longer with chitosan than
with ALG.
Although chitosan is able to meet the TOC and colour
removal requirements in most cases, ALG turns out to be
more efficient in this respect, especially with regard to
TOC removal. When ALG is used for coagulation, the
results show that effluent turbidity is higher from filter F2
than F1. This is probably due to the increased minimum
Figure 11 |MW distribution in untreated raw waters RW15 and RW50, and in filter effluent water from anthracite-sand (F1) and
Filtralite (F2). Coagulation of RW15 (upper) and RW50 (lower) with 1.0 and 2.9 mg Al l−1 as ALG (left), and 1.6 and 7.3 mg l−1
as Chi (right).
330 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
grain size used in F2 (0.8 mm versus 0.4 mm in F1). Thus,
the relatively loose metal–NOM floc particles have a ten-
dency to penetrate the filter F2. However, when using
chitosan, effluent turbidities are low in both filters.
Figure 11 shows the distribution of TOC present in the
different molecular weight fractions in raw waters and
treated water samples, demonstrating how the different
fractions of NOM are removed in the process. It can be
seen that a large part of the total TOC is in the 5,000–
20,000 molecular weight fraction. There is a considerable
difference between the results from the two filters,
especially when coagulating the most concentrated raw
water (RW50) with ALG. There is a tendency for ALG to
be able to remove more of the lower MW fractions than
Chi, probably due to adsorption to aluminium hydroxide
From the data presented in Figure 12 it is evident that
although chitosan does not reduce TOC by more than
about 35%, the reduction in BDOC is close to 50%. This is
also indicated by the decrease in the BDOC to TOC ratio
as a result of water treatment. Hence, both ALG and Chi
are capable of removing the BDOC to a larger extent than
the DOC. It should be noted here that chitosan adds TOC,
and probably also BDOC, to the water.
The following conclusions can be drawn from this study:
1. Chitosan is able to remove colour and organic
carbon from NOM-containing raw waters. At doses
Figure 12 |Distribution of TOC in different molecular weight fractions in untreated and ALG or Chi coagulated waters (left).
Total TOC, BDOC and TOC/BDOC ratios for untreated and coagulated waters (right).Anthracite-sand filter (F1) only.
331 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
up to 7.5 mg l
, about 80% of the colour is
removed. However, the removal of organic carbon is
only 35–40%.
2. Sludge solids production with chitosan is less than
50% compared with alum.
3. Lightweight expanded clay aggregates (Filtralite) can
be used successfully as a substitute for anthracite in
dual media filters. Filtralite in two size and density
fractions (F-NC and F-HC) can also be used alone
as the only filter material. The size fractions of
1.6–2.5 mm F-NC and 0.8–1.6 F-HC used in this
study performed well although the grains of F-NC
increased in density and settling rate due to water
uptake during the first 2–3 months.
4. Because the minimum grain size used in the single
medium two-layer Filtralite filter was 0.8 mm in
order to avoid mixing of the layers, the effluent
turbidity was higher for this filter than from the
reference anthracite-sand filter when alum was used
for coagulation. However, with respect to colour and
TOC removal, no major differences were observed
between the Filtralite and the anthracite-sand
reference filters when ALG or chitosan were used as
5. When chitosan was used for coagulation, a similar
effluent quality was obtained from the Filtralite and
the anthracite-sand reference filter. However,
Filtralite was advantageous in terms of initial
headloss and rate of headloss increase.
6. Both chitosan and alum were able to remove
biodegradable organic carbon more efficiently than
dissolved organic carbon. The dominating molecular
weight fractions in the raw waters used were in the
range of 5,000–20,000.
7. Although the best TOC removal with ALG and
chitosan was achieved in the molecular weight range
of 5,000–20,000, TOC was removed to some extent
over a wide range of MW.
Charnock, C. & Kjo¨ nno¨, O. 2000 Assimilable organic carbon and
biodegradable dissolved organic carbon in Norwegian raw and
drinking waters. Wat. Res. 34(10),2629–2642.
Eikebrokk, B. 1996 Removal of humic substances by coagulation. In
Chemical Water and Wastewater Treatment V (ed. H. H. Hahn,
E. Hoffmann & H. Ødegaard), pp. 173–187. Springer-Verlag,
Eikebrokk, B. 1999 Coagulation-direct filtration of soft, low
alkalinity humic waters. Wat. Sci. Technol. 40(9),55–62.
Eikebrokk, B. 2000 Pilot scale testing of Filtralite as an alternative
to anthracite in dual media filters treating coagulated humic
waters. SINTEF report STF22 F00311, Trondheim, Norway.
Eikebrokk, B. & Saltnes, T. 2000 Removal of natural organic matter
(NOM) using different coagulants and lightweight expanded
clay aggregate filters. Proceedings IV International Conference:
Water Supply and Water Quality, 11–13 September, Krakow,
Ives, K. J. 1979 The basis for the application of multiple layer filters
to water treatment. Z. Wass. Abwass. Forsch. 12(3/4),
McEwen, J. B. (ed.) 1998 Treatment Process Selection for Particle
Removal. AWWARF/IWSA-report, Denver, Colorado.
Ødegaard, H., Eikebrokk, B. & Storhaug, R. 1999 Processes for the
removal of humic substances from water—an overview based on
Norwegian experiences. Wat. Sci. Technol. 40(9),37–46.
Østerhus, S. W. & Eikebrokk, B. 1994 Coagulation and corrosion
control for soft and coloured drinking water. In Chemical
Water and Wastewater Treatment III (ed. R. Klute & H. H.
Hahn) pp. 137–153. Springer-Verlag, Berlin.
Smidsrød, O. & Moe, S. 1995 Biopolymerkjemi. Tapir, Trondheim,
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Rule. Fed. Reg. 63:241:69478, USA.
First received 13 August 2001; accepted in revised form 29 November 2001
332 B. Eikebrokk and T.Saltnes |NOM removal using chitosan and expanded clay aggregates Journal of Water Supply: Research and Technology—AQUA |51.6 |2002
... Water pollution is one of the greatest concerns in developed and underdeveloped countries. The substantial pollution of water bodies is standard of developing countries affected by the maximum serious effects of this resource degradation, the spreading of water-related illnesses [1], [2]. Waterborne illnesses that launch parasitic and diseased microorganisms into water bodies are a result of the lack of expertise and resources to build and maintain a healthy sanitation apparatus [3], [4]. ...
... Bjӧrnar Eikebrokk et al. [1], found that: Chitosan is able to remove color and organic carbon from NOM-containing raw water. At doses up to 7.5 mg/liter−about 80% of the color is removed. ...
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Natural Organic Matter (NOM) is found in all surface waters. An increase in the amount of NOM over the past 10-20 years has been observed in raw water supply in many areas in Egypt, which has had a significant impact on drinking water treatment. Water scarcity and the increased contamination of drinking water has led to increased doses of coagulants and disinfectants used in water treatment, which has led to increased sludge volume and the production of harmful residual byproducts. In this paper, the results of experiments using an experimental model carried out to investigate improving the removal efficacy of NOM using a natural coagulant, such as chitosan, along with alum, are presented. The results show the use of chitosan is effective in removing NOM and reducing algae and turbidity. In addition, a dose of chitosan added to alum successfully reduced the amount of alum needed in the purification process.
... Due to the powers of static attraction and adsorption in the molecules and its polyelectrolytic nature, chitosan is an efficient coagulant to (i) remove particles (Divakaran & Pillai 2001;Roussy et al. 2005), turbidity (Pan et al. 1999;Chen et al. 2003;Roussy et al. 2005;Kang et al. 2007;Rizzo et al. 2008;Bina et al. 2009;Nyström et al. 2020), natural organic matter (NOM), and colored substances (Eikebrokk 1999;Liltved et al. 2001;Chiou & Li 2003;Bratskaya et al. 2004;Rizzo et al. 2008), (ii) bacteria inactivation (Chung et al. 2003), and (iii) metals removal ( Juang & Shiau 2000;Jeon & Höll 2003;Rae & Gibb 2003;Rizzo et al. 2008;Zeng et al. 2008;Zemmouri et al. 2013;Rustøen 2015). The performance of chitosan has been assessed on industrial wastewaters, and some studies have been conducted concerning the chitosan efficiency for drinking water treatment (Eikebrokk & Saltnes 2002;Fabris et al. 2010;Zemmouri et al. 2013), and less is published for road construction wastewater (Lee et al. 2013). Compared with other commonly used organic coagulants, chitosan requires less dosage and has quicker floc settling velocity, easier sludge treatment, and no secondary pollution (Lee et al. 2013). ...
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In this research, characterization of the wastewaters before and after treatment was carried out by chemical analysis and by various techniques for particle characterization. Based on the characterization, laboratory work was conducted to evaluate the effectiveness of sedimentation and the use of coagulants to remove particles and particle-associated contaminants. Both natural (i.e., chitosan) and chemical coagulants, including ferric chloride sulfates and polyaluminium chloride solution, were applied in a conventional jar-test system. The results indicated that short-time sedimentation alone substantially reduced the particle content and particle-associated pollutants, including metal(loid)s, while subsequent chemical coagulation was required to comply with discharge limits. The optimum dosages of chitosan, PIX, and PAX for water 1 after pretreatment (15 min sedimentation) were 1 mg/L, 3 mg Fe/L, and 3 mg Al/L, respectively, while a dosage of 2 mg Al/L gave the best results in water 3. Furthermore, chemical coagulation significantly decreased the volume density of particles in the diameter range of 1–100 μm, showing that coagulants are efficient for the removal of smaller particles not removed by conventional sedimentation.
... ere have been several attempts and methods that have been employed in removing heavy metals from wastewater [16]; methods such as liquid-liquid extraction [17], membrane filtration [18], chemical coagulation [19], phytoremediation [20,21], and ion exchange [22] are highly sensitive, not particularly effective, require costly equipment and instrumentation, laboratory system setup, complex procedural requirements, highly skilled personnel, and an immense recurrent expenditure and operating cost [14]. ese drawbacks make these methods unsuitable for longterm continuous use or on-site or field investigation [23]. ...
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The monocomponent adsorption process of Cu(II) ions in synthesized industrial wastewater were investigated using activated carbons (BACs) derived from sugarcane bagasse as the precursor. Batch adsorption studies were done by treating the precursor with H3PO4 (BAC-P) and ZnCl2 (BAC-Zn) in order to observe the effects of experimental variables such as contact time, pH of the solution, and adsorbent dose. The Langmuir isotherm model excellently described the adsorption data for both the derived BACs, indicating monolayer coverage on the BACs with the determination coefficients close to the value of one. Furthermore, the maximum adsorption capacities of 589 and 225 m g g − 1 at 30°C were obtained for BAC-P and BAC-Zn adsorbents, respectively. The modeling of kinetic data of Cu(II) ions adsorption onto BAC-P and BAC-Zn adsorbents illustrated that the Elovich kinetic model fitted well. Here, the adsorption process was film-diffusion controlling, while being principally governed by external mass transport where the slowest step is the diffusion of the particles through the film layer. The mechanism of the adsorption process was proposed taking into cognizance of the ion exchange and surface complexation on active sites between the negatively charged surface of the BACs and the positively charged Cu(II) ions. The BACs were characterized using analytical methods such as SEM, FTIR, EDX, XRD, BET surface area, and zeta potential measurements. Both BACs mainly composed of mesopores and bonds of O-H, C-O, C=O, and C-O-C. The BET surface area of BAC-P and BAC-Zn was 427.5 and 282 m2/g before adsorption, and their isoelectric point (pHIEP) 3.70 and 5.26, respectively.
... Chitosanul este un polimer cationic cu masă moleculară de ordinul 10 6 extras din cochilii de crustacee și a fost testat pentru utilizare în tratarea apei ca floculant dar și coagulant primar [35]. ...
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Studiile efectuate la nivel monsial au arătat că utilizarea reactivilor de coagulare-floculare asigură reducerea aldehidelor, fenolilor și aminoacizilor. Substanțele organice cu masa moleculară mare sunt ușor îndepărtate, în timp ce zaharurile și hidrații de carbon sunt relativ puțin reduși. Faza de coagulare este capabilă de a reduce 30-50% din concentrația de carbon organic biodegradabil (BDOC) și între 50-80% a carbonului organic asimilabil (AOC). Apariția coagulanților prehidrolizați și apoi a celor bicomponenți a crescut eficiența în reducerea conținutului mineral, organic şi biobacteriologic al apelor de suprafață folosite pentru potabilizare, concomitent cu obținerea unor concentrații minime de metal rezidual Într-un proces convențional de tratare a apei, coagularea și flocularea reprezintă etapele cheie ce determină destabilizarea particulelor și aglomerarea lor, care pot fi apoi eliminate prin procese de sedimentare și filtrare. Utilizarea eficientă a acestor procese ca parte a unei strategii de bariere multiple pentru reducerea materiei organice naturale și microbiene reprezintă o abordare operațională pentru producătorii de apă în asigurarea biostabilității apei livrate. Datorită complexității conceptului de biostabilitate a apei, este necesară definirea unui set de indicatori şi a unor limite acceptabile la nivel internațional. Determinările privind indicatorii de biostabilitate din punct de vedere al tehnicii de laborator trebuie să fie simple şi rapide, astfel încât să asigure implementarea de măsuri corective şi preventive.
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Turbidity reduction by coagulation-flocculation in drinking water reduces microbes and organic matter, increasing effectiveness of downstream treatment. Chitosan is a promising household water coagulant, but needs parameters for use. This study tested the effects of chitosan dose, molecular weight (MW), degree of deacetylation (DD), and functional groups on bentonite and kaolinite turbidity reduction in model household drinking water. Higher MW or DD produced greater reductions. Highest reductions were at doses 1 and 3 mg/L by MW >50,000 or >70% DD (residual turbidity <5 NTU). Higher doses did not necessarily continually increase reduction. For functional groups, 3 mg/L produced the highest reductions by lactate, acetate, and HCl, and lower reductions of kaolinite than bentonite. Doses where the point of zero charge was observed clustered around 3 mg/L. Chitosan reduced clay turbidity in water; effectiveness was influenced by dose, clay type, MW, DD, and functional groups. Reduction did not necessarily increase with MW. Bentonite had a broader effective dose range and higher reduction at the optimal dose than kaolinite. Chitosans with and without functional groups performed similarly. The best of the studied doses was 3 mg/L. Chitosans are promising for turbidity reduction in low-resource settings if combined with sedimentation and/or filtration. This article has been made Open Access thanks to the generous support of a global network of libraries as part of the Knowledge Unlatched Select initiative.
Research on microorganism reduction by physicochemical water treatment is often carried out under the assumption that the microbiological enumeration techniques are not affected by the presence of coagulants. Data presented here indicate that bacteriophage enumeration by plaque assay and RT-qPCR (reverse transcription quantitative polymerase chain reaction) can be affected by these water treatment chemicals. Treatment of water samples with an alkaline protein-rich solution prior to plaque assay and optimization of RNA extraction for RT-qPCR were implemented to minimize the interference. The improved procedures were used in order to investigate reduction of three viral pathogens and the MS2 model virus in the presence of three coagulants. A conventional aluminium coagulant was compared to alternative agents (zirconium and chitosan) in a coagulation-filtration system. The highest virus reduction, i.e., 99.9-99.99%, was provided by chitosan, while aluminium and zirconium reduced virus by 99.9% in colour-rich water and by 90% in water with less colour, implying an effect of coagulant type and raw water quality on virus reduction. Although charge characteristics of viruses were associated with virus reduction, the results reveal that the MS2 phage is a suitable model for aggregation and retention of the selected pathogens.
Organic removal contaminants reclamation has increased over the past years as it has many advantages over other treatments. Product water from water treatment plants can be chemically complex resulting in physical and biological changes during transportation in the distribution systems. The general aim of this study was to evaluate the effectiveness of biofilters for reducing the concentration of organic matter in order to produce biologically stable water, avoiding biofouling formation downstream of the process units. Enhanced coagulation and media filters of expanded clay, sand, and biological activated carbon (BAC) have been assessed. PH and coagulant dose have been optimized to achieve maximum turbidity and organic removal. Filtration stages along the operation have been monitored, measuring parameters such DOC (Dissolved Organic Carbon), UVabs (ultraviolet absorbance), BDOC (Biodegradable Organic Carbon) and AOC (Assimilable Organic Carbon). Once the biological stage was achieved and the organic removal was constant and steady along the process units, the BDOC analysis showed evidence of the outcomes of each filtration system, with BAC filters in conjunction with enhanced coagulation giving outstanding performance.
Scientists continuously search for alternative coagulants that would be able to outperform traditionally used aluminium (Al) and iron (Fe). Use of a novel metal coagulant zirconium (Zr) has been associated with enhanced organic matter reduction. On the other hand, eco-friendly non-metal solutions, such as chitosan, can provide non-Toxic sludge and water with no metal residue. In fact, Zr and chitosan have been utilized in full-scale operation by several water plants in Norway providing over 50,000 recipients in small and large municipalities with drinking water. However, the use of these two agents is limited in other parts of the world. In the present work, Zr and chitosan coagulants were tested together with Al for drinking water production in both pilot and laboratory trials. All coagulants provided high quality effluents. However, the metals showed higher efficiencies in terms of reduction of humic substances, with better performance of Zr than Al. On the other hand, the amount of suspended solids in sludge produced with chitosan was 25% of the amount produced with metal salts. Chitosan also functioned over a broad pH range without affecting the pH of the treated water.
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Chitosan and lightweight expanded clay aggregates were investigated as alternatives to traditional metal coagulants and anthracite in pilot scale coagulation-filtration experiments for the removal of natural organic matter (NOM) from drinking water. The raw water tested covered a range of colour and organic carbon of 15-50 mg Pt/L and 2-5 mg NPOC, respectively. Aluminium sulphate, poly aluminium chlorides with different calcium content, iron chloride sulphate, and chitosan coagulants were tested. The dual media filter bed was built with 0.6 m of 0.8-1.6 mm lightweight expanded clay aggregates (Filtralite) above 0.35 m of 0.4-0.8 mm sand. A conventional anthracite-sand filter with the same layer depths and grain sizes was used as a reference. In general, the maximum permissible concentration level of 0.1-mg Me/L controlled the minimum coagulant dose requirements when metal-based coagulants were used (Norwegian water quality standard). Typical NOM removal efficiencies obtained with metal coagulants were in the range of 75-90% and 40-70% with respect to colour and organic carbon, respectively. Chitosan was able to remove colour quite effectively, but this coagulant was less effective with respect to organic carbon removal. Lightweight expanded clay aggregate was a good alternative to anthracite, with lower rates of head loss build-up, and increased filter run length and filter storage capacity. Only small differences in effluent water quality were detected with the two filters.
Soft, acidic, and coloured (humic substances) surface waters with a low turbidity are commonly used for the drinking water supply in Norway. For these waters, coagulation/direct filtration combined with a process for corrosion control is one of the most interesting water treatment alternatives. In the experimental work described here, coagulation/direct filtration of water from Lake Jonsvatnet was investigated in a pilot plant using three different coagulants, alum (ALG), prepolymerized aluminium chloride (PAX14), and a calcium containing prepolymerized aluminium chloride (Ca-PAX). Magnafloc LT20 as a filter aid and three different combinations of chemicals for corrosion control purposes were also included in the pilot plant experiments: 1) lime/CO2, 2) CaCO3-slurry/CO2/NaOH, and 3) CO2/NaOH (using Ca-PAX). A dual media (hydroanthracite on top of sand) gravity filter with a total depth of 0.85 m was used in the experiments. Headloss and effluent quality in terms of pH and turbidity were monitored continuously, and colour, Ca, alkalinity, and Al were analyzed from water samples taken throughout each filter run. Optimum type of coagulant and combinations of chemicals for corrosion control were evaluated in terms of effluent quality, utilization of chemicals, cost of treatment, headloss, and length of filter run versus filter load. Satisfactory treated water quality with respect to the Norwegian water quality standards was obtained with all the applied combinations of coagulants and chemicals for corrosion control. Lake Jonsvatnet is relatively low in humic content and moderate in corrosivity. The treated water quality was approximately: colour = 3 mgPt/1, pH = 8.0, alkalinity = 1.0 meq/1, and Ca = 20 mg Ca/1. However, the utilization of chemicals, filter performance and treatment costs were largely affected by the applied combinations of coagulants and chemicals for corrosion control. The results from the investigation show that the most cost effective choice of coagulant, coagulant dosage, and coagulation pH is largely affected by the type of corrosion control process and can be considerably different for a process without water treatment for corrosion control. The results may be used to design and optimize a more cost effective overall treatment process for these types of waters.
Three types of aluminum coagulants were tested in a coagulation direct filtration pilot plant for the treatment of humic waters at three different organic carbon concentration levels, ranging from 2.4 to 4.5 mg NPOC/L (Colour 13–51 mg Pt/L). A stoichiometric relationship was found between the required coagulant dosage and raw water humics concentration. Of the three coagulants, the prepolymerized PAX 14 and Ca-PAX (Ca: Al = 7–10) was more effective than alum with respect to the coagulant dosage required in order to meet the raw water quality standards. Residual aluminum was the decisive parameter for dosage requirement. Optimum filter effluent pH was around 5.8 to 6.0, and the dosage requirement in terms of mg Al per mg NPOC was 0.33 to 0.56 for alum and 0.29 to 0.44 for the two prepolymerized aluminum chlorides. Ca-PAX was effective over a broader range of pH probably due to the calcium content. Preozonation with dosages of 0.3 to 1.4 mg O3 per mg NPOC was tested for the most concentrated water with Ca-PAX as the coagulant. Preozonation improved organic carbon removal by coagulation only marginally. For pH values below 5.6 preozonation increased residual aluminum concentrations. At higher pH values, the aluminum residuals were reduced as a result of preozonation.
Both the nature of raw water suspended solids and the trophic state of a water body are relevant in the selection and design of unit operations in drinking water production. This paper presents a practical approach towards a first assessment and selection of appropriate processes for the removal of particles and algae in surface water treatment for drinking water production, on a basis of operational experiences. The major unit operations concerned for particle and algae removal, including rapid mix, flocculation, sedimentation, flotation and filtration, are briefly reviewed and their appropriateness for removing particulate pollutants discussed. A decision tree is proposed based on two simple and easily measurable water quality parameters, such as turbidity and chlorophyll-a, allowing to define a treatment configuration corresponding to the best available demonstrated technology for a given raw water and required final water quality. (Authors)
Optimisation of coagulation-direct filtration processes with respect to efficient removal of humic substances, i.e. natural organic matter (NOM) has gained a lot of focus in many countries over the last years. This paper presents experimental results from pilot scale research studies aimed at optimising the coagulation-direct filtration process applied to soft and humic raw waters with low turbidity and alkalinity levels. Comprehensive tests of 3 types of raw waters with different NOM content, 5 types of coagulants, and 3 calcium sources for the purpose of corrosion control have been conducted. Removal efficiencies with respect to relevant water quality parameters are presented, with typical relationships between raw water NOM content, coagulant dose requirements and pH. Generally, when applying metal-based coagulants, residual metal concentration was the critical parameter regarding minimum coagulant dose requirements. Typical NOM removal efficiencies were in the range of 75–90% and 40–70% with respect to colour and organic carbon, respectively. Optimum pH conditions for the removal of NOM and/or residual metals do not always coincide with that of turbidity. The experiments also showed that poly-aluminium and ferric chlorides might have some benefits over alum in terms of dose requirements and range of optimum pH values, and that chitosan may be used for colour removal with good results.
Assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) were measured in Norwegian raw and drinking waters. Several of the water-works investigated produce a drinking water which is, or approximates to, biological stability according to the AOC analysis. The reduction of AOC by water treatment was shown to be a function of the raw water quality and the particular treatment process. Levels of AOC were generally low in Norwegian raw and drinking waters, and thus the situation appears promising with respect to controlling microbial aftergrowth during distribution. Coagulation-filtration (mainly direct filtration) trains and anionic exchange achieved significant reductions in AOC, whereas membrane filtration had little effect. Treatment plants using limited or no specific measures for removal of dissolved organic carbon (DOC) and postchlorination, increased AOC levels. Disinfection with UV light may produce less AOC than chlorination. BDOC was effectively reduced by all water treatments. Membrane filtration performed at least as well as other treatments in removing BDOC. This suggests that bulk BDOC is typically of higher molecular weight than AOC. Correlations between AOC and BDOC in raw and drinking waters were not significant. This finding supports the contention that these parameters are independent measures of the labile organic fraction of natural waters. It seems likely that the AOC and BDOC analyses target different fractions of the biodegradable organic material (BOM). When AOC and BDOC were used to evaluate the effectiveness of treatment processes the results were more promising. Correlation factors showed that these parameters generally provided complementary information about the fate of BOM during water treatment. However, because BDOC decreased during water treatment at all but one plant, whereas AOC often increased, necessitates that the raw data and the correlation factors be presented together in studies of this nature. The addition of nutrient salts in the AOC assay usually gave moderate increases in the values obtained. Consequently, nutrients other than organic carbon may limit aftergrowth in Norwegian drinking water. Use of an alternative bioassay organism gave lower AOC values, thus confirming the suitability of the standard assay organism.
Humic substances can be removed from water by a number of different treatment processes because the humic substances are high molecular weight organic molecules carrying a negative charge, like colloids. The conventional treatment method is by coagulation/floc separation, but also sorption processes like ion exchange and adsorption on activated carbon as well as membrane filtration processes and oxidatiort/biofiltration processes can be used. In this paper an overview of design and operational experiences with all these treatment processes is given based on the experiences that have been gathered in Norway during the last 25 years.
  • O Smidsrød
  • S Moe
Smidsrød, O. & Moe, S. 1995 Biopolymerkjemi. Tapir, Trondheim, Norway (in Norwegian).
Pilot scale testing of Filtralite as an alternative to anthracite in dual media filters treating coagulated humic waters
  • B Eikebrokk
Eikebrokk, B. 2000 Pilot scale testing of Filtralite as an alternative to anthracite in dual media filters treating coagulated humic waters. SINTEF report STF22 F00311, Trondheim, Norway.