ArticlePDF Available

Turbidity removal improvement for Yangtze River raw water

Authors:

Abstract and Figures

Coagulation-flocculation followed by sedimentation and filtration is the most commonly used water treatment process, in which turbidity or particle removal is strongly dependent on proper coagulant dosage, flocculation mixing time, mixing intensity (Gt), and effective size (ES) of filter media. Jar tests and filtration column tests were preformed in this study to evaluate the turbidity removal of the Yangtze River raw water that has medium turbidity and low dissolved organic matters. The new internal standard of 1 NTU for settled water and 0.2 NTU for outlet water were targeted. Operational conditions of primary flocculation (coagulant amount, mixing time and Gt), secondary flocculation, and filter media ES, were tested. Results showed that under the same amount of coagulant, longer flocculation time and higher Gt with tapered mixing can enhance the turbidity removal. The optimal dosage and Gt were estimated as 12 mg l PACL and 29,000, respectively. Secondary flocculation further reduced the turbidity of settled water by 80%, suggesting that the smaller particles retained in the primary settled water was focculable. Compared to using 0.95 mm ES, using 0.65 mm ES as filter media obtained higher turbidity removal and can lower the residual turbidity to 0.15 NTU.
Content may be subject to copyright.
Desalination and Water Treatment
www.deswater.com
1944-3994/1944-3986 © 2012 Desalination Publications. All rights reserved
doi: 10/5004/dwt.2012.3262
*Corresponding author.
45 (2012) 215–221
July
Turbidity removal improvement for Yangtze River raw water
Chin Nang Lei
a
, In Chio Lou
a,b,
*, Heng Un Song
b
, Pei Sun
b
a
Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau,
Av. Padre Tomás Pereira, Taipa, Macau SAR
b
Sino French Water Development Co. Ltd., 718 Avenda do Conselheiro Borja, Macau SAR., P.R.China
Tel. +853 8397 8469; Fax: +853 2883 8314; email: iclou@umac.mo
Received 9 September 2011; Accepted 8 November 2011
ABSTRACT
Coagulation-fl occulation followed by sedimentation and fi ltration is the most commonly used
water treatment process, in which turbidity or particle removal is strongly dependent on proper
coagulant dosage, fl occulation mixing time, mixing intensity (Gt), and effective size (ES) of
lter media. Jar tests and fi ltration column tests were preformed in this study to evaluate the
turbidity removal of the Yangtze River raw water that has medium turbidity and low dissolved
organic matters. The new internal standard of 1 NTU for settled water and 0.2 NTU for outlet
water were targeted. Operational conditions of primary fl occulation (coagulant amount, mix-
ing time and Gt), secondary fl occulation, and fi lter media ES, were tested. Results showed that
under the same amount of coagulant, longer occulation time and higher Gt with tapered mix-
ing can enhance the turbidity removal. The optimal dosage and Gt were estimated as 12 mg l
−1
PACL and 29,000, respectively. Secondary fl occulation further reduced the turbidity of settled
water by 80%, suggesting that the smaller particles retained in the primary settled water was
focculable. Compared to using 0.95 mm ES, using 0.65 mm ES as fi lter media obtained higher
turbidity removal and can lower the residual turbidity to 0.15 NTU.
Keywords: Coagulation; Filtration; Optimization; Turbidity; Particle size; Yangtze River
1. Introduction
Today, increasing regulatory pressure, cost compe-
tition and occurrence of process upset require that the
water business units consider more thoroughly on the
treatment process, ensuring that each water parameter
can meet the regulation with the lowest amounts of
chemicals and power consumed. Turbidity is the princi-
ple parameter, which is caused by the suspended matters
or impurities, interfering with the clarity of the water.
Positive correlation between turbidity and pathogens
has been reported in previous studies, and high residual
turbidity in the treated water may promote the re-
growth of pathogens in the distribution system, leading
to waterborne disease outbreaks [1,2]. Thus the US regu-
latory limit for treated water turbidity has reduced from
1 NTU in 1989 to 0.3 NTU in 2002, and some water utili-
ties are even committed to a lower internal guideline of
less than 0.1 NTU to guard against pathogen contamina-
tion [3]. However, ineffi ciency of turbidity removal in
conventional water treatment process (coagulation-fl oc-
culation-fi ltration) is occasionally observed, particularly
in the developing countries.
Coagulant dosage and hydrodynamic environment
are the two important factors affecting the effi ciency
of coagulation-fl occulation [4]. The amount of coagu-
lant added is determined by the levels of pH, salts and
Downloaded by [University of Macau Library] at 01:04 16 May 2012
C.N. Lei et al. / Desalination and Water Treatment 45 (2012) 215–221
216
alkalinity in raw water, while the degree or extent of fl oc-
culation is controlled by the applied velocity gradients
(G) and the time of fl occulation (t) [3]. If the mixing is too
mild, it is diffi cult for the fl ocs to grow and requires a lon-
ger fl occulation time; if the mixing is too intensive, the
already formed fl ocs may re-disperse again [5–7]. In prac-
tice, jar test is usually carried out to determine the opti-
mal coagulant amount and mixing intensity (
Gt) required.
To further remove residual turbidity before fi ltration,
a secondary fl occulation for the primary settled water
can be considered to produce an effl uent with lower sus-
pended solids concentration [8]. During secondary fl oc-
culation, the surface charge of the small particles can be
neutralized and larger particles may be formed. How-
ever, additional secondary fl occulation tank with pump-
ing and mixing accessories is necessary to be installed
in the plants.
Another factor controlling the turbidity removal is
ES of the fi lter media. The performance of the fi ltration
process depends on two distinct steps: (1) the transport
of the particles to the surface of the solid-liquid inter-
face of the media and (2) attachment of these particles
onto the media or other particles which have previ-
ously been deposited on the media [9,10]. The trans-
port mechanisms of the particles within the fi lter media
include interception, diffusion and sedimentation, and
the size of the particles to be removed is a dominant
parameter determining the transport mechanism of the
particles [11]. For this reason, changing media size and/
or particle size may enhance the transport mechanism
[12]. Filter aids are sometimes added to increase the size
of the particles by inter-bridging the particles [13].
Due to the new Chinese National Drinking Water
Quality Standard (GB 5749-2006), in which a more
stringent monitoring scheme for turbidity and micro-
biological risk parameters was established, the coagu-
lation-fl occulation-fi ltration process of Changshu WTP
was evaluated in this study in order to improve the tur-
bidity removal of Yangtze River raw water, for comply-
ing with the new internal guideline set for the Chinese
Subsidiaries of Suez Environment, 1 NTU for settled
water and 0.2 NTU for outlet water. The amount of
coagulant, fl occulation mixing time and intensity, sec-
ondary fl occulation, and the ES of fi lter media were
investigated.
2. Materials and methods
2.1. Changshu full-scale WTP
Changshu WTP, located in the downstream of Yang-
tze River, is a subsidiary of SUEZ Environment WTP and
also the largest WTP in Changshu city, with a maximum
daily production capacity of 400,000 m
3
d
−1
. The raw
water has medium turbidity and low dissolved organic
matter, and is treated with the conventional coagulation-
occulation-sedimentation-fi ltration process. Polyalu-
minum Chloride (PACl) is used as coagulant, and the
occulator is designed to be in four compartments to
provide different mixing strengths, with the approximate
Gt value of 14,500. Filter media with an 0.95 mm ES are
currently used.
2.2. Jar tests
Coagulation jar tests were conducted in 1 l plexiglass
beakers using a programmable jar testing apparatus,
Model ZR4-6 (Zhongrun, China), and operated under
several mixing scenarios that mimicked different slow
mixing scenarios. Mixing intensity was quantifi ed by
the Gt value. Liquid PACl with Al
2
O
3
content of 10–11%
and 70–75% in base saturation degree (Tianshu Purifi ca-
tion Material Co. Ltd, Tianjin), were used as coagulant
and a stock solution of 10,000 mg l
−1
PACl was prepared
before the test. Supernatant samples were withdrawn at
2 cm below the water surface. Coagulation dosage was
measured by a calibrated pipette.
2.2.1. Determination of optimal coagulant dosage
The mixing simulated the in-practice operation by
using a 3 min rapid mixing followed by 20 min slow
mixing, with the corresponding fi xed rotation speeds of
250 rpm (G = 102.5 s
−1
) and 40 rpm (G = 11.9 s
−1
), respec-
tively. The Gt value for the fl occulation (slow mixing)
was about 14,500. The samples were then allowed to
stand for 20 min after mixing and the supernatant was
taken for turbidity analysis for particle number and size
distribution. PACl dosages of 8, 12, 16, 20, 24, 28 mg l
−1
were used by diluting the stock solution.
2.2.2. Flocculation under different fl occulation time
using 60 rpm
The PACL dosage was maintained as 12 mg l
−1
in this
test and the slow mixing speed used was 60 rpm (G =
20.5 s
−1
) with Gt value of 29,000, i.e., twice of that using
40 rpm. The fl occulation time examined varied from
5 min to 30 min. The samples were then allowed to settle
for 20 min before analysis.
2.2.3. Flocculation under different slow tapered mixing
Instead of using the fi xed velocity gradient, the
slow tapered mixing was introduced in this scenario
to simulate the WTP fl occulation operation, in which
four descending velocity G were used in the four cor-
responding compartments for the whole slow mixing
process. The operation of the slow tapered mixing was
shown in Table 1. The samples were then settled for
20 min before analysis.
Downloaded by [University of Macau Library] at 01:04 16 May 2012
C.N. Lei et al. / Desalination and Water Treatment 45 (2012) 215–221
217
2.2.4. Secondary fl occulation
The settled water from the WTP was collected before
the test and stirred at 60 rpm for 40 min, with the PACl
of 1, 2, 4, 6, 8 mg l
−1
added into the beaker, respectively.
Samples were then allowed to settle for 20 min before
analysis.
2.3. Filtration column test
The fi ltration column is made of PVC cylinder that
has 50 mm in diameter and 300 mm in height. Sand was
used as media, fi lled up to 90 mm high in the column.
The turbidity removal by 0.65 mm ES and 0.95 mm ES
media were examined in this test, with the addition of
2 mg l
−1
and 4 mg l
−1
of fi lter aid (PACl), mixed under
100 rpm (G = 40.7 s
−1
) for 3 min, before the test. The sand
media was backwashed with tap water before the test,
and fi ltration velocity was maintained as 7.5 m h
−1
. The
rst sample taken for turbidity analysis was collected
after 1000 ml of water was fi ltered to minimize the effect
of the backwash water. Sample was taken every 500 ml
thereafter.
2.4. Analytical methods
Turbidity and particle size measurement were mea-
sured using a HACH 2100AN turbid-meter (Hach Com-
pany, USA) and an IBR particle counter (IBR, USA),
respectively. Only the particles with sizes larger than
2 μm can be measured. Dissolved oxygen (DO), pH,
and conductivity were determined using HACH LDO
probe (Hach company, USA) meter, DKK-TOA HM-30R
pH meter and DKK-TOA CM-30R conductivity meter
(DKK-TOA corporation, Japan), respectively. Dissolved
organic carbon (DOC) was analyzed using UV-persul-
fate technique and the infrared carbon dioxide analyzer
(Phoenix 8000), and calibrated with potassium hydro-
gen phthalate as standard. UV-254 was measured by
following the organic constituents’ procedure using the
DR/2010 spectrometer (Hach Company, USA). Ammo-
nia and chemical oxygen demand (COD) measurement
followed standard procedures of the Chinese Environ-
mental Protection Bureau [14].
3. Results and discussion
3.1. Water characteristics of the WTP
Samples of the raw water and treated water were
obtained from May to August, 2009 and the character-
istics were measured and summarized in Table 2. The
results showed that the turbidity of the raw water in
Yangtze River was about 40 NTU, which was considered
as low to medium turbidity, and the value is a bit lower
than the previous results reported from other research
groups [15,16]. It is considered to be diffi cult to treat the
raw water with low turbidity using the traditional coag-
ulation-fl occulation process, as the concentration of par-
ticles in the water is too low to cause effective particle
collision and aggregation [17,18]. The DOC, UV254, and
specifi c ultraviolet absorbance (SUVA) values were 1.53
mg l
−1
, 4.06 m
−l
, and 2.65 l (mg m)
−1
, respectively, indicat-
ing that the water has a low potential to form the disin-
fection by products [19]. Thus this type of raw water may
not cause a disinfection problem when chlorine is used.
The removal effi ciency of COD
Mn
(COD measurement
Table 1
Operation of the slow tapered mixing
Duration (s) Impeller speed of the jar tester (rpm)
Gt = 14,500 Gt = 21,750 Gt = 29,000
300 60 80 100
300 45 60 75
300 30 45 55
300 18 25 35
Fixed impeller speed (rpm) of equivalent Gt 40 60
Table 2
Raw water and treated water characteristics of WTP (average ± standard deviation)
Turbidit y
(NTU)
pH COD
Mn
(mg l
−1
)
Conductivity
(μs cm
−1
)
Total alkalinity
(mg l
−1
as CaCO
3
)
Raw water 40.3 ± 10 7.84 ± 0.13 2.65 ± 0.76 323 ± 50 91 ± 5
Treated water 0.3 ± 0.06 7.66 ± 0.10 0.96 ± 0.26 317 ± 25 86 ± 3
Downloaded by [University of Macau Library] at 01:04 16 May 2012
C.N. Lei et al. / Desalination and Water Treatment 45 (2012) 215–221
218
using Potassium Permanganate Method) in the WTP
was about 60%, which suggests that the organic matters
in raw water can be removed by this conventional treat-
ment process. The typical hourly PACl dosage and tur-
bidity of raw water, settled water and outlet water are
shown in Fig. 1. It has to be noted that the settled water
and outlet water residual turbidity was above 2 NTU,
and 0.15 NTU respectively, which can meet the current
Chinese regulation. However, the coagulant dosage was
as high as 40 mg l
−1
. To comply with the new internal
guidelines and the microbiological parameters closely
related to turbidity, as well as to reduce the chemical
costs, further improvement and optimization in turbid-
ity removal are necessary.
3.2. Jar tests to determine the optimal coagulant dosage
and slow mixing condition
3.2.1. Determination of optimal coagulant dosage
A preliminary jar test was conducted for the inlet
water to determine the optimal dosage of coagulant.
Water samples were taken from the inlet of the WTP and
the initial turbidity was measured as 52 NTU. Results
showed that the residual turbidity and particle number
decreased as the PACl dosage increased (Fig. 2). Under
PACl dosage of 8 mg l
−1
, colloid suspension was observed
in the supernatant after 20 min settling and the residual
turbidity was 5.3 NTU, which was beyond the current
internal standard of 3 NTU for the settled water. When
PACl dosage increased to 12 mg l
−1
or more, larger fl ocs
were formed after 5 min slow mixing and clearer super-
natant was observed. The turbidity and particle numbers
(> 2 μm) decreased to 2.9 NTU and 10,000 particle ml
−1
,
respectively at PACl dosage of 12 mg l
−1
. At PACl dosage
of 28 mg l
−1
, the residual turbidity could be lowered to
0.91 NTU, and no re-stabilization was observed within
the range of the PACl dosage change. Considering the
chemical costs as well as operational performance, PACL
dosage of 12 mg l
−1
was considered as the dosage for
optimization in the following further studies.
3.2.2. Flocculation under different fl occulation time
using 60 rpm
Effect of fl occulation time on the removal of turbid-
ity was explored. Using different fl occulation time, it
showed that the residual turbidity decreased linearly
as the fl occulation time increase from 5 min to 20 min
(Fig. 3), which suggests that a certain fl occulation time
was essential for maintaining satisfactory fl occulation.
When the fl occulation time is too short, there may not
be suffi cient collision between particles for fl ocs forma-
tion. When the time reached 20 min, the residual turbid-
ity was approximately 1 NTU, which can meet the new
internal standard of Suez Environment. Besides, as the
slowing mixing time increased to more than 20 min, the
turbidity did not decrease much. Even though the higher
velocity G would induce more turbulence in water, lead-
ing to more collisions among the particles within a given
time, there would be an ultimate fl oc size due to a con-
tinuous breakdown of the large fl ocs, and thus there will
be a limiting fl occulation time beyond which fl oc par-
ticles will not grow (Bratby 2006). Compared to the tests
using 40 rpm, under the same PACl dosage, the turbidity
0
5
10
15
20
25
30
35
40
45
50
0:00 3:00 21:0018:0015:0012:009:006:00
Time
PACL dosge (mg/L)
0
2
4
6
8
10
12
14
16
18
20
22
Turbidity (mg/L)
Raw Water PACL Dosage
Settled water Outlet water
Fig. 1. Hourly PACL dosage and turbidity of raw water,
settled water and outlet water.
0
1
2
3
4
5
6
53025201510
PACl dosage (mg/L)
Residual Turbidity (NTU)
0
2000
4000
6000
8000
10000
12000
14000
16000
Residual Particle Number
(particle/mL)
Turbidity
Particle number
Fig. 2. Residual turbidity and particle at different PACl dosage.
0
0.5
1
1.5
2
2.5
3
05 353025201510
Flocculation Time (min)
Residual Turbidity (NTU)
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Residual Particle Number
(particle/mL)
Turbidity
Particle Number
Fig. 3. Residual turbidity under different fl occulation time.
Downloaded by [University of Macau Library] at 01:04 16 May 2012
C.N. Lei et al. / Desalination and Water Treatment 45 (2012) 215–221
219
removal using 60 rpm in this test increased from 2.9 NTU
to 1 NTU. Considering the power consumption, the opti-
mal fl occulation time was taken as 20 min.
3.2.3. Flocculation under different slow tapered mixing
Using different types of slow tapered mixing and
PACl dosage, it showed that the residual turbidity
decreased as Gt or PACl dosage increased (Fig. 4). Com-
pared to fi xed rate mixing that produce the settled water
of 2.9 NTU when Gt of 14,500 was applied (Fig. 1), the
tapered mixing can further reduce the residual turbid-
ity to 2.5 NTU. This result was consistent with previous
studies [20] that tapered mixing helps the fl occulation
process, as the bigger the particle aggregates form, the
more gentle agitation is required to avoid breaking up
the existing aggregates. While keeping the PACl dosage
of 12 mg l
−1
, increasing the mixing Gt value to 29,000 that
has the same value using fi xed 60 rpm can further lower
the turbidity to below 1 NTU.
3.2.4. Secondary fl occulation
A secondary fl occulation test was conducted to study
the fl occulability of the settled water after primary fl occu-
lation. The settled water with water turbidity of 2.4 NTU,
was used to investigate the fl occulation possibility, thus to
further increase the turbidity removal for the remaining
small particles, before fi ltration. It showed in Fig. 5 that the
residual turbidity decreased from 2.4 NTU to 1 NTU after
addition of second coagulant aid of 6 mg l
−1
PACl, suggest-
ing the secondary fl occulation can solve the high turbidity
problem in settled water to meet the new internal guide-
line of 1 NTU before fi ltration. It was also reported that
secondary fl occulation can improve the removal effi ciency
of algae and dissolved organic matters [8].
3.2.5. Correlation between particle numbers and turbidity
Large particles are more easily than small par-
ticles to form aggregate and would fi rst settle in the
sedimentation process, while the small particles form
colloids are still in the settled water. Thus turbidity is a
good indicator representing the particle number in the
water. Fig. 6 showed that there are strong correlation
between residual particle numbers and turbidity that
measured in the previous tests. Besides, under the same
particle number, the turbidity in the primary fl occula-
tion was higher than that in the secondary test, implying
the very small particles (<2 μm) that was not detected by
the particle counter and contributed to the turbidity, can
be removed during the secondary fl occulation, assum-
ing the light-scattering properties of small particle sus-
pension in both tests were the same.
3.3. Filtration column test
Settled water with the turbidity of 3.23 NTU and the
particle number of 8886 particles ml
−1
, was used as infl u-
ent for fi ltration. The results (Fig. 7) showed that more
than 60% of the initial turbidity can be removed for both
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
14500 2900021750
Flocculaiton Intensity (Gt)
Residual Turbidity (NTU)
PACl=6mg/L PACl=9mg/L
PACl=12mg/L PACl=15mg/L
PACl=18mg/L
PACl=21mg/L
Fig. 4. Residual turbidity under different Gt value and PACl
dosage.
0
0.5
1
1.5
2
2.5
0108642
PACl dosage (mg/L)
Residual Turbidity (NTU)
0
2000
4000
6000
8000
10000
12000
14000
Residual Particle Number
(particle/mL)
Turbidity
Particle Number
Fig. 5. Residual turbidity and particle number under differ-
ent PACl dosage in the secondary fl occulation test.
y = 3278x - 523.69
R
2
= 0.9741
y = 5237x - 479.66
R
2
= 0.999
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
0
Residual Turbidity (NTU)
Residual Particle Number
(particle/mL)
654321
original flocculation
secondary flocculation
Fig. 6. Correlation of particle number and residual turbidity
in the tests (Notes: in original fl occulation, water samples
were from the raw water while in secondary fl occulation,
the water samples were from settled water after the primary
occulation).
Downloaded by [University of Macau Library] at 01:04 16 May 2012
C.N. Lei et al. / Desalination and Water Treatment 45 (2012) 215–221
220
sizes of fi lter media. Without fi lter aid addition, the resid-
ual turbidity after 1000 ml water fi ltration was 1.1 NTU
for 0.95 mm ES and 0.48 NTU for 0.65 mm ES. The 0.95
mm ES fi lter has 20% less turbidity removal effi ciency
than 0.65 mm ES fi lter. However, the smaller the grain
size is, the slower the water moves through the media
and the smaller amount of water that can be fi ltered,
reducing the fi ltration ow rate, i.e., if equal amounts
of water is fi ltered, small ES media increases the head
loss and thus requires more frequent backwash. These
are disadvantage using smaller ES media, even though
it can increase the turbidity removal. In addition, as the
ltered volume increase the difference of removal effi -
ciencies became less and reached only 10% (0.58 NTU for
0.95 mm ES fi lter and 0.28 NTU for 0.65 mm ES fi lter),
after the 4000 ml fi ltrated volume. Furthermore, addition
of fi lter aid would greatly improve the turbidity removal,
e.g., using 2 mg l
−1
of PACl the residual turbidity after
the fi rst 1000 ml fi ltrated volume, the turbidity was 0.50
NTU for 0.95 mm ES fi lter and 0.29 NTU for 0.65 mm ES
lter, which was only about one half of that without PACl
addition. It was also noted that the 0.65 mm ES combined
with the PACl dosage of 4 mg l
−1
, the fi nal residual tur-
bidity can be reduced to 0.15 NTU, which meet the new
internal standard of 0.2 mg l
−1
for the outlet water.
To further understand the fi ltration mechanism of
both fi lters, water samples after 1500 ml, 3000 ml and
4000 ml fi ltrated volume, were collected to determine
the corresponding particle numbers and fl oc sizes
(Fig. 8), from which the particle and turbidity removal
effi ciencies can be calculated (Fig. 9). The tests were
performed without addition of coagulant aids. It was
observed that the residual turbidity and particle num-
bers decreased with increasing the fi ltrated volumes.
Large particles have high removal effi ciency than small
particles. 0.65 mm ES fi lter have higher particle and
turbidity removal than 0.95 mm ES fi lter that after 1500
ml of water sample was fi ltered, more than 90% of par-
ticles can be removed using the 0.65 mm ES. Using the
0.000
0.200
0.400
0.600
0.800
1.000
1.200
45003500 4000300025002000150010005000
Filtrated Volumn (mL)
Residual Turbidity (NTU)
d=0.65mm PACl=0mg/L
d=0.95mm PACl=0mg/L
d=0.65mm PACl=2mg/L
d=0.95mm PACl=3mg/L
d=0.65mm PACl=4mg/L
Fig. 7. Residual turbidity in the fi ltrate under different fi lter
media size and coagulant dosage.
Media size d=0.95mm
0
500
1000
1500
2000
2500
3000
3500
Source
water
1500 40003000
Filtrated volume (mL)
Source
water
1500 40003000
Filtrated volume (mL)
Particle Number
0
500
1000
1500
2000
2500
3000
3500
Particle Number
2-3um
3-5um
5-7um
>7um
2-3um
3-5um
5-7um
>7um
a.
Media size d=0.65mm
b.
Fig. 8. Particle numbers and size distribution in the fi ltrate
for (a) media size d = 0.95 mm and (b) media size d = 0.65 mm.
Media size d=0.95mm
0
10
20
30
40
50
60
70
80
90
100
Source
water
1500 40003000
Filtrated volume (mL)
Source
water
1500 40003000
Filtrated volume (mL)
Particle/turbidity removal (%)
Particle/turbidity removal (%)
2-3um
3-5um
5-7um
>7um
Turbidity
2-3um
3-5um
5-7um
>7um
Turbidity
a)
Media size d=0.65mm
0
10
20
30
40
50
60
70
80
90
100
b)
Fig. 9. Particle and turbidity removal percentages in the fi ltrate
for (a) media size d = 0.95 mm and (b) media size d = 0.65 mm.
Downloaded by [University of Macau Library] at 01:04 16 May 2012
C.N. Lei et al. / Desalination and Water Treatment 45 (2012) 215–221
221
Acknowledgements
This project was supported by Sino French Water
Research Fund, Fundo para o Desenvolvimento das Cien-
cias e da Tecnologia (FDCT), under grant No. 016/2011/A
and Research Committee at University of Macau under
grant No. MRG002/LIC/2012. The authors are very
grateful to all staffs of Technical Department in Changshu
Sino-French Water Supply Co. Ltd., who provided full
supports to this research.
References
[1] M.W. LeChevallier and W.D. Norton, Treatments to Address
Source Water Concerns: Protozoa. Safety of Water Disinfec-
tion: Balancing Chemical and Microbial Risks, G.F. Craun
(ed.), ILSI Press, Washington, D.C., 1993.
[2] K.R. Fox, Turbidity as It Relates to Waterborne Disease Out-
breaks. Presentation at M/DBP Information Exchange, Cincin-
nati, Ohio, AWWA white paper, 1995.
[3] J. Bratby, Coagulation and Flocculation in Water and Wastewa-
ter Treatment, IWA publishing, London, UK, 2006.
[4] A. Amirtharagjah and C.R. O’Meli, Coagulation Processes:
Destabilzation, Mixing, and Flocculation. Water Quality
and Treatment: A Handbook of Community Water Supplies,
F.W.A.W.W.A. Pontius (ed.), McGraw-Hill, New York, 1990.
[5] K. Miyanami., K. Tojo and Y. Yokota, Effect of mixing on oc-
culation, Ind. Eng. Chem. Fundam., 21 (1982) 132–135.
[6] W.Y. Sheng, X.F. Peng and D.J. Lee, Coagulation of particles
through rapid mixing, Drying Technol., 24 (2006) 12711276.
[7] J. Churchill, M.W. Beutel and P.S. Burgoon, Evaluation of opti-
mal dose and mixing regime for alum treatment of Matthiesen
creek in ow to Jameson Lake, Washington, Lake Reservoir
Manage., 25 (2009) 102–110.
[8] A.W. Timonthy and G.P. Nicholas, Optimizing fi lter perfor-
mance, J. New Engl. Water Works Assoc., 3 (1999) 6–21.
[9] K.J. Ives and J. Gregory, Basic concepts of fi ltration, Proc. Soc.
Water Treat. Exam., 16 (1967) 147169.
[10] C.R. OMelia and W. Stumm, Theory of water ltration,
J. AWWA, 59 (1967) 1393–1412.
[11] K.M. Yao, M.T. Habibian and C.R. OMelia, Water and waste
water fi ltration: concepts and applications, Environ. Sci. Tech-
nol., 5 (1971) 1105–1112.
[12] J.S. Chang, S. Vigneswaran and J.K. Kandasamy, Effect of pore
size and particle size distribution on granular bed fi ltration
and micro ltration, Sep. Sci. Technol., 43 (2008) 17711784.
[13] H. Zhu, D.W. Smith and H. Zhou, Improving removal of tur-
bidity causing materials by using polymers as a fi lter aid,
Water Res., 30 (1996) 103–114.
[14] CEPB, Analysis Method for Monitoring Water and Waste.
Environmental Science Press, Beijing, China, 2002.
[15] A. Halawik, Effect of Aluminium and iron salts in coagula-
tion on turbidity removal of Yangtze River, J. Hehai Univ. (Nat.
Sci.), 29 (2001) 114–118.
[16] Y. Zhang, Y.X. Li and J. Jia, Studies on turbidity removal of tiny
polluted autumn Yangtze River raw water using composite
coagulants of polyaluminum chloride, Fine Chem., 26 (2009)
493497.
[17] S.K. Dentel and J.M. Gossett, Mechanisms of coagulation with
aluminum salts. J. AWWA, 80 (1988) 187–198.
[18] W.P. Cheng, F.H. Chi and C.C. Li, A study on the removal of
organic substances from low-turbidity and low-alkalinity
water with metal-polysilicate coagulants, Colloids Surf., 312
(2008) 238–244.
[19] US EPA, Enhanced Coagulation and Enhanced Precipitative
Softening Guidance Manual, United States Environmental
Protection Agency, 1999.
[20] M. James, Water Treatment Principles and Design. Wiley-
Interscience, John Wiley & Sons, New York, 1985.
0.95 mm ES, the removal effi ciency of larger particles
(>7 μm) was much higher than that of smaller particles
(2–3 μm) at the beginning of the test, with the removal
effi ciencies of 85% and 53%, respectively. However,
when the fi ltration proceeded, the removal effi ciency
of smaller particles increased to 74% after 4000 ml
ltrated volume. These results supported the mecha-
nisms of straining, sedimentation and interception in
the fi ltration, as small ES media has small openings
that retain the particles.
Comparing the residual turbidity and the particle
removal effi ciencies (Fig. 9), it was found that using
both media the turbidity removal was lower than the
removal of particles with sizes greater than 3 μm, sug-
gesting that small particles contributed to turbidity
more than large particles. As the particle counter can
only determine the number of particles greater than
2 μm, the diffusion mechanism applied to small par-
ticles (typically <2 μm) cannot be verifi ed in the stud-
ies. However, using 0.95 ES media, the 2–3 μm particles
removal effi ciency is lower than the turbidity removal
effi ciency, which can be hypothesized that some portion
of the small particles less than 2 μm was removed by
other mechanism, probably by diffusion. The mecha-
nism of diffusion will be systematically investigated in
the future study. Thus, to increase the turbidity removal
in fi ltration, addition of coagulant acid to increase par-
ticle sizes, and using the smaller media fi lter will be the
effective approaches.
4. Conclusions
Jar tests and fi ltration column tests were performed
to improve the turbidity removal of the conventional
coagulation-fl occulation-fi ltration process in Changshu
WTP to meet the new internal standard for turbidity
with reducing chemical and power consumption. The
parameters investigated were coagulant dosage, fl oc-
culation mixing time, tapered mixing and fi lter media
size. The results showed that using PACl dosage of 12
mg l
−1
with the tapered mixing for 20 min (Gt = 29,000),
or implementing an additional secondary fl occulation
process with 6 mg l
−1
PACl, can reduce the settled water
turbidity to 1 NTU. Secondary fl occulation process can
further remove the smaller particles that retained in the
settled water. However it would need more space for
construction additional settling tank. It was found that
there were strong correlation between turbidity and par-
ticles. Besides, small particles contributed to turbidity
more than large particles in the fi ltration, and compared
to 0.95 mm ES, 0.65 mm ES with 4 mg l
−1
PACl fi lter aid
can reach the residual outlet water to below 0.15 NTU.
The approaches will be further studied in the full-scale
Changshu WTP.
Downloaded by [University of Macau Library] at 01:04 16 May 2012
... The most well-known process for water treatment includes coagulation, flocculation, sedimentation, and filtration steps [3]. Proper coagulant dosage, flocculation mixing time, mixing intensity, and effective size of filter media are the most significant influential parameters that affect water turbidity treatment [4]. In the last decade, various experimental, analytical and numerical studies have been performed in order to understand and resolve this turbidity phenomenon. ...
... In the last decade, various experimental, analytical and numerical studies have been performed in order to understand and resolve this turbidity phenomenon. Nang et al. [4] conducted the removal of turbidity from Yangtze River raw water using Jar tests and filtration column tests. They concluded that under the same amount of coagulant, longer flocculation time and higher mixing intensity with tapered mixing can enhance the turbidity removal. ...
Article
Full-text available
Turbidity is considered a classical problem in Malaysian rivers. The level of turbidity is dependent on the amount of sediments and biological matter contained in the water. Therefore, this study proposes an approach to turbidity mitigation that involves simulating the effect of density and diameter of vegetation on water flow. This paper presents the numerical modelling of vegetation effect on water flow using Lattice Boltzmann Method for Shallow Water Equations (LABSWE™) integrated with Rigid Vegetation Modelling (RVM). The proposed model was implemented on the Kinta River in Perak state, Malaysia as a case study. The simulation results show the effect of density and diameter of vegetation on water flow velocity. The optimum vegetation density and vegetation diameter values for river water turbidity reduction were found to be 0.05 and 0.005, respectively.
... The optimal pH level for alum coagulation and ferric-based coagulation were observed to be 5.0-6.5 and 4.5-6.0, respectively, leading to high turbidity, DOC (dissolved organic carbon), and UV 254 removal [4][5][6][7]. Although coagulation using metallic salts can lower the pH level, the high alkalinity water still provides excessive OH À for metal hydrolysis and the formation of hydroxide precipitates, therefore demanding a high metal salts dosage. ...
... The ferricbased coagulant associated with the optimized coagulation pH range produces treated water with less buffering capacity, and requires greater chemical addition for stabilization and corrosion control. However, PACl is composed of partially neutralized, prehydrolyzed aluminum chloride, and contains large amounts of high-charged and moderate-molar-mass hydrolysis species, such as Al 13 , in the coagulation process [5,20]. These coagulation species are considered to be the most efficient Al-species due to their higher positive charge and larger size. ...
Article
Full-text available
Coagulation optimization using coagulants of ferric chloride (FeCl3), polyaluminum chloride (PACl), and their combinations (FeCl3/PACl) were evaluated through jar tests, by treating source water with high algal content (10–40 million cells/L) and high alkalinity (80–110 mg/L). The results indicated that when compared to single coagulants, the combined coagulants showed a superior coagulation performance in terms of turbidity, UV254, and algal removal. The optimal dosage was determined as 30–35 mg/L by using the combined PACl/FeCl3 (1:2 by mass) and dosing PACl followed by FeCl3. By adding the coagulant aids of polymerized diallyl dimethyl ammonium chloride (HCA) and polyacrylamide (FO4190), the floc sizes may enlarge up to 1.75–2.0 mm. Scanning electron micrographs showed that the coagulant combination can form a more compact reticular aluminum-ferric structure, and thus increased the settleability of the flocs. The combined coagulation was further evaluated in full-scale water treatment plants, confirming the improvement of the removal of algae, turbidity, and residual iron in the treated water.
... Yang et al., 2012;Leia et al., 2012;Katrivesis et al., 2019;Adebayo et al., 2021). ...
Article
Full-text available
The lightly micro-polluted raw water of Yangtze River (YRW) in autumn was treated via enhanced coagulation by composite coagulants composed of polyaluminium chloride (PAC) and polydimethyldiallylammonium chloride (PDMDAAC), named PAC/PDMDAAC. Coagulation mechanism and removal efficiency were investigated by assessing the water quality parameters of the resulting supernatant, i.e. turbidity, COD Mn, and NH3-N, at the same dosage and supernatant turbidity (SDST) point as using PAC only, with controlled residual turbidity of 1.0-1.50 NTU to mimic drinking water production plant supernatant condition when using lightly micro-polluted water as raw water source . In addition, the zeta potential, floc morphology, and size analysis under the condition of SDST using PAC and composite coagulants PAC/PDMDAAC for getting insight about removal mechanism were done. The results showed that, firstly, most of the composite coagulants PAC/PDMDAAC with intrinsic viscosity [η] = 0.65, 1.60, and 2.6 dL/g; and mass ratio PAC:PDMDAAC of 5:1, 10:1, and 20:1 (mm)) could meet the requirements of controlled supernatant turbidity between 1.0 and 1.5 NTU to mimic drinking water production plant condition using YRW (Nanjing section) that comply with the new national drinking water standards. Secondly, the seven kinds of composite coagulants PAC/PDMDAAC can maintained the advantage of enhanced coagulation removal efficiency within the SDST point as using PAC only. The COD Mn and ammonia nitrogen removal rates using composite coagulants at SDST points were 0-6.19 %; 0-15.62%, respectively higher than using PAC only. Finally, this study deepened and expanded the existing research knowledge about composite coagulant PAC/PDMDAAC and offered the maximum limitations in removing the water quality parameters via enhanced coagulation treatment of lightly micro-polluted surface raw water in order to meet new national drinking water standards.
... Coagulation is a well-known process in water treatment used for removal of different organic substances from water for human consumption [4,5]. It is also the most commonly used method for turbidity and particle removal during water treatment [6]. ...
Article
Full-text available
The coagulant and disinfectant qualities of Moringa oleifera and Citrus paradisi were investigated on various water samples acquired from sachet water (packaged water), borehole water, river water and well water. The results revealed that Moringa oleifera functioned adequately at settling time beyond 2 h in highly turbid river water but was more effective when combined with Citrus paradisi. Moringa oleifera or its combination with Citrus paradisi is less effective for turbid water treatment but effective for river water (sample) purification. The number of total Coliforms and Escherichia coli reduced with the increasing treatment time.
... Several substances, either organic or inorganic, have been used as coagulation agents up to now. Most common of them include natural polymers [21][22][23], inorganic polymers [24,25], aluminum and other metal salts [9,[26][27][28][29][30][31][32] as well as a combination of polymer and metal salt [33,34]. A very recent trend is the usage of various types of industrial waste as coagulants in the coagulation/flocculation processes [35]. ...
Article
In the current research, three industrial by-products containing useful iron and aluminum chemical components were introduced as potential alternative coagulants in marble processing wastewater treatment for possible water reuse. Specifically, the coagulation performance of lignite highly-calcareous fly ash (FAc), siliceous fly ash (FAs) and electric arc furnace dust (EAFD) was compared with that of two commercial coagulants (Al2(SO4)3.18H2O and FeCl3.6H2O). The kinetic studies were conducted at times up to 60 min by using coagulant dosages up to 4 mg/L. Turbidity (NTU), pH and conductivity were recorded during the kinetic studies. FAs and EAFD revealed enhanced coagulation performance, having similar turbidity removal efficiencies (%ΔNTU) to those of commercial coagulants, with short sedimentation times (~5 min). The pH values recorded for the three industrial by-products/coagulants were in the basic range (7-9.7). Only the pH values for EAFD, at high dosages, were found to be close to neutral, while, for all commercial coagulants, neutral pH values were recorded at intermediate dosages. The experimental results presented may contribute to the formation of integrated and cost-effective strategies for marble wastewater management with low environmental footprint.
... For 8 samples, the value of turbidity was very high which reflects disinfection of water to be carried out effectively. Proper treatment methods could be used to significantly lower down the turbidity of water at large scale [31]. ...
Article
The quality of drinking water is vital for humans in order to remain alive, healthy and disease free. Consequently, it is indispensible to make sure that the available drinking water is uncontaminated. This study aimed at finding the quality of drinking water in Jampur, which is one of the tehsils of district Rajanpur in South Punjab, Pakistan. Thirty water samples were collected from different locations of the study area. These samples were gathered from different sources such as hand pump, injector pump, tube well and water supply line. The water quality was examined by comparing its standards with World Health Organization provided guidelines. It was found that majority of the Jampur’s population were using contaminated water, which is very harmful and alarming. This contaminated water could cause a potential risk to people’s health through many waterborne and skin diseases. The contamination of water could be due to dissolved contaminants and excessive ions such as arsenic, sodium, calcium or nitrate, etc. It is recommended that safety measures should be taken before exploiting this water for drinking. For the purification of contaminated water, filtration plants must be installed in the region.
... The daily runoff data of Pingshan hydrological station on the Jinsha River in China are considered for the present study [16]. The length of its trunk is 2,316 km, and the drainage area is 0.34 million km 2 . ...
Article
The significance of accepting runoff processes as nonlinear has been gaining considerable in recent times. However, it is hard to explore the types of nonlinearity acting underlying the runoff processes and the intensity of the nonlinearity at different timescales. Daily runoff time series observed at the Pingshan hydrometric station are used for this study. An attempt is made to identify the existence of chaos and the intensity of nonlinear behavior at three characteristic time scales (one day, 1/3 month, and one month). Six nonlinear dynamic methods are used: (1) phase space reconstruction and the delay time is estimated using average mutual information; (2) the sufficient embedding dimension is estimated using the false nearest neighbor algorithm; (3) correlation dimension method; (4) Lyapunov exponent method; (5) 0–1 test algorithm for chaos; and (6) the multi-step Volterra adaptive method. A comparison of results reveals the presence of low-dimensional chaos in the runoff dynamics at the various time scales and the time scales composes only a limit fraction of the intensity of nonlinear behavior. The reasonably good predictions indicate the efficiency of the nonlinear prediction method for predicting the runoff series.
Article
Full-text available
Kota Langsa merupakan salah satu kota yang berada di Provinsi Aceh, Kota Langsa memiliki sebuah sungai yang disebut dengan Sungai Langsa. Penelitian ini bertujuan untuk mengetahui ketersediaan air baku daerah aliran sungai hulu Langsa. Saat ini ketersediaan air mengalami pengurangan yang disebabkan oleh pertumbuhan penduduk yang semakin padat. Sungai Langsa memiliki jenis sungai musiman yang artinya jika saat musim hujan ketersediaan air di sungai tersebut meningkat, namun jika musim kemarau ketersediaan airnya relatif berkurang. Daerah aliran sungai merupakan salah satu alternatif sumber air baku yang dikelola oleh Perusahaan Daerah Air Minum Kota Langsa untuk memenuhi kebutuhan masyarakatnya. Penelitian ini menggunakan metode observasi lapangan, yang menghasilkan sebuah data yaitu debit aliran sungai, curah hujan dan kualitas air sungai. Untuk mengetahui data debit aliran maka dilakukan perhitungan debit aliran DAS, peta curah hujan, dan kualitas air sungai yang diambil dari sampel air yang berada di Sungai Langsa. Hasil dari penelitian ini yaitu menghasilkan peta Daerah Aliran Sungai, peta curah hujan, dan perhitungan kalkulasi debit aliran sebesar 113,742 m3/s yang dapat dikatakan maksimal dalam memenuhi ketersediaan air baku. Berdasarkan hasil penelitian tersebut, peneliti merekomendasikan agar pemerintah dapat memperhatikan ketersediaan dan kebutuhan air baku secara optimal di Kota Langsa mengingat saat ini pertumbuhan penduduk terus mengalami peningkatan setiap tahunnya.
Article
Full-text available
This study was developed using data from a drinking water treatment plant located at Boudouaou, Algeria, it is located at about 7 km from the Keddara dam which supplies potable water to Algiers capital of Algeria. The treatment consists essentially of preliminary disinfection, coagulation–flocculation, settling, filtration and final disinfection. Traditionally, optimum coagulant dosages are determined using jar tests. However, jar tests are relatively expensive and time consuming. In this study, we present a new Artificial Intelligence Techniques model called dynamic evolving neural-fuzzy inference system (DENFIS) based on an evolving clustering method, for modelling coagulant dosage rate used in the coagulation stage. Six online variables of raw water quality including turbidity, conductivity, temperature, apparent colour, ultraviolet absorbance, water pH and alum dosage were used to build the coagulant dosage model. Two DENFIS-based evolving neural-fuzzy inference system are presented and compared. The two DENFIS systems are: (1) Offline-based system named DENFIS-OF and (2) Online-based system, named DENFIS-ON. The performances of the models are evaluated using root-mean square errors (RMSE), mean absolute error and correlation coefficient (CC) statistics. The low RMSE and high CC values were obtained with DENFIS-ON method.
Article
The large quantity and sharp appearance of influent flow of combined sewerage system always exceed the hydraulic capacity of wastewater treatment plant (WWTP) and the deterioration of the performance of WWTP and the discharge of bad effluent water quality to surface water occur during rainfall events. To determine the influence of rainfall, the upriver combined sewerage system and the performance of WWTP were simulated by InfoWorks CS and Biowin software, respectively. Three kinds of intensive processes, i.e. chemically enhanced primary treatment (CEPT), CEPT combined with secondary treatment and CEPT combined with secondary treatment with decreased hydraulic retention time were proposed based on the original process of WWTP. The results showed that the proposed wastewater treatment processes are all powerful to weaken the adverse impacts of rainfall on WWTP and to reduce greatly the pollution to receiving waters during the rainfall events.
Article
Full-text available
An innovative method of reducing external phosphorus (P) loading to lakes uses engineered systems to treat lake inflows with aluminum sulfate (alum). In this study we used a series of jar tests to examine the optimal alum dose and mixing regime to remove P from Matthiesen Creek, an important external source of P to Jameson Lake. Matthiesen Creek is a good candidate for alum treatment because the creek runs year round, and the majority of P in the spring-feed creek is in the form of bioavailable dissolved P that can be efficiently captured in alum floc. The mixing regimes in this study mimicked a range of possible treatment scenarios that relied on natural turbulence in the creek or conventional mechanical mixing, and presumed the discharge of alum floc either directly to the lake or to an on-shore settling basin. Jar tests showed that an alum dose of 5 mg-Al/L was sufficient to decrease P from around 0.13 mg-P/L to below 0.02 mg-P/L for most mixing regimes. For all mixing regimes, doses of up to 20 mg-Al/L did not depress pH below the recommended minimum pH of 6. Flash mixing prior to low-intensity mixing did not enhance P removal over low-intensity mixing alone, but flash mixing alone resulted in lower levels of P removal from creek water. Jar testing with a mixture of alum-treated creek water and lake water showed that lake waters tended to inhibit P uptake by alum floc. This, combined with the fact that high pH favors the formation of the aluminate ion which could exhibit chronic toxicity to aquatic biota, suggests that discharge of alum solids directly to the lake should be avoided. We recommend an engineered inflow treatment system on Matthiesen Creek that maintains an alum dose of 5-10 mg-Al/L under moderate mixing conditions (Gt of 1,000-3,000) with alum floc collected in an on-shore settling basin. © 2009
Chapter
The objective of municipal water treatment is to provide a potable supply, one that is chemically and microbiologically safe for human consumption. Common water sources for municipal supplies are deep wells, shallow wells, rivers, natural lakes, and reservoirs. Sources of water pollution can be classified as both non-point sources and point sources. Primary, secondary, and tertiary treatment methods including their design aspects and merits and disadvantages are discussed in this chapter. A reader of this chapter will be able to design a water treatment system based on the source and type of pollution to be treated along with the quantity of potable water required for the town or city.
Article
Good filter performance in a surface water treatment plant (WTP) is key to the protection of public health. This paper presents some practical concepts that operators of surface WTPs can implement to optimize the removal of particles in their rapid-sand filters. A brief history of the importance of the filtration process in treating drinking water is provided to encourage operators to evaluate their filters. The basic parameters important to achieving good filter performance are discussed (i.e., particle removal, head loss development, unit filter run volumes and backwashing procedures). A detailed description of a useful filter-coring procedure is presented so operators can check: 1) the performance of their filters, 2) the condition of their existing media, and 3) the adequacy of the backwash procedures being used to maintain their filters in top operating condition.
Article
Coagulation and flocculation are considered to be an essential part of drinking water treatment as well as wastewater treatment. A number of separate primary coagulant types, various combinations of coagulants, and mixing regimes should be studied over a range of imposed experimental conditions to optimize the treatment of water. The enhanced coagulation approach recognizes that the constituents of any given water govern the practical degree of treatment achievable. A chemical phosphorus removal is a common example of the practice of chemically enhancing primary treatment to reduce suspended solids and organic loads from primary classifiers. A book from IWA Publishing on coagulation and flocculation presents the properties of materials present in waters and wastewaters, details of experimental procedures for assessing primary coagulants and flocculant aids, sludge conditioners, and flocculation parameters.
Article
This article briefly summarizes certain aspects of filtration theory, and outlines the framework for a conceptual model for the filtration process. Water filtration is generally considered to include both physical and chemical phenomena. Experimental evidence related to the chemical aspects of water filtration is presented and discussed.
Article
As is often assumed, rapid mix effectively distributes the dosed coagulant in suspension to promote subsequent flocculation of suspended particles and coagulant molecules. This study determined that the role of rapid mix is considerably more complex than conventionally assumed. Particles in the raw water samples from the Banxing Water Works of Taipei City were coagulated at high shear environment, during which flocs of size 40–70 μm were produced. The produced floc interior was compacted, and residual turbidity and the amount of dissolved natural organic matter (NOM) in suspension were substantially reduced. The subsequent stage of rapid mix slightly reduces floc size, further compacts the floc interior, and expels fine particles and some adsorbed NOM from the flocs. A sudden reduction in shearing rate produced large sized flocs with not so compact structures. Moreover, this action released fine particles from flocs into the suspension and enhanced adsorption of NOM onto solid surfaces.
Article
The paper reviews the effect of particle size distribution and pore size distribution on granular bed filter and crossflow microfiltration performance. The experimental results of the granular bed filter with pollen particles in suspension showed that the presence of large particles improved the filter efficiency of smaller particles in suspension. Microfiltration results with bi and tri‐modal latex suspensions showed that the permeate flux and the quality were significantly affected by the particle size and its distribution, especially when the particle size was smaller than the pore size of the membrane. The mathematical model simulation results of granular bed filtration show that media pore size distribution is an important parameter of filtration for the particle removal and pressure drop across the filter.
Article
The effects of mixing intensity and flocculation time on the suspended solids concentration in the effluent from a wastewater treatment system for heavy metals removal have been investigated by using a coagulant of lime sulfurated solution and aluminum sulfate or ferric sulfate solution. Two types of mechanical agitation, i.e., rotary agitation by an impeller and vibratory agitation by a vibrating disk, are employed. The behavior of the suspended solids is explained quite well by a model based on Smoluchowski's collision theory in a mild mixing region and the liquid-liquid dispersion model in a rapid mixing region. The optimum Ḡt, the product of average shear rate Ḡ and the flocculation time t, can be determined from the intersection of the lines calculated based on the collision theory and the dispersion model. The treatment capacity is almost independent of the type of agitation if the power requirement per unit volume of content is of the same amount.