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Roughing filtration can be considered as a major pre-treatment process for wastewater, since they efficiently separate fine solids particles over prolonged periods without addition of chemicals. This review article summarizes and evaluates modifications to roughing filtration technology, which may address these limitations without compromising the simplicity of the treatment process. Successful modifications includes broken burnt bricks, charcoal and coconut fibre as filter media. The paper also reviews the design concept and process capabilities for roughing filter and it also discusses recent innovations in roughing filter design that now enable this technology to be applied more widely than would have been appropriate 2 decades ago. Achieved results in this study shows that roughing filtration may be considered as efficient pretreatment process incase surface water is used as water supply.
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International Journal of Physical Sciences Vol. 4 (9), pp. 455-463, September, 2009
Available online at http://www.academicjournals.org/ijps
ISSN 1992 - 1950 © 2009 Academic Journals
Review
Roughing filter for water pre-treatment technology in
developing countries: A review
Onyeka Nkwonta* and George Ochieng
Department of Civil Engineering, Tshwane University of Technology, private bag x680, Pretoria 0001, South Africa.
Accepted 27 July, 2009
Roughing filtration can be considered as a major pre-treatment process for wastewater, since they
efficiently separate fine solids particles over prolonged periods without addition of chemicals. This
review article summarizes and evaluates modifications to roughing filtration technology, which may
address these limitations without compromising the simplicity of the treatment process. Successful
modifications includes broken burnt bricks, charcoal and coconut fibre as filter media. The paper also
reviews the design concept and process capabilities for roughing filter and it also discusses recent
innovations in roughing filter design that now enable this technology to be applied more widely than
would have been appropriate 2 decades ago. Achieved results in this study shows that roughing
filtration may be considered as efficient pretreatment process incase surface water is used as water
supply.
Key words: Roughing filter, sedimentation, absorption, turbidity.
INTRODUCTION
Surface water is sometimes the only available safe water
source for rural homeowners. Typical problems encoun-
tered can be caused by high suspended solids, turbidity,
coliform bacteria, agricultural runoff (Blackburn, 1997).
Previous studies have shown roughing filtration to be an
effective and reliable method for removing suspended
solids, turbidity and coliform bacteria (Clarke et al., 1996;
Collins, 1994; Galvis et al., 1998; Wegelin, 1986). For
suspensions with particulates that do not readily settle,
roughing filtration provides superior treatment to basic
sedimentation methods (Wegelin, 1996) and represents
an attractive alternative to more costly conventional
coagulation methods.
Roughing filters are primarily used to separate fine
solids from the water that are only partly or not retained
at all by stilling basin or sedimentation tanks. Roughing
filters mainly acts as physical filters and reduce the solid
mass. However, the large filter surface area available for
sedimentation and relatively small filtration rates also
supports absorption as well as chemical and biological
processes.
Therefore besides solid matter separation, roughing
*Corresponding author. E -mail: ifeanyio@tut.ac.za.
filters also partly improve the bacteriological water quality
and to a minor extent, change some other water quality
parameters such as colour or amount of dissolved orga-
nic matter (Wegelin, 1996). Roughing filters are classified
as deep-bed filters, whereby proper filter design pro-
motes particle removal throughout the depth of the filter
bed, maximizing the capacity of the filter to store
removed solids. Particle removal efficiency in roughing
filters is dependent on filter design, particulate and water
quality parameters (Boller, 1993; Collins, 1994; Wegelin,
1986).
TRADITIONAL DESIGN OF ROUGHING FILTERS
The natural water treatment potential was adopted long
before chemical water treatment methods, such as chlori-
nation and flocculation, were discovered and applied.
Gravel and sand used as filter media are key compo-
nents in natural treatment processes. Although sand was
able to maintain its important role since the development
of the first slow sand filters at the beginning of the last
century, the use of roughing filters was successively
replaced by chemical water treatment processes
(Wegelin, 1986). However, a few examples presented
hereafter document that the roughing filter technology is
456 Int. J. Phys. Sci.
an old water treatment process used in the past and
rediscovered in recent years.
Numerous castles and forts were constructed in Europe
during the middle ages. They were often located at
strategically important points, difficult to conquer and also
to supply with water. A good example is the former castle
of Hohentrins located on top of a steep rocky reef in the
Swiss Alpine valley of the river Rhine. During periods of
war, the people who sought protection in this castle
depended on rainwater collected in the yard and stored in
a cistern. In this extensively used area, it was, however,
not possible to avoid water pollution caused by man and
animal. Therefore, in order to treat the water, a gravel
pack was installed around the inlet of the cistern. This is
probably 1 of the first roughing filters used to treat
surface water (Wegelin, 1996).
In 1804, John Gibb constructed the first water filtration
plant for a public water supply at Paisley in Scotland. In
order to pretreat the muddy river water, John Gibb
designed and constructed an intake filter described as
follows: "Water from the River Cart flowed to a pump well
through a roughing filter about 75 feet long, composed of
"chipped" freestone, of smaller size near the well than at
the upper end. This stone was placed in a trench about 8
feet wide and 4 feet deep, covered with ‘Russian mats"
over which the ground was leveled”. The pretreated raw
water was then lifted by a steam engine-driven pump to a
place 16 feet higher than the river from where it flowed by
gravity to the water treatment plant. This installation
consisted of 3 concentric rings each 6 feet wide and
arranged around a central clear water tank measuring
23.5 feet in diameter. The water flowed in horizontal
direction from the outer ring, which was used as settling
basin; through the 2 other rings towards the centre into
the clear water tank. The 2 inner rings contained coarse
and very fine gravel or sand as filter material respectively.
John Gibb applied, already then, the multi-stage treat-
ment approach; that is, the intake filter, the settling basin
and the gravel filter were used as pretreatment processes
prior to sand filtration.
RECENT DESIGN CONCEPT
With the renewed interest in roughing filter has come
fresh thinking on design concepts related to plant layout,
access to filter performance, monitoring and kinds of ma-
terials to use for filter media. Wegelin design can simplify
construction of a filter and can make the design job
easier. Now the conceptual filter theory for evaluating the
efficiency of the filter is still based on the filtration theory
described by Wegelin (1996). When a particle in the
water passes through a gravel bed filled up with gravel
there is a chance to escape the particle either on the left
side or on the right side or a chance to settle at the sur-
face of the gravel. Hence the probability of chance of the
success of removal and the failure is 1/3 and 2/3.
According to Fick’s law the filter efficiency can be ex-
pressed by the filter coefficient or,
d
c
d
x
=−c
(1)
Where;
c = Solid concentration.
x = Filter depth.
= Filter coefficient or coefficient of proportionality
From the above equation it can be stated that the remo-
val of the suspended particles is proportional to the
concentration or the particles present in the water.
The total length of the filter can be described as the
number of parallel plates and act as a multistage reactor
so the performance of the HRF can be ascertained on the
basis of the results obtained from the small filter cells.
The total suspended solid concentration after a length of
x of the filter cell can be expressed,
c
=
C
inlet
e
-
i
x
(2)
Where;
i = Filter efficiency of each filter cell.
x = Length of experimental filter cell.
cinlet and coutlet = Concentration of particles in the inlet &
outlet of the filter.
It is to be stated that after evaluating the filter depth
(length) and the filter coefficient and the Suspended So-
lids concentration, the performance efficiency of the filter
can be predicted.
According to Wegelin (1996), the effluent quantity for
the n number of compartments is given by:
C
e=
C
0
*
E
1
*
E2
*
E3
*
E4
*
. ....
...En
(3)
Where;
C0 = Concentration of the HRF influent.
Ce = Concentration of the HRF effluent.
E1, E2, E3, E4. ...... ...En = Filtration efficiency for the each
compartment (1, 2, 3 respectively).
The basic expression for the above relationship is
expressed by:
Ce = Coe
ëL
(4)
Where:
ë = Coefficient of filtration
L = Length of the filter.
The Filter efficiency is given by:
E = Ce/C
0
= e
ëL
Ce = Co* E
(5)
Ei = Filter efficiency for (i−1, 2, 3 . . . n) compartments.
The description of the theory above showed that solid
removal by filtration can be described by exponential
equation.
ARTIFICIAL NEURAL NETWORK
Artificial Neural Network is a distributed information pro-
cessing system that has certain characteristics that
resemble with the biological neural network of the human.
The development of an artificial neural network as
prescribed by ASCE (ASCE, 2000), must follow the
following basic rules:
1. Information must be processed at many single
elements called nodes.
2. Signals are passed between nodes through connection
links and each link has an associated weight that
represents its connection strength.
3. Each of the nodes applies a non-linear transformation
called as activation function to its net input to determine
its output signal.0.0 (Yitian and GU, 2003).The accuracy
of results obtained from the network can be assessed by
comparing its response with the validation set. The
commonly used evaluation criteria include percentage
MSE, correlation coefficient (r), coefficient of efficiency
(C.E.) and Standard Deviation (STDEV).
%MSE= (TpOp)/Tp) × 100
r = [X (Tp Tm)(Op Om))/(Xn1(Tp Tm)2Xn1 (Op
Om)2)1/2]
C.E. =1− (Xn1 (TpOp) 2/ Xn1 (TpTm) 2)
STDDEV= En (T n−¯ T n) 2
n
Where, Tp is the target value for the pth pattern; Op is
the estimated value for the pth pattern, Tm and Om is the
mean target and estimated values respectively and n is
the total number of patterns. MSE shows the measure of
the difference between target (Tp) and estimated (Op)
value, r defines the degree of correlation between 2 va-
riables. C.E. Criterion has the basis of standardization of
the residual variance with initial variance (Nash and
Sutcliffe, 1970).
In this criterion, a perfect agreement between the
observed and estimated output yields an efficiency of 1.
A negative efficiency represents lack of agreement and
zero agreement means all the estimated value is equal to
the observed mean. STDDEV is the measure of deviation
of the estimated value from the target output. A perfect
match between observed data and model simulations is
obtained when STDDEV approaches.
Nkwonta and Ochieng 457
TYPES OF ROUGHING FILTERS
Vertical flow roughing filters
Vertical-flow roughing filters operate either as down flow
or up flow filters. They are hence either supplied by
inflowing water at the filter top or at the filter bottom. The
vertical flow roughing filters incorporates a simple self
cleaning mechanism and occupies minimal floor space
when compared to horizontal flow roughing filters.
The filter material of vertical-flow roughing filters is
completely submerged. A water volume of about 10 cm
depth usually covers the gravel and other local available
materials like coconut fiber and broken burnt bricks. The
top should be covered by a layer of coarse stones to
shade the water and thus prevent algal growth often
experienced in pretreated water exposed to the sun.
Drainage facilities, consisting in perforated pipes or a
false filter bottom system, are installed on the floor of the
filter boxes. Finally, pipes or special inlet and outlet
compartments are required to convey the water through
the subsequent 3 filter units and they are shown in Figure
1.
Horizontal flow roughing filters
As shown in figure 1, unlimited filter length and simple
layout are the main advantages of horizontal roughing
filters. Horizontal roughing filters have a large silt storage
capacity. Solids settle on top of the filter medium surface
and grow to small heaps of loose aggregates with
progressive filtration time. Part of the small heaps will drift
towards the filter bottom as soon as they become
unstable. This drift regenerates filter efficiency at the top
and slowly silts the filter from bottom to top.
Horizontal-flow roughing filters also react less sensi-
tively to filtration rate changes, as clusters of suspended
solids will drift towards the filter bottom or be retained by
the subsequent filter layers. Horizontal-flow roughing
filters are thus less susceptible than vertical-flow filters to
solid breakthroughs caused by flow rate changes.
However, they may react more sensitively to short circuits
induced by a variable raw water temperature.
ROUGHING FILTER DESIGN PARAMETERS
Filter media size
Media types commonly used in roughing filtration are
quartz sands and gravels but can be replaced by any
clean, insoluble and mechanically resistant material
(Graham, 1988).
Previous work by Wegelin (1986) showed that the
effect of surface porosity and roughness of filter media on
particle removal efficiency in roughing filtration was insig-
nificant compared to the size and shape of macropores in
the filter. Rooklidge and Ketchum (2002) studied the
removal efficiencies in calcite limestone, basaltic river
458 Int. J. Phys. Sci.
Figure 1. Diagram of horizontal, up flow and down flow roughing filters.
Source: (Wegelin, 1996).
Table 1. Different sizes of roughing filter media.
Roughing filter
description
First
compartment
(mm)
Second
compartment
(mm)
Third
compartment
(mm)
Coarse 24-16 18-12 12-8
normal 18-12 12-8 8-4
Fine 12-8 8-4 4-2
rock, and limestone-amended basalt horizontal roughing
filters and found only marginally improved efficiency (7%)
for calcite amended basalt filters over unaltered filters.
Improved removal efficiencies are generally correlated to
smaller media sizes (Collins, 1994; Wegelin, 1986).
The use of multiple grades of filter media in a roughing
filter promotes the penetration of particles throughout the
filter bed and takes advantage of the large storage capa-
cities offered by larger media and high removal effi-
ciencies offered by small media. The size of filter media
decreases successively in the direction of water flow and
ideally the uniformity of filter media fractions is maximized
to increase filter pore space (storage capacity) and aid in
filter cleaning (Boller, 1993).
Common grades of media used in roughing filters are
provided by Wegelin (1996) and shown in Table 1.
Alternative filter media
The filter material should have a large specific surface to
enhance the sedimentation process taking place in the
roughing filter and high porosity to allow the accumulation
of the separated solids. Generally speaking, any inert,
clean and insoluble material meeting the above 2 criteria
can be used as filter medium. Filtration tests revealed
that neither the roughness nor the shape or structure of
the filter material have a great influence on filter effi-
ciency. The following material could therefore be used as
filter media:
a) Gravel from a river bed or from the ground.
b) Broken stones or rocks from a quarry.
c) Broken burnt clay bricks.
d) Plastic material either as chips or modules (e.g. used
for trickling filters) may be used if the material is locally
available.
e) Burnt charcoal, although there is a risk of disintegra-
tion when cleaning the filter material, it should only be
considered in special cases (e.g. for removal of dissolved
organic matter).
f) Coconut fibre, however, due to the risk of flavouring the
water during long filter operation, it should be used with
care.
Researchers like Ochieng (2006) noted that broken burnt
bricks and improved agricultural waste (charcoal Maize
cobs), can also be effectively used as pretreatment media
Nkwonta and Ochieng 459
Figure 2. Shows the mechanism of roughing filters.
media and therefore could serve as alternatives where
natural gravel is not readily available. It was observed
that in general both broken burnt bricks and charcoal per-
formed better than gravel. This observation could have
resulted from the reason that both charcoal maize cobs
and broken burnt brick have a slightly higher specific
surface area and porosity respectively to enhance the
sedimentation and other filtration processes compared to
gravel.
Filtration rate
Filtration rate also has a significant influence on the treat-
ment removal. Good removal in roughing filters are best
achieved with low filtration rate (Boller, 1993), because
low filtration rates are critical to retain particles that are
gravitationally deposited to the surface of the media.
While as pretreatments used for removal of iron and
manganese were able to operate at filtration rates of 1.5 -
3 m/h (Hatva, 1988). Researchers like (Dastanaie, 2007)
reported that horizontal flow roughing filter is capable of
removing metals like iron, manganese, turbidity and
colour at a filtration rate of 1.8 m/h.
Wegelin et al. (1986) found that at increased filtration
rates (2 m/h), coarse particles penetrate deeper into the
bed and these will cause decrease in filter efficiency.
Whereas at 1 m/h there was good distribution of solids
loading throughout the bed. Hendricks (1991) also sug-
gested that normal filtration rate of horizontal roughing
filters is between 0.3 and 1.5 m/h.
Filter length
Improved cumulative removal efficiencies are typically
correlated to longer filter lengths (Collins, 1994; Wegelin,
1986). However, incremental removal efficiencies tend to
decrease with increasing filter length due to the prefe-
rential removal of larger particles early in the filter
(Wegelin, 1996). The rate of decline is dependent on filter
design variables and the size and nature of particles in
suspension. The use of different media sizes may allow
for treatment targets to be met by a shorter filter with
multiple media sizes compared with long filter packed
with one media size.
MECHANISM OF ROUGHING FILTERS
As illustrated in Figure 2, water has to undergo a step to
step treatment especially if it contains differently sized
impurities. The first and easiest step in sound water treat-
ment schemes is coarse solids separation. Finer particles
are separated in a second pretreatment step and finally,
water treatment will end with the removal or destruction
of small solids and microorganisms. These different pre-
treatment steps will contribute to reducing the pathogenic
microorganisms. The pathogens attached to the surface
of suspended solids will get stranded when the solids are
separated. Some of the microorganisms floating in the
water might also get pushed to the surface of the treat-
ment installations and adhere to biological films. Solid
matter and microorganisms, therefore, face a multitude of
treatment barriers. Since treatment efficiency of each bar-
460 Int. J. Phys. Sci.
Figure 3. Solids removal in HRF (Wegelin, 1996).
of each barrier increases in the direction of flow, it becomes
increasingly difficult for the impurities to pass through
each subsequent treatment barrier. Removal of sus-
pended solids in RF requires laminar flow (Galvis et al.,
2006). Hydrodynamic forces that move the water through
the pore system create patterns of flow retardation and
acceleration that have pockets of stagnant water near the
media surface allowing particles to settle and it was
shown in Figure 3. A sticky organic film on the surface of
the media in the pores retains the suspended solids by
mass-particle attractions through the Vander Waals
forces and electrostatic forces between charged particles
(Wegelin, 1996).
PRACTICAL EXPERIENCE WITH ROUGHING FILTERS
Experience in Iran
A Vertical flow pilot plant was designed and run by
Dastanaie (2007) at the bank of Zayandehroud River
near the village of Chamkhalifeh in 2003. In order to
provide required head, the pilot was installed 2 m below
the elevation of river bed. Water was conducted towards
the filter via a man made conduit. The filter is comprised
from 3 different parts which are separated with perforated
baffles. Each compartment is filled with some local sand
and gravel considering a special decreasing size regime.
In other words, the diameter of stuffs in the compart-
ments is decreased from 25 - 15 mm in the first compart-
ment to 15 - 8 mm in the second and 8 - 4 in the last one.
The average height of materials in the filter is 2.5 m and
water always undergoes a subsurface flow beneath the
surface of the filter. In order to monitor the quality of
outlet water, parameters like total suspended solids
(TSS), turbidity, color and fecal coliforms as well as ions
like iron and manganese are being compared between
inlet and outlet water.
The comparison between the values of mentioned
parameters in inlet and outlet water is illustrated in table
2. As it is shown in the figures, the overall function of the
filter in removing turbidity and TSS is acceptable. Addi-
tionally, iron, manganese and color removal are also
been covered to some extent.
Experience in Malaysia
A pilot plant was constructed in Malaysia by Nordin Adlan
and he examines and evaluates the removals of turbidity,
suspended solids and BOD and coliform organisms from
wastewater using different sizes of limestone roughing
filter. Results indicated that removal efficiencies
depended on the size of the filter medium and applied
flow rates. Turbidity, suspended solids, BOD and coliform
organisms’ removals were between 75 and 92%, 79 and
88%, 51 and 67% and 67 and 96%, respectively, in a
combination of the 3 filter media with particle sizes
between 1.91 and 16.28 mm. Removal efficiency was
found to increase with slower flow rates.
Experience in Africa
Another study was investigated by Ochieng and Otieno
(2004) in a pilot plant built at Moi University in Kenya using
Table 2. Removal efficiencies of the filter.
Parameters Unit Inlet Outlet Removal
%
Turbidity NTU 3.528 1.29 63.4
Colour mg/l 0.8 0.6 20
Iron mg/l 0.083 0.07 15.6
manganese mg/l 0.0417 0.015 64
TSS mg/l 18.93 1.95 89.7
Coliforms MPN 112.6 6.74 94
broken burnt bricks and charcoal, as filter media for
removal of Suspended solids and turbidity. They noted
that broken burnt bricks and improved agricultural waste
(charcoal Maize cobs), can also be effectively used as
pretreatment media and therefore could serve as
alternatives where natural gravel is not readily available.
The design and sizing of the pilot plant was guided by
Wegelin design criteria and a constant filtration rate of
0.75 m/h was chosen for the HRF units. It was observed
that in general both broken burnt bricks and charcoal per-
formed better than gravel. This observation could have
resulted from the reason that both charcoal maize cobs
and broken burnt brick have a slightly higher specific
surface area and porosity respectively to enhance the
sedimentation and other filtration processes compared to
gravel.
Another pilot HRF was constructed and operated by
Tamar Rachelle Losleben at Ghanasco Dam in Tamale,
Northern region Ghana using three 7 m tubes filled with 3
sizes of granite gravel, local gravel and broken pieces of
ceramic filters arranged by decreasing size. The pilot
study was run for 52 days to test if HRF could reduce the
high turbidity (305 NTU) to < 50 NTU to make SSF a
viable option. There were a number of promising out-
comes: the best performing media, the granite gravel, by
removing an average 46% of the influent turbidity (filter
coefficient ë = 0.002 min -1), produced an average
effluent turbidity of 51 NTU which almost achieved the
goal of < 50 NTU. The granite gravel, HRF removed twice
as much turbidity (46%) as plain settling (25%). Overall,
the granite gravel removed 76 and 84% of the influent
turbidity according to the settling test and pilot HRF data
respectively.
Another pilot plant was constructed by University of
Zambia, Lusaka, Zambia, in collaboration with Delft
University of Technology, Delft; the Netherlands have
embarked on a research programme on surface water
treatment. The pilot plant comprises 2 identical treatment
lines each having 1 upflow roughing filter in layers
(URFL) and 1 inlet controlled slow sand filter (SSF). The
filter media for both URFL and SSF were obtained from
natural local sources. Raw water was drawn from the
Kafue River, 1 of the major rivers in Zambia. The river
normally exhibits low turbidity levels during the dry sea-
son (daily averages of 3 - 30 NTU), with peaks of 50 -300
Nkwonta and Ochieng 461
NTU occurring during the rainy season. Since the pilot
plant was operational during the dry season, clay suspen-
sions were prepared using clay from the Kafue river
banks to simulate turbidity peaks.
The URFL was operated at average filtration rates of
0.4, 0.5 and 0.75 m/h, while the SSF was operated at an
ave-rage rate of 0.2 m/h. The raw water and filtered
waters were checked for turbidity, total suspended solids
and coliform organisms. Filter resistance was also moni-
tored by means of piezometer tubes installed at various
heights of the filter. During the first trial (from March 2nd
until March 31st, 1997), the URFL was operated at a
filtration rate of 0.4 m/h. During this period, average
turbidity removal ranged from 32-93%, with average daily
influent turbidities between 1.08 - 10.67 NTU.
Experience in India
A pilot plant was constructed in the depth of water
resources engineering, Jadavpur University to investigate
the objectives of the research study. The structure of the
plant was made up from the Fiber glass sheeting which
consisted of three chambers of each 450 × 300 mm. The
filter medium namely gravel was placed in the 3 separate
chambers starting from the coarse size to the finer ones
in the direction of flow and the whole system was
operated in series. The first compartment was filled up of
gravel size 15 – 10 mm having the average size 12.5 mm
the second compartment consisted of average gravel
size 7.5 mm and the third one of average size 2.5 mm.
Each compartment was being separated by the perfo-
rated fiber glass partition to avoid mixing of the gravels of
different chambers. The filter bed was provided with the
under drainage system to enable flushing after a certain
running period of interval for hydraulic sludge extraction
by observing the filter resistance. A constant flow rate of
0.75 m/h was maintained through all the compartments
by the help of a peristaltic pump. The suspended solids
(SS) concentration of raw water for all the chambers at
the inlet and the SS concentration at the out let was
measured by the help of standard procedure describe in
the Standard methods. Sampling from the investigation
was done at least 3 times of week for a period of 70 days.
The experiment was carried out both in low flow (dry sea-
son) and high flow (rainy season) periods during the scan
of 70 days. The local pond water was used as raw water
which has the concentration of suspended solids ranges
from 40 to 150 mg/l. According to Weglin’s design guide
line this range is medium range of concentration (100
300) mg/l for which filtration rate is 0.75 – 10 m/h are
recommended. So a constant flow 0.75 m/h was chosen
in carrying out the project. E value and filter efficiency
was shown in Table 3.
Experience in Sri Lanka
Jayalath (2004) in a pilot plant built in Sri Lanka found out
462 Int. J. Phys. Sci.
Table 3. Removal efficiency of the filter.
Effective size
(dg) (mm)
Filtration rate
(m/h)
Length of
compartment (m) E-value % Total E –value
(dec)
5 0.75 0.45 E
1
= 21.3 0.026
10 0.75 0.45 E
2
= 19.6
15 0.75 0.45 E
3
= 26.0
Table 4. Performance of roughing filters.
Reference Filtration
Rates (m/h) Parameters Mean percent
removed (%)
Pacini(2005) 1.20 Iron and manganese 85 and 95
Dome (2000) 0.3 Algae and turbidity 95 and 90
Mahvi (2004) 1.5 Turbidity 90
Ochieng and Otieno (2004) 0.75 Turbidity and algae 90 and 95
Dastanaie (2007) 1.8 Turbidity, TSS and Coliforms 63.4, 89 and 94
Jayalath (1994) 1.5 colour and turbidity 50 and 60
Rabindra (2008) 1.0 TSS and turbidity 95 and 95
Mukhopadhay (2008) 0.75 Turbidity 75
that there is a considerable reduction in Synedra popula-
tion (80 – 87% in terms of cell count) as well as colour
and turbidity (50 – 60%). Highest percentage removal
was obtained form the filtration velocities below 1.5 m/h
for color and turbidity and below 2 m/h for algae removal.
Field-scale experiments show that filter length does not
provide a significant effect on the percentage reduction of
algae count, color and turbidity. Horizontal flow velocity
was maintained at 1.0 – 2.5 m/h. As the flow velocity
increased up to 4.5 m/h, algae removal reduced to 70%
while color and turbidity to 40%. It was observed in Table
4 that Paciani (2005) used 1.20 m/h filtration rate for his
pilot plant experiment. He achieved 85 and 90% respec-
tively on iron and manganese reduction in the plant.
Some also used 0.3 m/h filtration rate for his experience
and achieved 95 and 90% respectively for algae and
turbidity removal in the waste water. Experiences from
researchers are shown in Table 4.
DISCUSSION
Factors affecting roughing filter performance
The disadvantage of RF is low hydraulic load. The only
way to provide sufficient treated water to meet a high
drinking water demand would be to build a larger RF unit
(Boller, 1993). The filtration rate (m/h) depends largely on
the type of filter, the water characteristics, desired turbi-
dity reduction, Variations in the filter media (porosity),
each filter medium’s proportion, the number of filter frac-
tions and height and width of filter bed area (m2) dictate
filtration and optimize the removal of suspended matter.
The filter media size (mm) and type (gravel and broken
clay) is also an important consideration. The most
influential factor for turbidity removal efficiency in the raw
water is particle sizes and distribution.
Filter efficiency depends on the concentration of sus-
pended solids. The 1/3 and 2/3 Filter theory explains how
each layer removes about 1/3 of the particles letting the
other 2/3 flow to the next layer (Wegelin, 1996). This
continues at each layer, because there is a greater con-
centration of particles at the first layer, more particles are
removed than in latter layers. Intermittent flow operation
can greatly decrease the particle removal efficiency
because it is possible that the biofilm around the coarse
media might have dried and lost its sticky properties
(Galvis, 2006).
High sludge storage space can be advantageous in
lengthening filter runs but becomes problematic when the
filter finally needs to be cleaned. Its buffering capacity to
manage fluctuating solid concentrations exists because
the large pore spaces allow considerable amounts of
solids to be stored at very low head loss (Boller, 1993).
Periodic drainage through perforated or corrugated pipe
may be able to improve the filter run time between
cleanings and needs to be further developed (Boller,
1993). Scraping of the top layer of biofilm on a weekly
basis could also improve the filter run time. Fully
unpacking the media and cleaning it is 1 of the biggest
drawbacks of the RF even when the media is readily
accessible as it is in HRF.
Advantages of roughing filters over conventional
methods
Conventional system is quite demanding in chemical use,
energy input and mechanical parts as well as skilled
manpower that are often unavailable, especially in rural
areas of developing countries like Tanzania, Kenya and
Sri Lanka. But roughing filters does not require chemical
use, energy input and mechanical parts. Conventional
methods demand high operating costs.
Disadvantages of roughing filters over conventional
methods
Colour removal is fair to poor and in some cases it
requires a large area of land for effective treatment. It can
handle only relatively low strength wastes compared to
conventional methods. It also can handle only very low
organic loads compared to conventional treatment
methods such as activated sludge process.
Conclusion
With regards to water crises in Africa and throughout the
world, a decline in rainfall and drought threat throughout
numerous countries and considering the point that the
majority of easily accessed water resources are surface
water resources, by applying self reliant processes, which
are economic important, the mentioned process such as
roughing filtration, must be studied to provide healthy
refreshing drinking water to developing countries like
Tanzania. Considering removal efficiency for total sus-
pended solids, manganese, turbidity, colour, algae and
iron respectively, this system has shown convincible
results. Achieved results in previous study shows that
roughing filtration may be considered as efficient pretreat-
ment process incase surface water is used as water
supply for treatment. But this can be achieved, if applied
to appropriate source water and when designed and
operated properly. Ochieng and Otieno, 2004 found out
that in the high peak period, the suspended solids, even
though not to the design level, could have been high
enough to promote sedimentation and other filtration
processes such as adsorption to register high removal
efficiency. In the low-peak period, a lower reduction per-
centage for all the filters was recorded. This observation
could be attributed to the fact that low suspended solids
in the dry season could have possibly reduced the
sedimentation process due to a possible increase in the
colloidal stability and hence less particle interaction.
ACKNOWLEDGEMENT
The authors would like to thank Tshwane University of
Technology for offering the principal author scholarship to
undertake his studies for a Masters degree.
Nkwonta and Ochieng 463
REFERENCES
ASCE (2000). Task Committee on Application of Artificial Neural
Networks in Hydrology Artificial neural Networks in Hydrology I:
Preliminary concepts, ASCE J. Hydro. Eng. 5(2): 115–123.
Blackburn H (1997). Filter effective on surface water, www.watertechon
line.com, Vol. 2.
Boller M (1993). ‘Filter mechanisms in roughing filters’, J. Water
Supply Res. Technol. Aqua. 42(3): 174-85.
Clarke BA, Lloyd BJ, Crompton JL, Major IP (1996). ‘Cleaning of up flow
gravel prefilters in Multi-stage filtration water treatment plants’, in
Advances in Slow Sand & Alternative Biological Filtration, ed.
Collins MR, Westersmund CM, Cole JO, Roccaro JV (1994). Evaluation
of roughing filtration design variables, American Water Works
Association Research Foundation and American Water Works
Association.
Dastanaie J (2007). Use of horizontal roughing filtration in drinking
water treatment. Int. J. Sci. Technol. 4(3): 379-382.
Dome S (2000). How to estimate and design the filter run duration of a
horizontal flow roughing filter. Thammasat Int. J. Sci. Technol. 5(2).
Galvis G, Visscher JT, Latorre J (1998). Multi- stage filtration and
innovation water treatment technology. International reference centre
for community water supply and sanitation. The Hague, Netherlands
and Universidad del valle instituto CINARA, Cali, Colombia.
Graham N Ed (1988). Slow sand filtration, recent developments in water
treatment technology. Elis Horwood limited/ Wiley and sons
Chichester England.
Hatva T (1988). Treatment of groundwater with slow sand filtration.
Water Sci. Technol. 20(3): 141-147.
Hendricks DW (1991). Manual of design for slow sand filtration.
American water works association research foundation Denver co.
Jayalath J (1994). Algae removal by roughing filter. 20th WEDC
conference.
Mahvi AH (2004). Performance of a DHRF system in treatment of highly
turbid water. Iranian J. Environ. Health Sci. Eng. 1(1): 1-4.
Mukhopadhay B, Majumder M (2008). Verification of filter efficiency of
horizontal roughing filter by wegelin design criteria and artificial
neural Network. Copernius publication.
Nash JE, Sutclie JV (1970). River flows forecasting through conceptual
models, J. Hydrol. 10(20): 282–290.
Ochieng GM, Otieno FAO (2004). Performance of different filter media
against conventional water treatment system. Watersa Vol. 30.
Ochieng GM, Otieno FAO (2006). Verification of wegelin design
criteria for horizontal flow roughing filters with alternative filter
materials. Watersa Vol. 32.
Pacini V (2005). Removal of iron and manganese using biological
roughing up flow filtration technology. Water Res. 399: 4463-4475.
Rabindra NB (2008). Performance of HRF as a pretreatment unit before
conventional water treatment system. Published in engi@philica.com.
Rooklidge SJ, Ketchum KL (2002). Calcite amended horizontal roughing
filtration for clay turbidity removal, J. Water Supply Res. Technol.
5(6): 333-342.
Wegelin M (1996). Surface water treatment by roughing filters. A
design, construction and Operation manual, Swiss Federal Institute
for Environmental Science and Technology (EAWAG) and Depart-
ment Water and Sanitation in Developing Countries (SANDEC).
Wegelin M, Bolller M, Schertenleib R (1986). ‘Particle removal by
horizontal-flow roughing filtration’, Aqua. 2: 80-90. Yitian L, GU RR
(2003). Modeling Flow and Sediment Transport in a River System
Using an Artificial Neural Network, J. Environ. Manage. 31(1): 122–
134.
... This is due to the smaller size of bacteria that allows them to evade the screening process (Matuzahroh et al. 2020). Other water quality parameters that can be improved by the roughing filter include color, dissolved organic matter, nutrients, heavy metals, and COD (Lee & Jayalath 1998;Nkwonta & Ochieng 2009;Nkwonta 2010;Munasir et al. 2015). ...
... Referring to the 3D surface and 2D contour plots, it can be seen that suspended solids removal increased with a decrease in flow rate and particle size. This tendency may be attributed to smaller sand particle sizes having a lower porosity than larger ones, hence retaining an increased volume of solid matter (Nkwonta & Ochieng 2009). Lower flow rates also prevent penetration of coarse solid particles through the filter bed and increase the retention time, thus offering better removal efficiencies (Nkwonta 2010). ...
... To overcome the relatively low removal efficiencies by roughing filters, filtration media materials with superior adsorption and/or filtration properties such as plastic and coconut fibers (Hashimoto et al. 2019), anthracite (Karki & Amatya 2020), broken burnt bricks and agricultural residues (Nkwonta & Ochieng 2009) as well as zeolite (Al-Zou'by et al. 2017) could replace silica and gravel. Additionally, turbidity, TSS, and colour removal by roughing filters could be enhanced by introducing a coagulant in the raw wastewater prior to its filtration (Hasnain & Khan 2014;Hashimoto et al. 2019). ...
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... During the roughing filter process, some suspended particles were settled by the settling process due to their gravity (Khazaei et al. 2016). Also, low filtration rates are critical to retain particles that are gravitationally deposited to the surface of the media which is accepted by (Nkwonta and Ochieng 2009). Meanwhile, the conditions for the minimal turbidity removal efficiency (15%) were with a 20 mm raw limestone under a 100 mL/min flow rate. ...
... Meanwhile, the conditions for the minimal turbidity removal efficiency (15%) were with a 20 mm raw limestone under a 100 mL/min flow rate. As per Nkwonta and Ochieng (2009), if a faster flow rate were used, along the settling distance, the particle of the limestone could travel faster and then stick onto the media layer or be absorbed. Laminar flow (Mushila et al. 2006) is implicated by removal of suspended particles in the roughing filters mechanism. ...
... (2) Roughing filters: These are the filters that are mostly used to reduce the suspended solid organic matter from the wastewater. They not only reduce the pathogens but also reduce the amount of iron and manganese in the wastewater (Nkwonta and Ochieng 2009). They usually operate in downstream processing; if the organic loading is very high, then there will be a continuous shedding of the microbial slime. ...
... • Horizontal flow roughing filters: Filters have horizontal flow direction; type of filter medium used in this kind of filter is coconut husk fiber. Among three types, upflow roughing filters are most widely used as they are cheap and easily maintained (Nkwonta and Ochieng 2009). ...
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... Similar results have also been observed by Ochieng et al. [20,23]. Nkwonta et al. [24] reported the total value of E of 0.026 for the filtration rate of 0.75 m/h and for three compartments of length equal to 0.45 m. ...
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