Reviving Traditional Slow Sand
Filtration Technology For Clean, Safe And Sustainable Drinking Water Supply In
Rural Himalaya
R.B.P.
Singh*, Pallavi P. Chouhan, Vikas Vatsa, Vijay Kumar and Rakesh Bahuguna
* Corresponding
Author: Advisor, HIMCON & Head, Department of Environmental Sciences,
Uttaranchal College of Science &
Technology, Dehradun (UK)
Email: rambhushan401@gmail.com; himconindia@gmail.com Vijaysharma.evs@gmail.com; messageforhumanity@gmail.com, http://mfhngo.co.nr
Introduction
Water
is a prime natural resource, a basic human need and a precious natural asset.
Access to clean and safe drinking water has direct bearing on both quality and
prosperity of human life. Availability of clean and safe drinking water is a
basic need of life. Drinking or potable water should have sufficiently high
quality, so that it can be consumed or used without risks of immediate or
long-term harmful effect on human health. Over large parts of the country,
people have inadequate access to clean and safe drinking water. Most of the
supply sources made for drinking and other domestic uses either gets
contaminated with disease vectors, pathogens or having unacceptable level of
dissolved chemicals and suspended impurities. Drinking such contaminated water
may leads to widespread acute and chronic illness and ultimately it may cause
death of people. Recent estimates of WHO & UNICEF’s estimate suggests that
about one-sixth of world population lacked access to clean and safe drinking
water. Each year, over 5 million people die because of water related diseases.
About 80 percent of diseases caused due to use of contaminated water in the
developing countries.
Scenario of
Drinking Water Supply in Tehri Garhwal
Although,
Himalaya has been often referred to “Water
Tower of Asia” but it is an irony, people living in its lap now faces severe
drinking water crisis. A large volume of data on water availability in
Himalayan states clearly indicates the vulnerability of springs and small
streams which are the main source of drinking water for the Himalayan people.
According to a conservative estimate, about 80 percent of total drinking water
supplies are fulfilled by these water sources.
Conservation,
management and sustainable development of natural resources of Himalaya and improvement of quality of life of its people
are the main objective of the HIMCON. Since its inception Himalayan Consortium
For Himalaya Conservation (HIMCON) – a non profit voluntary organization has
been engaged in sustainable water resource management in the Himalayan villages
through various measures of rooftop rainwater harvesting and watershed
development activities. Two decades earlier, Himalaya
was considered pristine and pollution free. Hill people proudly referred their
spring water as ‘Jadi-pani’ having magical properties, rich in minerals and are
supposed to be healthy water from public health point of view. But increasing
population pressure, unplanned developmental activities, open defecation
practices of people, grazing animals, spreading cattle dung in agricultural
terraces and mixing of lechate from percolating soak pits of toilets has been
contaminated majority of drinking water supply sources in rural Himalaya
(HIMCON, 2000, NEERI, 2005). Now, the ground reality has altered this myth,
rich and elite people installed costly water purifiers in their home, outside
visitors came with their own packaged drinking water. They hesitate to drink
water from the natural source. There is no alternative for the rural poor
people but to drink unhygienic and contaminated water and became victim of
diseases.
Water Quality
Status in Tehri Garhwal
Observing
the serious health consequences among the people living in the rural areas
causes due to consumption of contaminated water, HIMCON conducted extensive
water quality monitoring programme to assess water quality of major drinking
water supply sources in more than 50 villages of Chamba Block of Their Garhwal
district in 2000. Samples of more than 250 water sources were analyzed. Further
in 2004, NEERI conducted detailed and extensive survey of water quality both at
supply sources and at the household level in more than 23 villages of Chamba
Block. The summary of water quality status in the region is depicted in Table 4,
5 and 6. The analytical results clearly depict an alarming picture of water
quality that warrants an immediate action as consumption of water from these
sources have the potential of posing serious health hazards to people. The 1st
and 2nd order springs were observed to more susceptible to
contamination than 3rd order springs located in valley side. Some
springs located in the valley side however, showed safe water quality at the
source but water gets contaminated during transport or at household level. Overall,
about 90 percent of water sources were found bacteriological contamination.
Provision
of sustainable, clean and safe drinking water to the local community was
observed to be urgently required so that the consumer can be protected against
the health hazard of contaminated water. With the technical support of premier
institute in this field, ‘National Environmental Engineering and Research Institute
(NEERI), Nagpur, HIMCON initiated development of suitable, reliable and low
cost and eco-friendly technology of water purification at community level. In
2005, two large sized Slow Sand Filters was installed in Nakot and Gajna
village by NEERI & HIMCON. Proper training was provided to the villagers so
that they can properly maintain their own SSF. The population of these two
villages was more than 60 families. Proper maintenance of the SSF was not properly
followed by the villagers mainly due to differences among the villagers.
Observing the differences of opinion among the diverse community in large
villages for cleaning and maintenance of the installed filter, HIMCON make slight
modification in the existing SSF and developed ‘Mand Baloo Chhanna’ suitable
for smaller community. HIMCON ‘s ‘Mand Baloo Chhanna’ which is basically
developed with the technical support of NEERI, Nagpur, permits slow sand filter
cleaning without the removal of upper few centimeters of the filter bed. This
is achieved by recognizing that virtually all of the processes provided by the
slow sand filtration occur at or near the surface of the filter bed popularly
called ‘schmutzdeke’ - a German word that means dirty layer or dirty blanket.
Previously it was believed that the entire sand bed constitute the schmutzdeke.
If the upper surface of the filter bed of SSF can be cleaned by removing the
material that inhibit flow while leaving the filter media (schmutzdeke)
completely intact, the capacity of the filter to remove bacteria, viruses and
certainly the parasites is not affected by the act of filter cleaning itself
(David P. Manz &P. Eng., 2004). This innovation developed over the past 10
years has revolutionized the slow sand filtration technology worldwide that
make it simple, inexpensive, user friendly and can be built in any size
required at household level to community level.
Till
now, with the financial support of ARGHYAM & Himalaya Sewa Sangh, people of
more than 12 villages in Chamba Block of Tehri Garhwal have been provided clean
and safe drinking water round the year. Water quality of raw and filter water
has been properly monitored at regular interval to check the performance of
SSF. Mahila Mangal Dal has been formed in each of the selected village where
filter installed. They were properly trained and entrusted for proper
maintenance of SSF. Local people are happy and enjoy clean and safe drinking
water round the year with their own SSF. These initiatives undertaken by HIMCON
have been highlighted in both print and digital media. The details of
construction, function and performance efficiency of SSF are given below.
Principle of Slow Sand
Filtration
A slow sand filter contains biological
activity and is therefore often referred to as a bio-sand filter. As
micro-organisms such as bacteria, viruses and parasites travel through the
sand, they collide with and adsorb onto sand particles. The organisms and
particles collect in the greatest density in the top layers of the sand,
gradually forming a biological zone. The biological zone is not really a
distinct and cohesive layer, but rather a dense population that gradually
develops within the top layer of the sand. The population of micro-organisms is
part of an active food chain that consumes pathogens (disease-causing organisms)
as they are trapped in and on the sand surface. The uppermost 1-3cm of this
biological zone is sometimes referred to as 'schmutzdecke' or
'filter cake'. Slow sand filters are usually cleaned by scraping of the
bio-film and/or the top sand layer.
Construction Design of a Slow Sand Filter
Basically a slow sand filtration unit
consists of a rectangular concrete tank with the following components:
1. Filter Housing
Filters can be
constructed in tanks with non-reactive surfaces such as plastic or galvanized
tanks, poly or concrete tanks of various sizes from 205 liters up to 100,000
liters tank. The capacity of the filter is determined by the surface area of
the filter top and not the overall volume of the filter. Consideration must be
made of the flow rate to be used when determining tank size. A slow flow rate of 100 L/ hr/ m2
of surface area have been found to be preferable in high risk situations.
Table 1: Measurement of volume of water
filtered in a 24 hour period by filters of varying size surface area filter bed
Surface Area (m2)
|
Low Rate
|
||
100
|
200
|
300
|
|
0.25
|
600
|
1200
|
1800
|
0.50
|
1200
|
2400
|
3600
|
1.0
|
2400
|
4800
|
7200
|
2.0
|
4800
|
9600
|
14400
|
5.0
|
12,000
|
24,000
|
36,000
|
10.0
|
24,000
|
48,000
|
72000
|
15.0
|
36,000
|
72,000
|
108,000
|
2. Water layer
The water layer above the filter bed provides the head to
push water through the filter bed. It is convenient as a water storage zone and
provides an effective temperature buffer to stabilize the filter and protect
the biological activity occurring in the top layers of filter bed. A maximum
depth of 5 cm of water layer above the sand bed is found to be most suitable to
maintain dissolved oxygen level up to 3.0 mg/l.
3. Filter bed
The filter bed consists of a uniform fine particle sand
mixture as specified in Design summary table. The most critical design feature
of the SSF is using correct sand. The filter bed is built to a depth of 1.0 -1.5
m with a minimum of 0.7 m of sand bed. This depth of sand will allow for losses
which will occur if the top portion of the sand is removed when particulate
matter and algae is cleaned from the top of the sand.Sand needs to be of a fine
grade (0.15 - 0.35 mm is generally recommended) and be washed free of loam,
clay, and organic matter.
4. Drainage system
A gravel drainage system is provided at the bottom of the
filter to prevent movement of the fine sand into the filter outlet. It
consisted of 3 layers gravel, 2.0 mm, 10 mm and, 25 mm. The bottom layer of
gravel supports perforated drainage pipes which may simply bisect the filter or
in a large filter form a network of connecting pipes across the base.
5. Flow control
A regulating tap should be connected to the filter outlet
to control the flow rate. The flow rate is specified in terms of liters / hour
per unit area of the surface of the filter (m2). The flow rate
through the filter is less than gravitational fall. An open clear pipe (poly
tube) fixed to the exterior of the filter can be used to monitor head loss.
Table 2: Design
Summary of Slow Sand Filter (Mand Baloo Chhanna)
S
|
Design Parameters
|
Recommended
range of values
|
1.
|
Raw
water inlet
|
Can
be directly connected to spring source through pipe. If turbidity of raw
water is higher it should first diverted into sedimentation tank than to SSF
inlet
|
2.
|
Surface
Area of filter bed (m2)
|
One
square meter
|
3.
|
Filtration
rate
|
0.1
– 0.2 m3/m2/hour
|
4.
|
Depth
of over-flow water on the sand bed
|
5
cm
|
5.
|
Depth
of filter bed
|
1
meter (minimum of 0.7 m of sand bed depth)
|
6.
|
Number
of different sand layer in the filter bed
|
3
layers
|
1st
Sand Layer
|
Effective
size: 0.15mm (Sand Depth – 30 cm)
|
|
2nd
Sand Layer
|
Effective
size: 0.35 mm (Sand Depth – 30 cm)
|
|
3rd
Sand layer
|
Effective
size: 0.60 mm (Sand Depth – 10 cm)
|
|
7.
|
Under
drain system:
|
Three
layers of gravels of different size and bricks
|
1st
Gravel Layer
|
Effective
size: 02.0 mm (Gravel Depth- 10 cm)
|
|
2nd Gravel Layer
|
Effective size: 10.0 mm (Gravel Depth-
10 cm)
|
|
3rd Gravel Layer
|
Effective
size: 25.0 mm (Gravel Depth- 10 cm)
|
Schematic and 3-D Diagram of “Mand Baloo
Chhanna” are presented in figures
  |
||
 |
||
Table 3: Performance / Removal Capacity of Modern SSF
(Mand Baloo Chhanna) Developed by NEERI, Nagpur & HIMCON, Tehri Garhwal
(Average
data collected during performance evaluation of raw & filter water)
S#
|
Water
Pollution Parameters
|
Removal
Capacity/ Performance of Mand Baloo Chhanna
|
1.
|
Colour
Removal
|
Up
to 100 percent
|
2.
|
Odour
Removal
|
Up
to 100 percent
|
3.
|
Taste
Improvement & freshness
|
Highly
Satisfactory as it is oxy-rich water
|
4.
|
Improvement
of water clarity
|
Water
turbidity can be reduced less than 1 NTU, if properly operated along with
sedimentation tank
|
5.
|
Removal
of non-colloidal suspended particles
|
Up
to 100 percent
|
6
|
Removal
of biodegradable & dissolved organic carbon and organic matter
|
Up
to 85 to 100 percent
|
7.
|
Removal
of Faecal Coliform and other pathogenic bacteria
|
Up
to 99.9 percent
|
8.
|
Removal
of E. coli bacteria
|
Up
to 99.9 percent
|
9.
|
Removal
of Enteric and other harmful viruses
|
Up
to 99.9 percent
|
10.
|
Removal
of Parasites
|
Up
to 100 percent
|
11.
|
Removal
of Cercariae of schistosoma, cysts and ova
|
Up
to 100 percent
|
12
|
Removal
of Cryptospordium Oocysts
|
Up
to 100 percent
|
13.
|
Removal
of Giardia cysts
|
Up
to 100 percent
|
14.
|
Removal
of colour producing iron & manganese
|
Up
to 38 to 100 percent, if a layer GAC applied in the filter bed
|
15.
|
Removal
of hazardous heavy and trace elements viz. Zn, Cu, Cd, Pb and others
|
Up
to 95 percent, if a layer GAC applied in the filter bed
|
16.
|
Removal
of arsenic
|
Up
to 40 to 65 percent, if a layer GAC applied in the filter bed
|
17.
|
Removal
of pesticides
|
Up
to 40 to 65 percent, if a layer GAC applied in the filter bed
|
Advantage of Slow Sand Filter
The
effectiveness of SSF for raw water treatment has been very well documented. No
other single process can effect such an improvement in the physical, chemical
and bacteriological quality of waters (Buzunis, B.J., 1995). Its advantages
have been proved in practice over more than 150 years, and it is still the
chosen method of water purification in certain highly industrialized cities as
well as in small communities in rural areas both in developed and developing
countries in the world. There are several advantages of SSF technology over
other methods of water purification for drinking purposes. These are as follows
·
SSF
filtration technology is very simple, reliable and inexpensive.
·
Simplicity
in operation and maintenance as it required minimum operator skills and
training to operate SSF.
·
The
design of SSF is so simple that it can be easily built and installed by laymen using
locally available materials.
·
Cost of building and running of SSF is
significantly lower than the other existed methods of water purification.
·
SSF
does not produce any type of harmful byproducts as do in chlorine and ozone
disinfection processes in modern hi-tech water filter. No chemicals are added
to enhance the process of slow sand filtration. Hence, it does not pollute the
environment and are 100 percent eco-friendly green technology.
·
SSF
can be used as a suitable replacement to other forms of chemicals, ozone or UV
treatment for disinfection of polluted water.
·
No
requirement of any power supply, as it function on the power of natural gravity,
hence it can be easily operate in remote and inaccessible areas where
electrical power is not available.
·
SSF
is a technically viable and sustainable water purification technology to
provide clean and safe drinking water round the year.
·
SSF
is highly valuable, especially in rural areas where majority of people still
drinking superficial water that does not meet the required standard of drinking
water quality set by WHO and BIS from public health point of view.
·
Compare
to other costly hi-tech domestic water purifiers where complains of immunity
problem among the users are common. These purifiers are primarily based on R.O.
technology, most of the desirable minerals especially calcium and magnesium also
removed by the membrane. SSF does not remove any minerals from the water but it
also enhances the taste of water mainly because of oxygen enrichment. Oxy-rich
drinking water considered healthy for health point of view.
·
Recently
a large number of hand pumps has been installed by the government in rural
areas of Uttarakhand to fulfill drinking water need of the people. Most of the
hand pumps installed with iron removal equipment become defunct only after few
months of its installment. The water of these hand pumps are not even fit for
washing clothes and utensils. If used in combination with slight modification
using a layer of Granulated Activated Carbon (GAC) in the filter bed, SSF can
be used to treat not only for removal of pathogens but also for removal of iron
and manganese, arsenic and other heavy metals (David P. Manz &P. Eng.,
2004).
Disadvantage:
Two
major problems often encountered by users of Slow Sand Filter.
- Conventional
SSF does not work well with the raw water having high turbidity. High
turbidity greater than 20 NTU in raw water often quickly clog the filter
bed, hence it reduces cleaning interval of filter bed. To overcome turbidity
problems, simple remedies such as establishment of sedimentation tank and
gravel roughing. This application can reduce the turbidity of raw water up
to 50 to 80 percent and can provide excellent pre-treatment for SSF.
- Earlier
conventional SSF are not effective for the removal of organics which tie
up with the pesticides and hazardous heavy metals. Hazardous heavy metals
and pesticides present in raw water can be completely reduced if one layer
of granular activated carbon (GAC) used between the sand bed layers.
Table 4: Summary of Physico-chemical characteristics
of major sources of drinking water in the villages of Chamba,Block, Tehri
Garhwal
(Average
and range of data collected from 2000 to 2011by HIMCON & NEERI)
Parameter
|
Average
|
Range
|
BSI & WHO Standard
|
1. Ambient Temperature
(0C)
|
24
|
2.8 – 29.8
|
NA
|
2. Water Temperature (0C)
|
12
|
8.4 – 21.9
|
NA
|
3. Total Dissolved
Solids (TDS)
|
134
|
38 - 1460
|
500
|
4. Total Suspended
Solids (TSS)
|
132
|
64 - 3000
|
100
|
5. Conductivity (umho/cm)
|
271
|
63 – 1396
|
NA
|
6. pH
|
7.6
|
5.5 – 10.4
|
6.5 – 8.5
|
7. Free Carbon-dioxide
(FCO2)
|
2.5
|
ND – 54.6
|
NA
|
8. Dissolve Oxygen
(DO)
|
1.4
|
0.9 - 4.7
|
NA
|
9. Total Alkalinity
(TA)
|
52
|
18 - 604
|
300
|
10 Total Hardness (TH)
|
116
|
10 - 518
|
300
|
11. Calcium (Ca++)
|
17
|
2.4 - 180
|
75
|
12 Magnesium (Mg ++)
|
5.4
|
0.8 - 94.4
|
30
|
13. Sodium (Na+)
|
19.4
|
ND - 69
|
NA
|
14. Potassium (K+)
|
2.9
|
ND - 45
|
NA
|
15. Fluoride (F-)
|
0.2
|
0.1 - 0,8
|
0.5 – 1.0
|
16. Chloride (Cl-)
|
23.4
|
05 - 189
|
250
|
17. Sulphate (SO4)
|
42.6
|
2.6 – 288
|
300
|
18. Nitrate (NO3)
|
0.4
|
ND - 28.5
|
45
|
19. Phosphate (PO4)
|
1.3
|
0.2 - 14.8
|
NA
|
*
All the values are in mg/L, otherwise mentioned
ND- Not Detected, NA – Not applicable
Table 5: Summary of Heavy and trace element content
in major drinking water supply source in some villages of Chamba Block, Tehri
Garhwal
(Average and
range of data collected from 2000 to 2011by HIMCON & NEERI)
Heavy Metals
|
Average
|
Range
|
BSI & WHO Standard
|
1. Iron (Fe)
|
0.219
|
0.016 - 6.47
|
0.3
|
2. Manganese (Mn)
|
0.187
|
0.003 - 0.895
|
0.5
|
3. Copper (Cu)
|
ND
|
ND
|
0.1
|
4. Cadmium (Cd)
|
0.002
|
0.001 - 0.007
|
0.1
|
5. Chromium (Cr)
|
0.003
|
0.001 - 0.008
|
0.1
|
6. Lead (Pb)
|
0.097
|
0.017 - 0.262
|
0.1
|
7. Zinc (Zn)
|
2.158
|
2.158 - 4.554
|
5.0
|
8. Aluminum (Al)
|
0.258
|
0.136 - 0.505
|
NA
|
9. Cobalt (Co)
|
0.006
|
0.001 - 0.021
|
0.5
|
10. Arsenic (As)
|
0.121
|
0.072 - 0.165)
|
0.1
|
ND-
Not Detected, NA – Not applicable
Table 6: Bacteriological quality of major drinking water
supply at source and at household level in some villages of Chamba Block, Tehri
Garhwal
(Average
and range of data collected from 2000 to 2011, by HIMCON & NEERI)
Parameters
|
Average
|
Range
|
BSI & WHO Standard
|
I. Bacteriological
quality at supply sources:
|
|||
1. Total Coliform (TC)
|
Present
|
60 - TNC
|
Absent
|
2. Faecal Coliform
(FC)
|
Present
|
08 - 180
|
Absent
|
II. Bacteriological
quality at house-hold level:
|
|||
1. Total Coliform (TC)
|
Present
|
60 - TNC
|
Absent
|
2. Faecal Coliform
(FC)
|
Present
|
04 - 638
|
Absent
|
*
TMC – To numerous to count
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