Technologies

Pond Sand Filter (PSF) with Raised Embankment [Bangladesh]

FILTER

technologies_550 - Bangladesh

Completeness: 90%

1. General information

1.2 Contact details of resource persons and institutions involved in the assessment and documentation of the Technology

Key resource person(s)

WASH Specialist & Civil Engineer:
Name of project which facilitated the documentation/ evaluation of the Technology (if relevant)
Book project: where people and their land are safer - A Compendium of Good Practices in Disaster Risk Reduction (DRR) (where people and their land are safer)
Name of the institution(s) which facilitated the documentation/ evaluation of the Technology (if relevant)
Terre des Hommes (Terre des Hommes) - Switzerland

1.3 Conditions regarding the use of data documented through WOCAT

When were the data compiled (in the field)?

16/08/2016

The compiler and key resource person(s) accept the conditions regarding the use of data documented through WOCAT:

Yes

1.4 Declaration on sustainability of the described Technology

Is the Technology described here problematic with regard to land degradation, so that it cannot be declared a sustainable land management technology?

No

2. Description of the SLM Technology

2.1 Short description of the Technology

Definition of the Technology:

The combination of pond sand filters (PSF) and raised pond embankments protect drinking water sources and increase the resilience to flood and tidal surge events in low-lying coastal areas.

2.2 Detailed description of the Technology

Description:

Coastal areas along the Bay of Bengal experience extreme seasonal variance in the presence of surface water including flooding, tidal surge, and drought. Many families living in these rural communities construct small ponds to ensure water availability for a variety of uses, such as washing, bathing, fish farming and animal watering as well as domestic use. Some families build larger ponds that are open to the use of all community members; whereby water is carried by women and children to households. Use of pond surface water may last up to several months during the year depending on the location, seasonal weather patterns, geologic conditions, capacity of the pond and user habits. Residents rely on ponds as a source of drinking water during the dry season when household rainwater harvesting techniques are no longer viable, making treatment essential.

Pond sand filters (PSF) is acentralised or semi-centralised water treatment technology often employed in many coastal areas where surface water is the only option due to saline aquifers and lack of resources for more robust, safely managed community water supply systems. The technology uses slow-sand filtration to remove turbidity (sediments) and pathogenic organisms whereby freshwater flows through layers of sand and gravel populated by a thin layer of microorganisms and treatment happens through physical and biological processes. Due to resource constraints, the number of PSF serving as water sources is usually limited. The technology considerably reduces the risk of infection with enteric pathogens. In conjunction with PSF, safe water transport (covered and cleaned containers) and household water treatment systems (chemical or additional filtration devices) are essential.
As stated in the Sustainable Sanitation and Water Management Toolbox (SSWM) slow sand filtration systems are characterised by a high reliability and rather low lifecycle costs. Moreover, neither construction nor operation and maintenance require more than basic skills. Hence, slow sand filtration is a promising filtration method for small to medium-sized, rural communities with a fairly good quality of the initial surface water source. As stated by the the World Health Organisation, slow sand filtration provides a simple but highly effective and considerably cheap tool that can contribute to a sustainable water management system.
Once a SSF facility is built, only clean sand is required for occasional replacement. The sand layers are put in gradually according to their grain sizes: rather coarse grains at the bottom and fine grains at the top. The sand-bed is usually covered with one meter of supernatant water (LOGSDON 2003). As the process of biological filtration requires a fair amount of time in order to improve effectiveness of water treatment, SSFs usually operate at slow flow rates between 0.1 – 0.3 m3/h per square metre of surface (WHO n.y.). The water thus remains in the space above the medium for several hours and larger particles are allowed to separate and settle. It then passes through the sand-bed where it goes through a number of purification processes (HUISMAN 1974).

Due to the risk of inland flooding and (seawater) tidal surges from offshore storms, communities build earthen embankments around the ponds to prevent contamination. Local authorities and community members must be involved in the design height of the embankment—which should be equivalent to the highest pre-recorded flood level. In the geo-referenced area (Patharghata) this is equivalent to the tidal surge of Cyclone Sidr (2007). Constructed roadways are often a good reference point. In southern Bangladesh , rural roadways are built to at a ten-year flood return period, so exceeding this height according to the means of the community and/or project is recommended.
Pond embankments are best raised with soil preferably of a clayey nature. The final covering layer must be rich in clay. Embankments should be planted with native grasses and flora that have strong root systems to stabilize slopes and prevent erosion during the rainy season and in cases of tidal surge due to storms. In Bangladesh, the native kolmi (Ipomoea) has proven effective. Community members have also planted crops on the embankments, such as banana trees, medicinal plants and even small garden trenches in the middle of the slope. Beyond structural support, the horticulture helps diversify nutrition and can provide a source of income for maintaining the pond sand filter.
Fences should be installed to prevent animals from entering ponds reserved for drinking water. Community members must guarantee that the ponds selected for PSF construction shall not be used for purposes such as: washing, bathing, fish farming (natural fish however can be allowed), direct cattle access washing and watering. Furthermore:
• Fertilizers and other chemicals shall never be allowed to go into the pond.
• The flow of any polluting materials in the vicinity of the pond shall always be directed away from the pond.
• Latrines, cowsheds, garbage dumps, graveyards, fuel outlets and similar polluting structures shall not be constructed within a distance of 30 meters from the pond.
• Duck or poultry rearing hanging sheds shall never be constructed over the pond.

2.3 Photos of the Technology

2.5 Country/ region/ locations where the Technology has been applied and which are covered by this assessment

Country:

Bangladesh

Region/ State/ Province:

Patharghata, Barguna district in coastal region

Further specification of location:

Baratangra, Ward:4, Union: Patharghata Union Parishad

2.6 Date of implementation

If precise year is not known, indicate approximate date:
  • less than 10 years ago (recently)

2.7 Introduction of the Technology

Specify how the Technology was introduced:
  • as part of a traditional system (> 50 years)
  • through projects/ external interventions

3. Classification of the SLM Technology

3.1 Main purpose(s) of the Technology

  • reduce risk of disasters
  • adapt to climate change/ extremes and its impacts

3.2 Current land use type(s) where the Technology is applied

Cropland

Cropland

  • Annual cropping
  • Perennial (non-woody) cropping
  • Tree and shrub cropping
Mixed (crops/ grazing/ trees), incl. agroforestry

Mixed (crops/ grazing/ trees), incl. agroforestry

  • Agroforestry

3.3 Further information about land use

Water supply for the land on which the Technology is applied:
  • rainfed
Number of growing seasons per year:
  • 2

3.4 SLM group to which the Technology belongs

  • surface water management (spring, river, lakes, sea)

3.5 Spread of the Technology

Specify the spread of the Technology:
  • applied at specific points/ concentrated on a small area
Comments:

This technology may be applied to selected ponds within a community.

3.6 SLM measures comprising the Technology

structural measures

structural measures

  • S2: Bunds, banks
  • S5: Dams, pans, ponds
  • S7: Water harvesting/ supply/ irrigation equipment

3.7 Main types of land degradation addressed by the Technology

soil erosion by water

soil erosion by water

  • Wt: loss of topsoil/ surface erosion
water degradation

water degradation

  • Hs: change in quantity of surface water
  • Hp: decline of surface water quality
Comments:

Preventing salt water intrusion, the surface water quality and quantity is protected. Turfing and planting the embankment prevents erosion.

3.8 Prevention, reduction, or restoration of land degradation

Specify the goal of the Technology with regard to land degradation:
  • not applicable

4. Technical specifications, implementation activities, inputs, and costs

4.1 Technical drawing of the Technology

Author:

Terre des hommes

Date:

30/06/2016

4.2 Technical specifications/ explanations of technical drawing

PSF is built on top of the raised embankment as a reinforced concretes structure consisting of a sand filter chamber, filtered water chamber and the sedimentation tank. The height is 4 feet 2 inches; Length-14 feet 5 inches; Width-7 feet. The capacity of PSF is 2500 liters. The construction materials used include include brick, sand, brick chips, cement, galvanized iron pipe, water tap and rebar.

The medium in the filter chamber shall comprise of three layers: 1) filter sand of 2 feet (60 cm) depth placed above 2) a 3” layer of fine gravel and 3) a 3" layer of coarse gravel.
1) The filter sand shall have the following size and grade: (a) Sand grains in the range 0.1 to 1 mm, with (b) effective size ( d10) in the range 0.15 to 0.20; and (c) Uniformity Coefficient ( d60/d10) in the range 1.5 to 2.5. Sieves are used to test sand size and grade.
The "under drainage" bottom gravel layers:
2) Fine gravel: 3” layer ¼” to 1 mm grains (gravel that passes through the ¼” sieve and are retained on 1 mm sieve)
3) Coarse gravel: 3" layer of ½” to ¼” grains (gravel that passes through ½” sieve and are retained on ¼” sieve)
Use different sized sieves made of wire mesh in wooden frame to prepare the media to prepare the two layers of gravel.

Every 5-6 weeks (or when flow rate is limited) cleaning the filter should be performed. Remove the filter aggregate layers, clean the PSF by removing any remaining objects in the three chambers (sand filter chamber, filtered water chamber and the sedimentation tank). Clean these chambers thoroughly using hard brush in necessary. Sequentially clean and replace t the coarse gravel media, then the fine gravel media, and finally the filter sand. For cleaning the gravel and sand place about 1/4th bucket of grave or the sand in plastic bucket (8, 10 or 12 liters, whichever may be convenient), pour about ½ bucket of water and then wash lifting the gravel or the sand from the bottom with hand several times, then decant the water by tilting the bucket. (Only fine particles less than 0.1 mm should be poured out while washing the sand.)

Raised Pond embankments are built with earthworks of clayey soils designed per the maximum flood height. The design depicted in this section is an indication, however the services of a qualified structural/civil engineer will be required. In general building the embankment is raised 0.6m above the maximum flood level is recommended, at a slope of 1:2. From the ground level, the average height of an embankment is two meters, and the average excavation depth is also two meters. All plans for both embankment works and PSF construction were reviewed and approved by the Bangladesh Government Department of Public Health and Engineering.

4.3 General information regarding the calculation of inputs and costs

Specify how costs and inputs were calculated:
  • per Technology unit
Specify unit:

Pond Sand Filter with raised earthen embankment

Specify volume, length, etc. (if relevant):

2,500 Litres capacity of filter; embankment average of 100 meter perimeter.

Specify currency used for cost calculations:
  • US Dollars
Indicate average wage cost of hired labour per day:

5 $ per day for labor

4.4 Establishment activities

Activity Type of measure Timing
1. Community consultation for Committee Formation Management Before onset of rain
2. Create PSF Users' Committee, agre on user contributions Management Before onset of rain
3. Committee / pond selection approved by local Government Management Before onset of rain
4. Technical orientation to PSF Committee, input on designs Management Before onset of rain
5. Excavation of Pond Structural Before onset of rain
6. Embankment Construction Management Before onset of rain
7. PSF Construction Structural
8. Fencing Structural
9. Turfing and hortiuclutre on the embankment Agronomic Before onset of rain
10. PSF Training on Media Selection and maintenance Management Regular intervals throughout the year (every 1-2 months)
11. Pond embankment maintenance Structural Before onset of rain
Comments:

In general, the community approach begins with several consultation meetings in the community (inclusive: gender balanced and representative of the diversity makeup of the community) and with municipal authorities. An Outcome Mapping process is initiated to observe signs that a village is prepared and mobilized to receive support for PSF and pond embankment construction. Families must be willing to participate and contribute in the construction and take complete responsibility for operation and routine maintenance.
During the initial phase, a PSF Users’ Committee is formed and approved by the municipal government. Its members make time to participate in trainings on the design, use, maintenance and community organization for managing a PSF. Importantly, the PSF User’s committee must seek public commitments toward the construction costs in cash and/or in kind (labor, construction materials, embankments plants, etc). In Bangladesh this was 10% and usually in kind. Roles and responsibilities of the PSF Users’ Committee:
1) Be responsible for regular operation, maintenance and cleanliness of the pond sand filter;
2) Ensure that the maintenance points for pond water quality is respected per the manual;
3) Advocate for local authorities to conduct regular water quality testing; and to promote household water treatment systems
4) Establish a system of collecting money from users for the regular maintenance;
5) Organize Committee meetings before the start of each season and whenever needed. Similarly if required organize a wider meeting with users in connection with resolving any O&M issues.
6) Care for the tools and other materials that may be purchased for the pond sand filter.
Selection of ponds for PSF construction should be participative with criteria agreed and communicated with the community members and local authorities. The following criteria are suggested based on Terre des hommes’ experience in Bangladesh:
• Ponds that are large enough to retain water throughout the dry season.
• The salinity of the pond water must not exceed 600 ppm at any time of the year.
• While the location of the PSF should be close to a family to ensure its security, it must be as centrally located as possible for ease of access
• Freely accessible to the public; ideally donated for public use.
• Ponds located on higher ground and thus more resistant to flooding / sea water intrusion.
• Space available for raising the embankments around the ponds
• Ponds most accessible to a largest segment of the population during disaster.
• Each PSF should have an effective drainage space and system.

4.5 Costs and inputs needed for establishment

Specify input Unit Quantity Costs per Unit Total costs per input % of costs borne by land users
Labour Pond Excavation and Embankment Raising Person-days 180.0 5.0 900.0 10.0
Labour Pond Fencing Works Person-days 20.0 5.0 100.0
Labour Masonry Person-days 36.0 6.25 225.0
Equipment Repairing tools Set 1.0 15.0 15.0
Equipment Tubewell/handpump Pieces 1.0 35.0 35.0 10.0
Equipment Sanitary Fittings Set 1.0 100.0 100.0
Fertilizers and biocides Bleaching powder for disinfection kg 2.0 1.0 2.0 10.0
Fertilizers and biocides Lime for cleaning kg 50.0 0.5 25.0
Construction material
Construction material
Construction material bricks pieces 6000.0 0.075 450.0 10.0
Construction material cement 50 Kilo Bags 50.0 5.75 287.5 10.0
Construction material sand cubic feet 52.0 0.375 19.5
Construction material mild steel round bar kg 210.0 0.75 157.5
Other Materials Transport Cost Lump Sum 1.0 185.0 185.0 10.0
Total costs for establishment of the Technology 2501.5
If land user bore less than 100% of costs, indicate who covered the remaining costs:

The project requested 10% contribution in kind (materials, transport, labor) from each community. The remaining costs were covered by the project.

Comments:

The budget is for raising a 100m perimeter length of embankment.

4.6 Maintenance/ recurrent activities

Activity Type of measure Timing/ frequency
1. Repairing Other measures Before onset of rains
2. Cleaning Management Before onset of rains

4.7 Costs and inputs needed for maintenance/ recurrent activities (per year)

Specify input Unit Quantity Costs per Unit Total costs per input % of costs borne by land users
Labour two-monthly cleaning of filter materials Person days 12.0 5.0 60.0 100.0
Labour Seasonal erosion control Person days 12.0 5.0 60.0 100.0
Fertilizers and biocides bleeching powder bag 5.0 2.0 10.0 100.0
Total costs for maintenance of the Technology 130.0

4.8 Most important factors affecting the costs

Describe the most determinate factors affecting the costs:

Comparatively, construction materials costs was reflected as the most expensive consideration.

5. Natural and human environment

5.1 Climate

Annual rainfall
  • < 250 mm
  • 251-500 mm
  • 501-750 mm
  • 751-1,000 mm
  • 1,001-1,500 mm
  • 1,501-2,000 mm
  • 2,001-3,000 mm
  • 3,001-4,000 mm
  • > 4,000 mm
Indicate the name of the reference meteorological station considered:

www.discoverybangladesh.com

Agro-climatic zone
  • semi-arid

5.2 Topography

Slopes on average:
  • flat (0-2%)
  • gentle (3-5%)
  • moderate (6-10%)
  • rolling (11-15%)
  • hilly (16-30%)
  • steep (31-60%)
  • very steep (>60%)
Landforms:
  • plateau/plains
  • ridges
  • mountain slopes
  • hill slopes
  • footslopes
  • valley floors
Altitudinal zone:
  • 0-100 m a.s.l.
  • 101-500 m a.s.l.
  • 501-1,000 m a.s.l.
  • 1,001-1,500 m a.s.l.
  • 1,501-2,000 m a.s.l.
  • 2,001-2,500 m a.s.l.
  • 2,501-3,000 m a.s.l.
  • 3,001-4,000 m a.s.l.
  • > 4,000 m a.s.l.
Indicate if the Technology is specifically applied in:
  • not relevant

5.3 Soils

Soil depth on average:
  • very shallow (0-20 cm)
  • shallow (21-50 cm)
  • moderately deep (51-80 cm)
  • deep (81-120 cm)
  • very deep (> 120 cm)
Soil texture (topsoil):
  • fine/ heavy (clay)
Soil texture (> 20 cm below surface):
  • fine/ heavy (clay)
Topsoil organic matter:
  • medium (1-3%)

5.4 Water availability and quality

Ground water table:

5-50 m

Availability of surface water:

poor/ none

Water quality (untreated):

poor drinking water (treatment required)

Is water salinity a problem?

Yes

Specify:

groundwater table is salty along the Bay of Bengal, salt water intrusion. Tidal surge following cyclones also creates soil salinity.

Is flooding of the area occurring?

Yes

Regularity:

frequently

5.5 Biodiversity

Species diversity:
  • medium
Habitat diversity:
  • medium

5.6 Characteristics of land users applying the Technology

Sedentary or nomadic:
  • Sedentary
Market orientation of production system:
  • mixed (subsistence/ commercial
Off-farm income:
  • 10-50% of all income
Relative level of wealth:
  • poor
Individuals or groups:
  • individual/ household
  • groups/ community
Level of mechanization:
  • manual work
  • animal traction
Gender:
  • women
  • men
Age of land users:
  • youth
  • middle-aged

5.7 Average area of land owned or leased by land users applying the Technology

  • < 0.5 ha
  • 0.5-1 ha
  • 1-2 ha
  • 2-5 ha
  • 5-15 ha
  • 15-50 ha
  • 50-100 ha
  • 100-500 ha
  • 500-1,000 ha
  • 1,000-10,000 ha
  • > 10,000 ha
Is this considered small-, medium- or large-scale (referring to local context)?
  • small-scale

5.8 Land ownership, land use rights, and water use rights

Land ownership:
  • individual, not titled
  • individual, titled
Land use rights:
  • individual
Water use rights:
  • open access (unorganized)

5.9 Access to services and infrastructure

health:
  • poor
  • moderate
  • good
education:
  • poor
  • moderate
  • good
technical assistance:
  • poor
  • moderate
  • good
employment (e.g. off-farm):
  • poor
  • moderate
  • good
markets:
  • poor
  • moderate
  • good
energy:
  • poor
  • moderate
  • good
roads and transport:
  • poor
  • moderate
  • good
drinking water and sanitation:
  • poor
  • moderate
  • good
financial services:
  • poor
  • moderate
  • good

6. Impacts and concluding statements

6.1 On-site impacts the Technology has shown

Socio-economic impacts

Production

crop production

decreased
increased
Comments/ specify:

Embankments provide a modest space for small scale gardening and fruit/medicinal tree cultivation. Such agriculture activities would be protected from tidal surge waters that destroy agriculture in low-lying areas.

Water availability and quality

drinking water availability

decreased
increased
Comments/ specify:

Terre des hommes had raised embankments on ten community ponds prior to cyclone Mahasen (2013). Nine of the ten ponds embankments remained intact, preserving valuable fresh water from sea water contamination for drinking after treatment with PSF.

drinking water quality

decreased
increased
Quantity before SLM:

>1000 fecal coliform units

Quantity after SLM:

<10 fecal coliform units

Comments/ specify:

The PSF water source considerably reduces the risk of infection with enteric pathogens from the pond water. In Terre des hommes’ field experience, although a reduction in presence of fecal coliform (FC) by over 99% is possible, the PSF technology rarely eliminates all FC. A level of 1-10 fecal coliform units (FCU: colonies of E. coli per 100 mL of water) has been achieved, which is equivalent to an intermediate risk, or “probably safe” as defined by WHO. In conjunction with PSF, safe water transport (covered and cleaned containers) and household water treatment systems (chemical or additional filtration devices) are essential.

Income and costs

economic disparities

increased
decreased

Socio-cultural impacts

health situation

worsened
improved
Comments/ specify:

Users reported a decrease in water borne diseases through use of PSF water compared to surface water.

6.2 Off-site impacts the Technology has shown

water availability

decreased
increased
Comments/ specify:

During disaster, the use of the PSF increased, with people walking from further distances to take water from the PSF to their homes.

6.3 Exposure and sensitivity of the Technology to gradual climate change and climate-related extremes/ disasters (as perceived by land users)

Climate-related extremes (disasters)

Climatological disasters
How does the Technology cope with it?
drought well
Hydrological disasters
How does the Technology cope with it?
storm surge/ coastal flood very well
Comments:

PSF serves as disaster resilient Technology that helps residents in coastal villages along the Bay of Bengal to cope with the effects of climate change; such as increased incidence and intensity of storms and salt water intrusion.

6.4 Cost-benefit analysis

How do the benefits compare with the establishment costs (from land users’ perspective)?
Short-term returns:

slightly positive

Long-term returns:

positive

How do the benefits compare with the maintenance/ recurrent costs (from land users' perspective)?
Short-term returns:

neutral/ balanced

Long-term returns:

positive

6.5 Adoption of the Technology

  • more than 50%
Of all those who have adopted the Technology, how many have did so spontaneously, i.e. without receiving any material incentives/ payments?
  • 0-10%

6.6 Adaptation

Has the Technology been modified recently to adapt to changing conditions?

No

6.7 Strengths/ advantages/ opportunities of the Technology

Strengths/ advantages/ opportunities in the land user’s view
The Technology is useful for supplying drinking water at household level and supports cultivation of fruit trees, medicinal plants and vegetables at the pond embankment, above the flood line.
Strengths/ advantages/ opportunities in the compiler’s or other key resource person’s view
The Technology is conducive for ensuring supply of water for drinking, cooking and irrigation purposes if the community is motivated and understands the impact of PSF when faced with water shortage during dry season and other disaster events.

6.8 Weaknesses/ disadvantages/ risks of the Technology and ways of overcoming them

Weaknesses/ disadvantages/ risks in the compiler’s or other key resource person’s view How can they be overcome?
Every five to six weaks, the PSF filter media needs to be maintained, requiring some training, as well organising labor and collecting petty funds for bleaching powder. The PSF User's Manual has been translated into local language with images and tips for maintenance. This is distributed following the training. The PSF User's Committee must regularly collect user fees for smooth operations. A bank account promotes transparency. Sale of crops harvested on the embankments can help defray costs of maintenance.
Although not laborious, the hand pump requires some degree of force, and the taps are often a target of children's play. Children should be supervised and small children must not be allowed to operate or play near the pump. Investing in sturdy tap systems is essential.
The bio-film will form after seven days of operating the pump.

Users must boil or treat water very carefully in this period.
Private owners could lose interest availing their asset for the communty. For example, they may start using the pond for fish farming in order to sustain their livelihoods. Formal agreements with the municipality about the usage rules for the pond, and public commitments taken by the pond owners are important. Posting signboards that identify the pond as "Drinking Water Only" and specify forbidden activities is also helpful. Owners can take a higher share of crops cultivated on the embankment.

7. References and links

7.1 Methods/ sources of information

  • field visits, field surveys

Interviews with six informants

  • compilation from reports and other existing documentation

Compilation from five documents from past projects.

7.2 References to available publications

Title, author, year, ISBN:

SSWM University Course Module 6: Disaster Situations: Planning and Preparedness Further Resources: Water Purification Slow Sand Filtration, Marco A. Bruni, Dorothee Spuhler (seecon international gmbh), 2012.

Available from where? Costs?

https://www.sswm.info/sswm-university-course/module-6-disaster-situations-planning-and-preparedness/further-resources-0/slow-sand-filtration

Title, author, year, ISBN:

Pond Sand Filter (PSF) Manual – community operation and maintenance, Laxman Kharal (Terre des hommes), 2012

Available from where? Costs?

Contact: info@tdh.ch

Title, author, year, ISBN:

Guidelines for Drinking Water Quality, 4th Edition, WHO, 2011

Available from where? Costs?

http://www.who.int/water_sanitation_health/publications/2011/dwq_guidelines/en/

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