Villagers collecting drinking water from PSF Technology (Sultan Mahmud, WASH Promotion Officer)

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

FILTER

Descrição

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.

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.

Localização

Localização: Baratangra, Ward:4, Union: Patharghata Union Parishad, Patharghata, Barguna district in coastal region, Bangladesh

Nº de sites de tecnologia analisados: 10-100 locais

Geo-referência de locais selecionados
  • 89.95625, 22.06989

Difusão da tecnologia: Aplicado em pontos específicos/concentrado numa pequena área

Em uma área permanentemente protegida?:

Data da implementação: menos de 10 anos atrás (recentemente)

Tipo de introdução
Pond Sand Filter after construction (Md. Saiful, WASH Infrastructure Officer)
Raised embankment protecting the pond from Cyclone Mahasen tidal surge waters to the left of the embankment. (Shahid Kamal)

Classificação da Tecnologia

Objetivo principal
  • Melhora a produção
  • Reduz, previne, recupera a degradação do solo
  • Preserva ecossistema
  • Protege uma bacia/zonas a jusante – em combinação com outra tecnologia
  • Preservar/melhorar a biodiversidade
  • Reduzir riscos de desastre
  • Adaptar a mudanças climáticas/extremos e seus impactos
  • Atenuar a mudanças climáticas e seus impactos
  • Criar impacto econômico benéfico
  • Cria impacto social benéfico
Uso da terra
Uso do solo misturado dentro da mesma unidade de terra: Sim - Agrofloresta

  • Terra de cultivo
    • Cultura anual: plantas e ervas medicinais/ aromáticas/pesticidas
    • Cultura perene (não lenhosa): banana/planta/abacá
    • Cultura de árvores e arbustos
    Número de estações de cultivo por ano: 2
  • Floresta/bosques
Abastecimento de água
  • Precipitação natural
  • Misto de precipitação natural-irrigado
  • Irrigação completa

Objetivo relacionado à degradação da terra
  • Prevenir degradação do solo
  • Reduzir a degradação do solo
  • Recuperar/reabilitar solo severamente degradado
  • Adaptar à degradação do solo
  • Não aplicável
Degradação abordada
  • Erosão do solo pela água - Wt: Perda do solo superficial/erosão de superfície
  • Degradação da água - Hs: mudança na quantidade de água de superfície, Hp: declínio da qualidade de água de superfície
Grupo de GST
  • Gestão de água de superfície (nascente, rio, lagos, mar)
Medidas de GST
  • Medidas estruturais - S2: Barragens, bancos, S5: Represa, bacia, lago, S7: coleta de água/ equipamento de abastecimento/irrigação

Desenho técnico

Especificações técnicas
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.
Author: Terre des hommes

Estabelecimento e manutenção: atividades, insumos e custos

Cálculo de insumos e custos
  • Os custos são calculados: Por unidade de tecnologia (unidade:Pond Sand Filter with raised earthen embankment volume, length: 2,500 Litres capacity of filter; embankment average of 100 meter perimeter.)
  • Moeda utilizada para o cálculo de custos: USD
  • Taxa de câmbio (para USD): 1 USD = n.a
  • Custo salarial médio da mão-de-obra contratada por dia: 5 $ per day for labor
Fatores mais importantes que afetam os custos
Comparatively, construction materials costs was reflected as the most expensive consideration.
Atividades de implantação
  1. Community consultation for Committee Formation (Periodicidade/frequência: Before onset of rain)
  2. Create PSF Users' Committee, agre on user contributions (Periodicidade/frequência: Before onset of rain)
  3. Committee / pond selection approved by local Government (Periodicidade/frequência: Before onset of rain)
  4. Technical orientation to PSF Committee, input on designs (Periodicidade/frequência: Before onset of rain)
  5. Excavation of Pond (Periodicidade/frequência: Before onset of rain)
  6. Embankment Construction (Periodicidade/frequência: Before onset of rain)
  7. PSF Construction (Periodicidade/frequência: None)
  8. Fencing (Periodicidade/frequência: None)
  9. Turfing and hortiuclutre on the embankment (Periodicidade/frequência: Before onset of rain)
  10. PSF Training on Media Selection and maintenance (Periodicidade/frequência: Regular intervals throughout the year (every 1-2 months))
  11. Pond embankment maintenance (Periodicidade/frequência: Before onset of rain)
Estabelecer insumos e custos (per Pond Sand Filter with raised earthen embankment)
Especifique a entrada Unidade Quantidade Custos por unidade (USD) Custos totais por entrada (USD) % dos custos arcados pelos usuários da terra
Mão-de-obra
Pond Excavation and Embankment Raising Person-days 180,0 5,0 900,0 10,0
Pond Fencing Works Person-days 20,0 5,0 100,0
Masonry Person-days 36,0 6,25 225,0
Equipamento
Repairing tools Set 1,0 15,0 15,0
Tubewell/handpump Pieces 1,0 35,0 35,0 10,0
Sanitary Fittings Set 1,0 100,0 100,0
Fertilizantes e biocidas
Bleaching powder for disinfection kg 2,0 1,0 2,0 10,0
Lime for cleaning kg 50,0 0,5 25,0
Material de construção
bricks pieces 6000,0 0,075 450,0 10,0
cement 50 Kilo Bags 50,0 5,75 287,5 10,0
sand cubic feet 52,0 0,375 19,5
mild steel round bar kg 210,0 0,75 157,5
Outros
Materials Transport Cost Lump Sum 1,0 185,0 185,0 10,0
Custos totais para a implantação da tecnologia 2'501.5
Custos totais para o estabelecimento da Tecnologia em USD 2'501.5
Atividades de manutenção
  1. Repairing (Periodicidade/frequência: Before onset of rains)
  2. Cleaning (Periodicidade/frequência: Before onset of rains)
Insumos e custos de manutenção (per Pond Sand Filter with raised earthen embankment)
Especifique a entrada Unidade Quantidade Custos por unidade (USD) Custos totais por entrada (USD) % dos custos arcados pelos usuários da terra
Mão-de-obra
two-monthly cleaning of filter materials Person days 12,0 5,0 60,0 100,0
Seasonal erosion control Person days 12,0 5,0 60,0 100,0
Fertilizantes e biocidas
bleeching powder bag 5,0 2,0 10,0 100,0
Custos totais para a manutenção da tecnologia 130.0
Custos totais de manutenção da Tecnologia em USD 130.0

Ambiente natural

Média pluviométrica anual
  • <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
Zona agroclimática
  • úmido
  • Subúmido
  • Semiárido
  • Árido
Especificações sobre o clima
Nome da estação meteorológica: www.discoverybangladesh.com
Inclinação
  • Plano (0-2%)
  • Suave ondulado (3-5%)
  • Ondulado (6-10%)
  • Moderadamente ondulado (11-15%)
  • Forte ondulado (16-30%)
  • Montanhoso (31-60%)
  • Escarpado (>60%)
Formas de relevo
  • Planalto/planície
  • Cumes
  • Encosta de serra
  • Encosta de morro
  • Sopés
  • Fundos de vale
Altitude
  • 0-100 m s.n.m.
  • 101-500 m s.n.m.
  • 501-1.000 m s.n.m.
  • 1.001-1.500 m s.n.m.
  • 1.501-2.000 m s.n.m.
  • 2.001-2.500 m s.n.m.
  • 2.501-3.000 m s.n.m.
  • 3.001-4.000 m s.n.m.
  • > 4.000 m s.n.m.
A tecnologia é aplicada em
  • Posições convexas
  • Posições côncavas
  • Não relevante
Profundidade do solo
  • Muito raso (0-20 cm)
  • Raso (21-50 cm)
  • Moderadamente profundo (51-80 cm)
  • Profundo (81-120 cm)
  • Muito profundo (>120 cm)
Textura do solo (superficial)
  • Grosso/fino (arenoso)
  • Médio (limoso, siltoso)
  • Fino/pesado (argila)
Textura do solo (>20 cm abaixo da superfície)
  • Grosso/fino (arenoso)
  • Médio (limoso, siltoso)
  • Fino/pesado (argila)
Teor de matéria orgânica do solo superior
  • Alto (>3%)
  • Médio (1-3%)
  • Baixo (<1%)
Lençol freático
  • Na superfície
  • < 5 m
  • 5-50 m
  • > 50 m
Disponibilidade de água de superfície
  • Excesso
  • Bom
  • Médio
  • Precário/nenhum
Qualidade da água (não tratada)
  • Água potável boa
  • Água potável precária (tratamento necessário)
  • apenas para uso agrícola (irrigação)
  • Inutilizável
A qualidade da água refere-se a:
A salinidade é um problema?
  • Sim
  • Não

Ocorrência de enchentes
  • Sim
  • Não
Diversidade de espécies
  • Alto
  • Médio
  • Baixo
Diversidade de habitat
  • Alto
  • Médio
  • Baixo

Características dos usuários da terra que utilizam a tecnologia

Orientação de mercado
  • Subsistência (autoabastecimento)
  • misto (subsistência/comercial)
  • Comercial/mercado
Rendimento não agrícola
  • Menos de 10% de toda renda
  • 10-50% de toda renda
  • >50% de toda renda
Nível relativo de riqueza
  • Muito pobre
  • Pobre
  • Média
  • Rico
  • Muito rico
Nível de mecanização
  • Trabalho manual
  • Tração animal
  • Mecanizado/motorizado
Sedentário ou nômade
  • Sedentário
  • Semi-nômade
  • Nômade
Indivíduos ou grupos
  • Indivíduo/unidade familiar
  • Grupos/comunidade
  • Cooperativa
  • Empregado (empresa, governo)
Gênero
  • Mulheres
  • Homens
Idade
  • Crianças
  • Jovens
  • meia-idade
  • idosos
Área utilizada por residência
  • < 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
Escala
  • Pequena escala
  • Média escala
  • Grande escala
Propriedade da terra
  • Estado
  • Empresa
  • Comunitário/rural
  • Grupo
  • Indivíduo, não intitulado
  • Indivíduo, intitulado
Direitos do uso da terra
  • Acesso livre (não organizado)
  • Comunitário (organizado)
  • Arrendado
  • Indivíduo
Direitos do uso da água
  • Acesso livre (não organizado)
  • Comunitário (organizado)
  • Arrendado
  • Indivíduo
Acesso a serviços e infraestrutura
Saúde

Pobre
x
Bom
Educação

Pobre
x
Bom
Assistência técnica

Pobre
x
Bom
Emprego (p. ex. não agrícola)

Pobre
x
Bom
Mercados

Pobre
x
Bom
Energia

Pobre
x
Bom
Vias e transporte

Pobre
x
Bom
Água potável e saneamento

Pobre
x
Bom
Serviços financeiros

Pobre
x
Bom

Impactos

Impactos socioeconômicos
Produção agrícola
diminuído
x
aumentado


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.

Disponibilidade de água potável
diminuído
x
aumentado


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.

Qualidade da água potável
diminuído
x
aumentado

Quantidade anterior à GST: >1000 fecal coliform units
Quantidade posterior à GST: <10 fecal coliform units
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.

Disparidades econômicas
aumentado
x
diminuído

Impactos socioculturais
Estado de saúde
Agravado
x
Melhorado


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

Impactos ecológicos
Impactos fora do local
disponibilidade de água (lençóis freáticos, nascentes)
diminuído
x
aumentado


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

Análise do custo-benefício

Benefícios em relação aos custos de estabelecimento
Retornos a curto prazo
muito negativo
x
muito positivo

Retornos a longo prazo
muito negativo
x
muito positivo

Benefícios em relação aos custos de manutenção
Retornos a curto prazo
muito negativo
x
muito positivo

Retornos a longo prazo
muito negativo
x
muito positivo

Mudança climática

Extremos (desastres) relacionados ao clima
Seca

não bem em absoluto
x
muito bem
Maré de tempestade/inundação costeira

não bem em absoluto
x
muito bem

Adoção e adaptação

Porcentagem de usuários de terras na área que adotaram a Tecnologia
  • casos isolados/experimental
  • 1-10%
  • 11-50%
  • > 50%
De todos aqueles que adotaram a Tecnologia, quantos o fizeram sem receber incentivos materiais?
  • 0-10%
  • 11-50%
  • 51-90%
  • 91-100%
A tecnologia foi recentemente modificada para adaptar-se as condições variáveis?
  • Sim
  • Não
A quais condições de mudança?
  • Mudança climática/extremo
  • Mercados dinâmicos
  • Disponibilidade de mão-de-obra (p. ex. devido à migração)

Conclusões e experiências adquiridas

Pontos fortes: visão do usuário de terra
  • 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.
Pontos fortes: a visão do/a compilador/a ou de outra pessoa capacitada
  • 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.
Pontos fracos/desvantagens/riscos: visão do usuário de terracomo superar
Pontos fracos/desvantagens/riscos: a visão do/a compilador/a ou de outra pessoa capacitadacomo superar
  • 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.

Referências

Compilador/a
  • John Brogan
Editores
  • Shahid Kamal
  • Md. Rahmatullah Faruque
Revisor
  • Alexandra Gavilano
  • Hanspeter Liniger
  • Nicole Harari
  • Deborah Niggli
Data da documentação: 22 de Agosto de 2016
Última atualização: 19 de Março de 2019
Pessoas capacitadas
Descrição completa no banco de dados do WOCAT
Dados GST vinculados
A documentação foi facilitada por
Instituição Projeto
Referências-chave
  • 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.: https://www.sswm.info/sswm-university-course/module-6-disaster-situations-planning-and-preparedness/further-resources-0/slow-sand-filtration
  • Pond Sand Filter (PSF) Manual – community operation and maintenance, Laxman Kharal (Terre des hommes), 2012: Contact: info@tdh.ch
  • Guidelines for Drinking Water Quality, 4th Edition, WHO, 2011: http://www.who.int/water_sanitation_health/publications/2011/dwq_guidelines/en/
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