WORLD WATER FORUM WORLD WATER CHALLENGE

Multi-Part Solution to Rural

Water Problem

Incorporating Biosand

Filters

RISE Tsinghua

January 2015

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1. ABOUT RISE

Rural-International Student Exchange (RISE) Tsinghua is a student-based organisation with a focus on rural development projects in China. The organisation is located in Beijing, China, and draws upon the student body, bringing together both international and local graduate students from Tsinghua University to work with rural communities in China to provide local and sustainable solutions.

2. OUR PROPOSED SOLUTION

Our proposed solution to the rural water problem consists of four parts and is based on our experience in China: 1. Protected underground water cellars in the yard of each village household – rainwater collection stage 2. Water storage vessels for keeping water temporarily – settling stage 3. Biosand filters – filtration stage 4. Boiling water – disinfection stage

3. PREVIOUS APPLICATION OF SOLUTION

RISE carried out the ‘Ningxia Biosand Filter Project’ to install biosand filters (BSFs) in rural households of Mahuangshan county, Ningxia province, China. Village households already had underground water cellars to collect rainwater, many used urns or containers to store the water for settling and almost all boiled the water before drinking. Our project focused on introducing BSFs as a method of water filtration.

The project began in the summer of 2012 with a survey of villagers’ perceptions of their water quality. Given that a significant number of villagers expressed dissatisfaction with their water quality, 100 BSFs were constructed in the county’s main village as part of a pilot project in winter of 2013. In summer of 2013, we disseminated materials for over 1000 BSFs (full-scale project) and gave construction and maintenance training to village representatives. We returned twice in 2014 for a follow-up trip and maintenance training. The project was done with the collaboration of local government. The government subsidised the cost of the materials and village households paid the remainder. The total cost of the BSF project for all involved was around US$50 000 (US$1 = 6.2CNY).

4. HOW OUR SOLUTION RESPONDS TO ‘RURAL WATER PROBLEM’

4.1. Underground water cellars

Description: Water cellars (known in China as ‘shui jiao’) are large underground cavities that are generally lined with concrete. If servicing households, they are often located in enclosed yards and have a circular raised opening. Rain that falls on the yard runs into the water cellar through the opening. Water can be taken from the cellar in the same way as it taken from a well: using a plastic or metal bucket attached to a rope. See Figure 1. Benefit:

The water cellar is a way of balancing the difference in water availability between the dry and wet season. The cellars are common in northern provinces of China like Gansu and Ningxia where most rain falls during the summer and almost no rain falls during the winter. Rain collected by means of the cellar in the summer period is then available for use during the winter period.

Each household has control of its own water source, which is close to the house. Houses in scattered rural villages generally have space for an attached yard. If a water cellar is installed in each yard, this means people do not have to walk far to access water. It also means they do not have to compete for water.

Capital costs and difficulty are reduced. No centralised water source or pipe network is needed to collect and distribute water. Building the water cellar entails some capital costs (around US$160 each in China; $US1 = 6.2CNY) but these are not as great as those required for a water treatment plant and water distribution network. It is also not as difficult to build and does not need energy input for pumping.

Individuals have some control over the quality of stored water. It is possible to choose the location of the water cellar and control the type of water flowing in. According to our experience, water cellars near roads were more likely have high turbidity. Cellars with openings inside yards were more likely to have lower turbidity, particularly if the yard was kept clean and the water cellar opening was only unblocked after the first 5-10min of rain.

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Figure 1: Water cellar for storing rainwater, Ningxia province, China. Figure 2: Example of earthenware urn and biosand filter.

4.2. Water storage vessel

Description: The ideal water storage vessel should be made out of a material that is durable, lightweight, non-oxidising, easy to clean, inexpensive, and able to be locally produced and it should have a single opening about 5-8cm in diameter with a tightly fitting cover that makes it easy to fill the container with water but difficult to insert hands or immerse utensils (Mintz et al. 1995).This has been found to reduce the likelihood of bacterial contamination during the settling period. In Ningxia, China, rural households traditionally use large earthenware urns to store water after it is taken out of the water cellar. See Figure 2. Benefit:

Reduces water turbidity. When water taken from the water cellar is stored in a storage vessel for a few hours to a day, many of the particles inside the water have time to settle to the bottom. This can greatly reduce the turbidity and improve the clarity of the water. Taking the example of a household in Ningxia, we tested the turbidity of water taken directly from the water cellar to be around 10NTU, whereas water left to settle in urns had turbidity of 2NTU.

Controls turbidity during rainy season. One of the issues in Columbia is the difference in water turbidity between the dry and rainy seasons. According to our experience, water in underground water cellars in Ningxia tends to be much more turbid in summer when there is a large increase of rainwater flowing in. For example, we tested water from the same water cellar for turbidity in both summer and winter and found that turbidity rose from <2NTU in winter to around 16NTU in summer. The use of water storage vessels helps to regulate the turbidity of water. This is extremely important for water with high levels of turbidity (>50NTU).

4.3. Biosand filter

Description: The biosand filter (BSF) is a low-cost adaptation of the traditional slow sand filter that is smaller and suitable for daily use. It contains two layers of two different sizes of gravel, followed by two layers of two different sizes of sand. This material must be washed before it is added to the BSF container. The containers we use for the BSF in our projects are plastic buckets. A hole is drilled near the bottom and a PVC pipe is fitted to the bucket. If built properly, the BSF is capable of improving the quality of source water by removing large particles as well as a significant amount of bacteria, viruses, and parasites. It uses locally-sourced materials and simple skills. It is accessible and durable, with no recurring costs, and the relatively high flow rate and ability to deal with turbidity give it an advantage over methods like ceramic filtration and solar disinfection (Jenkins et al. 2011). See Figure 3 for BSF construction and Figure 2 for an example of the BSF used in Ningxia.

Contamination in influent water is partially removed by the BSF through a combination of physical and biological processes that mostly occur in the top sand layer and the biolayer. Large suspended solids and microorganisms get physically trapped between

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sand grains. Trapped microorganisms form the biolayer. Over time, this layer is capable of trapping smaller and smaller particles. The biolayer is an ecological environment in which predation can occur between larger and smaller microorganisms. Microorganisms can also compete against or assist each other. Microorganisms can also obtain nutrients (e.g. iron, nitrogen) from the incoming water, which helps make the water cleaner. At the end of their life cycle, microorganisms will die in the biolayer. According to our experience in Ningxia, BSFs constructed and maintained correctly are capable of significant turbidity removal. BSFs of the size we use in Ningxia should not have flow rates exceeding 85L/hr. For a BSF in Ningxia with a flow rate of 79L/hr, turbidity of the influent was 23NTU and turbidity of the effluent was 1.5NTU. Turbidity reduction for a sample of BSFs in Ningxia is shown in Figure 4.

Figure 4: Turbidity removal for a sample of biosand filters in Mahuangshan, Ningxia. Notes: Initials represent village names. Unfiltered = water from water cellar; Filtered = biosand filter water. The figures on the x-axis represent the flow rate of the BSF.

0

5

10

15

20

25

30

35

40

Turb

idit

y (

NT

U)

Turbidity Removal in Ningxia

Unfiltered

Filtered

Figure 3: The 5 components of the biosand filter, the 5 zones of filtration and the heights of each layer. Source: CAWST 2009

Sand diameter <0.2 mm

Sand diameter <0.2-2mm

Gravel diameters: 2-6mm

(upper); 6-12mm (lower)

0.2 – 2mm

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Benefits:

This is a decentralised method of reducing turbidity and microorganisms. Rainwater collected in water cellars and stored in water storage vessels can have problems with turbidity and growth of microorganisms so there should be treatment after settling. The BSF provides a simple way for each household to filter microorganisms and suspended solids from the influent water. Water from the BSF should then be boiled for disinfection.

Maintenance of biosand filters is infrequent and not difficult. Every two to three months, build-up of particles in the top layer of sand will cause the flow rate of treated water from the BSF to reduce to a point that is inconvenient for the user. At this stage, maintenance is required. Maintenance of the BSF involves adding water to the top, lightly touching the top layer of sand and moving your hand around in a circular motion. This releases dirt and sediment into the water. The water must then be scooped out and discarded.

Capital costs are low and construction is simple. The total cost of materials required to construct the BSF is generally under US$30. The most time-consuming part of the construction is washing the sand.

5. HOW TO INCREASE LIKELIHOOD OF ACHIEVING EXPECTED RESULTS

The expected results of this project are: 1. The provision of a low-cost, sustainable way of storing and treating water for drinking and other purposes in rural areas. 2. The reduction of competition over local water resources. 3. The reduction of exposure to waterborne diseases. 4. Balance between dry and rainy season water supply and demand. 5. This solution is low cost and does not require expert knowledge during use, which means there is potential for high coverage for households in rural villages. Uptake of the biosand filter by village households is crucial to achieving the desired results. According to our experience, paying attention to the following points during project implementation will increase the likelihood that households will begin using and continue to use the BSF: 1. Identify whether the water source quality has an issue and advise households if it does. If they are not convinced water quality is an issue, they are unlikely to use the BSF. 2. Clearly explain what the BSF consists of, how it works and what construction and maintenance involves to households before providing the materials. 3. Trusted people should oversee or review the construction of the BSF to ensure that all materials are used and that they are used properly. In particular, not using enough sand will diminish the filtration effect of the BSF. 4. Households should be reminded of the maintenance procedure 2-3 months after first constructing. 5. If the filters are highly subsidised or free, it is possible that households will not value them or will accept materials despite having no intention of building a BSF.

6. REFERENCES

For more information on biosand filters, see: Biosand Filter Manual, 2009, Centre for Affordable Water and Sanitation Technology

(CAWST), www.cawst.org. and Jenkins M.W., Tiwari S.K. and Darby J. 2011. Bacterial, viral and turbidity removal by intermittent slow

sand filtration for household use in developing countries: Experimental investigation and modeling. Water Research, 45: 6227-6239.

Many water cellars in Ningxia and other Chinese provinces were installed by the Mother’s Cellar project (Mu Qin Shui Jiao). For more

information, see: http://www.mothercellar.cn/html/mothercellar/report/145447-1.htm

For more information on choosing water storage vessels, see: Mintz E., Rei F., and Tauxe R.1995. Safe water treatment and storage

in the home: A practical new strategy to prevent waterborne diseases. JAMA, 273:948-953.

CONTACT US RISE, School of Environment, Tsinghua University

Haidian District, Beijing, China, 100084

www.rise-thu.org

contact@rise-thu.org

WATER QUALITY PROJECT DIRECT CONTACT katesmith1986@hotmail.com