4 GREY WATER TREATMENT
Recycling of Water at Community Sanitation Centres using Slow Sand Filtration and UV Disinfection Supplying 2.500 L water each day Water plays an important role in the toilet ritual of people in India. A typical Community Sanitation Centre caters 300 people, requiring up to 2.5 m3/day for the purpose of flushing, hand washing and anal cleansing. The latter two streams are separately collected and fed into an on-site grey water treatment system. This reduces the impact on the transportation and drying of human waste and establishes an economical and reliable source of water in areas where this is not secured.
Step-by-step Neutral/defecating mode Waste flap (orange) keeps toilet outlet closed. It opens due to the weight of excrements or flushing water.
Anal cleansing mode User opens self-closing faucet. At the same time the water flap (blue) comes up, directing water away from waste.
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Every day 2 m3 is fed into the grey water system. This includes water from hand washing, anal cleansing and the cleaning of the toilet. A simple settler first removes the largest load of solids in the water.
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Waste Water
Designed for a local-fit
Water diverting toilet
The grey water treatment system is designed to recycle water on-site up to a level that is safe for skin-contact (salts will not be removed, which makes drinking undesirable). With the foreseen combination of settling, slow sand filtration, followed by UV disinfection, it is expected that for hand washing and anal cleansing water the guidelines found in literature will be met regarding suspended solids (< 5 mg/l), BOD (< 10 mg/l), nutrients (< 10 mg/l) and E.coli (< 200 cfu/100ml). The picture on the right shows a possible configuration that is designed for accessibility and ease of maintenance by local servicemen.
The majority of the water that is treated with the grey water system origins from anal cleansing and the cleaning of the toilet. The separate collection of these two streams is established by means of a water diverting mechanism underneath the toilet that is activated as soon as the user uses the handheld shower inside the cubicle.
Settling of solids
Slow sand filtration
This 1 m3 slow sand filter removes suspended solids and dissolved organics at the same time. The top layer becomes biologically active to form what is often called a ‘schmutzdecke’. Slow sand filters have proven to remove 99% of the Helminth eggs (further research will have to demonstrate if this high removal efficiency is enough to allow recycling of water). The two compartments of the sand filter can be used intermittently to let the biological active layer recover and to perform maintenance. During peak hours both compartments are in use.
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Buffer tank 1
Holds up to 5 m3 - twice the amount that is collected daily. This is necessary in case the UV system is not operational due to very low UV conditions.
4 Solar UV disinfection with TiO2 catalyzation
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Community Sanitation Centre
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UV disinfection is a proven concept that does not require chemicals and relies on a sustainable energy source. It can be further enhanced by adding an immobilized TiO2-catalyst. This will improve the effectiveness and also make it possible for the system to oxidize any remaining Photo credit: Ferdandez et.al., CIEMAT, Spain organic matters, like coloring components or traces of hormones or medicines. Together with UNESCO Institute for Water Education, TU Delft is conducting experimental studies to determine more precise design criteria. The 12 m2 UV panel located on the rooftop of the Community Sanitation Centre consists of parabolic mirrors that direct (diffused) sunlight to the water that is running through a series of plastic tubes. In the experimental set-up of (Fernandez, 2005) TiO2 is applied as an immobilized catalyzer on top of PP tubes running inside the water tubes. Other designs considered by TU Delft are TiO2 coated meshes and TiO2 between glass plates.
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Buffer tank 2
Holds up to 5 m3 of treated water, which should be sufficient for 2 days of supply. To make up for the water losses in the system (up to 0.5 m3/day - mainly flushing water that goes with human waste) new water is added to this tank.
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7.0 m
Will people accept recycled water? The public acceptance of recycled water for skin-contact (i.e. anal cleansing and hand washing) can be more challenging than water being recycled for lower grade purposes such as flushing. Interviews in India showed that people are more likely to accept this when there is increased awareness of water scarcity inside their communities. The visibility of the treatment system and the feedback of water quality, connected to a reliable brand, may further guarantee the uptake.
23° (towards South)
1 Max Min
3 2
Feed to UV system: 0-600 l/hr (2500 l/day) pump is actuated by UV sensor
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5.0 m
Daily consumption - 2500 l
Emptying black water tank Daily collection - 2000 l
Stable
Next steps The main challenge of this proposal for grey water treatment lies in the integration of proven solutions and more advanced solutions such as UV+TiO2 disinfection.
6.5 m
Collect samples of hand washing and anal cleansing water (in India) to establish design parameters for effective treatment.
Test the integration of UV+TiO2 in the proposed system. Build a one-seat testing set-up to evaluate the fully integrated system.
Expand study on (stimulation of) public acceptance of recycled water within toilet facilities.
Water losses - 500 l/day Feed to sand filter: 100-150 l/hr (2000 l/day)
Max
0.5 m 0m
Min Max level (after 500 l refill) -1.2 m
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3 -1.6 m
www.tudelft.nl/reinventthetoilet