Lime treatment – unplanted drying beds – July 2019

Lime treatment – unplanted drying beds – July 2019
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Location of the case study

Bangladesh - Cox's Bazaar - Kutupalong Camp


Main treatment objectives

BOD/COD reduction, Pathogen reduction, Solid/liquid separation

Capex per design input flow

2531 USD/m3/day

Opex per real input flow


Required space


Description of the treatment process

The Lime Stabilization method is a process where hydrated lime (also known as calcium hydroxide) is added and mixed manually by using simple mixing pump in pits. Addition of the hydrated lime elevates the pH that eventually kills the pathogens (disease causing micro-organism) and stabilizes the sewage, reducing odors and allowing further processing. Allowing the solids to settle in the bottom of the pit, the water can then be removed and spread over the ground area. Further, the remaining solids can be dried and be used to cover for landfill or decomposed to be used later as fertilizer.

Besides, there is a provision of filtration unit and drying bed using gravel and sand of different sizes. The separated liquid part (leachate) of raw FS pre-treated on drying beds further goes on a filtration chamber and is followed by a soak pit. A roof was constructed over the top of the drying bed to keep the sludge dry during the treatment process. The benefits of these beds include no requirement and use of power. The drying process is enhanced by evaporation and solid-liquid separation by gravity percolation of leachate. There is a scope of use dried sludge as soil conditioner. After the sludge has dried (around 15 days during the dry season) it is burned and buried.

Description of the emergency context

Living area of community: Kutupalong Camp Area in different locations

Local and international WaSH institutions with WaSH active role in the community: NGO Forum and other development organizations such as BRAC, ACF, PCCR, IFRC, Friendship etc.

Main waterborne diseases: Cholera, Diarrhea, Dysentery, Typhoid etc.



Lessons learned

If we construct small sewerage boreholes and increase secondary transfer stations and safety tanks then the cost will be reduced.

Constructing small sewerage boreholes or transfer stations, it can reduce contacts between staff and sludge.

Ensuring community engagement and engaging skilled volunteer can guarantee the sustainability of the plant.

The risk of environmental contamination from burial of lime treated sludge is relatively low, since the bacteria and viruses in the sludge are destroyed during the treatment process, leaving only the helminth eggs which are relatively large and are efficiently removed through the physical filtration process in the soil. A burial site which is 6 inch above the water table can therefore be considered safe considering the risk. After burial, sludge should be covered with a 6-inch layer of soil.

Specific challenges:
• the emptying frequency is too high, as a result it is difficult to maintain the retention period
• leakage of convenes pipe
• quality of effluent water
• space in the camps is limited due to the number of people and the topography
• landslides in the rainy season

In this system, there is a possibility of health hazards, by damaging the skin and causing burns for those who are involved in this activity. Gloves were worn when handling lime. Gloves have been issued to workers who are handling sludge or chemicals (lime or chlorine) and Eye protection also have been issued to workers who are handling chemicals (lime or chlorine). Forum has mitigated this risk through proper use of PPE. Besides these, there is a provision of water containing vinegar for washing. If dry lime is spilled on the skin, then it has to be brushed away as much of the lime as possible before it causes burns.

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