Organisation : NC
Required space0.15 m2/person
Short description of the emergency context
The project site – Unichiprang is a hilly area and is currently hosting an estimated 21,300 Rohingya refugees (ISCG Full Situation Report, 11 March 2018). Refugees are continuing to cross the border into Bangladesh, with a total of 3,236 new arrivals reportedly entering the country in February 2018 alone, bringing the number to over 5,000 newly arrived refugees so far in 2018. The population is predominantly Muslim. The latrines provided for the refugees are simple pit latrines. Pits are emptied approximately every 4 to 8 weeks depending on the number of users.
Excreta containement, Solid/liquid separation, Sludge drying, Stabilisation of sludge, Sludge volume reduction, Reduction of odour/flies, Reduction of pathogens, BOD reduction, TSS and TDS reduction
Life expectancy and reliability
Short term (months)
Skill level required for design
Low (easy design)
Technology suitable for context with high water table
Source of sludge
From public toilet, From septic tank, From pit latrines affected by groundwater infiltration
Mountains and hills
Design input flow
Type of outputs
Using locally available material
Real input flow
Exclusively communitarian operation
Safety and hygiene: washing capacity availability
Safety and hygiene: PPEs availability
Skill level required for upgrading & decommissioning
Low skilled: general WASH officer and local labour required
The Lime treatment is carried out in 50 L barrels. Prior to the collection and transport of faecal sludge, 15 g/l lime (CaOH2, 2 kg per barrel) is added to the empty barrels. The faecal sludge from the pit latrines is removed from different ways: manual using buckets, manualy pumped using submersible pump and pumping with dedicated Oxfam trash/sludge pumps, which facilitates the mixing of the lime and the faecal sludge. Bucket desludging is used in place where it’s difficult to access with the heavy Oxfam pump. The lime creates a highly alkaline environment, which results in the inactivation of pathogens and stabilizes the sludge (if the alkaline environment of pH>12 is sustained for at least 1 hour).
From the barrels, the sludge is poured through a screen (to remove any solid waste) and into the Geotube. The time the leachate filters into the sand portion of the filtration unit still need to be determined. The primary filtration units are comprised of three layers of filter media. The bottom layer is 17 cm of coarse gravel 1’’ the second layer is 14 cm of medium size gravel ½’’, topped off by a 20 cm of 2.5 fineness modulus (FM) sand appropriate for filtration. After this filtration phase, the liquid drains through a 6’’ pipe installed below the filtration media and flows through gravity force to a secondary filtration unit comprised of a 20 cm layer of medium size gravel ½’’. The effluent from the secondary filtration phase is then discharged into the environment. The Geotube and primary filtration unit are protected with a roof to keep rain water out of the system. The solid phase of the faecal sludge is retained in the Geotube and is then emptied after a time to be determined. The Geotubes are single use and a new one must be installed after it is emptied. For the final disposal, two options are planned, depending on the final characteristics of the sludge. The first one is direct disposal of the remaining dried sludge into onto land in a nearby area and the second is, incineration of the dried sludge with basic equipment.
Hydrated Lime Treatment requires a barrel to prepare the the lime slurry (e.g. a 50 L plastic barrel). For an even distribution of hydrated lime throughout the sludge, constant mixing is required (either manually or with a mixing pump). The Geotubes are made from membrane material that is either woven and non-woven material. The project team initially piloted the non-woven membrane as it is easily available in Bangladesh and shipping time for woven material is expected to be time consuming (material pictures below). However, woven membranes have been successfully tested and may therefore be preferred, if available. Non-woven materials have mainly been used for dewatering purposes and have less been used for the treatment of sludge. Further materials required are all available in the local market such as; sand, gravel, cement, drainage pipes, bamboo, roofing, tarpaulins and fitting materials.
The overall operation and maintenance of the system is simple. However, in the hilly terrain of Cox’s Bazaar, the transportation of the sludge is challenging and time consuming. The pit latrines are desludged by trained operators using a Oxfam pump (Atalanta Pelican 351 Diaphragm sludge pump with Lombardini 15LD225 diesel engine) with a capacity of approximately 10 min for a 500 L pit. The sludge is transported in a 50 L barrel fixed to a pole and jointly carried by two emptiers (manual transport, see Figure 2 below). Due to potential health risks when handling Lime (see below Health and Safety section), and removal of the dewatered sludge, the process requires trained personnel following health and safety protocols and wearing proper personal protective equipment (PPE). Daily washing and disinfection of all used equipment is required.
- Low complexity and cost of the system,
- Non-permanent infrastructure,
- Rapid implementation,
- Possibility of scaling up of capacity by adding more geotextile tubes and filter units.