The faecal sludge treatment site is designed with the primary objective of pathogen elimination. It consists of lime stabilisation for pathogen elimination, unplanted drying beds for solid liquid separation and dewatering and a sludge drying area.

The adddition of hydrated lime (Ca(OH)2) to faecal sludge increases pH and results in pathogen inactivation and limited sludge stabilization [1]. Different combinations of pH and exposure times result pathogen removal, field research has shown that faecal sludge from pit latrines treated at pH > 11.5 for a period of 2 hours meets WHO standards [2].

Loading rate                5 m3/day           assumption: 0.5 l/person/day, 10,000 people

Lime dosage rate       20 kg/m3           sludge typical range: 1 – 17 kg/m3 faecal sludge

Lime consumption    100 kg/day        actual lime use 110 kg/day

Before desludging a 1:1 lime-water mixture is added to the barrels. Once the barrel is carried back to the site the content is stirred for approximately one minute followed by pH measurement.

The unplanted drying beds are designed for a hydraulic loading rate of 30 cm/m2 and a solid loading rate of 200 kg TS/m2/year [1; 3]. The unlined beds (5×2 metres) are filled with coarse gravel topped with sand and a permeable sand bag cover to allow for easy removal of the dried sludge and to avoid sand removal during bed emptying.

Loading rate                      5 m3/day                          assumption: 10,000 people, 0.5 l/person/day

Hydraulic loading rate    30 cm/m2                         typical range: 25 – 30 cm/m2 [1]

Solid loading rate             150 kg TS/m2/year         typical range: 100 – 200 kg TS/m2/year [3]

Drying time                       7 days                                 assumption: 1% total solids concentration

Drying area required       100 m2                              0.01 m2 / person equivalent

The area required for the FSM site is roughly 600 m2 (0.06m2/person). This includes all facility buildings, office and warehouse and ample free space but excludes the area needed for safe sludge disposal. An area of only 140 m2 is directly occupied by drying beds. Guidelines developed by USAID for lime stabilisation of septage in the Philippines state a land use of 400 square meters for a daily flow of 5 cublic meters per day [6].

The current FSM site has a spacious lay-out and part of the land is left undeveloped, the total area is estimated at 2,000 m2.

On average 5m3 sludge is treated per day, which is in accordance with a target population of 10,000 people served with FSM activities and a sludge accumulation rate of 0.5 l/person/day. It has a safe disposal of 0.5 m3 dried sludge per day.

Desludging and sludge treatment efforts seem to answer to the need in our 23 blocks (9,383 people). However the actual number of people reached is somewhat lower as all latrines constructed under supervision of Save the Children and Friendship are normally emptied by these respective organisations.

Other FSM actors state a two-week period between desludging, which calculates to a sludge accumulation rate of 2.9 l/cap/day (assuming full latrines, 0.8 m3, after two weeks).

Lime stabilisation is a simple and robust technology that can be designed, constructed and operated in the local context. The key component hydrated lime is a common building material and can be purchased locally. Other materials such as gravel, sand and building material will also be readily available. Design is straightforward and can be done by a WaSH officer. Construction and operation and maintenance do not require prior knowledge and experience.