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Faecal Sludge Extraction

April 28th, 2010 in Sanitation Times by admin

Developing Environmental Assistance Partnerships (DEAP)


The need to empty pit latrines is self evident, the urban dwelling poor are unable to locate and establish a new facility due to lack of space and financial constraint. The usual methods of vacuum pumping are costly and the manual removal of waste excreta is both dangerous and demeaning, often an occupation for those of the under classes of society. The element that is needed is the development of the local sanitary engineer. There is a cornucopia of euphemisms in the UK for such workers, the Night Soil Collectors. In less developed regions the need for the service of such emptying operatives with the use of tools for the trade, not large and expensive, but robust, safe to employ and use, plus a growing professional identity and status.

The job, in the past has been achieved by hand pumping or bailing the liquid fraction of the waste from the pit with as much of the solids that can be persuaded to leave the collection chamber. The residual waste being made up of deposited layers from soft to near solid; caused by the compression of the later deposits onto the earlier, thus forcing the waters of mineralization out of the lower layers. This would normally be dug out of the chamber manually and brought to the surface in baskets or buckets raised on a rope by an assistant.

This waste is normally then taken to outside the urban area (this practise has been witnessed in Addis Ababa, Ethiopia and Sana’a, Yemen) and dumped or a drain, in many cases a road drain is used as a disposal point. The nature of the waste and invariably the lack of rainfall sees the waste dry on the side of a rural road or block the drainage system; this only being discovered at the time of rains or monsoon.

An Answer.

The emptying of the waste would be achieved faster and less laboriously if the solid and liquid fractions were melded together allowing a hand pump to remove the entire contents of the latrine pit, thus negating the need to physically descend into the excrement, and avoiding the risks of unlined latrine pit wall collapse; this being not uncommon and due to the walls of the void being reliant on the forces exerted by the faecal fill over the time keeping the structure stable. There have been deaths due to this form of accident where ever latrine pits are used.

The resolution of this problem may be found in other industries; bakeries, potteries and building. A mixer that is able to be used up to the sides and bottom of the pit, so as to macerate, aerate and blend the various layers into uniform liquid slurry. The process would require practice and in time allow an operator to empty more pits per day. Almost more importantly the pits would be better emptied than just by suction alone, so elongating the times between emptying. The use of blungers or mixers to blend casting slips for making pots, or the blenders used for the mixing of cool butter and other, less dense, substances in bakeries are reasonable analogies.

The Equipment.

The basic equipment that would allow a mixer to operate would be a rotating whisk/blade that is attached to a steering device or handle. The power to be taken to the mixing head would be a form of semi-flexible power transmission feed as in a garden trimmer or other such device. The air input would be introduced with the mixing instrument

The power unit and air supply could be produced by small petrol; electric or geared peddle/treadle mechanism. The later being the favoured option in a poor community and could allow paid employment for an assistant or apprentice. The geared pedal power unit would be the simplest to maintain as bicycle parts are more readily available than motor mechanics and the reliance on spare parts and issues of obsolescence.

The Research.

To understand the standard waste matrix of the latrine fill; so allowing the design of the blade/whisk to be both robust enough and capable of macerating other deposits such as vegetable matter. To source a semi-flexible dive shaft and linkage mechanism to a gearing system that was easily powered by a peddle or treadle sourced mechanism.

The project would need to be carried out at field sites where the waste could be characterised, and in a workshop that allowed for basic engineering techniques to be carried out. Ideally much of the construction materials and manufacturing skill would be found or developed locally so as to allow the communities to take control of their own resource.

The experimentation would trial the principal mechanisms and techniques of liquidisation of different pit fill matrices and consider the ideal liquefaction for the raising of faecal waste by hand pump.

In the field the standard or average depth of pits to be encountered so as the head of the machine is easily manoeuvrable with-in the confines of the space. This may require a form of telescopic or sectional drive mechanism so that the whole machine is not too heavy or cumbersome. Ideally the operation could be achieved by the labours of two persons, male or female (the culture and custom of specific regions needs to be understood).


The outcome of this project should allow a two person team to empty the solid and liquid fractions of the latrine pit together without physically entering the confines of the structure and allowing a more professional approach to the issues of excrement removal to be developed. This could develop a better standard of life for the marginalised workers who by tradition undertake this work.

Product Development Needs.

The equipment that is envisaged should be made primarily from readily available materials and the need for specialist manufacture should be unnecessary. The most specialist parts would be accessible in most parts of the world. All the elements of the machine would use low cost components.

Author: admin

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