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Screening and Drying Technologies


    The use of Filtration, Screening and Drying Technologies

    Filtration, screening and drying technologies can be used in different industries. Some of the most diverse industrial applications make use of these technologies. Refining metallurgical and mineral substances represents the inorganic application. Dealing with human bio-waste, excreta and effluent as a need for sanitation represents the organic application of these technologies. A way in which the organic problem is addressed by making use of drying technologies can be found in Parsep’s LaDePa (Latrine Dehydration and Pasteurisation) proces.

    The focus is on the organic application of drying technologies for the purposes of sanitation.


    Population Growth and the Need for Safe Sanitation

    Population growth is leading to an increased need for applications which rely on applications of filtration, screening and drying technologies.


    The need for safe sanitation is as old as humanity itself. In Biblical times extensive prescriptions were practised for the purposes of sanitation. Consequences of unclean or unsanitary actions were punishable offenses. There are examples of how to purify water, and dealing with human effluent, which represent primitive forms of filtration, screening and drying.


    Many civilisations prior to our modern 20th and 21st century world realised that human excreta can be put to constructive use. Peoples like the Incas in Peru, Aztecs in Mexico, the Greeks, and Romans and Chinese have all made use of human faeces and urine for the many purposes. Using faeces for fertilisation represents a natural method of drying. Urine has also been used for bleaching purposes because of its high ammonia and Phosphate content.


    One of the most pressing needs in the modern world is for safe sanitation. Population growth is leading to relative scarcity of resources like clean water and earth which have previously been taken for granted. The accumulation of human excreta is happening at a rate which is putting serious strain on the environment.


    The Problem

    The largest problem in dealing with any waste, offal and human excreta is the unhealthy accumulation of it in any particular place. Pit Latrine sludge for instance has 5 basic problems which need to be overcome, also referred to as the “Big Five of Sludge Management” 1:

    • Detritus
    • Stickiness
    • Pathogens
    • Space and access
    • Transportation


    The first three issues are a natural consequence of organic waste. The latter two are consequences of high population growth and density, which exacerbate the problem. This is particularly true of rapidly growing informal settlements.


    How the Solution Works

    Waste can be described as a composite of any human and non-human product disposed of in an undifferentiated mass of material. Separating the detritus from human excreta is the first stage in the process. This is done by using a compaction extruder which separates -6 mm material from +6 mm material. Following extrusion, drying represent another problem in dealing with human waste because the associated liquids are bound and from part of the sludge. The LaDePa process developed by PSS makes use of Parsep Drying Technology in the sanitation process.



    Once sludge has been extruded onto a woven steel belt, the matrix of voids created allow for a high open area which can then be exposed to a heat source in order for it to be dried. In the LaDePa process this is done by means of a mechanical and thermal drying combination using airflows (suction) and medium wave infrared radiation (heat radiation) PSS uses the infrared emitter wires which emit at 60 kWatt/m² power density and are mounted on specially treated fibre boards. The purpose of this process is to pasteurise and dry sludge so that it can then be used as a grade 2 organic fertiliser – registered as GroweThek. (eThek for eThekwini)


    Possibly the biggest challenge is to make sanitation processes affordable for poor communities. Effective drying technologies need not be beyond poor people’s means. Methods like the LaDePa process can bring huge benefits to communities where sanitation is an issue.


    • Wilson, D & Harrison, J. (undated) Towards a Sustainable Pit Latrine Management Strategy through LaDePa Technology, eThekwini Municipality, Dept. of Water and Sanitation, Durban, South Africa.


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