Civil Engineering June 2021 | Vol 29 No 5

Civil Engineering June 2021 27 the purest available form of the polymer in order to be assured that the final product will have the desired mechanical properties. Ordinarily, in order to be used by industry, recycled plastic needs to be rig- orously sorted and cleaned to ensure the purity required by the food, automotive and other industries. The cost of sorting increases the cost of the recycled plastic; removing or reducing the cost of sorting will, therefore, reduce the final cost of the recycled plastic. The recycled plastic available in Eswatini, where the research is taking place, and where it is hoped production of the UDDTs will begin, is currently from one major commercial supplier, who coarsely separates polymers before recycling them into flakes. The recycled plastic is cheaper, but of a slightly more variable composition than is usually required by industry. The purpose of the research to be undertaken by the author is therefore to determine a recycled polymer mix composition that will provide the required mechanical properties while still allowing for the variability in recycled plastic content. An interesting possible addition to the design of the UDDT is the use of reinforce- ment should the recycled plastic mix not guarantee the required strength. While several reinforcing materials are possible, the author has chosen to investigate pineapple leaf fibre which, according to the literature, has excellent stress and strain properties and is abundantly available from commercial farmers in Eswatini. MOULDING PROCESS A variety of possible moulding processes are available for the manufacture of the UDDTs, including injection moulding, rotation moulding, compression moulding and blow moulding. Each of these pro- cesses places requirements on the type of polymer used, primarily through the workability (or melt flow index) of the molten plastic and the shape, size and thickness of the structure being produced. Ordinarily, the melting point and other mechanical properties are accurately known if virgin plastic or highly sorted recycled plastic is used. The use of a less well sorted recycled plastic will mean that an allowance must be made in deciding on the final moulding process. CONCLUSION In summary, the mass production of UDDTs is an attempt to reduce water use and production of water-borne sewage in South and southern Africa. For the user of the UDDT, there are the potential benefits of reduced water and wastewater ac- counts. In addition, the recovery of toilet waste will create an industry in reuse of these nutrients. Given the greater convenience of an indoor toilet, UDDTs may also go some way to replacing pit latrines (with their associated health and hygiene problems). The aim of the research by the author is to determine a recycled plastic mix (possibly using pineapple leaf fibre rein- forcement) and moulding process that will give the required mechanical properties at a cost lower than if virgin plastic were used. Once a prototype has been success- fully produced, the challenge will then be to make it commercially viable for mass production.  AutoCAD ® World-Leading CAD Software WaterMate Water Reticulation Design SurfMate Survey & Digital Terrain Modelling AeroTURN Aircraft Movement & Space Analysis RebarMate Reinforced Concrete Detailing & Scheduling Autodesk Civil 3D ® Site Development & Transportation AutoTURN Vehicle Manoeuvre Simulation & Analysis DatumMate Datum Conversion of Drawings RoadMate Urban & Rural Road Design ParkCAD Automated Parking Area Layouts Architecture Engineering & Construction Collection PipeMate Sewer & Stormwater Design and Analysis