Civil Engineering June 2021 | Vol 29 No 5

26 June 2021 Civil Engineering O ne form of UDDT has been used extensively by eThekwini Municipality and is therefore well-known in South Africa’s sanitation sector (see Figure 1). It was introduced to deal with groundwater pollution caused by ventilated improved pit (VIP) latrines. These UDDTs are located outside the home. Several other NGOs and govern- ments around the world have used varia- tions of this design in areas that are prone to flooding, are too rocky for waterborne sanitation, or are simply meant to be an improvement on the existing system. UDDTs suitable for indoor use are commercially available from overseas sup- pliers, but not for less than about US$500 (±R7 000). Figure 2 shows an example manufactured by Separett. These UDDTs are usually used as re- placements for chemical toilets in boats and campervans, and as replacements for flush toilets in remote locations like national parks and in homes of eco-aware consumers, and therefore have a limited market. If operated correctly, these UDDTs give the same level of service as a flush toilet. OPERATION OF UDDTS UDDTs store solids separately from liquid waste, allowing for reuse of both. Liquids are stored in an airtight container beneath the pedestal, preventing release of odours. The container needs to be emptied regularly, depending on the number of users. Solids are concealed from view by a flap while the seat is being lifted and are deposited and stored inside the pedestal. A small electric fan drawing air from the storage chamber to the outside prevents odours from escaping into the home and speeds up the drying of the solids, drasti- cally reducing their volume and making them inert. Handling and removal of the liquid and solid waste is required, and safe dis- posal is necessary. This is done through storage (on site or off site) until the liquids and solids are safe to reuse or through dis- posal in a wastewater system. While not its main purpose, the UDDT is also often used for ecological sanitation purposes i.e. sanitation methods that allow the reuse of nutrients. If this is to be done, the waste must be stored until inert (dry and unable to further biologically react) and pathogen free, which can take several months. Because of the inherent com- mercial value of the waste for agricultural or landscaping uses, it would make sense that contractors could remove the waste, although the logistics and number of UDDT users required to make this viable would have to be carefully planned. Homeowners who replace their water- borne sewage systems with UDDTs will enjoy the benefit of a reduced water and wastewater bill. RECYCLED PLASTIC MIX FOR UDDTS In order to make these UDDTs commer- cially viable alternatives to flush toilets, they need to be constructed cheaply while still providing the required mechanical proper- ties of a toilet, such as strength and impact resistance. This will be achieved through the use of different polymer types which possess different mechanical properties. For example, HDPE provides good rigidity and toughness while PET is lightweight, strong and flexible. Regardless of the mechanical properties required, it is desirable to have Urine diverting dry toilets: 30% less domestic water use Evan Nurcombe-Thorne Pr Eng Project Manager Zutari evan.nt@zutari.com The increasing water scarcity in South and southern Africa has prompted the author of this article to start researching the design of a urine diverting dry toilet (UDDT) to be used as a replacement for ordinary flush toilets. The UDDT is a waterless toilet that separates urine and faeces allowing for safe storage and disposal. Figure 2 Self-contained urine diverting dry toilet (by Separett) Figure 1 Poster issued by eThekwini Municipality (2005): How a urine diversion toilet works Thefly screen stops theflies fromflying inandout thepit. Close thedoor to keep the toiletdarkand cool,and to keepfliesaway. Smellsblow away through theventpipe. Urine isdiverted toa trenchfilledwith rocks under theground. Onlyhumanwaste mustgo into thepit. It is importantto:   Make sure that thefly screen isnot brokenorblocked.Replace if it isbroken.   Keep the toiletdoor shut.   Close the lidof the toilet.