Field testing of a prototype mechanical dry toilet flush

Abstract

A prototype of a non-fluid based mechanical toilet flush was tested in a semi-public, institutional setting and in selected peri-urban households in eThekwini municipality, Republic of South Africa. The mechanism's functionality and users' perception of the flush were assessed. User perception varied depending on background: Users accustomed to porcelain water flush toilets were open to, yet reserved about the idea of using a waterless flush in their homes. Those who commonly use Urine Diversion Dehydration Toilets were far more receptive. The user-centred field trials were complemented by a controlled laboratory experiment, using synthetic urine, -faeces, and -menstrual blood, to systematically assess the efficiency of three swipe materials to clean the rotating bowl of the flush. A silicone rubber with oil-bleed-effect was found to be the best performing material for the swipe. Lubrication of the bowl prior to use further reduced fouling. A mechanical waterless flush that does not require consumables, like plastic wrappers, is a novelty and could - implemented in existing dry toilet systems - improve acceptance and thus the success of waterless sanitation.

Keywords: Iterative design; Reinvent the toilet challenge; Science-design Interface; User testing; WASH.

Graphical abstract

Fig. 1

Cross section showing the rotating bowl and swipe – through gears connected to the toilet lid, the bowl rotates downward (from this perspective: counter-clockwise), and the swipe moves in concert to clean the bowl's surface.

Fig. 2

a) Prototype pedestal with mechanical waterless flush, installed in a dedicated toilet room adjacent to the laboratories of the Pollution Research Group at the University of KwaZulu-Natal; b) schematic of the installation: The pedestal is connected to the sewer mains and has a ventilation pipe from inside the unit. The gear system is shown to be on the side of the pedestal, underneath the cover.

Fig. 3

Image analysis using ImageJ software: a) with the polygon selection tool, the total area of the bowl is measured; b) with the color threshold tool, the fouled area was identified; c) shows the selection of the fouled area.

Fig. 4

Potential vs Challenges as seen by the 8 interviewees at UKZN. *MHM: Menstrual Hygiene Management – only the four female interviewees were questioned about this aspect.

Fig. 5

User survey replies from the households, answering the questions “How much do you agree with the statement…?” a) “…the toilet didn't smell bad”, b) “…the toilet was easy to use”, c) “…the toilet was clean”, and d) “…I prefer this toilet to my usual one”.

Fig. A.1

Survey questionnaire for user testing at UKZN.

Fig. C.1

Using ImageJ Software to determine covered area in toilet bowl.

Fig. E.1

Bristol stool chart; image created by Kyle Thompson for Michigan Medicine, University of Michigan, under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.