Odour and Fly Control

The control of insects and odour are important issues to deal with in improved toilet facilities. The elimination of odours makes the toilet far more pleasant to use, and the control of insects, particularly flies, is important for health reasons. Too many flies are also a nuisance.

8.1 Odour control

A screened ventilation pipe can reduce odours and flies in all the compost- making toilets described in this book. The vent pipe draws out air from the pit or vault, mostly by the action of air passing across the top of the pipe (Figure 8-1). One option for the vent pipe material is to use 110mm PVC. The air that flows out of the pipe is replaced by air passing down the squat hole or pedestal. This is most efficient when the slab and pit collar are sealed and airtight and the head of the pipe is not surrounded by trees. Any foul odour from the pit or vault does not escape into the superstructure, but is diluted by air and passes out of the pipe into the atmosphere. The effect is that the toilet becomes almost odourless. The vent also helps to remove moist air from the pit or vault which helps to reduce the moisture content of the excreta.

Also a urine-diverting pedestal which separates urine from faeces (Figure 8-2) will also have the effect of reducing odours, since the faeces are drier when not mixed with urine. The drying effect is increased by adding wood ash or dry soil to the deposit. This will also control flies.

But PVC pipes and urine-diverting pedestals may be too expensive to fit to very low cost pit toilets. In this case the regular addition of soil, wood ash and leaves to the pit will help to reduce odour. Keeping the toilet clean and covering the squat hole can also help. It is possible to upgrade a simple pit toilet by adding a vent pipe or urine-diverting pedestal or both at a later date. The urine-diverting pedestal should ideally be one where the urine

off-take is above slab level. This makes plumbing arrangements on pit toilets easier.

Figure 8-1: The effect of a vent pipe Figure 8-2: Urine-diverting pedestal

8.2 Fly control

In urine-diverting toilets, the faeces are deposited separately and covered with dry soil and ash. Flies do not breed well under these conditions. But if soil and ash are not added, fly breeding can begin. However fly breeding is easier to control in urine-diverting toilets, simply by adding more dry ash and dry soil to the deposit. It is essential that the urine-diverting vault is not flooded with water or urine added. This will make things very messy. User education is required on the proper use and maintenance of urine-diverting toilets.

The method used in the ventilated improved pit (VIP) latrine effectively controls flies as well as odours if the conditions are met, such as fitting a screened vent pipe. Corrosion resistant aluminium or stainless steel screens must be used. The toilet house must be kept in semi-darkness and a roof is essential. Open doors allow flies to escape through the house. Where the interior of the toilet is kept semi-dark, flies will enter the pipe from the pit or vault and become trapped by the screen. This is because flies are

attracted to light when they leave the pit and enter the pipe which is the most obvious light source. From the outside, flies are attracted by odours coming from the pit or vault and most of these are expelled through the head of the vent. If the head of the pipe is screened, flies cannot enter the pit. This simple effect can dramatically reduce fly breeding inthe pit toilet or vault and thus reduce the passage of fly-born disease. This is the principle of the VIP toilet. Fly breeding will also be reduced if the pit contents are drier. Thus adding a urine-diverting pedestal to a shallow pit system will help.

Figure 8-3: Addition of wood ash to the pit to control fly breeding

But for lower cost shallow pit composting toilets a vent pipe or urine- diverting pedestal may be too expensive to fit. Then fly breeding, which is a natural phenomenon in pit toilets, must be controlled by some other means. This is because the mix of faeces and urine is far more fluid than faeces alone produced in urine-diverting toilets. Flies breed most in pits which are moist and also during the warm wet season in Southern Africa, from December to March. The liberal addition of wood ash is known to reduce the potential for fly breeding in pit toilets (Figure 8-3). But it may not eliminate them altogether. So if flies build up, it helps to add ash liberally if it is available, especially during the hotter wetter months when the fly problem is worst. The liberal addition of ash will also reduce odours. Where soil, ash and leaves are added in combination, the pit gets a mix of soil organisms, potash and composting matter which helps to make

better pit compost for later use in agriculture and tree growing. So the more of these additional materials is added the better the final compost and the greater the degree of fly and odour control. The pit filling time is reduced as more soil, ash and leaves are added and a balance must be struck between adding too much or too little. In rural projects, homesteaders are often reluctant to add to much soil or ash at first, but soon learn that flies and odours are controlled better if more is added.

9. A Matter of Hygiene and Hand Washing