Outside of cities and large towns there is no access to any form of waste water treatment, and even within cities sewerage coverage is extremely limited, in Kampala at less than 10%. Pit latrines are consequently the default sanitation option in East Africa, essentially a large pit dug in the ground and covered with a floor slab that contains a hole to accept human waste. Improvements can be made to facilitate cleaning such as embedding a ceramic squatting toilet pan or plastic saTon pan. When the pit is full, it is usually sealed over and the area is rendered unusable. There are several preferred sanitation options to consider. Sanitation blocks should be built away from other accommodation and functional spaces to minimise the smell and insect nuisance.
Ventilated Improved Pit Latrine
Adding a ventilation pipe to a pit latrine can eliminate odours and aid fly control. Lining a pit latrine ensures it can be mechanically emptied and reused.
Ventilated Improved Latrines have a vertical vent pipe directly over the pit. Wind that passes over the pipe causes air to escape, creating a downward draught through the drop hole. This effectively channels odours away from the user. The vent pipe also aids fly control as flies are prevented from leaving through a fly screen at the top. The pit is lined so that solid waste can be emptied when required. A school requires a pit with a volume of 6,000L for every 100 children, provided it is emptied once a year.
Ecological sanitation principally involves separating out urine from solid waste (urine diversion) and recycling both for use as fertiliser.
Ecological sanitation or ecosan toilets require user training and a toilet bowl which collects the urine and diverts it to a holding tank or soakaway. Fecal matter is collected in a separate chamber and usually combined with layers of ash or sawdust to keep the composting chamber dry. Constructing the toilet cubicles in pairs allows one to to be in use while the other goes through a composting cycle of 6 months before it can be emptied and used as fertiliser. Ecosan toilets reduce the risk of underground water contamination and have a lower lifetime maintenance cost than an equivalent pit latrine system.
The vermifilter toilet is a cheap and low maintenance composting toilet system, which uses tiger worms to create a rich and odour-free fertiliser.
Vermifilter toilets or 'Tiger Worm Toilets' use tiger worms to speed up the composting process reducing sludge build-up by up to 80%. This removes the need for traditional desludging as the vermicompost is simpler to remove, saving in the long term on operation and maintenance costs. The system does not require a special toilet bowl for urine diversion, instead operating as a pour flush latrine, where a small amount of water reduces the urine acidity. In Uganda, testing is being undertaken by the Appropriate Technology Centre and Water for People.
The Appropriate Technology Centre has set up a wormery to supply worms for their Tiger Worm Toilets
A bio-latrine is a low maintenance system comprising of a toilet and simple biodigester unit that turns human waste into fuel and fertiliser.
A bio-latrine can be constructed using local materials, and requires no water or additional input other than human waste. Faeces are fed via a pipe into the biodigester chamber, which is normally constructed of bricks in a cylindrical or fixed dome design to minimise gas leakage. As faeces are broken down through anaerobic digestion, methane gas collects in the upper part of the chamber and passes through an outlet pipe, either to a storage facility or directly to where it is required. The remaining slurry/biodegraded waste is an ideal organic fertiliser.
Water flush systems require substantial amounts of water. To deal with water-based waste a complex settlement tank and soakaway system is required.
Water based systems are common in cities with water supply and centralised drainage. In rural areas, a septic tank is required to receive both the black eater from toilets and grey water from showers. A septic system consists of a plastic or concrete underground settlement chamber that flows into a soakaway system. The soakaway is a leach field of perforated pipes in a gravel bed to allow water to drain away. The tank should be sized to approximately 20,000L for every 100 children. A dual flush system should be utilised to reduce water demand, which can be supplemented through grey water recycling.
A typical underground concrete settlement chamber.