Pit emptying

The process of pit emptying is sometimes called desludging. There are manual and mechanical methods for desludging, but the manual removal of faecal sludge from pit latrines poses severe risks to those undertaking the task.

Whether using manual or mechanical methods, the personal safety of anyone employed in pit emptying should be of primary importance. Operatives should wear gloves, masks and protective clothing.

Vacuum trucks

Vacuum trucks are vehicles equipped with a storage tank and pump with a hose that is lowered into the pit to suck the sludge up and out into the storage tank (Figure 6.1). The sludge can then be easily transported to a suitable disposal site. Vacuum trucks are quick, powerful and efficient, but they are large vehicles and so access to the pits can be a problem. The size of the truck can limit their use in areas where roads are narrow and twisting. Truck operators will charge a fee for their services, which is another factor that needs to be considered.

Figure 6.1 Vacuum trucks are used to empty pit latrines and septic tanks.

Vacutug

The Vacutug, shown in Figure 6.2, is basically a smaller version of the vacuum truck. It was devised by UN-Habitat as a system that could replace manual emptying. The Vacutug is a mechanical system that can be manufactured locally using readily available components. It is affordable, easily serviceable, able to operate in narrow passageways where vacuum trucks cannot go and is capable of sucking out waste sludge for transportation to a larger tanker vehicle (UN-Habitat, 2003). It can empty pits down to 2 m deep (Thye et al., 2009).

Figure 6.2 The Vacutug.

Hand-operated pumps

Even the Vacutug cannot get everywhere. The Sludge Gulper, like the one shown in Figure 6.3, is an example of a smaller hand-operated pump. These can be taken to pit latrines that are inaccessible to larger pumps. It is a simple design consisting of a PVC pipe containing two valves and can be built using locally available materials. The sludge is pumped up by hand, collected in a container and taken away for disposal. Care is needed to ensure that the operator and other helpers do not come into contact with the sludge and that it is not spilled.

Figure 6.3 Hand-operated sludge pump. The pump is located over the pit and the operator (wearing suitable protective clothing) pumps the handle up and down. Sludge rises up the vertical pipe and is expelled into the container. (Tilley et al., 2014)

Disposal of the sludge

Several options are available for disposal of the collected sludge (Pickford and Shaw, 2005). It can be put directly onto land and used as a soil conditioner, but this is only possible if it has been left untouched for at least two years (Brikke and Bredero, 2003). Fresh, untreated wet sludge poses high risks for human health and so should not be put on land used to grow crops.

Drying the sludge will kill most pathogens. This can be achieved using drying beds (Figure 6.4), where sludge is put into shallow tanks to a depth of about 300 mm. The base of the tank is sloped and covered with a layer of sand (forming a ‘bed’) to allow liquid to drain out of the sludge. In warm climates and without rain, after about a week the sludge will be dry enough to be lifted by a shovel.

Figure 6.4 Sludge in drying beds.

The sludge can also be composted by mixing it with vegetable matter, or biogas can be obtained by anaerobic digestion. Whichever method is used, faecal sludge disposal must be carefully managed and operated in order to ensure that the associated risks to health and the environment are avoided.