Adventures in search of the ideal portable pit-emptying machine

Abstract

In South Africa, as in a number of other countries, on-site sanitation has a dominant place in the landscape of basic sanitation infrastructure. If the question ‘What happens when the pit is full?’ has been thought of at all, it is generally assumed that the pits will be emptied by vacuum tanker. However, owing to site access constraints and the nature of the sludge itself (it can be dense and have a high trash content) vacuum tankers are not always practical. The alternative - manual pit emptying - is hazardous and unpleasant. The Water Research Commission of South Africa funded experimental development of a number of technologies designed to fill the gap between large vacuum tankers and manual emptying. This paper describes these attempts, which include the Gobbler, which uses chains and scoops to lift sludge from the pit, the motorized pit screw auger, which uses a soil auger to lift sludge from a pit, and the NanoVac and eVac, which are small vacuum pumps designed to suck relatively wet sludge from pits. The eVac shows the most promise, but it seems unlikely that any one machine will be able to successfully deal with the greatly varying conditions found in pit latrines.