Pit emptying systems
Practical Action
The two predominant problems facing such trucks are cost (both capital and maintenance)
and, in urban areas, access to facilities. The machine cost will vary between locations, but a
value exceeding US$100,000
should be expected. The ability to
afford and access spare parts locally
will also vary between locations, but
if the technology is not widely used
there is the likelihood of having to
import spare parts.
The use of such technologies has
exhibited a low cost to customers,
but only when considered on a unit
cost basis. Due to the speed with
which a tanker can exhaust a pit,
despite its higher cost, it often
costs less per m3 removed.
However, some households would
Figure 5: A vacuum tanker discharges its load in
still prefer to pay a small amount
Accra, Ghana. Photo Credit: Niall Boot, 2007
for a small volume removed as this
is what local monetary conditions
permit. There should be adequate planning to assess people’s willingness to pay, both in
quantity and regularity.
Table 5 – Advantages and Disadvantages of Vacuum Tankers
Advantages
Disadvantages
Removes waste safely for both workers and Haulage distances are likely to be key in
public health
overall expenditure
It is a low odour technology
Costs too much for many SSIPs
Fastest means with which excreta can be
Access problems in many areas
exhausted
Relatively fast travelling speeds has better
Maintenance costs are also high due to
possibility of economical disposal of waste
imported technology
Despite being ‘high technology’ it does not
overcome the lack of a disposal site
Tractor Trailer Units (Towing)
One method often cited as a means of reducing the overall cost of machinery is to have a
towed unit that contains a form of pump. This potentially can save a lot of money on the
capital cost, as such a system is likely to be cheaper than a large vacuum tanker. It is also
likely to overcome the problems of containerisation facing some technologies and will
facilitate haulage of waste at reasonable economic scale.
Submersible Pumps
It is generally accepted that vacuum pumps (whereby a vacuum is created in a tank which
results in the waste being sucked into it) are the most appropriate systems for emptying pits.
An alternative is a pump that is submersed within the pit and allows fluid to pass through it
before pumping it upwards. The problem with such pumps is the ease with which solids can
damage them. Despites this, in some areas the pumps have proven reasonably successful,
however they should not be used where solid anal cleansing materials are used. Furthermore,
the process requires containerisation and separate transportation.
Conclusion
This technical information is intended as a background to the possible options available for
emptying an on-site sanitation facility. It also describes some of the more important wider
issues such as the need for the correct institutions and an acknowledgement of the entire
FSM chain.
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