Biogas use in Reconstruction
Practical Action
Using Biogas units to reduce waste
In a post-disaster scenario it is likely that toilet provision will
be limited to pit latrines, at least until more advanced
solutions can be implemented. The pit can fill up quickly,
which can easily lead to pollution, contamination and
unsanitary conditions unless either a new pit is dug or the
existing pit is emptied. In rural settings it is generally easier
to construct a new latrine, but this is probably not possible in
a confined urban setting.
Therefore, in urban reconstruction contexts there is a
requirement for latrines to be emptied as they become full of
waste sludge. Currently this is dominated by manual methods,
which are inefficient and expose the operators to severe
health risks. Practical Action’s technical brief Pit Emptying
Systems examines some of the advanced mechanical
emptying solutions that are being developed.
Another option is to combine biogas digester technology with
the latrines; this gives the opportunity to control human waste
and reduce pollution, whilst providing useful fuel and by-
product in the process. Despite the several benefits that this
can achieve, there are certain barriers to implementation that
must be considered, including ‘soiling-up’ (a hard
irretrievable layer grows with use), social acceptance and
logistical constraints. Refer to the Practical Action technical
brief Using Biogas Technology to Solve Pit Latrine Waste
Disposal Problems for a detailed study on this.
Figure 4: Pit latrines in the
Kibera informal settlement
(slum) in Nairobi, Kenya.
Photo: Karen Robinson /
Practical
Action.
A combination of both shallower pits and permanent suction pipes could be beneficial to solving
fluidity/emptying issues and soiling up in pits, but also provide hygiene benefits to the emptier
and fresher feedstock for the digester. The critical factor when assessing digester placement is
space, because without it there will be no other problems. Regarding pressure issues, the use of a
storage vessel is proposed rather than just a comprehensive maintenance program because it
provides the user with the ability to alter the pressure, however further assessment would be
required.
The issues regarding technology when using biogas to reduce
waste can be split into collection, haulage, disposal and
treatment:
Collection: the sludge will be partially degraded upon emptying
therefore decreasing the maximum methane yield. This means,
to make the system feasible the frequency of pit emptying will
have to increase. Pit emptying frequency is inversely
proportional to the operational life of the pit. Dismantling is
often required when emptying a pit.
A solution proposed is to fit an in-situ pipe to the pit that has
an exit outside the super structure (Figure 5). This addition will
limit the disruption caused by emptying as well as making the
whole process more hygienic because the hose will no longer
have to be dropped into the faeces. The addition will also help
deal with the problems regarding viscosity and soiling up in pits
because emptying will happen from the bottom and water can
be added through the pipe to decrease the viscosity.
Figure 5: A diagram conveying
the use of an in situ pipe.
Source: Practical Action
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