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and E in different years (1996-2002) were sampled. The systems in Blocks C (1996) and D (1996) were old and from
the R & D phase and the systems in Blocks B (2001) and E (2002) were from the promotion and installation phase.
Out of the 4 systems, soak pits were present in the systems of Blocks B and C and absent in the systems of Blocks
D and E. Samples from each of the biogas based sewerage systems were collected from the locations as shown in
Figure 6.5.
The wastewater was collected for testing from the following points: (1) from inside a connection pit at the end of
lane collecting waste from 24 plots, (2) from inside an inlet tank just in front of the biogas chamber, (3) from inside
a hydraulic chamber, and (4) from inside a soak pit. When there was no soak pit, sample 4 was collected from the
outlet pipe of the hydraulic chamber as it discharged wastewater into the canal or big surface drain of the area.
Sample 5 was collected from the canal at the point where the effluent was discharged. Raw wastewater was also
collected from the connection pit of a pit latrine that was not connected to the biogas based sewerage system.
In most of the following collection points 2 (inside inlet tank), 3 (inside hydraulic chamber) and 4 (inside soak pit),
the wastewater was found in a solidified state in most of the facilities except for the facility in Block D. Thus, the
sampling was done by either rubbing/cutting the solidified waste or by collecting the overflowing wastewater.
It was observed during the sample collection that most of the sampling points, particularly biogas chamber,
hydraulic chamber and all the soak pits, were buried a few to several meters under the surface as concrete roads
were constructed on top of them. The digging and breaking of the roads to such depth was not an easy task, as
much care was necessary not to damage the system itself while digging up the road. Due to this difficulty, it was
not possible to reach a biogas based sewerage system in Block A to collect samples, thus excluding Block A from the
analysis.
According to the local people, the systems were not cleaned or opened since their installation. This was due to the
fact, as mentioned earlier, that it was not an easy task to reach the systems.
It appeared that the sewage was solidifying and being deposited in the different chambers, leading the untreated
wastewater to flow over the solidified sewage in the biogas chamber and hydraulic chamber in three out of the
four sampled systems (this occurrence is known as short-circuiting). Therefore, the waste was not given a chance to
sufficiently decompose, which indicated inadequate treatment. In addition, one of the systems was
also observed
to
be leaking wastewater from the hydraulic chamber.
The
results of this chemical analysis are summarized
in Table 6.3. The bio-chemical
condition
of the systems can
be observed from the data in Figures 6.6-6.9. Referring to Figures 6.6-6.9, the overall treatment of wastewater in
general
showed problems, as very little difference was observed when the influent (point 2) and effluent (point 4) of
the
different biogas systems were compared. It is not easy to comment on the merits of the individual components
of each of the systems, because there were too many operational variations on how each system was functioning
and the size of the sample was too small for a concise comparison (4 out of 20 systems).
Table 6.3: Results of the chemical analysis of the wastewater from each biogas based sewerage system.
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