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Sites for possible development for sewerage treatment have been identified in both the west and central areas and these can be further investigated once the level and possible position of the collecting sewers along the coast have been more accurately determined.

These possibilities may be summed up as follows:

  • Again it must be emphasised that it is necessary to avoid the old methods of discharging sewerage into the sand along the beach. Such methods will result in serious pollution of the lagoon with time as seepage through the sand takes place and this is unacceptable to tourists of the future;

  • Any hotel development or major source of sewerage will have to allow for pre- treatment and construction costs for part of the sewer necessary to discharge to the sea;

  • We consider that the basis for a sensible pragmatic solution exists which can be adapted and applied as development takes place. This requires better definition by careful investigation and checking details on site. It is also necessary to define the system on plans so that future development can take place in positions and at levels to suit.

5.2.5 Preliminary Sewage Projects Description of Projects

At present, there is no operational vacuum tanker available to serve Xai-Xai and its surroundings. Therefore, septic tank systems cannot be put into operation, especially for larger populations as in hotels, busy restaurants, etc. as there is no means of emptying the tanks to remove solids as periodically required.

Along the seafront it is possible to lay a 200 diameter sewer at a fall of 1 in 300 or a 250 diameter sewer at 1 in 400 from the main hotel to discharge through the reef at the low water level 800m west of the hotel. Provision will be made for an intercepting pump station to be installed as a point along this line and to pump to a future waste water treatment works 600m inland. These works would be of the activated sludge type with chlorinated treated sewage effluent being returned by gravity along the same route in a parallel sewer to the pump station site and will, then, connect to the existing sewer again to discharge treated effluent to the sea. This same pipeline would act as an emergency overflow in the case of pump break down.

The advantage of this system is that it never needs vacuum tanker services, all pipeline constructed are used in perpetuity with nothing wasted, and that the system when fully in operation will meet required discharge standards. A disadvantage is that sewage is not treated initially unless funds are available for the sewerage works from the beginning.

Estimated Cost of Project

The survey of the pipeline route and establishing a possible outlet to the sea had not been completed by the Xai-Xai technical staff at the end of the period. Detailed design will only thus be completed when data is collated and also when the sizes of the hotels to be built are established.

As a preliminary estimate some 900 m of 200 mm diameter concrete sewer pipe will be required to be laid along the esplanade and at the foot of the sand dunes in difficult conditions at:

Estimated cost of approximately Plus reinforcement across beach, etc Total - estimated

US$ 45 000 US$ 20 000 US$ 65 000

Allowing for contingencies and unknowns at this stage a sum of US$100 000 should be reserved from developers of the hotel sites as a preliminary estimate subject to review when requirements are properly known.


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