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1.2.2 Problems with sewers

The total cost of operating a water-flushed toilet is nearly 8 times that of a pit latrine ($5,885 to $750) in Botswana. Endemic sewer blockage could result because guidelines for sewer operation usually call for 50 l/c/d to keep waste flowing. This sums up to 7.5 m3 per month, just to keep the sewer flowing. That amount alone is more than most families consume in a month in Gaborone (national per capita water use is 175 litres /day, and the poorest half of the families use about 60 l/c/d). By Africa�s standard this is a high level of service, yet it is hardly adequate to operate water-bone sewage system for half of the population. It is perhaps obvious sewerage systems may not be generally sustainable in most African cities. In South Africa some 31% of the urban population have inadequate sanitation. Most of its communities desire raw waterborne sewage systems as their first choice, but adequate funds are not available to provide this system to all in need of sanitation facilities. The country has therefore developed increasing interest in alternative technologies, e.g. settled sewerage systems that provide for flush toilets but have lower cost implications.

In Africa about 80% of water consumption of those connected to the sewer ends up discharged into the municipal sewer, but in Gaborone, the return flow is 50-65%. This is why it is feared that if poor people are added in great numbers, the resultant reduced sewer flows could upset the operation of the sewer system because of too little water to keep waste flowing. The ultimate solution perhaps lies in the pursuit of lower cost alternative technologies that suit this water short Region which is much drought prone.

A full waterborne sewerage system was installed by Ghana Water Sewerage Corporation in central Accra with World Bank assistance and completed in 1973, covering 1000 ha and involving 28.5 km of sewers. It is a classic example of unaffordable services by prospective beneficiaries. The system never worked well, because of narrow and crooked streets and below standard housing and plumbing that exist predominately in central Accra hampered connection to the system (Poster et al., 1997). Table 1.11 shows that only 6.5% of the available connections were utilized. The old agenda of supply driven sanitation system wasted immense investments. Inappropriate designs, neglect of user requirements, inadequate maintenance, and ill-equipped operating agencies create continuous drain on government resources, and a disincentive to governments and donors contemplating further sector investment. Users become disillusioned when promised improvements fail to materialize, and refuse to pay for inadequate services which leads to further deterioration.

The existing waterborne sewerage schemes in Greater Lagos are in various states of disrepair and operational conditions and are of three categories:

• Housing estates - have the larger systems - Festac, Abesan, Oke-Afa, Amuwo Odofin, Iponri, Alausa Secretariat, Victoria Island, Lagos Island.
• Institutional and commercial schemes - generally much smaller and a total number of 65 separate schemes have been constructed.
• Only a small number of industries have sewerage schemes and treatment plants although the Federal Regulations require this provision: Lever Brothers, Apapa, WEMABOD plant, Ikeja.

Festac (Festival of Arts and Culture) Town, a satellite of Lagos municipality, is a "new" town built to house the participants in the World Black Arts Festival which Nigeria hosted in 1977. Thereafter it was settled. It is situated on the Lagos-Badagry road which links Nigeria with the Republic of Benin, on a land are of 770 ha. There were three communities with 4220, 4053 and 2052 dwelling units, while 1000 units were added later. Some 68% of the inhabitants belong to the low-income group (by designation, but many of them are anything but low-income group), 11% middle- and 21% high-income group. The revised plan for the town provided for a total of 61,600 persons.

The sewerage system was designed to serve the whole population of the town. Altogether there are 72 km of sewerage pipes, 24 km of open drains, 81 km of storm sewers (drain pipes), while 112 km constitute the water supply network. There are 7 pump stations, and the wastewater from the whole town is conveyed to a nearby settlement known as Sattellite Town where the treatment plant is located.

Abuja, the new Federal Capital of Nigeria is designed to be served entirely by sewerage system. On account of sharply varying topography, however, there would be some four central sewage systems (Pers. comm. Emmanuel I. Ovbiebo, 1999). The system in place now is the one serving the central city of 200,000, in the Wupa drainage basin. It is designed to have 5 treatment plants, which are under construction. The temporary plant now in use has capacity to serve only 50,000 people. Wastewater design flow is 210-230 l/c/d, but the actual flow is about 200l/c/d.

Topography favoured gravity flow at Abuja with an elevation of 495 m. The landscape slopes gently towards Abaji, one of the satellite towns at 300m, such that a lift station is required only near the plant. The sewer pipes are laid along the lowest river valleys, parallel to the main river course, and such valleys were designated green belts. But already, developers are encroaching on the green belts and tampering with the manhole and sewer pipes.

The satellite towns of Gwagwalada, Sheda, Abaji and Yanyan of the Federal capital of Abuja have central sewerage systems designed but not yet constructed. At the moment they use septic tanks which would be disconnected, and filled up with laterite when the sewerage system is ready. The question is why can�t the septic tanks be sewered instead of wasting such huge investments?

Only 5% of the inhabitants of Lagos Metropolis is connected to sewerage and associated sewerage treatment plants which do not treat the sewage to acceptable standards, and are poorly maintained and operated. The Federal Government 1004 Housing Estate sewerage system is served by a package treatment plant. Breakdown of various electrical and mechanical components and lack of funds for adequate maintenance, sees the bulk of the wastewater that enters the plant by gravity sewers or discharges from vacuum trucks, bypass the treatment units and discharge untreated direct to the lagoon.

The district has one of the largest existing sewerage schemes within metropolitan Lagos, the Victoria Island sewerage scheme' though it has never been commissioned or used. It was designed in the early 1970s to cover most of Victoria Island. The following data summarize the stage of its completion as at December 1978 when all works appear to have ceased as the contractor abandoned site without notice, and never returned.

• total length of sewers laid (100 mm, 150mm 200mm, 250mm, 300mm diameter asbestos cement sewer) representing 40% completion : 23,780 metres
• total number of manholes constructed : 341
• total depth of manholes constructed representing 31% completion: 476 metres

Total wastewater flows to Lagos lagoon in 1995 and by 2010 have been estimated as in Table 1.12.

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