ENVIRONMENT AND ENERGY
25
BOX 1: SEWAGE AND WASTE DISPOSAL
IN LAGOS, NIGERIA
Although Lagos State generates 1.5 million m 3 of wastewater
per day (about 550 million m 3 per year), there is no central
sewage system in the megacity. Less than 2% of the
population is served by off-site sewage treatment plants,
and only toilet wastewater is connected to septic tanks and
soakaway systems.
Other household liquid waste is discharged directly into the
mostly open gutters in front of houses or on the streets. The
wastewater eventually percolates or is washed into water
bodies by rainstorms. Septic tanks and soakaway systems used
in the collection of toilet wastewater often contaminate and
pollute the shallow groundwater — a vital source of water to
most low- and middle-income residents.
Also, there is no septage treatment plant in the megacity and
the untreated septage is mostly evacuated into the Lagos
Lagoon, especially in areas like Iddo, Makoko, Ajegunle and
other locations. The faecal contamination of the megacity’s
water system and the environment through the inadequate
management of wastewater is an important health concern.
A combination of official neglect, corruption and extreme
poverty, coupled with rapid, largely uncontrolled population
growth has led to the decay of Lagos’s existing city
infrastructure. With a current estimated population of 18
million and a 3% annual growth rate, Lagos State is expected
to become home to over 23 million people by the year 2020.
Concerted efforts are needed urgently to minimize further
contamination of water resources.
Source: Major et al. (2011) and NLÉ (2012)
Based on a review of typical urban forms, the following typologies
cover most situations in developed and developing countries: –
Large urban centres include megacities, urban areas with a clear
central business district (CBD) and well-developed suburbs with
varying levels of progressively decreasing population density
with increasing distance from the CBD. The large centre may
be connected (or not) to smaller satellite centres by transport
corridors. These cities often have extensive sewer networks, but
some, like Lagos, Nigeria, are poorly served by sewer networks
(see Box 1).
Large urban centres resulting from conurbations, where two or more
distinct urban centres progressively grow and see their population
density increase, until they more or less merge into one metropolitan
area. These areas have extensive sewer networks in developed
sections of each of the former city centres, which may have formed
in different ways, and often have separate treatment facilities and
municipal administrations.
September 2018 Volume 24 I Number 7