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Engineers have a word for it!… Central Sewage System to end perennial flooding

BY: Enimil Ashon
library photo
library photo

Last week, I included in my examples of visionary projects (as opposed to a 450-seater Parliament Complex) the first Central Sewerage System being built in Kigali, Rwanda, at a cost of 96 million euros.

It started last June to be completed in 2022.

I am old enough to recall that just before its overthrow in 1972, the government of Prime Minister Kofi Abrefa Busia was on the verge of signing a contract with an Israeli company for the construction of a central sewage system in Ghana, starting from Accra.
Before him, the first President, Kwame Nkrumah had designed and constructed a central sewage system for Tema.

Under this system, sewage is collected and transported via a network of pipes and pump stations to a municipal treatment plant. That system avoids the unsightly and unhygienic situation where human waste is transported by vehicles to a site and is dislodged directly into the sea without any treatment whatsoever.

Depending on how old you are, you may remember that once upon a time, in Ghana, human excreta was poured with human hands from our domestic pan latrines and carried in larger containers on human heads through town by ‘Kru’ labourers imported from a particular part of West Africa.

That was the era before manholes were incorporated into building designs.

Ghanaians from Sekondi old enough to remember, will hate to be reminded about “Bin Bon” (literally “excreta smells”), a dumping site between Ngyiresia and Esipun.

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In Accra, the disposal of faecal matter has been by cesspit emptiers which take it from household manholes and from other sources in the Korle Bu, Accra Central, Ministries and the 37 Military Hospital areas and carried to that colony behind the Korle Bu Teaching Hospital that has gained notoriety by its pet name, Lavender Hill.

It has been so named for the smell of putrefaction that hangs over the beach area where cesspit emptiers discharge human faeces into the sea. Mercifully, two treatment plants have, since 2016, been built in the area to treat 80 per cent of sewage (200 trucks a day) in Greater Accra.
This is the municipal system.

Under a centralised system, sewage, including household liquid waste from toilets, baths, showers, kitchens, and sinks generated by residential, institutional, commercial and industrial establishments, drain into sewers.

By a system of pipes, chambers and tunnels, the sewage and storm water are directed to a plant and treated before it is discharged into the environment.

In other jurisdictions (I saw one in China and have read about the system in the USA), the treated greywater is used for watering plants or recycled for flushing toilets and even for bathing. It cannot be drank because of the excess chlorine.

A Ghanaian engineer, Mr James Adjei, is proposing a central sewage system, such as what Kwame Nkrumah and Busia had in mind, as Ghana’s solution to our perennial flooding.

A Hungary trained mining engineer with over three decades under his belt at the erstwhile Akwatia Consolidated Diamonds Mining Company, Ghana Energy Board and Minerals Commission, Mr Adjei envisages a centralised system that will transport both surface run-off and sewer through pipes, chambers and tunnels to a treatment centre.

“It would serve a dual purpose of waste and flood water management. In the event of a downpour, rain water seeps underground and is, by a network of pipes, directed into underground tunnels, often as large as 30 feet in diameter.

“Within minutes after rains, all the water would have seeped underground. With a central sewage system, we don’t need all these investments in perennial desilting of drains, for, as we have all seen, these drains, though not totally useless, have not solved flooding in Ghana.

The central system is what exists in the so-called advanced countries; that is why, no matter how heavy the downpour, there is no flooding.”

I reminded him that it does flood in the UK and USA but Mr Adjei was quick to reply: “Of course, occasionally, once in a very long while, in extraordinary circumstances, we may hear of flooding, but even in those situations, the flooding lasts only a while.”

The dual system of faecal matter and storm water treatment kills many birds with one stone. The bonus is that aside providing an antidote to the flooding problem, it allows us to turn human waste into value-added products fertiliser, biogas for cooking and briquette (charcoal)

Mr Adjei is emphatic: “It is clear that the solution to the perennial flooding of parts of Accra and the piecemeal approach to the management of sewer is the provision of a combined central sewage system (CCSS). It will end the practice of individual houses having to provide their own sewage system.

With the advent of a CCSS, one only has to connect their sewage to the central system – no manholes and therefore, no cesspit emptiers.

Flood waters will be directed in a regulated manner through underground tunnels for discharge into the environment.”
That is for the long term.

In the interim, Mr Adjei proposes the construction of retention dams upstream. “It is a sure way to reduce the amounts of run-off into the system”.