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Insights into Sewerage management in Harare
Councillor Michael Laban
February 01, 2003

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The last two weeks I have spent a lot of time with the Department of Works, looking at the structure, facilities, people, etc. and finding out how it works. I have started concentrating on Sewerage and Water, and have come to the conclusion that it is here that our highest priority as City Council must be. The majority of the staff I have found to be very helpful and very pleased to have someone who takes an interest and wants to understand what is going on – so I will pass as much on to you as possible. Some of you will be bored, and hopefully some of you will know more than I do and will give me some pointers and questions to ask. The next steps are tours of the sewerage works (how exciting) and the water plants.

Sewerage
This is the biggest problem – we simply produce more than we can deal with. And because we live upstream of our water supply, we could not even ignore the problem if it was morally possible to do so.

There are five sewerage works around Harare. Three small ones are at Marlborough, Hatcliffe, and Mabvuku Tafara (Donnybrook). These serve the small areas nearby – Hatcliffe taking Borrowdale Brook as well.

The two biggest are Crowborough and Firle, both down to the South West. Crowborough is on the North bank of Marimba Stream, West of Mufakose, and Firle is on the North Bank of the Makuvisi, South of Glen View. Crowborough takes effluent from the Industrial areas (Workington etc), Avondale, Mount Pleasant and "Little Marimba" an outfall pipe that runs West of Bluff Hill and through Kuwadzana and Dzivaresekwa. Crowborough takes a lot of industrial waste.

Firle takes from the Makuvisi valley South of the railway, the central business district, the eastern suburbs (Vainona, Borrowdale, Greendale, Chisipite etc.) southern suburbs (Waterfalls, Hatfield etc) and the eastern industrial area (Marimba, ZimPhos, etc.).

The capacities and inflows (per day, in mega litres) are as follows:

So it is obvious that Crowborough is spilling over 50 megalitres a day of untreated sewerage into Chivero. This is the biggest problem.

Sewerage comes through three sets of pipes – Collector pipes (about 150 mm) lead to Trunk pipes (225 to 600 mm with an average size of 350 mm), which go to Outfall pipes (600 mm or over). The sewerage pipes are made of Asbestos cement and concrete, Clay, or PVC. Clay is the least used because it has lots of joints. PVC is now getting expensive because there is a foreign currency component.

Most are dealt with from the sewerage workshops in Coventry Road. A particularly bad spot is the Central Business District, where some pipes are 10 to 15 m beneath the surface. Anything over 6 m deep requires the city to hire equipment since the equipment in stock (pumps and excavators) cannot go that deep.

Most of the sewerage runs on gravity, but there are three major pump stations – Chisipite, the North East Commonage (Gunhill) and Avonlea. There is a private pump (Zim Phos) at Lorelei, and a city pump at Budiriro. When this last pump (actually three pumps in one building pumping 10 megalitres a day) breaks down, Budiriro sewerage goes down the Marimba to Chivero.

On treatment, Crowborough and Firle use the conventional, or mechanical system. It is filtered through stone medium, then through other tanks, and the effluent is pumped out on to the farms, where the city runs 12 000 head of cattle. The treated water then flows down to Chivero.

At Hatcliffe, the Biological Nutrient Removal (BNR) system is used. This process has an efficiency of 99 percent, and apparently in Windhoek, it is pumped from these tanks into the water treatment plants. The effluent is allowed to settle, where anaerobic bacteria remove the nitrates, and it is then aerated, where aerobic bacteria remove the phosphates. It should then be processed to kill the microorganisms, but this is not currently being done.

At Donnybrook and Marlborough the effluent is stabilised in ponds and then sifted out. Epworth does not belong to the City of Harare. It is still being administered by the Central government, and their sewerage is all going into septic tanks.

There are plans for a new sewerage treatment work at Lyndhurst Farm (South East of Jaggers), which will be a BNR system, and plans to move more waste through the Marlborough system to another new work at Selby, about 15km North West.

The money for all this is unknown. I understand they asked for $ 6 bn for the year (for everything sewerage wise) and received $4 bn in the budget (of $ 32 bn), but I must say I have not fully understood how the budget, and votes etc. works.

So my conclusion is that we need to improve/build more treatment capacity, while maintaining the pipes and pumps in place already. Is there any way to reduce sewerage? Industry (especially Zim Phos, it seems) can be made to treat their waste, or produce less of it, at a large cost to them (and therefore to us down the line). For individual/household waste – I am sure there is more that I do not know.

The treatment of all our sewerage will have cost benefits. If we stop spilling into Chivero, we can use less chemicals (specifically Ecol 2000) to treat the water before it is taken out. This will reduce costs, and foreign currency costs, which can be used for other things. It all has a snowball effect, but will take time (perhaps years) to have a noticeable effect, and will cost money.

For more information, contact Cllr Laban by email at: mlaban@mango.zw

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