(Zimbabwe) sewage system rehabilitation - AGW-Net
(Zimbabwe) sewage system rehabilitation - AGW-Net
The Municipality of
St. Mary’s Sewage
Site: The Municipality of Chitungwiza, St. Mary’s Sewage Pipelines
Start Date: October 2010
Duration: Initial treatment process- 8 weeks, maintenance- ongoing.
Coordinators: City Engineers for the Municipality of Chitungwiza
Project Consultants: Dave Kempen and Tim Fennell
Timing of Treatments: During normal working hours.
Population using this Sewage Pipeline: 300,000 to 500,000 people
Volume of wastewater in Sewage Pipelines: 9.6 Mega liters/day.
Length of Sewage Pipeline: 30,000m of pipes. 15,000m were treated.
Average Daily Temperatures: 25 C
The Municipality of Chitungwiza is located south of Harare. It is the
third largest municipality and the fastest growing population centre
in Zimbabwe. Today’s population count, including a migrant
component, are estimated at approximately 2 million inhabitants.
This high density commuter town was formed in 1978 from the
amalgamation of three
St. Mary’s. It received
The Treatment Process
The AZAcomp compound was applied on a daily basis to
predetermined manholes on the Sewage Pipeline network.
These were sites experiencing higher than average blockage
The treatment process was initiated shortly before the onset of
the rainy season which has previously proven to be a very
chaotic time for the municipal sewer team.
The sewer lines all converge to flow into Pump Station 1. The
lines vary from 100mm (4’’) to 600mm (24’’) in diameter.
Blockages caused by tree roots etc, were removed manually by
digging them out.
ST MARY’S AZACOMP APPLICATION
Attn: Town Clerk, Town Engineer
The following is the proposed action programme to clear a portion of St
Mary’s blocked sewer pipes using AZAcomp for 8 weeks, every 1000m.
150 mm Pipe.
18 kg– 126 kg total requirement
1 bag a day for first 14 days.
1 bag per week for 6 weeks.
200 mm Pipe.
40 kg – 72 kg total requirement
2 bags day for first 14 days.
2 bags weekly for 6 weeks
300 mm Pipe.
70 kg – 156 kg total requirement
3 bags for first 14 days.
2 to 3 bags per week for 6 weeks
Note: The bags are water-soluble and & each bag contains 1 kg of AZAcomp.
Avoid any contact of bag with water/sweat until application.
These application rates are intended a guide only.
After regular AZAcomp treatment for four weeks, all treated
pipelines and manholes appeared clear and operating as
designed. The foul odour around the manholes was vastly
reduced, and surrounding areas experienced a reduction in the
There were no blockages reported on any of the AZAcomp
treated pipelines during heavy rains.
There was a large increase in the volume of sand deposited at
Pump Station 1 which is the final outlet.
From Pump Station 1, where no transfer pumps are operational,
the effluent has been diverted to the Manyami River, which
flows into Lake Chivero.
The effluent water released has changed from a black brackish
water with foul odour, to a odour free greenish water which
has a degree of visibility.
The Municipality of Chitungwiza initiated the St. Mary’s Sewage
Pipeline Rehabilitation project to establish AZAcomp’s efficiency in
reducing the blockages, and reduced flow capacity in underground
sewage pipelines. The majority of blockages were due to an
accumulation of sand mixed with biodegradable organic effluent
consisting primarily of human excrement, some fats and oils, and
other organic waste matter.
The restricted flow in the pipelines resulted in manholes overflowing,
and raw sewage flowing freely down residential streets. This problem
was getting worse each year. Entire sections have been non-functional
some for up to 5 years.
Compounding the pollution issue of raw sewage in the streets for
residents of these high density neighborhoods was an overabundance
of flies, and foul odour. This problem was exacerbated during the
rainy season in previous years.
The objective of this project was to use AZAcomp to liquefy the
sludge component of the compacted sand/effluent mass, increasing
the porosity of the mixture thereby enabling the sand to be washed
away with the increased water flowing through the pipes.
The initial cost for this rehabilitation process was less than
US$ 0.10 per person.
The only alternative to this treatment process would have required
replacement of the pipelines as high-pressure cleaning of the lines
failed to work. A guide for the cost of these pipes alone came to US$
1.5 million. The whole replacement project would exceed US$ 3
million, and years to complete.
Aside from the degraded concrete, these manholes are extremely clean.
Note the absence of any organic sludge on the walls. Without the
presence of organic matter, the foul odour and fly populations at all
manholes were greatly reduced.
Effluent with floating biomass
filling the manhole
Manhole no longer filled with effluent.
Shows the hole at the bottom of the
culvert and effluent flowing through the
With improved flow capacity, the manhole
is no longer filling up.
Effluent with floating
Effluent flowing into the manhole
through one pipe system into the main
The Chaminuka Manhole is a 300mm (12 ‘’) mainline. This line has been
constantly problematic, with continual blockages and overflowing. City
engineers believed this line had been incorrectly installed in a positive
gradient. They had never witnessed it flowing freely before. However, it is
now free flowing.
The Chitungwiza Medical Clinic Manhole was previously completely
blocked. It is now clean and virtually empty with the underneath pipeline
free flowing. This manhole posed grave potential health risks.
With blockages and flow restrictions no longer an issue,
the amount of effluent water reaching Pump Station 1 has
increased, and the pipeline system is operating much
The problem of sewer/manhole overflow of raw sewage was so
chronic that people had vegetable gardens planted along the
edges of the overflow where organic matter had accumulated.
Note the vegetable garden next to
the manhole and overflow.
Hmm…wonder what the E.coli and
coliform counts here are?
A newly planted vegetable garden making
use of raw sewage for ‘flood irrigation’.
The Chitungwiza suburbs of Seke and Zengeza will begin their
pipeline rehabilitation projects early in 2011, provided they are able to
secure sufficient funds to finance the project.
The below pictures are some examples of what they are, and have
With the AZAcomp treatment of the sewage pipeline system, the
foul odour and fly population problems were so drastically reduced
that the city engineers were inundated with phone calls from
residents thanking them for fixing the problems.
There were no reported cases of Cholera from the St. Mary’s area
this rainy season.
An interesting note, and one with widespread implications. Raw
sewage from the populace in the Lake Chivero watershed (approx. 5
million), both urban and rural, flows directly into Lake Chivero.
This same lake is where the-so-called “fresh” water supply is drawn
for the City of Harare.
A maintenance dosage of AZAcomp is suggested to greatly increase
the wastewater outflow quality and to keep the sewer system