BULK WASTEWATER INFRASTRUCTURE AND STATISTICS
1.
INTRODUCTION
The responsibility of the Wastewater Department is to provide the bulk wastewater conveyance
and treatment services. The major portion of the wastewater flow of approximately 567 Mℓ/day
generated within the CMA is conveyed through pumping installations and treated at 20
wastewater treatment works. Only 32,5 Mℓ/day is disposed of via the three marine outfall
pipelines.
The CMC’s bulk wastewater infrastructure consists of:
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2.
20 Wastewater Treatment Works
3 Marine Outfalls
27 Major pump stations
15 Major interceptor sewers
Approximately 120 km of bulk gravity sewers
WASTEWATER TREATMENT WORKS
Figure 1 shows the location of the Wastewater Treatment Works in the CMA.
A list of all the bulk wastewater treatment works within CMA is tabulated below:
NAME OF WASTEWATER TREATMENT
CAPACITY
NORTHERN AREA
Athlone Wastewater Treatment Works
120 Mℓ/day
Potsdam Wastewater Treatment Works
32Mℓ/day
Dover Wastewater Treatment Works
0,1 Mℓ/day
Melkbosstrand Wastewater Treatment Works
2,5 Mℓ/day
Wesfleur Wastewater Treatment Works
14,0 Mℓ/day
Llandudno Wastewater Treatment Works
0,5 Mℓ/day
Oudekraal Wastewater Treatment Works
0,03 Mℓ/day
SOUTHERN AREA
Cape Flats Wastewater Treatment Works
200 Mℓ/day
Mitchells Plain Wastewater Treatment Works
37,5 Mℓday
Wildevoëlvlei Wastewater Treatment Works
14 Mℓ/day
Simon’s Town Wastewater Treatment Works
5,0 Mℓ/day
Miller’s Point Wastewater Treatment Works
0,03 Mℓ/day
Macassar Wastewater Treatment Plant
34 Mℓ/day
Zandvliet Wastewater Treatment Plant
55 Mℓ/day
EASTERN AREA
Borcherd’s Quarry Wastewater Treatment Works
30 Mℓ/day
Bellville Wastewater Treatment Plant
46 Mℓ/day
Kraaifontein Wastewater Treatment Plant
7,0 Mℓ/day
Parow Wastewater Treatment Plant
1,2 Mℓ/day
Scottsdene Wastewater Treatment Plant
4,5 Mℓ/day
Gordon’s Bay Wastewater Treatment Plant
3,5 Mℓ/day
All technical and other relevant information concerning operation and processes of the
Wastewater Treatment Plants is contained in Annexure “A”.
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FIGURE 1
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FIGURE 2
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3.
WASTEWATER PUMP STATIONS
The Wastewater Department has 27 major pump stations. The pump station locations are
shown in Figure 2.
4.
BULK WASTEWATER STRATEGIC INVESTIGATION
The Strategic Bulk Wastewater Study assessed performance of existing wastewater equipment,
processes and management systems and identified where improvements were necessary for
more effective performance. In addition the development predicted to take place in the CMA
over the next 20 years, identified the need for facilities to be extended or new ones put in place.
The comprehensive (37 vol.) Strategic Report on Bulk Wastewater requirements over the next
20 years forms the basis of guidance for effective planning of conveyance and treatment of
wastewater in the CMA.
The basis of the study included the following main issues:
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catchment analysis
performance of existing facilities
expected growth in the CMC over the next 20 years
strategic planning and prioritisation
environmental impacts
effluent re-use
sludge management
rationalisation of wastewater facilities
odour control
tariff calculation and funding requirements
It is the intention that the Study be reviewed every five or six years and updated in line with
development and another issue which have an influence on bulk wastewater service provision in
the CMA.
Cape Wastewater Consultants were appointed in September 2001 to undertake an investigation
into various new factors which could influence the previous recommendations contained in the
Study.
The following issues are going to be studied in greater detail:
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Water Demand Management
In the Strategic Study it was felt that the reduction in flow due to water demand management
will be off-set by the increase in run-off due to improved living standards. Since this study
the “Integrated Water Resource Planning Study” for the City of Cape Town has been
completed. This study made an assessment of the possible savings in water demand that
could be achieved through various water demand management options. This report gives
an indication of the expected saving in the different user sectors. This information can be
used to make an estimate of the potential impact of these measures, if implemented, on
wastewater flow while organic loading will remain unaffected. An assessment of the impact
of the reduced flow on the design requirements for the treatment works will be made.
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Aids
Aids will have an impact on future wastewater flow to the extent in which it limits population
growth.
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The most recent known studies on the impact on Aids in the Western Cape are:
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The National Demographic Study commissioned by the DWAF and
“A review of the long-term urban demand for water in the Cape Town-Saldanha
Supply Area” compiled by the Institute for Futures Research at the University of
Stellenbosch. (January 2000)
Metropolitan Population Projection : Figures by Spatial Distribution (a report
commissioned by CCT - 26 July 2001).
These studies will be used together with the mid-year estimates (2001) of Statistics South
Africa to make an estimate of the impact that Aids can have on future wastewater flow.
Following the above the future wastewater flow and load scenarios will be revised to give
high, medium and low future flow forecasts. These will be used in the re-assessment of
areas mentioned in Section 3 below.
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Effluent Standards and Design Approach
The DWAF require that all wastewater treatment works meet the “2010-standard”. A
calculation will be made of the effect of this higher effluent standard on the capital and
operating cost of wastewater treatment works versus that of a lower standard (eg the
General Standard).
Storm water infiltration into the sewer reticulation network is a real problem that results in
unnecessary high peak factors. The impact of these high peak flows, i.e. designing for it to
achieve a theoretical 100% compliance to the effluent standard, versus a lower compliance
target will be investigated. This “lower target” will include the possibility of alternative
approaches such as diverting additional flow away from the treatment works during peak wet
weather conditions. The financial impact of a lower compliance level will be calculated.
Other issues to be considered are the poor upstream quality emanating from informal
settlements and high nutrient content, of e.g. Table Bay water, due to the upwelling
phenomenon. Where appropriate reference will be made to other international policies in
this regard.
The allowable lower compliance level will have to be agreed with the DWAF and the
Government Departments consulted by them when discharge permits are issued. In the
Strategic Study work has been done by Southern Waters and the Institute for Marine Studies
on the status of the freshwater and coastal environment into which treated effluent is
discharged, as well as its capacity to receive more treated effluent in future. Any work on
lower compliance without the input of these parties is not recommended. Provision is made
for a workshop at which the above proposals will be presented before the compilation of a
final position paper on the above issues.
The above work will be compiled into a document reflecting the impacts of the higher
standards, the input of governmental and environmental agencies and the outcome of the
above process. It is envisaged that this will serve as a guiding document for design
standards to be applied to all the treatment works and as a basis for further discussions with
the DWAF on the relaxation of effluent standards if required. It must be realized that this is a
national issue and therefore no decision could be expected from DWAF in the short term.
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Rationalisation
The Strategic Study covered the rationalisation of treatment works in a fair amount of detail.
This work was, amongst other factors, based on an assumed formula for calculating the
capital cost of wastewater treatment works. Since the completion of the Strategic Study it
became clear that this formula needs to be adjusted mainly due to the devaluation of the
Rand and the implementation of the “2010-standard”. Depending on the outcome of the
workshop on, and investigation into, effluent standards referred to above, this costing
formula will be adjusted. A reassessment of this work could only be justified in view of these
changes or a revision of forecast future flows. It is proposed that such a reassessment
should be done for two areas only, viz the areas incorporating the Kraaifontein and Potsdam
treatment works respectively. These will include the proposed regional treatment works at
Fisantekraal and the one to the north of Potsdam WWTW. These areas are chosen firstly
because a final decision on the future of the works in the area is required in the near future,
and since an alternative result to that obtained in the Strategic Study could still make a
difference to the final decision. Only if the results of this investigation with regard to
rationalisation prove to be largely different from that in the study, will it be necessary to
consider re-evaluating other scenarios. The cost estimate only allows for a re-assessment
of the areas given above.
The output from the above will be an economic comparison of the different future
development options in the respective areas. The development options to be investigated
will be the most favourable options chosen from those covered in the Strategic Study and
will include new regional works on greenfields sites. This will take cognizance of the
opportunity cost of land.
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Evaluation of Capital Requirements
In the Strategic Study a combination of the capital requirements for the recommended future
development options for the different treatment works was used to compile an aggregate
capital requirement for the whole of the area under jurisdiction of the CCT. Using the results
of the revised costing formula referred to above this requirement will be adjusted to reflect
the present costing structure for treatment works. It was shown that the ideal capital
requirement to address the needs at the different treatment works will, at least in the initial
years, exceed the financial ability of the CCT to provide for capital works.
One option to balance the capital requirement and the available capital budget would be
simply to distribute the proposed refurbishments and extensions over a longer time period.
It will therefore be necessary that the proposed refurbishments and extensions be listed and
prioritised in order to identify the work which should be executed first. The proposed
refurbishments and extensions identified in the Strategic Study and updated as per the
above investigation will be prioritised in consultation with CCT-staff.
The outcome of this process might require that extensions cannot be implemented as
envisaged and the works be extended over a longer time period. The proposed action may
imply that sub-standard effluent be released into watercourses until the proposed ultimate
extensions are implemented. This approach will again require approval from permitting
authorities such as DWAF and DECAS. The viewpoint of the authorities as obtained at the
proposed workshop referred to above will give guidance in this regard. Further specialist
studies might be required to assess the impact of the lower standard effluents. No allowance
has been made for such studies if required.
Another option for alleviating the demand on the capital budget would be to consider
alternative funding and implementation options. These might also be linked to alternative
management options (e.g. BOT). Such options will be identified together with possible
schemes to which it could be applied.
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The impact of both the redistributed capital requirements and alternative funding options on
unit rates will also be calculated. The actual impact of the latter will be influenced by specific
agreements on repayment and operational efficiency. Agreed assumptions on levels of
repayment and operational efficiency will be used to calculate these impacts. It is
specifically important that the impact of alternative funding on unit rates be determined in the
medium to long term to avoid unreasonably high unit rates due to repayment of higher than
normal capital investment.
The outcome of this will be revised capital requirements for the two alternative options listed
above with associated impact on unit rates.
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Estimated Planning Horizon
The Strategic Study considered a planning horizon of 20 years. Questions have been raised
as to the sufficiency of this horizon in considering rationalisation. This specifically relates to
the economic life of civil structures. For this part of the study it is proposed to do some
research on international strategies with regard to works in urban areas which have come to
the end of their economic life. This will be used to create a long-term vision for Cape Town
by incorporating these ideas with knowledge gained during the previous study and at local
treatment works.
The impact of extending the planning horizon to 50 years on the two areas identified to be
investigated for rationalisation will be analysed and reported on. In view of these results a
broader vision for the rest of the CMA and treatment works whose continued existence could
be impacted on by the longer horizon will be given.
The outcome of this work will be specific recommendations regarding the long-term future of
treatment works in the Kraaifontein/Scottsdene/Fisantekraal area and the
Potsdam/Vissershok/Melkbos area. Based on this a broader vision of the future of other
treatment works such as Gordons Bay, Mitchells Plain, Borcherds Quarry and Athlone will
be given.
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Infiltration
With reference to discussions in this regard we confirm our notion that this issue will best be
addressed through identifying a target catchment in which infiltration is a critical problem and
to systematically work through this area to identify and address problem areas. It is also
believed that an effective public awareness programme is a key requirement for alleviating
this problem. A dedicated team should preferably be set up to deal with this specific
problem.
A proposal will be made on how this problem should be addressed and on the areas to be
targeted.
The extent to which infiltration has impacted on the design of treatment works and its impact
on future planning will be addressed.
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