Post on 17-May-2018
ADDRESSING FINANCIAL AND TECHNICAL SUSTAINABILITY CONSIDERATIONS
DURING THE SELECTION OF SMALL WATER TREATMENT SYSTEMS
G.S. Mackintosh
Cape Water Programme, CSIR, P O Box 320, Stellenbosch, South Africa,
(E-mail: gmackint@csir.co.za)
1. BACKGROUND
When considering water treatment options and alternatives for a particular project it is crucial to consider all aspects
that input into the ultimate long term viability and sustainability of the project. The South African Water Services
Act of 1997, and the associated draft Regulations, oblige water service authorities to progressively ensure
“efficient, affordable, economical and sustainable access to water services”. This is easier said than done, and in
essence requires that the responsible project engineer consider technology choice with regards to technical
sustainability, financial sustainability, environmental sustainability and socio-political sustainability. If any one of
these “legs of sustainability” is defective, the overall project viability will become suspect.
Much has been written and discussed about the need for environmental and socio-political sensitivity for rural water
treatment and water supply projects in South Africa. However, what has received less attention is the technology
choice and the financial implications thereof. These decisions are usually left to technical experts, such as
engineers and hydrogeologists, whom it is presumed are suitably skilled. However, inappropriate decisions can
result in the project being financially or technically unsustainable thereby leading to the ultimate collapse of the
water treatment process. At this stage, it is often the community that are erroneously blamed for their inability to
maintain the system. This paper attempts to show, by virtue of two case studies, the importance of addressing
financial and technical sustainability considerations when deciding on small water treatment systems.
2. SUSTAINABILITY
When considering water treatment in small, rural communities sustainability needs to be considered from the
financial, technological, environmental and socio-political perspectives. It is common place in South Africa that
well designed, effective water treatment plants are non-functional as a result of either financial non-sustainability or
socio-political non-sustainability. However, it is also found that where financial and socio-political sustainability
occur, a poor technology has been chosen and with time the water treatment system has become non-sustainable.
2.1 Technological Sustainability
Traditionally in South Africa, small water treatment systems have made use of conventional processes such as
chemical pre-treatment, coagulation, settling and dual media filtration in a scaled-down manner. These unit
processes, although effective on large-scale applications, inevitably prove troublesome for small-user systems – the
result being production of sub-standard water, and non-sustainability with the plant eventually falling into disuse.
This issue of non-sustainability of water supply schemes resulting from imposition of non-appropriate technologies
on communities requires considered attention in South Africa. It is generally recognized that an effort should be
made to use so-called “appropriate technologies”, which are usually low cost, robust, low operator attention
systems (such as slow sand filters). Paradoxically, at times the use of semi-automated “high-tech” plants (for
example, incorporating membrane technology) will also be appropriate for rural water treatment. The critical
deciders here should include:
o The ability of a local community member to operate the water treatment system, with minimal outside
support.
o The ongoing and ready availability of necessary consumables (typically, chemicals).
o The availability, response time and affordability of technical backup where required (especially wrt higher
tech solutions, eg membranes).
2.2 Financial Sustainability
A significant influencing factor as to sustainability is community affordability in terms of the ongoing running costs
of water treatment. It is particularly important to consider this aspect in instances where the initial capital layout of
a technologically attractive system is considered to be too high in comparison to competing, yet technologically less
sustainable technologies. Examples of such instances include:
o Slow sand filters vs pressure filters;
o Electro-chlorinators vs gas chlorination;
o Membrane based processes vs conventional clarification processes.
In such instances, the higher capital outlay projects have potentially lower operating costs; hence this is
advantageous to the community that must guarantee payment thereof into the future. However, the funding
organisation that incurs the upfront capital costs is often discouraged by the significantly higher capital costs. It is
hence important that a clear and unambiguous financial comparison be carried out to enable informed decision-
making. In this paper the Net Present Value (NPV) based approach considers operating costs/cash flow projection
of a project over a ten-year period. This simple NPV assessment captures both the capital and operating costs for
alternative technologies and relates these as one financial sum in terms of today’s monetary value. This approach
clearly indicates which alternative is financially more viable, or the magnitude of any variation.
3. CASE STUDY ONE: MEMBRANE BASED WATER TREATMENT PLANT
3.1 Background
In this case study, the treatment of poor quality and problematic surface water at two neighbouring rural
communities in the Western-Cape, South Africa is contrasted. Both communities number about 2 000 people and
make use of the same raw water source; however, in one instance treatment is being considered via a membrane
based process and in the other instance treatment is via a conventional processes. A critical comparison will be
made between mentoring and training of community-based plant operators, operability and maintenance
requirements, plant performance, sustainability, community acceptance and affordability of both a conventional and
a membrane-based water treatment plant.
3.1 Technical Assessment of Membrane Based Water Treatment
The pilot scale membrane-based plant considered is a movable package water treatment plant designed to condition
surface water so as to comply with international water quality standards. The unit incorporates flocculation and pre-
filtration, membrane filtration, adsorption and chemical disinfection and treats approximately 2000 L/hr depending
on the raw water characteristics. Chemicals used to treat the raw water included those required for aiding
flocculation (polyaluminium chloride - PAC and polyelectrolyte), pH adjustment (soda ash) and disinfection
(calcium hypochlorite - HTH). In addition, calcium hypochlorite and citric acid were used as cleaning chemicals for
the membranes. The membrane-based water treatment plant is shown in Figure 1.
Figure 1: Membrane based water treatment plant
Figure 1: Membrane based pilot plant
The membrane-based plant was installed at the town of Suurbraak, Western-Cape; and a community member with
no previous water treatment training or experience was trained over 2 weeks in all aspects of plant operation.
Sample analysis to evaluate plant performance was based on SABS 241-2001: South African Standard for Drinking
Water (SABS, 2001), which is similar to international drinking-water quality standards.
Typical results obtained from the membrane based water treatment plant are shown in Table 1. The results obtained
during the initial trial period indicated that the plant performed well, consistently providing a high quality drinking
water (De Souza and Mackintosh, 2000). During the subsequent eight-month assessment period, the plant failed on
two occasions (Mackintosh and De Souza, 2001). On the first occasion the problem was found to be a faulty relay,
which was rapidly rectified with the assistance of a local electrician. In the second instance the plant malfunctioned
as a result of the failure of an air valve, which was subsequently replaced under specialist supervision. Hence, the
only problems that occurred during the eight-month period were trivial and easily rectified. However, in both cases
plant downtime was approximately 1 week, which highlighted the requirement for adequate back-up
service/support.
Table 1: Membrane based water treatment plant: typical physico-chemical and microbiological results
Determinant Raw Final
Calcium as Ca (mg/L) 0.5 1.6
Alkalinity as CaCO3 (mg/L) 0.0 4.0
Iron as Fe (mg/L) 0.5 0.05
Aluminium as Al (mg/L) 0.4 0.06
Electrical Conductivity (mS/m @ 25ºC) 4.7 4.7
PH 4.6 7.2
Total Dissolved Solids (mg/L) 30 30
Turbidity (NTU) 0.44 0.28
Colour (Unfiltered) (mg Pt/L) 250 < 10
Colour (Filtered) (mg Pt/L) 250 < 10
Determinant Raw Final
Heterotrophic Plate Count (per 1
mL @ 35ºC)
291
+10000
277
+10000
291
+100001 3 5
Total Coliform (per 100 mL) 1660 1613 1810 0 0 0
Faecal Coliform (per 100 mL) 193 177 162 0 0 0
3.3 Technical Assessment of Conventional Water Treatment Plant Performance
SABS Class 0 (Ideal) Comparable to international water quality standards
SABS Class I (Acceptable) Acceptable for lifetime consumption
SABS Class II (Max. allowable) Acceptable for short term consumption
Failure SABS Class II Unfit for human consumption
No SABS guideline
The performance of the membrane-based plant was compared to a nearby conventional plant, which treats
essentially the same source water. This existing water treatment system treats approximately 10 000 L/hr and
employs conventional water treatment principles of coagulation, flocculation, sedimentation, sand filtration and
disinfection (see Figure 2).
Typical results obtained from the conventional water treatment plant are shown in the following Table 2. The
results obtained during the assessment period showed that the conventional plant is highly vulnerable to passing on
contaminated treated water to the end-user when not operating optimally. Frequent episodes of treated water quality
failing SABS 241-2001 Maximum Allowable standards (i.e. not fit for human consumption) occurred. Both the
plant operator and the community confirmed that the plant did not continuously operate at an optimal level, and
often passed on sub-standard water.
Figure 2: Conventional water treatment plant
Table 2: Conventional water treatment plant: typical physico-chemical and microbiological results
Determinant Raw Final
Calcium as Ca (mg/L) 1.6 1.5
Alkalinity as CaCO3 (mg/L) 5.3 0.5
Iron as Fe (mg/L) 1.3 0.11
Aluminium as Al (mg/L) 0.62 0.57
Electrical Conductivity (mS/m @ 25ºC) 8.0 9.8
PH 6.1 4.7
Total Dissolved Solids (mg/L) 51 63
Turbidity (NTU) 2.5 1.5
Colour (Unfiltered) (mg Pt/L) 300 20
Colour (Filtered) (mg Pt/L) 250 10
Determinant Raw Final
Heterotrophic Plate Count (per 1 mL @ 35ºC) 3100 6550
Total Coliform (per 100 mL) 1575 90
Faecal Coliform (per 100 mL) 730 28
3.3 Comparative Financial Assessment – Membrane-Based Vs. Conventional Water Treatment Plant
The cost comparison was based on a water treatment plant capacity of 10 000 L/hr operating for 20 hours/day,
using April 2001 prices. The cost comparison shown in Table 3 shows that the total installed capital cost of the
membrane based plant is significantly more expensive (~ 1.9 times) than that of the conventional water treatment
plant. Furthermore, the cost comparison showed that the membrane based plant shows significant operating cost
savings over the conventional plant. This can mostly be attributed to lower labour and chemical requirements.
Table 3: Cost comparison input variables
Membrane ConventionalPLANT CAPACITY 10 000 L/hr 10 000 L/hr
TIC COST R600 000 R320 000
TOTAL OPERATING COSTS R1.54/kL R1.12/kL
Chemicals Chemical Dose Cost (R/kL) Chemical Dose Cost (R/kL)
PAC @ R8.96/kg 35 mg/L 0.315 60 mg/L 0.54
Polyelectrolyte @ R8.96/kg 0.1 mg/L 0.001-
-
HTH @ R14.00/kg 0.5 mg/L 0.007 2 mg/L 0.028
Soda Ash @ R2.40/kg 50 mg/L 0.120 50 mg/L 0.12
Citric acid (membrane cleaning) @ R30.00/kg 0.1 mg/L 0.003-
-
HTH (membrane cleaning) @ R14.00/kg 0.1 mg/L 0.001-
-
Chlorine gas @ R14.00/kg - - 2 mg/L 0.028
Chemical Wastage @ 5% - 0.022 - 0.0358
SABS Class 0 (Ideal) Comparable to international water quality standards
SABS Class I (Acceptable) Acceptable for lifetime consumption
SABS Class II (Max. allowable) Acceptable for short term consumption
Failure SABS Class II Unfit for human consumption
No SABS guideline
Electricity @ R0.2/kWh Power consumption Cost (R/kL)Power
consumptionCost (R/kL)
Plant power consumption 8.5 kW 0.150 10 kW 0.20
Labour @ R18.75/hr Time Cost (R/kL) Time Cost (R/kL)
Plant operation, maintenance, etc 1 hr a day 0.094 4 hrs a day 0.376
Maintenance @ 5% of capital cost Cost (R/kL) 0.411 Cost (R/kL) 0.216
Meaningful comparison of the capital and running cost figures given in Table 3 is difficult. A more useful manner
of comparing the two processes is to use a Net Present Value (NPV) based approach. The NPV approach relates
the cash flow projection of a project over a specific time period (in this case 10 years). The NPV assessment
captures both the capital and operating costs for the two alternative technologies and relates these as one financial
sum in terms of today’s money. An important aspect is the discount rate used. For this case study the total discount
rate included: inflation [@ 7% in South Africa], required real return [@ 0%, as no return on investment required by
government funders] and risk [@ 10% for the membrane based process, as membrane based processes are less
familiar for rural use in South Africa].
The NPV based cost comparison shown in Table 4 shows that the use of a membrane based plant (with higher
capital costs and higher risk but lower running costs), yields a nominally negative NPV of R33 500 (and an Internal
Rate of Return of 14%). This result shows that there is very little difference in financial performance between the
two technologies when compared over ten years. It is important to note that this observation is contrary to
conventional thinking in South Africa, where the initial significantly higher capital costs of membrane-based plants
are considered to make the use thereof a non-option.
Table 4: Project financial assessment summary – membrane vs. conventional (10 kL/hr)
Conventional Membrane
Capital cost (R) 320 000 600 000
Total Operating cost (R/kL) 1.54 1.12
Discount rate
Average inflation
Required real return
Estimated risk
7%
0%
0%
7%
0%
10%
Internal Rate of Return (IRR) 14%
Net Present Value (NPV) - R33 500
4. CASE STUDY TWO: LIMESTONE MEDIATED STABILISATION
4.1 Background
The majority of water sources in South Africa require stabilisation, to mitigate against corrosive and
aggressive attack of distribution systems, prior to discharge of treated water. Conventional stabilisation (via
the addition of lime and carbon dioxide, or sodium alkali’s and carbon dioxide) is well documented and
understood, and practised worldwide. However, control of the process is expensive and requires well-trained
staff and reliable equipment. Hence, in many cases only lime is dosed, such that pH is adjusted from low
levels to more desirable levels of, say, 8.0, thereby providing a partially stabilised water. Even so, for smaller
water treatment system stabilisation using lime remains notoriously problematic and difficult to control, and
the reality is that most lime based stabilisation processes are ineffective. In addition, the increasing limited
availability of high quality (white) lime locally is resulting in increased operating chemical costs at water
treatment facilities. An alternative approach is partial stabilisation using limestone. In this case study,
reference is made to Sedibeng Water’s proposed 110 ML/day Fika Patso Water Treatment Plant, Qwa-Qwa
(Mackintosh et al, 2000) .
Figure 3: Lime dosing system at Sedibeng Water’s 5.5 M:/day Makwane Water Treatment Plant, QwaQwa
•1 mFigure 4: Limestone contactors, Stellenbosch4.2 Comparative Technical Assessment of Lime and Limestone Mediated Stabilisation Partial stabilisation has been shown to be effective in preventing cement aggression, copper corrosion and greatly
reducing corrosion of any ferrous material in the water system (De Souza et al, 2002). On-site pilot plant tests at
Fika Patso were carried out. Chlorinated Fika Patso Dam water is soft, and aggressive and corrosive and would
benefit from stabilisation. The trials showed that the limestone stabilisation process was shown to be capable of
bringing about effective partial stabilisation within a retention time of about 10 minutes. CCDP was effectively
reduced to about 2 mg/L as CaCO3, and pH increased to desirable levels of about 8.2. Importantly, the limestone
system has the ability to handle fluctuations in water quality, as often recorded at the Fika Patso Dam.
Limestone mediated stabilization has been shown to have the following technical sustainability advantages over
lime:
o Very little operator input. (Approximately monthly flushing and chemical recharge, versus the round
the clock attention that lime dosing requires).
o Very little operator skill required. (pH is controlled naturally at desirable levels as the water
approaches chemical equilibrium, versus the carbonate chemistry skill required to maintain steady
lime based stabilisation).
o Very robust equipment, which requires little maintenance, versus lime dosing equipment, which is
generally problematic on small water treatment plants.
o No risk of alkali overdosing.
4.3 Comparative Financial Assessment of Lime and Limestone Mediated Stabilisation
The cost comparison was based on a water treatment plant capacity of 110 ML/day, using November 2000 prices.
Costs considered included Capital costs, Chemical costs, Routine labour costs, Preventative and line maintenance
equipment costs, and Preventative and line maintenance labour costs. The total installed cost of the limestone
contactor was estimated to be the same as that of a conventional lime dosing facility (R 7 700 000). However, as
seen in Figure 5, the running costs associated with limestone stabilisation are significantly lower.
Rozendal, 6 ML/day
• Height 5.1 m
• Diameter 4.5 m
Jonkershoek, 2.5 ML/day
• Height 4.1 m
• Diameter 3.9 m
Figure 5: Operational Cost Comparison: total stabilisation costs
5. CONCLUSION
This paper set out to illustrate the importance of addressing financial and technical sustainability considerations
during the selection of small water treatment systems. The paper also set out to illustrate that under some
circumstances a “low tech” solution will be the better solution, from both a financial and technical perspective; and
yet however, almost paradoxically, under other circumstances a “high tech” solution can be both technically and
financially preferable.
From analysis of both case studies, the following points should be noted:
Wrt financial sustainability:
o Considering that South African rural communities are required to guarantee the payment of the operational
costs of water treatment whilst the capital costs are usually covered by a funding organization, it is crucial
to consider the perspective of community financial sustainability ie ongoing operational costs.
o The NPV based assessment ensures that a balanced assessment of project finance is acquired; importantly,
capital costs are seen in respect of running costs. In the case of the higher capital cost of the membrane
based process, it was shown that there is very little difference in financial performance between the two
technologies when compared over ten years.
Wrt technical sustainability:
o Technological sustainability must be seen in the light of the ability of local community based plant
operators to provide a consistently desirable level of water quality. Where regular malfunction of the
conventional plant occurs, with time the technology will become unsustainable from a socio-political
perspective.
In conclusion, technical experts (such as engineers and hydrogeologists) must carefully consider technology choice
with regards to technical sustainability, financial sustainability, environmental sustainability and socio-political
sustainability. If any one of these “legs of sustainability” is defective, the overall project viability will become
suspect.
6. ACKNOWLEDGEMENTS
The author would like to acknowledge the generosity of Suurbraak Town Council and Sedibeng Water for allowing
publication of the operational findings.
7. REFERENCES
De Souza, P.F. and Mackintosh, G.S. (2000) A Critical Assessment of a Membrane-based Package Plant for Small-
User Systems Water Treatment. Conference proceedings, WISA 2000 Biennial Conference, Sun City, South Africa,
28 May – 1 June 2000.
De Souza, P.F; Manxodid, T and Mackintosh, G.S. (2002) Addressing the Efficiency of Aggression and Corrosion
Mitigation via Limestone Contactor Mediated Partial Stabilisation; Conference proceedings, WISA 2002 Biennial
Conference, Durban, South Africa, 20 May – 23 May 2002.
Government Gazette, South Africa (1997) Water Services Act (Act 108 of 1997).
Mackintosh, G.S. and De Souza, P.F. (2001) A Critical Assessment of the Suitability of a Membrane-based Package
Water Treatment Plant for Application at Suurbraak. CSIR Report no. ENV-S-C 2001-039.
Mackintosh, G; Du Plessis, G; and De Souza, P.F. (2000) On-Site Assessment Of The Suitability Of Limestone
Mediated Stabilisation For Application At Fika Patso Dam.. CSIR Report no. ENV-S-C 2000-134.
South African Bureau of Standards SABS 241:2001: South African Standard for Drinking Water (2001) Pretoria,
South Africa.