THE RISING COSTS OF BOTH SEWAGE TREATMENT AND THE PRODUCTION OF POTABLE WATER ASSOCIATED WITH INCREASING LEVELS OF POLLUTION IN A PORTION OF THE CROCODILE-WEST MARICO WATER MANAGEMENT AREA (A CASE STUDY)
Roux, S.P.*, Oelofse, S.H.H.**
*CSIR (Pretoria), NRE, PO Box 395, Pollution & Waste, [email protected] (012 841 3461) **CSIR (Pretoria), NRE, Pollution & Waste
ABSTRACT
Substantial quantities of water can be made available for use if the quality of return flows is of sufficient quality or treated to the desired quality. In 2006, in the order of 50% of urban and industrial drainage were returned for re-use in urban and industrial areas such as Johannesburg and Pretoria (3). The reuse potential of return flows is however largely dependent on the quality of the return flow combined with the quality requirements of the users. The four most important water quality problems are salinity, eutrophication, microbial pollution and sediments.
The results of this study clearly indicate that pollution reduces the quality and therefore the economic value of the available water in the case study area. The most measurable impact in economic terms is the analysis of the costs incurred by municipal and private entities responsible for waste water treatment and potable water purification. Technology used to treat relative good quality water less than a decade ago must now be viewed as outdated and inadequate based on the deteriorated quality of intake water. The cost of recent technology upgrades in order to continue to produce water of potable quality clearly indicates the financial impact of pollution in the study area.
This investigation clearly indicates the importance of pollution prevention over attempts to control the inevitable effects of current pollution practices in this study area.
INTRODUCTION
The White Paper on Integrated Pollution and Waste Management for South Africa (1) identifies salinisation of fresh waters, nutrient enrichment of fresh water bodies, microbial degradation of water quality and sediment and silt migration as key water pollution issues that need to be addressed. In addition, the national water policy for South Africa (2) set as a principle that water quality management options shall include the use of economic incentives and penalties to reduce pollution. The Department of Water Affairs has already started the development of the Waste Discharge Charge System (WDCS) aimed at providing economic incentives and penalties to implement the “polluter pays principle”, as adopted by both policies mentioned above. The level at which the charges will be set, however, will have to be determined on the basis of the costs associated with prevention measures (abatement costs) as compared to the costs of treating polluted water and the associated environmental impacts (damage costs).
The purpose of this study was therefore to estimate the cost of prevention and treatment, associated with pollution of the water resources in a portion of the Crocodile-West Marico water management area.
BACKGROUND
In 2006, in the order of 50% of urban and industrial drainage were returned for re-use in urban and industrial areas such as Johannesburg and Pretoria (3). The potential for return flow reuse depends largely on the quality of the return flow combined with user requirements and the affordability of the treatment processes to meet these user requirements. Increasing urbanisation, progress towards meeting basic human requirements for water as well as industrial activity increases the pressures on existing sewage and industrial effluent collection and treatment infrastructure. Shortages in capacity at these facilities to cope with the increased demand require expensive upgrades of existing infrastructure, the construction of new wastewater treatment facilities and/or improvement of the technology available for water purification to meet user requirements. Although the upgrade or expansion of wastewater treatment infrastructure is capital intensive, the release of untreated or inadequately treated wastewater into surface water resources have a negative impact on the environment and downstream water users due to deteriorating water quality.
Eutrophication, salinisation, sedimentation and microbial contamination are all symptoms of polluted water resources which require increasingly sophisticated treatment technologies to render the available water fit for downstream use. Currently, most industries in urban areas use water of potable quality obtained from the distribution system of a water services provider (municipality or water utility) and discharge their wastewater into the municipal sewer system in accordance with the requirements of the Water Services Act, 1997, Section 7 (4). As such, wastewater treatment facilities play a major role in pollution prevention and the associated costs can be compared to the cost of supplying water of potable quality from polluted water resources. The results of this cost comparison provide insight into the cost implications of current water pollution management strategies and future pollution remediation costs.
By analysing the available data regarding ongoing pollution, the costs due to its prevention as well as costs associated with the remediation of polluted water for drinking purposes, this paper attempts to elucidate an issue that has become a national focus point regarding the country’s available surface water resources. Could point of use water treatment practises of increasingly polluted surface water (to potable standards) be cost effective as a national strategy or should the focus of future water pollution management strategies be aimed at preventing water pollution by investing in improved wastewater collection and treatment systems as suggested by national legislation through the implementation of a Waste Discharge Charge System (WDCS).
STUDY AREA SELECTION
Since the focus of the study is on urban and industrial water use, a portion of the Upper Crocodile-West Marico water management area (sub-catchment A21) was chosen. The study area selected comprises the entire southern region of the A21 catchment area but excludes the area north of the town of Brits in the Madibeng local municipality. The area includes parts of Johannesburg, Pretoria, Krugersdorp and Kempton Park. Wastewater from this area includes contributions from mining activities and light industries as well as urban and agricultural areas. The surface water pollution in this catchment area impact on
the water quality of the Rietvlei- and Hartbeespoort dams, both of which are water resources used for the provision of potable water as well as human recreational activities and irrigation farming in the case of Hartbeespoort Dam.
Another important point in selecting this study area is the availability of analytical and flow data for the rivers of this catchment area. This information is vital in describing the pollution load carried by the rivers. Water quality and flow data for the period January 1990 to May 2008, incorporating exceptionally wet and dry periods, seasonal flow and rainfall patterns was obtained from the Resource Quality Services (RQS) website of the Department Water Affairs of the Republic of South (DWA) (5). In addition, data on changes to the existing wastewater treatment infrastructure and Rietvlei water purification works (WPW) over this period was sourced from the operators of the various treatment facilities (table 1).
Detailed description of study area The study area (Figure 1) stretches from Kempton Park in the East to Krugersdorp in the west with the Witwatersrand Mountains forming the Southern border and the Brits water purification works the northern boundary.
Figure 1: The Study Area (A portion of catchment A21) (Source: GoogleEarth)
The main rivers of the study area are schematically presented in figure 2 to provide a clearer picture of the rivers and water related infrastructure of concern.
Schematic Map of A21 catchment area Br its WPW Crocodile North Wa ste Wate r Tre atm ent Work s (WWTW) Hartbeespoort Dam Schoemansvil le WPW Water Purification Works (WPW) Magalies river Swart river
8 Unnamed river Hennops river
4 Rietvlei WPW Swartbooispruit Rietvlei Dam Crocodile south
Rietspruit
5
Vlakf ont ein Swartsprui t Jukskei
Kaalspruit 3 Crocodil e river 1 Bloubankriver
6 Klein-Jukskei 7 Braamf ontei nsprui t Blougatspruit Tweelopiespruit 2
Figure 2: A schematic representation of the rivers, WWTWs, WPWs and major water reservoirs in the selected study area.
On the eastern side of the study area the Swart River flows from Kempton Park and Esther Park where the Esther Park waste water treatment works (WWTWs) discharges into it, through residential areas and past the new Serengeti golf and housing estate. The Hartbeesfontein WWTW discharges treated wastewater into this river before it flows through agricultural land, Marais Lake and wetland until entering the Rietvlei Reserve and finally discharges into the Rietvlei dam. The stream discharging from the Rietvlei dam is known as the Sesmyl spruit and joins the Kaalspruit which flows through Centurion. This river is known as the Hennops River.
Several streams from the Modderfontein/Chloorkop area join the Kaalspruit in the Thembisa, Ebony and Ivory Park residential areas upstream of the Olifantsfontein WWTW discharge point. The Kaalspruit then continues north through agricultural land past the Irene Research Institute and is joined by the Sesmylspruit from Rietvlei Dam near the Smuts House museum just to the south of Irene. The Kaalspruit flows north through Centurion and Centurion Lake where it becomes known as the Hennops River. This river flows past the Zwartkops golf course (GC) and then west past the Zwartkop nature reserve. The Hennops is joined by the Rietspruit from the residential areas of Raslow, Wierda Park and Rooihuiskraal that flows past the Sunderland Ridge industrial park. The Sunderland Ridge WWTW discharges into the Hennops just after it receives water from the Rietspruit. From here the Hennops flows mainly in a westerly direction, is joined by the Swartbooi Spruit from Gerhardsville until it discharges into the Crocodile River just before Kalkheuwel.
The Magalies River flows from the west of the study area past Skeerpoort, where it is joined by the Skeerpoort river. The Magalies River flows past the town of Magalies, mainly through agricultural land and discharges into the Hartebeespoort dam.
The Braamfonteinspruit, upper-Jukskei and Klein Jukskei originates in the Alexandra, Sandton and Randburg areas. These rivers join up to continue north as the Jukskei River and receive treated effluent from the Great Northern Works WWTW.
The Crocodile River originates near Krugersdorp and Roodepoort and is joined by the Bloukrans River that flows past Randfontein and Krugersdorp. The Blougatspruit, Tweelopie spruit and Elandsfontein spruit joins the Bloukrans River carrying pollution generated from mining activities in the Randfontein area as well as treated effluent from domestic origin. The Percy Stewart WWTW discharges into the Blougatspruit and the Driefontein WWTW discharges into the Crocodile River. The Tweelopie Spruit flows from Robinson’s lake and is polluted with mining effluent. The entire pollution load is therefore carried by these rivers into the Crocodile River. The Crocodile River is joined by the Jukskei River (carrying pollution from informal settlements) and later also by the Hennops River before discharging into the Hartbeespoort dam.
The Crocodile River that flows northwards from the Hartbeespoort Dam represents the only large outflow of water from this dam and supports the farming activities as well as the inhabitants of the town of Brits further downstream at the Northern Border of the study area. The impacts of the water quality of this river downstream of Brits are not included in this study.
The two major surface water reservoirs are the Rietvlei dam and the Hartbeespoort dam.
The WWTWs in this area are represented in Figure 2 by the numbers allocated to them in table 1.
Table 1: WWTWs in the selected study area. The capital (current replacement) value is supplied according to the information supplied by the owner/operators of the different WWTWs. Various factors including location, specific design and size determine that the different WWTWs are valued at different capital amounts/ML.day.
Operating Average Discharge Capacity costs Planned expansion of Replacement value/ No WWTW flow River (ML/day) ZAR/ML facilities Capital value in ZAR (ML/day)
New 120 ML/day WWTW 1 500 (an on the Swartspruit. Hartbees- average price 1 Swartspruit 45 50 Phase one (50 ML/day to 315m at R7m/ML.day fontein (6) for all ERWAT be completed in 2013 @ WWTWs) R260m Esther Park See 2 Swartspruit 0.4 0.4 (6) Hartbeesfontein Olifants- See 3 Kaalspruit 105 70 735m at R7m/ML.day fontein (6) Hartbeesfontein Increase capacity to 95 ML/day by 2010 – 2013 @ R300m; New 50 Sunderland Hennops ML/day WWTW near 4 65 58 794.1 585m at R8m/ML.day Ridge (7) River Skurweberg on Hennops River to be completed in 2016 @ R260m
Phase two to be completed in 2013 with Northern phase 3, (an additional 2 700m at 5 Jukskei 450 380 Works (8) 50 ML/day) planned for R6m/ML.day 2025
Expansion of additional Driefontein 6 Crocodile 35 35 25 ML/day @ R150m 210m at R6m/ML.day (8)
Percy Blougat Increasing the capacity to 139.5m at 7 15 18 Stewart (9) Spruit total 25ML/day by 2012 at R9.3m/ML.day
a cost of R94.3m 8 Magalies n/a n/a n/a n/a
WPWs in the study area are the Rietvlei WPW, the Schoemansville and Brits WPWs. Unfortunately data from the latter two facilities has not been made available for inclusion in this study.
DATA USED FOR THIS STUDY
The available analytical data from the DWA chemical water quality monitoring programme as well as DWA flow rate monitoring points (Table 2) in the study areas was used. Additional analytical data was also supplied by the Rietvlei WPW and Tshwane Municipality.
The information in Table 1 includes the recent technology and capacity upgrade costs, operating costs and information regarding planned future upgrades and the related capital expenditure obtained from the various WWTWs owner/operators.
Table 2: Monitoring points for analytical and flow data used to determine the pollution loads for certain rivers in this study area and the Hartbeespoort Dam (5).
DWA monitoring station Location River 90166 Skurweberg Hennops Crocodile prior to discharge 90164 Kalkheuwel into Hartbeespoort Dam Magalies after confluence 90165 Skeerpoort with Skeerpoort River Swart River prior discharge 90202 Near Hartbeespoort dam into Hartbeespoort dam Downstream of Crocodile River flowing north 90214 Hartbeespoort dam wall from the dam Crocodile prior to confluence 90190 Vlakfontein with Jukskei Jukskei prior to confluence 90189 Vlakfontein with Crocodile
METHODOLOGY
The analytical data (dissolved nitrogen, phosphate and total dissolved solids) indicating trends of nutrient pollution, as well as the flow data supplied by the various sources was extracted into a database and converted to monthly averages. This allowed the calculation of the monthly pollution loads carried by the various rivers and streams since 1990. The aim of this analysis was to obtain a clear indication of pollution loads entering the water resources, especially the Rietvlei and Hartbeespoort dams. As sufficient data for the outflow quality of Rietvlei dam was not available, Hartbeespoort dam data was used to demonstrate the build-up of pollution in both these two large dams. The effect of pollution on the production of potable water is demonstrated by the Rietvlei facility only; as similar data from the Madibeng municipality was not forthcoming.
The costs associated with increasing wastewater treatment infrastructure and the cost required to improve the efficiency and available technology for the production of potable water of adequate quality was obtained from the relevant owner/operators and analysed to find the information required to achieve the stated goal of this investigation.
RESULTS AND DISCUSSION
Rivers and Flows in the study area All the rivers and streams included in this study area flow towards and ultimately contribute to the water volume and pollution load entering the Hartbeespoort dam. The results indicate monthly average flows as observed for the period 1990 to 2008 and highlight the pollution contribution by the main rivers that discharge into the Hartbeespoort dam.
The contributions (%) of the major rivers to the total inflow (& outflow) for Hartbeespoort dam as a percentage of the total inflow Magalies river
Crocodile South
100.0 90.4
) 90.0 Swartrivier 61.0 80.0
70.0 % of total inflow 60.0 leaving with 50.0 % of total inflow leaving Crocodile North with Crocodile North 40.0 0.3 Swartrivier 30.0 20.0 Crocodile South 9.3 Percentage Contribution (% 10.0 0.0 Magalies river
% contribution
Figure 3: A graphic representation of the flow contributions of major rivers to the inflow into the Hartbeespoort dam.
As illustrated in Figure 3, the Crocodile River contributes 90.4% of the total inflow of water into the Hartbeespoort dam. The contribution of the other rivers is comparatively small with the Magalies River contributing 9.3% and Swart River only 0.3%. It is further illustrated that only 61% of the water flowing into the Hartbeespoort dam continues downstream via the Crocodile River towards the town of Brits (Figure 3). The remaining 39% water loss can be attributed to direct abstraction from the dam for irrigation, other consumptive uses and evaporation.
Pollution loads The data presented in figures 4, 5 and 6 respectively indicates that nutrients and dissolved salts contributing to eutrophication and salinisation respectively are trapped in the dam resulting in a steady deterioration in dam water quality. This build-up of the phosphate and nitrogen load in the dam is one of the major causes of eutrophication. The data presented in figure 6 suggests that the fraction of salinity leaving the dam downstream is significantly higher (53.5%) than that of the nutrients phosphate (18.1%) and nitrogen (22.6%). Salinity build-up therefore occurs at a slower rate than nutrient enrichment.
Phosphate load entering Hartbeespoort dam, flowing out and remaining in the dam for the period December 1992 to January 2008
Total P into dam 2500 Total P flowing out 1934 P Remaining in Dam 2362 2000
1500
1000 428 P Remaining in Dam Tons of of Phosphate Tons 500 Total P flowing out
0 Total P into dam 1
Figure 4: Phosphate loads in the Hartbeespoort Dam.
Nitrogen load (as N) in Hartebeespoort dam for the period January 1990 to February 2008 25000 Nitrogen load (as N) in Hartebeespoort dam 24798
20000
15000 19184
10000
Nitrogen (tons) N) (as 5000 5614
0 Nitrogen load (as N) in Total N into dam Hartebeespoort dam Total N flowing out N Remaining in Dam Nitrogen load distribution
Figure 5: Nitrogen load in the Hartbeespoort Dam
TDS load remaining in the Hartbeespoort Dam for the period December 1992 to February 2008
2500000
2000000 2012290
1500000 1076566 935724 1000000 TDS (tons) TDS
500000
0
Total TDS into TDS load in Hartebeespoort dam dam Total TDS flowing out TDS Remaining in Dam TDS (tons) load distribution
Figure 6: Salinity in the Hartbeespoort Dam.
Origins of pollution The main sources of the different pollutants can be traced back by following the pollution load contributions of the various rivers and streams feeding into the Hartbeespoort Dam. This information can assist in identifying target areas for intervention and inform pollution prevention strategies.
Pollution load over the period Jan 1990 to February 2008 into Hartbeespoort dam
Magaliesriver at Scheerpoort 30000 Swartspruit north Crocodile River
25000
20000
15000
Nutrient(tons) load 10000
5000 Crocodile River
Swartspruit north 0 rivers
Magaliesriver at Scheerpoort P Load in different Loads NH4+ Load Nutrients Nitrate Load
Figure 7: Nutrient contributions by the rivers discharging into the Hartbeespoort Dam.
Dissolved solids (salinisation) that entered the Hartbeespoort dam over the period January 1990 to February 2008
2500000 Magaliesriver at Scheerpoort Swartspruit north Crocodile River 2000000
1500000
1000000 TDS load (tons) load TDS Crocodile River
500000 Swartspruit north
Magaliesriver at Scheerpoort rivers 0
TDS load different Loads from Total dissolved solids (tons)
Figure 8: The contributions of TDS by the major rivers discharging into the Hartbeespoort Dam.
The contribution to the TDS and Nutrient loads of the Crocodile river sampled after Kalkheuwel by its tributaries as well as the individual contributions (%) of the these tributaries
P Load 100.0 95.8 83.0 90.0 90.4 N load 80.0 TDS load 70.0 72.0 53.6 60.0 50.0 65.1 40.0 15.7 13.3 30.0 0.2 20.0 21.5 Contribution (%) 10.0 8.1 TDS load 0.0 3.7 . P Load .. s ro p . f o .. n n n n i o n o te ti e kf n u H a fo ib l k tr V la n t V o a t c ile a l d i ta o e o c sk T o k r u C J
Figure 9: Pollution load contributions from the Tributaries of the Crocodile River upstream of the Hartbeespoort Dam.
The Crocodile River not only contributes the highest flow volume to the Hartbeespoort Dam (Figure 3) but also the biggest pollution load in terms of P and N (Figure 7) as well as TDS (Figure 8). The Magalies River and Swartspruit contributes significantly less flow and pollution loads (Figure 3, 7 and 8 respectively).
In light of the magnitude of the flow and pollution coming from the Crocodile River, it is further broken down into its tributaries upstream. The flow contribution by the Hennops, Jukskei and Crocodile Rivers upstream of their confluences is illustrated in Figure 10. The
Jukskei contributes 56.7% of the flow followed by the Hennops at 27.5% and the Crocodile with 14.1%. Flow Contribution (%) by the tributaries of the Crocodile river to its total flow measured at Kalkheuwel Flow Contribution 100.0 98.3
50.0 56.7
River 27.5
Crocodile Crocodile 14.1 Contribution Contribution to total flow of of flow total to 0.0
i.. Flow ut
... Contribution ennops H Vla... contrib ile at t tal cod To Cro JukskeiTributaries a
Figure 10: Percentage contribution of the tributaries of the Crocodile River.
The Jukskei River sampled prior to its confluence with the Crocodile River at Vlakfontein also contributes the most of the nitrogen (72%), phosphate (65.1%) and salinity (53.6%) load measured for the Crocodile River just prior to its discharge into the Hartebeespoort dam (Kalkheuwel). This is however not only due to the fact that the Jukskei contributes the highest volume of water of the three tributaries of the Crocodile River. Comparing the percentage contribution of pollutants versus the contribution to flow volumes, the Jukskei can be identified as the most polluted river of the three tributaries. Both the Crocodile and Jukskei rivers appear to contribute to TDS contamination equally in relation to their flow contributions.
Pollution Trends The trends of pollution loads entering the Hartbeespoort Dam is illustrated in Figures 11 to 13. All pollution loads (P, N and TDS) are showing an increasing trend over time.
Phosphate load (monthly averages) measured at for the Crocodile (south) at Kalkheuwel for the period January 1990 to May 2008 Crocodile at Kalkheuwel Linear (Crocodile at Kalkheuwel) 70.0
60.0
50.0
40.0
30.0
20.0 Phosphate load (tons) load Phosphate 10.0
0.0 Jan-90 Sep-92 Jun-95 Mar-98 Dec-00 Sep-03 Jun-06 Dates
Figure 11: Trend in phosphate loads entering the Hartbeespoort Dam via the Crocodile River for the period indicated.
N load for the Crocodile (south) at Kalkheuwel for the period January 1990 to May 2008
N load 800.0 Linear (N load) 700.0
600.0
500.0
400.0
300.0 N load (tons) load N
200.0
100.0
0.0 Jan-90 Sep-92 Jun-95 Mar-98 Dec-00 Sep-03 Jun-06 Date
Figure 12: Trend in N loads entering the Hartbeespoort Dam via the Crocodile River for the period indicated.
TDS load (monthly averages) entering the Hartebeespoort dam via the Crocodile river from January 1990 to May 2008 TDS load Linear (TDS load) 70000 60000 50000 40000 30000
TDS (tonnes) 20000 10000 0 Jan-90 Jun-95Dates Dec-00 Jun-06
Figure 13: Trend in TDS loads entering the Hartbeespoort Dam via the Crocodile River for the period indicated
The increasing trend in pollution load entering the dam must be viewed in conjunction with the data indicating that much of these pollutants remain behind in the receiving water body, as demonstrated by data for the Hartbeespoort Dam (fig. 4, 5 & 6). Although there is not enough recent data available for the Swart Spruit until it discharges into the Rietvlei dam, it is assumed that a similar situation must exist for this surface water reservoir. The continuous increase in pollution of these two surface water resources causes eutrophication, already indicated by the DWA classification of both of these two dams as hypertrophic (10), and negatively impacts on the quality of the water in these dams and potable water treatment processes. This increasing degradation of the water surface quality due to eutrophication is indicated by the data represented in Figure 14 showing an increase in the chlorophyll a in the intake water of the Rietvlei water purification works. This analytical parameter is used to indicate algal activity in the dam.
Chlorphyll a as indication of algae present in Rietvlei dam
Chlorphyll a 1000
800
600
400 Chlorophyl a Chlorophyl (ug/L)
200
0
6 7 7 8 8 9 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 2 2 2 2 2 2 2 r l r r e ri e e e ly ry b p b n b u a o A u J u t m J m 6 n c 8 e 1 e 0 a O 2 v 0 c J 0 o e 2 N D 2 1 4 8 1 1 Sampling dates
Figure 14: Chlorophyll a counts in the intake water of Rietvlei WPW.
The continuous degradation of the water quality in the Rietvlei and Hartbeespoort dams is reason for concern as both dams are used to supply potable water to certain areas. The fact that the pollution increases in magnitude on a yearly basis can only be combated by increasing the available infrastructure and regulations required to deal with this problem.
The data in figure 14 shows how algal growth in Rietvlei dam has become a serious problem, especially in the last two years. This problem is exacerbated by the fact that Cyanobacteria, “blue green algal species” have become the dominant algal species in this dam as is also the case in the Hartbeespoort dam. Blue-green algae are difficult to remove via flocculation during water treatment processes and releases toxins that causes objectionable odour and taste problems. This toxin can also be harmful to human health under certain conditions.
The available data does not provide sufficient evidence to single out any specific entity as being responsible for this increasing pollution loads. However, the current plans to upgrade many of the existing WWTWs in this study area clearly indicate that the relevant authorities are of the opinion that the bulk of the problem can be addressed through wastewater treatment upgrades. The planned upgrades include expansions for increased volumes of wastewater to be treated in order to improve the overall treatment efficiency of the WWTW.
The impact of the increased pollution loads of water resources on agriculture and human health cannot be estimated with a great degree of accuracy as yet.
Costs associated with expanding WWTW The current capital costs of building the infrastructure for a modern WWTW are estimated at between R6 – 9 million per ML/day capacity (table 1). This value varies depending on location and the capacity of the facility (the larger the facility, the lower the cost per ML). This allows the valuation of the WWTWs in this study area. The calculation of the capital value of the WWTWs in this study area is based on the costs that would be required to
replace the current capacity of these WWTW except for Magalies WWTW (lack of current information) and the very old and small WWTW at Esther Park (Table 1).
The current capital replacement value of these WWTWs can therefore be estimated at approximately R4.55 billion for the total treatment capacity of 700 ML/day of mixed domestic and industrial wastewater (Table 1). This figure translates into an average capital cost of treatment capacity equal to R6.5m/ML.day.
The operational cost of waste water treatment at Sunderland Ridge WWTW is estimated as R794.1/ML (7) while the utility ERWAT estimates their operating cost at R1500/ML for its entire operation. These numbers include all expenses associated with the waste water treatment operations i.e. salaries, energy, chemicals and amortisation of equipment.
Potable water treatment The severity of the algal blooms in the Rietvlei dam is increasing as illustrated by the sharp increase in the chlorophyll a since June 2008 (Figure 14). The data presented in Figure 14 is further elaborated by personal communications with the WPW staff indicating that algal blooms in the Rietvlei dam presented difficulties during the production of potable water well before 2006 (the earliest date for which the information in figure 14 is available). Specific technology interventions for the continued production of good quality potable water from this resource were required. A dissolved air flotation (DAF) system was installed in 1980 followed by an activated carbon system in 1999. More recently ozonation equipment was introduced. Cyanobacteria that have dominated the algal populations in Rietvlei Dam in recent years are more difficult and expensive to remove than other (green) algae species through flocculation technology. The latest technology intervention is the introduction of the “Solarbee” system aimed at the management of the algal population in the dam by reducing the dominance of the toxic algae species. One Solarbee 10 000 unit is currently priced at $64 590.00 (R484 425.00 at $/R exchange rate of 7.5). These units cost on average R20 000/unit to ship to South Africa and Rietvlei Dam currently has 16 of these units in operation. This is an example of how eutrophication affects the necessary technology interventions and costs required for the production of potable water. These technology upgrades were not aimed at increasing the production capacity of the WPW but necessary to ensure existing production levels (11).
The water purification works at Brits is another example where increasing pollution of the water resource is now impacting on the ability of the WPW to deliver good quality water. This plant is failing and the inhabitants of the town revert to buying bottled water for human consumption [personal communication with various community members]. Unfortunately no analytical or operational data were made available for this study by the Madibeng municipality officials.
The current replacement value of this WPW at Rietvlei is estimated at R175m (7). This capital value can be normalised against the volume (ML) of potable water produced per day and this provides a value for the capital investment in the water purification infrastructure of R4.6m/ML.day capacity.
Production costs Rietvlei WPW is producing approximately 37 – 38 ML/day of potable water and supplies an estimated 18% of the potable water for Pretoria. Their current operating costs are estimated at R1 030/ML of potable water (11).
Cost analysis
According to the information presented in this paper the capital costs for the waste water treatment facilities (R6.5m/ML.day) in this study area is higher than the capital costs for our example of a modern water purification plant (R4.6m/ML.day). Production costs associated with waste water treatment clearly varies greatly from R794.1/ML to R1 500/ML (Table 1) depending on the location, size and technology used. The production costs of potable water (R1 030/ML) are therefore comparable to that of waste water treatment.
The costs of waste water treatment and potable water purification including the costs/unit of treated water indicate that there is little to choose between a “point of use”- or “pollution treatment prior to release” philosophy. Clearly, the scale of waste water treatment is far greater that our example for potable water treatment. It is important to note that the potable water in this study area is mostly supplied by Rand Water and therefore the two philosophies cannot be directly compared regarding the volumes of potable water imported to waste water produced. However, the data presented show that the production of potable water in this study area is directly influenced by the quality of the available raw water and therefore by pollution and eutrophication of surface water resources. Accelerated eutrophication impacts directly on the technology for potable water production. Salinisation of surface water is also occurring at accelerating rates and conventional water purification technology in this study area is not adequate for desalination. Desalination may well be required in the near future, especially for industrial users of this water where scaling and corrosion will affect operational costs or for the irrigation of saline sensitive crops.
It is well documented that the Gauteng area, including the selected study area can expect to experience shortages in potable water in the very near future. To this point in time water has been imported into this study area as required but this is not a long-term solution. Water for import may become scarce and therefore more expensive. Increasing pollution levels coupled with ever increasing demand in the catchments from where water is imported will make the dependency of an area on its local surface water resources far greater than is currently the case. It is therefore vital that pollution is combated rigorously prior to the release of water of poor quality into the environment. Polluted surface water resources will rely on ever more sophisticated technologies for continuous production at increasing costs.
The data presented suggests that pollution of the surface water should be prevented and more effort and funding should be directed towards pollution prevention measures. Therefore, future investments should be aimed at increased waste water collection and treatment infrastructure as well as methods to reduce both the volume and pollution load from both domestic and industry that eventually must be treated at the current WWTWs.
CONCLUSIONS
Pollution reduces the quality and therefore the economic value of the available water in the case study area. This deterioration of water quality impacts on users abstracting water directly from the streams for irrigation and domestic use and may even affect the value of property adjacent to polluted streams. The most measurable impact in economic terms however, is the analysis of the costs incurred by municipal and private entities responsible for sewage treatment as well as water purification for potable use. The technology used to treat relative good quality water less than a decade ago must now be viewed as outdated and inadequate based on the deteriorated quality of intake water. The cost of recent technology upgrades in order to continue to produce water of potable quality at Rietvlei WPW clearly indicates the financial impact of pollution in the study area.
It is clear from the results that the main source of inflow water into the Hartbeespoort Dam is the Crocodile River. The dam acts as a sink for nutrients and to a lesser degree salts, with the result that the quality of the dam water is inevitably deteriorating over time. The data further clearly indicates that the pollution loads carried by rivers in the study area, are steadily increasing over time. It is specifically of note that the phosphate load from the Crocodile River continues to increase, despite the implementation of the so-called special standard for phosphate of 1 mg/l-1 ortho-phosphate, since 1988 (12). The pollution prevention measures implemented in the catchment of the Crocodile River is therefore clearly not adequate or very efficient. The cost implications for downstream users to treat the water to acceptable quality for use or to use alternative sources of water such as bottled water, is therefore a direct cost of the water pollution.
The cost of nutrient enrichment over time is clearly outlined in the technology interventions implemented at the Rietvlei Dam. It should further be noted that more sophisticated technologies are also more expensive. It can therefore be concluded that increasing pollution results in ever rising treatment costs to users. Both industrial and human activities demands access to clean water, but the current trends of increasing pollution and associated treatment costs could affect the availability and affordability of potable water in the near future.
It is clear from this analysis that more should be done to prevent pollution and reduce the influx of wastewater to the surface water resources of this study area but equally in any catchment area. Legislation limiting the use of potable water for the sewerage systems, gardening and other non-critical water uses should be explored while industrial water use and waste production should also be minimised through cleaner production practices. More emphasis is also required to addressing diffuse sources of pollution especially from informal settlements as is the case in the Jukskei catchment. The costs of potable water can be expected to rise sharply as the quality and availability of water continues to be reduced. The data presented here also indicate that waste treatment measures should be given a high priority by the authorities of any catchment area or municipality as the costs of remediation of polluted water in the environment to potable standards will be much more expensive, directly influencing the concept of water as a basic human right.
REFERENCES
1. Department of Environmental Affairs and Tourism (DEAT). (2000). White Paper on Integrated Pollution and Waste Management for South Africa: A Policy on Pollution Prevention, Waste Minimization, Impact Management and Remediation. 2. Department of Water Affairs and Forestry (DWAF) (1997), White Paper on a National Water Policy for South Africa. (Department of Water Affairs and Forestry, Pretoria). 3. Department of Environmental Affairs and Tourism (DEAT) (2006). South Africa Environment Outlook: A Report on the State of the Environment. (Department of Environmental Affairs and Tourism: Pretoria). 4. Republic of South Africa (RSA) (1997) Water Services Act, 1997. Act No 108 of 1997. 5. Resource Quality Services (RQS) website of the Department Water Affairs of the Republic of South Africa (DWA) [http://www.dwaf.gov.za/iwqs/wms/data/000key.asp] 6. ERWAT, Terblanche, J., 011 929 7006, (Telephonic Interview), Rosslee, W., 083 676 7027 (Telephonic Interview and documentation) 7. Municipality of Tshwane, Van der Merwe, S., 011 358 0691, 082 897 1994 (Telephonic Interview and documentation)
8. Johannesburg Water, Deacon, S., 011 688 1400, Telephonic Interview, Schutte, D., 011 688 1432 & Coetzee, R., (Telephonic Interview and documentation) 9. Water & Sanitation Africa, November/December 2009, “Percy Stewart WWTW upgrade complete”, 29-35. 10. The Trophic Status classification of South African impoundments, October 2002 to September 2003, Available on the DWA website, http://www.dwaf.gov.za/iwqs/eutrophication/NEMP/default.asp 11. Rietvlei WPW (Municipality of Tshwane), Taljaard, K., 012 358 1802, Coetzee, L., 012 358 1803, Lues, D., 012 853 8017 (Telephonic Interview and documentation) 12. Hohls BC, Quibell G, Du Plessis BJ and Belcher T. (1998). Assessment of the Implementation of the Phosphate Standard at the Baviaanspoort and Zeekoegat Water Care Works. Report No N/A230/01/DEQ0797. Institute of Water Quality Studies, Department of Water Affairs and Forestry, Pretoria, South Africa.