Water-resilient cities can only be achieved through decentralised systems that harness appropriate advanced technology solutions.
By Musawenkosi Ndlovu, director, QFS The cost of water production has more than tripled in recent years. As the traditional technologies used in our manually operated water treatment plants fail to keep up, operating and maintenance costs have soared, leading to higher water tariffs. However, intelligent solutions can be employed to reduce the cost of water production and ultimately build water-resilient communities.
Traditional water treatment
Traditional water treatment plants use a combination of coagulation, sedimentation, filtration and disinfection to provide clean, safe drinking water – technology that dates to the 20th century.Figure 1 Typical water treatment process flow diagram Conventional technologies are mainly centralised, as they are mechanically intensive and involve substantial civil works; however, these centralised systems typically result in a loss of water through leakages as well as high water pumping costs, and pressure monitoring becomes a challenge.
Implementing intelligence
South Africa does not have to reinvent the wheel, but rather add intelligence to existing systems to maximise their efficiency. One example of this is through the implementation of membrane technology, which offers several benefits, namely:
can be decentralised
80% reduced footprint
80% chemical cost reduction
fully automated (no labour costs)
resultant low-water tariffs
reduced pump sizes.
Figure 2 Water treatment process flow diagram with the introduction of membrane technology
Benefits of advanced technology
Figure 3 A typical turnkey 6 Mℓ/day advanced technology water treatment plant Using advanced technology to treat water has a positive effect on capital and operating costs. For starters, the use of membrane technology eliminates flocculation, sedimentation and sand filtration. This optimises the efficiency of the system and substantially reduces the amount of chemicals dosed into the system. Table 1 shows the typical volumes and costs of water treatment chemicals used by a conventional water treatment plant. Using these numbers, a municipality would spend R1.43/m3 on chemicals to treat 6.5 Mℓ/day volumes of water – amounting to R9 321 per day. However, by using advanced technology water treatment methods, like membranes, chemical usage can be reduced by approximately 80%.
Chemical name
Dosage (ppm)
ZAR cost (ppm)
Total cost
Aluminium sulphate
202
5
R1 010.00
Sodium aluminate
39
6
R234.00
Soda ash
50
3
R150.00
Chlorine
10
4
R40.00
Table 1 Cost of water treatment chemicals for a conventional water treatment plant.
Furthermore, automated advanced technology water treatment plants have a high recovery rate. The waste generated through the treatment process is minimal and usually disposed of down municipal drains. This eliminates any sludge drying beds, which can occupy 1 500 m2 on a plant that produces 6 Mℓ/day. In addition, the modular orientation of the advanced technology water treatment skid makes increasing capacity easy to implement, as it just takes the addition of membranes. These plants are also light on mechanical installation, using smaller, lighter pumps. The elimination of sedimentation and settling reduces the overall amount of civil and mechanical works needed, and thereby reduces both capex and opex costs. Municipalities rely on revenue collected from water sales to maintain infrastructure and the servicing of water production. Due to superior reliability and the elimination of human error in the production of water through advanced treatment methods, plant availability is maximised and the water quality is not jeopardised.
Conclusion and recommendations
It critical for South Africa to follow innovative ways of producing water efficiently. The implementation of advanced treatment technologies and the decentralisation of these systems is the future of the water industry. These advanced treatment technologies reduce the cost of producing water, as they occupy smaller footprints, are environmentally friendly and more cost-effective – by using significantly less chemicals – as well as reduce the labour component and potential for human error. To ensure that the system works perfectly, it is important to use equipment that has been industry-tested and has integrity test certificates. It is also vital to conduct proper feasibility study and data analysis before designing a plant, as abnormal variations in the feedwater can influence the percentile availability of the plant. Lastly, the proper running of a plant is key to ensure that it operates within its design specifications, and this will ultimately help to ensure that membranes and other capital equipment last.
