1. Appropriate Technologies Conference 2007 1 Simple chemical dosing systems in small water works Cape Peninsula University of Technology G. Mwiinga Cape Peninsula University of Technology

2. Appropriate Technologies Conference 2007 2 1. Introduction 2. Simple chemical dosing systems – a brief literature review Gravity driven solution feeders, 3. Chemical dosing applications in small water works - South Africa Literature and plant visits, 4. A simple chemical dosing system developed for small water works Gravity driven solution feeder 5. Concluding statements

3. Appropriate Technologies Conference 2007 3 1. Introduction Water treatment chemicals dosed in various forms: – influence complexity of dosing system. dosing systems range from simple to complex types – Simple systems include those that pump predetermined dosages directly from a solution tank and those that dose dry or wet chemicals by gravity or volumetric measurements. – Complex systems include electronically controlled pump metering systems that automatically adjust dosing rates based on water flow rates and quality. hydraulically and gravity driven systems are simpler and are more appropriate as solution-feeders in small water treatment plants.

4. Appropriate Technologies Conference 2007 4 2. Simple chemical dosing systems – a brief literature review Simplest dosing systems generally appropriate for small plants are those that dose chemical solutions by gravity: –predetermined amount of a solution drips into the water at a point that has enough mixing energy. –usually have no moving parts and their construction is possible from local materials –Key aspect is the control of dosing rates –Low operation and maintenance demands, but operator training still essential –Calibration still very important –Solution preparation

5. Appropriate Technologies Conference 2007 5 The erroneous general practice reported in some plants entails drip-dosing from a solution tank without taking into consideration the decreasing solution level and its concentration (see Figure).

6. Appropriate Technologies Conference 2007 6 Examples of simple (gravity) chemical dosing systems

7. Appropriate Technologies Conference 2007 7 Constant - level box solution feeder

8. Appropriate Technologies Conference 2007 8 Floating-arm type solution feeder

9. Appropriate Technologies Conference 2007 9 Floating-bowl type solution feeder

10. Appropriate Technologies Conference 2007 10 Detail of floating-bowl

11. Appropriate Technologies Conference 2007 11 3. Chemical dosing applications in small water works Good and bad practices A summary of problems: –Lack of control of dosage –malfunctioning or not in use due to breaking down – lack of maintenance / replacement –Although lack of adequate financial resources contributes to lack of sustainability, technical inappropriateness reported to be common.

12. Appropriate Technologies Conference 2007 12 Electronic dosing systems at a plant in EC (1 pump out of use at time of visit)

13. Appropriate Technologies Conference 2007 13 Operation electronic dosing systems at some plants in Western Cape

14. Appropriate Technologies Conference 2007 14 Electronic dosing system at a plant in Eastern Cape (no standby pump)

15. Appropriate Technologies Conference 2007 15 Electronic dosing systems replaced by drip dosing at a Plant in Eastern Cape

16. Appropriate Technologies Conference 2007 16 Manual drip - dosing control at a plant in Eastern Cape

17. Appropriate Technologies Conference 2007 17  Solution tanks that feed a dosing tap by gravity at the Western Cape  Volumetric measurements used to check dosing rates

18. Appropriate Technologies Conference 2007 18 Solution tank equipped with a dosing tap at plant in the Western Cape

19. Appropriate Technologies Conference 2007 19 Pump and flow meter dosing system at plant in the Western Cape

20. Appropriate Technologies Conference 2007 20 Emergency gravity dosing system at a plant in the Eastern cape (bin equipped with a tap used ); only option which served the purpose, but unsustainable / ineffective

21. Appropriate Technologies Conference 2007 21 4. A simple chemical dosing system developed for small water systems Requirements : The dosing was to be achieved by gravity. Constant dosing rate independent of solution level. Easy adjustment of dosing rates/ calibration. Easy chemical mixing Sustainable materials chemical dosing system that utilises a constant head orifice was developed.

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23. Appropriate Technologies Conference 2007 23  Main components :  A constant-level inlet,  A chemical solution tank,  A constant-head orifice and dosing tube,  A hand-mixer  Solution tank is supplied with a lid that has provisions to hold the hand-mixer, constant-level inlet system and dosing tube.

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25. Appropriate Technologies Conference 2007 25 Inlet pipe Float Stopper housing outlet hole Flange Soft rubber stopper fixed on end capping Open end Details of constant-head inlet

26. Appropriate Technologies Conference 2007 26 Mixer Provision for mixer Guide (provision) for the hard dosing tube inlet pipe for constant level system Details of lid for solution tank

27. Appropriate Technologies Conference 2007 27 Details of constant-head orifice and dosing tubes

28. Appropriate Technologies Conference 2007 28  Evaluation and results  Influence of orifice/float position  Dosing rates:  consistence, reproductivity, calibration  Operation - calibration  Maintenance and materials

29. Appropriate Technologies Conference 2007 29 Evaluated float positions relative to outlet point

30. Appropriate Technologies Conference 2007 30 Time (min) 0 o Position45 o Position90 o Position135 o Position180 o Position Run 1Run 2Run 3Run 1Run 2Run 3Run 1Run 2Run 3Run 1Run 2Run 3Run 1Run 2Run 3 07.427.197.137.507.757.287.647.727.627.637.627.697.627.477.36 307.086.806.377.397.526.757.527.177.507.597.647.597.64 7.25 606.696.766.507.137.156.707.497.757.517.747.397.617.107.177.12 906.56 6.386.376.906.457.377.517.367.627.397.617.637.047.16 1206.206.166.436.506.636.097.157.417.257.507.487.407.507.247.40 1505.206.166.416.386.645.606.686.827.017.517.397.347.487.277.28 1805.305.735.686.436.575.256.657.177.007.397.287.367.387.197.29 2105.345.726.536.416.435.776.677.156.997.367.417.387.377.17 2405.675.836.325.686.675.967.047.087.127.637.397.537.287.167.40 2705.735.526.776.326.775.836.867.167.147.507.477.377.407.157.27 3005.776.445.726.776.715.977.037.287.227.637.597.367.597.277.28 3306.726.555.505.124.515.216.797.187.167.507.377.267.507.277.28 3604.363.944.173.502.743.346.907.277.557.447.407.397.387.177.33 3901.583.223.692.172.272.165.204.835.527.617.657.277.14 7.41 4200.292.382.273.691.671.454.425.125.317.507.477.167.527.047.39 450 4.294.404.844.17 4.39 480 2.852.743.053.573.346.08

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33. Appropriate Technologies Conference 2007 33 Summary results Parameter 0 o position : retention time = 330 min 45 o position : retention time = 300 min 90 o position : retention time = 360 min 135 o position : retention time = 420 min 180 o position : retention time = 420 min Minimum (l/h) 5.205.256.657.167.04 Average (l/h) 6.256.557.207.487.32 Maximum (l/h) 7.427.75 7.747.64 STDV 0.5760.5890.2920.1320.164

34. Appropriate Technologies Conference 2007 34 Calibration: Orifice head versus dosing rates

35. Appropriate Technologies Conference 2007 35 Concluding statements Appropriate is relative – simple is not always equal to appropriate – Capacity to effectively use and maintain a given technology determines appropriateness Simple systems exist and must be promoted, though may not be attractive business wise Electronic solution feeders not generally appropriate in small water works

36. Appropriate Technologies Conference 2007 36 Gravity solution feeders have potential and must be promoted – more appropriate in small and rural plants, as an alternative to electronic dosing equipment or – stand-by dosing system where electronic pumps are in use Preparation of the stock solution, determination of dosing rates and calibration aspects very important Knowledge sharing and technology transfer important

37. Appropriate Technologies Conference 2007 37 Stormsvlei village Western cape Directly use high colour raw water from River

38. Appropriate Technologies Conference 2007 38 Pilot plant at Stormsvlei village Western cape

39. Appropriate Technologies Conference 2007 39 Pilot plant at Stormsvlei village Western cape

40. Appropriate Technologies Conference 2007 40 Acknowledgements: WISA and supporting organisations Conference Organisers WRC / NRF for their support THANK YOU

41. Appropriate Technologies Conference 2007 41 Presenter’s Contact Details: Cape Peninsula University of Technology Faculty of Engineering Civil Engineering Department (Bellville Campus) email address: mwiingag@cput.ac.za Tel: + 27 21 959 6663 (o), +27 822020826 (cell); Fax: + 27 21 9596660 Presenter’s Contact Details: G. Mwiinga, Pr. Eng. (Civil / Water Eng.) (Lecturer ) Cape Peninsula University of Technology Faculty of Engineering Civil Engineering Department (Bellville Campus) email address: mwiingag@cput.ac.za Tel: + 27 21 959 6663 (o), +27 822020826 (cell); Fax: + 27 21 9596660mwiingag@cput.ac.za