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

Appropriate Technologies Conference 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

Appropriate Technologies Conference 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.

Appropriate Technologies Conference 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

Appropriate Technologies Conference 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).

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

Appropriate Technologies Conference Constant - level box solution feeder

Appropriate Technologies Conference Floating-arm type solution feeder

Appropriate Technologies Conference Floating-bowl type solution feeder

Appropriate Technologies Conference Detail of floating-bowl

Appropriate Technologies Conference 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.

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

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

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

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

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

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

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

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

Appropriate Technologies Conference 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

Appropriate Technologies Conference 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.

Appropriate Technologies Conference

Appropriate Technologies Conference  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.

Appropriate Technologies Conference

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

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

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

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

Appropriate Technologies Conference Evaluated float positions relative to outlet point

Appropriate Technologies Conference 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

Appropriate Technologies Conference

Appropriate Technologies Conference

Appropriate Technologies Conference 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) Average (l/h) Maximum (l/h) STDV

Appropriate Technologies Conference Calibration: Orifice head versus dosing rates

Appropriate Technologies Conference 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

Appropriate Technologies Conference 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

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

Appropriate Technologies Conference Pilot plant at Stormsvlei village Western cape

Appropriate Technologies Conference Pilot plant at Stormsvlei village Western cape

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

Appropriate Technologies Conference Presenter’s Contact Details: Cape Peninsula University of Technology Faculty of Engineering Civil Engineering Department (Bellville Campus) address: Tel: (o), (cell); Fax: 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) address: Tel: (o), (cell); Fax: