Scada aids the extraction of sludge

SCADA/HMI

October 2005 SCADA/HMI

Few people realise what huge volumes of sludge are produced in the process of water purification - and the problems associated with the disposal thereof. A definition for sludge, as found during a water purification process, is best found in the Oxford Dictionary "thick, soft, wet mud or similar viscous mixture...." During the sedimentation phase of raw water treatment, suspended particles (mainly clay and fine particulate matter) are removed from the water. These particles form the basis of the sludge, and together with the residue of chemicals used during coagulation and flocculation, constitute the waterwork's sludge.

At Zuikerbosch Water Purification Plant, sludge is scoured from the sedimentation tanks and pumped approximately 2,5 km to Panfontein sludge disposal site for treatment. Depending on the solids consistency, this varies between 600 and 1000 dry tons. The raw sludge is stored in a balancing pond where mechanical agitation keeps the solids in suspension. An anionic polyelectrolite flocculant is added to the raw sludge, flocculation occurs, and aggregration of the solids causes a phases separation within the sludge. These solids particles settle to the base where mechanical moving rakes scrape the thickened sludge to the centre. Underflow pumps extract this product for dispersion onto the sludge air dry paddocks in cycles, where it is left to dry.

Clear supernatant water recovered during this treatment process can be as high as 90 to 95% of the raw sludge volume, and is recycled to Zuikerbosch for reprocessing with the raw water.

This whole process is automated and this is where FactoryLink scada comes into play. The density and pH of the incoming raw sludge is measured and calculated to control the dosing pumps to apply the correct amount of flocculant for treatment of the sludge. Parameters like mud bed levels, pump status, flow, turbidity, set points, hydraulic pressure, etc, are monitored continuously and displayed on a computer monitor. Alarm conditions including, pump trip, over/under levels, temperature, sump overflow and various critical set points are recorded in the SQL Server database (standard with FactoryLink) from where reports can be generated and printed on hard copy.

There is a need, from time to time, to fine tune the process and because changes can be made while FactoryLink is on-line, there is no need to stop the process thus eliminating production losses.

For more information contact Johan de Villiers, Process & Information Technologies, 012 664 6622.

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SCADA/HMI

Scada aids the extraction of sludge

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