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One of North West England's largest Water Treatment Plant's, located near Chester, supplies over 450Ml/day (120 million gallons / day) of drinking water to over 1 million consumers. Over 1.2 million per annum is spent on coagulant chemical alone, thus any potential methods for minimising its use are thoroughly examined. One recent success story relates to a dynamic and simulation study undertaken to generate stable, precise and optimal pH conditions for the coagulation process. This was achieved by implementing a novel pH real-time control system based on the Smith Predictor algorithm and subsequently tuned using knowledge gained from open-loop data obtained from the plant.

A series of open-loop acid step tests were applied to the process and the resulting plant responses used to postulate and verify off-line computer-based dynamic models of the actual pH process within the MATLAB/SIMULINK™ environment. The model was used a platform to emulate and evaluate alternative control strategies. Having established an appropriate algorithm that performed well under all perceived site conditions, it was tuned, optimised and assessed for stability and robustness.

The system now accurately maintains the desired set-point of pH 5.5 to within a very impressive +/- 1% deviation, despite many external, sizable disturbances. The controller responds particularly well to external disturbances. The plant's Operators have managed to reduce the coagulant usage by up to 23% as a direct result of the new pH correction system. The clarified water's turbidity and colour parameters are noticeably improved, allowing the nominal plant flow throughput to be increased. The number of filter backwash's has also been significantly reduced.

Document Type: Research Article


Publication date: January 1, 2001

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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