The influence of dosing sequence of lime and alum as a coagulant in the treatment of soft humic waters (requiring pre-alkalinisation of raw water) was studied. The experiments show that the traditional dosing order, i.e. pre-alkalinisation first and coagulant second, might give worse results in comparison with the reversed order, i.e. coagulant dosing followed by pre-alkalinisation. The influence of aggregation time on residual coagulant and UV absorbance was also studied.

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