Applications of the Streaming Current Detector in Water Treatment
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report No UWRAA 44
The use of Streaming Current Detectors (SCD) as a method of controlling coagulant dosing in water treatment plants has been reviewed. This involved a theoretical and practical study over two years that included laboratory tests, pilot plant trials and full scale plant operation.
A laboratory examination of several electrolytes and standard suspensions showed excellent correlation between data obtained from SCD measurements and from conventional electrokinetic techniques, namely electrophoretic mobility and streaming potential and led to the development of an improved theory of SCD measurement.
The SCD was used in extensive pilot plant trials at the North Pine Water TreatmentWorks in Brisbane. SCD signals responded to changes in coagulant dose and pH for alum, ferric chloride, poly aluminium chloride and two cationic polyelectrolytes. Nonionic polyelectrolytes gave no SCD response due to the absence of a charge neutralisation mechanism. Full scale trials at Westbank Water Treatment Plant, Brisbane, confirmed these data as raw water characteristics varied during several rainfall events.
Westbank Water Treatment Plant at Mt Crosby was the site of a full-scale plant investigation of the SCD’s capacity to control alum dose. Plant parameters including alum dose, pH, raw water turbidity, conductivity and colour and SCD response were monitored. Several high turbidity and high colour events occurred during an unusually wet summer period providing an opportunity to study the proficiency of the instrument over a wide range of conditions.
Finally, the SCD was used to control alum dose on the full scale plant for a shortperiod. It is concluded that the SCD has the capability of controlling coagulation processes provided plant operators have sufficient working knowledge of the instrument.