Applicationsof the Streaming Current Detector in Water Treatment

ReportNo WSAA 44

July 1992

SYNOPSIS

Theuse of Streaming Current Detectors (SCD) as a method of controlling coagulantdosing in water treatment plants has been reviewed. This involved a theoreticaland practical study over two years that included laboratory tests, pilot planttrials and full scale plant operation.

Alaboratory examination of several electrolytes and standard suspensions showedexcellent correlation between data obtained from SCD measurements and fromconventional electrokinetic techniques, namely electrophoretic mobility andstreaming potential and led to the development of an improved theory of SCDmeasurement.

TheSCD was used in extensive pilot plant trials at the North Pine Water TreatmentWorks in Brisbane. SCD signals responded to changes in coagulant dose and pHfor alum, ferric chloride, polyaluminium chloride and two cationicpolyelectrolytes. Nonionic polyelectrolytes gave no SCD response due to theabsence of a charge neutralisation mechanism. Full scale trials at WestbankWater Treatment Plant, Brisbane, confirmed these data as raw watercharacteristics varied during several rainfall events.

WestbankWater Treatment Plant at Mt Crosby was the site of a full-scale plantinvestigation of the SCD’s capacity to control alum dose. Plant parametersincluding alum dose, pH, raw water turbidity, conductivity and colour and SCDresponse were monitored. Several high turbidity and high colour events occurredduring an unusually wet summer period providing an opportunity to study theproficiency 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 controllingcoagulation processes provided plant operators have sufficient workingknowledge of the instrument.

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