The use of Streaming Current Monitors in optimising coagulant dosage in Water Treatment Plants

Abstract

All water sources contain a mixture of organic/inorganic particulate or dissolved contaminants, in addition to microbes (i.e. bacteria, viruses and protozoa), which can be pathogenic (i.e. disease causing) to humans. Irish Water introduced 'The National Disinfection of Drinking Water' strategy in 2016 to ensure compliance with the European Communities (Drinking Water) Regulations, S.I. No. 122. One method of purification of raw water is the introduction of a chemical coagulant for the removal of particulate or dissolved contaminants through coagulation and flocculation. Coagulant is dosed along with pH correction chemical to ensure the correct metal hydroxide floc formation for optimum organics removal. A coagulant is dosed at a rate/volume based on achieving and maintaining suitable chemical dosing conditions in responses to changing raw water conditions. The plant operator may face challenges during a rainfall event because the turbidity of the raw water can change, causing difficulties in maintaining the optimum coagulant dose. A Streaming Current Monitor (SCM) can be used to automate the coagulant control process. A SCM is a continuous sampling, online instrument that enables the treatment plant operator to know precisely, and at all times, the optimum coagulant dosage. The SCM responds to changes in raw water characteristics (turbidity, pH, colour, etc.), flow rate, and allows the operator to make the necessary adjustments if required. This paper describes the introduction of a SCM to a Water Treatment Plant (WTP) in Galway County Council, Western Division and the calibration of this instrument to the WTP. The effectiveness of the SCM to optimise coagulant dosage automatically on a real-time basis in the WTP is also investigated.