Following severe drought in 2018-19, bushfires in late 2019, and three successive extreme rain events between 2020 and 2022, the water quality in Warragamba Dam, the largest water source in Sydney, has significantly deteriorated. This resulted in a turbidity of >110 NTU and a true colour of >100 CU420, representing a significant increase of suspended particles and natural organic matter respectively in raw water, after heavy rainfall in July 2022. Through advanced testing and optimisation at the pilot-scale contact filtration plant and designing an emergency pre-treatment strategy, Sydney Water was able to produce safe drinking water (turbidity <0.20 NTU) from full-scale Water Filtration Plants (WFPs) that have contact filtration technology, to avoid potential severe impacts on 85% of Sydney’s water supply and ensure drinking water met Australian Drinking Water Guidelines, while water quality remained outside the design envelope of the plants. The novel optimisation in a pilot-scale contact filtration plant for increased suspended particles (turbidity) and natural organic matter (true colour) in raw water caused by extreme events is discussed in this paper. The increase of true colour and dissolved organic carbon (DOC) represents a significant increase of natural organic matter (NOM) in the raw water due to extreme events. The characterisation of DOC of raw water and its impact on the contact filtration water treatment process is also discussed in this paper.
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