Small water treatment system upgrade for improved water quality in flood-prone areas: A report on the upgrade of the Gunbower WTP in northern Victoria

Many small water treatment systems throughout Australia using microfiltration (MF) followed by chlorine disinfection for raw water treatment experience elevated disinfection by-product levels in treated water. In some cases, this is the result of using MF systems without pre-treatment processes and the inability of MF membranes to remove dissolved organic carbon (DOC) to required levels. If raw water DOC levels are high, subsequent chlorination can form total trihalomethanes (TTHMs) and Haloacetic acids (HAAS). Even in cases where DOC levels are relatively low, the presence and subsequent chlorination of low molecular weight DOC can result in elevated disinfection by-products. Long distribution systems with extended residence times can further exacerbate disinfection by-product formation. An additional water treatment challenge facing many small water treatment system operators is the variability of raw water quality from source waters - in particular, river systems that draw raw water from exposed flood-prone areas. The Gunbower Water Treatment Plant (WTP) is located in the north of Victoria. The raw water source (Taylor's Creek) used for the Gunbower WTP was significantly affected by the floods in the summer of 2010/2011 . Since the floods the characteristics of the raw water have changed, with high DOC, UV254 and colour levels, making water treatment difficult and compliance with existing drinking water guidelines a challenge.