Towards safer management of supernatant return in drinking water plants

The filter backwash recycling rule (FBRR) was introduced by the US EPA in 2002, and has been since implemented around the world as best practice to address the risk associated with pathogens present in supernatant waters (i.e. spent filter backwash water, sludge thickener supernatant and liquids from dewatering processes). Since its introduction, the FBRR has been considered as a significant factor limiting the opportunity to improve practices for supernatant return in drinking water plants. As increasing water scarcity in Australia forces utilities to continuously optimise their separation systems and their water recovery, it is now required to critically demonstrate the health risk associated with supernatant return and establish recommendations for new set of guidelines.

Water Research Australia has recently recognised the need for research on this topic and has awarded a project to A/Prof Pierre Le-Clech and Prof Stuart Khan from the Schools of Chemical Engineering and of Environmental Engineering. This project is significantly supported by the in-kind contribution of a large number of industrial partners, especially water utilities such as TasWater, Seqwater and Hunter Water, who committed to share existing data and know-how.

Based on the critical importance of water quality and customer health protection, recent advances in risk assessment techniques are expected to allow the development of improved, more appropriate, but still safe management of supernatant return. Ultimately, the project is expected to produce a set of guidelines to be used within the water industry for the design, operation and control of best supernatant recycling scheme in water treatment.