Case Study: Odour Risk Management at the WTP, One of Australia’s Largest & Most Unique WWTPs

The Western Treatment Plant (WTP) is one of Australia’s largest and most unique wastewater treatment plants (WWTP) treating over 52% of Melbourne’s sewage in a series of large lagoons. WTP has an existing, comprehensive Environmental Improvement Plan in place, which includes an ongoing focus on odour management in the context of a recently completed significant program of upgrade works that have resulted in an estimated reduction in odour emissions from the WTP site of about 90%. In this context, the purpose of the odour risk management project was to assess any ongoing residual odour impact risks for the plant and to identify any further odour mitigation approaches that may be available to appropriately manage this risk if required. Due to the scale and the unique nature of the facility, changes in odour emissions from any of the various sources may have a significant effect on off site odours, and reliably assessing the varying impact of these sources is much more complex than for other WWTPs. For these reasons, the data collection and assessment phase of the project was more comprehensive than would normally be undertaken for an odour impact assessment, and integrated some unique and interesting new tools. There were concerns that causality effects in AUSPLUME could result in overly conservative predictions. Therefore, the investigation also assessed the available odour dispersion models, (AUSPLUME, CALPUFF and TAPM) and their appropriateness for assessing odour impacts from this unusually large site. In particular, the predictions of AUSPLUME will be compared to the predictions of CALPUFF, community surveys and field olfactometry data to ascertain the relative accuracy of each model. This paper will present the results of this investigation so far, including some interesting findings about the relationships between odour strength, perception (how humans interpret odour strength) and odour annoyance in the community.