Waste to energy

ENERGISING SYDNEY THROUGH CO-DIGESTION FOODWASTE  
Sydney Water’s Waste to Energy Program
B Galway, P Denyer, M Kelly, P Woods, H Bustamante
Publication Date (Web): 5 September2018
DOI: https://doi.org/10.21139/wej.2018.029


Sydney Water’s Food Waste to Energy 2020 Plan established the vision that by 2020 Sydney Water will provide a sustainable food organics disposal service to our business customers. To achieve this vision the plan outlined a series of research and pilot programs to be established from 2015.  

The aim of the co-digestion pilots has been to prove that co-digesting trucked, high strength organic waste at a WWTP increases biogas production and gain a better understanding on how to receive trucked organic waste. The pilot success is measured against two objectives.

This paper highlights the steps that Sydney Water has followed in developing the program to this point. It will also detail how the process has altered as we continue to accumulate learnings in this new area. The program has evolved from an ad hoc lab scale research, to a pilot, now it is a more defined research and development (R&D), pilot and implement life cycle.  The initial research used glycerol, a by-product from the manufacture of biodiesel.  This product looked very promising and the lab scale research indicated impressive biogas production.  The first pilot plant constructed was at Bondi Wastewater Treatment Plant (WWTP). As the program evolved a second pilot plant was designed and constructed to receive fruit and vegetable waste at the Cronulla WWTP, this plant became operational in late 2016 and is currently within the commissioning phase.

The results from our pilots identified the complexity of identifying positive and negative impacts in operational treatment plants. The Bondi pilot identified that lab and bench scale digesters provided good data on expected gas and energy outputs. They could not reproduce the limitations of using the material in a functioning treatment plant because we were unable to dose to the same level. As Sydney Water moves through available products from basic glycerol and sugary water such as soft drinks to more complex food wastes such as commercial kitchen and grease trap waste, a better understanding of impact on digester operation and digestion outputs is required.

Limitations in lab scale research and natural variability of gas production within operating WWTPs has highlighted the need for a middle ground, a large-scale research digester.  Through the support of the Australian Research Council, the University of Wollongong, University of NSW, DC Water and Sydney Water a 3-year research program was designed which included the construction of two 1 kilolitre anaerobic digesters at our Shellharbour WWTP.  This program will provide more accurate outcomes and outputs from more complex co-digestate products for future pilot plants. 
 

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