Dr Liu Ye is an Associate Professor, School of Chemical Engineering at The University of Queensland, Australia with research focus on sustainable and cost-effective water and wastewater treatment. Most recently she has taken a lead on emissions and is the lead editor of the IWA open-access book on process emissions. This inspirational work is world-leading and is focused on providing a deeper understanding of quantification and modelling of greenhouse gas emissions and subsequent mitigation measures.

Tell us about your career in wastewater treatment, and how your research into process emissions came about?

I work in sustainable wastewater treatment and process control and started looking at process emissions in 2009 when the ‘carbon tax’ was proposed and being debated in Australia. At that time, the focus in the water industry was still on energy efficiency and bio-gas production. There was little knowledge about the emission of the two major direct greenhouse gases (GHG), namely nitrous oxide (N2O) and methane (CH4), from wastewater treatment processes and so I found lots of unknowns to explore.

My current research is centered around how the water industry can treat wastewater in a sustainable and cost-effective way by finding innovative and practical solutions to tackle the challenges in achieving net-zero emissions. The outcome will not only help to solve real problems for the water industry but also help with the entire environment.

How significant are process emissions in terms of the overall water sector and global emissions?

Direct process emissions from water utilities (treatment plants and sewers) are the seventh largest contributor to global emissions.

13 Australian water utilities serving 16.3 million Australians have committed to reach net-zero GHG emissions by as early as 2030 (WSAA 2021). As the electricity grids become renewable, carbon footprints of many utilities become dominated by process emissions from sewage treatment. N2O is a particularly potent GHG and the most significant sink for the stratospheric ozone. In Australia, emissions of N2O may contribute up to 90% of the total carbon footprint of wastewater treatment plants, and its global warming potential is 265 times of CO2.

When we look at the 17 UN Sustainable Development Goals, this area corelates with three goals of the 17, which are clean water (SDG6), sustainable cities and communities (SDG11) as well as climate actions (SDG13).

Tell us more about your research and where you hope it will lead.

Through past research, we have developed a real-time monitoring system that incorporates diurnal, spatial and temporal variations into N2O accounting, which was crucial to accurately quantifying overall Wastewater Treatment Plant emissions. However, out of >1,000 Wastewater Treatment Plants in Australia, only nine carried out such quantification.

To get a nationally representative emissions factor to change the current reporting guideline and eventually develop mitigation guidelines, more national, full-scale quantification and mitigation studies are required. I’m developing a full-scale monitoring protocol at the moment and I hope it’ll guide water utilities to carry out monitoring themselves.

Together with Water Research Australia and eight Australian water utilities, I am establishing a ‘Net-zero for Wastewater Services’ research program, which aims to develop a national framework for water utilities to monitor and reduce direct process emissions from wastewater systems, reduce energy consumption and improve energy recovery. This will lead to a more sustainable water industry and inform GHG accounting guidelines for the water industry worldwide.

What do you need from industry to progress this research and enable Net Zero targets to be met?

The collaboration between researchers and water utilities is the key to success in achieving net-zero. If this is compared to a fleet sailing on the sea, then industry is the driving force of the ships, and researchers are the navigators. I hope more industry partners can pay attention to scope 1 – the direct GHG emissions and do not rush to offset carbon but try to reduce emissions and recover as much energy as possible.

The nationwide emissions monitoring campaign will underpin the development of new methods and models to accurately predict emissions for different treatment ponds and guide the reduction of the direct GHG emissions. Often, reducing GHG emissions will also result in optimized plant operational and enhanced energy recovery (carbon offset).

How do you think chemical engineering skills can contribute to reaching global Net Zero targets around the world, particularly in the wastewater treatment field?

Chemical Engineers will and should be the main contributors to the global sustainability and net-zero mission, especially in the wastewater treatment field. Reducing emissions requires a good understanding of process flows, unit operations, process control, mass/energy balance and modeling skills - all of which are key in Chemical Engineering degrees.