There are not many people working in Nutrient Neutrality who have spent four years studying what microorganisms do inside a wastewater treatment system at a molecular level. Dr Chang Gao is one of them.
A Civil and Environmental Engineer at Enviren Ltd, part of the National Rivers Consortium, Dr Gao brings a depth of scientific expertise to this work that is genuinely rare in the industry. She holds a PhD from Wageningen University and Research, one of the world’s leading institutions in Environmental Science, where her doctoral research examined anaerobic granulation: specifically, how microbial communities behave and interact within wastewater treatment systems, and the physical properties that determine how effectively those systems perform. She completed her master’s thesis at Delft University of Technology, has published peer-reviewed research in Bioresource Technology, and has led more than 20 building water system designs across her career. In her day-to-day role at Enviren, she produces Technical Mitigation Reports, Nutrient Neutrality Assessments and Provisional Drainage Plans, bringing the same scientific rigour she applies in research to the technical work that underpins every Nutrient Neutrality compliance case.
I met with her to understand what that background truly signifies for those who depend on NRC and Enviren to ensure accuracy. Written by Elsa Poulter, Marketing and PR Manager for National Rivers Consortium (NRC).
Why biology is the foundation
Discharge standards for wastewater treatment are tightening. From 2030, permitted levels will decrease, and Dr Gao is clear on what that requires from the industry.
“Generally, biological and/or chemical treatment processes are applied to meet the new requirements,” she says. “Biological treatments are more sustainable and more cost-effective. We rely on the activities of the microorganisms themselves. So, we don’t introduce anything into the wastewater. That makes it far more environmentally sound as a long-term approach.”
Understanding how those microorganisms behave is not an abstract academic concern. It is, in Dr Gao’s view, the foundation of whether a nutrient reduction claim can be trusted. As she explains: “When you understand the microbiology at depth, you understand how to optimise the process and how to recover the system once it fails. That knowledge is what makes it possible to design genuinely bespoke programming.”
It is precisely this kind of thinking that shapes how Enviren approaches every assessment it produces, and why NRC’s credits are grounded in science rather than assumption.
What others overlook
The practical difference Dr Gao’s background makes becomes clearest when she talks about how treatment performance figures are typically used across the industry.
“Most businesses take the stats that a Package Treatment Plant manufacturer publishes and apply them directly to their nutrient calculations,” she says. “But wastewater treatment is a complex problem. The same system in England and in Germany will produce different results, resulting from the variations in weather conditions, influent characteristics, and flow rates. If you are not accounting for that, your removal claims are not reliable.”
NRC’s programme includes long-term effluent testing and independent verification for exactly this reason. The figures used to generate credits reflect actual field performance over time, not a specification sheet. Having someone of Dr Gao’s calibre involved means the questions that need to be asked are being asked. “Our effluent data is reliable and valid in terms of certification because we monitor long-term and consider the whole picture.”
The performance gap that few people discuss
Dr Gao also raises something few people in the industry talk about openly: what happens when a treatment plant is not loaded as its design assumed.
“Package Treatment Plants are designed around an expected population figure, but real-world occupancy fluctuates, particularly where properties are rented or used as holiday lets,” she explains. “If the system is not loaded correctly, the process will not perform as specified. It needs careful calibration. Not all businesses that install Package Treatment Plants do that.”
This is the kind of detail that only surfaces when someone with genuine technical depth is involved. For Enviren and NRC’s clients, and for the developers and planning consultants who rely on NRC’s credits, it is the difference between mitigation that performs and mitigation that merely appears on paper.
What genuine credibility looks like
When asked what she would want a developer or planning consultant to take away from this, Dr Gao’s answer reflects something broader than technical process.
“We have people monitoring these systems long term, making sure they are working correctly. That is what makes a certification valid. For us, it is about the whole picture: contributing to better water quality, improving the environment, and being able to demonstrate that. Some businesses work with numbers alone. We don’t.”
That ethos and the scientific foundation behind it are what Dr Gao brings to Enviren and National Rivers Consortium. In a field where the difference between a credible credit and an unreliable one determines whether a project stays on schedule and planning permission can move forward, having that depth of knowledge in the team is not a detail. It is the point.