The most effective ways of teaching students to reduce waste in the laboratory are rarely dramatic. More often, they rely on repeated messages, small changes to laboratory systems and careful attention to the everyday practices students learn to adopt. The interventions we recommend may appear modest, but they are crucial. By embedding them consistently across teaching laboratories, we can help students to recognise that sustainable laboratory practice is not separate from good science, but integral to it.
Part one of this series outlined ways to foster low-waste habits and introduce constraints to encourage better solvent use. Part two explores how to move beyond basic waste reduction to teaching students responsible decision-making in experimental work.
Introduce more advanced sustainability choices in specialist labs
In advanced teaching laboratories, which are designed to reflect a research environment more closely, students can begin to think about how experimental design, apparatus and scale affect sustainability.
Cooling methods provide a particularly striking example. Overnight reflux reactions traditionally relied on a continuous flow of tap water through condensers, with the water then discharged into sink drains. This approach was not only wasteful (a traditional reflux set-up uses about six and a half litres of water per minute, meaning an 18-hour overnight reaction may consume 7,020 litres of water) but also carried flood risks. To move away from this model, we incorporated recirculating chillers into our teaching laboratories. These units, which require only five litres of water to fill the tank, allow for continuous, closed-loop, circulation of coolant (10°C), thus enabling students to carry out substantial synthesis experiments in a safer and far less wasteful way.
Students can also learn about alternative equipment choices. For the past year, we have been using air condensers for reflux reactions to reduce reliance on water-cooled systems. In their current form, these are most suitable where the reaction temperature is below that of the solvent boiling point, but we are now exploring more flexible designs that could broaden their use further.
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In collaboration with Dixon Glass, we have tested a prototype air condenser intended not only for reflux but also for distillation. The model is now being refined for further testing and, if successful, could soon support a much wider move towards air condensers across synthetic teaching laboratories. Adaptations such as this help students to understand that sustainability is not only about following set rules; it is also about choosing appropriate apparatus for the task in hand.
Another important lesson concerns scale. In more research-like practical work, students are often given greater autonomy over how they carry out a reaction. For example, in our third-year “synthesis project”, students carry out a multi-step synthesis of a target molecule. As part of this, they must research and choose appropriate starting materials before submitting an order form based on their proposed synthetic route. In doing so, they must consider and then justify both the quantities required and the associated costs of the materials, reinforcing the importance of working on an appropriate scale. This encourages them to produce only the quantity of material needed for their practical and analytical work to reduce solid chemical waste, solvent use and energy consumption. This pre-lab exercise helps develop the habit of treating scale not as an automatic decision, but rather as a critical part of responsible experimental design.
Make sustainability part of scientific laboratory identity
Another way of highlighting sustainability in teaching laboratories is to embed it in the culture. UCL’s laboratory efficiency assessment framework (Leaf) scheme can support with this. It is now used by 85 institutions across the sector, including ours.
Within our department, Leaf has helped to formalise efforts to minimise unnecessary chemical purchasing and use, improve equipment energy efficiency and reduce waste across teaching spaces. Lab 360, the third-year undergraduate teaching laboratory, became the first teaching lab at our university to achieve Gold Leaf accreditation in 2023 and successfully revalidated this in 2026; a second has followed. This matters not only as a mark of good laboratory management, but also because it shows students that sustainability is not an optional add-on to practical work. When sustainable practice is visibly embedded in the standards, systems and expectations of the laboratory, it becomes part of what students understand to be professional scientific practice.
The measures outlined in this series should not be seen as the final word on sustainable laboratory teaching. They are important steps in the right direction, but there is still more to do. Sustainable lab practice must remain an ongoing process of review, reflection and improvement. In the end, the aim is not to claim that the problem has been solved, but rather to keep building sustainability into the culture and everyday practice of laboratory teaching.
Rebecca L. Jones is a teaching fellow and theme lead: sustainability; Sara Thayammal and Fatema Khatun are senior teaching technicians; Roberta Stinga is a teaching technician. All work in the department of chemistry, Imperial College London.
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