The whole subject of waste is characterised by contradictions. It is unglamorous, yet offers huge potential to achieve very desirable closed-loop systems. It is largely ignored by designers, yet projects that explore this area demonstrate wonderful ingenuity. Much more value can be made from the same resources, while moving towards zero waste. Biological systems teach us to see waste as an opportunity: a vital lesson. Cities involve vast resource flows and in a linear system these become waste or they build up as stocks which, in the absence of good design, will ultimately become waste as well. The waste water was used for cultivating Spirulina algae, rich in protein and micronutrients and therefore effective at combating malnutrition. The production of caviar from the sturgeon demonstrated the potential to turn a waste material into a high-value product while yielding social, economic and environmental benefits.