Hong Kong is one of the most populous cities in the world with a density of 130,000 people per square kilometre, generating more than 6 million tons of trash per year. Waste management is particularly difficult due to the geography of the archipelago which, like other island regions, lacks space. What strategies are implemented for treating trash and wastewater? What are their limits? Our PhD student Julie Metta, under the supervision of Dr. Lin Zhang, shares her opinions with Tara expeditions, a French non-governmental organisation.