Waste management in urban areas.
The production of waste is an inevitable consequence of life on Earth and the functioning of human economies. Over time, living systems have adapted to processing waste, and organisms such as dung beetles play a critical role in breaking down the feces of other species. However, waste management remains a major challenge within human societies.
With continued global population growth and rapid urbanization (two-thirds of humans will live in cities by 2050, according to the United Nations), our waste is fueling an increasingly serious global crisis. Microplastics cover the planet and infiltrate our bodies, sewage pollutes our waterways, and greenhouse gas emissions are driving global climate change.
“We, as a society, tend to ignore the unpleasant side of our production,” says Mingzhen Lu, assistant professor at New York University and former SFI Omidyar Complexity Fellow.
Lu and SFI Professor Chris Kempes are co-authors of a new paper published in Nature Cities that explores waste production as a function of urban systems.
Results and implications for urban planning.
“The key question is whether waste is produced more or less efficiently as systems expand and how big the recycling burden is as a result,” says Kempes.
To address this question, the authors used scaling theory to analyze waste products (municipal solid waste, wastewater, and greenhouse gas emissions) from more than a thousand cities around the world. Scaling theory has been used in biology to describe how the physiology of organisms changes with body mass and has proven relevant to understanding how waste production increases with the growth of a city.
“Scale theory allowed us to extract broad, universal patterns and transcend the individuality of each city,” explains Lu.
The resulting models show clear differences in waste production as cities grow. Solid waste increases linearly: because it is linked to individual consumption, it increases at the same rate as population growth. In contrast, wastewater production increases superlinearly while emissions increase sublinearly. In other words, larger cities contribute disproportionately more liquid waste than smaller cities, but emit fewer greenhouse gases. The findings suggest an economy of scale for emissions, as growth generally leads to more efficient energy and transportation infrastructure, but a diseconomy for liquid waste.
Cities tend to deviate from the universal law of scale as they become richer. Cities with higher GDP per capita generate more waste overall, underscoring the relationship between waste generation and economic growth.
Towards a new science of waste
The findings highlight the need for new waste science that can help predict the future state of urban ecosystems and inform policies to reduce waste and improve sustainability.
“Fungi discovered how to break down lignin waste from trees and created sustainable ecosystems that have lasted for hundreds of millions of years,” Lu says. “We take them and throw them away; we can no longer neglect plant waste in our societies.”
Environmental sustainability in cities
Mingzhen Lu and Chris Kempes’ research explores how three types of waste production (municipal solid waste, wastewater, and greenhouse gas emissions) increase with city size. This study highlights the need for better waste management strategies in growing urban areas and the development of new waste science to ensure sustainability and reduce environmental impact.
Solid waste production increases linearly with population growth, while wastewater and greenhouse gas emissions increase differently. This highlights the need to improve waste management strategies in growing urban areas and the development of new waste science to ensure sustainability and reduce environmental impact.
New waste science can help predict the future state of urban ecosystems and inform policies to reduce waste and improve sustainability. Fungi have discovered how to break down lignin waste from trees and created sustainable ecosystems that have lasted for hundreds of millions of years. We, however, take them and throw them away, we can no longer neglect the waste of our societies.