New Model Explains Waste Separation Behavior Gap

Household waste constitutes 30–40% of municipal solid waste globally. Separating waste at the household level into compostable, recyclable, and non-recyclable is a crucial first step for local governments to process solid waste effectively. However, large gaps between a person's willingness to separate waste and actually separating waste have been seen across the world. Understanding the factors that affect people's intention and behavior of separating household waste can help create more effective policies regarding household-level waste separation.

However, existing theoretical frameworks, such as the Theory of Planned Behavior (TPB), do not fully account for external factors that affect waste separation behavior. Drawing from the existing research, a team of researchers led by Professor Xuepeng Qian from the Graduate School of Global Environmental Studies (GENV) at Sophia University in Tokyo, Japan, has developed a new behavioral model for waste separation. Other collaborators on the team were Assistant Prof. Nkweauseh Reginald Longfor and Jiarong Hu, also from GENV, and Prof. Liang Dong from the Department of Public and International Affairs and the School of Energy and Environment, City University of Hong Kong. Their work was made available online on July 14, 2025, and will be published on January 1, 2026 in Volume 116 of the journal Environmental Impact Assessment Review.

According to the authors of this paper, "Researchers have no clear guidance on which external variables should be prioritized when extending TPB, and policymakers are unclear which levers are likely to yield the greatest behavioral gains," and hence the team was motivated to conduct their study.

In their study, Prof. Qian's team analyzed 46 papers on waste separation covering 30,250 participants in various geographies. The team drew from two other behavioral frameworks to understand differences in intrinsic characteristics not covered by TPB. They also looked at the effect of external factors such as waste collection infrastructure, consequence awareness, publicity and education programs, and previous recycling habits.

The team found that some intrinsic characteristics, such as a person's belief that they will be able to successfully separate waste for collection, have a large effect on their behavior. They also found that heterogeneous demographic variables, such as age, gender, and socioeconomic status, moderate the impact of intrinsic characteristics on the intention to separate waste.

Based on these findings, Prof. Qian's team has developed an expanded framework that they call the Theory of Planned Behavior + External influences + Heterogeneity or TPB + E + H. Incorporating the effects of external factors along with the three internal factors of the original TPB, increases the framework's explanatory power with regards to waste separation. They also account for the influence of heterogeneous demographic variables on the effect size of the internal factors. As a result, this is not a one-size-fits-all framework and the impact of each individual factor will vary based on local contexts.

As concluded in this research, "The proposed TPB + E + H framework provides a flexible platform for the integration of intention, external factors, and social contexts, allowing future studies to systematically incorporate policy-level and institutional variables into behavioral models… and to facilitate meaningful behavioral change," According to the team, the TPB + E + H model can guide policymakers on specific interventions that will ease and encourage greater participation in household waste separation. "Future studies can move toward more actionable, context-sensitive, and intervention-oriented models of sustainable behavior," the team describes.

Looking forward, Prof. Qian notes that a lot of the current research on waste separation behavior is from developing countries with newly established environmental policies. "Future research should actively incorporate evidence from underrepresented developed regions to build a more balanced and inclusive understanding of global waste separation behavior," the team shares.

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About Sophia University

Established as a private Jesuit affiliated university in 1913, Sophia University is one of the most prestigious universities located in the heart of Tokyo, Japan. Imparting education through 29 departments in 9 faculties and 25 majors in 10 graduate schools, Sophia hosts more than 13,000 students from around the world.

Conceived with the spirit of "For Others, With Others," Sophia University truly values internationality and neighborliness, and believes in education and research that go beyond national, linguistic, and academic boundaries. Sophia emphasizes on the need for multidisciplinary and fusion research to find solutions for the most pressing global issues like climate change, poverty, conflict, and violence. Over the course of the last century, Sophia has made dedicated efforts to hone future-ready graduates who can contribute their talents and learnings for the benefit of others, and pave the way for a sustainable future while "Bringing the World Together."

Website: https://www.sophia.ac.jp/eng/

About Professor Xuepeng Qian from Sophia University

Xuepeng Qian has served as a Professor at the Graduate School of Global Environmental Studies at Sophia University, Japan, since 2021. He completed his PhD in Engineering from Ritsumeikan University in 2007 and has published 95 papers to date. In 2022, he was awarded the Plutus Consulting Research Excellence Award by the Japan Finance Association & Pacific-Basin Finance Journal. Prof. Qian's research focuses on urban environmental planning, urban development, transportation, resource sustainability, water, energy, and lowering carbon emissions through interdisciplinary and systems approaches.