Preliminary Research on Moss-Based Biocomposites as an Alternative Substrate in Moss Walls

Addressing urban air pollution is a pressing challenge, prompting the exploration of mitigation strategies such as urban greening. However, certain innovative greening approaches, while promising, may inadvertently incorporate unsustainable elements that undermine their eco-friendly philosophy. In this context, our research focuses on addressing the replacement of a petroleum-based filter substrate in an existing ‘green’ outdoor air purification system that utilizes ‘moss filters’, known as a ‘moss wall’. This initiative is driven by concerns about microplastic leakage from the substrate and the need to optimize the moss wall system in terms of circularity. This preliminary study presents a crucial first step, aiming to assess the feasibility of developing a circular, bio-based plate as a replacement for the existing microfiber filter substrate. The focus is on the potential of this plate to recycle moss from the system itself as raw material, ensuring structural integrity and the ability to support its own weight. To achieve this goal, a series of controlled experiments were conducted in a laboratory setting using cellulose, corn starch, and metakaolin binders. Our findings indicated that cellulose was crucial for the structural integrity, starch significantly enhanced the sample strength, and metakaolin improved the water resistance. These insights culminated in the creation of a laboratory-scale moss-based composite prototype, with moss constituting more than half of the total mass. This prototype demonstrated promising results as a starting point for a more environmentally friendly and bio-based moss wall substrate. Subsequent research efforts will concentrate on optimizing the binder and fiber composition, evaluating and improving the bioreceptivity and filter properties, conducting outdoor testing, and scaling up the prototype for practical implementation.