Exploring the Environmental Performance of Urban Symbiosis for Vertical Hydroponic Farming

TLDR

Vertical farming in cities relies heavily on external materials, but urban waste streams offer a promising source of inputs for more circular food production. This study evaluates the environmental performance of using residual urban material flows in vertical hydroponic farming to promote a circular, resilient, and sustainable urban food supply. A life‑cycle assessment examined substituting conventional growing media and fertilizers with paper, compost, brewers’ spent grains, and biogas digestate in a vertical hydroponic system. Replacing conventional media yielded substantial environmental benefits, and using residual fertilizers also produced significant gains, indicating both streams can enhance circularity in hydroponics.

Abstract

Vertical farming has emerged in urban areas as an approach to provide more resilient food production. However, a substantial share of the material requirements come from outside their urban environments. With urban environments producing a large share of residual and waste streams, extensive potential exists to employ these material and energy streams as inputs in urban farming systems to promote more circular economy approaches. The aim of this article is to assess the environmental performance of employing residual material flows for vertical hydroponic farming in urban environments in order to support more circular, resilient, and sustainable urban food supply. Life cycle assessment (LCA) is used to assess replacing conventional growing media and fertilizers with urban residual streams. Paper, compost, and brewers’ spent grains were assessed for replacements to conventional gardening soil employed in the studied system. Biogas digestate was also assessed as a replacement for conventional fertilizers used in the recirculating water bath. The results suggest that large environmental performance benefits are illustrated when conventional growing media is replaced. Although not as significant, employing fertilizers from residual urban streams also leads to large potential benefits, suggesting the two residual streams have the potential for more circular hydroponic systems.