Improving efficiency for vertical aquaponic farms : a combined approach of life cycle assessment and light quality management

Abstract

Vertical farming has attracted a lot of attention since it can significantly increase plant productivity and land-use efficiency by combining hydroponic and multiple-layer planting units. Plant growth in a vertical farming system relies on chemical nutrient solutions. The Aquaponics system integrates the hydroponic and recirculating aquaculture, using fish excrement as nutrient for vegetable growth. To date, the integration of vertical farming with aquaponics systems has rarely been reported. In this study, we built a small scale vertical aquaponic system and compared its environmental burden and ratio of investment and return with Open Field Agriculture (OFA) and Controlled Environment Agriculture (CEA) systems by using a cradle-to-gate Life Cycle Assessment (LCA) method based on a monetary functional unit. The result shows that the vertical aquaponic approach the wished-profit, with low environmental impacts, compared with other systems when running in a land-scarce city, such as HK. By analyzing the LCA of the vertical farming system, we found that light plays a dominant role in manipulating plant development, morphology and resource use efficiency in vertical farming systems. LED is superior to conventional lighting technologies, such as high-pressure sodium (HPS) fluorescent light (FL), and tuning of the light intensity and spectra can be achieved by combining LED with informatics tools. However, experiments on the plant growth under different light recipes, which included five important light components (B, R, G, Fr, UV), have not been reported in the literature. Therefore, this research is aimed at developing a light recipe containing five spectra components for lettuce growth. And moreover, explores how single-light-component-induced light intensity change affects lettuce growth. Furthermore, introducing a new research method for light intensity experiment, an orthogonal method is applied with intelligent LED panels which integrate five dimmable-controlled spectra components. The result shows that plant growth response is more significant at optimal light intensity. The insufficient intensity of a single light component will result in a decrease in plant development. With few exceptions, over-dosed light components generally inhibit plant growth, which can also guide people who are engaged in CEA work. For example, a blue-light-induced light intensity increase promotes the fresh weight of lettuces by increasing the water content in the leaves. Plant growth is significantly sensitive to UV-A and a small dose of UV-A could improve plant growth.

Date of Award	2021
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Guanghao CHEN (Supervisor) & Li LING (Supervisor)