Plant factories can be described as structures that facilitate the indoor cultivation of crops and are typically considered to be closed-loop (isolated) systems which are situated within the urban environment. This paper explores the extent to which external industries can be integrated with plant factories by defining an open-loop (integrated) plant factory system boundary. A multi-criteria decision-support process was developed and included the use of a mixed-indicator assessment method and the use of fuzzy Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) to account for the uncertainty associated with indicator-based assessment methods. The assessment of theoretical industrial symbiosis scenarios showed that the fuzzy TOPSIS ranking provided a clearer hierarchy of optimal scenarios, when compared to using the indicator rankings. The novelty of the paper included the clear illustration of the points of integration between plant factories and external industries, which can be used to identify alternative integration scenarios in the future. Furthermore, this paper provided detailed descriptions and motivations of the indicator scoring of theoretical industrial symbiosis scenarios so that the early phase assessment method can be used beyond the scope of this paper and can be expanded with more well-defined indicators in the future.

The use of a plant factory is typically associated with the cultivation of edible biomass for local markets within the urban environment and leads to economic feasibility being evaluated in this context. This paper explored the use of plant factories to produce biomass and value-added compounds for the biorefining industry to help frame the debate regarding the expansion of plant factory applicability to the greater biorefining value chain. Information regarding plant factory technology, crop selection for biorefining markets, and the industrial integration potential of plant factories was used to evaluate the economic feasibility of theoretical plant factory scenarios. From these scenarios, it was shown that plant factories showed economic feasibility while serving the food market and had significant potential in the biopharmaceutical market when accumulating adequate levels of biopharmaceutical products within the plants grown in the plant factories. These results suggested economic feasibility beyond the food market by selecting appropriate crops, based on plant factory and end-user market demands, and value-added compounds which could be accumulated in economically viable quantities.