Extended use and optimization of struvite in hydroponic cultivation systems

Hydroponic systems are an attractive form of urban agriculture due to their low weight load, inert substrate conditions, and overall better control of plant nutrition and growth. However, gaining urban food sovereignty cannot be at the cost of increasing environmental impacts, such as eutrophication and nonrenewable resource depletion, associated with phosphorus fertilizer use. Struvite, a wastewater byproduct, is a potential slow-releasing P source that can serve as a substitute for mineral P fertilizer. In this study, we explored the adequacy struvite in hydroponic systems, testing different quantities (5 g, 10 g and 20 g per plant) compared with monopotassium phosphate for pepper and lettuce hydroponic production. The results show competitive productions for both crops with the use of struvite, especially during the first lettuce harvest (225.5 g, 249.9 g, 272.6 g, and 250 g for 5 g, 10 g, 20 g and control, respectively) where a greater struvite dissolution was seen. Although all struvite treatments in pepper show low phosphorous content in the biomass, yields do not deviate greatly from the control (3.6 kg, 4.3 kg, 7.5 kg and 5.3 kg for 5 g, 10 g, 20 g and control, respectively). The environmental performance of all lettuce treatments showed a reduction in all impact categories, especially freshwater eutrophication and mineral resource scarcity, except for marine eutrophication. All impact categories were reduced for all pepper treatments with 10 g and 20 g of struvite. When the results are extrapolated to a full year of production, we find that the slow dissolution of struvite can sustain competitive production with an initial 20 g, with less impact in all categories except marine eutrophication