Biogas Digestate in Vegetable Hydroponic Production: pH Dynamics and pH Management by Controlled Nitrification

Abstract

Soilless cultivation of vegetables with digestate fertilizer from biogas production as a nutrient source is a promising method for integrating food production and organic waste management. In this study, bok choy (Brassica rapa var. chinensis) was cultivated in a hydroponic nutrient film technique system with biogas digestate as the only fertilizer source. Nitrification in moving bed biofilm reactors (external and/or integrated into the hydroponic cultivation system) was employed to lower the high ammonium concentration in the digestate prior to use. Treatments with differing nitrification and digestate input strategies were compared with respect to pH dynamics, crop growth, shoot water content, and shoot mineral content. The results showed that < 20% longer cultivation time (< 1 week) gave similar yield in biogas digestate-based hydroponics as in conventional hydroponics based on synthetic fertilizers. Automatic pH control through addition of digestate resulted in similar shoot dry weight as in the mineral fertilizer reference system. It can be concluded that biogas digestate is a suitable plant nutrient source for hydroponic production of bok choy, considering productivity and circularity aspects. The combined impact of digestate ammonium content, digestate pH, and the nitrification step needs to be considered when designing a hydroponic system with biogas digestate as the fertilizer source.

Organic Waste-Based Fertilizer in Hydroponics Increases Tomato Fruit Size but Reduces Fruit Quality

“…With time, as ammonium was nitrified to nitrate, the pH again declined. A large variation in pH was also reported in the cultivation of bok choi in a closed system with an integrated MBBR (Pelayo Lind et al, 2020).…”

“…Plants grown by organic fertilization often develop stress symptoms related to the presence of phytotoxins in organic fertilizer or the accumulation of phytotoxins released by plants. For instance, bok choi plants showed reduced biomass accumulation when cultivated in a closed hydroponic system with plant-derived digestate as a fertilizer (Pelayo Lind et al, 2020 ).…”

Hydroponic horticulture using residual waters fromOreochromis niloticusaquaculture with biofloc technology in photoautotrophic conditions withChlorellamicroalgae

“…In general, for the management of effluents from BFT aquaculture, conductivity, and pH are important parameters that should be controlled. In these integrated systems, the modulation of conductivity can contribute to the diversification of vegetables, and the regulation of pH can maintain nitrification and nutrient availability (Lind et al, 2020). As an advantage, these parameters can be easily monitored by farmers with ordinary equipment to control water quality in the BFT aquaculture and NFT hydroponic systems.…”

Exploring Interactions Between Fruit and Vegetable Production in a Greenhouse and an Anaerobic Digestion Plant—Environmental Implications

“…However, higher concentrations of it can also be toxic to plants (Siddiqi et al, 2002). Specifically, tomato plants are highly sensitive to ammonia concentrations above roughly 10% of the total nitrogen, and it has been already established by many authors (Sonneveld and Voogt, 2009;Stoknes et al, 2018;Pelayo Lind et al, 2020) that a nitrification process is necessary when using digestate. It was then assumed that the liquid fraction of the digestate used as a nutrient solution went through a nitrification process with a conversion efficiency of 75% from ammonia to nitrate (Botheju et al, 2010), and a maximum dose of no more than 14 g ammonium per ton of nutrient solution, representing 9% (Voogt, 1993;Strandmark, 2017).…”