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.Graphic
Highlights
In order to avoid linear use of natural resources, a circular bioeconomy approach is needed to integrate organic waste management and food production [1,2,3]
The possibility of using biogas digestate (BD) for hydroponic production has earlier been addressed from a circular bioeconomy perspective by Ronga et al [2]
The results obtained in the present study further supports this use and suggest that hydroponic production of leafy vegetables based on BD might be a viable solution for problems with digestate disposal from biogas production and increasing demand for food
Summary
In order to avoid linear use of natural resources, a circular bioeconomy approach is needed to integrate organic waste management and food production [1,2,3]. Anaerobic biodigestion fits well into the principles of a circular bioeconomy, as it allows for efficient production of storable energy, through biogas production, and fertilizer, the biogas digestate (BD), from organic waste [3,4,5,6]. High production of organic waste in urban areas and lack of nearby agricultural land of sufficient area impede the expansion and profitability of biogas and BD production [9]. If conducted in a controlled environment, soilless cultivation allows for food production independent of external climate factors [13, 14]. Food production from soilless cultivation and controlled environment agriculture can supply a platform for higher biogas and BD production in cases where arable soil scarcity, seasonality, and transportation cost to agricultural fields are limiting factors
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