Novel strategy for effective utilization of anaerobic digestate as a nutrient medium for crop production in a recirculating deep water culture hydroponics system

Anaerobic digestion is considered a potential technique for substantial waste management and valorization. The residual digestate from anaerobic digestion is a promising fertilizer rich in organic content; however, the high concentrations of phytotoxic compounds are an obstacle in the application as nutrients in advanced farming methods. This study aimed at cultivating spinach (Spinacia oleracea) in a recirculating deep water hydroponic system using an anaerobic digestate (AD) as a sole nutrient medium (bioponics). Three different systems were constructed to understand the influence of pH, precolonized biofilter on nutrient availability, nitrification efficiency, plant yield, and nutrient composition. Phytotoxicity study of 5 different leafy greens against varying concentrations of AD revealed that 30% v/v AD showed the highest germination index (GI) and biostimulation effect. Spinach exhibited highest GI of 118%. Influence of pH study revealed the significance of automated pH control and the nitrification efficiency experiments demonstrated the need for a precolonized nitrifying biofilter to efficiently utilize and recover maximum nutrients from AD. The novel approach of including a biofilter component in the system increased the ammonia conversion efficiency by 48% and doubled the overall crop yield. Comparatively, the nutrient composition of the produce from the proposed system was found to be energy-dense and rich in micronutrients.