Agronomic Performance and Phytochemical Profile of Lettuce Grown in Anaerobic Dairy Digestate

Anaerobic liquid dairy digestate is a by-product of dairy waste anaerobic digestion from dairy operations and is associated with environmental risks if not handled properly, particularly nutrient leaching losses, water contaminations, and greenhouse gas emissions. We tested the applications of anerobic digestate (AD) as a biofertilizer and water source in greenhouse vegetable production to integrate food production and industry waste management for sustainable environments. We used a deep water culture system to assess the effects of AD effluent alone, inorganic nutrient solution (NS), and a combination of AD and NS on the growth, yield, and phytonutrient profile and heavy metal contamination assessment of hydroponically produced lettuce. Lettuce produced in AD had a lower leaf area, total chlorophyll content, and fresh biomass; however, it displayed significantly higher chicoric acid (200%), chlorogenic acid (67%), luteolin (800%), quercetin-3-O-β-d-glucuronide (378%), quercetin-3-glucoside (200%), quercetin-3-O-(6″-O-malonyl)-β-D-glucoside (1077%), folate (248%), pantothenic acid (200%), total phenolics (111%), total antioxidants (44%), and soluble sugars (253%) compared to control (inorganic feed). The AD-produced lettuce also showed significantly lower heavy metal bioaccumulation risks associated with the human consumption. Based on various results, we may conclude that AD utilization in hydroponics can offer a sustainable solution to harvest a better lettuce yield, higher phytonutrients, and environmental benefits.