Food waste to new food: Risk assessment and microbial community analysis of anaerobic digestate as a nutrient source in hydroponic production of vegetables

Urban Farm DB summary

A study evaluating the microbiological food safety of using anaerobic digestate — a liquid residue from food-waste biogas production — as a fertilizer in hydroponic vegetable production. The biofertilizer's microbial community was analyzed via 16S rRNA gene amplicon sequencing, challenge-tested with Salmonella enterica, Listeria monocytogenes and Bacillus cereus, and assessed for microbial activity using isothermal calorimetry. The microbial community changed distinctly through a necessary initial nitrification process, with Mycobacterium as the most abundant genus. Deliberate contamination of the nitrified biofertilizer with 5 log10 CFU/mL of S. enterica or L. monocytogenes became undetectable by selective plating after 48 hours of incubation at 20°C. B. cereus was present naturally at low levels (~10 CFU/mL), and an inoculation of 5 log10 CFU/mL declined to these background levels within 24 hours at 20°C. The biofertilizer did not support microbial activity without an added external nutrient source containing an accessible carbon source and trace elements. The digestate type studied was judged microbiologically safe for hydroponic use, but the constant presence of viable B. cereus was noted as underscoring the need for continuous risk assessment whenever the fertilizer's production process is modified.