Post-Inoculation Drying and Storage Effects on HAB Viability and Nutrient Retention in Biochar

BACKGROUND/OBJECTIVES: The effects of thermal drying on the viability of beneficial microorganisms immobilized in biochar, as well as on biochar nutrient retention, remain insufficiently understood. This study aimed to evaluate how drying temperature influences the survival of hyper-ammonia-producing bacteria (HAB) immobilized on pine wood biochar and to assess the impact of subsequent storage on bacterial recovery and nutrient stability. METHODS: Biochar was inoculated with HAB and subjected to drying at temperatures ranging from 40 to 60 °C. Following drying, samples were characterized and stored for 30 days. Microbial revival was assessed through reculturing, while changes in surface functional groups were analyzed using FTIR spectroscopy. Nutrient retention, particularly nitrogen content, was also evaluated. RESULTS: Higher drying temperatures resulted in reduced immediate microbial revival during reculturing. However, samples exhibiting limited immediate recovery demonstrated enhanced revival after the 30-day storage period. FTIR analysis revealed that drying temperature modified the availability of surface functional groups associated with microbial attachment and activity. Nutrient analysis indicated only minor reductions in nitrogen retention in biochar dried at temperatures above 55 °C. CONCLUSIONS: Drying temperature significantly affects both the short-term survival and post-storage recovery of beneficial microorganisms immobilized in biochar. While elevated temperatures may initially suppress microbial activity, recovery potential during storage remains substantial. Optimizing drying conditions is therefore essential to balance microbial viability with nutrient retention in biochar-based formulations.