Bacteriological and Physicochemical Assessment of Digestates after Anaerobic Digestion

The demand for an alternative to inorganic fertilizer is steadily increasing due to the drawbacks associated with its usage. The utilization of digestates has gained significant recognition recently due to their remarkable benefits even after being applied to the soil. Hence, this investigation aimed to assess the bacteriological profile of digestates, effluents, and feedstock originating from various waste streams, as well as the isolates’ ability to enhance plant growth. Conventional methods were employed in the analyses. Data analysis was conducted using the Microsoft Excel package, and basic descriptive statistics were employed to interpret the acquired data. The results unveiled that the heterotrophic bacterial counts (expressed as log10 cfu/g or ml) in the digestates, effluents, and feedstock samples ranged from 4.80±0.14 (effluent samples) to 6.09±0.01 (cow dung sample). The coliform counts (log10 cfu/g or ml) obtained from the samples varied from 4.24±0.34 (effluent samples) to 5.67±0.03 (cow dung). The bacterial species isolated from the digestates, effluents, and feedstock samples comprised Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Serratia marcescens, and Klebsiella oxytoca. Among these isolates B. subtilis exhibited the highest frequency of occurrence (27.8%), while P. aeruginosa demonstrated the lowest occurrence (11.1%). Regarding the plant growth promoting characteristics (rhizobacterial properties) of the bacterial isolates, all isolates exhibited ammonia production, while Bacillus, Klebsiella, and Serratia demonstrated nitrogen-fixation capability. Overall, Bacillus and Klebsiella were positively associated with at least three out of the four tests for plant growth promotion in the study. The findings of this study revealed the importance of these bacterial isolates from the digestates as organic biofertilizer for plant growth enhanced performance, thus guaranteeing food security and safety.