Assessment of Aerobic Microbial Activity of Ash and Vegetable-Amended Digestate

Abstract Anaerobic digestion (AD) of organic wastes results in biogas and digestate production. The digestate from AD may fall short of vital nutrients required for an optimal plant growth due to feedstock quality. Thus, digestate amendment with biomass and aerobic metabolic activities becomes an essential process for nutrient enhancement. This study aimed to investigate the microbial quality of digestate amended with wood ash, and vegetable matter during treatment. Digestate from cattle rumen (CR), food waste (FW), fruit waste (FRW); and their combinations were obtained. The various digestates were amended with wood ash, vegetable matter and a blend of both. Amendment was carried out for a duration of 5 weeks and samples were analyzed weekly. Enumeration and identification of bacteria and fungi were carried on culture media. The rhizobacterial potential of the identified bacterial isolates was also investigated using standard procedures. The results showed high bacteria and fungal loading in the amended digestate from the first to the fourth week. Comparatively, cattle rumen and food waste digestate, amended with vegetable were highly significant with mean value of 0.8 and 0.6 respectively. The identified bacterial isolates, Bacillus subtilis, Salmonella sp, Pseudomonas sp, Proteus sp, Enterobacter sp, Chromobacterium sp Bacillus spp. and Escherichia coli were found to be involved in solubilization of phosphate, nitrogen fixation, ammonia production and induction of indole acetic acid. Specifically, digestate amended with vegetable waste improved the soil nutrient compared to the wood ash in both bacterial and fungal load. Hence, digestate amendment is crucial for nutrient enhancement, increase in carbon level and overall, improves soil nutrient.