A phosphorus-enriched biochar fertilizer from bio-fermentation waste: A potential alternative source for phosphorus fertilizers

It is necessary to explore alternative resources for phosphorus (P) in an effort to address the lack of available P source for crops in an agricultural sector. In this study, bacterial biomass waste of Escherichia coli from a fermentation industry was converted to “P-enriched biochar”, and its possibility as a P fertilizer was assessed. Biochar yields (5.2 ± 0.74% to 19.7 ± 1.54%) highly depended on pyrolysis conditions such as initial weight of feedstock and residence time. Inorganic elemental analysis revealed that the biochar did not consist of any elements with high toxic concentration levels regardless of its yield and that it was rich in P. Biochar with lower yield showed higher water soluble P. Subsequently, a rapid P-release in water and citric acid was initially observed, and a gradual decline one day later was followed. The extractable P in water and citric acid reached 52% and 61%, respectively, of initial P content (84.7 mg g−1) in the biochar in five days. Scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) results showed that P was evenly distributed in macropore-sized biochar matrix, and the contents of P and O decreased after P release into water. Fourier transform infrared spectroscopy (FT-IR) revealed that the peaks related to phosphate form significantly decreased after P release. SEM-EDS and FT-IR results indicated that released form of P was phosphate. Hydroculture bioassay showed that biochar had a positive effect on the early growth of Lactuca sativa. This study suggested that conversion of bacterial waste to the P-enriched biochar could be a feasible strategy for recycling P source as a P fertilizer as well as valorization of wastes from fermentation industry.