Improved biofertilizer properties of digestate from codigestion of brewer’s spent grain and palm oil mill effluent by manure supplementation

Abstract

Abstract The biofertilizer quality of anaerobically codigested agroindustrial residues from brewer’s spent grain and palm oil mill effluent was evaluated after supplementation with different livestock manure in order to validate its use as organic fertilizer. Manure supplementation assay was performed using different animal manure-inoculum to demonstrate the influence of inoculum-type on the nutrient status, plant growth promoting bacteria (PGPB) and other plant growth promoting attributes of the resultant digestate. In addition to elevated nutrient levels (K > P > Ca > Mg > S > N), the plethora of essential microbial groups (phosphate solubilizers > diazotrophs > auxin producers) that enhance nutrition and promote plant growth was evinced in the supplemented digestate compared to the control. On the other hand, environmental risk assessment revealed a notable yet inadequate reduction in indicator bacteria and putative pathogens (> 3.0 log CFU mL− 1) with potentially toxic elements within publicly available requirements. The preponderance of PGPB with excellent biofertilizing attributes observed in this study could be leveraged upon by plants thus substantiating its potential for use as organic fertilizer. However, the presence of pathogens highlights the importance of post-treatment hygienization to eliminate its biosafety risk.

Keywords

• PGPB
• Manure supplementation
• Biofertilizer
• Environmental risk
• Digestate