Algal sludge from Taihu Lake can be utilized to create novel PGPR-containing bio-organic fertilizers

• Addition of algal sludge contributed to efficient SSF with PGPR strains.
• Addition of algal sludge improved the nutrient contents in the novel BIO.
• Microcystins were rapidly degraded during SSF process.
• A high germination index value was observed.
• The novel BIO efficiently promoted plant growth.

Large amounts of refloated algal sludge from Taihu Lake result in secondary environmental pollution due to annual refloatation. This study investigated the possibility to produce bio-organic fertilizer (BIO) using algal sludge as a solid-state fermentation (SSF) medium. Results showed that addition of algal sludge contributed to efficient SFF by a plant growth-promoting rhizobacteria (PGPR) strain SQR9 and improved the nutrient contents in the novel BIO. The optimum water content and initial inoculation size were 45% and 5%, respectively. After 6 days of SSF, the biomass of strain SQR9 was increased to a cell density of more than 5 × 107 CFU g−1. Microcystins were rapidly degraded, and a high germination index value was observed. Plant growth experiments showed that the produced BIO efficiently promoted plant growth. Additional testing showed that the novel SSF process was also suitable for other PGPR strains. This study provides a novel way of high-value utilization of algal sludge from Taihu Lake by producing low-cost but high-quality BIOs.