Solid-state fermentation (SSF) process appears to be an efficient way to recover and valorise organic residues from industries and to generate other products of industrial significance, such as enzymes. As the reproducibility of SSF is one of the main drawbacks in the development of this process, a complete study on this point was carried out. Materials with high nitrogen content, soy waste (SW) and hair waste (HW), were treated by SSF to obtain both proteases for different uses and a stabilized material for soil amendment. The bench scale reactors used in the experiments had a 4.5 l volume. Eight and five experiments were performed with the SW and HW, respectively, over a period of 2.5 years with different batches of each material. The highest production of proteases was observed after 3 days and after 14 days of fermentation, for soy and hair wastes, respectively. In the case of hair waste (HW), the overall CV was close to 4.0% for both the maximum protease activity (PA) and the maximum specific protease activity (sPA). In the case of SW, the overall CVs recorded were 43% and 18.6% for the maximum PA and the maximum sPA, respectively. This demonstrates that SSF can be a reproducible process in bench scale reactors. This is the first study and a help to researchers to develop SSF experiments in a consistent and conclusive way.Solid-state fermentation (SSF) process appears to be an efficient way to recover and valorise organic residues from industries and to generate other products of industrial significance, such as enzymes. As the reproducibility of SSF is one of the main drawbacks in the development of this process, a complete study on this point was carried out. Materials with high nitrogen content, soy waste (SW) and hair waste (HW), were treated by SSF to obtain both proteases for different uses and a stabilized material for soil amendment. The bench scale reactors used in the experiments had a 4.5 l volume. Eight and five experiments were performed with the SW and HW, respectively, over a period of 2.5 years with different batches of each material. The highest production of proteases was observed after 3 days and after 14 days of fermentation, for soy and hair wastes, respectively. In the case of hair waste (HW), the overall CV was close to 4.0% for both the maximum protease activity (PA) and the maximum specific protease activity (sPA). In the case of SW, the overall CVs recorded were 43% and 18.6% for the maximum PA and the maximum sPA, respectively. This demonstrates that SSF can be a reproducible process in bench scale reactors. This is the first study and a help to researchers to develop SSF experiments in a consistent and conclusive way.
