Bioprocessing of cardboard waste for cellulase production

Waste paper, a major source of cellulosic biomass, could be utilized as a potential substrate for cellulase production. In this work, different pretreated waste papers were used as substrates for cellulase production. Among them, cardboard treated with 0.1% H₂SO₄ was found to be the best substrate for cellulase production by Bacillus subtilis S1 (Accession number MG457704). The optimization of the culture conditions for cellulase production was performed using the Plackett-Burman design (PB) and response surface methodology (RSM). The factors considered for PB design were cardboard concentration, yeast extract, inoculum concentration, cultivation temperature, and pH, with cellulase activity (FPase) as a response. PB design at 30 h was highly significant (F = 0.0018 and R² = 0.99). Cardboard, yeast extract, and inoculum concentrations were the variables selected for optimization by RSM. The model with 15 runs was highly significant (F = 0.0004). The model that predicted a maximum FPase activity of 2.956 U/mL could be achieved with 7.78% inoculum concentration, 3.99 g/L yeast extract, and 25.89 g/L cardboard. The results showed that the predicted values agreed well with the experimental values. The validation experiment proved the adequacy and accuracy of model. This study demonstrates that cardboard could serve as a low-cost substrate for cellulase production.