Sardine Processing Waste: Biological Treatment Strategies and Their Implications

This study explores sustainable methods for Sardine Processing Waste (SPW) valorization. Two approaches were investigated: (a) SPW microbial pretreatment adding Saccharomyces cerevisiae or Bacillus sp. in a two-stage anaerobic digestion (AD) for enzyme and biomethane production and (b) a single-stage AD without SPW pretreatment. Both S. cerevisiae and Bacillus sp. secreted proteases (0.66 and 0.58 U mL−1, respectively) and lipases (3.8 and 4.3 U mL−1, respectively) during hydrolysis, thus reducing viscosity (2.8 and 2.9 cP, respectively) compared with the untreated SPW (4.1 cP). Biomethane production was higher in the single-stage AD (1174 mL CH4 g−1 VS−1) when compared with the two-stage AD (821.5 and 260 mL CH4 g−1 VS−1 with S. cerevisiae and Bacillus sp., respectively). S. cerevisiae addition enhanced SPW degradation as implied by VS and sCOD values (70 and 84%, respectively), but this also resulted in a higher toxicity due to a three-fold increment in NH4-N content, reducing methanogen activity. This research demonstrates the innovative application of S. cerevisiae, a common bread-making yeast, in the biotechnological enhancement of SPW hydrolysis. Non-genetically engineered S. cerevisiae not only co-produced proteases and lipases but also significantly improved solubilization, degradation, and viscosity reduction, thereby rendering the yeast a key player in solid fish waste valorization, beyond its traditional applications.