This thesis investigates the production of citric acid through the fermentation of Aspergillus niger, with a focus on optimizing conditions to improve yield, efficiency, and environmental sustainability. The study explores the biological and metabolic mechanisms of Aspergillus niger in citric acid synthesis, examining how parameters like pH, temperature, and nutrient availability influence productivity. A special emphasis is placed on manganese (Mn) regulation, analyzing its impact on enzyme activity and citric acid output. The research also evaluates cost-effective substrates and eco-friendly practices, aiming to make citric acid production more sustainable. Ultimately, this work contributes valuable insights into optimizing microbial fermentation processes for industrial applications.