Copperas supplementation during anaerobic digestion of aquaculture sludge: methane production, organic matter removal, and process optimization

Abstract Anaerobic digestion is considered an environmentally friendly approach as it converts organic waste into valuable resources such as biogas and organic fertilizers while reducing solid waste. This study enhanced methane production from aquaculture sludge under different operating parameters: temperature (30 °C, 35 °C), S/I ratio (0.5, 1.0), and iron supplement concentration (6 g/L, 10 g/L). The biomethane potential test was conducted using full factorial design to evaluate the effects and interactions of these parameters on methane production. Copperas was utilized as an iron supplement in this study due to its cost-effectiveness and ability to reduce hydrogen sulfide formation, which can hinder microbial activity. Sample 1, which had a S/I ratio of 1.0, an iron supplement concentration of 10 g/L, and a temperature of 35 °C, had the maximum methane yield, with 22 ± 6 mL/g COD removed . The ANOVA findings showed that the model was significant ( p < 0.05), with the S/I ratio ( A ) and iron supplement concentration ( B ) as significant main effects. The interaction effects between S/I ratio and iron concentration ( AB ), and between iron concentration and temperature ( BC ) were also significant. The R 2 value of 0.9959 confirmed that the model fitted well with the experimental values. These findings emphasize the potential of copperas as a sustainable and effective iron supplement to improve methane production during anaerobic digestion while supporting the waste-to-energy concept. Graphical abstract