Enhancing biogas production through statistical modeling and optimization of co-digestion of water hyacinth, microalgae, and poultry manure

To support a growing population and decrease polluting emissions associated with conventional energy sources, which have mainly caused elevated CO₂ concentrations and climate change, sustainable, renewable energy sources are essential. The present study is aimed at optimizing biogas production from the anaerobic co-digestion of water hyacinth, macroalgae, and poultry manure by examining the effect of different operational parameters. Proximate and ultimate analyses of the three collected biomasses were performed, as per the ASTM standard method. Moreover, the experiment was implemented using a central composite design, and operational parameters (pH, substrate particle size, and carbon-to-nitrogen ratio) were optimized using response surface methodology. A total of 20 experimental runs were performed to map out the response surface, and results were confirmed using Analysis of Variance for the quadratic model. The present work showed that poultry manure had a richer ash content and a lower initial C/N ratio (9.55 ± 0.35) compared to the water hyacinth (17.26 ± 0.31) and macroalga (74.421 ± 0.57), where it was found that the percentage of the volatile matter for poultry manure, water hyacinth, and macroalga was 62.7, 60.95, and 55.75, respectively. Operational parameters of focus had a statistically significant effect on biogas yield, and a gain of 33.27% in biogas was observed when the pH rose from 6.8 to 7.15. Similarly, a gain was also observed in the C/N ratio when it rose from 20 to 25.2. The numerical optimization parameter showed that optimum values for biogas yield would be a C/N of 25, a pH of 7.15, and a substrate particle size of 1 mm. Under these optimum conditions, a maximum cumulative biogas yield of 8.09 L was produced, validating the effectiveness of the RSM approach. This study identified the optimal conditions for maximizing biogas yield through the co-digestion of the three biomasses, demonstrating that the process plays a vital role in achieving efficient waste-to-energy conversion.