Model Performance Evaluation of Continuous Stir Tank Bioreactor of Municipal Organic Solid Waste in Biogas Production
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This study presents the development, modelling, and performance evaluation of a continuous stirred tank bioreactor (CSTR) for biogas production from municipal organic solid waste (MSW). Mathematical models describing biogas yield were developed and statistically evaluated using analysis of variance (ANOVA) and response surface methodology implemented in MINITAB version 17.1. The influence of key operational parameters—pH, hydraulic retention time, and organic loading rate—on biogas yield was investigated. Results from the first-order model revealed that increasing slurry pH from 6.0 to 7.2 produced only a marginal improvement in biogas yield, as indicated by the relatively small inclination of the response line. In contrast, retention time and organic loading rate exerted pronounced effects on biogas production, with organic loading rate showing the strongest influence. The second-order (quadratic) model demonstrated superior predictive capability, evidenced by insignificant lack-of-fit, high coefficients of determination (R² ≈ 0.999), and reduced error variance. Residual diagnostics confirmed uniform distribution of errors, with maximum error frequency of approximately 5.8 occurring within standardized residuals of 0.0–1.0, indicating minimal deviation between predicted and experimental values. Overall, the quadratic model was statistically adequate for representing biogas production behaviour in the CSTR, with improved accuracy and minimal outliers.
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