Statistical Optimisation of Medium Constituent Variables for Biogas Production from N-acetylglucosamine by Clostridium beijerinckii and Clostridium paraputrificum
Owoh, Barnabas Chinyere
Statistically based experimental designs were applied to optimise medium constituent for biogas production utilizing N-‐acetylglucosamine as a carbon source for Clostridium beijerinckii and Clostridium paraputrificum. The important medium constituents influencing total biogas produced, identified by the Plackett and Burman method, were FeSO4.7H2O and initial pH for C. beijerinckii cultures whilst for C. paraputrificum cultures N-‐acetylglucosamine, L-‐ cysteine.HCl.H2O and MgCl2. A one factor L-‐cysteine.HCl.H2O optimization design was applied to investigate the ideal concentration of L-‐cysteine.HCl.H2O required to achieve an anaerobic environment for optimum C. beijerinckii total biogas production. The Method of Steepest Ascent was then employed to locate the optimal area of the significant medium variables. Using the Box-‐behnken method, experimental results showed that there were significant linear effects of independent variables, N-‐acetylglucosamine for C. beijerinckii cultures and for C. paraputrificum cultures N-‐acetylglucosamine, L-‐cysteine.HCl.H2O and MgCl2 on total biogas volume. Significant curvature or quadratic effects of N-‐ acetylglucosamine and L-‐cysteine.HCl.H2O were identified for C. paraputrificum cultures. There were no significant interaction effects between medium constituent variables on resulting biogas volume. The optimal conditions for the maximum volume of biogas produced for C. beijerinckii cultures were 21 g/l of N-‐ acetylglucosamine, 0.1 g/l of FeSO4.7H2O and initial pH of 6.11 and for C. paraputrificum were 29 g/l of N-‐acetylglucosamine, 0.27 g/l of L-‐ cysteine.HCl.H2O and 0.4 g/l of MgCl2. Using this statistical optimization strategy, the total biogas volume from N-‐acetylglucosamine utilization increased from 150 ml/l to 6533 ml /l in the C. beijerinckii cultures and 100 ml/l to 5350 ml/l in the C. paraputificum cultures. The maximum yield of bio-‐hydrogen by C. paraputrificum from N-‐acetylglucosamine was 2.55 mol of H2 / mol of N-‐ acetylglucosamine and by C. beijerinckii was 2.43 mol of H2 / mol of N-‐ acetylglucosamine.