Evaluation of two statistical methods for optimizing the feeding composition in anaerobic co-digestion: Mixture design and central composite design

To investigate the feasibility of statistical methods in optimizing the feeding composition in anaerobic co-digestion, a simplex-centroid mixture design (SCMD) and central composite design (CCD) were evaluated with methane potential as the response variable. Dairy manure, chicken manure, swine manure and rice straw (RS) were selected as raw materials and two kinds of manures and RS were mixed in each blend. Each component served as an independent variable in the SCMD and CCD and involved two factors, the manure and C/N ratios. Co-digestion of three-component substrates resulted in higher methane potentials than single and two-component substrates. In response surface plots, SCMD showed the interactions among each component in the co-substrates and CCD presented the interaction between the ratio of manures and the C/N ratio. SCMD and CCD are both suitable methods for optimizing the feeding composition during anaerobic co-digestion.