Optimizing Methane Production from Co-digestion of Cassava Biomass and Winery Solid Waste Using Response Surface Methodology

  • Unathi Mkruqulwa
  • Vincent OkudohEmail author
  • Oluwaseun Oyekola
Original Paper


Renewable energy security for the future and better use of natural resources are key challenges that can be concurrently managed by a practical anaerobic co-digestion approach where substrates with a high carbon/nitrogen (C/N) ratio are combined with lower ones to create a balance of the nutrients during the production of methane. This study determined the optimal conditions for methane production from anaerobic co-digestion of cassava biomass (CB) and winery solid waste (WSW) using response surface methodology (RSM). A three-factor central composite design was used to set-up the anaerobic co-digestion experiments. The individual and interactive effects of temperature (25–45 °C), pH 6–8 and a range of substrate (CB/WSW) ratios (0–100) on the methane yield were explored. Optimisation using RSM showed a close fit between the predicted and experimental data as indicated by the coefficient of determination (R2) value of 0.9521. The RSM model predicted a maximum methane yield of 346.28 mL CH4/g VSadded for the optimal conditions of pH 7, temperature of 35 °C ± 0.5 and 70/30 ratio of CB/WSW. The verification experiment produced 396 mL CH4/g VSadded, 12.6% higher than the predicted value at the same conditions. Although, there was a gap between the predicted and actual yield, the significance of the variables in the analysis of variance (ANOVA) shows the model could be relevant to similar research. The substrate ratio at 70 CB:30 WSW was the most significant factor during methane production. The RSM model proved successful in the optimisation process of methane yield.

Graphic Abstract


Cassava Co-digestion Methane Response surface method Winery solid waste 



Cassava biomass


Winery solid waste


Central composite design


Response surface methodology


Anaerobic digestion




Greenhouse gas


United Nations


Carbon to nitrogen ratio


Zebra dung


Agricultural Research Council


Republic of South Africa


Analysis of variance


Total solids


Volatile solids


Total organic carbon


Moisture content


Inductively coupled plasma


Sodium hydroxide


Hydrochloric acid


Volatile fatty acid


Sulphuric acid



This work is based on the research supported in part by the National Research Foundation (NRF) of South Africa for the Grant, Thuthuka Unique Grant No. 99393. Our sincere thanks goes the staff of the Agricultural Research Council (ARC) Stellenbosch, the Language Editor Dr. Solani Ngobeni from the Centre for Scholarly Publishing, Mr. Taiwo Abiola for assistance in modelling and the Staff of the Research Directorate at Cape Peninsula University of Technology for their support.


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Department of Biotechnology, Faculty of Applied SciencesCape Peninsula University of TechnologyCape TownSouth Africa
  2. 2.Department of Chemical Engineering, Faculty of Engineering and Built EnvironmentCape Peninsula University of TechnologyCape TownSouth Africa

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