Anaerobic co-digestion of human excreta, food leftovers and kitchen residue: 1 ternary mixture design, synergistic effects and RSM approach

Blissbern Appiagyei Osei-Owusu; Richard Arthur; Martina Francisca Baidoo; Sampson Oduro-Kwarteng; Andrew N Amenaghawon

doi:10.1016/j.heliyon.2024.e24080

Anaerobic co-digestion of human excreta, food leftovers and kitchen residue: 1 ternary mixture design, synergistic effects and RSM approach

Heliyon. 2024 Jan 11;10(2):e24080. doi: 10.1016/j.heliyon.2024.e24080. eCollection 2024 Jan 30.

Authors

Blissbern Appiagyei Osei-Owusu¹, Richard Arthur², Martina Francisca Baidoo³, Sampson Oduro-Kwarteng⁴, Andrew N Amenaghawon⁵

Affiliations

¹ Regional Water and Environmental Sanitation Centre, Kumasi. Department of Civil Engineering, College of Engineering Kwame Nkrumah University of Science and Technology, UPO, Kumasi, Ghana.
² Department of Energy Systems Engineering, Koforidua Technical University, Koforidua P.O. Box KF 981, Ghana.
³ Department of Chemical Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana.
⁴ Regional Water and Environmental Sanitation Centre, Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, UPO, Kumasi, Ghana.
⁵ Department of Chemical Engineering, University of Benin, Nigeria.

Abstract

Anaerobic digestion of multiple substrates can generate more biogas while remaining stable, if positive synergistic effects are achieved. The type of co-digested substrates and the mixing ratio used, are the most important variables as each substrate has unique set of characteristics. Optimizing the volume ratios by testing various substrate mixing ratios is a popular method for determining the best-performing ratio of substrate mixture. The ternary mixture design has reportedly been found to quicken the process of testing different mixing ratios with high accuracy without running several experiments. Therefore, a ternary mixture design and a response surface approach are used in this work to ascertain the relationship between substrate mix and responses (biogas yield, methane yield, and synergy). The findings of the experiment revealed that R9 comprising 78.8 % human excreta, 11.8 % food leftovers and 9.4 % kitchen residue, had the highest methane production of 764.79 mLCH₄/gVS and a synergistic index of 3.26. Additionally, the 3D response surface plots from the response surface model showed important and shared interactions between Human Excreta, (HE), Food Leftovers (FLO), and Kitchen Residue (KR). HE and KR had a similar positive synergistic effect on biogas yield, methane yield, and synergy, which was not the case for FLO. The response surface plots showed that the predicted responses (methane yield, biogas yield and synergy) increased with increasing HE and KR fractions and decreased with increasing FLO fractions in the substrate mixtures.

Keywords: Anaerobic Co-Digestion; Biogas; Biogas Potential; Food Waste; Human Excreta; Mixture Design; Response Surface Method.