Optimization of substrate mixing ratios and conditions for enhanced Biochemical Methane Potential (BMP) in small-scale biogas digesters

Moses Wonyanya; Afam Uzorka; Moses Wonyanya; Afam Uzorka

doi:10.3934/ctr.2025010

Clean Technologies and Recycling

2025, Volume 5, Issue 2: 178-197. doi: 10.3934/ctr.2025010

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Research article

Optimization of substrate mixing ratios and conditions for enhanced Biochemical Methane Potential (BMP) in small-scale biogas digesters

Moses Wonyanya ,
Afam Uzorka ^,

Department of Physical Sciences, Kampala International University, Kampala, 256, Uganda

Received: 22 July 2025 Revised: 30 September 2025 Accepted: 10 October 2025 Published: 13 November 2025

Biogas production through anaerobic digestion (AD) provides a dual solution to addressing energy scarcity and managing organic waste. However, performance strongly depends on substrate type, composition, and mixing ratios. This study evaluated the biochemical methane potential (BMP) and cumulative biogas yield (CBY) of five substrates—cow dung, swine manure, poultry droppings, food waste, and crop residues—both individually and in mixed ratios. Substrates were characterized for total solids (TS), volatile solids (VS), and pH, and performance was assessed over 15 days under mesophilic conditions. Results showed that individual substrates varied widely: food waste exhibited the highest BMP per g VS (350 ± 20 mL CH₄/g VS) but low CBY due to acidic inhibition, while crop residues, despite high TS (22.12%), produced limited methane from recalcitrant lignocellulose. In contrast, co-digestion of cow dung, swine manure, and poultry droppings in a 1:1:1 ratio achieved the most stable pH (6.9–7.3), moderate TS (11.56%), VS (63.72%), and the highest CBY (2.92 ± 0.03 m³) with BMP of 380 ± 14 mL CH₄/g VS. These findings confirm that balanced co-digestion optimizes nutrient profiles, enhances stability, and maximizes methane yield, offering practical guidelines for efficient small-scale biogas systems.
- biogas production,
- organic waste,
- substrate,
- renewable energy,
- efficiency
Citation: Moses Wonyanya, Afam Uzorka. Optimization of substrate mixing ratios and conditions for enhanced Biochemical Methane Potential (BMP) in small-scale biogas digesters[J]. Clean Technologies and Recycling, 2025, 5(2): 178-197. doi: 10.3934/ctr.2025010

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Abstract

Biogas production through anaerobic digestion (AD) provides a dual solution to addressing energy scarcity and managing organic waste. However, performance strongly depends on substrate type, composition, and mixing ratios. This study evaluated the biochemical methane potential (BMP) and cumulative biogas yield (CBY) of five substrates—cow dung, swine manure, poultry droppings, food waste, and crop residues—both individually and in mixed ratios. Substrates were characterized for total solids (TS), volatile solids (VS), and pH, and performance was assessed over 15 days under mesophilic conditions. Results showed that individual substrates varied widely: food waste exhibited the highest BMP per g VS (350 ± 20 mL CH₄/g VS) but low CBY due to acidic inhibition, while crop residues, despite high TS (22.12%), produced limited methane from recalcitrant lignocellulose. In contrast, co-digestion of cow dung, swine manure, and poultry droppings in a 1:1:1 ratio achieved the most stable pH (6.9–7.3), moderate TS (11.56%), VS (63.72%), and the highest CBY (2.92 ± 0.03 m³) with BMP of 380 ± 14 mL CH₄/g VS. These findings confirm that balanced co-digestion optimizes nutrient profiles, enhances stability, and maximizes methane yield, offering practical guidelines for efficient small-scale biogas systems.

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