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From waste to energy and fertilizer: Optimizing laying hen manure valorization via anaerobic digestion and composting in Benin Republic, West Africa

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Author Affiliations

  • 1Université Nationale des Sciences, Technologies, Ingénierie et Mathématiques, Benin and Laboratoire de Chimie Physique, Matériaux et Modélisations Moléculaires, Benin
  • 2Faculté des Sciences Agronomiques, Université d'Abomey-Calavi, Benin
  • 3Université Nationale des Sciences, Technologies, Ingénierie et Mathématiques, Benin and Laboratoire de Chimie Physique, Matériaux et Modélisations Moléculaires, Benin
  • 4National Institute of Agricultural Research of Benin
  • 5Institute of Urban Environment, Chinese Academy of Sciences, China
  • 6Institute of Urban Environment, Chinese Academy of Sciences, China
  • 7Université Nationale des Sciences, Technologies, Ingénierie et Mathématiques, Benin
  • 8Faculté des Sciences Agronomiques, Université d'Abomey-Calavi, Benin

Int. Res. J. Environment Sci., Volume 14, Issue (4), Pages 20-32, October,22 (2025)

Abstract

This research assesses the potential of composting and anaerobic digestion (AD) to convert laying hen manure into valuable resources in Benin Republic, offering solutions to pressing environmental and agronomic issues. Field surveys revealed that 85% of farms use litter systems, producing 38.5 tons/month of manure, primarily managed by direct spreading (95% of farmers), leading to plant burns and ammonia emissions. Physicochemical analysis showed litter manure (LM) had higher organic matter (OM: 16.2% vs. 5.7%) and potassium (1.22% vs. 0.61%) than battery manure (BM), but both exhibited low nitrogen (<1%) and imbalanced C/N ratios (5.4 - 15.8). Composting with sawdust improved C/N (17.5) and OM (37.9%), meeting fertilizer standards. AD of LM yielded 32.6m³ biogas/ton, significantly outperforming BM (3.4 m³/ton). Kinetic modeling identified the modified logistic model (R² = 0.993) and first-order kinetic model (R 2 = 0.999) as best describing biogas production, respectively for LM and BM, with LM showing biphasic degradation of complex organics. Temperature profiles confirmed efficient composting, with thermophilic phases (>55°C for 15 days) ensuring hygienization. The results underscore the promise of a dual-output system that generates renewable biogas alongside nutrient-rich compost. Optimal amendments included LM (C/N 15.8, OM 16.2%), composted BM (N 1.64%, OM 34.7%), and sawdust-amended LM compost (OM 37.9%, C/N 17.5). Digestates required further composting (N 0.07%, C/N 43.4). These findings advocate for replacing direct spreading with circular economy approaches, emphasizing scalable C/N adjustment and substrate optimization for West African contexts. Future research should pilot these methods with techno-economic analyses to facilitate adoption.

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