Optimization of substrate mixing ratios for the anaerobic digestion of chicken manure and slaughterhouse waste: a case study of Irvine’s Zimbabwe (Pvt) Ltd, Zimbabwe

Abstract

This study investigated the biogas potential of co-digesting chicken manure (CM) and slaughterhouse waste (SW) at Irvine’s Zimbabwe (Pvt) Ltd farm. Four different mixes of CM to SW as a percentage of total solids (TS) as follow: Mix 1 (100%: 0%); Mix 2 (67%: 33%); Mix 3 (33%: 67%) and Mix 4 (0%: 100%) were considered for co-digestion using cow dung as inoculum. The mixes were characterised in terms of carbon to nitrogen (C/N) ratio, chemical oxygen demand (COD), pH, TS, and volatile solids (VS). After 15 days of digestion, Mix 1 produced the highest biogas of 51 mL/gTS (24.4 m^3/m³ feedstock) with a methane content of 30.2 mL/gTS (59.1%). The COD, pH, and TS values for the mixes after digestion ranged from 11,250 mg/L (Mix 1) to 25,000 mg/L (Mix 4), 5.54 (Mix 1) to 6.48 (Mix 4) and 11.5% (Mix 4) to 14.7% (Mix 2), respectively. Unlike findings from other studies that suggest that co-digestion increases gas production, mono-digestion of CM had the highest biogas potential and produced the most stable sludge. Therefore, mono-digestion of CM can be used for biogas production at Irvine’s Zimbabwe (Pvt) Ltd farm.

Keywords:

• Biogas
• chicken manure
• co-digestion
• methane
• slaughterhouse waste

Acknowledgements

This paper presents part of the research results of a thesis study by Clarence Farai Mapenzauswa for a BSc Degree in Civil Engineering at the University of Zimbabwe under the supervision team of Eng. Zvikomborero Hoko and Dr. Shepherd Misi and further work carried out after the thesis study by the authors. The authors are grateful to the staff of Irvine’s Zimbabwe, Mr. D. Hasluck and Mr. V. Moyo for allowing the study and for support in purchasing of the equipment used for the study. The authors would also like to acknowledge the support given by the University of Zimbabwe Department of Civil Engineering Laboratory Staff (Mr. M. Souta and Mr. O. Kativhu).

Disclosure statement

The authors declare there is no conflict.

Data availability statement

All relevant data are included in the paper or its Supplementary Information.