Biomethanization of the Mixture of Cattle Manure, Pig Manure and Poultry Manure in Co-Digestion with Waste Peels of Pineapple Fruit and Content of Chicken-Gizzard - Part II: Optimization of Process Variables

O. A. Aworanti1, S. E. Agarry2, *, O. O. Ogunleye1
1 Biochemical and Chemical Engineering Biotechnology Laboratory, Department of Chemical Engineering, Ladoke Akintola University of Technology, P. M. B. 4000, Ogbomoso, Nigeria.
2 Biochemical and Bioenvironmental Laboratory, Department of Chemical Engineering, Delta State University, Oleh Campus, Abraka, P.M.B. 22, Nigeria

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© 2017 Aworanti et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: ( This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Biochemical and Bioenvironmental Laboratory, Department of Chemical Engineering, Delta State University, Oleh Campus, Abraka, P.M.B. 22, Nigeria; Tel:+2348055529705; E-mails:,



The indiscriminate discharge of industrial waste, agricultural-biomass waste, waste of municipal, domestic and kitchen waste has negatively impacted on the environment and human health. It is very pertinent to reduce these impacts to the barest minimum through conversion of the waste to useful products. The conversion of these wastes to generate alternative energy to fossil fuel through the technology of anaerobic fermentation is one of the viable and more fascinating options for the management of waste.


To investigate the interactive effect and optimization of process parameters of temperature, total solid content and feed/inoculum ratio on the biomethanization of the mixture of cattle manure, pig manure and poultry manure in co-digestion with waste peels of pineapple fruit and content of chicken-gizzard.


Full-factorial central composite design of experiment (RCCD) of the response surface method (RSM) was adopted to assess the possible interactive effects of the process variables and the optimal parameters (i.e. optimization) for biogas/biomethane production in an anaerobic digester.


The process variables had a significant (P < 0.05) positive and negative interactive effect on the biomethanization process. A second-order quadratic polynomial regression model which is statistically significant (p < 0.0001) was respectively obtained for cumulative biogas yield (CBY), biomethane content (BC) and hydraulic retention time (HRT). Temperature of 55.2°C; total solid content of 6.25%; and feed/inoculums ratio of 1:2 were found to be the optimum values required to attain a predicted optimum values of 6.261 dm3/g CBY, 71.54% BC within a minimum 8 days of HRT. At this optimum process conditions, the experimental observed maximum CBY, and BC with a minimum HRT were found to be 6.217 dm3/g of slurry, 71.10% and 7 days, respectively.


Biogas/biomethane generation through co-substrate anaerobic fermentation of animal waste with waste of fruits constitute a reasonable and applicable renewable energy alternative and this can be optimized through response surface methodology.

Keywords: Response Surface Methodology (RSM), Hydraulic retention time, Pineapple wastes, Biomethane, Feed/inoculums ratio.