eng Science and Education Publishing Biomedicine and Biotechnology 2328-4137 2014-12-25 2 4 93 101 10.12691/bb-2-4-5 BB2014245 article C. I. Nwoye nwoyennike@gmail.com 1 I. C. E. Umeghalu 2 S. E. Ede 3 N. I. Amalu 4 W. C. Onyia 4 N. E. Idenyi 5 Department of Metallurgical and Materials Engineering, Nnamdi Azikiwe University, Awka, Nigeria Department of Agric and Bioresoures Engineering Department of Metallurgical and Materials Engineering, Enugu State University of Science & Technology, Enugu, Nigeria Project Development Institute Enugu Department of Industrial Physics, Ebonyi State University, Abakiliki, Nigeria The yield response of methane gas during microbial digestion of fruit wastes was evaluated based on the operational input ratio of organic loading rate (OLR) and hydraulic retention time (HRT). Computational analysis of generated experimental results indicates that the yield response was empirically a two-factorial quadratic model which was validated for predictive analysis and evaluation. The validity of the model; ζ = 2.1863 (ϑ/ɤ)2 - 2.4573 (ϑ/ɤ) + 0.72 was rooted on the core model expression ζ - 0.72 = 2.1863(ϑ/ɤ)2 – 2.4573 (ϑ/ɤ) where both sides of the expression are correspondingly approximately equal. Results of methane gas yield were generated using regression model and its trend of distribution was compared with that from derived model for the purpose of verifying its validity relative to experimental results. The results of the verification process show very close dimensions of covered areas and shapes designating methane gas yield, which precisely translated into significantly similar trend of data point's distribution for experimental (ExD), derived model (MoD) and regression model-predicted (ReG) results. Methane gas yield per unit input ratio OLR/ HRT were evaluated from experimental, derived model & regression model predicted results as 1.0035, 0.9893 & 0.9574 m6 Kg -2 d2 respectively. Standard errors incurred in predicting methane gas yield for each value of OLR, HRT & OLR/HRT considered as obtained from experiment, derived model and regression model were 0.1237, 0.1032 & 0.0226%, 0.1214, 0.1055 & 0.0221 % and 0.122, 0.1032 & 2.5336 x 10-5 respectively. The operationally viable deviation range of model-predicted methane gas yield from the experimental results was 3.75-15.25 %. This translated into 84.75-96.26 % operational confidence and reliability level for the derived models, as well as 0.85-0.96 yield response coefficient of methane gas to the input ratio OLR/ HRT. http://pubs.sciepub.com/bb/2/4/5/bb-2-4-5.pdf quadratic yield response methane gas input ratio of hydraulic retention time organic loading rate microbial digestion fruit wastes