Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 947-952 Published Online October 2012 (http://www.SciRP.org/journal/jmmce) Model for Assessment Evaluation of Methane Gas Yield Based on Hydraulic Retention Time during Fruit Wastes Biodigestion Chukwuka Nwoye 1* , Asuke Ferdinand 2 , Ijomah Agatha 1 , Obiorah Samuelmary 1 1 Department of Metallurgical and Materials Engineering, Nnamdi Azikiwe University, Awka, Nigeria 2 Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria, Nigeria Email: chikeyn@yahoo.com Received July 13, 2012; revised August 15, 2012; accepted August 25, 2012 ABSTRACT This paper presents an assessment evaluation of methane gas yield using a derived model based on the hydraulic reten- tion time (HRT) of the feed stock (waste fruits) undergoing biotreatment in the digester. The derived model; γ = e (3.5436 α + 2.0259) indicates an exponential relationship between methane yield and the HRT. Statistical analysis of the model-predicted and experimental gas methane yield for each value of HRT considered shows a standard error of 0.0081 and 0.0114% respectively. Furthermore, the correlation between methane yield and HRT as obtained from de- rived model and experimental results were evaluated as 0.9716 and 0.9709 respectively. Methane gas yield per unit HRT as obtained from derived model and experiment are 0.0196 and 0.0235 (m 3 ·kg −1 VS) days −1 respectively. Devi- ational analysis indicates that the maximum deviation of the model-predicted methane yield from the corresponding experimental value is less than 16%. It was also found that the validity of the model is rooted on the expression 0.2822 ln γ = α + 0.5717 where both sides of the expression are correspondingly approximately equal. Keywords: Model; Methane Gas Yield; Biodigestion; Fruit Wastes 1. Introduction Biowastes such bovine bones and fish scales which could find application in energy generation have also found [1] application in medicine, being developed to produce suit- able materials that act as an interface between the im- plant and tissue in the body. These materials have been proved to be biocompatible for tissue engineering. Solid wastes products such as used tires and lubricant oils which could be processed for heat energy generation have been found [2] to cause serious environmental pro- blems when littered around. Therefore the recycling or burning of these materials for heat generation and trans- mission to industries is most appropriate for environ- mental cleanliness and cheap energy supply. The need to diversify sources of energy for industrial growth has resulted to the use of various raw materials like sugarcane juice and molasses [3,4] sugar beet, beet molasses [4,5], Sweet sorghum [6] and starchy materials like sweet potato [7], Corn cobs and hulls [8,9], cellu- losic materials like cocoa, pineapples and sugarcane waste [10] and milk, cheese, and whey using lactose hy- drolyzing fermenting strains [11] for ethanol production. The possibility and potentialities in fruit wastes mi- crobial treatment, to produce methane gas used as energy source have been studied [12]. A research work in re- spect of this has shown [12] that tomato, mango, pineap- ple, lemon, and orange processing waste, yielded 0.62, 0.56, 0.77, 0.72 and 0.63 m 3 of methane gas/kg of VS respectively. Mango peel supplemented with urea was found [13] to adjust the C:N ratio to 20 - 30:1 resulting in the stability of the digester. Addition of nitrogen in the form of silkworm waste and oilseed extracts, such as neem and castor, was found [13] to increase the methane content of the biogas pro- duced. Successive addition of fruit and vegetable solid wastes on the performance of biogas digester shows that the digester was stable at a loading rate of 3.8 kg VS m −3 ·d −1 [14]. The researchers further observed that no noticeable changes in the rates and yields of biogas oc- curred as a result of minor manipulation in nutritional and operational parameters which practically helped in the functioning of the digester fed with different fruits (mango, pineapple, tomato, jack fruit, banana, and or- ange) and vegetable wastes for a considerably long time. Studies [13] carried out on Pilot plant (of volumetric capacity 1.5 m 3 and digester type KVIC) with mango * Corresponding author. Copyright © 2012 SciRes. JMMCE