Edem, I. E., and O. A. . Adebimpe. “A Taguchi fractional factorial design approach to assessing Cattle-Poultry-Hog manure mix ratio influences on biogas yield”. Engineering and Applied Science Research, vol. 51, no. 3, May 2024, pp. 419-33, https://ph01.tci-thaijo.org/index.php/easr/article/view/255284.