Phowan, N. “Methane Production from the Effluent of Bio-Hydrogen Fermentation Process by Anaerobic Sludge Using Statistical Method”. Journal of Advanced Development in Engineering and Science, vol. 2, no. 4, Aug. 2023, pp. 21-30, https://ph03.tci-thaijo.org/index.php/pitjournal/article/view/778.