ธนารักษ์ ป., เพชรสุวรรณ ว., and ขาวสะอาด ณ. “The Factors Affecting Biogas Usage of Restaurants in Phitsanulok Municipality”. Progress in Applied Science and Technology, vol. 7, no. 1, Apr. 2017, pp. 105-14, https://ph02.tci-thaijo.org/index.php/past/article/view/243117.