Li, Qiang, et al. “Microorganism Population in Two-Phase Anaerobic Fermentation of Separated Liquid of Dairy Manure”. International Journal of Agricultural and Biological Engineering, vol. 11, no. 1, Jan. 2018, pp. 206-11, https://ijabe.migration.pkpps03.publicknowledgeproject.org/index.php/ijabe/article/view/3206.