Heriyanti, Septina Is, et al. “Scale Up of Biogas Starter Production: Enrichment of Activated Sludge from Biogas for Bio-Hydrogen Production”. Jurnal Ilmiah Teknik Kimia, vol. 5, no. 2, July 2021, pp. 115-23, doi:10.32493/jitk.v5i2.11101.