Pratiwi, Dzikria Sari, et al. “Synthesis of Hydrochar Cassava Peels With Hydrothermal Carbonization Method and Applications As Hard Water Softener”. Journal of Natural Sciences and Mathematics Research, vol. 7, no. 1, June 2021, pp. 34-43, https://journal.walisongo.ac.id/index.php/JNSMR/article/view/11283.