The Effect of Acid Pre-Treatment using Acetic Acid and Nitric Acid in The Production of Biogas from Rice Husk during Solid State Anaerobic Digestion (SS-AD)Winardi Dwi Nugraha, Syafrudin, Cut Fadhila Keumala, Hashfi Hawali Abdul Matin and BudiyonoE3S Web Conf., 31 (2018) 01006DOI: https://doi.org/10.1051/e3sconf/20183101006