Apr 1, 2024 · 2.2. Fermentation operation. The mixed sludge and chicken manure were fermented at different pH under the optimal dosage ratio. The pH was adjusted by appropriate dosage of 2 M hydrochloric acid (HCl) or 2 M sodium hydroxide (NaOH) to 3.0, 5.0, 7.0, 9.0 and 11.0, respectively.