Relationship between Oxidation Reduction Potential (ORP) and Volatile Fatty Acid (VFA) Production in the Acid-Phase Anaerobic Digestion Process
Thesis DisciplineCivil Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
The purpose of this research was to investigate the relationship between the oxidation-reduction potential (ORP) measurement and volatile fatty acid (VFA) production in the acid-phase anaerobic digestion process under different conditions of temperature and residence time. Two identical anaerobic digesters were operated while VFAs, SCOD, VSS, alkalinity, ORP and pH were measured. In digester 1, VFA production of 5,556 mg/L was generated with an ORP of -315 mv at a 10 day SRT; while 5,400 mg/L of VFA with an ORP of -389 mv was recorded in digester 2. The SRT was adjusted at 5, 8, 10, 12 and 15 days and the optimum SRT was 10 days in both digesters. The results of this study indicate there were no tight relationship between VFA production and ORP values, thus ORP by itself is not a good predictor of the amount of VFAs generated. However, ORP combined with temperature had good linear relationship with VFA production. An ORP range of -315 to -390 mv was desirable for maximizing VFA production in both anaerobic digesters. Different temperatures (14, 29 and 37 ℃) were trialed and the results indicate that the conditions at 29 ℃ and 37 ℃ were not significantly different in terms of VFA production, however, less VFAs were generated at the lowest temperature of 14 ℃.