Shock-adaptation in a three-stage anaerobic reactor treating tofu whey wastewater

Abstract

Anaerobic digestion is often used to treat wastewater with high organic content. The effectiveness of anaerobic digestion is determined by organic loading rate and hydraulic retention time, as well as influenced by temperature, pH, and wastewater composition. The multi-stage reactor system is stable towards sudden changes in the influent and fluctuations in hydraulic and organic loadings. The objective of the study was to investigate the adaptability and stability of the three-stage anaerobic reactor after a hydraulic shock loading. This study used tofu whey wastewater due to its enormous generated volume, varying COD concentration, and the low pH. A three-stage anaerobic packed-bed reactor system that had operated for 26 days at a total hydraulic retention time of 3.75 days or 1.25 day per reactor (0.33 l-wastewater per hour) was used in the experiment. The reactor was filled with wastewater at 4 l/h, twelve times the usual flow rate, for one hour. During this period, the changes in pH, COD concentration, and biogas production were monitored. Compared with the performance before the shock loading, COD and pH did not show changes after the 24-hour observation period, except for the pH in the second stage. In addition, biogas and methane production in the second stage was lower than production before the shock loading, even though the total production remained constant. This suggests that the second stage acted as the buffering reactor during the shock loading.