The Effect of pH and Hydraulic Retention Time on Production of Volatile Fatty Acids from Primary Sludge Anaerobic Fermentation

Primary Sludge (PS) from wastewater treatment plants contains high biodegradable organic matter and therefore can be used to produce Volatile Fatty Acids (VFAs). The produced VFAs can be utilized in biological nitrogen and phosphorus removal processes as an external carbon source. The objective of this research was to investigate the effect of pH and hydraulic retention time (HRT) on the production of VFAs from PS through the anaerobic fermentation process. The experiments were conducted in both batch and semi-continuous flow regimes using bench scale fermenters under the mesophilic temperature. The Design of experiments included the HRT of 1 – 3 days and pH range of 4.5 - 11.0 for batch and 4.5 - 6.5 for semi-continuous modes. According to the obtained results, the VFAs production increased with an increase in HRT from 1 to 3 days. For the batch study, the pH range for maximum VFAs yield was pH 6.5 –10.0 achieved at HRT of 3 days. For the semi-continuous study, the maximum amount of VFAs production was observed at a pH of 6.5 and HRT of 3 days.