Acidogenic anaerobic digestion of primary sludge as a supplement in biological nutrient removal

Abstract

The objective of this research was to investigate the performance of acidogenic anaerobic digestion of primary sludge to produce Soluble Chemical Oxygen Demand (SCOD) by using three similar completely mixed reactors. The experimental research was a 32 factorial design with 9 running conditions at various hydraulic retention times (HRTs) and total solids concentrations. The HRTs were set at 6.12 and 24 hours, and the total solids concentrations were 5,000, 10,000 and 20,000 mg/l respectively. Based on the experimental results, the specific production rate of SCOD (SCOD/VSS). SCOD/TKN and SCOD/TP ratios were in the ranges of 0.040-0.063, 3.28-5.33 and 21.75-75.88, respectively. From the statistical analysis, the results illustrated that the specific production rate of SCOD at HRTs of 12 hours was significantly higher than at 6 and 24 hours (p<0.05), and at HRTs of 24 hours production was significantly higher than that at 6 hours (p<0.05). The comparative analysis of SCOD/TKN ratio indicated that the rate at HRTs of 12 hours was significantly higher than at 6 and 24 hours (p<0.05). The specific production rate of SCOD at total solids concentration of 10,000 mg/l was significantly higher than at 5,000 and 20,000 mg/l (p<0.05). The SCOD/TKN ratio at total solids concentration of 10,000 mg/l was significantly higher than at 20,000 mg/l (p<0.05). while the SCOD/TP ratio at total solids concentration of 5,000 mg/l was significantly higher than at 10,000 and 20,000 mg/l (p<0.05). The optimum running condition was found at the HRTs of 12 hours and the total solids concentration of 10,000 mg/l with specific production rate of SCOD, SCOD/TKN and SCOD/TP ratio of 0.062, 5.33 and 46.04, respectively. The VFA/SCOD ratio at the optimum condition was 0.50-0.55