The Characteristic And Treatment Efficiency Of Granular Sludge In An Anaerobic/Aerobic SBR System

Aerobic granular sludge has been one of focuses in the biological wastewater treatment area. In this study, a pilot-scale anaerobic/aerobic SBR was used to treat domestic sewage. The characteristics of granular sludge was investigated, as well as the efficiency of pollutants removal.The granular sludge can be cultivated with domestic sewage. Because the organic pollutants content in the domestic sewage used in this treatment was low, the diameter of the granular sludge was relatively small (average 95.79μm). The granules are tawny, looks like fine sand. The morphology of granules is nearly spherical or elliptical with dense structure and clear outline. Scanning electron microscope (SEM) showed that the shape of the granular is irregular. The bacteria were seen enclosed on the surface of the granular, and the structure of the granular was seen firmly. At steady state, the granules had an average diameter of 245.4μm and SVI of 45～55.The whole experiment process was divided into there phases including acclimati-on period, stable operation period and high COD loading rate period. During the acclimation period and the stable operation period, the average removal efficiencies of COD, NH4+-N, TN, TP were 65.37%, 92.93%, 37.14% and 52.76%, respectively. The high COD loading rate period lasted for 5 months. In this period, the average removal efficiencies of COD, NH4+-N, TN, TP were 91.63%, 74.02%, 68.42% and 96.41%, respectively. Most of the organics were removed in anaerobic stage with the release of phosphate. During the high COD loading rate period, the phosphorus uptake efficiency was high.In order to find a better operating condition, the effects of various DO, water exchange rate and operation cycle were studied. The removal rate of DO 2～3mg/L, DO 3～4mg/L, DO 4～6mg/L was nearly the same. The system has the best efficiency when the water exchange rate was 70%. In order to improve the nitrogen and phosphorus removal efficiency, an anaerobic stirring process was added in the aerobic process. The time of aerobic process was also prolonged.