Start-up And Stable Operation Strategy For Aerobic Granular Sludge Reactor

Aerobic granular sludge technology has been widely used in the biological treatment of municipal and industrial wastewater because of the high pollutant loading capacity, excellent sludge settling ability, strong impact resistance and less installation space. Lots of studies have been focus on physicochemical properties, microbial ecology, mass transfer and simulation model, and formtion mechanism of aerobic granular sludge, but there are still many problems such as long start-up period and poor stability of granular sludge, which restricted its practical application. Taking the lab-scale SBR as platform, the start-up and stable operation strategies for aerobic granular sludge reactor were studied in this paper. Main conclutions were as follows:1. By enhancing nitrogen and phosphorus removal and shorten the sludge settling time, the aerobic granular sludge reactor was successfully started up and achieved good performance of nitrogen and phosphorus removal. The initial sludge settling time was set at 10 min, and the loading rates of TN and TP were controled at 0.29±0.05kg·m-3·d-1and 0.066±0.010kg·m-3·d-1, respectively. After three weeks running of the reator, the removal efficiencies of TN and TP reached above 50% and 40%, respectively. In order to enhance the biological selection pressure, the sludge settling time was reduced to 5 min and the granulation significantly occurred in the reactor. The removal efficiencies of TN and TP were stabled at 84.1±4.0% and 78.77±4.4%, respectively. The analysis results of Extracellular polymeric substances(EPS)'s structure and content showed that the PN content in tightly bound EPS(TB-EPS) increased notablely during aerobic sludge granulation, and it's speculated that the PN content in TB-EPS is the key factor for aerobic sludge granulation.2. In view of the periodic deterioration in the long-running aerobic granular sludge reactor, the operation strategies of aerobic starvation and selected sludge discharge were applied for the running of aerobic granular sludge reactor. The separation of granular sludge and flocs during the sludge sedimentation was appeared rapidly after the application of aerobic starvation strategy, but the system was easy to deteriorate again and the nitrogen removal efficiency was low. The selected sludge discharge strategy was controlling the sludge retention time of the granular sludge and floes at 10.0±0.9d and 2.7±0.5d. The granular rate and nitrogen removal efficiency rapidly increasedto 75.4±2.6% and 82.9±2.0%, and the average granular diameter reached 1.98±0.06mm. The aerobic granular sludge reactor could keep stable operation in a long time.3.The influence of gradient aeration for aerobic granular sludge reactor was studied. Results showed that the poly-β-hydroxybutyrate(PHB) and EPS in aerobic granular sludge could be synthetized twice in onecycle after gradient aeration method applied. The average granular size was stabilized at about 1.2mm, and the sludge concentration was maintained at 13.38±1.15mg·L-1. The aerobic granular sludge reactor was stable.4. In order to improve the feasibility of practical application of aerobic granular sludge process, five kinds of storage technologies of aerobic granular sludge such as anaerobic ex-situ storage (-20℃freezed in the PBS; 4℃PBS; 4℃refrigerated in the nutrient solution) and aerobic in-situ storage (high and low gas velocity at room temperature), were studied in the paper. Results showed that the aerobic granule was greatest destroyed under the condition of -20℃freezed in the PBS. The sludge granulation rate decreased to approximately 65% under aerobic in-situ storage,but the microbial activity and structural integrity of aerobic granule were still high. Futhermore, microbial activity of aerobic granule treated by all of the storage methods, could be recovered in a short period, especially after aerobic in-situ storage. In summary, through controlling superficial gas velocity for fitly granular sludge suspension the microbial activity could been quickly recovered after aerobic in-situ storage and the aerobic granular sludge reactor could keep stable operation again.