The Study On An Improved Sequencing Batch Reactor Activated Sludge Process

In this paper, an improved sequencing batch reactor activated sludge process was introduced. This process combined an anaerobic reactor with the SBR reactor, in which excess sludge of the SBR was discharged into the anaerobic reactor, and some anaerobic sludge was recycled into the SBR reactor. This anaerobic-aerobic cycling sludge digestion system is designed to treat sewage and reducing excess sludge. Throughout the experiment, an aerobic SBR reactor followed by an anaerobic reactor without anaerobic sludge recycling was run as the control group. The stage of fill、react、settle and draw respectively last for 0.5 h、6h、1 h and 0.5h, and organic sludge loading of SBR was 0.16-0.19kgCOD/kgMLSSd. The removal efficiency of SBR was high with sludge age of 30d under the above operational condition.The results showed that:(1) TOC, NH4-N and TN concentration in effluent had no significant difference between the experimental group and the control group. Removal rate of TOC was 96.4%±2; NH4-N concentration in effluent was less than 0.15 mg/L, however, TN concentration in effluent couldn’t meet the requirement of A in first grade discharge standard of GB18918-2002. TN was mainy consisted of NO3--N, which means denitrification in SBR reactor was poor.(2) Under the level of 30%、50% recycling rate, the experimental group had high removal efficiency on TP, and TP concentration in the effluent was less than 0.5 mg/L. The experimental group’s removal rate was faster that reached 0.317 mg/(L.min), while the control group’s was 0.152 mg/(L.min). The possible reason could be that the recycling anaerobic sludge can increase PAOs in SBR reactor.(3) The recycling of anaerobic sludge was found to help to improve settling properties of the sludge in the SBR. Microscopic examination showed that the zoogloea structure of the experimental group was more compact. Because anaerobic sludge particles adhered to the zoogloea, and increased the density of the sludge, thus leading to good settling sludge property.(4) The experimental group with 50% sludge recycling rate discharged 12.23 g sludge, and sludge yield was 0.106 gMLSS/gCOD which was 47% less than the control group. Sludge recycling made experimental group’s sludge age extended, which could explain why sludge was reduced. Soluble components (including soluble proteins and polysaccharides) in anaerobic sludge digestion of the experimental group were higher, as compared to the control group. It showed that sludge reduction was related to cell lysis, the experimental group had more microorganism lysis. NO3--N or NO2--N concentration in anaerobic sludge digestion was observed to be negligible, indicating denitrification in anaerobic reactor was strengthened.(5) Absorption property of SBR sludge was studied. It showed that in the initial 15 min absorption rate in terms of TCOD removal was 7.838 mg/(g · min) and 5.136 mg/(g · min) for the experimental and control group, respectively. The absorption capacity of the experimental group was lower than that of control group. In addition, adsorption rate constant for TCOD and SCOD were 0.043 and 0.037 for the experimental group while 0.093 and 0.083 for the control group.The advantages of this improved SBR process are of less sludge discharge, simple process flow, easy operation, low effluent concentration in terms of TOC、NH4-N and TP, by which its engineering perspective is bright and broad.