PRELIMINARY STUDY ON APPLICATION OF SLUDGE DENSIFICATION SYSTEM TECHNOLOGY IN AN INVERTED AAO CONTINUOUS FLOW WASTEWATER TREATMENT PLANT

The sludge densification system technology (SDST) was applied in a wastewater treatment plant (WWTP) for engineering modification, located in Wuxi, with a designed treatment capacity of 150000 m³/d, and a sludge densification module was added in the external reflux process section to effectively improve sludge settling performance. The inverted AAO (anoxic/anaerobic/oxic) process was adopted in the WWTP with the Phase Ⅰ project (40000 m³/d) and Phase Ⅱ project (110000 m³/d), acting as the experimental group and control group, respectively. After the engineering modification, the densification module was successfully operated for 90 days in a half-scale mode, which maximum treatment capacity was 50% of the original design surplus sludge volume. The removal capacity of TN in the Phase Ⅰ project was significantly improved, and the effluent concentration decreased by 14.7% (from 6.32 mg/L to 5.39 mg/L). During the start-up stage (day 1 to 36), the settling rate of aerobic sludge increased to 1.92 m/h. In the stable and lifting stage (day 42 to 90), the settling rate and SVI₃₀ were (3.62±0.52) m/h and (49.3±5.5) mL/g, respectively, while the counterparts of sludge in the Phase Ⅱ project were (1.93±0.35) m/h and (59.3±5.5) mL/g. The densification device had a stable sludge densification effect so that the densified sludge MLSS was (19.3±2.75) g/L, and the SVI₃₀ was only (36.7±9.0) mL/g. Many small granular flocs in densified sludge were successfully observed through microscopic examination, but the degree of granulation was limited. This study found that the massive fibrous and inert inorganic matters in activated sludge were important factors affecting the operation of the densification module, while a spiral grating was added to ensure its operation. Moreover, the effects of these inorganic substances such as sand, iron salt, and aluminum salt on the system still need to be further discussed. In addition, coupling sand removal measures and adopting full coverage treatment to optimize and transform the densification module were the key to further improving the granulation degree of densification sludge. Our team has successfully applied the SDST in an inverted AAO continuous flow WWTP in China for the first time, providing an important method for the upgrading and modification of existing wastewater treatment plants.