Research on Ammonia Removal from Reject Water Produced from Anaerobic Digestion of Thermally Hydrolyzed Sludge Through Partial Nitrification—Anammox
2022
Wang, Guopeng | Dai, Xiaohu | Zhao, Shuheng | Zhang, Dong
Anaerobic digestion of thermally hydrolyzed sludge was an important method for sludge treatment. But a large amount of rejected water (TRW) containing high ammonia was produced, which was difficult to treat. In this study, two-stage reactors were used for TRW treatment using partial nitrification-anammox technology. The results demonstrated that nitritation initiated rapidly. The NH₄⁺–N conversion load reached 1300 mg N/(L·day) and could be further improved. The consumption of NH₄⁺–N and the formation of NO₂⁻–N were linear with time. So, the right ratio of NH₄⁺–N/NO₂⁻–N can achieve by controlling time for anammox. Dissolved oxygen and sludge concentration had important effects on nitritation. Increasing dissolved oxygen or sludge concentration can shorten the reaction time. Nitrosomonas were the dominant ammonia-oxidizing bacteria, and nitrite-oxidizing bacteria were not detected. Aerobic treatment achieved more than 50% chemical oxygen demand removal in TRW, and this water was used in an anammox reactor. Accumulated flocculent sludge could inhibit anammox activity but could be removed by increasing the flow velocity. The anammox reactor load was above 600 mg N/(L·day); even under high conductivity (18.2 ms/cm) condition, the load reached 320 mg N/(L·day), and the total nitrogen removal rate was greater than 85% under stable condition. After approximately 190 days of operation, the abundance of anammox bacteria decreased from 29% to less than 10%, but the reactor operated stably. The results demonstrated two-stage reactors were suitable for ammonia removal in TRW using partial nitrification-anammox technology.
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