[Effect of HRT on Denitrifying Phosphorus and Nitrogen Removal in Modified A2/O-BAF].

The effect of hydraulic retention time (HRT) on denitrifying phosphorus and nitrogen removal in a modified two sludge A2/O-BAF system was studied. The influent COD, NH4+-N, and TP were 189.6, 60.4, and 5.1 mg·L-1, respectively. When HRT was 9, 8, 7, and 6 h, the average effluent COD was less than 42 mg·L-1. The average effluent NH4+-N levels were 2.4, 2.8, 3.3, and 6.5 mg·L-1, respectively. The average effluent TP values were 0.3, 0.4, 0.7, and 0.8 mg·L-1, respectively. The ratio of the denitrifying phosphorus accumulation organisms (DPAOs/PAOs) in the system of anoxic zone was reduced from 76.8% to 48.8%. When HRT was 8 h, the ratio of denitrifying phosphorus to nitrogen (ΔPO43-/ΔNO3--N) was increased by 37.5% by a mathematical statistics method. The ΔPO43-/ΔNO3--N in the anoxic zone was 1.24 (the theoretical value is 1.41). At this time, the effect of denitrifying phosphorus to nitrogen was the best. The SVI value was lower than 100 mL·g-1 throughout the experiment, and the MLVSS/MLSS gradually decreased from 0.74 to 0.63, indicating that the sludge activity was reduced.

[Effect of Aeration Rate on Shortcut Nitrification Recovery in Intermittent Aeration Mode].

Shortcut nitrification sludge, which was set aside for two months, was recovered using Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ. The aeration rates of Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ were 120, 100, 80, and 60 L·h-1, respectively, while treating real domestic sewage, and the ratio of aerobic/anoxic was 30 min/30 min at the temperature of 25℃. The influent of ammonia was 50-80 mg·L-1, and the concentration of effluent ammonia was stable, at below 5 mg·L-1, after the 12th, 18th, 21st, and 21st cycles. The removal ratio of ammonia nitrogen was about 95%. The highest concentrations of nitrite for Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ were 20.83, 22.81, 21.50, and 20.73 mg·L-1, respectively, which occurred in the 30th, 35th, 38th, and 42nd cycles, respectively. The concentrations of effluent nitrate were lower than 0.5 mg·L-1, and the nitrite accumulation rates were higher than 99%. The activity of ammonia-oxidizing bacteria (AOB) increased gradually and finally stabilized at 100.00%; however, the activity of nitrite-oxidizing bacteria (NOB) was gradually inhibited. The recovery of shortcut nitrification was achieved successfully in the different aeration modes.

[Effect of Step Feed on Denitrifying Phosphorus and Nitrate Removal in a Modification of the Two Sludge A2/O-BAF System].

A modification of the two sludge A2/O-BAF system was used to treat low C/N real domestic sewage. In order to improve the utilization of the carbon source, the effects of two step feeds (pre-anoxic zone and anoxic zone) on denitrifying phosphorus and nitrate removal were studied. According to the formula of material balance for COD, the utilization of carbon source was analyzed and evaluated under different ratios of step feed, simultaneously. The results showed that when the ratio of step feed was 7:3 and the influent concentrations of COD, NH4+-N, TN, and TP were 174.99, 58.19, 59.10, and 5.15 mg·L-1, respectively, their effluent concentrations were 29.48, 4.07, 14.10, and 0.40 mg·L-1, and the removal rates were 82.12%, 92.76%, 75.45%, and 91.20%, respectively. It was found that when the ratio of the denitrifying phosphorus accumulation organisms to the phosphorus accumulation organisms(DPAOs/PAOs) was 98.81%, the efficiencies of denitrifying phosphorus and nitrate removal were optimum. By optimizing step feed, the carbon source was utilized effectively, and the efficiencies of nitrogen and phosphorus removal were improved simultaneously. The theoretical basis has thus been provided for the modification of the two sludge A2/O-BAF system to treat low C/N waste water.

[Effects of Temperature on Shortcut Nitrification and Nitrification Activity of Nitrification in an Intermittent Aeration Sequencing Batch Reactor].

Real domestic sewage was treated with sequencing batch reactors (SBR). The aerobic/anoxic modes were alternated 4 times at 30℃ and 7 times at 18℃ in a single-cycle, respectively, and the ratio of aerobic/anoxic cycles was 30 min/30 min. The influent concentration of ammonia and nitrite was 61.44 mg·L-1 and 0.77 mg·L-1, respectively. After the experiments were run for 61 and 90 cycles, the effluent of the ammonia was 0.68 mg·L-1 and 1.28 mg·L-1 and the removal rate for ammonia was 98.94% and 99.57%, respectively. The nitrite concentrations were 20.57 mg·L-1 and 20.18 mg·L-1, and the nitrite accumulation rate reached 95.92% and 99.58%, respectively. During shortcut nitrification, the activity of the ammonia oxidizing bacteria (AOB) increased gradually before finally stabilizing at 100.00%, however the activity of nitrite oxidizing bacteria (NOB) increased first and then decreased gradually, the activity of AOB exceeded NOB at 32 and 74 cycles respectively, where the AOB became the dominant bacteria and the activity of NOB was completely inhibited at 61 and 90 cycles.