[Effect of Free Nitrous Acid on the Activity of Nitrifying Bacteria in Different Sludge Concentrations Under Anoxic Conditions].

This study investigated the inhibitory effect of free nitrous acid (FNA) on the activity of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) under anoxic conditions with different mixed liquid suspended solids (MLSS). Sequencing batch reactors were used to study the changes in the activity of AOB and NOB in nitrifying activated sludge based on four different MLSS (8398, 11254, 15998, and 19637 mg·L-1), after treatment, under anoxic conditions with FNA (at an initial concentration of 1.3 mg·L-1) for 48 h. The results showed that the pH increased by approximately 0.9, but the concentration of NO2--N did not decrease significantly. With over-aeration, the concentration of NH4+-N gradually degraded to 0 mg·L-1, and the removal rate of NH4+-N gradually increased to a maximum of 4.4-6.8 mg·(L·h)-1 which time used was shorter with the increase of the inhibition MLSS. The nitrite accumulation rate was more than 92% when the sludge concentration was 8398, 11254, 15998, and 19637 mg·L-1 and with over-aeration for 0-396 h, 0-396 h, 0-372 h, and 0-168 h, respectively. When aerated for 468 h, 468 h, 444 h, and 264 h, the NO2--N concentration and NAR decreased to 0, and NO3--N concentrations increased to their highest with the values of 42.6, 49.9, 42.9, and 47.9 mg·L-1 respectively.

[Start-up of Combined Floc-granule CANON Process and the Effects of SRT on Reactor Performance].

To shorten the start-up time of CANON process and guide the sludge dischargement in the practical project, the start-up of CANNON process and influence of different flocs SRT were studied by inoculation ANAMMOX granules of different proportions in two same specifications of SBR reactor. During the experiment, the temperature was controlled at 30℃±1℃ and pH was 7-8. The results showed that it was not good for CANON process rapid start-up when the two reactors were inoculated with 5% and 10% ANAMMOX granules respectively and the initial FA concentration exceeded 44 mg·L-1. When the two reactors were inoculated with 5% and 10% ANAMMOX granular sludge, the reactors were started-up successfully on Day 46 and Day 35, respectively. When the flocs SRT was maintained at 30 d, 90 d and un-initiative discharge respectively, the average total nitrogen removal rate could reach 0.35 kg·(m3·d)-1 stably. The quantitative PCR results of the three different flocs SRT showed that with increasing flocs SRT, the abundance of AOB was relatively stable, the abundance of ANAMMOX increased slightly, while the abundance of NOB significant increased. Therefore, it is necessary to elutriate flocs from reactor for decreasing the quantity of NOB and long-term stable operation of the CANON process.

[Start-up of Granule CANON Process and the Strategy for Enhancing Total Nitrogen Removal Rate].

To shorten the start-up time of the CANON granular sludge process and improve the total nitrogen removal rate in the engineering, the start-up method of CANON granular sludge process and the strategy for enhancing the total nitrogen removal rate were studied in an SBR reactor. During the experiment, the temperature was controlled at 30℃±1℃ and the pH was 7-8, the aeration rate and settling time were operated according to the sludge properties and effect of nitrogen removal. The results showed that the transition of the sludge properties from combined floc-granule to granule was realized after 55 d. The total nitrogen removal rate reached 0.32 kg·(m3·d)-1 and remained stable after 117 d, thus the reactor was started up successfully. With constant improvement of the aeration rate, the average NRR was maintained at 1.35 kg·(m3·d)-1 after 77 d and improvement of the process load was achieved. The results showed that there was good correlation between the NRR and DO, therefore, the NRR can be determined by observing the DO and the process can be maintained stably.

[Stability of the CANON Process Based on Real-Time Control Technologies].

In order to achieve the optimization of the CANON process, ensuring the stability of water quality and increasing the removal rate of ammonia nitrogen, the stability of CANON process water quality under real-time control was studied in the SBR reactor. During the experiment, the temperature was controlled at 30℃±1℃ and the pH was 7-8, based on the corresponding relationship between indirect parameters and nitrogen pollutants, the real-time control strategy was formulated. The results showed that when the influent ammonia nitrogen concentration was 917-1540 mg·L-1, the residual ammonia nitrogen concentration of 6 mg·L-1 can be used as the control parameter to meet the requirements of process stability but the ammonia nitrogen sensor had many problems such as high costs and large errors. The characteristic points and platforms of pH, DO, and ORP value can be the automatic control parameters, which can maintain the long-term stable operation of the CANON process and ensure that the average ammonia nitrogen removal rate is above 99% and the effluent quality is stable.