[Effects of Solid Retention Time on the Phosphorus Removal and Nitrosation Granules System].

In this paper, the low C/N ratio of domestic sewage was studied, and mature phosphorus removal granules were inoculated to investigate the effect of solid retention time(SRT)on phosphorus removal and nitrification granular sludge at middle-low temperatures (14-21℃). The test showed that at room temperature (20℃±1℃), the enrichment of AOB in the phosphorus removal granules can be achieved with 30 d SRT and 5 L·(h·L)-1 aeration intensity, while the NAR was over 90%. When the temperature was lowered to 15℃ and the SRT was 40 d, the phosphorus removal performance deteriorated, and the granule structure became loose with the formation of filamentous bacteria. Relatively sufficient oxygen destabilized nitrosation and the NAR dropped by 22.4%. NOB does not have the ability to quickly adapt to environmental changes. The 12 d anaerobic starvation and sludge removal strategy weakened the relative activity of NOB and quickly restored the performance of phosphorus removal and nitrosation. Batch experiments showed that the temperature dropped from 20℃ to 15℃, and the PAOs still maintained a high oxygen utilization rate, but the SOUR of the AOB decreased by 18%. At this time, the temperature, not the dissolved oxygen concentration, restricted the ammonia oxidation ability. Controlling the sludge age to 30 d, while reducing the aeration intensity to 4 L·(h·L)-1, achieved stable operation of phosphorus removal and nitrosation at a low temperature (15℃±1℃).

[Effect of Influent Ammonia Concentration on a Biological Phosphorus Removal Granules System].

Mature biological phosphorus removal granules were inoculated into a SBR. The effect of the ammonia concentration on biological phosphorus removal granules system was investigated by increasing the concentration of ammonia in the influent. The ability of the system to withstand ammonia loading was determined. The results showed that when the influent ammonia concentration was below 45 mg·L-1, the biological phosphorus removal granule system showed good performance. The TP removal efficiency was above 96%, the COD removal efficiency was over 89%. The effluent TP concentration and COD concentration were 0.4 mg·L-1 and 25 mg·L-1 respectively. The particle size was above 950 µm and the SVI was below 45 mL·g-1. When the influent ammonia concentration was 60 mg·L-1, the removal efficiency of TP was more than 95%. The effluent TP concentration was below 0.5 mg·L-1, the particle size was 760 µm, and the SVI was 56 mL·g-1. Furthermore, the biological phosphorus removal granules partially disintegrated and the metabolism and growth of PAOs began to be inhibited in the system. When the influent ammonia concentration reached 70 mg·L-1, the removal efficiency of TP was 70%, the effluent TP concentration was about 3 mg·L-1, the particle size was 570 µm, the SVI was 75 mL·g-1, and the value of PN/PS was about 7.50. The biological phosphorus granules severely disintegrated and the metabolism and growth of PAOs was severely inhibited in the system. Moreover, as the influent ammonia concentration increased, the protein increased and polysaccharide decreased from the microbial secretion of biological phosphorus removal granules. Moreover, the value of PN/PS increased, the biological phosphorus removal granules disintegrated, the particle size decreased, the SVI increased, and the structure and function of the biological phosphorus removal granules were destroyed.

[Startup and Stabilization of Nitrosation in an Anoxic-aerobic Continuous-flow Reactor with Granules].

Matured nitrosation granules were inoculated to an anoxic-aerobic continuous-flow reactor at room temperature (17-19℃). The startup and stabilization of nitrosation with granules were studied. The results show that the nitrosation of the continuous-flow was successfully achieved with an average nitrite accumulation rate (NAR) above 95%. With the increase of the dissolved oxygen (DO) content from (3±0.2) to (4.5±0.2) mg·L-1 in the aerobic zone, the NAR remained above 95%. The effect of the hydraulic retention time (HRT) of the continuous-flow reactor was investigated. The short HRT (8.4 h) sped up the circulation of the sludge particles in the continuous-flow system such that the broken granular sludge could not be integrated in time, resulting in the deterioration of granular sludge settling and the loss of sludge granules. The performance of the system was restored with the increase of the HRT to 12.2 h and the continuous-flow system stabilized. The ammonia removal efficiency and NAR were 86.7% and 96.2% on day 166, respectively.

[COD Requirement for Biological Phosphorus Removal Granule System Under Different Phosphorus Concentrations].

In this study, the effect of COD loading on a biological phosphorus removal granule system under different phosphorus concentrations was investigated by changing the concentration of total phosphorus (TP) and COD in the influent. The lowest concentration of COD for good performance of the biological phosphorus removal system under different phosphorus concentrations was obtained. The results show that when the concentration of TP was 10 mg·L-1 in the influent, the lowest concentration of COD for good performance of the biological phosphorus removal system was 175 mg·L-1. The concentration of TP in the effluent was below 0.5 mg·L-1; the particle size and SVI were 1020 µm and 36 mL·g-1, respectively; and the contents of PN and PS (by MLSS) were 78 mg·g-1 and 39 mg·g-1, respectively. Furthermore, the PN/PS was lower and the granules had good structure and performance. When the concentration of TP was 6 mg·L-1 in the influent, the lowest concentration of COD for good performance of the biological phosphorus removal system was 150 mg·L-1. The concentration of TP in the effluent was below 0.3 mg·L-1; the particle size and SVI were respectively 960 µm and 35 mL·g-1; and the contents of PN and PS were 75 mg·g-1 and 35 mg·g-1, respectively. Moreover, the PN/PS was lower and the granules had good structure and performance. The removal efficiency of COD was above 83% and the concentration of COD in the effluent was below 25 mg·L-1 throughout the operational process. Under different the influent phosphorus concentrations, the contents of PN and PS decreased, PN/PS increased, particle size decreased, SVI increased, and the structure and performance of the biological phosphorus removal granules deteriorated as the COD concentration decreased.

[Effect of Aerobic/Phosphorus Granules on Start-up of Partial Nitrification Granular Sludge].

The different effects of additional aerobic granules (AGs) and phosphorus removal granules (PRGs) on the start-up and stable operation of partial nitrification granular sludge (PNGS) were compared at room temperature(22-28℃). The results showed that in the first stage (days 0-22), partial nitrification was accomplished on day 19 for the three reactors (R1, R2, and R3). In the second stage (days 23-56), 20% AGs and 20% PRGs were added to R2 and R3 to induce PNGS. The start-up of the granules of the three reactors was successfully achieved. The mean particle sizes of R1, R2, and R3 reached 412 µm at day 76, 468 µm at day 42, and 400 µm at day 56. In the third stage (days 57-108), because the influent ammonia load increased from 0.4 kg·(m3·d)-1 to 0.5 kg·(m3·d)-1 and the COD load increased from 0.2 kg·(m3·d)-1 to 0.5 kg·(m3·d)-1, the mean particle sizes of R1 and R2 increased significantly. The average particle sizes of R1 and R2 reached 689 µm and 893 µm by the end of the operation (day 108), but sludge expansion occurred in R3. The inoculation of either AGs or PRGs could quickly achieve granulation, but the PNGS inoculated with the AGs could adapt to higher C/N and be more tolerable to shock loads and long-term stable operation.

[Effect of Different Ratios of Anaerobic Time and Aeration Time on the Formation of Partial Nitrification Granules].

Flocculent sludge with good nitritation performance and MLSS and SVI values of 3500 mg ·L-1 and 162 mL ·g-1, respectively, was inoculated in the R1, R2, and R3 groups of the same SBR reactors at room temperature (22-28℃). The effects of different anaerobic time and aeration time ratios (1:2, 1:1, and 2:1) on the formation of partial nitrification granular sludge were studied. The results showed that granules in three reactors were successfully formed at 103 d, 82 d, and 64 d. The nitrosation rate of R1, R2, and R3 were 86%, 98%, and 96%, respectively, and SVI decreased to 89, 75, and 58 mL ·g-1 and MLSS increased to 2314, 2781, and 2946 mg ·L-1, respectively, at the 85 d. The larger ratio of anaerobic time and aeration time was more conducive to sludge granulation, better settling, and nitritation performance. When the anaerobic time and aeration time ratio was 1:2, the nitritation performance of the sludge decreased since the NOB could not be suppressed, and the settling performance of the sludge became better and then worse. In addition, at the larger ratio of anaerobic time and aeration time, there was more PN and PS from microbial secretion. The PN of R1, R2, and R3 was smaller at the end of the anaerobic phase compared to that of the aerobic phase in the early stage of granular formation, but were reversed in the stabilization stage. The PS of the anaerobic phase was larger than that of the aerobic stage over the entire process.