[Characterization of Sludge Morphology and Bacterial Community Evolution in the Rapid Activation of Freeze-stored PN/A Granular Sludge].

Inoculating granular sludge is an alternative method for the quick start-up of a high-performance autotrophic nitrogen removal reactor. In order to establish the response relationship between sludge activation and reactor performance, the freeze-stored granular sludge was inoculated into a continuous-flow reactor, and a control strategy of the high loading rate and high hydraulic selective pressure was carried out in this study. As a result, a one-stage partial nitritation/ANAMMOX process was started up in 34 days, and the removal efficiency of total nitrogen was over 83%, with a removal loading rate of total nitrogen of 1.67 kg·(m3·d)-1. During this period, the Image pro-plus software was employed to analyze the evolution of the characteristic dimensions of particles. A good linear positive correlation (R2=0.988) between the projected area of the erythrine zone in the inner layer and the specific nitrogen removal rate of granules was found, which provide a simple method to estimate the activity of the PN/A granules. The results of MiSeq high-throughput sequencing showed that the enrichment of aerobic ammonia-oxidizing bacteria (Nitrosomonas) and the wash-out of heterotrophic bacteria (such as Denitratisoma and Haliangium, etc.) were achieved in the start-up of the reactor. Meanwhile, the improvement in granular compactness was in favor of activating anaerobic ammonia oxidizing bacteria (Candidatus_Kuenenia, abundance>30%) that colonized the inner layer of the granules.

[Effects of Cold Acclimation on the Activity of Autotrophic Nitrogen Removal in Granular Sludge and Its Bacterial Population Structure].

Cold acclimation is an effective approach for improving the nitrogen removal performance and operational stability of partial nitritation/ANAMMOX (PN/A) combined processes at low temperatures. To explore the specific effects of cold acclimation on the characteristics of sludge, differentiations in temperature sensitivity, granular morphology, composition of extracellular polymer substance (EPS), and bacterial community structure between PN/A granular sludges cultivated at medium-high temperature (30℃) and acclimated to low temperature (15℃) were investigated in this study. The results of reaction thermodynamics showed that the nitrogen removal performance of the granules acclimated to low temperature (GL) was significantly higher than that of those cultivated at medium-high temperature (GH) under the low temperature (10-20℃), and the apparent activation energy (Ea) of total inorganic nitrogen removal for the former was decreased by 28.4%. Compared with GH, GL had a smaller average particle size of 25.8% and higher EPS contents of 16.6%, resulting in a significant lower settling property. Based on the high-throughput sequencing results, GL exhibited a higher diversity of bacterial community, and a lower relative abundance ratio (0.04) of aerobic ammonium-oxidizing bacteria (Nitrosomonas) and anaerobic ammonium-oxidizing bacteria (Candidatus_Kuenenia) than 0.34 for GH. It indicated that the PN/A granules held a strong ability to retain slow-growing autotrophic bacteria in the system, even under low temperatures. These findings could provide meaningful references for analyzing the self-adaption mechanisms of PN/A sludge to low temperature conditions and promote the industrial application of combined processes.

[Adaptability of Completely Autotrophic Nitrogen Removal over Granular Sludge to Low-Strength at Low Temperature].

A single-stage PN-ANAMMOX (PN/A) granular sludge cultured at room temperature was used to investigate the completely autotrophic nitrogen removal efficiency and microbial community structure of low-strength wastewater based on the completely autotrophic nitrogen removal over nitrite in granular sludge at a low temperature. The results showed that at the low temperature (15±1)℃, the ammonia nitrogen load was maintained at 1.29 kg ·(m3 ·d)-1, and the ammonia nitrogen concentration in the injection was gradually reduced from 70 mg ·L-1 to 40 mg ·L-1. DO/TAN was controlled at 0.22-0.25. The total nitrogen removal rate was maintained at (85±4)%, and the average TN concentration in the effluent was 8.9 mg ·L-1. There was no significant proliferation of nitrite-oxidizing bacteria (NOB) during the operation period, and the Nitrospira abundance was less than 1%. Elutriation of the floc sludge and the control of low DO/TAN values can be used as effective control strategies to inhibit NOB proliferation. Through completely autotrophic nitrogen removal over nitrite in granular sludge operated under low-temperature and low-substrate conditions, the particle size became smaller, and the color changed from brown red to brown yellow. The total amount of PS decreased slightly, and the ratio of PN/PS stabilized at 2.5-3.0. Planctomycetes and Proteobacteria dominated the community, and Candidatus_Kuenenia and Candidatus_Brocadia were two AMX bacteria in the sludge.

[Analysis of Rapid Start-up and Mixed Nutritional Nitrogen Removal Performance of Complete Autotrophic Granular Sludge].

A rapid start of the completely autotrophic nitrogen removal over nitrite (CANON) process based on granular sludge and efficient nitrogen removal under mixotrophic conditions are important steps in a continuous flow reactor for CANON engineering applications. In this study, an aged CANON granular sludge was mechanically crushed to 0.3 mm as inoculum in an airlift internal-loop reactor (AIR) to achieve simultaneous COD removal and mixotrophic denitrification of the single-stage granular sludge. The system achieved stable partial nitrification by controlling DO after 26 days of startup. Granulation and anaerobic ammonia oxidation were then promoted by shortening the HRT to increase the ammonia nitrogen load to 5.65 kg ·(m3 ·d)-1. The total nitrogen removal rate reached 58% on the 68th day. Subsequently, the C/N ratio of influent was increased from 0 to 0.25 and 0.5, which promoted the synergistic growth of AOB, AMX, and heterotrophic microorganisms. The removal rates of ammonia and total nitrogen were 95% and 85% respectively, and the removal of COD reached approximately 80%. The activity of NOB such as Nitrospira was effectively inhibited as the COD concentration was increased. q(NH4+-N) and q(TN) were stable at 0.4 g ·(g ·h)-1 and 0.34 g ·(g ·h)-1, respectively, while q(NO3--N) was approximately 0.02 g ·(g ·h)-1. Microbial diversity was observed using MiSeq high-throughput sequencing. It showed that organic carbon had no significant effect on the abundance of Nitrosomomas and Candidutus_Kuenenia, while increasing the abundance of Candidutus_Brocadia and Denitratisoma in the sludge. This study provides ideas for the rapid start of continuous flow CANON granular sludge process to treat wastewater with low C/N ratio.

[Impact of Hydraulic Retention Time on Performance of Partial Nitrification Granular Sludge in Continuous Stirred-Tank Reactor].

The effects of different hydraulic retention time (HRT) on short-cut nitrification granular sludge were studied in a continuous stirred-tank reactor (CSTR) by maintaining stable influent ammonia nitrogen load. Particle size distribution, extracellular polymeric substances (EPS), and functional bacterial kinetics were analyzed. The morphology of granular sludge, the performance of the CSTR, and the activity of functional microorganisms were investigated. The high throughout sequencing technology of MiSeq was employed to analyze the structure of the microbial community in sludge. The results showed that the ammonia nitrogen removal rate in the reactor was gradually increased from 80% to 95%, and the nitrite accumulation rate was always over 85% when the HRT was decreased from 4 h to 1 h. Particle size distribution of granular sludge was greatly influenced by HRT. The mass fraction of granules with a diameter smaller than 0.3 mm and larger than 1.6 mm was gradually declined, whereas the mass fraction of granules with a diameter between 0.3 mm and 0.8 mm was increased when HRT was shortened from 4 h to 1 h. The dominating proportion of granules with a diameter between 0.3 mm and 0.8 mm reached about 50% when HRT was 1 h. The impact of HRT on the activity of functional microorganisms was studied, and HRT activity was found to be closely related to the size of granular sludge. Proteobacteria were dominant in the system. AOB enrichment was represented by Nitrosomonas, which was more than 56%. Shortening HRT is beneficial for the enrichment of AOB.

[Start-up of a Three-stage PN/A Granular Sludge Reactor for Treating Wastewater with High Concentrations of Ammonia].

In order to apply partial nitritation-ANAMMOX (PN/A) technology to treat wastewater with high concentrations of ammonia, autotrophic nitrogen-removing granular sludge was crushed and inoculated into a three-stage continuous flow reactor. The nitrogen loading rate (NLR), dissolved oxygen (DO) concentration, and free ammonia (FA) levels in each compartment of the reactor were controlled over a 106-day period. Results showed that the nitritation process occurred with the inoculated granules during the initial phase. A limited aeration strategy was employed in the reactor at relatively high NLRs. Given the effective suppression of nitrite-oxidizing bacteria and the prevention of ANAMMOX bacteria from high DO conditions, the compact structure and nitrogen-removal activity of the granules could be improved. When the ammonia-nitrogen concentration was increased in the influent to 350 mg·L-1, the adverse impacts of high FA concentrations on the functional microbe activity in the first compartment should be eliminated. This occurs by reducing the influent pH and alkalinity dosage. This occurs by reducing the influent pH and degree of alkalinity. As a result, a total nitrogen removal rate of 7.2 kg·(m3·d)-1 was achieved in the reactor, which is 50 to 100 times higher than that of conventional activated sludge systems. The consistent improvement in the nitrogen-removal activity of the granules was demonstrated by batch testing at different aeration intensities. This showed that activity was greatest in the first compartment, which showed the highest granular maturity. In addition, a clear linear correlation (R2>0.97) was observed between the amount of extracellular polymeric substance and the specific nitrogen removal rate. This indicated that the dense granules played a positive role in enhancing the performance of the reactor.

[Start-up Performance and Sludge Characteristics of Single-stage Autotrophic Nitrogen Removal System with Granular Sludge at Low Ammonia Nitrogen Concentration at Room Temperature].

The start-up and stable operation of single-stage autotrophic nitrogen removal process under low ammonia nitrogen substrate at room temperature appears as the premise and basis for the application in municipal wastewater treatment. In this study, the PN/A (partial nitritation and ANAMMOX) granular sludge for long-term storage was inoculated into an air-lift bioreactor to investigate the nitrogen removal performance during the start-up of single-stage partial nitritation and ANAMMOX process under the following conditions:temperature at (23±2)℃, pH at 7.7-8.0. Synthetic wastewater with ammonia nitrogen concentration of 70 mg·L-1 was used as influent. By stepwise shortening hydraulic retention time (HRT) (1.1 h→0.9 h→0.7 h→0.5 h) and increasing ammonia nitrogen loading rate[1.53 kg·(m3·d)-1→1.87 kg·(m3·d)-1→2.40 kg·(m3·d)-1→3.36 kg·(m3·d)-1], the bioactivity as the synergy between the ammonia oxidizing bacteria (AOB) and anaerobic oxidizing bacteria (AMX) were gradually restored. After 95 d operation and regulation, the process was successfully established and the removal rate of NH4+-N and TN were 85% and 69%, respectively. According to the performance of sludge at each stage, the nitrite oxidizing bacteria (NOB) were selectively inhibited by controlling dissolved oxygen strictly. The average particle size gradually increased and finally was reached to 1.30 mm after the sludge was adapted to the environment. The profile of the mature autotrophic granular sludge was smooth and clear, SEM showed that the center of granular sludge formed a cavity with porous structure on the surface, the sludge morphology consisted mainly of cocci, with a small amount of bacilli and short bacilli. The major component of EPS in granular sludge was protein (81.48%) indicating that it had a good settling performance.

[Contamination Characterization and Human Exposure Levels to Polybrominated Diphenyl Ethers in Indoor and Outdoor Air in Industrial Park of Suzhou City].

Eight polybrominated diphenyl ether (PBDE) congeners in indoor and outdoor air particles were collected using higher-volume active sampling techniques from different functional areas, including an industrial workplace, office, domestic area, and scenic area in an industrial zone, in Suzhou city, and the samples were analyzed by GC-MS. The total concentration of PBDEs ranged from 9.22-64.15 pg·m-3 (average 20.93 pg·m-3), and 1.06-8.44 pg·m-3(average 5.11 pg·m-3)in indoor and outdoor air, respectively. The results showed that the concentrations of PBDEs in indoor PM10 was significantly higher than that in the outdoor PM10. The average concentrations of PBDEs in the air of the different sampling areas were in the order:industrial workplace

[Effects of Environmental Factors on the Synergy of Functional Bacteria in Completely Autotrophic Granular Sludge].

To obtain experimental evidences for optimizing a completely autotrophic nitrogen removal process based on granules, the effects of dissolved oxygen (DO) concentration, temperature (t), initial ammonium (NH4+-N) concentration, and solution pH conditions on the synergy between the aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AMX) were investigated using a single factor batch experiment, while the analysis of the microbial community structure within them was conducted using MiSeq high-throughput pyrosequencing. Results revealed that AOB (genus Nitrosomonas) and AMX (genus Candidatus Kuenenia) dominated in the granules, representing relative abundances of 32.9% and 9.8%, respectively. For the granules, the highest specific nitrogen removal rate of q(TN)=(17.7±1.0) mg·(g·h)-1 was obtained at a DO concentration of 2 mg·L-1, while the initial NH4+-N concentration was set at 100 mg·L-1. And a lower DO level resulted in partial nitritation became the rate-limiting step of process, otherwise, it would be the ANAMMOX reaction instead. According to the free energy of the reactions, the activity of AMX was more sensitive to low temperature than that of AOB. When the reaction temperature was lower than 30℃, nitrite accumulation could be observed in bulk liquid, with the significant decrease of q(TN) for the granules. Under the same oxygen supply conditions, an initial NH4+-N concentration lower than 100 mg·L-1 could inhibit the activity of AMX partly. However, with an initial NH4+-N concentration over 150 mg·L-1, either oxygen-limiting or high free ammonia concentration could lead to the dramatic decrease of q(TN). In addition, the effective synergy of the two types of ammonium oxidizers in granules was always achieved at solution pH in the range of 7.0-8.5.

[Effects of Nanoscale Zero-valent Iron (nZVI) on Denitrifying Performance of an Upflow Granular Sludge Bed Reactor].

In order to examine the effects of nanoscale zero-valent iron (nZVI) on the performance of denitrifying granular sludge (DGS) in a continuous flow model, the variations of nitrogen removal efficiency in the reactor, sludge morphology, and denitrifying characteristics at different influent nZVI concentrations were investigated in an upflow sludge bed (USB). The results showed that nZVI concentrations lower than 5 mg·L-1 did not influence the nitrogen removal performance of the reactor significantly, and the activity of DGS was improved slightly. When the influent nZVI concentration was in the range of 5 to 10 mg·L-1, the DGS could adapt to the biological inhibition of nZVI partially, with the increase of sludge concentration and grain size. However, the higher total iron contents in the sludge resulted in the lower denitrifying activity of the DGS. The removal efficiencies of COD and NO3--N in the reactor decreased to 23.3% and 20.3%, respectively, at the influent nZVI concentration of 30 mg·L-1. Moreover, the DGS was a dark color and of a smaller grain size because of the adsorption of a large amount of nZVI, while the microbe density, such as that of the bacillus species, on the granule surface decreased significantly. In the recovery phase, the nitrogen removal performance of the reactor could almost reach its initial level at nZVI=0 mg·L-1 during an operation of 20 days due to the fast growth of heterotrophic microbes on the surface of the DGS.

[High-rate Nitrogen Removal in a Two-stage Partial Nitritation-ANAMMOX Process Under Mainstream Conditions].

A two-stage partial nitritation (PN)-ANAMMOX process was successfully carried out for low-strength NH4+-N (50 mg·L-1) wastewater treatment at ambient/low temperatures. The results show that an average total nitrogen removal rate and removal efficiency above 0.6 kg·(m3·d)-1and 80% could be maintained, respectively, at temperatures between 20℃ and 14℃. The two-stage PN-ANAMMOX process was successful both under NO2--N-limited and NH4+-N-limited conditions. When the two-stage PN-ANAMMOX process was operated under NH4+-N-limited conditions, the "limit of technology" for nitrogen removal (TN<3 mg·L-1) could be easily achieved by following anoxic denitrification. Lowering the temperature to 12℃ resulted in the reduction of the total nitrogen removal rate to~0.5 kg·(m3·d)-1. Due to the low temperature, the anammox reaction became the rate-limiting step for nitrogen removal, while the PN reaction was not impacted. In the temperature range of 10-20℃, the activity-temperature coefficients (θ) of the PN granules and ANAMMOX sludge were 1.056 and 1.172, respectively, suggesting that the anammox bacteria have a higher temperature sensitivity than the ammonium oxidizing bacteria (AOB). Overall, the results clearly indicate that the nitrogen removal loading rate of the two-stage PN-ANAMMOX process is mainly controlled by the activity and quantity of anammox biomass. In contrast, the process nitrogen removal efficiency mainly depends on the performance of the first-stage PN (i.e., effluent NO2--N/NH4+-N ratio and NO3--N concentration) under a constant nitrogen removal loading rate (no overload). Based on these results, a hierarchically separate control strategy was proposed to obtain a high-rate nitrogen removal during the two-stage mainstream PN-ANAMMOX process.

[Impact of Biodegradable Organic Matter on the Functional Microbe Activities in Partial Nitrification Granules].

To explore the short-term impact of biodegradable organic matter on the activities of different functional microbes in autotrophic partial nitrification granular sludge (PNG),the variations of both nitrogen transformation performance and dissolved oxygen (DO) uptake of PNG were investigated in this study,by carrying out successive batch tests with and without the organics stressing.The results showed that the higher the C/N ratio,the lower the specific nitrite accumulation rate of q(NO2--N).Meanwhile,the increase of heterotrophic bacteria (HeB) activities caused the fast DO uptake by PNG,which could effectively suppress nitrite oxidizing bacteria (NOB) with the low oxygen affinity.When inorganic substrate culture was employed in the following phase,both HeB and NOB showed low activities,with significant increase in q(NO2--N).In short,the adverse effects of biodegradable organic matter on the performance of PNG system were partially reversible,which could benefit to enhance the advantage of ammonium oxidizing bacteria (AOB) and improve the stability of partial nitrification reaction.

[Start-up of a High Performance Nitrosation Reactor Through Continuous Growth of Aerobic Granular Sludge].

In order to examine the continuous growth capacity of the nitrosation granular sludge (NGS), the sludge was inoculated to start up the columnar sequencing batch reactor (SBR). During 130 d, the concentration of mixed liquor suspended solids (MLSS) in SBR increased from 0.1 g·L-1 to 11.8 g·L-1, corresponding to the nitrite-nitrogen accumulation rate of 0.4-4.9 kg·(m3·d)-1, promoted by a higher ammonia-nitrogen loading rate (NLR) from 0.74 kg·(m3·d)-1 to 6.66 kg·(m3·d)-1in the influent. Because of the obvious increase in small granules (size<200 µm), the mean average diameter of NGS decreased significantly at NLR<4.44 kg·(m3·d)-1. At higher NLR values, the growth of the mean average diameter of NGS could be fitted well using a modified logistic model. The specific growth rate of the k value was 0.0229 d-1. In addition, the combined inhibition of nitrite oxidizing bacteria (NOB) was expected at relatively high concentrations of both free ammonia (FA) and free nitrite acid (FNA); thus, the nitrite accumulation ratio (NAR) in the effluent was always higher than 80%. These results provide a feasible approach to start up a high-performance NGS reactor at the industrial-scale.

[Performance Recoverability of Denitrifying Granular Sludge Under the Stressing Effect of Nanoscale Zero-valent Iron].

To explore the potential stressing effect of nanoscale zero-valent iron (nZVI) on denitrifying granular sludge (DGS), the evolution of DGS denitrifying performance under different C/N ratios was investigated in this study, by carrying out batch tests of eight successive periods with the nZVI shock-loading. The results showed that the specific denitrification rate of µ value decreased when the nZVI dosage was higher than 5 mg · L⁻¹. Meanwhile, a positive correlation between the inhibition ratio (IR) of µ value and substrate C/N ratios or nZVI dosage was observed. When the nZVI dosage reached 100 mg · L⁻¹, both extracellular protein and polysaccharides concentrations decreased obviously. It would be beneficial to promote the recovery of DGS denitrifying activity and reduce the COD demanding to remove unit mass of nitrate, by increasing external carbon source with C/N ratios of higher than 4. On the basis of Freundlich and Langmuir adsorption isotherms, when higher C/N ratio was provided, stronger bioadsorption of nZVI would be achieved. During the recovery period, a significant improvement of DCS denitrifying performance under the high C/N ratio was expected, due to the continuous washout of total iron in sludge phase (Qe), while the µ value would reach or approach the one of the control group when Qe was lower than 0.4 mg · g⁻¹.

[Effect of Increasing Organic Loading Rate on the Formation and Stabilization Process of Aerobic Granular Sludge].

In order to evaluate the effect of organic loading rate ( OLR) on the formation of aerobic granular sludge (AGS), a lab-scale cylindrical SBR reactor (sodium acetate as carbon source) was constructed and inoculated with collected sewage sludge. The evolution of morphology, microbial activity and extracellular polymeric substances (EPS) characteristics of sludge samples in the reactor were recorded and analyzed. The results showed that AGS has the highest growth rate under the condition of 3. 20-4. 84 kg.(m3.d)-1 OLR, and a selective discharging strategy of the floccular sludge was suggested to maintain the predominance of AGS in reactor. The accumulated sludge concentration, SVI30, mean granule size, settling velocity and SOUR value of the AGS in steady-state operated SBR was 23. 9 g.L-1, 20 mL.g-1, 1. 4 mm, 102 m.h-1 and 50. 2 mg.(g.h)-1, respectively. The granulation process not only obviously changed the sludge appearance, but also significantly improved the microbial activity. Meanwhile, linear correlation was observed between the variation of protein/polysaccharide concentration and the granule size of AGS. Thus, variation of protein/ polysaccharide concentration of the EPS could be applied as an indicator for optimization of the cultivation method of AGS.

[Study on removal effect of different organic fractions from bio-treated effluent of dye wastewater by UV/H2O2 process].

The pretreatment of bio-treated effluent of dye wastewater by UV/H2O2 process was studied. The influencing factors, such as H2O2 dosage, reaction time and pH values were evaluated for the removal efficiency of UV254, ADMI7.6, DOC and DOC of dye wastewater by UV/H2O2 process. The experimental results showed that,the optimal conditions determined were as follows: initial pH 7.4-8.1, H2O2 dosage 4.5 mmol x L(-1) and UV irradiation time of 50 min. Under the optimal conditions, UV254, ADMI7.6, DOC and COD removal rate could reach 77%, 94%, 40% and 69%. Removal effects of four different DOM fractions, hydrophobic acids, non-acid hydrophobics, tasnsphilics and hydrophilics separated by XAD-8 and XAD-4 resins. The experimental results show that: hydrophobic material was the main substance causing color, when it was characterized by ADMI7.6, the proportion could reach 92%, of which 53% was non-acid hydrophobics. It indicated that removal efficiencies of tasnsphilics, hydrophobic acids and non-acid hydrophobics were high through UV/H2O2, process, while hydrophilics' efficiencies were lower. The experimental results showed that organic molecules with molecular weight over 10,000 contributed greatly to UV254, ADMI7.6 and DOC removal rate.