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A sequencing batch reactor (SBR) was operated in this study to investigate the effect of temperature on the kinetics of Nitrobacter activity among nitrite oxidizing bacteria. At the beginning of the experiment, the NO 2 - -N concentration in the influent was changed to enrich Nitrobacter . Then, the sludge with enriched Nitrobacter was employed to determine the variation of the specific nitrite oxidation rate (SNiOR) during the nitrite oxidation process in batch tests. Metagenomics species annotation and abundance analysis showed that Nitrobacter accounted for 40.3% of the total bacterial population. The variation of SNiOR in the nitrite oxidation process was investigated under different NO 2 - -N concentrations. The effect of temperature on the kinetics of Nitrobacter was investigated using the Monod model. Furthermore, the kinetics model of the effect of temperature on Nitrobacter activity was fitted for statistical analysis. The results showed that SNiOR reached its maximum at 30℃, which was 1.31 g·(g·d) -1 . Statistical analysis showed that the Monod equation could describe the effect of substrate concentration on Nitrobacter activity under different temperature conditions. Calculating the temperature coefficient ( θ ) in different temperature intervals based on the Phelps equation, showed that when the system temperature is lower than 25℃ or higher than 30℃, the reaction rate is more sensitive to temperature changes.

In order to explore the mechanism of NH(4+)-N removal in drinking water biofilter, water quality parameters, such as NH(4+)-N, NO(2-)-N, NO(3-)-N, total phosphorus, permanganate index, nitrogen gas, temperature and dissolved oxygen etc, were determined in the inflow and outflow of biofilter. Samples of granular activated carbon (GAC) at different height (0, 10, 20, 40, 60 cm) of the biofiter media were collected and analyzed for the bacterial community with molecular biology techniques. The bacterial diversity in the activated carbon biofilm sample was studied based on the phylogenetic analysis of sequences. The results showed that there were three stages according to the NH(4+)-N concentration in the influent. The "nitrogen loss" phenomenon (total inorganic nitrogen in the effluent was less than that in the influent) occurred at the first, second and third stages and the amount of nitrogen loss were 0.94, 0.32 and 0.15 mg x L(-1), respectively. The amount of nitrogen loss had a good positive correlation with the NH(4+)-N concentration in the influent, but not a linear relationship with the concentration of the permanganate index in the influent. The average concentrations of N2 increased gradually with the height of media in the biofilter, with values of 14.04 and 14.67 mg x L(-1) in the influent and the effluent, respectively. Based on the sequencing results, the ammonia-oxidizing bacteria (AOB) in the activated carbon biofilm were classified into three common genera: Nitrosococcus, Nitrosomonas and Nitrosospira. When the NH(4+)-N concentration in the influent was relatively high, the "nitrogen loss" phenomenon in biofilter was caused by the AOB.

Microorganisms in nitrogen cycle serve as an important part of the ecological function of soil. The aim of this research was to monitor the abundance of nitrogen-fixing, denitrifying and nitrifying bacteria during bioaugmentation of petroleum-contaminated soil using real-time polymerase chain reaction (real-time PCR) of nifH, narG and amoA genes which encode the key enzymes in nitrogen fixation, nitrification and ammoniation respectively. Three different kinds of soils, which are petroleum-contaminated soil, normal soil, and remediated soil, were monitored. It was shown that the amounts of functional microorganisms in petroleum-contaminated soil were far less than those in normal soil, while the amounts in remediated soil and normal soil were comparable. Results of this experiment demonstrate that nitrogen circular functional bacteria are inhibited in petroleum-contaminated soil and can be recovered through bioremediation. Furthermore, copies of the three functional genes as well as total petroleum hydrocarbons (TPH) for soils with six different treatments were monitored. Among all treatments, the one, into which both E. cloacae as an inoculant and wheat straw as an additive were added, obtained the maximum copies of 2.68 x 10(6), 1.71 x 10(6) and 8.54 x 10(4) per gram dry soil for nifH, narG and amoA genes respectively, companying with the highest degradation rate (48% in 40 days) of TPH. The recovery of functional genes and removal of TPH were better in soil inoculated with E cloacae and C echinulata collectively than soil inoculated with E cloacae only. All above results suggest that the nitrogen circular functional genes could be applied to monitor and assess the bioremediation of petroleum-contaminated soil.

Anammox (anaerobic ammonium oxidation) is an important process of nitrogen cycle, with great potential for the practical use in removing nitrogen from the wastewater containing high concentration ammonium. However, the presence of high concentration organic carbon source is considered unfavorable to anammox. Coupling anammox and denitrification under the presence of organic carbon source could be a useful technique for removing both nitrogen and carbon. This paper reviewed the mechanisms of anammox-denitrification coupling process, functional microbial groups, initiation of the coupling process and its control, and related environmental affecting factors. The future research prospects and potential applications of anammox-denitrification coupling process in wastewater treatment were discussed.

This study investigated the performance of one-step aerobic biological oxidation process and anoxic/aerobic two-step biological oxidation process treating modeled river water containing low carbon and rich ammonia. Biofilm microbial ecology was analyzed with multiple molecular technologies including PCR-DGGE, FISH/CLSM and FISH/FCM to investigate the succession of bacteria community and space distribution along with abundance of the main functional bacteria, and to research the micro-influential factors and the mechanism of different biological contact oxidation processes for their performance. Results showed that two-step contact oxidation process achieved higher removal percentage than that of the one-step process, with COD and NH4(+) -N removal enhanced about 10% and 32%-59%, respectively. A much thicker biofilm was obtained by the one-step process compared to the two-step process, and nitrobacterium was mainly distributed in the depth of 180-200 microm and 105-125 microm, respectively. PCR-DGGE results found that the two-step process demonstrated less microbial diversity than that of the one-step process, FISH/FCM results showed that ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) abundance increased in the two-step process with the increase of operation time, while that of the one-step process declined. Experiment results demonstrate that functional partitioning of the anoxic-aerobic two-step biological contact oxidation process could be in favor for harvesting nitrobacteria and other special bacteria in different reactor spaces, which can improve removal efficiency for organics and ammonia finally.

Previous studies showed that setting aerobic and anaerobic paragraph segments in the subsurface constructed wetlands (SFCWs) can improve the COD, NH4(+)-N, and TN removal rate, whereas the oxygen enrichment environment which produced by the artificial aeration could restrain the NO3(-)-N and NO2(-)-N removal process, and to a certain extent, inhibit the denitrification in SFCWs Therefore, in this research the structure and technology of SFCW with aerobic and anaerobic paragraph segments were optimized, by using the multi-point water inflow and setting the corresponding section for the extra pollutant removal. Results showed that with the hydraulic load of 0.06 m3 x (m2 x d)(-1), the COD, NH4(+)-N and TN removal efficiencies in the optimized SFCW achieved 91.6%, 100% and 87.7% respectively. COD/N increased to 10 speedily after the inflow supplement. The multi-point water inflow could add carbon sources, and simultaneously maximum utilization of wetland to remove pollutants. The optimized SFCW could achieve the purposes of purification process optimization, and provide theoretical basis and application foundation for improving the total nitrogen removal efficiency.

A comparative study was conducted to determine nitrification potentials and ammonia-oxidizing bacterial (AOB) community composition in 0-20 cm soil depth in adjacent native forest,natural grassland, and cropland soils on the Tibetan Plateau, by incubation experiment and by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA, respectively. Cropland has the highest nitrification potential and nitrate concentration among the three land-use types (LUT), approximately 9 folds and more than 11 folds than that of the forests and grasslands, respectively. NO3(-) -N accounted for 70%-90% of inorganic N in cropland soil, while NH4(+) -N was the main form of inorganic N in forest and grassland soils. Nitrification potentials and nitrate concentrations showed no significant difference between native forest and grassland soils. The native forest showed the lowest nitrification potentials and the lowest AOB diversity and community composition among the three LUT. Conversions from natural grasslands to croplands remarkably decreased the AOB diversity and composition, but croplands remain high similarity in AOB community composition compared with grasslands. The minimal and the lowest diversity of AOB in native forests directly resulted to the lowest nitrification potentials compared to natural grasslands and croplands. From the fact of the highest nitrification potentials and nitrate concentrations in croplands indicated that there were the most substantial AOB with higher activity and priority. The results provide evidence that changes of land-use type can affect both soil nitrogen internal cycling process, the diversity, community and activity of AOB, which further affect soil environment quality and the long-term sustainability of ecosystems.

The dynamic succession of ammonia-oxidizing bacteria (AOB) community during the agricultural waste composting was investigated using the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The changes of pile temperature, pH, moisture content, soluble NH4(+) -N and NO3(-)-N were measured. DGGE results showed that the Shannon-Weaver index changed from 2.58 to 2.02 during the composting process, which reflected the diversity trends downward overall. Nitrosospira and Nitrosomonas were dominant species. Nitrosomonas eutropha,which was found throughout the whole composting process, was identified as a kind of well-tolerated species. Redundancy analysis (RDA) was applied to explore the correlation between the dynamic succession of AOB community and composting physic-chemical parameters. Compared with the slight change referring to its structure during the earlier phase of thermophilic period (4-9 d), the AOB community experienced a more significant change during the later phase of thermophilic period (9-12 d) as well as the following temperature falling phase (12-25 d). Significant relationships have been found between pile temperature, soluble NH4(+) -N (P < 0.01) and NO3(-)-N (P < 0.05) with the dynamic succession of AOB community, which suggested those three parameters were likely to influence, or be influenced by AOB during the agricultural waste composting.

The approach and factors for realizing the rapid startup of nitrosation were researched at the low level of dissolved oxygen (DO) in sequencing batch reactor (SBR). The main parameters of the reactor were controlled as follows: DO were 0.15-0.40 mg/L, pH values kept from 7.52 to 8.30, temperature maintained at 22.3-27.1 degrees C, and time of aeration was 8 hours. The purpose of rapid startup for nitrosation was achieved after 57 cycles (36 d) with the alternative influent of high and low ammonium wastewater (the mean values were 245.28 mg/L and 58.08 mg/L respectively) in a SBR, and the nitrosation rate was even 100%. Factors of accumulation of nitrite were investigated and the effects of DO and pH were analyzed during the startup for nitrosation. The results showed that it could improve the efficiency of nitrosation when DO concentration was increased appropriately. The activity of nitrite oxidizing bacteria (NOB) was recovered gradually when DO was higher than 0.72 mg/L. The key factor of controlling nitrosation reaction was the concentration of free ammonia (FA), while the final factor was the concentration of DO. pH was a desired controlling parameter to show the end of nitrification in a SBR cycle, while DO concentration did not indicate the finishing of SBR nitrification accurately because it increased rapidly before ammonia nitrogen was oxidized absolutely.

In August 15-28, 2009, a preliminary study was conducted on the spatial distribution characteristics of heterotrophic bacteria (HB), inorganic phosphate bacteria (IPB), organic phosphate bacteria (OPB), denitrifying bacteria (DB), and ammonifying bacteria (AB) in the hypoxic zone of Yangtze River Estuary. In the water surface, water bottom, and sediment surface of the zone, the average quantity of AB was the largest, being 307.52 x 10(4) cells x L(-1), 184.50 x 10(4) cells x L(-1), 199.97 x 10(2) cells x g(-1), followed by that of HB (87.35 x 10(4) cfu x L(-1), 86.85 x 10(4) cfu x L(-1), and 19.56 x 10(2) cfu x g(-1)), and of OPB (19.26 x 10(4) cfu x L(-1), 18.82 x 10(4) cfu x L(-1), and 19.56 x10(2) cfu x g(-1), respectively). IPB was only observed within the Yangtze Estuary, south passage of the Estuary, and Zhoushan inshore, and its average quantity in the water surface, water bottom, and sediment surface was 18.50 x 10(4) cfu x L(-1), 31.00 x 10(4) cfu x L(-1), and 7.17 x 10(2) cfu x g(-1) respectively. DB had a wide distribution, but its average quantity was low, being 3.94 x 10(4) cells x L(-1), 23.08 x 10(4) cells x L(-1), and 6.22 x 10(2) cells x g(-1) in the water surface, water bottom, and sediment surface, respectively. Salinity, NO3(-)-N, PO4(3-)-P, SiO3(2)-Si, and pH were the main factors affecting the distribution of HB, IPB, OPB, and DB in water body and sediment surface. The HB, IPB, and OPB in water bottom and sediment surface had significant positive correlation with water temperature; the HB and OPB in water bottom and the IPB in sediment surface were significantly positively correlated with dissolved oxygen (DO); while the AB in sediment surface was significantly negatively correlated with DO. Cluster analysis showed that hypoxia affected the bacterial community structure in sediment surface.

Nitrobacteria, nitrification and its impact factors were discussed based on the method of on-site incubation and laboratory simulation in Liaohe estuary wetland sediments in June and August 2009, respectively. The results showed that the number of ammonia-oxidizing bacteria (AOB) ranged from 0.54 x 10(4) to 5.69 x 10(4) cells x g(-1) with an average of (2.21 +/- 2.32) x 10(4) cells x g(-1) in June and ranged from 1.90 x 10(4) to 7.90 x 10(4) cells x g(-1) with an average of (3.61 +/- 2.87) x 10(4) cells x g(-1) in August. The potential nitrification rates ranged from 9.72 to 16.45 mmol x (m2 x h)(-1) with an average of (12.54 +/- 3.14) mmol x (m2 x h)(-1) in June and ranged from 14.66 to 24.62 mmol x (m2 x h)(-1) with an average of (18.71 +/- 4.21) mmol x (m2 x h)(-1) in August. The net nitrification rates were 0.41 mmol x (m2 x h)(-1) in June and ranged from 0.20 to 0.53 mmol x (m2 x h)(-1) with an average of (0.35 +/- 0.16) mmol x (m2 x h)(-1) in August. The potential nitrification rates were apparently higher than the net nitrification rates. The AOB abundance and nitrification rates were all higher in August than in June. Ammonia concentration in the overlying water, pH, organic matter, total nitrogen content, total phosphorus content, ammonia nitrogen content and the number of AOB in sediments were the main environmental impact factors on nitrification by SPSS 13.0 statistical analysis (p < 0.05), and it also showed ammonia concentration in the overlying water, total phosphorus content and ammonia nitrogen content in sediments were key impact factors on nitrification by partial correlation analysis. The flux of transformed ammonium into nitrate by nitrification process was 1.14 x 10(5) kg per day, suggesting that nitrification was important on nitrogen cycle in Liaohe estuary wetland sediments.

With A/O phosphorus removal process of secondary effluent as raw water, the stable accumulation of nitrite was achieved under low DO. Total nitrogen loss, hydraulic retention time (HRT) and sludge recycle ratio(R) was separately studied on the effects of stable nitrosation. According the result, apparent nitrosation rate was affected by the concentration of COD influence, when COD < or = 50 mg/L, apparent nitrosation rate was reduced; when COD > 50 mg/L, it was increased. Extension and shortening of HRT has positive and negative effects on nitrosation efficiency, dynamic controlling was an effective method. The system stability would be undermined leading to the risk of nitrification by elevating sludge recycle ration. In addition, low DO concentration did not reduce nitrosation rate. Under the condition of HRT = 6 h, R = 0.5, T = 22-24 degrees C, the average ammonia nitrogen removal rate reached 83%, the ammonia nitrogen removal load reached 0.28 kg/(kg x d), the nitrite accumulation ratio was close to 100%.

Air-drying is always accompanied by soil moisture loss. The different influences of air-drying on soil nitrification might due to the different nitrification responses to moisture changing of acid subtropical soils. So, after applying 0 and 150 mg x kg(-1) of ammonium bicarbonate, a 35-day incubation study was conducted to determine the nitrification potential of four acid subtropical soils under 5 soil moisture levels, namely 30% water-holding capacity (WHC), 45% WHC, 60% WHC, 75% WHC and 90% WHC. Four soils, designated QR, QU, SR and SU, derived from Quaternary red earth and Tertiary red sandstone, were collected from rice and upland field. The results indicated that the soil nitrification was significantly influenced by the moisture content (p < 0.01), and the nitrification sensitivities to soil moisture content varied with land-use types. For the treatments without ammonium input, the ranges of nitrification ratio were 11% and 8% in upland soils, QU and SU respectively, which were obviously lower than those in paddy soils (35% for QR, and 20% for SR). The ammonium input would increase the ranges of nitrification ratio which were 56%, 26%, 31%, and 26% for soil QR, QU, SR, and SU, respectively. And the ammonium input would accelerate soil acidification under high moisture levels. In a word, the land-use type presents a significant influence on the nitrification response to moisture content, which might lead to the difference of air-drying effect.

The feasibility of heterotrophic nitrification-aerobic denitrification bacteria applied in shortcut nitrification system was studied. Four heterotrophic nitrification-aerobic denitrification strains mixed with halotolerant activated sludge was added into SBR in order to test their bioaugmentation ability for shortcut nitrification system, which was treating for sewage containing sea water, and the difference between bioaugmentation system and original system was compared. The results showed that the maximum accumulation of NO2(-) -N in bioaugmentation system was 34.92% lower than that in original system, and the time of maximum accumulation of NO2(-) -N was 2 hours earlier than that in original system. The TN and COD was continuously decreasing in the later phase of nitrification in bioaugmentation system, and finally the removal rate of TN and COD were 15.24% and 5.39% higher than that in original system respectively, as well as the removal rate of NH4(+) -N and the nitrosation rate were 6.85% and 14.47% higher than that in original system. And the pH was 0.46 higher than that in original system, whereas the ORP was 25.84 mV lower. It was considered that the function of heterotrophic nitrification-aerobic denitrification bacteria should strengthen the performance of bioaugmentation system. When the seawater content raised to 70%, the stability of bioaugmentation system was better than that in original system, and the current that transforming shortcut nitrification to complete nitrification was restrained by heterotrophic nitrification-aerobic denitrification bacteria effectively. The number of heterotrophic nitrification-aerobic denitrification bacteria was changed when bioaugmentation system and original system ran in different phase and the bacteria had a great loss with the discharge of activated sludge. These results may provide a theoretical reference about the feasibility that the heterotrophic nitrification-aerobic denitrification bacteria applied in shortcut nitrification system.

A set of automatically titrimetric system to monitor the hydrogen ion variation during biological wastewater treatment process in a batch bioreactor was developed, which consists of a batch bioreactor, data auto-acquisition and preservation unit, and titrant autodosing unit. The accuracy of measurement for the system was evaluated by measuring the stoichiometric ratio of hydrogen ion production amount to ammonium consumption amount of ammonium oxidation in an activated sludge system. The ratios measured in a 1L bioreactor with NH4+ -N concentrations of 1.67, 3.33, 8.33, 16. 66 and 30.00 mg/L as N respectively were very close to the theoretical value, and the relative errors were among 2.09%-6.34%. However, the relative errors in bioreactors of 1, 2, 3 and 4 L with NH4+ -N concentration of 16.66 mg/L as N were among 2.09%- -18.57%, and increased significantly with accretion of the volume of bioreactor. The buffers of bicarbonate and the ammonium, especially the titrimetric dynamic effects in a larger bioreactor are the primarily factors resulting in errors. This study provides an important approach for monitoring hydrogen ion variation in the process of biological wastewater treatment by titrimetry.

Populations and activities of nitrifier can be significantly influenced by air-drying. A 35-day incubation study was conducted to determine the effects of air-drying on nitrification potential of four acid subtropical soils after applying 0 and 150 mg x kg(-1) of ammonium bicarbonate. Four soils, designated QR, QU, SR and SU, derived from Quaternary red earth and Tertiary red sandstone, were collected from rice and upland field. The results indicated that, without ammonium input, the responses of nitrification in upland soils to air-drying were insignificant (p > 0.05). The nitrification ratio in fresh and air-dried samples of soil QU were 48% and 54% respectively, and 76% and 78% for SU; however, air-drying did have a significant effect on the nitrification in paddy soils (p < 0.01). Nitrification ratios were 40% and 89% for fresh and air-dried samples of QR, 76% and 94% for SR, and there was a lag-phase of the nitrification in air-dried paddy soils. Ammonium input would accelerate nitrification and make the nitrification ratios of fresh samples significantly higher than those of air-dried ones. In generally, land-use type presents a significant impact on the response of nitrification to air-drying effect, and there was a significant interaction of land-use type and fertilization.

Autotrophic granular sludge was developed in an SBR reactor using inorganic carbonal substrate. The variation of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) during the densification process and their effects on granulation have been evaluated. It was found that the autotrophic bacteria granular sludge was compact with the density reached up to 1.06 g/mL, and the rod-like bacteria predominated in granules on the evidence of scanning electron microscopic (SEM) results. Ammonia, nitrite and nitrate in the effluent were 4.5-15.2 mg/L, 10.2-20.3 mg/L and 17.9-30.1 mg/L, respectively, and the ammonia removal efficiency was 78% -92%. By evaluating the profile of various types of nitrogen and their conversion rates, it was found that short settling time was the main factor that enriched the AOB at the beginning of this experiment, and the granulation did not correlate with AOB. On the contrary, nitrification rate well correlated with granulation, and evidence demonstrated that the formation of granulation was in favorate of immoblization of NOB and the metabolite of NOB stabilized granules, therefore granules and NOB mutually enhanced. Additionally, it was found that the autotrophic denitrification was gradually increased with the process of granulation.

The influence factors and environmental effects of nitrification process were discussed based on the measurements of nitrifier quantities and nitrification rates at eight sites off Yangtze River Estuary in June 2006. Using FISH (Fluorescence in situ hybridization) method, the nitrifying bacteria were counted as 1.87 x 10(5) -3.53 x 10(5) cells/g wet weight and exhibited salt tolerance to some extent. The nitrification rates, measured by acetylene inhibition technique, ranged from 101.3 to 514.3 micromol/(m2 x h) and had a decreased gradient from nearshore to offshore sediment with two high value regions located at the mouth of Yangtze River and Hangzhou Bay respectively. The nitrifier quantity was a main factor to effect nitrification rates at high-salinity sea area, with an influence ratio of 87.7%. Fluxes of transformed nitrogen and consumed oxygen by nitrification process were 4.68 x 10(5) kg and 6.07 x 10(4) mol per day respectively, suggesting that nitrification would be an important factor for the distribution of DIN species and DO at bottom water in early summer.

Taking simulated domestic sewage as treatment object, the characteristics of separate-stage phosphorus, organic substrate and nitrogen removal were studied in two-stage SBR by contrast experiment and mechanism analysis under the normal temperature, its efficiency-predominance was analyzed. The results indicate that the heterotrophic PAOs and nitrobacteria can be dominant growth in individual reactor respectively, under the effluent quality is more superior, the treatment efficiency is one time higher than that in the single SBR by controlling the sludge age (the phosphorus removal stage 5-7 d, the nitrogen removal stage about 50 d). The two-stage SBR can relieve the attack of organic load to nitrification process effectively, its nitrogen removal stage (SBR2) can still maintain stable nitrification rate under the higher COD concentration and the final effluent of the system is easy and stable to reach national standards (TP < or = 0.5 mg x L(-1)). In addition, the nitrogen removal stage (SBR2) of two-stage SBR not only can maintain nitrobacteria predominant, but also can cultivate heterotrophic bacteria which can remove difficult degraded organic substrate, that results in lower COD concentration than in the single's at the end of nitrification.

According to nitrogen-containing wastewater, effects of salinity variation on nitrification and denitrification in internal circulation sequencing batch biofilm reactor (SBBR) and sequencing batch reactor (SBR), and the process of recovery as decreased salinity were investigated. The results show that nitrosation process is effected in internal circulation SBBR and SBR as the increase of salinity, and as the salinity is less than 1.0 x 10(4) mg x L(-1), the speed of ammonia-oxidize is quicker in the SBR than in the SBBR, but the state is opposite as the salinity beyond 1.5 x 10(4) mg x L(-1). As the salinity increased to 4.0 x 10(4) mg x L(-1), the process of ammonia-oxidize was restrained strongly both in SBBR and SBR. The nitrite accumulation is attained continually as the salinity at 1.5 x 10(4) mg x L(-10 and 2.5 x 10(4) mg x L(-1) in the SBBR and SBR respectively. In the SBBR, the removal rate of TN was about 60% as the salinity was less than 1.5 x 10(4) mg x L(-1), and the SND was restrained strongly as the salinity beyond 3.0 x 10(4) mg x L(-1).

The community of nitrifiers cultivated with reject water were investigated by fluorescent in situ hybridization (FISH) performed with 16S rRNA-targeted oligonucleotide probes, and the kinetic properties such as temperature correction factor tauN and the half saturation coefficient K(N) were also investigated. The results showed that the percentage of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in the activated sludge was 15.7% +/- 3.7% and 12.9% +/- 3.2%, Nitrosomonas europaea-Nitrosococcus mobilis lineage were the dominant AOB, Nitrobacter spp. were the dominant NOB. The temperature correction factors of ammonium utilized rate (AUR) and nitrite utilized rate (NUR) were 1.092 and 1.061 respectively; the K(N) of AOB and NOB were (1.60 +/- 0.29) mg/L (NH4(+) -N), (2.78 +/- 0.30) mg/L (NO2(-) -N) respectively.

Nitrogen cycling bacteria, including ammonifying, nitrobacteria, nitrosobacteria and denitrifying bacteria were screened, carrier was made and immobilized nitrogen cycling bacteria (INCB) was prepared. The results demonstrated that ammonifying, nitrobacteria, nitrosobacteria and denitrifying bacteria were increased markedly in the experimental areas and root zone of aquatic plants by releasing of INCB. The results also showed that the average removal efficiencies for total N (TN), NH4(+) -N, NO3(-) -N and NO2(-) -N were 44.70%, 67.17%, 31.79% and 74.21%, respectively. Furthermore, NH4(+) -N, total N (TN) reached the National Standard II and IV for surface water, respectively. With INCB, local lake water quality could improve. Therefore, the technique of INCB could play an important role for remedying and rehabilitating in desertification water.

Paddy soil samples were collected in layers (0-5, 5-12, and 12-20 cm) during rice growth period to investigate the characteristics of the N forms and N-transforming bacteria in the soil profile under different tillage patterns (no-tillage with straw returning, NTS; conventional tillage with straw returning, CTS; no-tillage, NT; and conventional tillage, CT). In the whole rice growth period, ammonifying bacteria in 0-5 cm soil layer had the highest number under NTS, and nitrosobacteria in 0-5 cm and 5-12 cm soil layers were more abundant but in 12-20 cm soil layer were lesser under CT than under NT. Nitrosobacteria and denitrobacteria in 0-20 cm soil layer were lesser under NTS than under CTS. At elongating and ripening stages, anaerobic N-fixing bacteria in 0-5 cm soil layer were more abundant under NT than under CT. In the whole rice growth period, the alkali-hydrolyzable N and total N contents in 0-5 cm soil layer were significantly higher but in 5-12 cm and 12-20 cm soil layers were lower under NT than under CT, and the NH4(+)-N and NO3(-)-N contents in 0-20 cm soil layer were higher under NTS but in 12-20 cm soil layer had no significant differences between NT and CT. Correlation analysis and multiple polynomial regression analysis further revealed that there were significant relationships between soil NH4(+)-N and soil ammonifying bacteria, nitrosobacteria and denitrobacteria, and between soil alkali-hydrolyzable N and soil anaerobic N-fixing bacteria. Among the test tillage patterns, NTS could be the more desirable one for the N supply and fertility maintenance of paddy soil.

An expanded granular sludge bed (EGSB) reactor inoculated simultaneously with aerobic ammonium oxidation sludge and anaerobic ammonium oxidation sludge were start-up to enrich completely autotrophic nitrogen removal granular sludge. Total nitrogen (TN) removal rate reached 0.101 kg x (m3 x d)(-1). Based on hypothesis of boundary layer, the transfer process between granular sludge and bulk liquid was modified, which was coupled with substance transfer process in granular sludge and aerobic ammonium oxidation, anaerobic ammonium oxidation, nitrite oxidation process, and completely autotrophic nitrogen removal model was found. The model was validated with the experimental results. According to simulation results, the operation of the reactor was optimized, TN removal efficiency and TN removal rate were increased from 52% to 61% and 0.103 kg x (m3 x d)(-1) to 0.114 kg x (m3 x d)(-1) respectively.

The 16S rDNA-based molecular technique was applied to investigate the functional microbial community of a membrane-aerated biofilm bioreactor (MABR) that was used for completely autotrophic nitrogen removal over nitrite (CANON). The relationships among two kinds of key bacteria responsible for CANON: aerobic ammonia-oxidizing bacteria (AOB) and ANAMMOX bacteria, and their possible distributions in the MAB were discussed based on the microbial community analysis. FISH analysis showed the existence of two visible active layers in experimental MAB. One was the partial nitrifying layer located in the region of oxygen-rich membrane-biofilm interface, dominated by NSO190-positive AOB. The other was the ANAMMOX active layer located in the region of anoxic liquid-biofilm interface, dominated by PLA46 and AMX820-positive ANAMMOX microorganisms. As a result, the AOB as well as ANAMMOX bacteria were present and active in experimental MABR, and the cooperation between AOB and ANAMMOX bacteria was considered to be responsible for CANON.

At normal temperature of 19 degrees C +/- 1 degree C and seed sludge from the system of conventional nitrogen removal via nitrate composed of both ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB), the competition and optimization of AOB and NOB was investigated in a lab-scale SBR treating domestic wastewater. The reactor was operated under the aeration rate of 40 L/h with the average DO concentration below 1.0 mg/L, and combined with the control of aeration time, i.e., aeration was stopped before the pH "ammonia valley" was detected. After AOB became pre-dominant nitrifying bacteria (nitrite accumulation rate NO2(-)-N/NOx(-)-N reached 50%), the aerobic durations were gradually prolonged from 3 h to 4 h and 5 h to improve the ammonia removal efficiencies and enhance AOB dominant. By the above operational pattern, nitrogen removal via nitrite was successfully achieved with NO2(-)-N/NOx(-)-N over 95%. Fluorescence in-situ hybridization (FISH) analysis showed that AOB was accounted for 9.97% of total biomass. The on-line control of aerobic duration was an effective method to maintain the partial nitrification and the NH4(+)-N removal efficiency was above 97%. The research results also proved that at normal temperatures, for the seed sludge from the conventional nitrogen removal via nitrate, AOB would not become dominant nitrifying bacteria only by the aeration time control without the DO restriction.

In order to investigate shortcut nitrification, an intermittent-aeration SBR was employed to treat the domestic wastewater containing low concentration of NH4+ . The results shows that under the SRTs of 10, 5, 2.5 and 1.25 d, NO2- produced in effluent were built up to 18, 19, 14 and 5 mg/L, respectively, with accumulation ratio of 73%, 85%, 91% and 78% respectively. As to the continuous-aeration SBR, however, the NO2- accumulation ratios were only 14%, 21%, 31% and 34%. In addition, the corresponding removals of NH4- in the intermittent-aeration SBR were maintained at a comparable level in contrast to those for the continuous-aeration SBR, i.e., 97%, 95%, 76% and 39% vs. 92%, 97%, 71% and 47%. By exploring the growth kinetics of nitrifiers, ammonia-oxidizing bacteria (AOB) in the intermittent-aeration system was capable of increasing its biomass in the reactor by an elevation in growth yield (Y(AOB)), which as a result compensated the decreased specific substrate utilization rate at low DO level and further led to the unchanged microm value and NH4+ oxidation rate. On the contrary, nitrite-oxidizin bacteria (NOB) was lack of the function of compensability, and it hence lowered the microm value and NO2-oxidation rate, and therefore resulted in an accumulation of NO2- in the effluent.

Nitrification is a key step in the global nitrogen cycle. Classically, nitrifying bacteria are chemoautotroph. Recently, bacteria that have the ability of heterotrophic nitrification have been intensively studied as potential microorganisms that may be used to overcomeproblems inherent in the conventional method. This review gives a broad overview of the current status of heterotrophic nitrification including the heterotrophic species which nitrify actively, optimal condition for nitrification, heterotrophic nitrification pathway, enzymatic system and isolation methods. Also, the promising prospects of heterotrophic nitrification are especially introduced.

A sequencing batch airlift reactor (SBAR) was conducted to study the performance of physical characteristics and respirometric activities during reactivation of aerobic granules after a 2-month storage time. Results showed that the color of the aerobic granules had completely become dark, the size and settleability did hardly change during the storage period. The color turned to be brownish-yellowish when the reactor was restarted for 2 weeks. The MLSS, granule size, and settleability increased rapidly along with reactivation. The heterotrophic activity resumed 86% within 1 day and was fully reactivated after 5 days. Then the COD removal rate was stabilized above 80%. Higher aeration rate and longer cycle time facilitated the reactivation of nitrifiers. When aeration rate was increased from 0.05 m3 x h(-1) to 0.10 m3 x h(-1) at 41st day, activities of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were improved from 88% and 82% to 122% and 92%, respectively. The removal rate of ammonium-nitrogen promptly reached above 96%. Nitrite-oxidizing bacteria were fully reactivated after the cycle time was prolonged from 4 h to 6 h.

At the high level of dissolved oxygen (DO) in sequencing batch biofilm reactor (SBBR), the approach and mechanism for realizing shortcut nitrification were researched. Landfill leachate was used as handling of object, the mainly environment parameters of the reactor were controlled as follow: DO 5 mg/L, pH 7.0, temperature 25 degrees C, adopted all drainage mode and 12-hour cycle influent. Through mathematical derivation and modeling analysis, determined free ammonia (FA), CO2 and HNO2 as the direct control factors, whereas the influent cycle time was the indirect one, shortcut nitrification was achieved effectively in SBBR. When the volume load of ammonia (NH4(+) -N) was 0.52 kg/(m3 x d) and NaHCO3 was 1.5 mg/L in the reactor, the shortcut nitrification effect was apparent as NH4(+) -N conversion rate was 89% and NO2(-) -N accumulation rate achieved 83% at the same time. With adequate oxygen supply, the key factors of achieving NO2(-) -N accumulation is FA concentration, and as the carbon source of ammonia-oxidizing bacteria, CO2 can upgrade the reactor performance further.

Sequencing batch reactor, treating simulated municipal wastewater for N removal and operated at near the minimum SRT (solids retention time) for nitrification (in reactor 2), was seeded daily with nitrifying biomass accumulated with reject water (in reactor 1) came from Xi' an Dengjiacun wastewater treatment plant. Comparison of the nitrification ability, the characteristics of the activated sludge before seeding and after seeding was made. The experiment result shows that, the maximum nitrification rate of the activated sludge in the reactor 1 reached 81.4 mg/(L x h). The effluent concentration of NH4+ -N of the reactor 2 decreased at a rate of 0.992 mg/(L x d) (R2 = 0.903), and the maximum nitrification rate increased 1.36 times. Once seeding was terminated, the effluent concentration of NH4+ -N increased at a rate of 1.956 mg/(L x d) (R2 = 0.999), and nitrification caused by seeding was not completely disappeared after seeding was stopped for 34 d. The amount and varieties of protozoa and the value of SVI in the reactor seeded with nitrifiers increased during the initial time of seeding, but were recovered when the reactor 2 reached stable state.

The physical properties and microbiological characteristics of aerobic short-cut granular sludge, which was cultivated in a lab-scale aerated upflow sludge bed (AUSB) reactor, were investigated. When the short-cut nitrification process was performed stably, the ratios of VSS/ SS of short-cut granules were kept at about 80%, the amount of granules with diameter larger than 1.0 mm was about 70% of the total, and the wet density of granules with diameter larger than 0.8mm was about 1022 kg/m3. The fluorescence in situ hybridization (FISH) results indicated the ammonia oxidation bacteria (AOB) were mainly located in the surface layer of the granules, and the nitrite oxidation bacteria (NOB) were in the inner layer. The results of most probable number (MPN) showed that, as the short-cut process was operated stably, the amount of AOB was much more than that of NOB, and sometimes the AOB amount was even 10 thousands times more than that of NOB. All these results indicated that, using the seed granules or their debris as the support media, AOB and NOB were attached and grown on the surface of the media, and finally the aerobic short-cut nitrification granules were formed.

The conventional microorganism techniques and the molecule biological techniques such as PCR and DGGE were utilized to study the approaches of biological nitrogen removal in a single sequencing batch biofilm reactor (SBBR). The main approach of biological nitrogen removal, no less than 65% of the total NH4(+)-N was removed in this approach, was composed of partial nitrification, anaerobic ammonium oxidation and denitrification. The second approach included twain processes such as partial nitrification and denitrification, and the third one was conventional nitrogen removal process (nitrification and denitrification). All approaches accomplished simultaneously or asynchronously. When the approach occurred in the simultaneous way, it performed as nitrogen-loss. The accomplisher of asynchronous way depended on the microbe's different activity between aerated phase and anaerobic phase. First, ammonia was converted to nitrite in the aerated phase when the nitrite bacteria performed high activity, and then anaerobic phase was operated in turn when the denitrifying bacteria and the anammox bacteria eliminated the nitrogen form gases.

Morphological characteristics of aerobic nitrifying granules that were utilized to treat the diluted source-separated urine were investigated in two lab-scale sequencing batch reactors. In the first sequencing batch reactor, which was inoculated with nitrifying bacteria, the COD of effluent was markedly decreased while the nitrification rate was very low. Aerobic nitrifying granules were not appeared in the first bioreactor. In the other SBR system that was inoculated with aerobic granules cultivated in the laboratory, the COD and ammonia in source-separated urine were effectively removed and the removal rate was more than 90%. Under operational condition that influent ammonia volume rate was 0.5 kg/(m3 x d) for 70 days, the aerobic nitrifying granules were stable in the reactor. Aerobic nitrifying granules have well settleability and metabolize activity, the surface of granules was occupied by nitrifying bacillus and cocci bacteria. Contrast to the inoculating aerobic granules, the diameter of aerobic nitrifying granules dramatically decreased to more than 2 mm and the settle velocity were greater than that of aerobic granules which have the same diameter.

Complete nitritation process in an biofilm moving bed system was started-up by inoculating nitrobacteria and controlling pH, and the effects of nitrogen loading rate (NLR) and hydraulic retention time (HRT) on the stability of the system were investigated. The results showed that the system could achieve complete nitritation after 10 day's acclimation by controlling pH within the range of 7.7 - 8.2, under the conditions of temperature (30 +/- 1) degrees C, DO 1.5 - 2.0 mg/L, HRT 24 h,ammonia concentration 150 mg/L. Conversion rate of ammonia was above 96% and nitritation rate (NO2(-) -N/NO(x)(-) -N) was more than 95%. In addition, the system remained complete nitritation when NLR increased from 0.15 kg/(m3 x d) to 0.24 kg/(m3 x d), and conversion rate of ammonia was still above 90%, nitritation rate maintained at 96%, but the type of nitrification turned from completely nitritation to completely nitrification under the condition of over aeration by extended HRT under low NLR. However, it could be resumed by shortened HRT.

The performance and feasibility of immobilization biological activated carbon (IBAC) were investigated to treat micro-pollutant water containing nitrobenzene. IBAC has been developed on the granular activated carbon by immobilization of selected and acclimated species of engineering bacteria to treat the micro-pollutant water containing nitrobenzene. The IBAC removal efficiencies for nitrobenzene, permanganate index, turbidity, UV, ammonia and nitrite were compared with granular activated carbon (GAC) process. Biological toxicity of influent and effluent of filter were determined. Amount of bacteria in carbon was measured when carbon filter was inoculated and circulated stably. The results showed that compared with GAC, it took short time for IABC to startup and recover to normal after impact burden. In addition, IBAC was more effective to treat micro-pollutants. In order to ensure security of drinking water, the influent nitrobenzene should be controlled below 26 microg/L. Effluent biological toxicity treated with IBAC was less than that with GAC. The performance of IBAC was much better than that of GAC. Amount of bacteria in both activated carbon filter increased first and then declined from inlet to outlet.

Short-cut nitrification process was studied to remove the ammonium nitrogen from the anaerobically pretreated leachate using aerobic moving-bed biofilm reactor (MBBR) at ambient temperature. The effect of DO concentration, pH and C/N ratio on the ammonium removal efficiency and nitrite accumulation rate was investigated, respectively. Experimental results showed that, more than 70% of ammonium removal efficiency and about 90% of nitrite accumulation rate could be achieved when the reaction conditions were controlled as follows: HRT at 24 hours, DO concentration at 2 mg x L(-1), pH at 8 and C/N ratio less than 3. Batch experiments showed that the quantity and activity of ammonia oxidizing bacteria were much higher than those of nitrite oxidizing bacteria. MBBR could effectively remove ammonium nitrogen from leachate and easily obtain a stable nitrite accumulation rate due to the selective immobilization and accumulation of ammonia oxidizing bacteria on the bio-carrier.

The structure and function of activated sludge community were studied in an A/O pilot-scale plant treating actual domestic wastewater. FISH results show the feasibility and effectiveness of sludge population optimisation. A/O process short-cut nitrification with process control of DO and aeration based on DO and pH on-line sensors can be achieved, and gradually eliminated nitrite oxidising bacteria, and therefore achieved nitrogen removal via the nitrite pathway. It can be realized sludge population optimisation, improving nitrogen removal and saving operational cost at the best with on-line process control.

In order to improve the ammonium-nitrogen (NH4+ -N) biodegradation rate, a suspended carrier was exploited and biofilm was cultivated in three different phases in a sequencing batch reactor (SBR). A flimsy honeycomb-shape biofilm was formed between the endocentric columns on the suspended carrier,which increased the cling amount of nitrobacteria and provided the better condition for nitrobacteria. The bioreactor was operated at the temperature ranges of 24-29 degrees C and pH between 7.8 and 8.2. When the influent COD and NH4+-N concentrations varied in a range of 140-300 mg x L(-1) and 40- 78 mg x L(-1) , respectively, under 90 min aeration, the effluent concentrations were less than 40 mg x L(-1) and 2 mg x L(-1) , respectively. Under 180 min aeration, the influent COD concentration varied from 150 to 350 mg x L(-1) and NH4+-N concentration in the range of 80 - 130 mg x L (-1), the effluent concentration below 45 mg x L(-1) and 3.5 mg x L(-1), respectively. The results indicated that the ammonium-nitrogen biodegradation rate is much greater than that of the conventional activated sludge process. The active fraction of the biofilm is affected by the concentration of substrates in the bulk liquid, the actual metabolic rates within the biofilm, and the thickness of the biofilm. The suspended carrier configuration used in this investigation and the method of cultivating biofilm are beneficial for decreasing biofilm thickness, for increasing the activated biomass of nitrobacteria, and for increasing surface area of the biofilm relative to the volume of the reactors, which insulting in a high rate of nitrification.

It is realized short-cut nitrification and denitrification in an A/O pilot-scale plant treating actual domestic wastewater controlling DO concentration (0.5 mg/L) in low level at normal temperature, the average nitrite accumulation rate reached 85 % or above. Three operational modes: low DO short-cut nitrification and denitrification (Mode 1), low DO complete nitrification and denitrification (Mode 2) and high DO complete nitrification and denitrification (Mode 3) were briefly compared, based on the nitrogen removal, operating cost, sludge characteristics and operational mechanism. Experimental results showed that the Model is the best modes of biological nitrogen removal, in terms of improving nitrogen removal and reducing operating cost. The net pH change in aerobic zones and anoxic zones is high for Mode 1, but the net pH change in anoxic zones is very small for Mode 3. The nitrification rate is the smallest for Mode 2, and the nitrification rate for Mode 3 is little higher than that of Mode 1; the denitrification rate for Model is larger than that of Mode 3 about 15 %. It is feasible using DO and pH on-line sensors to control the nitrification process.

Spatial distributions of ammonia oxidizing bacteria (AOB) and nitrobacteria in a renovated suspended carrier biofilm reactor (SCBR) were investigated by using fluorescence in situ hybridization (FISH) with 16S rRNA oligonucleotide probes in combination with confocal laser scanning microscopy (CLSM). Three bench-scale structurally identical SCBR reactors were operated under different ratios of COD to NH4(+) -N in influents, 5, 10 and 15, respectively. Each SCBR reactor was consisted of a 6 L of aeration basin and a 2L of clarifier, with the hydraulic retention time (HRT) of 1.0h. The monitoring results showed that the thickness of biofilm in the SCBR was about 80 to 120 micron. Both the total amount of AOB and nitrobacteria decreased with depth in biofilm, most of the nitrification bacteria communities lied in the upper layer of biofilm, about 20 to 30 micron. The proportion of AOB to all bacteria in biofilm decreased when the ratio of COD to NH4(+) -N increased.

By using a lab-scale aerated upflow sludge bed reactor, the inoculated anaerobic granule was cultivated to aerobic nitrification granule, and then converted to short-cut nitrification granule with the short-cut nitrification efficiencies above 90%. Appling real-time quantity PCR, and florescent in situ hybridization techniques, the ecological community structure of nitrification bacteria in aerobic granules were studied. The results show that there existed a layered structure in the aerobic granule, the ammonia oxidizing bacteria (AOB) was mainly located in the surface area of the granule, and the nitrite oxidizing bacteria (NOB) was mainly located in the inner area of the granule, was just adjacent to the AOB. There was no active bacteria in the inner core area. The amount of AOB in the granules increased, as the ammonia loading rate of the reactor was increased gradually. The percentage of AOB in the total amount of Eubacteria in the granule was 0.45%, 5.20%, 15.37%, 48.55% respectively, as the ammonia loading rate of the reactor were 0, 0.4, 1.0 and 2.2 kg/(m3 x d) respectively, and the nitrosofication efficiency were 0%, 35%, 50%, 99% relatively.

A conventional activated sludge system was used to treat the ammonium-bearing inorganic wastewater for 260 days under decreased HRTs. When treating 500 mg x L(-1) NH4+ -N wastewater, over 98% ammonia removal could be obtained at HRT > or =20 h. Sharp washout of biomass occurred when HRT was further decreased, resulting in the accumulation of ammonium and nitrite. Changes in the community structure were monitored by microbial quinone and conventional analytical methods. Quinone profiles indicated that ammonia-oxidizing bacteria (AOB) in beta-Protevbacteria and Nitrobacteria in alpha-Proteobacteria were the predominant species to oxidize ammonia and nitrite, respectively. The number of AOB decreased with the reduction of biomass in bioreactor, while that of nitrite-oxidizing bacteria (NOB) changed little and fluctuated at 10(5) CFU x L(-1)

The start-up experiment on nitrification of mid-low NH4+ -N concentration wastewater was carried out in four SBR biofilm reactors for the establishment of completely autotrophic nitrogen removal process by the control of DO and HRT and different medias. The results show that on the conditions of temperature 30 degrees C +/-2 degrees C, ammonia concentration 60-120 mg/L, DO 0.8 - 1.0 mg/L and hydraulic retention time 24 h, the inoculating general active aerobic sludge and anaerobic sludge was nitrified stably after 130 days, and the YJZH media was more suitable for microorganism coherence.

Method of isolating the heterotrophic nitrifiers and the characterization of the heterotrophic nitrification were studied. Two heterotrophic nitrifiers were newly isolated from a membrane bioreactor (MBR) in which the TN removal efficiency was 80.1%. The batch test results indicate that Bacillus sp. LY and Brevibacillus sp. LY could utilize the organic carbon as the source of assimilation when they grew on glucose and ammonium chloride medium companying the formation of oxidized-nitrogen. After 24 days incubation, the removal efficiencies of the COD by Bacillus sp. LY and Brevibacillus sp. LY were 71.7% and 52.6%, respectively. The removal efficiencies of ammonium nitrogen by the two isolates were 78.2% and 51.2% and the TN removal efficiencies by the two isolates were 61.2% and 35.6%, respectively.

A high ammonia micropolluted source water advanced treatment for ammonia removal by biological activated carbon filter was tested. The removal rate of ammonia was high than 95% when influent concentration was under 1.0 mg/L. The removal rate decreased with the influent concentration increased when the ammonia concentration was in range of 1.5 - 4.9 mg/L and the influent DO was under 10 mg/L, and the minimum removal rate was about 30%. The key factor of restrict nitrification in BACF was the influent DO. When the influent ammonia concentration was high, the DO in water was depleted quickly by nitrify and hetetrophic bacteria in 0.4 m deep of filter and the filter layer was divided to aerobic zone and anoxic zone. The denitrification was occurred in the anoxic zone, and because of very low concentration of electron donor led to accumulation of the denitrification intermediates such as NO2-. Aerobic bacteria was existed in the anoxic zone.

The effect of osmotic pressure on nitrification was investigated in the internal-loop air-lift nitrifying reactor. When influent ammonia concentration is kept at 420mg x L(-1) and influent osmotic pressure is increased from 4.3 to 18.8 x 10(5) Pa, the ammonia conversion of the nitrifying bioreactor is maintained between 93% and 100%. After influent osmotic pressure is further increased to 19.2 x 10(5)Pa, the ammonia conversion goes down to 69.2%. The influence of osmotic pressure on nitrification takes place without any alarm and the critical osmotic pressure is between 18.8 x 10(5) and 19.2 x 10(5) Pa. During osmotic stress, the nitrifying bacterial populations in the activated sludge become simplified, the cell size becomes smaller, the inner membrane becomes less and some unknown inclusion particles are formed. The cell structure is restored as soon as the osmotic pressure is removed. Addition of potassium is able to relieve the effect of osmotic pressure on nitrification. The nitrifying activity of the activated sludge is stimulated by the osmotic stress, and the specific ammonia conversion is increased from 0.083 kg x kg(-1) x d(-1) to 0.509 kg x kg(-1) x d(-1) and 2.569 kg x kg(-1) x d(-1), respectively.

The potential of nitrification and denitrification of sediment and the density of ammonium-oxidizing bacteria and nitrite-oxidizing bacteria in sediment in water quality purifying system with hydroponic bio-filter method (HBFM) were measured. The variation of nitrification and denitrification potential of the sediment along the stream way was quantitatively studied. The results show that among the sediments from front, middle and retral part of the stream way, the sediment from middle part reached a maximum nitrification potential . nitrification potential of 4.76 x 10(-6) g/(g x h), while the sediment from front part reached a maximum denitrification potential of 8 .1 x 10(-7) g/(g x h). The distribution of nitrification potential accords with the ammonium-oxidizing bacteria density. The key for improving nitrogen removal efficiency of HBFM system consists in changing nitrification & denitrification region distributing and accordingly enhances denitrification process.

The operation performance of membrane nitrification bioreactor to treat ammonia-containing wastewater as well as the capabilities of separation and filtration of polypropylene membrane modules were tested. The removal efficiency of ammonia was kept higher than 95% when the hydraulic retention time was set at 1 day, the influent concentration was increased up to 80 mmol (NH4+ -N) x L(-1) and the volume loading rate was increased up to 1.12 kg (NH4+ -N) x m(-3) x d(-1). The biomass in the reactor was accumulated from 5 g x L(-1) to 10 g x L(-1) within 50 days, which indicated that polypropylene membrane modules were efficient in retaining biomass. The biomass attached to the membrane also contributed to the conversion of ammonia and nitrite. When the hydraulic pressure was lower than 80cm, the increase of hydraulic pressure improved the permeation of membrane. However, when the hydraulic pressure was beyond 80cm, the increase of hydraulic pressure did not significantly improve the permeation of membrane. The permeate flux was the highest 2.51 (L x m (-2) x h(-1)) but the resistance was the lowest (2.63 x 10(-5)) m(-1) when the hydraulic pressure was about 20 cm. The results showed that the membrane nitrification bioreactor could be run normally without extra energy input.

Nitrification and denitrification in the different layers of the integrated vertical flow constructed wetlands (IVCW) are studied. The results show the constants rate of nitrification and denitrification in the strata of IVCW were 0.01 - 6.35microg x (gxd)-1 and 3.37 - 4.19microg x (gxd)-1 respectively. The most probable number (MPN) method are employed to determine the number and distribution of nitrifying and denitrifying bacteria in the strata of the system. The results show that the numbers of nitrifying and denitrifying bacteria were 7.5 x 10(3) - 1.1 x 10(5) MPN x g(-1) and 7.5 x 10(6) - 1.1 x 10 MPN x g(-1) respectively. The positive correlation between bacteria and their action was obvious (r = 0.9661, p < 0.001, r = 0.7722, p < 0.025). It is also observed that the number of nitrifying bacteria and nitrification rate was decreased along the direction of the water in the IVCW, while denitrifying bacteria and denitrification rate was increased. And there was the significant negative correlation between nitrification and denitrification rate(r = -0.9776, p < 0.001).