Biological inhibition of soil nitrification by forest tree species affects Nitrobacter populations.

Some temperate tree species are associated with very low soil nitrification rates, with important implications for forest N dynamics, presumably due to their potential for biological nitrification inhibition (BNI). However, evidence for BNI in forest ecosystems is scarce so far and the nitrifier groups controlled by BNI-tree species have not been identified. Here, we evaluated how some tree species can control soil nitrification by providing direct evidence of BNI and identifying the nitrifier group(s) affected. First, by comparing 28 year-old monocultures of several tree species, we showed that nitrification rates correlated strongly with the abundance of the nitrite oxidizers Nitrobacter (50- to 1000-fold changes between tree monocultures) and only weakly with the abundance of ammonia oxidizing archaea (AOA). Second, using reciprocal transplantation of soil cores between low and high nitrification stands, we demonstrated that nitrification changed 16 months after transplantation and was correlated with changes in the abundance of Nitrobacter, not AOA. Third, extracts of litter or soil collected from the low nitrification stands of Picea abies and Abies nordmanniana inhibited the growth of Nitrobacter hamburgensis X14. Our results provide for the first time direct evidence of BNI by tree species directly affecting the abundance of Nitrobacter.

Acyl-Homoserine Lactone Production in Nitrifying Bacteria of the Genera Nitrosospira, Nitrobacter, and Nitrospira Identified via a Survey of Putative Quorum-Sensing Genes.

The genomes of many bacteria that participate in nitrogen cycling through the process of nitrification contain putative genes associated with acyl-homoserine lactone (AHL) quorum sensing (QS). AHL QS or bacterial cell-cell signaling is a method of bacterial communication and gene regulation and may be involved in nitrogen oxide fluxes or other important phenotypes in nitrifying bacteria. Here, we carried out a broad survey of AHL production in nitrifying bacteria in three steps. First, we analyzed the evolutionary history of AHL synthase and AHL receptor homologs in sequenced genomes and metagenomes of nitrifying bacteria to identify AHL synthase homologs in ammonia-oxidizing bacteria (AOB) of the genus Nitrosospira and nitrite-oxidizing bacteria (NOB) of the genera Nitrococcus, Nitrobacter, and Nitrospira Next, we screened cultures of both AOB and NOB with uncharacterized AHL synthase genes and AHL synthase-negative nitrifiers by a bioassay. Our results suggest that an AHL synthase gene is required for, but does not guarantee, cell density-dependent AHL production under the conditions tested. Finally, we utilized mass spectrometry to identify the AHLs produced by the AOB Nitrosospira multiformis and Nitrosospira briensis and the NOB Nitrobacter vulgaris and Nitrospira moscoviensis as N-decanoyl-l-homoserine lactone (C10-HSL), N-3-hydroxy-tetradecanoyl-l-homoserine lactone (3-OH-C14-HSL), a monounsaturated AHL (C10:1-HSL), and N-octanoyl-l-homoserine lactone (C8-HSL), respectively. Our survey expands the list of AHL-producing nitrifiers to include a representative of Nitrospira lineage II and suggests that AHL production is widespread in nitrifying bacteria.IMPORTANCE Nitrification, the aerobic oxidation of ammonia to nitrate via nitrite by nitrifying microorganisms, plays an important role in environmental nitrogen cycling from agricultural fertilization to wastewater treatment. The genomes of many nitrifying bacteria contain genes associated with bacterial cell-cell signaling or quorum sensing (QS). QS is a method of bacterial communication and gene regulation that is well studied in bacterial pathogens, but less is known about QS in environmental systems. Our previous work suggested that QS might be involved in the regulation of nitrogen oxide gas production during nitrite metabolism. This study characterized putative QS signals produced by different genera and species of nitrifiers. Our work lays the foundation for future experiments investigating communication between nitrifying bacteria, the purpose of QS in these microorganisms, and the manipulation of QS during nitrification.

Quorum Quenching of Nitrobacter winogradskyi Suggests that Quorum Sensing Regulates Fluxes of Nitrogen Oxide(s) during Nitrification.

Quorum sensing (QS) is a widespread process in bacteria used to coordinate gene expression with cell density, diffusion dynamics, and spatial distribution through the production of diffusible chemical signals. To date, most studies on QS have focused on model bacteria that are amenable to genetic manipulation and capable of high growth rates, but many environmentally important bacteria have been overlooked. For example, representatives of proteobacteria that participate in nitrification, the aerobic oxidation of ammonia to nitrate via nitrite, produce QS signals called acyl-homoserine lactones (AHLs). Nitrification emits nitrogen oxide gases (NO, NO2, and N2O), which are potentially hazardous compounds that contribute to global warming. Despite considerable interest in nitrification, the purpose of QS in the physiology/ecology of nitrifying bacteria is poorly understood. Through a quorum quenching approach, we investigated the role of QS in a well-studied AHL-producing nitrite oxidizer, Nitrobacter winogradskyi We added a recombinant AiiA lactonase to N. winogradskyi cultures to degrade AHLs to prevent their accumulation and to induce a QS-negative phenotype and then used mRNA sequencing (mRNA-Seq) to identify putative QS-controlled genes. Our transcriptome analysis showed that expression of nirK and nirK cluster genes (ncgABC) increased up to 19.9-fold under QS-proficient conditions (minus active lactonase). These data led to us to query if QS influenced nitrogen oxide gas fluxes in N. winogradskyi Production and consumption of NOx increased and production of N2O decreased under QS-proficient conditions. Quorum quenching transcriptome approaches have broad potential to identify QS-controlled genes and phenotypes in organisms that are not genetically tractable. IMPORTANCE: Bacterial cell-cell signaling, or quorum sensing (QS), is a method of bacterial communication and gene regulation that is well studied in bacteria. However, little is known about the purpose of QS in many environmentally important bacteria. Here, we demonstrate quorum quenching coupled with mRNA-Seq to identify QS-controlled genes and phenotypes in Nitrobacter winogradskyi, a nitrite-oxidizing bacterium. Nitrite oxidizers play an important role in the nitrogen cycle though their participation in nitrification, the aerobic oxidation of ammonia to nitrate via nitrite. Our quorum quenching approach revealed that QS influences production and consumption of environmentally important nitrogen oxide gases (NO, NO2, and N2O) in N. winogradskyi This study demonstrated a novel technique for studying QS in difficult-to-work-with microorganisms and showed that nitrite oxidizers might also contribute to nitrification-dependent production of nitrogen oxide gases that contribute to global warming.

Development and Quality Control of Nanohexaconazole as an Effective Fungicide and Its Biosafety Studies on Soil Nitifiers.

The study was aimed to develop a nano form of an existing fungicide for improving plant protection and reducing crop losses caused by fungal pathogens. The protocol for the preparation and estimation of nanohexaconazole was developed. Technically pure hexaconazole was converted into its nanoform using polyethyleneglycol-400 (PEG) as the surface stabilizing agent. Nanohexaconazole was characterized using Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS) studies. The average particle size of nanohexaconazole was about 100 nm. An analytical method was also developed for quality control of the nanofungicide by GLC fitted with flame ionization detector. Its limit of detection was 2.5 ppm. Fungicidal potential of nanohexaconazole was better in comparison to that of conventional hexaconazole. Hydrolytic and thermal stability studies confirmed its stability at par with the conventional formulation of fungicide. Impact of nanohexaconazole on soil nitrifiers was tested in vitro and there were no significant adverse effect in their numbers observed as compared to conventional registered formulation, proving the safety of the nanofungicide.

Stable partial nitritation for low-strength wastewater at low temperature in an aerobic granular reactor.

Partial nitritation for a low-strength wastewater at low temperature was stably achieved in an aerobic granular reactor. A bench-scale granular sludge bioreactor was operated in continuous mode treating an influent of 70 mg N-NH4(+) L(-1) to mimic pretreated municipal nitrogenous wastewater and the temperature was progressively decreased from 30 to 12.5 °C. A suitable effluent nitrite to ammonium concentrations ratio to a subsequent anammox reactor was maintained stable during 300 days at 12.5 °C. The average applied nitrogen loading rate at 12.5 °C was 0.7 ± 0.3 g N L(-1) d(-1), with an effluent nitrate concentration of only 2.5 ± 0.7 mg N-NO3(-) L(-1). The biomass fraction of nitrite-oxidizing bacteria (NOB) in the granular sludge decreased from 19% to only 1% in 6 months of reactor operation at 12.5 °C. Nitrobacter spp. where found as the dominant NOB population, whereas Nitrospira spp. were not detected. Simulations indicated that: (i) NOB would only be effectively repressed when their oxygen half-saturation coefficient was higher than that of ammonia-oxidizing bacteria; and (ii) a lower specific growth rate of NOB was maintained at any point in the biofilm (even at 12.5 °C) due to the bulk ammonium concentration imposed through the control strategy.

Waveguide evanescent field scattering microscopy: bacterial biofilms and their sterilization response via UV irradiation.

Waveguide Evanescent Field Scattering (WEFS) microscopy is introduced as a new and simple tool for label-free, high contrast imaging of bacteria and bacteria sensors. Bacterial microcolonies and single bacteria were discriminated both by their bright field images and by their evanescent scattering intensity. By comparing bright field images with WEFS images, the proportion of planktonic: sessile (i.e., "floating": attached) bacteria were measured. Bacteria were irradiated with UV light, which limited their biofilm forming capability. A quantitative decrease in attachment of individual, sessile bacteria and in attached, microcolony occupied areas was easily determined within the apparent biofilms with increasing UV dose. WEFS microscopy is an ideal tool for providing rapid quantitative data on biofilm formation.

Performance evaluation and bacterial characterization of membrane bioreactors.

A bench-scale conventional membrane bioreactor (C-MBR), a moving bed membrane bioreactor (MB-MBR) and an anoxic/oxic membrane bioreactor (A/O-MBR), operating under similar feed, environmental and operating conditions, were each evaluated for their treatment performance and bacterial diversity. MBRs were compared for the removal of organics (COD) and nutrients (N and P) while pure culture techniques were employed for bacterial isolation and an API 20E kit was used to identify the isolates. Pseudomonas aeruginosa, selected as a representative of denitrifying microorganisms, was isolated only from the A/O-MBR using Citrimide Agar. Using PCR, the nitrifying bacteria Nitrosomonas europaea was detected only in the MB-MBR. On the other hand, Nitrobacter winogradskyi was detected in all three reactors. Addition of media and maintenance of a lesser DO resulted in the highest TN removal in the A/O-MBR as compared to the C-MBR and the MB-MBR, whereas better nitrification was observed in the MB-MBR than in the C-MBR.

Structure of nitrifying biofilms in a high-rate trickling filter designed for potable water pre-treatment.

This study examined the composition and structure of nitrifying biofilms sampled from a high-rate nitrifying trickling filter which was designed to pre-treat raw surface water for potable supply. The filter was operated under a range of feed water ammonia and organic carbon concentrations that mimicked the raw water quality of poorly protected catchments. The biofilm structure was examined using a combination of fluorescence in situ hybridisation and scanning electron microscopy. Biopolymers (carbohydrate and protein) were also measured. When the filter was operated under low organic loads, nitrifiers were abundant, representing the majority of microorganisms present. Uniquely, the study identified not only Nitrospira but also the less common Nitrobacter. Small increases in organic carbon promoted the rapid growth of filamentous heterotrophs, as well as the production of large amounts of polysaccharide. Stratification of nitrifiers and heterotrophs, and high polysaccharide were observed at all filter bed depths, which coincided with the impediment of nitrification throughout most of the filter bed. Observations presented here specifically linked biofilm structure with filter functionality, physically validating previous empirical modelling hypotheses regarding competitive interactions between autotrophic and heterotrophic bacteria in biofilms.

[Factors of the rapid startup for nitrosation in sequencing batch reactor].

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.

Seasonal variations of nitrifying community in trickling filter-solids contact (TF/SC) activated sludge systems.

Two full-scale trickling filter/solids contact (TF/SC) basin plants, each successfully performing nitrification, were sampled throughout various seasons over a period of one year. Concentrations of ammonia, nitrate and nitrite were measured at various sampling locations along the treatment train. DNA was also extracted from mixed liquor in the solids contact basins. These DNA samples were subjected to terminal restriction fragment length polymorphism (TRFLP) in order to profile the ammonia oxidizing bacteria and nitrite oxidizing bacteria communities. In both plants, there was a prevalence of Nitrosomonas europaea among the ammonia oxidizing bacteria (AOBs). However, during the summer months, there was increased diversity of Nitrosomonas species. Likewise, Nitrospira spp. was the dominant nitrite oxidizing bacteria (NOBs) in both plants regardless of season. Yet there was an increased presence of Nitrobacter among the NOBs in the summer months. These results add an important understanding of the ecology and dynamics in nitrifying population in full-scale TF/SC wastewater treatment plants.

[Characteristics of N forms and N-transforming bacteria in paddy soil under different tillage patterns].

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.

Fluctuation of microbial activities after influent load variations in a full-scale SBR: recovery of the biomass after starvation.

Due to variations in the production levels, a full-scale sequencing batch reactor (SBR) for post-treatment of tannery wastewater was exposed to low and high ammonia load periods. In order to study how these changes affected the N-removal capacity, the microbiology of the reactor was studied by a diverse set of techniques including molecular tools, activity tests, and microbial counts in samples taken along 3 years. The recover capacity of the biomass was also studied in a lab-scale reactor operated with intermittent aeration without feeding for 36 days. The results showed that changes in the feeding negatively affected the nitrifying community, but the nitrogen removal efficiencies could be restored after the concentration stress. Species substitution was observed within the nitrifying bacteria, Nitrosomonas europaea and Nitrobacter predominated initially, and after an ammonia overload period, Nitrosomonas nitrosa and Nitrospira became dominant. Some denitrifiers, with nirS related to Alicycliphilus, Azospirillum, and Marinobacter nirS, persisted during long-term reactor operation, but the community fluctuated both in composition and in abundance. This fluctuating community may better resist the continuous changes in the feeding regime. Our results showed that a nitrifying-denitrifying SBR could be operated with low loads or even without feeding during production shut down periods.

[Effects of influent flow distribution ratio on nitrogen removal in step-feed A/O process].

In order to optimize the utilization of influent carbon source, a feeding pattern so-called "coefficient of influent flow rate" was adopted in a pilot-scale step-feed A/O process treating domestic wastewater. The effects of influent flow distribution ratio on nitrogen removal efficiency were investigated when the reactor was operated at different loading rates and COD/TKN ratio of 3, 5, 7, 9, 11, 13, respectively. The experiment results indicated that the wasting of nitrification capacity occurred when high loading rate and low C/N ratio (COD/TKN <5) were applied, while ammonia removal efficiency was decreased obviously at the same time. When the system was operated at high loading rate and high C/N ratios, the insufficient nitrification occurred in first stage, which resulted in the absence of electron accepter in the downstream anoxic zone. Consequently, the total nitrogen (TN) removal efficiency was decreased even though the COD/TKN was higher than 9. However, due to the unlimited nitrification, the increased C/N ratio led to an enhancement of TN removal efficiency when the system was operated at low influent loading rate. When the influent COD/TKN was kept at 13 around, relatively low effluent TN concentration less than 2 mg/L, and a highest TN removal efficiency of 97.6% were achieved, respectively. For the feeding pattern selected for the study, the conclusions obtained from the experiment results showed that the influent flow coefficient method could use carbon source sufficiently and decrease the influent flow rate of last stage when the wastewater with higher C/N(C/N > alpha) was fed. However, a completely nitrification should be promised in each stage during this period. When the wastewater with low C/N ratio (C/N < alpha), due to the limited carbon source, C/N is the key parameter for TN removal efficiency. From the point view to favor the growth of nitrifiers and satisfy the ammonia effluent standard, the balanced loading of nitrifiers in each stage strategy maybe substitute the feeding pattern proposed in this study as an optimal choice.

[Control of shortcut nitrification in SBBR with adequate oxygen supply].

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.

[Complete nitritation process in an biofilm moving bed system by controlling pH].

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.

Development and calibration of a nitrification PDE model based on experimental data issued from biofilter treating drinking water.

To remove ammonia for production of drinking water, nitrification can be performed in a bio-filter. At least 1 month is necessary to capture from the groundwater and then grow a sufficient amount of nitrifying bacteria to reach the desired removal efficiency. Improving start-up of bio-filters at low substrate concentration is therefore a major challenge. In this connection, it is important to develop appropriate models for designing, monitoring or analysing biofilm systems during start-up or following disinfection events. This study discusses the development and calibration of a nitrification PDE model which reflects the compromise between the complexity associated with the description of the full physical and biochemical mechanisms and the search for a simplified model with identifiable parameters. This model takes only the relevant phenomena (considering the full operating range) into account. The validity of the calibrated model has been evaluated through experiments under very different operational conditions, at the laboratory and under real industrial conditions, involving the full upstream chain of water treatment (iron oxidation and sand filter).

Genome sequence of the chemolithoautotrophic nitrite-oxidizing bacterium Nitrobacter winogradskyi Nb-255.

The alphaproteobacterium Nitrobacter winogradskyi (ATCC 25391) is a gram-negative facultative chemolithoautotroph capable of extracting energy from the oxidation of nitrite to nitrate. Sequencing and analysis of its genome revealed a single circular chromosome of 3,402,093 bp encoding 3,143 predicted proteins. There were extensive similarities to genes in two alphaproteobacteria, Bradyrhizobium japonicum USDA110 (1,300 genes) and Rhodopseudomonas palustris CGA009 CG (815 genes). Genes encoding pathways for known modes of chemolithotrophic and chemoorganotrophic growth were identified. Genes encoding multiple enzymes involved in anapleurotic reactions centered on C2 to C4 metabolism, including a glyoxylate bypass, were annotated. The inability of N. winogradskyi to grow on C6 molecules is consistent with the genome sequence, which lacks genes for complete Embden-Meyerhof and Entner-Doudoroff pathways, and active uptake of sugars. Two gene copies of the nitrite oxidoreductase, type I ribulose-1,5-bisphosphate carboxylase/oxygenase, cytochrome c oxidase, and gene homologs encoding an aerobic-type carbon monoxide dehydrogenase were present. Similarity of nitrite oxidoreductases to respiratory nitrate reductases was confirmed. Approximately 10% of the N. winogradskyi genome codes for genes involved in transport and secretion, including the presence of transporters for various organic-nitrogen molecules. The N. winogradskyi genome provides new insight into the phylogenetic identity and physiological capabilities of nitrite-oxidizing bacteria. The genome will serve as a model to study the cellular and molecular processes that control nitrite oxidation and its interaction with other nitrogen-cycling processes.

[Spatial distribution of nitrifying bacteria communities in suspended carrier biofilm].

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.

[Study of ammonium-nitrogen removal in suspended carrier biofilm reactor].

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.

[Effect of denitrifying biofilm development on the surface configuration and chemical composition of PBS polymer].

PBS, a new kind of biodegradable polymers (BDPs), can be used as carbon source and biofilm carrier to remove nitrate from drinking water source. The effect of denitrification on the surface configuration and chemical composition of PBS was analyzed by using IR spectrum and SEM observation. The results showed that PBS could be only decomposed under attack of microbial enzymes and provided the carbon source for biomass. Influent nitrate concentration (53 mg x L- 1) can be reduced to less than 10 mg x L(-1) within 12 h. The IR spectrum showed that under development of denitrifying biofilm, absorption band at 2 925 cm(-1),2 850 cm(-1), 3200 cm(-1) -3410 cm-1 became weak, which suggested that the content of methyl or hydroxyl group in PBS decreased slightly, and the other functional groups were not influenced apparently. The main monomer gradients of PBS, such as starch and ethylene, could all be utilized as carbon source by denitrifiers. The SEM observation indicated that the cavity could be formed on the PBS granular surface, which increased the area for denitrifiers to attach. The formation of the cavity structure on the PBS surface was beneficial to further development of compact biofilm, which can protect denitrifiers.