Activity Of Nitrifying Bacteria Research Articles

Long-term operation of a two-reactor partial nitrification/anammox system with reverse sequence configuration and internal recirculation: Process performance and microbial community dynamics

Despite the higher investment costs of two-stage partial nitrification/anammox (PN/AMX) systems compared to single-reactor configurations, creating more favorable conditions for specific N-cycling microbial groups in different reactors can help more easily maintain the stability of the overall system. In this work, an unusual two-reactor PN/AMX system with brush-type carriers, reverse sequence configuration and internal recirculation was operated for 500 d using both high strength synthetic wastewater and real reject water. Feasibility of the proposed system was confirmed by relatively high (>70%) total N removal without strict control over the nitrification process due to synergistic activity of nitrifying, denitrifying and anammox bacteria. The limiting level of COD in the influent was ∼600 mg O2/L, exceeding which sharply deteriorated the process of nitrogen removal. The microbial community of the PN reactor naturally evolved into clearly distinguishable free-floating sludge and 2 types of biofilms (red and brown), which had different relative abundances of key N cycling groups in each phase of PN/AMX system operation. While the AMX community was dominated by the genus Candidatus Jettenia ecosi. Considering the ease of operation and relatively high N removal efficiency, the proposed PN/AMX system may merit further study for process optimization and practical use.

Enhanced granulation of activated sludge in an airlift reactor for organic carbon removal and ammonia retention from industrial fermentation wastewater: A comparative study

Ammonia retention and recovery from high-nitrogenous wastewater are new concepts being used for nitrogen management. A microaerophilic activated sludge system was developed to convert organic nitrogen into ammonia and retain it for its recovery; however, the settleability of activated sludge remains a challenge. Therefore, this study proposed an aerobic granular sludge system as a potential solution. Two types of sequencing batch reactors—airlift and upflow reactors—were operated to investigate the feasibility of fast granule formation, the performance of organic carbon removal and ammonia retention, and the dynamics of microbial community composition. The operation fed with industrial fermentation wastewater demonstrated that the airlift reactor ensured a more rapid granule formation than the upflow reactor because of the high shear force, and it maintained a superior ammonia retention stability of approximately 85 %. Throughout the operational period, changes in hydraulic retention time (HRT), settling time, and exchange ratio altered the granular particle sizes and microbial community compositions. Rhodocyclaceae were replaced with Comamonadaceae, Methylophilaceae, Xanthomonadaceae, and Chitinophagaceae as core taxa instrumental in granulation, likely because of their extracellular polymeric substance secretion. As the granulation process progressed, a significant decrease in the relative abundances of nitrifying bacteria—Nitrospiraceae and Nitrosomonadaceae—was observed. The reduction of settling time and HRT enhanced granulation and inhibited the activity of nitrifying bacteria. The success in granulation for ammonia conversion and retention in this study accelerates the paradigm shift from ammonia removal to ammonia recovery from industrial fermentation wastewater.

Impacts of Polylactic Acid Microplastics on Performance and Microbial Dynamics in Activated Sludge System

A large number of microplastics (MPs) have been found in various stages of wastewater treatment plants, which may affect the functional microbial activity in activated sludge and lead to unstable pollutant removal performance. In this study, the effects of different concentrations of polylactic acid microplastics (PLA MPs) on system performance, nitrification and phosphorus (P) removal activities, and extracellular polymeric substances (EPS) were evaluated. The results showed that under the same influent conditions, low concentrations (50 particles/(g TS)) of PLA MPs had no significant effect on effluent quality. The average removal efficiencies of chemical oxygen demand, phosphate, and ammonia were all above 80%, and the average removal efficiencies of total nitrogen remained above 70%. High concentrations (200 particles/(g TS)) of PLA MPs inhibited the activities of polyphosphate-accumulating organisms (PAOs) and nitrifying bacteria. The specific anaerobic P release rate decreased from 37.7 to 23.1 mg P/(g VSS·h), and the specific aerobic P uptake rate also significantly decreased. The specific ammonia oxidation rate decreased from 0.67 to 0.34 mg N/(g VSS·h), while the change in the specific nitrite oxidation rate was not significant. The dosing of PLA MPs decreased the total EPS and humic acid content. As the concentration of PLA MPs increased, microbial community diversity increased. The relative abundance of potential PAOs (i.e., Acinetobacter) increased from 0.08 to 12.57%, while the relative abundance of glycogen-accumulating organisms (i.e., Competibacter and Defluviicoccus) showed no significant changes, which would lead to improved P removal performance. The relative abundance of denitrifying bacteria (i.e., Pseudomonas) decreased from 95.43 to 58.98%, potentially contributing to the decline in denitrification performance.

Isolation and screening of indigenous nitrifying bacteria to enhance nutrient recovery in an aquaponics system

AbstractThe recycling processes of aquaponic waste into fertilizers are highly dependent on the type and activity of nitrifying bacteria in the system. This study aims to find indigenous nitrifiers to enhance nutrient recovery in an aquaponics system. Twelve indigenous nitrifiers consisting of ammonia and nitrite‐degrading bacteria were isolated from a local earthen pond of Nile tilapia (Oreochromis niloticus), and two isolates (AQ4 and AQ12) were selected due to their highest capacity to degrade either ammonia or nitrate respectively. Based on the 16S rRNA gene sequences, these isolates were identified as Marinobacter nauticus (AQ4) with 98.64% similarity, and Bacillus sp. (AQ12) with 99.89% similarity. When these bacterial isolates were applied in aquaponics systems with bacterial enhancement (aquaponicsBE), the nutrient recovery was significantly higher compared to the control (aquaponicsctrl), indicated by a 500 g higher total harvested biomass. With a significance value of p < 0.05, aquaponicsBE gives 17% higher crude fat and protein retention in vegetables while in fish 14% higher crude fat was found. Energy retention in vegetables was 23% higher than in the control. Furthermore, fish grew better in the aquaponicsBE system, with 0.6%BW/day higher specific growth rate, and 0.05 better feed conversion ratio compared to that of fish reared in the control.

Micro-aeration and low influent C/N are key environmental factors for achieving ANAMMOX in livestock farming wastewater treatment plants

Anaerobic ammonium oxidation (ANAMMOX)-mediated system is a cost-effective green nitrogen removal process. However, there are few examples of successful application of this advanced wastewater denitrification process in wastewater treatment plants, and the understanding of how to implement anaerobic ammonia oxidation process in full-scale is still limited. In this study, it was found that the abundance of anaerobic ammonia-oxidizing bacteria (AnAOB) in the two livestock wastewater plants named J1 and J2, respectively, showed diametrically opposed trends of waxing and waning with time. The microbial communities of the activated sludge in the two plants at different time were sampled and analyzed by high-throughput sequencing of 16S rRNA genes. Structural equation models (SEMs) were used to reveal the key factors affecting the realization of the ANAMMOX. Changes in the concentration of dissolved oxygen and C/N had a significant effect on the relative abundance of anaerobic ammonia oxidation bacteria (AnAOB). The low concentration of DO (0.2∼0.5 mg/L) could inhibit the activity of nitrifying bacteria (NOB) to achieve partial oxidation of ammonia nitrogen and provide sufficient substrate for the growth of AnAOB, similar to the CANON (Completely Autotrophic Nitrogen removal Over Nitrite). Unlike CANON, heterotrophic denitrification is also a particularly critical part of the livestock wastewater treatment, and a suitable C/N of about 0.6 could reduce the competition risk of heterotrophic microorganisms to AnAOB and ensure a good ecological niche for AnAOB. Based on the results of 16S rRNA and microbial co-occurrence networks, it was discovered that microorganisms in the sludge not only had a richer network interaction, but also achieved a mutually beneficial symbiotic interaction network among denitrifying bacteria (Pseudomonas sp., Terrimonas sp., Dokdonella sp.), AnAOB (Candidatus Brocadia sp.) at DO of 0.2∼0.5 mg/L and C/N of 0.6. Among the top 20 in abundance of genus level, AnAOB had a high relative abundance of 27.66%, followed by denitrifying bacteria of 3.67%, AOB of 0.64% and NOB of 0.26%, which is an essential indicator for the emergence of an AnAOB-dominated nitrogen removal cycle. In conclusion, this study highlights the importance of dissolved oxygen and C/N regulation by analyzing the mechanism of ANAMMOX sludge extinction and growth in two plants under anthropogenic regulation of AnAOB in full-scale wastewater treatment systems.

Research on Greenhouse Gas Emission Reduction Methods of SBR and Anoxic Oxic Urban Sewage Treatment System

With the rising awareness of environmental protection, more sewage treatment plants have been built. However, this is also one of the main sources of greenhouse gas emissions. This study carried out a series of sewage treatment experiments to analyze the factors affecting the greenhouse gas emissions of the two commonly used treatment processes in the current urban sewage treatment: the A/O and SBR methods. The experimental results showed that the total amount of greenhouse gases emitted by the A/O method was 415.63 gCO2-eq/m3, and the total amount of greenhouse gases emitted by the SBR method was 879.51 gCO2-eq/m3. The N2O emission factor in the A/O method experimental group was 0.76% of the nitrogen content in the influent. In the aerobic section, when the content of dissolved oxygen was in the range of 1.30~2.10 mg/L, and the content of dissolved oxygen was 1.90 mg/L, the minimum N2O emission factor was reduced to 0.29% of the nitrogen content of the influent. In the SBR experimental group, the ammonia oxidation rate of sewage decreased rapidly as the temperature decreased, thus affecting the discharge rate of N2O. At 25 °C, the biological enzyme activity of nitrifying bacteria was higher, thus promoting denitrification and generating more greenhouse gases. The research results provide reference for strengthening the management of sewage treatment plants and reducing greenhouse gas emissions from sewage treatment plants.

Impact of Chronic Crude Oil Pollution on Nitrification in Edaphic Systems

Nitrification plays a key role in regulating soil fertility, concentration of soil inorganic nitrogen and production of the highly potent greenhouse gas, nitrous oxide, from soil. This study investigated the effect of long-term crude oil pollution on the activity, abundance and diversity of autotrophic nitrifying bacteria in impacted soils from Bomu and Abonema in the Nigerian Niger Delta compared to unpolluted systems. Nitrifier activity was investigated by determining the soil oxidation potentials while the most probable number microtechnique using Winogradsky media was used to ascertain nitrifying bacteria abundance and soil DNA analysis alongside plate cultures defined nitrifying bacterial diversity. Nitrifier activity was found to be higher in the polluted soils than in the unpolluted soils while quantification of the nitrifying bacteria revealed that polluted samples had higher nitrifier counts. Statistically significant differences existed amongst nitrifier counts and activity (p≤0.05) between polluted and unpolluted systems with positive correlation between nitrifying bacteria counts and oxidation potential. The results highlighted the dominance of cultivable Nitrosomonas and Nitrobacter in both polluted and unpolluted soils while DNA analysis revealed that Nitrospira was the dominant nitrifier genus in unpolluted soils and Nitrobacter in polluted soils. Nitrospira was not detected the polluted ecosystems. No ammonia oxidisers were detected via metagenomics analysis. The ammonia oxidisers proved to be more sensitive to chronic crude oil pollution than the nitrite-oxidising bacteria. Long term crude oil exposure produced a 3 – 5 times increase in the activity of nitrifying bacteria in polluted soils with approximately twice the abundance when compared to the unpolluted systems.

Potential roles of acyl homoserine lactones (AHLs) in nitrifying bacteria survival under certain adverse circumstances

Potential roles of quorum sensing (QS) in nitrifying bacteria activity and ecology, particularly under adverse circumstances have been rarely reported. Herein, eight lab-scale nitrification sequencing batch reactors, with or without adding acyl homoserine lactones (AHLs) were operated under adverse circumstances respectively. The results indicated that the introduction of AHLs significantly enhanced the nitrogen removal efficiency in the presence of nitrification inhibitors (dicyandiamide, DCD), accelerated the low temperature (10 °C) group into stable stage, and improved the utilization efficiency of AHLs in these two groups. Community analysis and qPCR further confirmed that AHLs significantly increased the abundance of nitrifying bacteria in low temperature group and DCD group, especially AOB. For normal condition (28 °C, pH = 8) or low pH level (5.5), however, the AHLs had no significant effect. Canonical correspondence analysis showed that nitrifying bacteria positively responded to AHLs, indicating that adding AHLs was an effective strategy to regulate nitrification process. However, under acid conditions, the effect of this regulatory mechanism was not significant, indicating that the influence of pH on the system was greater than that of AHLs. This study demonstrated that exogenous AHLs could enhance the competitiveness of nitrifying bacteria to utilize more resource and occupy space under some adverse environmental conditions.

APLIKASI KULIT LABU Curcubitaeae sp. SEBAGAI SUMBER STIMULASI UNTUK PROSES NITRIFIKASI DAN DENITRIFIKASI DI LINGKUNGAN BUDIDAYA UDANG VANAME (Litopenaeus vannamei)

Aplication of pumpkin skin flour Curcubitae sp. to improve of the water quality performance and support shrimp Litopenaeus vannamei growth, it necessary to do an analysis. Pumpkin skin Curcubitae sp. as a source of stimulants needed by bacteria to survive in the nitrification denitrification processes in aquaculture as an alternative to environmental friendly with bioremediation system evaluation. Its mesophilic nature and a organic ions source for bacterial growth. Pumpkin skin can support the growth and activity of nitrifying denitrifying bacteria in the environment. This study aims to determine the best of dose of pumpkin skin as a biostimulator of nitrifying denitrifying bacteria growth. The treatments used were pumpkin doses of 0%, 2%, 4%, 6% for 20 L culture water. Giving pumpkin flour can improve the performance of abundance and activity of nitrification denitrification bacteria. The activity of nitrifying bacteria can be seen from the presence of ammonia value which is relatively more stable compared to other treatments. The best oxidation of ammonia in 6%, and reduction nitrite in the 4% treatments. The treatment of 4% was effective in maintenance for 30 days which could maintain the stability of water quality and increase the growth of vaname shrimp.

The Abundance and Potential Activity of Nitrifying, Denitrifying, and Nitrate-ammonifying Bacteria in the Vanamae Shrimp Culture in Karawang

The existence of inorganic nitrogen in the shrimp pond ecosystem will not be separated from the nitrogen cycle and microbiological processes including the activity of microbes. This study aimed to analyze the abundance and potential rate of nitrifying, denitrifying, and nitrate-ammonifying bacteria in Vanamae shrimp cultivation. Water samples were collected on a shrimp pond in Karawang, West Java. Water sampling was carried out at the age of shrimp rearing 0 days, 21 days, 65 days, and 89 days. Water sampling was conducted at four points representing an area of the pond. The bacterial abundances were analyzed using Most Probable Number (MPN) method. The potential rates of bacteria were calculated by Michaelis-Menten kinetics. The highest abundance of nitrifying bacteria was 3.690 log cells ml-1 on 65 days, denitrifying bacteria was 3.415 log cells mL-1 on 89 days, and nitrate-ammonifying bacteria was 3.079 log cells mL-1 on 65 days of shrimp cultivation. The affinity of enzymes related to ammonia oxidation from nitrifying bacteria was higher than nitrate reduction from denitrifying and nitrate-ammonifying bacteria. Generally, nitrifying bacteria were the most abundant and dominant activity over shrimp cultivation.

Bioaugmentation of Anammox Activated Sludge with a Nitrifying Bacterial Community as a Way to Increase the Nitrogen Removal Efficiency

—Bioaugmentation, i.e., increasing the abundance of certain microorganisms in the community by adding appropriate cells or establishing the conditions promoting their growth, is widely used in environmental technologies. Its application for launching of the anammox reactors is usually limited to introduction of anammox bacteria. We expected addition of nitrifiers during anammox bioreactor launching to stimulate the anammox process due to rapid production of nitrite, which anammox bacteria use for ammonium oxidation. The present work investigated the effect of introduction of a nitrifying community on the composition and activity of the microbial community in an anammox reactor. At the time of inoculation of a laboratory SBR reactor, an active nitrifying community (5 days old) (ASB) (bioaugmenting activated sludge, ASB) containing group I nitrifiers, primarily Nitrosospira, was added (1 : 100 by biomass) to anammox activated sludge (ASA) stored for 1 month at 4°C and exhibiting low metabolic activity. The use of ASB resulted in increased efficiency of nitrogen removal. While noticeable nitrogen removal in the control (7%) was observed since day 11 of incubation, nitrogen removal in the experimental reactor began on day 4 at the level of 20%. Nitrogen removal after 30 days of incubation was ~60% in the experiment and 20% in the control. The rate of ammonium oxidation in the presence of ASB increased due to activity of nitrifying bacteria (during the first 10 days of operation) and anammox bacteria of the genus Brоcadia, which were already present in ASA (throughout all period of operation). Activity of group II nitrifiers (genera Nitrobacter and Nitrococcus), which were present in ASB, prevented accumulation of nitrite, which in high concentrations is toxic to both nitrifiers and anammox bacteria. High activity of the Nitrosospira nitrifiers introduced with ASB probably provided the anammox bacteria with one of the substrates (nitrite), promoting their rapid growth. During subsequent operation of the reactor, nitrifiers of the genus Nitrosomonas from the initial ASA community were mainly responsible for growth of the anammox bacteria. Thus, ASA bioaugmentation at the loading of the anammox reactor by active nitrifiers resulted in significantly improved efficiency of ammonium removal via the anammox process and accelerated transition of the reactor to the working mode.

Some Results of Poultry Litter Processing into a Fertilizer by the Wet Torrefaction Method in a Fluidized Bed

Poultry litter mass is formed in large quantities at poultry farms producing poultry meat (1–3 kg of litter mass per 1 kg of produced meat). These wastes represent a threat to the environment because of the presence of pathogenic microflora in them and the greenhouse gas emitted during the storage of these wastes. The procedure of poultry litter mass processing by wet torrefaction in a superheated water vapor environment at a temperature of 150–260 °C is studied. It is shown that after torrefaction at a temperature of 150 °C, the poultry litter mass retains high humidity, i.e., it represents an environment suitable for the re-development of pathogenic microflora. Only after wet torrefaction at a temperature of 260 °C does the humidity of the poultry litter mass decreases to 4%, and the risk of re-infection with pathogenic microflora decreases sharply. The absence of nitrates in the samples after torrefaction at a temperature of 260 °C indicates the termination of the activity of nitrifying bacteria. After torrefaction at a temperature of 260 °C, the poultry litter mass has a pH close to 7. This increases the mobility and availability of microelements for plants. Torrefaction at a temperature of 260 °C increases the content of ash, phosphorus and potassium by 30–40% and nitrogen by 15–20%, which makes the fertilizer more concentrated and optimizes the ratio of nitrogen, phosphorus and potassium. After wet torrefaction, due to the burning of the most easily degradable nitrogen-containing organic compounds and the destruction of some organophosphorus compounds, the mobility of nitrogen decreases, and the mobility of phosphorus increases. As a result of the research, it was found that the treatment of poultry manure by wet torrefaction in an environment of superheated water vapor at a temperature not lower than 260 °C makes it possible to obtain organic fertilizer with the most optimal nutrient content.

Performance of partial nitrification process in a zeolite biological aerated filter with the addition of sulfamethoxazole

Due to the rapid development of medical industries, wastewater treatment plants have become sinks for residual antibiotics. However, the contribution of novel partial nitrification processes to the bioremediation of antibiotics remains unclear. In this study, the removal rate of a partial nitrification process on the biotransformation of sulfamethoxazole (SMZ) was evaluated. A biological aerated filter made from zeolite successfully achieved stable partial nitrification. A nitrite accumulation percentage (NAP) greater than 85% was obtained when the influent ammonium concentration was increased to 300 mg/L with a nitrogen loading rate of 1.24 kg/(m3 d). Batch tests were performed on support collected from different heights of the up-flow reactor at the end of the pilot monitoring experiment. The maximum ammonium oxidation rate of 5.63 mg/(g VSS·L) in one hour was recorded at a height of 0.32–0.48 m in the reactor, indicating nitrifying bacteria activity link between the free ammonia (FA) and biomass concentration was found. After the addition of SMZ (2.5 mg/L), the NAP declined to approximately 70%, and the abundance of Nitrosomonas (the main ammonia oxidizing bacteria (AOB) genus in the zeolite biological aerated filter (ZBAF)) decreased 7.24–6.10%. Lower abundance and activity of AOB oxidized ineffectively the primary amine of SMZ, which led to lower than 19% of the SMZ removal efficiency.

Toxicity of pulp and paper industry effluent on the bioremediation activity of saprophytic and nitrifying microorganisms

In this work, initially, the effluent of pulp and paper industry was subjected to analyse physical, chemical and physicochemical parameters and concentration of heavy metals. The detrimental effects of the effluent of pulp and paper industry on the biological activity of saprophytic and nitrifying bacteria has been studied using different volume percentages of effluent (0-6.67%). A concentration of 5.0 mg/L glucose was used as control and source of carbon for microorganisms. An increase in percentage inhibition of biological activity of microorganisms has been observed with the increasing concentration of the effluent in the proposed systems. The kinetic parameters, i.e., rate constant (K) and ultimate biochemical oxygen (L) were also evaluated using first and second order kinetics. Overall study resulted in the high resistivity of nitrifying bacteria than saprophytic bacteria to the pulp and paper industry waste.

Use of ozone for Vibrio parahaemolyticus inactivation alongside nitrification biofilter treatment in shrimp-rearing recirculating aquaculture system

Disease suppression is an essential aspect of shrimp farming. To control water quality, a recirculating aquaculture system (RAS) is employed in worldwide. In RAS, water quality is achieved by nitrification biofilter treatment, whereas disease prevention is achieved by the application of an oxidizing agent such as ozone (O3). This study investigates the proper residual ozone concentration (ROC) dosage for controlling pathogenic bacteria Vibrio parahaemolyticus (VP) and minimizing mal-effects on nitrifying bacteria activity in the biofilter media inside an RAS. Juvenile Pacific white shrimp, Litopenaeus vammanei, were cultured for 4 months in a lab-scale brackish RAS integrated with ozonation. Results showed that although the system biofilter's nitrification activity was influenced by ROC, the 0.3 mg L−1 ROC dosage provided an optimum condition which effectively eliminated VP in the biofilter but did not inhibit ammonia removal. At a higher ROC (approximately 0.4 mg L−1) ozonation dosage, the biofilter's ammonia oxidation rate significantly reduced. Over a 40-day shrimp-rearing operational period, the viable VP count in an aerated (non-ozonated RAS) gradually increased, but the viable VP counts in both biofilm and water in a 0.3 mg L−1 ROC treated RAS significantly reduced down to undetectable levels. As such, the conclusion was drawn that a 0.3 mg L−1 ROC ozonation treatment in the biofilter tank of a RAS can effectively control VP pathogens without influencing the activity of the nitrification biofilter, thus providing a balanced control between water quality and safety to the shrimp.

Sustained and enhanced anaerobic removal of COD and nitrogen in a zeolite amended glycogen accumulating organism dominated biofilm process

Activated sludge, the most widely used biological wastewater treatment process is known to be expensive to operate, largely due to energy expense for oxygen transfer into the bulk wastewater solution. The alternative of using passive aeration facilitates oxygen supply directly from the air resulting in aeration energy savings. The current study demonstrated sustained and improved removal of chemical oxygen demand (COD) and nitrogen in a zeolite modified glycogen accumulating organisms (GAOs) dominated biofilm reactor, which achieved anaerobic removal of COD and ammonium by the activity of GAOs and zeolite, respectively. Draining of the batch-operated reactor enabled the biofilm to directly uptake oxygen from air (passive aeration) to carry out simultaneous nitrification and denitrification due to the activity of GAO (Candidatus competibacter) and nitrifying bacteria (Nitrosomonas and Nitrospira). Under stable long-term (4-months) operation, the process achieved COD and nitrogen removal at rates of 1354 and 79.1 g m−3 d−1, respectively. The biofilm process demonstrated >90% nitrogen removal efficiency in multi-cycle (4/8 cycles) strategy with a short treatment time of 8 h. Due to the passive aeration scheme, the energy consumption of the proposed wastewater treatment process is calculated to be about 13-times less than that of traditional activated sludge process. Therefore, the Passive Aeration Simultaneous Nitrification and Denitrification (PASND) biofilm process is a promising low-energy treatment step for efficient removal of COD and nitrogen from wastewater.

Diversity, prevalence, and expression of cyanase genes (cynS) in planktonic marine microorganisms

Cyanate is utilized by many microbes as an organic nitrogen source. The key enzyme for cyanate metabolism is cyanase, converting cyanate to ammonium and carbon dioxide. Although the cyanase gene cynS has been identified in many species, the diversity, prevalence, and expression of cynS in marine microbial communities remains poorly understood. Here, based on the full-length cDNA sequence of a dinoflagellate cynS and 260 homologs across the tree of life, we extend the conserved nature of cyanases by the identification of additional ultra-conserved residues as part of the modeled holoenzyme structure. Our phylogenetic analysis showed that horizontal gene transfer of cynS appears to be more prominent than previously reported for bacteria, archaea, chlorophytes, and metazoans. Quantitative analyses of marine planktonic metagenomes revealed that cynS is as prevalent as ureC (urease subunit alpha), suggesting that cyanate plays an important role in nitrogen metabolism of marine microbes. Highly abundant cynS transcripts from phytoplankton and nitrite-oxidizing bacteria identified in global ocean metatranscriptomes indicate that cyanases potentially occupy a key position in the marine nitrogen cycle by facilitating photosynthetic assimilation of organic N and its remineralisation to NO3 by the activity of nitrifying bacteria.

Critical flux on a submerged membrane bioreactor for nitrification of source separated urine

Membrane fouling is the biggest challenge in membrane based technology operation. Studies on critical flux mainly focused on membrane bioreactor for municipal wastewater and/or greywater treatment, which can significantly differ from the ultrafiltration membrane bioreactor (UF-MBRs) to treat source separated urine. In this work, the inhibitory factors on nitrifying bacteria activity were investigated for fast acclimation of nitrifying bacteria with high ammonium concentration and optimization of a high-rate partial nitrification MBR. The maximum nitrification rate of 447 ± 50 mgN L–1 d–1 was achieved when concentration of ammonia in feed urine is approximately 4006.3 ± 225.8 mg N L–1 by maintaining desired pH around 6.2 and FA concentrations below 0.5 mgL−1. Furthermore, for the first time, the impact of different operational and filtration conditions (i.e. aeration intensity, filtration method, imposed flux, intermittent relaxation, biomass concentration) on the reversibility of membrane fouling was carried out for enhancement of membrane flux and fouling mitigation. Fouling mechanisms for minor irreversible fouling observed under sub-critical condition were pore blocking and polarization. To mitigate membrane fouling, the UF module with effective membrane surface area of 0.02 m2 is recommended to be operated at the aeration intensity of 0.4 m3 h−1, intermittent relaxation of 15 min, biomass concentration of 3.5 g L−1.

Responses of nitrification and bacterial community in three size aggregates of paddy soil to both of initial fertility and biochar addition

Biochar has been suggested to increase the soil nutrient retention capacity. The interaction of biochar addition and soil initial fertility through modifying soil aggregates on soil bacterial community and nitrogen transformation is still unclear. A 60-day incubation experiment was conducted to investigate the influences of biochar addition on soil nitrification and associated nitrifying microbial community in three size aggregates of different derived soils. The results indicated that potential nitrification rates (PNRs) in three size soil aggregates of biochar addition treatment were significantly (P < 0.05) higher than those of no biochar addition, especially in small size aggregates or in the soils collected from no fertilizer plots. The results of 16S rRNA gene profiling showed that biochar addition significantly (P < 0.05) increased community alpha-diversity. Nitrosomonas was relatively more abundant in microaggregates, whereas Nitrospira was more abundant in macroaggregates. Biochar addition could modify structure of soil microbial communities by changing soil properties, and consequently regulate the nitrification processes as suggested by canonical correlation analysis. Conclusively, biochar addition can promote the nitrification process with the higher community diversity and activity of nitrifying bacteria in soils, more strongly in fertile soils or in the small macroaggregates. The initial soil fertility should be fully considered in practical application of biochar.

Effects of predator movement patterns on the biofouling layer during gravity-driven membrane filtration in treating surface water

Biological predation has a significant effect on biofouling layers in gravity-driven membrane (GDM) filtration systems. However, the detailed process of predatory activities is still not well known. This study explored the effects of predator movement patterns on the biofouling layer at different temperatures and the factors affecting the stable flux level. The results indicated that Demospongiae, Spirotrichea and Saccharomycetes were the main species, with the body contracting or rotating in one position at 5 °C, and Litostomatea accounted for 55.1% at 10 °C. The weak agility of these species resulted in a less porous biofouling layer with a high extracellular polymeric substance (EPS) concentration, which was responsible for the low permeate flux and the time to reach flux stability. Bdelloidea was dominant at 20 and 30 °C, and the more heterogeneous biofouling layer with a lower EPS concentration was related to their intense creeping and swimming movements and their ability to create current in the water. The grazing of spongy flocs by predators affected the GDM system performance, and a high stable flux was obtained with large and loose flocs. In addition, the diversity of the eukaryotic community decreased after the flux stabilized due to the particular predominance of Bdelloidea at high temperatures, corresponding to a high stable flux. Pollutant removal was less affected by eukaryotes, and decreased ammonia nitrogen removal rates were related to the lower activity of nitrifying bacteria. Moreover, the reliable linear correlation between the temperature and the stable flux implied that the stable flux could be well predicted in the GDM system. The findings are beneficial for developing new strategies for regulating flocs and the biofouling layer to improve the performance of GDM systems.