Abundance Of Nitrifying Bacteria Research Articles

Sulfamethoxazole removal in nitrifying membrane aerated biofilms: Physiological responses and antibiotic resistance genes.

Efficient removal of ammonia nitrogen and sulfamethoxazole (SMX) from wastewater has become increasingly critical due to their detrimental effects on aquatic ecosystems and public health. This study aimed to investigate the nitrogen transformation and SMX removal in a membrane aerated biofilm reactor (MABR) under different SMX concentrations (0 ∼ 200 μg·L-1) with a nitrifying membrane bioreactor (MBR) as a control. Results suggested that SMX removal in MABR was better than that of MBR with SMX addition (50 ∼ 200 μg·L-1). Membrane aerated biofilms tended to secrete more extracellular polymeric substances (EPS) and generate less antioxidant enzymes in response to SMX stress when compared with nitrifying sludge in MBR. Metagenomic analysis indicated that distinct succession of microbial community was observed in both systems after SMX addition, and the relative abundance of nitrifying bacteria (Nitrosomonas, Nitrospira, and Nitrobacter) evidently decreased under SMX concentration of 200 μg·L-1. The proliferation of predominant antibiotic resistance gene (ARG) sul2 was suppressed more obviously in MABR than that in MBR. Thus, this study provided extensive insights into the advantages of nitrifying MABR in simultaneous removal of ammonium and antibiotics with less risk of associated ARGs spread.

Impact of water depth and flow velocity on organic matter removal and nitrogen cycling in floating constructed wetlands

The configuration of water depth (WD) and flow velocity (FV) in floating constructed wetlands (FCWs) reflects the complex interactions between hydraulic conditions and wastewater treatment performance. Properly configuring hydraulic conditions can optimize performance. This study explored the removal and degradation of organic matter and nitrogen (N) in FCWs with three different WDs (50 cm (SD), 70 cm (MD), and 95 cm (DD)) under four FV conditions (0, 0.3, 1.0, and 1.5 m/d). It also analyzed the regulatory effects of hydraulic conditions on microbial community structure to provide new insights for configuring hydraulic conditions in FCWs. The results indicate that variations in WD and FV do not significantly affect COD removal (p > 0.05), with removal efficiency (RE) consistently reaching 90 % across all conditions. However, hydraulic conditions do influence the degradation rate (k) of COD, with increased FV enhancing the k in MD and DD. In contrast, WD significantly impacts the removal of NH4+−N (p < 0.05), with RE in SD exceeding 80 % across all four FVs. The primary reason is that increased WD reduced the abundance of nitrifying bacteria (Nitrosomonas and Nitrospira) and functional genes (hao and pmoABC-amoABC). Meanwhile, increased WD and FV significantly enriched the denitrifying bacteria genera (such as Massilia, Bacillus, Ensifer, and Rhodobacter) and certain functional genes (nap and nir), favoring the denitrification process and enhancing the dissimilatory nitrate reduction to ammonium (DNRA) process. Furthermore, microbial community diversity, richness, and the number of operational taxonomic units (OTUs) were highest in SD, but decreased with increased WD. This is mainly related to changes in oxygen (O2) transmission and nutrient concentration. These findings help us understand the mechanisms by which hydraulic regulation affects the removal of organic matter and N in FCWs. They also propose potential solutions from a hydraulics perspective to enhance N removal.

Runoff variation alters estuarine sediment microbiome and nitrogen removal processes by affecting salinity

Runoff variations shape the dynamics of the estuarine environmental factors, profoundly influencing the nitrogen cycle in estuarine sediments. However, our understanding of how these changes regulate microbially-mediated nitrogen removal processes remains limited. In this study, the impacts of changes in environmental factors caused by normal and low runoffs on denitrification and anammox in sediments of the Liao River Estuary in China, were investigated, using continuous-flow experiments combined with 15N tracing techniques and molecular methods. Results indicated that denitrification was the main nitrogen removal process in estuarine sediments under both runoff conditions. Elevated salinity under low runoff condition increased the abundance of nitrifying bacteria (Nitrospina, Nitrosomonas and Nitrosomonadaceae), thereby promoting the coupled nitrification-denitrification nitrogen removal process. Furthermore, seawater intrusion under low runoff contributed to dilute nitrite concentrations, resulting in decreased denitrification rates in sediments. Overall, this study highlighted the impacts of runoff variations on biological nitrogen removal process through affecting environmental factors, gene abundance and microbial community in the estuary.

Enhancing nitrogen transformation and humification in cow manure composting through psychrophilic and thermophilic nitrifying bacterial consortium inoculation

Excessive nitrogen release during composting poses significant challenges to both the environment and compost quality. Biological enhancement of humification and nitrogen conservation is an environmentally friendly and cost-effective approach to composting. The aim of this study was to develop a psychrophilic and thermophilic nitrifying bacterial consortium (CNB) and investigate its role in nitrogen transformation and humification during cow manure composting. Analysis revealed that CNB inoculation promoted microbial proliferation and metabolism, significantly increased the number of nitrifying bacteria (p < 0.05), and elevated the activity of nitrite oxidoreductase and nxrA gene abundance. Compared to the control, CNB inoculation promoted the formation of NO3–-N (77.87–82.35 %), while reducing NH3 (48.89 %) and N2O (20.05 %) emissions, and increased humus content (16.22 %). Mantel analysis showed that the higher abundance of nitrifying bacteria and nxrA facilitated the nitrification of NH4+-N. The improvement in nitrite oxidoreductase activity promoted NO3–-N formation, leading to increased humus content and enhanced compost safety.

Nitrogen removal performance of bioretention cells under freeze-thaw cycles: Effects of filler structure and microbial community

Cold climates have an adverse effect on the nitrogen-removal capacity of bioretention cells, especially during freeze-thaw cycles (FTCs). To explore the effects of FTCs on the nitrogen removal performance of bioretention cells, this research compared the effects of FTCs on the pore structure and microbial community composition of the filler, and analyzed the nitrogen removal performance of the bioretention cell before (RT), during (FTC) and after (RRT) FTCs. The results demonstrated that RRT filler had a much greater number of pores with equivalent diameter <500 μm than RT filler, and that RRT had a higher pore volume and pore density than RT. Microbial community analysis revealed that the diversity and richness of the microbial community in FTC were lower than in RT, and the relative abundance of Lacunisphaera, Pseudomonas, and Dokdonella decreased significantly. There was no significant difference in microbial community richness between RRT and RT, however RRT diversity was lower. RRT has a higher relative abundance of nitrifying bacteria (Subgroup_10, Bryobacter, etc.) than RT, but a lower relative abundance of denitrifying bacteria (Pseudomonas, Dokdonella, Arenimonas, etc.). The nitrogen removal efficiency of FTC was inhibited, resulting in a decrease of 13.0 ± 4.86%, 19.7 ± 9.17%, and 26.6 ± 1.74% in the removal rates of ammonia nitrogen(NH4+-N), nitrate nitrogen(NO3−-N), and total nitrogen(TN) when compared to RT, respectively. RRT improved nitrification and increased NH4+-N removal rate by 10.3 ± 2.69% compared to RT. However, because of denitrification inhibition, the nitrogen removal performance of RRT was not able to reach RT levels, and its NO3−-N and TN removal rates decreased by 100 ± 4.70% and 58.3 ± 3.71%, respectively. This study has demonstrated that FTCs can permanently harm the bioretention cell's filler structure and microbial community, resulting in a significant decrease in the nitrogen removal performance of the bioretention cell designed according to warm climate conditions after experiencing FTCs.

Preparation of slow-release carbon source fillers from agricultural solid waste for efficient nitrogen removal from municipal wastewater: Removal performance, microbial community and mechanisms

In this study, five types of agricultural wastes, were used as alternative materials for slow-release carbon source, alternative materials were prepared as slow-release carbon source fillers (ZCF) using a no-sintering method, and studied by leaching elements, carbon release, nitrification and denitrification potential, and bio-attachment performance, walnut shell-based filler was found to have better performance in terms of persistence of carbon release, impact stability, carbon biochemistry and green safety. When HRT was 8 h in H-O, 12 h in H-A, and R was 100 % and C/N was 2 in H-Z BAF, the average concentrations of effluent NH4+-N and TN were only 0.4 and 12.2 mg/L, which achieved the high efficiency and economy of H-Z BAF under low C/N conditions. The newly prepared ZCF had a rougher outer surface, a uniformly distributed flocculent structure and numerous microporous channels on the inner surface, and the carbon source inside the filler was degraded or transformed by microorganisms, as compared to the filler in H-O and H-A at the later stage of use. The abundance of nitrifying bacteria, denitrifying bacteria was increased in the H-Z BAF, and that functional CAZymes were enriched and involved in the degradation of cellulose and hemicellulose, can be efficiently utilized by microorganisms. This study provides technical support for the development of cheap, stable and efficient slow-release carbon sources and their application in denitrification of municipal wastewater plant tailwater.

Potential effects of Cu2+ stress on nitrogen removal performance, microbial characteristics, and metabolism pathways of biofilm reactor

Sequencing batch biofilm reactors (SBBR) were utilized to investigate the impact of Cu2+ on nitrogen (N) removal and microbial characteristics. The result indicated that the low concentration of Cu2+ (0.5 mg L−1) facilitated the removal of ammonia nitrogen (NH4+-N), total nitrogen (TN), nitrate nitrogen (NO3−-N), and chemical oxygen demand (COD). In comparison to the average effluent concentration of the control group, the average effluent concentrations of NH4+-N, NO3−-N, COD, and TN were found to decrease by 40.53%, 17.02%, 10.73%, and 15.86%, respectively. Conversely, the high concentration of Cu2+ (5 mg L−1) resulted in an increase of 94.27%, 55.47%, 22.22%, and 14.23% in the aforementioned parameters, compared to the control group. Low concentrations of Cu2+ increased the abundance of nitrifying bacteria (Rhodanobacter, unclassified-o-Sacharimonadales), denitrifying bacteria (Thermomonas, Comamonas), denitrification-associated genes (hao, nosZ, norC, nffA, nirB, nick, and nifD), and heavy-metal-resistant genes related to Cu2+ (pcoB, cutM, cutC, pcoA, copZ) to promote nitrification and denitrification. Conversely, high concentration Cu2+ hindered the interspecies relationship among denitrifying bacteria genera, nitrifying bacteria genera, and other genera, reducing denitrification and nitrification efficiency. Cu2+ involved in the N and tricarboxylic acid (TCA) cycles, as evidenced by changes in the abundance of key enzymes, such as (EC:1.7.99.1), (EC:1.7.2.4), and (EC:1.1.1.42), which initially increased and then decreased with varying concentrations of Cu2+. Conversely, the abundance of EC1.7.2.1, associated with the accumulation of nitrite nitrogen (NO2−-N), gradually declined. These findings provided insights into the impact of Cu2+ on biological N removal.

Material modification of electrodes in microbial electrochemical system to enhance electrons utilization on the electrode and its impact on microorganisms

Previous research has established a MES embedding a microbial electrode to facilitate the degradation of antibiotics in water. We modified microbial electrodes in the MES with PEDOT and rGO to enhance electron utilization on electrodes and to further promote antibiotic degradation. Density functional theory calculations on the SMX molecule indicated that the C4-S8 and S8-N27 bonds are the most susceptible to electron attack. The introduction of various functional groups and multivalent elements enhanced the electrodes' capacitance and electron mediation capabilities. This led to enhance both electron utilization on the electrodes and the removal efficiency of SMX. After 120 h, the degradation efficiency of SMX by PEDOT and rGO-modified electrodes increased by 45.47 % and 25.19 %, respectively, compared to unmodified electrodes. The relative abundance of sulfate-reducing and denitrifying bacteria significantly increased in PEDOT and rGO-modified electrodes, while the abundance of nitrifying bacteria and potential antibiotic resistance gene host microbes significantly decreased. The impact of PEDOT modification positively influenced microbial Cellular Processes, including cell growth, death, and motility. This study provides insights into the mechanisms of direct electron involvement in antibiotic degradation steps in microbial electrochemistry, and provides a possible path for improved strategies in antibiotic degradation and sustainable environmental remediation.

The effect of using nano and microbubbles as aeration strategies on the nitrification process, microbial community composition, and growth of Penaeus vannamei in a super-intensive biofloc system

The aim of this study was to evaluate the effect of using nano and microbubbles as aeration strategies on the nitrification process, microbial community composition of water and biofilm, microbial flocs proximate composition, and growth of Penaeus vannamei in a pilot scale super-intensive system with biofloc technology. A grow-out (stocking density: 450 shrimp m−3) was carried out for 74 days in a greenhouse with nine 35 m3 tanks, using the following treatments: T1: nanobubbles, T2: microbubbles, T3: mixed (nano + microbubbles). The nanobubbles were generated by nozzle-type air injectors and the microbubbles were generated by microperforated hoses. Artificial substrates, with an area equivalent to 200% of the lateral surface, were used into the experimental units. Molasses was used as an organic carbon source at a carbon:nitrogen ratio of 15:1. The main morphotypes of bacteria in the water and in the biofilm were analyzed using direct counting and a profile of the bacterial composition of the water was performed using metagenomic analysis. Control of total ammonia nitrogen (TAN) was better in treatments T2 and T3 than in T1. At the end of the experiment, treatment T3 showed a higher total abundance of bacteria in the water than T1 and T2. Bacillus abundance in the biofilm was higher in the T3 treatment than in T1 and T2. The relative abundance of nitrifying bacteria was <1% in all treatments. Treatment T1 had a higher relative abundance of nitrite-oxidizing bacteria than the others. However, the T3 treatment had a better distribution of nitrifying bacteria species. T3 treatment showed a higher diversity and evenness of operational taxonomic units. The microbial flocs in the T2 had a higher crude protein content than in the T1. These results indicate that the use of a mixed aeration system promotes a higher load of microorganisms, which has proven to improve water quality and can influence shrimp growth. The shrimp final weight was higher in T1 (12.57 g) and T3 (12.54 g) than in T2 (11.70 g), survival was higher in T3 (97.17%) than in T1 (80.33%), and yield was higher in T3 (4.61 Kg m−3) than in T1 (4.06 Kg m−3) and T2 (4.21 Kg m−3). The treatment that used nano and microbubble as aeration strategy (T3) proved to be the best as it provided better TAN control, higher abundance of bacillus bacteria in the biofilm, higher diversity and evenness of bacteria, and even higher shrimp growth and survival.

Effect of tire wear particle accumulation on nitrogen removal and greenhouse gases abatement in bioretention systems: Soil characteristics, microbial community, and functional genes

Tire wear particles (TWPs), as predominant microplastics (MPs) in road runoff, can be captured and retained by bioretention systems (BRS). This study aimed to investigate the effect of TWPs accumulation on nitrogen processes, focusing on soil characteristics, microbial community, and functional genes. Two groups of lab-scale bioretention columns containing TWPs (0 and 100 mg g−1) were established. The removal efficiencies of NH4+-N and TN in BRS significantly decreased by 7.60%–24.79% and 1.98%–11.09%, respectively, during the 101 days of TWPs exposure. Interestingly, the emission fluxes of N2O and CO2 were significantly decreased, while the emission flux of CH4 was substantially increased. Furthermore, prolonged TWPs exposure significantly influenced the contents of soil organic matter (increased by 27.07%) and NH4+-N (decreased by 42.15%) in the planting layer. TWPs exposure also significantly increased dehydrogenase activity and substrate-induced respiration rate, thereby promoting microbial metabolism. Microbial sequencing results revealed that TWPs decreased the relative abundance of nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Dechloromonas and Thauera), reducing the nitrification rate by 42.24%. PICRUSt2 analysis further indicated that TWPs changed the relative abundance of functional genes related to nitrogen and enzyme-coding genes.

Two-stage sequencing batch reactors with added iron shavings for nutrient removal and aerobic sludge granulation treating real wastewater with low carbon to nitrogen ratios

In response to the challenges of limited nutrient removal and the difficulty in forming aerobic granular sludge (AGS) with low carbon to nitrogen (C/N) ratios, a novel two-stage sequencing batch reactors (SBRs) (R1 and R2) system with added iron shavings was proposed and established. The results showed that AGS was developed and nitrogen (82.8 %) and phosphorus (94.7 %) were effectively removed under a C/N ratio at 1.7 ± 0.5. The average size of R1 and R2 increased from 45.3 μm to 138.7 μm and 132.8 μm. Under high biological selective pressure, phosphorus accumulating organisms like Comamonadaceae (14.8 %) and Chitinophagales (5.7 %) experienced enrichment in R1. Furthermore, R2 exhibited an increased abundance of nitrifying bacteria (2.3 %) and a higher proportion of nitrogen removal through autotrophic denitrification (＞17.5 %). Overall, this study introduces an innovative two-stage SBRs with added iron shavings, offering a novel approach for the treatment of low C/N ratios wastewater.

Soil Bacterial Community and Greenhouse Gas Emissions as Responded to the Coupled Application of Nitrogen Fertilizer and Microbial Decomposing Inoculants in Wheat (Triticum aestivum L.) Seedling Stage under Different Water Regimes

The soil microbial community is critically important in plant nutrition and health. However, this community is extremely sensitive to various environmental conditions. A pot experiment was conducted during the wheat seedling stage to better understand the influences of the coupled application of nitrogen (N) and microbial decomposing inoculants (MDI) on the soil bacteria community under different water regimes. There were two levels of water and six levels of fertilization. The results reveal that water stress increased the relative abundance of Acidobacteria and decreased that of Firmicutes and Proteobacteria. The application of 250 kg N ha−1 altered the diversity of the bacterial community but increased the relative abundance of nitrifying bacteria. Nitrous oxide (N2O) and carbon dioxide (CO2) emissions were negatively correlated with Myxococcota and Methylomirabilota while positively correlated with Patescibacteria. These two gases were also positively correlated with nitrifying bacteria, and the correlation was more significant under the full irrigation regime. These findings indicate that MDI does not substantially influence the soil bacterial community and its relationship with greenhouse gas emission at the wheat seedling stage and that the abundance of the soil bacterial community would mainly depend on the rational control of the amount of N and water applied.

Effect of in situ ultrasonic wave and influent ammonia nitrogen fluctuation on stability of aerobic granular sludge

ABSTRACT This study elucidates the impact of fluctuating influent conditions and in situ ultrasonic wave exposure on the stability of aerobic granular sludge (AGS) in the treatment of simulated wastewater emanating from rare earth mining operations. During a stable influent period spanning from Day 1 to Day 95, the seed granules underwent an initial disintegration followed by a re-granulation phase. The secondary granulation was achieved on Day 80 and Day 40 for the ultrasonic reactor (R1) and the control reactor (R2), respectively. Notably, granules formed in R1 exhibited a more porous structure compared to those generated in R2. Subsequently, when the ammonia nitrogen in the influent oscillated between 100 and 500 mg/L during Days 96-140, both reactors yielded compact and densely structured granules. Nitrogen removal profiles were comparable between the two reactors: the removal efficiencies for ammonia nitrogen and total inorganic nitrogen escalated from 95% and 80%, respectively, during Days 1-95, to 95% and 90%, respectively, post-Day 140. A suite of performance metrics indicated that steady-state granules from R1 outperformed those from R2 across several parameters. Specifically, the nitrification/denitrification rates, and relative abundance of denitrifying bacteria were all higher in granules from R1. Conversely, the relative abundance of nitrifying bacteria was comparable between granules from both reactors. However, R1 granules demonstrated lower sludge concentration and smaller average particle size than their R2 counterparts. In conclusion, the AGS system demonstrated robust resilience to fluctuating ammonia nitrogen, and the application of ultrasonic waves significantly enhanced granular activity while achieving in situ sludge reduction.

Enhanced nitrogen removal in the upgrading of municipal wastewater treatment plants by using zero-valent iron-modified biofilm carriers and clinoptilolite-modified biofilm carriers

A municipal wastewater treatment plant (WWTP) was initially operated as an anaerobic/aerobic (A/O) process and designed with the second grade of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002, Table S1). To upgrade for meeting the first grade A of the GB18918-2002 (COD, BOD5, NH4+-N, and TN are 50 mg/L, 10 mg/L, 5/8 mg/L, and 15 mg/L, respectively), the original process was reformed to a process of anaerobic/anoxic/aerobic-integrated free-moving biofilm and activated sludge (A2O-IFFAS) by filling zero-valent iron (ZVI)-modified biofilm carriers into anoxic bioreactors, as well as clinoptilolite-modified biofilm carriers into aerobic bioreactors. ZVI-modified biofilm carriers were used to enhance denitrification, whereas clinoptilolite-modified biofilm carriers were used to enhance nitrification. The effluent COD, BOD5, NH4+-N, and TN of the new process were 26 ± 14 mg/L, 7 ± 1 mg/L, 1.3 ± 0.2/4.7 ± 0.7 mg/L (summer/winter), and 12.1 ± 2.4 mg/L, respectively, and their removal efficiencies were 95 %, 96.1 %, 90.1 %/97.3 %, and 78.8 %, respectively, which meet the first grade A of the GB18918-2002. Compared with flocculent sludge, the biofilm of ZVI-modified biofilm carriers increased the relative abundance of Hyphomicrobium (facultative autotrophic denitrifying bacteria) from 1.5 % to 8.7 %, the biofilm of clinoptilolite-modified biofilm carriers increased the relative abundance of nitrifying bacteria (composed of Nitrosomonas and Nitrospira) from 4.0 % to 39.2 %. The case demonstrated that the A2O-IFFAS equipped with ZVI-modified biofilm carriers and clinoptilolite-modified biofilm carriers could significantly increase the nitrogen removal efficiency and had a good prospect for upgrading municipal WWTPs.

Nitrogen removal performance of bioretention cells under polyethylene (PE) microplastic stress

The use of bioretention cells as a stormwater control measure allows stormwater runoff to be collected and filtered, effectively removing microplastics and other pollutants from stormwater. This study investigated the effect of polyethylene microplastics (PE-MPs) retention on the bioretention cell, in terms of denitrification performance and microbial community structure. Four PE-MP exposures were compared at different concentrations of 0, 250, 500 and 1000 mg/L under alternating dry and wet period conditions. Results showed that the removal efficiency reduced by 14.99%, 28.37% and 18.59% with PE-MP concentrations of 250, 500 and 1000 mg/L. The NO3−-N removal efficiency increased by 36.19%, 20.19% and 35.39%. After 8 days of dry conditions, the NO3−-N removal efficiencies of the bioretention cells were reduced by 36.66%, 46.86% and 31.11% compared to those after 2 days of dry conditions. Microbial sequencing results indicated that the accumulation of PE-MPs changed the microbial community structure within the bioretention cell filler material, promoting the growth of bacteria such as Actinobacteria, Bacteroidetes and Firmicutes. Furthermore, PE-MPs reduced the relative abundance of nitrifying bacteria (e.g. Nitrospira) within the bioretention cell and promoted denitrifying bacteria (e.g. Dechloromonas and Hydrogenophaga), along with numerous other genera such as Azotobacter and Nocardia.

Effects of historical agricultural crops on the soil microbiome of a living agricultural museum in the Sonoran Desert

AbstractAlthough soil has been a central piece in agricultural knowledge for most of recorded history, introductions of exotic plant assemblages can produce loss of soil quality, especially in more fragile ecosystems such as drylands. Here, we investigate the impact of indigenous and introduced plant assemblages associated with ethno‐agricultural traditions of Tucson, AZ, on soil microbial communities using 16S rRNA gene (bacteria and archaea) and internal transcribed spacer region (fungi) metabarcoding. We found differences in soil microbial community diversity and composition across plant assemblages associated with ethno‐agricultural traditions. However, we found the largest community structure differences between managed cultivated plots and not cultivated desert soils. Managed cultivated plots were characterized by higher diversity (23% increment for bacteria/archaea, and 40% for fungi) and a higher abundance of nitrifying bacteria (19% higher) and cellulolytic bacteria (39% higher) relative to minimally disturbed plots, suggesting higher rates of decomposition and nitrogen cycling. Given the observed influence of management on soil microbial communities, we conclude that efforts to build arid‐specific sustainable agricultural solutions would benefit from the use of adapted plants that require minimal management.

Effect of hydraulic retention time on the performance of sequencing batch reactor under combined stress of ibuprofen and ciprofloxacin

The impacts of changes in hydraulic retention time (HRT) on nitrogen elimination, the activity of sludge and the structure of microbial communities in a sequencing batch reactor under the joint stress of ibuprofen (IBP) and ciprofloxacin (CIP) were investigated. Under the combined stress of IBP (belonged to nonsteroidal anti-inflammatory drugs) and CIP (belonged to antibiotics), the elimination level of ammonia nitrogen, chemical oxygen demand, and the rate of specific ammonia oxidation, specific nitrite oxidation, specific nitrate reduction in activated sludge declined with the shortening of HRT. Under the joint stress of IBP and CIP, the content of polysaccharide (PS) and protein (PN) together with the ratio of PN to PS in the extracellular polymeric substances grew with the shortening of HRT, and the content of aromatic proteins increased significantly, which indicated that aromatic proteins were the major protective response substances to the shortening of HRT. Under the joint stress of IBP and CIP, with the reduction of HRT, and the reduction rate of relative abundance of nitrifying bacteria was more evident than that of denitrifying bacteria. This exploration gives novel thoughts for understanding the impacts of HRT on biological nitrogen removal of wastewater under combined stress of IBP and CIP.

Impact of separate concentrations of polyethylene microplastics on the ability of pollutants removal during the operation of constructed wetland-microbial fuel cell

Microplastics (MPs) in water pose a great threat to the ecological environment, but the impact of MPs on constructed wetland microbial fuel cells (CW-MFCs) has not been studied, so in order to fill the research gap and enrich the research in the field of microplastics, a 360-day experiment was designed to determine the operating status of CW-MFCs at different concentrations (0, 10, 100 and 1000 μg/L) polyethylene microplastics (PE-MPs) at different times, focusing on the changes of the CW-MFCs' ability to handle pollutants, power production performance and microbial composition. The results showed that with the accumulation of PE-MPs, the removal effect of COD and TP did not change significantly, and that the removal rate was maintained at around 90% and 77.9% respectively, within 120 d of operation. What's more, the denitrification efficiency increased (from 4.1% to 19.6%), but with the passage of time, it decreased significantly (from 7.16% to 31.9%) at the end of the experiment, while oxygen mass transfer rate was significantly increased. Further analysis showed that the accumulation of PE-MPs did not affect the current power density significantly with the changes of time and concentration, but the accumulation of PE-MPs would inhibit the exogenous electrical biofilm and increase the internal resistance, thereby affecting the electrochemical performance of the system. In addition, the results of microbial PCA showed that the composition and the activity of the microorganisms were changed under the action of PE-MPs, that the microbial community in CW-MFC showed a dose effect on the input of PE-MPs, and that the relative abundance of nitrifying bacteria with time was significantly affected by PE-MPs concentration. The relative abundance of denitrifying bacteria decreased over time, but PE-MPs promoted the reproduction of denitrifying bacteria, which was consistent with the changes in nitrification and denitrification rates. The removal modes of EP-MPs by CW-MFC include the adsorption and the electrochemical degradation, with two isothermal adsorption models of Langmuir and Freundlich being constructed in the experiment, and the electrochemical degradation process of EP-MPs being simulated. In summary, the results show that the accumulation of PE-MPs can induce a series of changes in substrate, microbial species and activity of CW-MFCs, which in turn affects the pollutant removal efficiency and power generation performance during its operation.

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.

Agricultural practice negatively affects soil bacterial diversity and nitrogen functional genes comparing to adjacent native forest soils

Soil bacterial diversity and community are determined by anthropogenic activities and environmental conditions, which greatly affect the functioning of ecosystem. We investigated the soil bacterial diversity, communities, and nitrogen (N) functional genes with different disturbance intensity levels from forest, transition, to crop soils at three locations in the coastal region of Georgia, USA. Illumina high-throughput DNA sequencing based on the bacterial 16S rRNA gene was performed for bacterial diversity and community analyses. Nitrifying and denitrifying functional genes (amoA and nirK respectively) of bacteria were further detected using quantitative PCR (qPCR) and Denaturing Gradient Gel Electrophoresis (DGGE). Soil bacterial community structure determined by Illumina sequences was significantly different between crop and forest soils (p < 0.01) as well as between crop and transition soils (p = 0.01), however, there was no significant difference between transition and forest soils. Compared to less disturbed forest, agricultural practice significantly decreased soil bacterial relative abundance, richness, and Shannon diversity. Soil pH and nitrate contents together contributed highest to the observed different bacterial communities (Correlations = 0.381). Two operational taxonomic units (OTUs) belonging to Acidobacteriales species (OTU5, OTU8) decreased in crop soils, however, agricultural practices significantly increased an OTU of Nitrobacteraceae (OTU4). The relative abundance of ammonia-oxidizing bacteria (AOB) amoA gene was significantly higher in crop soils than in forest and transition soils. Distinct grouping of soil denitrifying bacterial nirK communities was observed, and agricultural practices significantly decreased the diversity of nirK gene compared to forest soils. Soil pH and organic contents together contributed highest to the observed different nirK communities (Correlations = 0.443). Anthropogenic effects through agricultural practices decreased bacterial richness and Shannon diversity, increased abundance of nitrifying bacteria, and decreased diversity of denitrifying bacteria, potentially affecting the N cycling processes for healthy soils, plant productivity, and water and air quality.