Inhibition of methane oxidation by nitrogenous fertilizers in a paddy soil

Nitrogenous fertilizers are generally thought to have an important role in regulating methane oxidation. In this study, the effect of ammonium on methane oxidation activity was investigated in a paddy soil using urea at concentrations of 0, 50, 100, 200, and 400 μg N per gram dry weight soil (N/g.d.w.s) and ammonium sulfate at concentrations of 0, 50, and 200 μg N/g.d.w.s. The results of this study demonstrate that urea concentrations of 200 μg N/g.d.w.s. and above significantly inhibit methane oxidation activity, whereas no statistically significant difference was observed in methane oxidation activity among soil microcosms with urea concentrations of less than 200 μg N/g.d.w.s after incubation for 27 days. Similar results were obtained in a sense that methane oxidation activity was inhibited only when the ammonium sulfate concentration was 200 μg N/g.d.w.s in soil microcosms in this study. Phylogenetic analysis of pmoA genes showed that nitrogen fertilization resulted in apparent changes in the community composition of methane-oxidizing bacteria (MOB). Type I MOB displayed an increased abundance in soil microcosms amended with nitrogenous fertilizers, whereas type II MOB dominated the native soil. Furthermore, although no statistically significant relationship was observed between pmoA gene and amoA gene abundances, methane oxidation activity was significantly negatively correlated with nitrification activity in the presence of urea or ammonium sulfate. Our results indicate that the methane oxidation activity in paddy soils might be inhibited when the concentration of ammonium fertilizers is high and that the interactions between ammonia and methane oxidizers need to be further investigated.

Chloramine Disinfection-Induced Nitrification Activities and Their Potential Public Health Risk Indications within Deposits of a Drinking Water Supply System

Microsensors were applied to study the diffusion reaction and activity of a nitrogen species of deposit sediment from a drinking water supply system. Microprofiles of dissolved oxygen (DO), NH₄⁺-N, NO₃^--N, and NO₂^-N in the sediment indicated that the DO concentration decreased from the highest at the sediment surface to zero at the bottom of the sediment. Similarly, with the increase of depth, NH₄⁺-N initially increased rapidly and then decreased slowly, while the concentration of NO₃^--N reached a maximum at around 6000 μm and then decreased to about 0.1 mg·L^-1 near the bottom of the sediment. Almost no change was observed for NO₂^--N. The decrease of NH₄⁺-N and DO corresponded well with the increase of NO₃^--N. Furthermore, based on a consumption and production rate analysis, DO has always been consumed; the NH₄⁺-N consumption rate increased rapidly within 0-1000 μm, reaching about 14 mg·L^-1·S^-1·10^-9. A small amount of NH₄⁺-N was produced in 2000-6000 μm, which could be attributed to denitrification activity. There was no change deeper than 6000 μm, while NO₃^--N was produced at a depth between 0 and 6000 μm and was consumed in the deeper zone. At the depth of 9000 μm, the NO₃^--N consumption reached a maximum of 5 mg·L^-1·S^-1·10^-9. The consumption of DO and NH₄⁺-N, which corresponded with the production of NO₃^--N in a specific microscale range within the sediment, demonstrated nitrification and denitrification activities. In addition, the time required for the diffusion of only DO, NH₄⁺-N, NO₃^--N, and NO₂^--N was estimated as 14 days; however, in the practical, even after 60 days of operation, there was still a continuous reaction, which provided further evidence towards microbial activities within the sediment.

[Effect of Ca2+ on the Nitrification Activity and the Flocculation and Sedimentation Performances of the Activated Sludge]

Ca²⁺ is an important microbial growth factor that can affect the activity, flocculation, and sedimentation of activated sludge. In order to study the roles of Ca²⁺ in the activated sludge system, the activity changes of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were analyzed using the specific oxygen uptake rates (SOUR_AOB and SOUR_NOB). The changes in composition and structure of extracellular polymeric substances (EPS) were analyzed using Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation emission fluorescence spectroscopy (3D-EEM). The effects of Ca²⁺on the nitrification activity and microbial metabolites were investigated. The results showed that when the Ca²⁺concentration increased from 0.45 mmol·L^-1 to 3 mmol·L^-1, SOUR_AOB and SOUR_NOB increased from 6.3 mg·(g·h)^-1 to 10.4 mg·(g·h)^-1 and from 2.3 mg·(g·h)^-1 to 3.7 mg·(g·h)^-1, respectively. The EPS concentrations increased from 68 mg·g^-1 to 93 mg·g^-1, and the flocculation ability (FA) of the sludge was improved. When the Ca²⁺ concentration was higher than 3 mmol·L^-1, SOUR_AOB and SOUR_NOBboth decreased. The FA was maintained at about 30%, and the particle size of the sludge continued to increase. Based on FTIR analysis, the main components of EPS were always amino, amide Ⅰ, and carboxyl with an increase in Ca²⁺ concentration. Based on EEM analysis, the composition of loosely-bound (LB)-EPS did not change, and humic acid substances appeared in the tightly-bound (TB)-EPS at low nitrification rates. Low concentrations of Ca²⁺ promoted nitrification activity and flocculation of the sludge. However, high concentrations of Ca²⁺ led to a decline in the sludge nitrification activity.

Effects of potassium monopersulfate on nitrification activity and bacterial community structure of sponge biocarrier biofilm in Litopenaeus vannamei aquaculture system

Effects of potassium monopersulfate (KMPS) on the nitrification activity, aquacultural water quality and bacterial community structure of sponge biocarriers with pre-cultured biofilm (SBBF) were analysed through shaking flask experiments and L. vannamei aquaculture experiments. Changes in the ammonia oxidation rate (AOR) and nitrite oxidation rate (NOR) of SBBF under six KMPS concentration treatments (0, 1, 2, 3, 4 and 5 mg/L) were studied. The results showed that the AOR and NOR of SBBF treated with high concentrations of KMPS (3, 4 and 5 mg/L) were significantly lower than those of the control group (CK) (p < 0.05). However, compared with the first dosing of NH4Cl and NaNO2, the inhibition of AOR and NOR by KMPS on AOR and NOR was weakened after the second and third dosing times. That is, AOR and NOR can recover partially or completely over time. The L. vannamei aquaculture experiment was performed using four concentrations of KMPS (0, 2, 4 and 8 mg/L). The results showed that with increasing KMPS dosage, the average and peak concentrations of NH4+-N and NO2--N in each treatment significantly increased (P < 0.05), and the final body weight of shrimp significantly decreased (P < 0.05). Furthermore the highest dose (8.0 mg/L) of KMPS reduced the survival rate by 9.33% compared to the CK. High-throughput sequencing analysis of the biofilm structure showed that the relative abundances of Nitrospirota, Nitrosomonas and Nitrococcus, which are related to nitrogen cycling, and beneficial bacteria including Firmicutes and Bacilli decreased with the addition of KMPS (p < 0.05).

A new strategy for greenhouse gas emission reduction in the anaerobic/anoxic/oxic biological treatment process using exogenous N-acyl-homoserine lactones, a quorum-sensing signaling molecules

In this study, the impact of exogenous N-acyl-homoserine lactones (AHLs) on greenhouse gas (GHG) emissions in anaerobic/anoxic/oxic (A/A/O) systems was analyzed by manipulating the type and dosage of AHLs. The mechanism behind AHLs' effects on GHG emissions was explored through changes in microbial community structure. Findings revealed that N-octanoyl-homoserine lactone (C8-HSL) and high-dose N-dodecanoyl-homoserine lactone (C12-HSL) increased GHG emissions, while low-dose C12-HSL decreased them. Moreover, C8-HSL and high-dose C12-HSL promoted methane (CH4) and nitrous oxide (N2O) production by affecting sludge particle size. Bacterial community analysis highlighted Acinetobacter and Flavobacterium's roles in N2O emissions and acetate methanogens in methane synthesis. Metabolic pathway analysis showed that the acetic acid (CH3COOH) methanogenic pathway was the main methanogenic pathway; C8-HSL and C12-HSL influenced methane emission by affecting the methanogenic pathway and N2O emission by changing nitrous oxide reductase (Nos) abundance. This research underscores AHL-based quorum sensing's potential in mitigating GHG emissions during activated sludge wastewater treatment, offering insights into their application and impact on key microbial activities. Limitations include the absence of methane emission reduction by signaling molecules and the need for further investigation into their effects on sludge accumulation.

[Effects of Temperature on Shortcut Nitrification and Nitrification Activity of Nitrification in an Intermittent Aeration Sequencing Batch Reactor]

Real domestic sewage was treated with sequencing batch reactors (SBR). The aerobic/anoxic modes were alternated 4 times at 30℃ and 7 times at 18℃ in a single-cycle, respectively, and the ratio of aerobic/anoxic cycles was 30 min/30 min. The influent concentration of ammonia and nitrite was 61.44 mg·L^-1 and 0.77 mg·L^-1, respectively. After the experiments were run for 61 and 90 cycles, the effluent of the ammonia was 0.68 mg·L^-1 and 1.28 mg·L^-1 and the removal rate for ammonia was 98.94% and 99.57%, respectively. The nitrite concentrations were 20.57 mg·L^-1 and 20.18 mg·L^-1, and the nitrite accumulation rate reached 95.92% and 99.58%, respectively. During shortcut nitrification, the activity of the ammonia oxidizing bacteria (AOB) increased gradually before finally stabilizing at 100.00%, however the activity of nitrite oxidizing bacteria (NOB) increased first and then decreased gradually, the activity of AOB exceeded NOB at 32 and 74 cycles respectively, where the AOB became the dominant bacteria and the activity of NOB was completely inhibited at 61 and 90 cycles.