Denitrification Ratio Research Articles

Nitrite accumulation and nitrous oxide emission during denitrification processes with quinoline or indole as the sole carbon source

AbstractBACKGROUNDBatch experiments were conducted to investigate nitrite accumulation and N2O emission during the denitrification processes when quinoline or indole was used as the sole carbon source. The effects of COD/NO3−‐N ratio and pH were studied.RESULTSWhile both significant transient nitrite accumulation and N2O emission occurred when quinoline was used as the carbon source, little denitrification intermediates were observed when indole was used as the carbon source. The optimal COD/NO3−‐N ratio for both complete denitrification and degradation of quinoline and indole were 6.8 and 5.1. Denitrification was inhibited under acidic conditions no matter with quinoline or indole as the carbon source. The optimal pH was 7.5 for both quinoline (or indole) degradation and denitrification. The nitrite accumulation and different carbon source further influenced N2O emission. When quinoline was used as the carbon source, N2O emission was observed at COD/NO3−‐N ≤ 5 and pH ≤ 7.5; when indole was used as the carbon source, N2O emission was observed at COD/NO3−‐N ≤ 3 and pH ≤ 6.5. Higher concentration of N2O was emitted at lower COD/NO3−‐N ratio and pH.CONCLUSIONCOD/NO3−‐N ratio, pH and the types of carbon source significantly influenced the accumulation of denitrification intermediates. © 2014 Society of Chemical Industry

Fluxes of CH4, N2O, and kinetics of denitrification in disturbed and undisturbed forest soil in India

Raut, N., Sitaula, B. K., Bakken, L. R. and Dörsch, P. 2014. Fluxes of CH4, N2O, and kinetics of denitrification in disturbed and undisturbed forest soil in India. Can. J. Soil Sci. 94: 237–249. Soil disturbance due to grazing has been severe in Indian forests. This may alter ecosystem functions such as the cycling of nitrogen, and may hence affect the emission of greenhouse gases. We measured fluxes of CH4 and N2O with a closed chamber technique throughout one year in a forest of Western Ghats, Karnataka state, southwest India and determined the product stoichiometry of denitrification under standard anoxic incubations in soil samples from disturbed and undisturbed forest. In both areas, there was a net flux of CH4 from the atmosphere to the soil, and the undisturbed forest soil was a stronger sink for CH4 than the disturbed (P<0.05). The accumulated CH4 uptake averaged for all four seasons was 1.5 times higher in undisturbed than disturbed forest. Contrary to our expectation, the N2O emission was significantly higher for undisturbed than for disturbed forest (P<0.05). The accumulated N2O emission averaged for all four seasons was 1.6 times higher in undisturbed than disturbed forest. Together our data suggest that increase of N2O release and decrease in CH4 sink in soil induced by grazing disturbance can affect the global warming potential (GWP) of forest in this region. The incubation study showed a strong correlation between oxic respiration rate (R) and subsequent denitrification rate (D) and the ratio D/R was 1:3 and 1:6 for soil from undisturbed and disturbed soils, respectively. The N2O/(N2+N2O) product ratio of denitrification tended to be higher in undisturbed than disturbed site, despite lower soil pH.

Excessive use of nitrogen in Chinese agriculture results in high N2O/(N2O+N2) product ratio of denitrification, primarily due to acidification of the soils

China is the world's largest producer and consumer of fertilizer N, and decades of overuse has caused nitrate leaching and possibly soil acidification. We hypothesized that this would enhance the soils' propensity to emit N2O from denitrification by reducing the expression of the enzyme N2O reductase. We investigated this by standardized oxic/anoxic incubations of soils from five long-term fertilization experiments in different regions of China. After adjusting the nitrate concentration to 2 mM, we measured oxic respiration (R), potential denitrification (D), substrate-induced denitrification, and the denitrification product stoichiometry (NO, N2O, N2). Soils with a history of high fertilizer N levels had high N2O/(N2O+N2) ratios, but only in those field experiments where soil pH had been lowered by N fertilization. By comparing all soils, we found a strong negative correlation between pH and the N2O/(N2O+N2) product ratio (r2 = 0.759, P < 0.001). In contrast, the potential denitrification (D) was found to be a linear function of oxic respiration (R), and the ratio D/R was largely unaffected by soil pH. The immediate effect of liming acidified soils was lowered N2O/(N2O+N2) ratios. The results provide evidence that soil pH has a marginal direct effect on potential denitrification, but that it is the master variable controlling the percentage of denitrified N emitted as N2O. It has been known for long that low pH may result in high N2O/(N2O+N2) product ratios of denitrification, but our documentation of a pervasive pH-control of this ratio across soil types and management practices is new. The results are in good agreement with new understanding of how pH may interfere with the expression of N2O reductase. We argue that the management of soil pH should be high on the agenda for mitigating N2O emissions in the future, particularly for countries where ongoing intensification of plant production is likely to acidify the soils.

Nitrous oxide (N2O) emissions from biotrickling filters used for ammonia removal at livestock facilities

Recently several manufacturers of nitrifying biotrickling filters for ammonia (NH3) removal at animal houses have started to add a denitrification step to the installation, aiming to reduce the amount of discharge water by conversion of NH3 to nitrogen gas (N2). The aim of this research was to quantify the possible formation of nitrous oxide (N2O), which is a potent greenhouse gas, in three of these farm-scale installations. Furthermore, the removal efficiency of NH3 and odor was determined. All installations were successful in reducing the amount of discharge water. The average NH3 removal efficiency for the three locations was 85, 71 and 86%, respectively. However, a significant part of the NH3 removed from the inlet air was not converted to N2 but to N2O, which is a potent greenhouse gas. The part of the inlet NH3-N that was converted to N2O-N amounted to 17, 66 and 24%, respectively. The high N2O production might have been caused by a too low scarcity of biodegradable carbon/N ratio for complete denitrification. The average odor removal efficiency was 21, 32 and 48%, respectively. Further research is necessary to explore how process conditions can be adjusted and controlled in order to reduce the production and emission of N2O from these types of systems.

New high precision approach for measuring 15N–N2 gas fluxes from terrestrial ecosystems

Dinitrogen (N2) production from denitrification and anaerobic ammonium oxidation represents a loss of reactive nitrogen (N) from terrestrial and aquatic ecosystems to the atmosphere. The large 15N additions required to detect 15N2 production against the high atmospheric background precludes the use of the 15N tracer technique in natural terrestrial ecosystems. We present an isotope ratio mass spectrometry technique that dramatically improves the precision of 15N2 measurements. The approach uses gas chromatography to remove oxygen and gas purification techniques to remove water vapor and trace gases that can interfere with 15N2 analysis. The analytical precision for manual gas sample injection was 0.018‰ δ15N; this translates to a minimum detectable N2 flux of 0.12 ng-N g−1 h−1 over a 24 h incubation using our experimental parameters. We measured denitrification-derived N2 production rates of 0.67 ± 0.04 ng N g−1 dry soil h−1 following the addition of 0.1 μg 98 atom % 15N–NO3− g−1 dry soil to anaerobically-incubated soils; rates were significantly higher with the addition of 1.0 μg 98 atom % 15N–NO3− g−1 dry soil (p < 0.001, n = 5), averaging 1.3 ± 0.03 ng N g−1 dry soil h−1. The N2:N2O ratio at 24 h after 15N addition was 48 ± 12 and 5.4 ± 1.9 for the 0.1 μg 15N g−1 and 1.0 μg 15N g−1 treatments, respectively. The decrease in the N2:N2O with the addition of only 1 μg 15N g−1 underscores the need to use very low rates of 15N addition to accurately characterize denitrification dynamics. This analytical advance will allow us to better estimate the N2:N2O ratio of denitrification, constrain ecosystem N budgets, and explore the mechanisms of and controls on N2 production.

Soil denitrification potential and its influence on N2O reduction and N2O isotopomer ratios

N2O isotopomer ratios may provide a useful tool for studying N2O source processes in soils and may also help estimating N2O reduction to N2. However, remaining uncertainties about different processes and their characteristic isotope effects still hamper its application. We conducted two laboratory incubation experiments (i) to compare the denitrification potential and N2O/(N2O+N2) product ratio of denitrification of various soil types from Northern Germany, and (ii) to investigate the effect of N2O reduction on the intramolecular (15)N distribution of emitted N2O. Three contrasting soils (clay, loamy, and sandy soil) were amended with nitrate solution and incubated under N2 -free He atmosphere in a fully automated incubation system over 9 or 28 days in two experiments. N2O, N2, and CO2 release was quantified by online gas chromatography. In addition, the N2O isotopomer ratios were determined by isotope-ratio mass spectrometry (IRMS) and the net enrichment factors of the (15)N site preference (SP) of the N2O-to-N2 reduction step (η(SP)) were estimated using a Rayleigh model. The total denitrification rate was highest in clay soil and lowest in sandy soil. Surprisingly, the N2O/(N2O+N2) product ratio in clay and loam soil was identical; however, it was significantly lower in sandy soil. The IRMS measurements revealed highest N2O SP values in clay soil and lowest SP values in sandy soil. The η(SP) values of N2O reduction were between -8.2 and -6.1‰, and a significant relationship between δ(18)O and SP values was found. Both experiments showed that the N2O/(N2O+N2) product ratio of denitrification is not solely controlled by the available carbon content of the soil or by the denitrification rate. Differences in N2O SP values could not be explained by variations in N2O reduction between soils, but rather originate from other processes involved in denitrification. The linear δ(18)O vs SP relationship may be indicative for N2O reduction; however, it deviates significantly from the findings of previous studies.

How to ascertain the importance of autotrophic denitrification process in a bioelectrochemical system

The ratio of autotrophic denitrification (Rauto) is proposed as a metric to better evaluate the nitrate removal efficiency of bioelectrochemical systems (BESs). Two methods for computing Rauto were compared, one based on electron charge transfer and the other on a controlled reaction. The experiment was conducted in a greenhouse with a temperature of 30±2 °C. A reaction with a constant voltage supply was used as a BES and open circuit control was used for the controlled reaction. The results indicated that calculating the Rauto based on electron charge transfer was more suitable for evaluating the performance of BESs. Further discussion about the factors influencing the result of this computing method is presented.

Simultaneous Removal of Nitrate and Sulfate from Greenhouse Wastewater by Constructed Wetlands

This study evaluated the effectiveness of C-enriched subsurface-flow constructed wetlands in reducing high concentrations of nitrate (NO) and sulfate (SO) in greenhouse wastewaters. Constructed wetlands were filled with pozzolana, planted with common cattail (), and supplemented as follows: (i) constructed wetland with sucrose (CW+S), wetland units with 2 g L of sucrose solution from week 1 to 28; (ii) constructed wetland with compost (CW+C), wetland units supplemented with a reactive mixture of compost and sawdust; (iii) constructed wetland with compost and no sucrose (CW+CNS) from week 1 to 18, and constructed wetland with compost and sucrose (CW+CS) at 2 g L from week 19 to 28; and (iv) constructed wetland (CW). During 28 wk, the wetlands received a typical reconstituted greenhouse wastewater containing 500 mg L SO and 300 mg L NO. In CW+S, CW+C, and CW+CS, appropriate C:N ratio (7:3.4) and redox potential (-53 to 39 mV) for denitrification resulted in 95 to 99% NO removal. Carbon source was not a limiting factor for denitrification in C-enriched constructed wetlands. In CW+S and CW+CS, the dissolved organic carbon (DOC)/SO ratios of 0.36 and 0.28 resulted in high sulfate-reducing bacteria (SRB) counts and high SO removal (98%), whereas low activities were observed at DOC/SO ratios of 0.02 (CW) to 0.11 (CW+C, CW+CNS). On week 19, when organic C content was increased by sucrose addition in CW+CS, SRB counts increased from 2.80 to 5.11 log[CFU+1] mL, resulting in a level similar to the one measured in CW+S (4.69 log[CFU+1] mL). Consequently, high sulfate reduction occurred after denitrification, suggesting that low DOC (38-54 mg L) was the limiting factor. In CW, DOC concentration (9-10 mg L) was too low to sustain efficient denitrification and, therefore, sulfate reduction. Furthermore, the high concentration of dissolved sulfides observed in CW+S and CW+CS treated waters were eliminated by adding FeCl.

Removal of ammonium in surface water at low temperature by a newly isolated Microbacterium sp. strain SFA13

The strain SFA13, isolated from Songhua River, demonstrates ability to convert ammonium to nitrogen under aerobic conditions at low temperature. On the basis of 16S rRNA gene sequence, the strain SFA13 was a species in genera Microbacterium. The isolate showed unusual ability of autotrophic nitrification with the ratio of 0.11 mg NH4(+)-N/L/h at 5°C. Ammonium was consumed by the strain SFA13 with the biodegradation of organic carbon and without nitrite or nitrate accumulation. NO3(-)-N or NO2(-)-N was reduced by the strain SFA13. The denitrification ratio was 0.24mgNO3(-)-N/L/h. Hydroxylamine oxidase, nitrite reductase and nitrate reductase were detectable. The putative nitrogen removal process by the strain SFA13 was as follows: NH4(+)→NH2OH→NO2(-)→NO3(-), then NO3(-)→NO2(-)→N2. Biological activated carbon attached with the strain SFA13 could effectively remove ammonium in surface water with the rate of 2.68±0.27-3.16±0.25 mg NH4(+)-N/L/h at C/N 2-10, temperature 10°C, and DO>5.2 mg/L.

The effect of C/N ratio on nitrogen removal in a bioelectrochemical system

The effect of C/N ratios of 2, 2.7, and 3.5 on nitrogen removal in a bioelectrochemical system (BES) was investigated. Starch was used as a carbon source for the electrogenesis phenomenon we observed in a previous study. The results showed that an increased C/N ratio helped the BES to remove nitrate and depress nitrite accumulation but did not increase autotrophic denitrification. Nitrate and total nitrogen removal were increased from 0.69±0.02gm−3h−1 to 1.09±0.16gm−3h−1, and from 0.52±0.08gm−3h−1 to 0.97±0.06gm−3h−1, respectively, when the C/N ratio was increased from 2.0 to 3.5. However, the autotrophic denitrification ratio decreased from 72.74% to 50.23% with the same increase in the C/N ratio. High C/N ratios postponed the excretion of soluble microbial products and increased electrogenesis, but did not improve the anode transformation efficiency.

A probabilistic estimate of global marine N‐fixation and denitrification

We determine the global rates of marine N‐fixation and denitrification and their associated uncertainties by combining marine geochemical and physical data with a new two‐dimensional box model that separates the Atlantic from the IndoPacific basins. The uncertainties are estimated using a probabilistic approach on the basis of a suite of 2500 circulation configurations of this box model. N‐fixation and denitrification are diagnosed in an inverse manner for each of these configurations usingN*, P*, and the stable nitrogen isotope composition of nitrate as data constraints. Our approach yields a median water column denitrification rate of 52 TgN yr−1 (39 to 66 TgN yr−1, 5th to 95th percentile) and a median benthic denitrification rate of 93 TgN yr−1 (68 to 122 TgN yr−1). The resulting benthic‐to‐water column denitrification ratio of 1.8 confirms that the isotopic signature of water column denitrification has a limited influence on the global mean stable isotopic value of nitrate due to the dilution of the waters with a denitrification signal with the remainder of the ocean's nitrate pool. On the basis of two different approaches, we diagnose a global N‐fixation rate of between 94 TgN yr−1 and 175 TgN yr−1, with a best estimate of 131 TgN yr−1 and 134 TgN yr−1, respectively. Most of the N‐fixation occurs in the IndoPacific suggesting a relative close spatial coupling between sources and sinks in the ocean. Our N‐fixation and denitrification estimates plus updated estimates of atmospheric deposition and riverine input yield a pre‐industrial marine N cycle that is balanced to within 3 TgN yr−1 (−38 to 40 TgN yr−1). Our budget implies a median residence time for fixed N of 4,200 yr (3,500 to 5,000 yr).

Enhanced denitrification with external carbon sources in a biological anoxic filter

Three parallel biological anoxic filters (BaFs) were operated to investigate the denitrification kinetics of methanol, brewery wastewater and bakery wastewater. The experiment was conducted within the temperature range of 15-20 °C, with an influent nitrate and carbon dosage of 30 mg/L and 150 mg COD/L (COD: chemical oxygen demand). The denitrification efficiencies of brewery wastewater, bakery wastewater and methanol were 84, 66 and 74%, specific denitrification rates were 1.44, 1.11 and 1.24 kg NO(3)-N/m(3) d, and total nitrogen (TN) removal rates were 74, 62 and 66%, respectively. The volatile attached solid (VAS) tests reveal that methanol has the minimum net biomass yield, so it needs the least carbon to nitrogen (expressed in COD to nitrate, C/N) ratio for complete denitrification. While the brewery wastewater and bakery wastewater need higher C/N ratio to remove all nitrate nitrogen, and they both may need pretreatment to remove phosphate when used as external carbon sources.

Soil acidification by intensified crop production in South Asia results in higher N2O/(N2 + N2O) product ratios of denitrification

Agricultural soils emit significant amounts of N2O to the atmosphere, and annual emissions are in some proportion to the input of reactive nitrogen to the system. Hence the ongoing intensification of cropping systems in South Asia will result in increased emissions of N2O. The prospects are potentially worse than those predicted by the increasing doses of N-fertilizers, however. The reason for this is that intensive cropping systems may acidify the soils, which could increase the N2O/(N2 + N2O) product ratio of denitrification due to interference with the expression of the different enzymatic steps in this process (Liu et al., 2010 FEMS Microbiol Ecol 72 407–417). We investigated this phenomenon for agricultural soils in the central mid-hills of Nepal. We sampled soils from fields that had been under intensified cultivation for ≥20 years, and adjacent fields with more traditional cultivation, in areas with permanently drained soils as well as areas with frequent flooding. The characteristic kinetics of NO, N2O and N2 production by denitrification in these soils was measured by anoxic incubations after flooding and drainage of the soils with 2 mM NO3−, to secure similar NO3-concentrations for all soils. The results demonstrate that intensification invariably lowered the soil pH and increased the N2O/(N2 + N2O) product ratios of denitrification. This effect of intensification was observed both for incubations with and without C-substrates (glutamic acid) added. The transient accumulation of NO varied grossly between sites, but was not affected by intensification. The results demonstrate convincingly that the intensification has resulted in higher intrinsic propensity of the soils to emit N2O to the atmosphere, and the correlation with pH suggests that acidification is responsible. This causal relationship is underpinned by emerging evidence that low pH interferes with the assembly of the enzyme N2O-reductase. We conclude that the ongoing intensification of agriculture in South Asia may result in severely increasing N2O emissions unless acidification of the soil is counteracted.

Denitrification capacity of a landfilled refuse in response to the variations of [formula omitted] in the injected leachate

Effects of different chemical oxygen demand (COD) to nitrate concentration ratios in the injected leachate on the denitrification capacity of landfilled municipal solid waste were evaluated. Results showed that the 6-year-old refuse possessed high denitrification capacity. The nitrate reduction rate increased with the increasing COD concentration in the injected leachate. When the initial COD concentration increased to 6500mgl−1, nitrate reduction rate could reach up to 6.85mgNO3--Nl-1h-1. At the initial biodegradable COD/NO3--N ratio lower than the stoichiometric ratio of heterotrophic denitrification, autotrophic bacteria was the dominant microbial communities for denitrification. With the increase of COD/NO3--N ratio, the primary functional denitrifier would shift from autotrophic Thiobacillus denitrificans to heterotrophic Azoarcus tolulyticus. These results suggested that the initial biodegradable COD/NO3--N ratio in the injected leachate should be adjusted to higher than 6.0 for rapid in situ denitrification of 500mgNO3--Nl-1.

N 2O emission and the N 2O/(N 2O + N 2) product ratio of denitrification as controlled by available carbon substrates and nitrate concentrations

Amending agricultural soils with organic residues is frequently recommended to improve soil fertility and to sequester carbon for counteracting global warming. However, such amendments will enhance microbial respiration, hence denitrification. Therefore, the assessment of effects on global warming must take N 2O emission and the N 2O/(N 2O + N 2) product ratio of denitrification into account. There are some indications that the product ratio of denitrification is positively correlated with the ratio of available NO 3 − and available organic C in soils, but more research is needed to unravel quantitative relationships in well defined experiments. We conducted two laboratory incubation experiments, with the objective (i) to test the impact of the application of various N containing organic substrates including biogas residue on the denitrification rate and on N 2O emission, and (ii) to investigate the effect of various NO 3 − concentrations on the denitrification rate and the N 2O/(N 2O + N 2) product ratio under standardized anoxic conditions in soils collected from long-term organic or inorganic fertilizer plots. In experiment 1, we found that biogas residue was more recalcitrant than maize straw, despite a high concentration of soluble organic C. High respiration (treatments with maize straw and sucrose) resulted in a transient peak in N 2O emission, declining rapidly towards zero as nitrate concentrations reached less than 20 mg NO 3 −-N kg −1 dry soil. Application of biogas residue had a more moderate effect on soil respiration and denitrification, and resulted in a more long lasting peak in N 2O emission. The results were interpreted as a result of a gradual increase in the relative activity of N 2O reductase (thus lowering of the N 2O/(N 2O + N 2) product ratio of denitrification) throughout the incubation, most likely controlled by concentration of available NO 3 − in soil. In the second experiment, we found low N 2O/(N 2O + N 2) product ratios for the treatment where NO 3 − concentrations were ≤2 mM, and the ratios were clearly lower in manure fertilized than in mineral fertilizer treated soil. Much higher N 2O/(N 2O + N 2) product ratios were found for the treatments with ≥10 mM NO 3 −, and the ratios were remarkably independent of the soil's fertilizer history. We conclude that (i) in N-fertilized agricultural soils, application of organic matter with high contents of labile C may trigger denitrification-derived N 2O emission whereas (ii) in soils with low NO 3 − contents such application may substantially lower the N 2O/(N 2O + N 2) product ratio and hence N 2O emission.

Research advances on community structure and function of denitrifiers

反硝化作用是生态系统氮循环的重要组成部分, 与地下水硝酸盐累积和温室气体排放密切相关。种类繁多的细菌、真菌和古菌参与反硝化过程, 并在调控反硝化速率和反硝化气体产物比例等方面发挥重要作用。反硝化微生物的种群结构是一系列环境影响因素长期作用的结果, 反硝化微生物种群对温度、水分、pH、O₂含量、资源可利用性和植被类型等因素产生不同的响应。环境因素通过对反硝化微生物的影响来调控反硝化速率和反硝化酶的生成。分子技术的应用为自然环境中反硝化微生物的研究开辟了广阔前景, 并为进一步认识反硝化微生物种群结构和功能的相互关系提供了新的发展方向。本文总结了关于环境中反硝化微生物种群的研究结果, 并为进一步研究反硝化微生物种群结构和功能的联系提供了总体框架。

미세기포와 교반을 이용한 호기성 액비특성에 관한 연구

본 연구는 양돈축사에서 발생하는 슬러리형의 폐수를 원수로 하여 미세기포(M.A)와 교반기(Mixer)을 통한 호기성 조건으로 액비화 처리시 특성을 분석하고자 한다. 실험초기 pH는 7.6으로 액비의 적정 pH 범위보다 조금 상회하는 것으로 나타났으며, pH상승은 VFAs와 연관성이 있는 것으로 나타났다. 호기성 조건으로 액비처리를 수행하였을 경우 BOD와 COD제거효율에 있어서 혐기성 조건에 비해 효과적으로 나타났으며, BOD의 경우 호기성조건에서 M.A+Mix는 70.9%, M.A는 67.8%로 나타났으며, COD는 M.A+Mix가 39%, M.A가 19%의 제거효율이 나타났다. $NH_3-N$ 의 경우 모든 조건에서 시간 경과에 따라 점차 낮아지는 경향을 보였으며, 이는 질소의 특성과 pH상승에 따른 것으로 판단된다. $NO_3-N$ 에서는 모든 조건에 증가추세로 나타나 반응조 내에 $NO_3-N$ 이 축적되어 탈질율이 낮아지는 것으로 판단된다. 또한, 돈분뇨 액비의 비료성분 분석결과, 혐기성 조건에 비해 호기성 조건인 M.A+Mix에서 비료성분 함유율이 높은 것으로 나타났다. 【The purpose of this study is to analyze the behavior of swine slurry wastewater from bogen, in the treatment of Aerobic Liquid-Composting treatment by Aerobic Liquid-Composting using a mixer and Micro Air Diffusion pH level was at the beginning and its rise was seemingly related to VFA. It appears that removal of BOD and COD are more effective by Aerobic than by Anaerobic. In terms of removal efficiency, it shows 70.9% of BOD and 39% of COD in M.A+Mix and 67.8% of BOD and 19% of COD in M.A. $NH_3-N$ decreases in all conditions, which is caused by both the characteristic of nitrogen and the rise of pH. $NO_3-N$ increases in all conditions. It is judged that the accumulation of $NO_3-N$ affects the reduction of the ratio of denitrification. In the result of the analysis of Manure in swine slurry of liquified fertilizer ingredients, content of Manure in swine slurry of liquified fertilizer ingredients in aerobic conditions (M.A+Mix) is higher than anaerobic conditions.】

Denitrification gene pools, transcription and kinetics of NO, N2O and N2 production as affected by soil pH

The N(2)O : N(2) product ratio of denitrification is negatively correlated with soil pH, but the mechanisms involved are not clear. We compared soils from field experiments where the pH had been maintained at different levels (pH 4.0-8.0) by liming (> or = 20 years), and quantified functional gene pools (nirS, nirK and nosZ), their transcription and gas kinetics (NO, N(2)O and N(2)) of denitrification as induced by anoxic incubation with and without a carbon substrate (glutamate). Denitrification in unamended soil appeared to be based largely on the activation of a pre-existing denitrification proteome, because constant rates of N(2) and N(2)O production were observed, and the transcription of functional genes was below the detection level. In contrast, glutamate-amended soils showed sharp peaks in the transcripts of nirS and nosZ, increasing the rates of denitrification and pH-dependent transient accumulation of N(2)O. The results indicate that the high N(2)O : N(2) product ratio at low pH is a post-transcriptional phenomenon, because the transcription rate of nosZ relative to that of nirS was higher at pH 6.1 than at pH 8.0. The most plausible explanation is that the translation/assembly of N(2)O reductase is more sensitive to low pH than that of the other reductases involved in denitrification.

Transformations and losses of swine manure 15N as affected by application timing at two contrasting sites

An improved understanding of the fate of manure N is necessary for developing efficient manure management plans that ensure adequate crop nutrition and minimum environmental problems. This study quantified the fate of 15N-labelled liquid swine manure applied at three different times (late-fall, spring pre-plant and side-dress) on two soil types (a well-drained fine sandy loam and an imperfectly drained silt loam). Manure N uptake by corn (Zea mays L.) was significantly lower with fall application than with two spring applications (14-18% vs. 30-38% of applied N) in both soil types. Manure application increased total N leaching (30-43 vs. 27 kg N ha-1 yr-1 in the control), especially with fall application. Manure N contributed 18-25% of the total N leached in the fine sandy loam and 8-10% of the total N leached in the silt loam. Application timing did not affect manure N leaching in the silt loam, which ranged between 3 and 5% of applied N. In the fine sandy loam, fall application resulted in significantly higher manure N leaching (15% of applied N) than with two spring applications (8-10% of applied N). Unaccounted losses, assumed to be in gaseous forms, over 6 mo following fall application were higher in the silt loam than in the fine sandy loam (29% vs. 16% of applied N). Estimated NH3 losses were low (&lt;7% of applied N); hence, denitrification is suggested to be the main mechanism for gaseous N losses. The estimated ratio of denitrification to leaching manure N loss for fall application was about 7:1 in the silt loam and 2:1 in the sandy loam. To maximize manure N use by corn and minimize environmental N losses, spring or side-dress application of liquid swine manure is recommended, particularly in well-drained soils.Key words: Swine manure, application timing, soil type, 15N, N losses

Hybrid membrane bioreactor technology for small water treatment utilities: Process evaluation and primordial considerations

A hybrid membrane bioreactor (MBR) technology was investigated for treatment of natural waters containing natural organic matter (NOM), nitrate, alachlor and viruses. The NOM are precursors to disinfection byproducts (DBPs) such as trihalomethanes, and potential cause for microbial growth in distribution systems. Batch bioreactor studies optimized the carbon-to-nitrogen (C/N) ratio, temperature and pH for biological denitrification. Mini-pilot MBR studies with ethanol as electron donor were conducted under three scenarios: no powder activated carbon (PAC) or biomass, biomass alone, and combination of PAC and biomass. The removals of nitrate, alachlor, total organic carbon (TOC), trihalomethane formation potential (THMFP) and MS-2 virus were revaluated. Nitrite and ethanol residuals were well below their detection limits in the MBR effluent under steady-state conditions. Using biomass alone, the removal efficiencies for NOM (as TOC), alachlor, and THMFP were 60, 36 and 61%, respectively; whereas, on combining PAC and biomass they increased to 84, 99.8 and 98%. The virus rejection mechanisms postulated were size exclusion, sorption to membrane surface, attachment to bio-particles, and sorption onto foulant or cake layers. The MS-2 removals exceeded 3.8-logs under optimal process conditions. Membrane fouling and flux decline patterns under the three experimental scenarios were well described by the resistance model. The flux decline was characterized by three distinct stages, namely, initial conditioning fouling, rapid fouling, and slow fouling. The Tustin groundwater was associated with lower organic fouling but higher inorganic fouling than the Fountain Valley groundwater.