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PubMed2004

Nitrification in freshwater sediments as influenced by insect larvae: quantification by microsensors and fluorescence in situ hybridization.

Sediment-reworking macrofauna can stimulate nitrification by increasing the O(2) penetration into sediments or it can reduce nitrification by grazing on nitrifying bacteria. We investigated the influence of Chironomus riparius larvae (Insecta: Diptera) on the in situ activity, abundance, and distribution of NH4+-oxidizing (AOB) and NO2--oxidizing bacteria (NOB) in two freshwater sediments with microsensors and fluorescence in situ hybridization. In organic-poor sediment, nitrification activity was reduced by the presence of C. riparius larvae, whereas no such effect was detected in organic-rich sediment. We explain this difference with the variable larval burrowing and grazing behavior in the two sediment types: In organic-poor sediment larval activities were intense and evenly distributed across the whole sediment surface, whereas in organic-rich sediment larval activities were locally restricted to the microenvironment of animal burrows. Surprisingly, the animals did not cause any significant change of the abundance of AOB and NOB. This implies that the observed reduction of nitrification activity was not density-regulated, but rather was due to the lowered metabolic activity of the nitrifiers. Partial digestion and redeposition of particle-associated bacteria by C. riparius larvae are believed to have caused this loss of metabolic activity.

Animals↗
PubMed2004

Biofilm morphology and nitrification activities: recovery of nitrifying biofilm particles covered with heterotrophic outgrowth.

Biofilm processes are commonly used for nitrification. Operationally, a whitish heterotrophic biofilm layer tends to develop onto nitrifying biofilm when it has been exposed to organic carbon-containing wastewater for a prolonged period. The development of a heterotrophic biofilm layer could lead to deterioration in nitrification activities and biofilm morphology. The recovery characteristics, in terms of biofilm morphology and nitrification activities, of deteriorated biofilm particles (i.e. nitrifying biofilm particles covered with heterotrophic outgrowth) were investigated by transferring the deteriorated biofilm particles (from an Ultra-Compact Biofilm Reactor (UCBR) which was part of a packed bed-UCBR system used for treating organic carbon and ammonia-containing wastewater) to a UCBR fed solely with ammonia wastewater (referred to as 'Recovery-UCBR'). At a hydraulic retention time (HRT) of 8.7 h and a sand-carrier concentration of 4.0% (v/v), density of the outer heterotrophic biofilm layer reduced progressively which led to subsequent detachment of this layer from the nitrifying biofilm particles. As a result, morphology of the nitrifying biofilm improved gradually in the Recovery-UCBR. A stable nitrification rate of up to 1.74 kg NH4+-N/m3 d was obtained in the Recovery-UCBR.

Ammonia↗
PubMed2006

Potential nitrification in alum-treated soil slurries amended with poultry manure.

Alum is used to reduce environmental pollutants in poultry production. Alum decreases NH3 volatilization and increases total N and NH4+-N compared to untreated poultry manure. Nitrification in poultry wastes could therefore be stimulated due to higher NH4+ concentrations or could be inhibited because the soil environment is acidified. A 10-day laboratory study was conducted to study potential nitrification rates in soil slurries (20 g soil in 150 ml water) amended with 2.0 g alum-treated poultry manure. Fecal bacteria, NH4+, NO2-, NO3-, orthophosphate, pH, and NH3 were measured at 2-day intervals. Alum significantly reduced fecal bacteria concentrations through day 6. Water-soluble P was reduced 82% by day 10. Alum-treated manure had significantly increased NH4+ concentrations by day 8 and 10, and significantly decreased NO2- and NO3- concentrations by days 6-10. Alum's effect on potential nitrification was inhibitory in the soil environment. Slurries with alum-treated poultry manure had reduced nitrification rates, fecal bacteria, and soluble P. Therefore, in addition to reducing P loss, alum could temporarily reduce the risk for environmental pollution from land-applied manures in terms of both NO3- and fecal bacteria loss.

Alum Compounds↗
PubMed2006

Nitrification in polluted soil fertilized with fast- and slow-releasing nitrogen: a case study at a refinery landfarming site.

The nitrifying activity and the effect of fertilization with urea and methylene urea were studied in a landfarming site. The site has been operative over 20 years and maintained by heavy nitrogen fertilization. The landfarming soil contained 4-6% (w/w) oil. The nitrate accumulation was 20-50mg NO3-N day(-1)kg(-1) observed after methylene urea fertilization of 889 g Nm(-2). Nitrification ex situ (in laboratory conditions) was 8.8 mg NO3-N day(-1) kg(-1) in the presence of 380 mg kg(-1) NH4+-N. The half-saturation concentration of nitrification was more than 200 mg NH4+-N kg(-1). The results show that nitrification was active in soil with high oil concentration. Urea fertilization of 893 g Nm(-2) caused an increase of soil NH4+-N concentration up to 5500 mg kg(-1) and pH>8.5. This led to inhibition of nitrification, which persisted after NH4+ concentration decreased below 200mg NH4+ kg(-1).

Agriculture↗
PubMed2006

Quantifying the contribution of nitrification and denitrification to the nitrous oxide flux using 15N tracers.

Microbial transformations of nitrification and denitrification are the main sources of nitrous oxide (N2O) from soils. Relative contributions of both processes to N2O emissions were estimated on an agricultural soil using 15N isotope tracers (15NH4+ or 15NO3-), for a 10-day batch experiment. Under unsaturated and saturated conditions, both processes were significantly involved in N2O production. Under unsaturated conditions, 60% of N-N2O came from nitrification, while denitrification contributed around 85-90% under saturated conditions. Estimated nitrification rates were not significantly different whatever the soil moisture content, whereas the proportion of nitrified N emitted as N2O changed from 0.13 to 2.32%. In coherence with previous studies, we interpreted this high value as resulting from the decrease in O2 availability through the increase in soil moisture content. It thus appears that, under limiting aeration conditions, some values for N2O emissions through nitrification could be underestimated.

Air Pollutants↗
PubMed2005

Phenol biodegradation and its effect on the nitrification process.

Phenol biodegradation under aerobic conditions and its effect on the nitrification process were studied, first in batch assays and then in an activated sludge reactor. In batch assays, phenol was completely biodegraded at concentrations ranging from 100 to 2500 mg l(-1). Phenol was inhibitory to the nitrification process, showing more inhibition at higher initial phenol concentrations. At initial phenol concentrations above 1000 mg l(-1), the level of nitrification decreased. In the activated sludge reactor, the applied ammonium loading rate was maintained at 140 mg N-NH(4)(+)l(-1)d(-1) (350 mg N-NH(4)(+)l(-1)) during the operation time. However, the applied organic loading rate was increased stepwise from 30 to 2700 mg COD l(-1)d(-1) by increasing the phenol concentration from 35 up to 2800 mg l(-1). High phenol removal efficiencies, above 99.9%, were maintained at all the applied organic loading rates. Ammonium removal was also very high during the operation period, around 99.8%, indicating that there was no inhibition of nitrification by phenol.

Bacteria, Aerobic↗
PubMed2006

Effects of temperature on tertiary nitrification in moving-bed biofilm reactors.

The effect of wastewater temperature on the rate of nitrification was studied in two pure-oxygen moving-bed biofilm reactors, fed on secondary effluent from a municipal wastewater treatment plant. The first Reactor (R1) was operated under ammonia-limiting conditions, while the second Reactor (R2) was operated under oxygen-limiting conditions. Quite surprisingly, the former showed a negligible influence of thermal changes on nitrification rates, while the latter showed a much higher dependence. In this paper, a temperature coefficient "theta" has been defined as the actual "intrinsic" biological temperature coefficient, similar to the corresponding coefficient that is usually adopted for the design of activated-sludge processes. In addition, an "apparent" coefficient theta(a) has been quantified independently, which was calculated according to the actual values of nitrification rates at different temperatures. The actual biological temperature coefficient "theta", ranged between 1.086 and 1.109 (average value 1.098) under ammonia-limiting conditions, while under oxygen-limiting conditions was in the range 1.023-1.081 (average value 1.058). The apparent value theta(a) was near to unity (i.e. no temperature effect) under ammonia-limiting conditions, while only under oxygen-limiting conditions and at constant dissolved oxygen concentration "theta(a)" coincided with "theta". An explanation was given that, under oxygen-limiting conditions, the specific biomass activity (i.e. the ratio of nitrification rate to biomass concentration) was strongly influenced by the combined effects of oxygen penetration through the biofilm and effluent temperature.

Biofilms↗
PubMed2001

Development of nitrification inhibition assays using pure cultures of Nitrosomonas and Nitrobacter.

Restricted requirements for nitrogen reduction at wastewater treatment plants have increased the need for assays determining the inhibition of nitrification. In this paper, two new assays studying ammonia oxidation and nitrite oxidation, respectively, are presented. As test organisms, pure cultures of Nitrosomonas and Nitrobacter isolated from activated sludge are used. The assays are performed in test tubes where the bacteria are incubated with the compound or wastewater to be tested. The nitrification rate is measured during 4 h and compared with reference samples. The test organisms were characterised with respect to temperature, pH and cell activity. Optimum temperature was 35 degrees C for Nitrosomonas and 38 degrees C for Nitrobacter; optimum pH was 8.1 for Nitrosomonas and 7.9 for Nitrobacter. There was a linear relationship between the nitrification rate and the cell concentration in the studied interval. The cell activity decreased slightly with storage time. A significant level of inhibition was calculated to 11% for the Nitrosomonas assay, and to 9% for the Nitrobacter assay. The assays are applicable to determination of nitrification inhibition in samples of industrial waste waters or influents of treatment plants, or chemical substances likely to be found in wastewater.

Ammonia↗
PubMed2001

Impact of temperature on nitrification in biological activated carbon (BAC) filters used for drinking water treatment.

The impact of temperature on nitrification in biological granular activated carbon (GAC) filters was evaluated in order to improve the understanding of the nitrification process in drinking water treatment. The study was conducted in a northern climate where very cold water temperatures (below 2 degrees C) prevail for extended periods and rapid shifts of temperature are frequent in the spring and fall. Ammonia removals were monitored and the fixed nitrifying biomass was measured using a method of potential nitrifying activity. The impact of temperature was evaluated on two different filter media: an opened superstructure wood-based activated carbon and a closed superstructure activated carbon-based on bituminous coal. The study was conducted at two levels: pilot scale (first-stage filters) and full-scale (second-stage filters) and the results indicate a strong temperature impact on nitrification activity. Ammonia removal capacities ranged from 40 to 90% in pilot filters, at temperatures above 10 degrees C, while more than 90% ammonia was removed in the full-scale filters for the same temperature range. At moderate temperatures (4-10 degrees C), the first stage pilot filters removed 10-40% of incoming ammonia for both media (opened and closed superstructure). In the full-scale filters, a difference between the two media in nitrification performances was observed at moderate temperatures: the ammonia removal rate in the opened superstructure support (more than 90%) was higher than in the closed superstructure support (45%). At low temperatures (below 4 degrees C) both media performed poorly. Ammonia removal capacities were below 30% in both pilot- and full-scale filters.

Ammonia↗
PubMed2003

Bio-augmentation by nitrification with return sludge.

Bio-augmentation can be used to obtain nitrification in activated sludge processes that operate at sub-optimal solid retention times. In this study, we evaluated the potential of augmenting the endogenous nitrifying bacteria, by implementing a nitrification reactor in the sludge return line. This reactor can be fed with an internal N-rich flow (e.g. effluent from the sludge treatment) or with an external ammonium source. A mathematical model based on ASM1 was developed and used to evaluate the potential of this technique. The bio-augmentation studied here aimed to enhance the nitrification process of highly loaded activated sludge systems. A calibrated simulation model of a high loaded wastewater treatment plant in The Netherlands was used for this study. A side stream process (the named BABE process) was included in the simulation. This process was fed with the ammonia-rich water generated by sludge digestion and subsequent thickening by centrifugation (the so-called rejectwater). An external source (artificial) of ammonium was also considered to evaluate the differences between the two origins of ammonium. The results showed that with the augmentation process, high loaded activated sludge systems can achieve nitrification even at low winter temperatures. The best effect is obtained for systems operating at approximately 50% of the minimal SRT without augmentation. The use of an internal ammonia source is more effective than an external source. The results of this study give a quantitative basis for the design of process internal bio-augmentation processes and the effect on the N-removal capacity of the treatment plant.

Bioreactors↗
PubMed2002

The evaluation of enhanced nitrification by immobilized biofilm on a clinoptilolite carrier.

This study was conducted to evaluate the effect of clinoptilolite on nitrification in activated sludge (AS), and was focused on a relationship between ammonium exchange capacity of this mineral and improvement of nitrification. In batch experiments, the adsorption property of biofilm-attached clinoptilolite did not show substantial difference from that of natural clinoptilolite, indicating that bioregeneration became completely achieved without any regenerant in the AS. The AS with added clinoptilolite (ZR) was compared to the control AS (CR) when the ratio of chemical oxygen demand (COD) to total kjeldahl nitrogen (TKN) of influent, i.e. C/N ratio, was varied from 3.25 to 7.5 at a hydraulic retention time (HRT) of 3 h. Enhanced nitrification was comparatively observed for the ZR as C/N ratio gradually increased. The results indicated that the clinoptilolite provided a relatively low C/N ratio for nitrifiers, due to ammonium adsorption of this mineral, and consequently nitrification was accelerated.

Adsorption↗
PubMed1999

A novel double-membrane system for simultaneous nitrification and denitrification in a single tank.

A novel biological treatment system, which contains two types of membrane modules in a single tank, was developed for simultaneous nitrification and denitrification. Both of the modules were fed with the substrates on the tube side of the silicone tubes by diffusing them to the biofilms which form on the surface of the tubes. One module was fed with methanol for denitrification and the other one was fed with pure oxygen for nitrification. As a result, the interference of organic carbon on nitrification, and that of oxygen on denitrification, were both hindered by the diffusion barriers (biofilms), thereby allowing two different niches for nitrifiers and denitrifiers to coexist in a single tank. Besides saving space and the amount of alkalinity required for nitrification, this system also produced low residual chemical oxygen demand (COD) and high nitrogen removal rates (2.9-3.4 gN m-2 d-1 of surface area of membrane).

Bacteria↗
PubMed2002

Nitrification utilizing CaCO3 as the buffering agent.

Nitrification utilizing chalk (calcium carbonate) as the buffering agent was investigated. Three different fluidized bed reactor configurations were examined in order to study the effect of reactor layout on nitrification and concomitant chalk dissolution. The first system consisted of two interconnected columns with high recycle rate, one containing zeolite as the carrier for the nitrifying biomass and the other chalk as the buffering agent. The second reactor system consisted of a single column containing both zeolite and chalk particles. In the third system, nitrification was carried out in a single column where chalk particles were used both as the carrier for the biomass and as the buffer. Results showed that only the reactor with chalk acting as both the buffering agent and the biomass carrier could be operated without external buffer (NaHCO3) addition. This system operated at high ammonium removal rates of up to 2.5 g N l(-1) reactor d(-1) even though the bulk solution of the reactor had a low pH of 5.5. The high nitrification efficiency at this low pH was probably mainly a result of a favorable microenvironment surrounding the nitrifying biomass attached to the chalk.

Antacids↗
PubMed2003

Molecular analysis of microbial communities in nitrification and denitrification reactors treating high ammonia leachate.

Molecular analysis of microbial populations in two bench-scale nitrification and denitrification reactors fed with high ammonia landfill leachate was conducted in this study by using DGGE, cloning, and FISH techniques in addition to classical efficiency control parameters. Nitrification tank was operated with a computer-controlled alkalinity dosing system to supply the alkalinity intermittently as consumed on the basis of on-line pH monitoring. By keeping the pH at 7.0 with this system, 99% nitrification efficiency and rates of about 0.14-0.18 mgNH4+-N/mgVSSday were obtained. Meanwhile, as ammonia oxidizing bacteria Nitrosomonas and Nitrosococcus mobilis-like cells and as nitrite oxidizing bacteria Nitrobacter-related cells were intensively indicated. Moreover, some aerobic denitrifiers as Thauera species were also identified. After the termination of pH adjustment in the preceding anaerobic reactors, nitrification tank was loaded with more biodegradable COD as a result of reduced COD removal in anaerobic reactors. Microbial diversity was immediately affected from this alteration and heterotrophic carbonaceous bacteria and aerobic denitrifiers have dominated. To provide the former high efficiencies, retention time has increased from 24 to 48 h and a second pump dosing HCl was included to the automatic control system. Subsequent to these precautions, numbers of ammonia (Nso190) and nitrite oxidizing bacteria (NIT3) were comparatively increased. In denitrification system, about 98% denitrification efficiencies were obtained at 2000 mg/L NOx-N concentrations if sodium acetate was supplied as carbon source. Meanwhile, with 20 gVSS/l biomass concentration, denitrification rates of about 1.34 mgNOx-N/mgVSSday were obtained. All sludge samples have represented similar DGGE patterns and Paraccoccus-related species were identified as dominant denitrifying bacteria.

Ammonia↗
PubMed2003

Using oxidation-reduction potential (ORP) and pH value for process control of shortcut nitrification-denitrification.

A new low cost technology for simultaneous carbon-nitrogen removal from soybean wastewater has been developed in this study. The technology is performed through shortcut nitrification-denitrification. The process operated under realtime control of aeration and mixing time. The shortcut nitrification-denitrification in sequencing batch reactor (SBR) was achieved efficiently and steadily by controlling temperature (28 +/- 0.5 degrees C) and using real-time control strategies. This enabled the prevention of nitrite oxidation, leading to lower operational costs. The feasibility of oxidation-reduction potential (ORP) and pH value as control parameter for shortcut nitrification-denitrification process was also investigated. Results showed that the average removal efficiency of ammonium was more than 95%, and nitrosation rate (NO2(-)-N/NOx(-)-N) was reached to 96%. At the same time, the variation of oxidation--reduction potential (ORP) and pH value was well related to organic matter degradation and ammonium oxidation in SBR. So that judgment on the ending of nitrification and denitrification can be based on the inflection point on the varied curve of ORP and pH throughout each SBR processing cycle, and thus reducing aeration and mixing time for saving energy source. The method saves organic energy up to 40% of chemical oxygen demand (COD) in denitrification process, which should reduce the need for an extra external source of organic carbon. Shorter hydraulic retention time should allow the volume of the reactors to diminish, and thus diminish investment costs. Lower oxygen demand of about 25% gives lower exploitation costs.

Agriculture↗
PubMed2004

Promoting nitrification by using functional gel as immobilizing medium under different temperature stimulation patterns.

Nitrification with nitrifiers immobilized by temperature stimuli-responsive N-isopropylacrylamide-Chlorophyll (NIPA-CH) gel was investigated under several patterns of temperature stimulation, compared with that at constant temperature. The results show that in response to a cyclic temperature stimulus of 32-36 degrees C or 32-34 degrees C with a period of 4 or 2 h, respectively, the gel swelled and shrank reversibly and promoted biological nitrification. But in the case of a cyclic temperature change of 32-36 degrees C with a stimulation cycle of 2 h, nitrite oxidization declined. The results suggested that adequate stimulus facilitated substrate transfer into gels that promoted nitrification in the reactor, but quite frequent swelling and shrinking of the gel squeezed nitrifier out of the gel resulting in washing nitrifier out and declining nitrification. When gels that undergone cyclic temperature stimuli began to swell at 32 degrees C, oxygen consumption of nitrifiers in the gels was more than that of nitrifiers in the gels at constant temperature of 32 degrees C all the time, but when gels of two reactors shrank at 36 degrees C, their oxygen consumption reduced and there was almost no difference between them regardless of their undergone temperature stimuli once or not. Practical application of nitrifier immobilized by NIPA-CH gel in wastewater treatment was also discussed.

Acrylamides↗
PubMed2005

Links between ammonia oxidizer species composition, functional diversity and nitrification kinetics in grassland soils.

Molecular approaches have revealed considerable diversity and uncultured novelty in natural prokaryotic populations, but not direct links between the new genotypes detected and ecosystem processes. Here we describe the influence of the structure of communities of ammonia-oxidizing bacteria on nitrogen cycling in microcosms containing natural and managed grasslands and amended with artificial sheep urine, a major factor determining local ammonia concentrations in these environments. Nitrification kinetics were assessed by analysis of changes in urea, ammonia, nitrite and nitrate concentrations and ammonia oxidizer communities were characterized by analysis of 16S rRNA genes amplified from extracted DNA using ammonia oxidizer-specific primers. In natural soils, ammonia oxidizer community structure determined the delay preceding nitrification, which depended on the relative abundance of two Nitrosospira clusters, termed 3a and 3b. In batch cultures, pure culture and enrichment culture representatives of Nitrosospira 3a were sensitive to high ammonia concentration, while Nitrosospira cluster 3b representatives and Nitrosomonas europaea were tolerant. Delays in nitrification occurred in natural soils dominated by Nitrosospira cluster 3a and resulted from the time required for growth of low concentrations of Nitrosospira cluster 3b. In microcosms dominated by Nitrosospira cluster 3b and Nitrosomonas, no substantial delays were observed. In managed soils, no delays in nitrification were detected, regardless of initial ammonia oxidizer community structure, most probably resulting from higher ammonia oxidizer cell concentrations. The data therefore demonstrate a direct link between bacterial community structure, physiological diversity and ecosystem function.

Ammonia↗
PubMed1983

Sediment nitrification, denitrification, and nitrous oxide production in a deep arctic lake.

We used a combination of N tracer methods and a C(2)H(2) blockage technique to determine the role of sediment nitrification and denitrification in a deep oligotrophic arctic lake. Inorganic nitrogen concentrations ranged between 40 and 600 nmol . cm, increasing with depth below the sediment-water interface. Nitrate concentrations were at least 10 times lower, and nitrate was only detectable within the top 0 to 6 cm of sediment. Eh and pH profiles showed an oxidized surface zone underlain by more reduced conditions. The lake water never became anoxic. Sediment Eh values ranged from -7 to 484 mV, decreasing with depth, whereas pH ranged from 6.0 to 7.3, usually increasing with depth. The average nitrification rate (49 ng of N . cm . day) was similar to the average denitrification rate (44 ng of N . cm . day). In situ N(2)O production from nitrification and denitrification ranged from 0 to 25 ng of N . cm . day. Denitrification appears to depend on the supply of nitrate by nitrification, such that the two processes are coupled functionally in this sediment system. However, the low rates result in only a small nitrogen loss.

Journal Article↗