Nitrification Period Research Articles

Quick start-up of partial nitrification in a novel anaerobic/ pulse washout (APW) process for treating municipal wastewater

This study proposed a novel anaerobic/pulse washout (APW) process that can rapidly inhibit nitrite-oxidizing bacteria (NOB) and enrich ammonia-oxidizing bacteria (AOB) to achieve the quick start-up of partial nitrification in an activated sludge system. The results showed that the start-up period of partial nitrification in the APW process (20 days) was shorter than that in the process operated without APW (45 days). Analysis of the microbial communities revealed that the activity and relative proportion of AOB (AOB/(AOB plus NOB)) in the APW process (88.64 mgN·L−1·d−1, 82%) were significantly higher than those in the process without APW (75.82 mgN·L−1·d−1, 62%). Furthermore, the directional change in the composition of extracellular polymeric substances (EPS) and intracellular polymeric substances of microorganisms under APW can affect the metabolic pattern and growth of nitrifiers, thereby, accelerating the start-up of partial nitrification. To further verify efficiency, the APW process was used to treat actual low carbon/nitrogen (C/N) sewage. The results showed that partial nitrification and denitrification were quickly achieved with high nitrogen removal capacity. Thus, this study offers a new process to improve partial nitrification and denitrification and develop a theoretical basis with which to solve low C/N issues in municipal wastewater treatment plants.

Evaluation of the integration of P recovery, polyhydroxyalkanoate production and short cut nitrogen removal in a mainstream wastewater treatment process

Wastewater treatment systems are nowadays evolving into systems where energy and resources are recovered from wastewater. This work presents the long term operation of a demo-scale pilot plant (7.8 m3) with a novel configuration named as mainstream SCEPPHAR (ShortCut Enhanced Phosphorus and polyhydroxyalkanoate (PHA) Recovery) and based on two sequencing batch reactors (R1-HET and R2-AUT). This is the first report of an implementation at demo scale and under relevant operational conditions of the simultaneous integration of shortcut nitrification, P recovery and production of sludge with a higher PHA content than conventional activated sludge. An operating period under full nitrification mode achieved successful removal efficiencies for total N, P and CODT (86 ± 12%, 93 ± 9% and 79 ± 6%). In the following period, nitrite shortcut (with undetectable activity of nitrite oxidising bacteria) was achieved by implementing automatic control of the aerobic phase length in R2-AUT using ammonium measurement and operating at a lower sludge retention time. Similar N, P and CODT removal efficiencies to the full nitrification period were obtained. P-recovery from the anaerobic supernatant of R1-HET was achieved in a separate precipitator by increasing pH and dosing MgCl2, recovering an average value of 45% of the P in the influent as struvite precipitate, with a peak up to 63%. These values are much higher than the typical values of sidestream P-recovery (12%). Regarding PHA, a percentage in the biomass in the range 6.9–9.2% (gPHA·g−1TSS) was obtained.

Nitrification in a biofilm-enhanced highly loaded aerated lagoon.

A full-scale biofilm-enhanced aerated lagoon using fixed submerged media was monitored using automated water quality monitoring stations over the span of one year to quantify its nitrification performance. The system was operating at a high organic loading rate averaging 5.8gtotalCBOD5 /m2 of media per day (23.9gtotalCBOD5 /m3 of lagoon per day), a total ammonia nitrogen loading rate averaging 0.9gNH4 -N/m2 day (3.7gNH4 -N/m3 day), and temperatures ranging from 1.6 to 20.8°C. The system showed an extended seasonal nitrification period compared with a simulated aerated lagoon system of the same dimensions. This extension of complete nitrification with approximately 1month was observed in the fall despite the decrease of operating temperature down to 4°C. During this maximum nitrification period, substantial denitrification occurred, and the effluent un-ionized ammonia ratio was reduced. A temporary loss of nitrification was also experienced in relation to an episode of elevated suspended solids concentration. Measured biofilm characteristics, namely the detachment dynamics and the biofilm thickness, were used to explain this temporary nitrification loss. During wintertime, a low nitrate production was still observed, suggesting year-long retention of nitrifying bacteria in the biofilm. PRACTITIONER POINTS: Nitrification in a highly loaded biofilm-enhanced aerated lagoon is mainly affected by operating temperature. Maximum nitrification is observed during the warmer months and occurs even at high organic loading rates (>5gCBOD5 /m2 day). Compared with a simulated suspended growth system, the biofilm-enhanced lagoon shows a significantly extended nitrification period. The extension is observed at the end of the summertime maximum nitrification period. Low amounts of nitrate still produced during winter in the biofilm-enhanced aerated lagoon suggest year-long retention of autotrophic nitrifying biomass in the biofilm. Nitrification in the biofilm-enhanced aerated lagoon is negatively impacted by the presence of important quantities of accumulated solids that resuspend when their digestion starts as temperature increases.

Characteristics of Biofilm During the Transition Process of Complete Nitrification and Partial Nitrification

The objective of the study was to investigate the change of biofilm characteristics when implementing the procedure of partial nitrification. A ratio control strategy (DO/NH4+-N) was taken to achieve partial nitrification, and biofilm samples were obtained at 10.27%, 52.12%, and 93.54% of the nitrite accumulation rate. The amount and spatial distribution of total bacteria, ammonia oxidizing bacteria (AOB), and nitrite oxidative bacteria (NOB) were observed by fluorescence in situ hybridization (FISH) and confocal laser scanning microscope (CLSM) through a three-dimensional excitation emission matrix (EEM) to observe the secretion and composition changes of extracellular polymer substances. Ratio control successfully enriched AOB and achieved partial nitrification under conditions when NOB was not completely washed. Heterotrophic bacteria and nitrifying bacteria coexist in the biofilm. The heterotrophic bacteria were in the outer layer, but nitrifying bacteria were distributed in the biofilm surface at 6-25 μm. During the process of short-range nitrification, the AOB/NOB value gradually increased, and the stable operation period was as high as 15.56. During the operation of the reactor, EPS and microbial flora changes are closely related. When microbial activity decreased, EPS secretion decreased. During the stable operation period of partial nitrification, NOB and other bacteria that are non-resistant to high nitrite nitrous acid declined, and the fluorescence intensity of aromatic protein-like bacteria decreased. However, the three-dimensional fluorescence spectra showed that the chemical composition of EPS was not obvious during the process of partial nitrification.

Realization of Shortcut Nitrification in the ABR-MBR Process Treating Domestic Wastewater

The operational control conditions for realizing shortcut nitrification in the membrane bioreactor (MBR) process was investigated in a lab-scale anaerobic baffled reactor (ABR)-MBR combined system, which laid the foundation for further research on the performance of denitrification phosphorus removal in the system. The experimental results under different conditions showed that shortcut nitrification in the MBR was achieved by controlling the dissolved oxygen (DO) concentration to low levels (0.5-1.0 mg·L-1 to 0.3-0.7 mg·L-1) and changing the effective volume of the MBR to control hydraulic retention time (HRT), with the HRT in the ABR equal to 6 h, sludge reflux ratio of 100%, NOx--N reflux ratio of 300%, and temperature of 30℃±2℃. Finally, the shortcut nitrification deteriorated as the HRT in the MBR increased from 3 h to 5 h, with nitrite accumulation rate dramatically dropping from 60% to 15%. The analysis of the influencing factors of shortcut nitrification showed that maintaining low DO concentration (0.3-0.7 mg·L-1) and gradually shortening HRT were the key factors. The pH, free ammonia (FA), free nitrous acid (FNA), temperature, and sludge retention time (SRT) had a slightly positive effect on shortcut nitrification. During the period of shortcut nitrification, a stable and high efficiency removal of COD and NH4+-N were achieved, and the average concentration of the effluent of COD and NH4+-N, whose removal rates were above 90%, were below 50 mg·L-1 and 2 mg·L-1, respectively, and the removal efficiency of total nitrogen (TN) reached 72%.

The response of ammonia-oxidizing microorganisms to trace metals and urine in two grassland soils in New Zealand.

An incubation experiment was conducted to investigate the response of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and the nitrification rate to the contamination of Cu, Zn, and Cd in two New Zealand grassland soils. The soils spiked with different concentrations of Cu (20 and 50mgkg-1), Zn (20 and 50mgkg-1), and Cd (2 and 10mgkg-1) were incubated for 14days and then treated with 500mgkg-1 urine-N before continuing incubation for a total of 115days. Soils were sampled at intervals throughout the incubation. The nitrification rate in soils at each sampling period was determined, and the abundance of AOB and AOA was measured by real-time quantification polymerase chain reaction (qPCR) assay of the amoA gene copy numbers. The results revealed that moderate trace metal stress did not significantly affect the abundance of AOB and AOA in the two soils, probably due to the high organic matter content of the soils which would have reduced the toxic effect of the metals. Nitrification rates were much greater and the observable nitrification period was much shorter in the dairy farm (DF) soil, in which the AOB and AOA abundances were greater than those of the mixed cropping farm (MF) soil. AOB were shown to grow under high nitrogen conditions, whereas AOA were shown to grow under low N environments, with different metal concentrations. Therefore, nitrogen status rather than metal applications was the main determining factor for AOB and AOA growth in the two soils studied.

Remediation of Nitrogen-Contaminated Sediment Using Bioreactive, Thin-layer Capping with Biozeolite

ABSTRACTIn situ amendment of nitrogen-contaminated sediment using bioreactive, thin-layer capping (BTC) with biozeolite (i.e., zeolite with heterotrophic nitrifiers as well as aerobic denitrifiers attached) was studied herein. BTC with biozeolite for nitrogen-contaminated sediment management was evaluated through long-term (170 days) sediment incubation laboratory experiments. The results showed that BTC with relatively small dose rates (<10 kg m−2) of biozeolite reduced the total nitrogen (TN) concentration in overlying water by over 90%, so it was effective in reducing the amount of N released from sediment. Higher-dose rates of biozeolite capping achieved an even higher removal efficiency. With the DO concentration of 1.5 ∼ 6.5 mg L−1 in overlying water, the reduction efficiency of TN in overlying water using BTC was higher than that less than 1 mg L−1. In BTC systems, biological regeneration (i.e., heterotrophic nitrifiers attached to zeolite can regenerate the zeolite ion exchange capacity for ammonium) occurred in biozeolite which was saturated with ammonium during the nitrification period. In addition, TN contents in surface sediment in BTC systems were reduced at different levels after the experiment. These findings indicate that the BTC can be a feasible remedial approach to reduce N in overlying water and sediment in eutrophic water bodies. In the BTC, N load was reduced by the added biozeolite through adsorbing ammonium (NH4+-N), converting NH4+-N into nitrate nitrogen (NO3−-N) and nitrogen gas (N2), and assimilating inorganic nitrogen.

Effect of alkalinity on nitrite accumulation in treatment of coal chemical industry wastewater using moving bed biofilm reactor

Nitrogen removal via nitrite (the nitrite pathway) is more suitable for carbon-limited industrial wastewater. Partial nitrification to nitrite is the primary step to achieve nitrogen removal via nitrite. The effect of alkalinity on nitrite accumulation in a continuous process was investigated by progressively increasing the alkalinity dosage ratio (amount of alkalinity to ammonia ratio, mol/mol). There is a close relationship among alkalinity, pH and the state of matter present in aqueous solution. When alkalinity was insufficient (compared to the theoretical alkalinity amount), ammonia removal efficiency increased first and then decreased at each alkalinity dosage ratio, with an abrupt removal efficiency peak. Generally, ammonia removal efficiency rose with increasing alkalinity dosage ratio. Ammonia removal efficiency reached to 88% from 23% when alkalinity addition was sufficient. Nitrite accumulation could be achieved by inhibiting nitrite oxidizing bacteria (NOB) by free ammonia (FA) in the early period and free nitrous acid in the later period of nitrification when alkalinity was not adequate. Only FA worked to inhibit the activity of NOB when alkalinity addition was sufficient.

Achieving and maintaining of short-cut nitrification in a cyclic activated sludge system

A lab-scale Cyclic Activated Sludge Technology (CAST) system was operated more than 5 months to evaluate the effects of the operation mode on nitrogen removal performance and investigate a feasible method for achieving short-cut nitrification in the system. Results showed that nitrogen was removed by conventional biological nitrification and denitrification in traditional operation mode (fill/aeration 2 h, settle 1 h, decant 1 h), whereas short-cut nitrification and denitrification was the main nitrogen removal pathway in modified operation mode and the nitrogen removal performance was enhanced. Short-cut nitrification was successfully achieved in CAST system at 17 ± 1 °C by adjusting operation conditions and the average total nitrogen removal efficiency increased by 11.4% compared to traditional mode. It was assumed that low dissolved oxygen (<1.0 mg/L) limitation combined with free ammonia (0.28-0.34 mg/L) inhibition on nitrite-oxidizing bacteria caused nitrite accumulation in modified mode. During maintaining period of short-cut nitrification, preset aeration time enhanced ammonium-oxidizing bacteria dominance. It was also found that low DO could result in overgrowth of filamentous microorganisms and poor sludge settleability. The pH variation could provide effective information for controlling aeration duration in modified mode. However, no evident breakpoint appeared on pH and DO profiles in traditional mode.

Monitoring and control of a partially packed biological aerated filter (BAF) reactor for improving nitrogen removal efficiency

This paper examines on-off systems and automatic monitoring and control of a biological aerated filter to identify the end point of nitrification and denitrification processes, and chemical oxygen demand (COD), ammonia-nitrogen removal (NH3-N) and aeration savings. Oxidation-reduction potential (ORP), pH and dissolved oxygen (DO) were measured on-line and chemical parameters were measured in the wastewater. The ‘nitrate knee’ in the ORP profile was characterised by a breakpoint at average 160 min, representing the complete removal of NO3-N, i.e. the end of the denitrification period, as well as the end of the nitrification period was clearly shown in the pH profile (ammonia valley) at average 210 min for all C/N ratios. The NH3-N removal efficiencies were 92.30, 97.57 and 98.02% whilst the COD removals of 95.06, 96.38 and 97.56% were achieved for the C/N ratios of 10, 4 and 1 respectively. Therefore, the on-off control was operated at average 230 min for aeration time and 130 min for the anoxic period. Thus significant improvements can be achieved with respect to the continuous aeration strategy, and average operational costs reduced by 36.11%. The study showed that an on-off controller can easily be implemented in wastewater process-control, and monitoring systems improve effluent quality and reduce energy consumption.

Nitrification Inhibition in Iowa Soils Treated with Stay‐N 2000 as Affected by Temperature and Matric Potential

The effects of temperature and water potential on nitrification were investigated in two Iowa soils treated with Stay‐N 2000. The soils were incubated at 10, 20, and 30 °C after soil water potentials of −1, −10, or −60 kPa were applied to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K max), duration of lag period (t′), period of maximum nitrification (Δt), and termination period of nitrification (t s). The highest K max were 18 and 24 mg kg−1 d−1 nitrate (NO3 −)–nitrogen (N), respectively, at 30 °C and −10 kPa in both the Nicollet (fine‐loamy, mixed, superactive, mesic Aquic Hapludoll) and Canisteo (fine‐loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) soils and reduced to 4 and 16 mg kg−1 d−1 NO3 −‐N when Stay‐N 2000 was added. The extension of t′ due to the addition of Stay‐N 2000 was as high as 7 d in the Nicollet soil at 10 °C and −1 kPa and as little as 2 d in the Canisteo soil at 20 °C and −10 kPa.

High reproducibility of ammonia-oxidizing bacterial communities in parallel sequential batch reactors

To investigate whether the ammonia-oxidizing bacterial (AOB) communities of replicate nitrifying bioreactors (i) co-evolve or diverge over time and (ii) are stable or dynamic during periods of complete nitrification. Three sequential batch reactors (SBR) were inoculated with sludge from a municipal wastewater treatment plant, fed with ammonium-enriched tap water and operated in parallel for 134 days. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) demonstrated co-evolvement of the AOB communities over time. During start-up, temporary decreases in nitrification were noticed, and the AOB community rate of change values (Delta(t(week))) were medium to high (12-22%). During the adjacent period of complete nitrification, low AOB community dynamics were observed (Delta(t(week)) < 5%). Further pragmatic processing of the DGGE profiles revealed a high range-weighted richness and a medium functional organization of the AOB communities. After a start-up period, high functional stability and low dynamics of the AOB communities were observed. Deterministic rather than stochastic driving forces led to AOB community co-evolvement in the replicate SBR. Replicates in identical set-ups are reproducible, and pragmatic processing of DGGE patterns is a straightforward tool to score and compare the functionality of the bacterial communities.

Seasonally varying nitrogen isotope biogeochemistry of particulate organic matter in Lake Kinneret, Israel

Large temporal variations in the nitrogen isotopic composition (δ15N) of particulate organic matter (POM) and dissolved inorganic nitrogen (DIN) species in Lake Kinneret occurred in response to seasonal phasing of dominant nitrogen cycle processes. The lowest δ15N POM values (25.5‰) were observed in early winter, a consequence of isotopic fractionation by chemoautotrophic microbial NH4+ assimilation, and during the first phase of the nitrification period, by seasonally dominant NH4+ oxidizers. Nitrification itself was strongly fractionating, producing 15N-depleted NO3− and strongly enriching water-column NH4+ in 15N. Toward the end of nitrification and into the phytoplankton bloom period in later winter and early spring, there was a corresponding 15-30‰ jump in POM δ15N because of assimilation of high-δ15N NH4+. Maximal δ15N POM values were thus measured during the algal blooms of Peridinium gatunense in 2004 and Debarya sp. and Microcystis sp. in 2005. Toward the end of the blooms in mid- to late spring, POM δ15N values decreased to values similar to δ15N for NO3− (8-12‰), indicating a switch to this DIN source. NO3− assimilation into POM appeared to occur without isotopic fractionation. Late spring was also the denitrification period with NO3− removal in the newly suboxic hypolimnion. Though δ15NO3− increased in the residual NO3−, complete consumption by denitrification suggests no net effect, as supported by a lack of increase in δ15N POM at this time. Oligotrophic conditions are found in the epilimnion in late summer and early autumn and low (3.3‰) δ15N POM was found during the bloom of the filamentous N2-fixing cyanobacteria Aphanizomenon ovalisporum and Cylindrospermopsis cuspis. The δ15N-dissolved organic nitrogen isotopic signature at this time was significantly higher, 8–12‰, suggesting a phytoplankton source from earlier in the seasonal cycle. Overall, the largest known seasonal variations in N isotope composition have been observed in Lake Kinneret, providing a uniquely useful biogeochemical tool for studying N cycling in lakes as well as detecting long-term changes in N source and cycling in response to watershed land use changes and climate change.

Heavy‐Metal Inhibition of Nitrification in Selected Iowa Soils Treated with Stay‐N 2000

Heavy‐metal inhibition of nitrification in soils treated with reformulated nitrapyrin was investigated. Clarion and Okoboji soils were treated with ammonium sulfate [(NH4)2SO4] and a nitrification inhibitor. Copper(II) (Cu), Zinc(II) (Zn), Cadmium(II) (Cd), or Lead(II) (Pb) were added to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K max), duration of lag period (t′), period of maximum nitrification (Δt), and the termination period of nitrification (t s). In the Clarion soil, the K max decreased from 12 mg kg−1 d−1 without the nitrification inhibitor to 4, 0.25, 0.86, and 0.27 mg kg−1 d−1, respectively, when the inhibitor and Cu, Zn, Pb, or Cd were applied. In the Okoboji soil, K max decreased from 22 mg kg−1 d−1 with no inhibitor to 6, 3, 4, and 2 mg kg−1 d−1, respectively, when an inhibitor and Cu, Zn, Pb, or Cd were added. The t′ varied from 8 to 25 d in the Clarion soil and from 5 to 25 d in the Okoboji soil, due to addition of Cu, Zn, Pb, or Cd and the inhibitor.

Treatment of low carbon-to-nitrogen wastewater using two-stage sequencing batch reactor with independent nitrification

Two-stage sequencing batch reactor (SBR) with independent nitrification was evaluated for simultaneous removal of COD, nitrogen, and phosphorus from a low carbon-to-nitrogen wastewater (C/N ratio ranged from 1.1 to 7.4). Independent nitrification proceeded by incorporating the contact period within the system and the nitrification period in the external reactor, which was an outsourcing resource dedicated to enhancing nitrification activity. The contact period enabled the fraction of organic substrate in the influent. Ammonia nitrogen was then able to be decanted to the external nitrification reactor, in which ammonia nitrogen was nitrified as much as 70%. During the nitrification period, dominate microbial group was an ammonia oxidizing bacteria such as Nitrosomonas sp. JL21, Nitrosomonas sp. JL2, and Nitrosolobus multiformis. During the react period, the nitrogen nitrified was not only denitrified, but organic matters were also biodegraded. It was revealed that the effective and preferential use of organic substrate enhanced the overall performance of the system without the supplement of any external carbon sources. Removal efficiencies of COD, nitrogen, and phosphorus were as high as 87% at the loading rate of 0.06–4.79 kg COD/m 3 day, 81% at the loading rate of 0.05–0.84 kg N/m 3 day, and 60% at the loading rate of 0.01–0.09 kg P/m 3 day, respectively.

Dynamic modelling of nitrification in an aerated facultative lagoon

Faced with the need to improve ammonia removal from lagoon wastewater treatment plants (WWTPs) operated in Quebec, Canada, mechanistic modelling has been proposed as a tool for explaining the seasonal nitrification phenomenon and to evaluate optimization and upgrade scenarios. A lagoon model that includes a modified activated sludge biokinetic model and that assumes completely mixed conditions in the water column and sediments has been applied to simulate 3 years of consecutive effluent data for a lagoon from the Drummondville WWTP. Successful prediction of results from this plant indicates that the seasonal nitrification is determined by temperature, dissolved oxygen (DO) concentrations, hydraulic retention time (HRT) of the water column and washout driven by a well-mixed water column. Results also indicate that sediments contribute to the ammonia load in the lagoon effluent, particularly in spring and early summer. Sensitivity analyses performed with the model indicate that the nitrification period could be prolonged by increasing DO concentrations in the lagoon and that bioaugmentation would be particularly effective in spring and early summer. Limitations of the model are discussed, as well as ways to improve the hydraulic model.

Nutrient effects on microbial transformation of pesticides in nitrifying surface waters

Multivariate analyses of a large set of physical, chemical, and biological measurements indicated possible effects that specific surface water properties have on biotransformation rates of pesticides. In this study, we investigated the roles of Mg, Mn, and P, which were identified as relevant, discriminating environmental variables in the overall biotransformation process as it occurred under nitrifying conditions. Nematicide aldicarb, herbicides simazine and MCPA were selected as their chemical group representatives. Series of mechanically aerated incubation vessels were set up to test nutrient enrichment effects on microbial development and subsequent pesticide transformation. Accounting for alterations in system conditions, relevant (physico)chemical characteristics were monitored. An increase in total microbial population was observed in surface water samples in the presence of both aldicarb and simazine. No increase was observed when MCPA was added, which was probably cometabolized. Large phosphorus concentrations not only favored bacterial growth, but also increased the residence time of dissolved Mn which under certain conditions promoted biotransformation. Furthermore, PO4 enrichment decreases aldicarb's aerobic metabolites' concentrations. Simazine was persistent over a period of at least 80 days, except for a short period coinciding with the nitrification period in which NH dissipates and NO2 and NO are formed. Selective bacterial growth was observed on simazine's transformation product DES. Relationships of Mg/Mn concentrations to MCPA transformation rates, and of PO4/PT concentrations to aldicarb transformation rates, are presented. These relationships are assessed as environmental indicators for potential biotransformation, but only under conditions warranting development and growth of a degrading population over a prolonged period. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 329–338, 1999

Interdependence of ammonia volatilization and nitrification in arid soils

The effect of applied-N (urea) on interdependence of ammonia volatilization and nitrification was studied in twelve arid soils varying mainly in soil texture and CaCO3. Ammonia volatilization from applied urea was observed only above a threshold N concentration in soil (Vi). Values of Vi ranged from 50 in sandy soils to 250 μg N g-1 in loamy and clay loam soils. Soils with higher CaCO3 showed lower values of Vi. Concentration of applied-N in soils, in relation to Vi determined its transformation pathway(s). Below Vi, all of the applied-N was nitrified in all soils with a delayed nitrification period ranging from 0 to 5 days. Above Vi, ammonia volatilization was first to start. This reduced NH4+ concentration in soil and nitrification started later after the delay period was over. Duration of delay period increased with applied-N, sand content and CaCo3. Often 80% or more of the total ammonia, volatilized during the delay period. NH4+ concentration in soil at which volatilization ended was generally higher than Vi. It was concluded that both ammonia volatilization and nitrification were interdependent only if concentration of applied N was more than Vi. Above Vi only one process predominated at a time as volatilization stopped soon after the start of nitrification even if NH4 concentration in soil was sufficient to sustain both processes.

Nitrification of Ammonium Nitrogen in Soils Treated with XDE‐474

AbstractRetardation of NH+4 nitrification constitutes one means to conserve fertilizers applied to soils. A new nitrification inhibitor, XDE‐474, has been developed by DowElanco Chemical Company (Indianapolis, IN) and needs to be evaluated. Laboratory studies evaluated the effect of nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] and XDE‐474 on nitrification rates in five Iowa soils varying markedly in organic C (OC), pH, and texture. A 10‐g sample of surface soil treated with 1 mL of solution containing 2 mg N as either NH4OH or (NH4)2SO4 and 4 µg a.i. g−1 soil of nitrapyrin or XDE‐474 was incubated at 20 ± 1°C for 0, 7, 15, 30, 45, and 60 d. First‐order equations were used to calculate the maximum nitrification rate (Kmax), duration of lag period (t′), period of maximum nitrification (Δt), and duration of lag plus maximum nitrification period (ts). Nitrification rates were significantly affected by N sources and inhibitors used. In the Okoboji soil (43.0 g kg−1 OC), nitrification of NH4OH was 19.5 mg kg−1 d−1 NO−3‐N in the control soil but reduced to 15.2 or 4.43 mg kg−1 d−1 NO−3‐N when nitrapyrin or XDE‐474 were added, respectively. Extension of the lag period due to the inhibitors varied from 0.73 d in the Okoboji soil to 18.8 d in the Storden soil (11.0 g kg−1 OC). Multiple regression equations expressing the dependence of Kmax on OC, pH, and clay showed that only OC and pH were significant in accounting for the variation in Kmax. The resulting three‐dimensional response surface indicated that XDE‐474 was less affected than nitrapyrin by changes in OC and pH.

Dynamics of population and biofilm structure in the biofilm airlift suspension reactor for carbon and nitrogen removal

The dynamics of population and biofilm structure of nitrifying and heterotrophic biomass in biofilms on small suspended particles in an airlift reactor were measured during shifts from purely nitrification to a heterotrophic medium and back to nitrification. Biofilms from a full scale reactor with predominantly heterotrophic activity were used as start material. In the first twenty days of the nitrification period ammonia was oxidized to nitrite. Hereafter the oxidation was mainly to nitrate. A conversion of nearly 5 kgN/(m3 d) was reached in fifty days. Following the change to heterotrophic medium the nitrifying biofilm served as carrier for the development of a heterotrophic biofilm layer. The nitrification capacity of the biofilms dropped to 1 kgN/(m3 d) due to oxygen diffusion limitation in the heterotrophic layer. After the switch back to nitrification the heterotrophic biofilm layer was sheared off very rapidly, while the nitrification activity increased very fast to the level at the end of the first nitrification period due to decreased diffusion limitation.