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PubMed2001

Simultaneous carbon and nitrogen removal from high strength domestic wastewater in an aerobic RBC biofilm.

High strength domestic wastewater discharges after no/partial treatment through sewage treatment plants or septic tank seepage field systems have resulted in a large build-up of groundwater nitrates in Rajasthan, India. The groundwater table is very deep and nitrate concentrations of 500-750 mg/l (113-169 as NO3(-)-N) are commonly found. A novel biofilm in a 3-stage lab-scale rotating biological contactor (RBC) was developed by the incorporation of a sulphur oxidising bacterium Thiosphaera pantotropha which exhibited high simultaneous removal of carbon and nitrogen in fully aerobic conditions. T. pantotropha has been shown to be capable of simultaneous heterotrophic nitrification and aerobic denitrification thereby helping the steps of carbon oxidation, nitrification and denitrification to be carried out concurrently. The first stage having T. pantotropha dominated biofilm showed high carbon and NH4(+)-N removal rates of 8.7-25.9 g COD/m2 d and 0.81-1.85 g N/m2 d for the corresponding loadings of 10.0-32.0 g COD/m2 d and 1.0-3.35 g N/m2 d. The ratio of carbon removed to nitrogen removed was close to 12.0. The nitrification rate increased from 0.81 to 1.8 g N/m2 d with the increasing nitrogen loading rates despite a high simultaneous organic loading rate. However, it fell to 1.53 g N/m2 d at a high load of 3.35 g N/m2 d and 32 g COD/m2 d showing a possible inhibition of the process. A simultaneous 44-63% removal of nitrogen was also achieved without any significant NO2(-)-N or NO3(-)-N build-up. The second and third stages, almost devoid of any organic carbon, acted only as autotrophic nitrification units, converting the NH4(+)-N from stage 1 to nitrite and nitrate. Such a system would not need a separate carbon oxidation step to increase nitrification rates and no external carbon source for denitrification. The alkalinity compensation during denitrification for that destroyed in nitrification may also result in a high economy.

Biofilms↗
PubMed2003

The inhibitory effects of heavy metals and organic compounds on the net maximum specific growth rate of the autotrophic biomass in activated sludge.

A respirometry technique can be applied as an effective method to determine the net maximum specific growth rate of autotrophic biomass under both normal conditions and when inhibition occurs. The net maximum specific growth rate of uninhibited autotrophic biomass, expressed as (mu(A)-b(A)), is approximately 0.8 per day [Proceeding of the International Congress on CHISA, Prague, 2002, p. 1]. Several heavy metals and organic compounds have inhibitory effects. Copper (Cu(2+)) has stronger inhibitory effects than zinc (Zn(2+)), and inhibits the nitrification process by 50% at 0.08 mg/l [(mu(A)-b(A)) = 0.4 per day], while the same concentration of Zn(2+) establishes 12% inhibition only [(mu(A)-b(A)) = 0.75 per day]. Inhibition with Cu(2+) starts at concentrations above 0.05 mg/l, while this is above 0.3mg/l for Zn(2+). The inhibition of the nitrification process is complete at 1.2mg/l for both Cu(2+) and Zn(2+). Among the selected organic compounds tested n the experiments, the degree of inhibition decreases as follow: chlorobenzene>trichloroethylene (TCE)>phenol>ethylbenzene. Chlorobenzene already inhibits the autotrophic biomass at 0.25 mg/l. The nitrification process is totally inhibited by adding 0.75 mg/l of chlorobenzene. TCE has a less inhibitory effect on the nitrification process and 50% inhibition is noticed at 0.75 mg/l TCE. The nitrification process is totally inhibited at 1mg/l TCE. Phenol inhibits the nitrification for 50% at 3 mg/l. The inhibitory effect of phenol is almost constant in the range 4-10 mg/l and complete inhibition is reached at 50 mg/l. The inhibitory effect of ethylbenzene is 50% at 8 mg/l and the autotrophic biomass is totally inhibited at 50 mg/l. Experimental findings are compared with literature data, which generally and significantly overestimate the inhibition threshold concentrations.

Bacteria↗
PubMed2002

Use of polymer mats in series for sequential reactive barrier remediation of ammonium-contaminated groundwater: laboratory column evaluation.

Large-scale column experiments were undertaken to evaluate the potential of in situ polymer mats (installed in series) to be used as permeable reactive barriers for delivery of oxidants and reductants to induce sequential bioremediation of ammonium-contaminated groundwater (approximately 120mg L(-1) NH4+-N), without bioaugmentation. The strategy was for the first group of polymer mats to deliver oxygen to induce bacterial nitrification of the ammonium to nitrite/ nitrate as the groundwater moved past and for the second group of polymer mats to deliver hydrogen or ethanol, to induce bacterial denitrification of the nitrite/nitrate to produce nitrogen gas. Once purging of the first polymer mat commenced, ammonium concentrations decreased downgradient from the polymer mats. Nitrification rates increased and stabilized over the 6-month experiment, with stable nitrification half-lives in the range 0.07-0.25 days. Nitrification most likely occurred in a biologically active zone at the polymer wall/aqueous interface. With hydrogen delivery via the polymer mats, a denitrification half-life (nitrate plus nitrite removal) of 3.5 days was induced. Denitrification rates were significantly enhanced when ethanol was delivered via a polymer mat, with denitrification half-lives in the range of 0.12-0.34 days. Nitrification/ denitrification rates were maintained for groundwater flow rates up to 300 m yr(-1), suggesting oxygen and ethanol delivery rates via the polymer mats were sufficient not to limit nitrification or denitrification. In soil columns, the polymer mat delivery system provided an effective and reliable technique for delivery of oxygen and hydrogen or ethanol for sequential nitrification/denitrification of ammonium-contaminated groundwater. Scale-up of this concept to a field pilot-scale is currently underway.

Biodegradation, Environmental↗
PubMed2001

The source and abatement of nitrous oxide emissions produced from the aerobic treatment of pig slurry to remove surplus nitrogen.

The removal of surplus nitrogen from pig slurry can be necessary in order to avoid pollution such as nitrate leaching. However, the treatment itself can create significant pollution; up to 20% of the removed slurry nitrogen has been shown to be released as nitrous oxide (N2O), which contributes to global warming and the breakdown of the ozone in the stratosphere. Avoiding such emission requires conditions that encourage the complete conversion of the nitrogen to the environmentally safe di-nitrogen gas (N2), and a clear understanding of the underlying biochemistry; for example, whether the nitrous oxide is the bi-product of incomplete nitrification (chemical oxidation) or denitrification (chemical reduction). The stable isotope of nitrogen ( N) was used in this investigation as a label. Results indicated a new route for substantial release of N2O: via nitrification (rather than denitrification), caused by a combination of high aeration levels and the presence of nitrification products. Sequential aeration, which leads to a cycling between nitrification and complete denitrification, was proposed as an abatement in view of this new mechanism. This process achieved 89% removal of ammoniacal nitrogen in laboratory scale treatment, with 94% of the nitrogen removed in the form of N2. These findings suggest that the possibility of N2O emissions from nitrification be considered in the design of treatment schemes. Increased aeration would be the intuitive response to incomplete nitrification. However, the results of this study suggested that although this response can increase nitrogen removal, this may be as N2O rather than N2.

Air Pollution↗
PubMedDate not supplied

Particulates, not plants, dominate nitrogen processing in a septage-treating aerated pond system.

In pond and wetland systems for wastewater treatment, plants are often thought to enhance the removal of ammonium and nitrogen through the activities of root-associated bacteria. In this study, we examined the role of plant roots in an aerated pond system with floating plants designed to treat high-strength septage wastewater. We performed both laboratory and full-scale experiments to test the effect of different plant root to septage ratios on nitrification and denitrification, and measured the abundances of nitrifying bacteria associated with roots and septage particulates. Root-associated nitrifying bacteria did not play a significant role in ammonium and total nitrogen removal. Investigations of nitrifier populations showed that only 10% were associated with water hyacinth [Eichhornia crassipes (Mart.) Solms] roots (at standard facility plant densities equivalent to 2.2 wet g roots L(-1) septage); instead, nitrifiers were found almost entirely (90%) associated with suspended septage particulates. The role of root-associated nitrifiers in nitrification was examined in laboratory batch experiments where high plant root concentrations (7.4 wet g L(-1), representing a 38% net increase in total nitrifier populations over plant-free controls) yielded a corresponding increase (55%) in the non-substrate-limited nitrification rate (V(max)). However, within the full-scale septage-treating pond system, nitrification and denitrification rates remained unchanged when plant root concentrations were increased to 7.1 g roots L(-1) (achieved by increasing the surface area available for plants while maintaining the same tank volume). Under normal facility operating conditions, nitrification was limited by ammonium concentration, not nitrifier availability. Maximizing plant root concentrations was found to be an inefficient mechanism for increasing nitrification in organic particulate-rich wastewaters such as septage.

Adsorption↗
PubMed2002

Comparison of combined and separated biological aerated filter (BAF) performance for pre-denitrification/nitrification of municipal wastewater.

The performance of two systems of semi-industrial up-flow biological aerated filters (BAF) with pre-denitrification followed by nitrification was studied and compared under various operating and loading conditions. The first system consisted of two separate reactors for the denitrification and the nitrification step, whereas in the second system the aerobic nitrification zone was packed on top of the anoxic denitrification zone in one reactor. The second system potentially offers substantial savings in investment costs and space requirements for a large scale treatment plant. Regarding the elimination of carbonaceous pollution and denitrification the systems did not show significant differences. However, nitrification in the combined system suffered from the mixing of different biocenosis by daily backwashing and was reduced to 50-70% of the separated system's performance. Factors such as oxygen concentration, raw water composition and loading rates affected both systems' nitrification rates in similar ways. Since it is impossible to optimise the nitrification and denitrification processes separately, the combined system should only be considered for large scale applications if space is very scarce and if a stable raw water composition can be expected. If strict limit values for nitrate have to be met in the effluent, a combination of pre- and post-denitrification is advantageous and advisable.

Bacteria, Aerobic↗
PubMed2004

Full-scale application of the BABE technology.

Bio-augmentation can be used to obtain nitrification in activated sludge processes that operate at sub-optimal solid retention times. A side-stream process, the so-called BABE process that incorporates N-removal and augmentation of nitrifiers has been developed. The principle is to implement a nitrification reactor in the sludge return line, the so-called BABE reactor. This reactor can be fed with an internal N-rich flow (e.g. effluent from the sludge treatment). Hence the nitrification capacity of an activated sludge process can be augmented by the addition of nitrifiers cultivated in the BABE reactor. A full-scale test of the BABE technology has been at the treatment plant Garmerwolde in Groningen, the Netherlands. The set-up allowed comparing between three different lines: with the BABE reactor, without rejectwater and with untreated rejectwater. Based on this, the two important tasks (N-removal and inoculation) performed by the BABE reactor could be quantified. The results of the practical work in Garmerwolde showed a higher nitrification rate in the water line where the BABE reactor was implemented and also lower effluent ammonia. The experiments on a practical scale have demonstrated univocally the effective and stable operation of the BABE technology. In addition, sludge samples in different streams as well as from the BABE reactor were analysed with FISH technique. The FISH results illustrated the augmentation effect of the BABE reactor on the stream with the BABE reactor. A mathematical model, based on ASM1 model and implemented in AQUASIM was developed and used for simulating the treatment plant of Garmerwolde. The simulation results indicated that better effect of the BABE technology is expected at lower ambient temperatures and smaller volume of the BABE reactor. The BABE reactor could also allow for providing more space for de-nitrification in the main water line when nitrification is efficient enough.

Ammonia↗
PubMed2004

Performance evaluation of hybrid and conventional sequencing batch reactor and continuous processes.

Bench-scale systems, using conventional and compact hybrid activated sludge configurations, were set up to evaluate the systems' nitrification-denitrification performance, operating sludge age/MLSS concentration and sludge settleability at a Hong Kong municipal STW. Configurations tested were the continuous clarifier modified Ludzack Ettinger (MLE) and the sequencing batch reactor (SBR) with and without hybrid suspended biofilm carriers. Results demonstrated that the hybrid SBR and MLE systems consistently achieved close to complete nitrification (effluent NH4-N = 2.4 and 6.9 mg/L) and 75% and 67% removal of nitrogen (N) (effluent NO3-N < 10 mg/L) with an overall hydraulic retention time of only 7.5 hours, operating sludge age as short as 5.2 days, and mixed liquor suspended solids concentration of approximately 1,300 mg/L with a sludge volume index of 109 and 229 mL/g, respectively. The most sensitive and slowest growing nitrifiers attached to the hybrid biofilm carriers. This allowed the hybrid processes to be operated at a sludge age shorter than the critical nitrifying sludge age while still retaining near complete nitrification. In contrast, to achieve complete nitrification, the conventional MLE system needed to be operated at 1.5 to 2.5 times the critical sludge age. These results indicate that the hybrid MLE configuration is a suitable process for use in upgrading existing conventional works for N removal and for increasing hydraulic capacity of existing N removal works, without major civil works modifications, in Hong Kong. For new works, consideration might be given to the use of the hybrid SBR, which shows a more stable N removal performance than the MLE process due to its inherent in-basin equalization capacity and better reaction conditions for nitrification in terms of higher initial NH4-N level. It was also observed that the conventional SBR produced better nitrification performance than the hybrid MLE process tested. Design parameters and operating conditions of the hybrid systems should be subjected to further full-scale trial for higher hydraulic capacity and N removal performance.

Ammonia↗
PubMed2006

[Relationship between the nitrogen removal and oxygen demand in constructed wetlands].

A simplified model of sequential N transformations and sink was applied to investigate the relationship between the nitrogen removal and oxygen demand to verify the validity of full nitrification-denitrification mechanism in a newly-built multi-stages constructed wetlands. Average net rates of N mineralization ranged from 0.01 to 0.28 g x (m2 x d)(-1), nitrification from 0.50 to 1.54 g x (m2 x d)(-1), denitrification from 0.41 to 1.13 g x (m2 x d)(-1)(3.4% approximately 35.4% of measured N removal in different stage) and plant assimilation from 0.07 to 0.26 g x (m2 x d)(-1) in the five tanks. Nitrification and denitrification occurred concurrently with BOD removal, even in the first stage receiving the higher-strength wastewater. Surprisingly, net areal nitrification rates, was correlated with BOD removal rates positively. Nitrification rates were also correlated linearly with average NH4+-N concentrations in the cascade tanks. The nitrogenous oxygen demand (NOD) required to support full nitrification of ammonia and mineralized Org-N in the wetland was in the upper range of that expected to be able to be supplied through surface and plant-mediated oxygen transfer. Some potential alternative nitrogen removal pathways with reduced overall oxygen requirements that have relevance to constructed wetlands were discussed.

Environmental Monitoring↗
PubMed2001

Simultaneous organic and nitrogen removal from municipal landfill leachate using an anaerobic-aerobic system.

An anaerobic-aerobic system including simultaneous methanogenesis and denitrification was introduced to treat organic and nitrogen compounds in immature leachate from a landfill site. Denitrification and methanogenesis were successfully carried out in the anaerobic reactor while the organic removal and nitrification of NH4+,-N were carried out in the aerobic reactor when rich organic substrate was supplied with appropriate hydraulic retention time. The maximum organic removal rate was 15.2 kg COD/m3 d in the anaerobic reactor while the maximum NH4+-N removal rate and maximum nitrification rate were 0.84kg NH4+-N/m3/d and 0.50kg NO3--N/m3/d, respectively, in the aerobic reactor. The pH range for proper nitrification was 6-8.8 in the aerobic reactor. The organic compounds inhibited nitrification so that the organic removal in the anaerobic reactor could enhance the nitrification rate in the following aerobic reactor. The gas production rate was 0.33 m3/kg COD and the biogas compositions of CH4, CO2, and N2 were kept relatively constant, 66-75, 22-32, and 2-3%, respectively.

Aerobiosis↗
PubMed2002

The effect of CO2 concentration on a nitrifying chalk reactor.

The effect of CO2 concentration on nitrification rate was studied in a fluidized bed reactor using chalk (solid calcium carbonate) as the biomass carrier and buffering agent. Using one chalk type and uniform particle size, carbon dioxide was found to limit the nitrification rate in the reactor at concentrations up to 0.3 mmol l(-1). At this concentration the nitrification rate was about 2.5-2.7g NH4+-Nl reactor(-1) d(-1). The pH established in the reactor varied between 4.5 and 5.5, remarkably with lower pH obtained remarked at higher nitrification rates. Kinetic parameters for nitrification rate with CO2 as the rate limiting substrate were determined: a Michaelis-Menten constant, Km, of 0.013 mmol l(-1) CO2 and a maximum ammonium oxidation rate of 2.33g NH4+-Nl reactor(-1) d(-1).

Biomass↗
PubMed2004

Optimizing settling conditions for treatment of liquid hog manure.

Sedimentation is a widely used separation method for treating agricultural waste. There are several chemical and biological characteristics, which can affect the settling behavior and liquid waste. The optimization of cation balances and potential for nitrification are among these processes. In addition to sedimentation, it can also affect the dewaterability of the samples. Liquid hog manure was used during the laboratory based experiments to investigate the effects of Ca2+ and Mg2+ ions and nitrification inhibition on the overall settling and dewatering characteristics. The results indicated that settling and dewatering characteristics improved during the course of the experiments. However, the improvement in settling and dewatering characteristics was inconsistent and not statistically significant. Cation addition in aerated reactor increased the highest settling velocity (94%). The improvement in dewaterability, as quantified by capillary suction time, was also not consistent. The greatest filterability observed in the supernatant was a capillary suction time of 40 s for a M:D ratio of 2:1. Initial NH 4 + concentration was more important than the nitrification inhibitor, as the presence of nitrification inhibitor increased the nitrification rate by over 300% because of the high initial NH 4 + concentration and low volatile suspended solid. The results from these experiments provide the basis for further field evaluation of cation optimization.

Agriculture↗
PubMed2006

Biodegradability and toxicity of pharmaceuticals in biological wastewater treatment plants.

In this experimental study both biological treatability of pharmaceuticals and their potential toxic effect in biological processes were evaluated. The pharmaceuticals were selected among those that are present at higher concentration in the Italian wastewater treatment plant effluents and widely used as antiulcer (ranitidine), beta-blocker (atenolol) and antibiotic (lincomycin). The present paper is the continuation of a work already presented,[1] which used a synthetic wastewater fed to laboratory scale SBR (Sequencing Batch Reactor) operated with different sludge ages (8 and 14 days), different biochemical conditions (aerobic or anoxic-aerobic mode) and several influent drug concentrations (2, 3 and 5 mg/L). In this case a real municipal wastewater was used as influent to the SBR. In parallel, batch tests were conducted to determine the removal kinetics of drugs and nitrogen. Toxicity tests using a titrimetric biosensor to verify possible inhibition on microorganisms were also performed. Finally, the possible adsorption of the pharmaceuticals on activated sludge was evaluated. The drugs under investigation showed different behaviours in terms of both biodegradability and toxicity effect on nitrifiers. Ranitidine showed generally low removal efficiencies (17-26%) and a chronic inhibition on nitrification. Atenolol showed generally higher removal efficiencies than ranitidine, even if the fairly good efficiency obtained in the previous experimentation with synthetic wastewater (up to 90%) was not attained with real wastewater (36%). No inhibition on nitrification was observed on both acclimated and non acclimated microorganisms with a high nitrification activity, whilst it was present with activated sludge characterised by a lower nitrification activity. Consistently with his pharmaceutical properties, lincomycin showed significant inhibition on nitrification activity.

Atenolol↗
PubMed1993

A comparison of NO and N2O production by the autotrophic nitrifier Nitrosomonas europaea and the heterotrophic nitrifier Alcaligenes faecalis.

Soil microorganisms are important sources of the nitrogen trace gases NO and N2O for the atmosphere. Present evidence suggests that autotrophic nitrifiers such as Nitrosomonas europaea are the primary producers of NO and N2O in aerobic soils, whereas denitrifiers such as Pseudomonas spp. or Alcaligenes spp. are responsible for most of the NO and N2O emissions from anaerobic soils. It has been shown that Alcaligenes faecalis, a bacterium common in both soil and water, is capable of concomitant heterotrophic nitrification and denitrification. This study was undertaken to determine whether heterotrophic nitrification might be as important a source of NO and N2O as autotrophic nitrification. We compared the responses of N. europaea and A. faecalis to changes in partial O2 pressure (pO2) and to the presence of typical nitrification inhibitors. Maximal production of NO and N2O occurred at low pO2 values in cultures of both N. europaea (pO2, 0.3 kPa) and A. faecalis (pO2, 2 to 4 kPa). With N. europaea most of the NH4+ oxidized was converted to NO2-, with NO and N2O accounting for 2.6 and 1% of the end product, respectively. With A. faecalis maximal production of NO occurred at a pO2 of 2 kPa, and maximal production of N2O occurred at a pO2 of 4 kPa. At these low pO2 values there was net nitrite consumption. Aerobically, A. faecalis produced approximately the same amount of NO but 10-fold more N2O per cell than N. europaea did. Typical nitrification inhibitors were far less effective for reducing emissions of NO and N2O by A. faecalis than for reducing emissions of NO and N2O by N. europaea.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobiosis↗
PubMed1999

Use of molecular and isotopic techniques to monitor the response of autotrophic ammonia-oxidizing populations of the beta subdivision of the class proteobacteria in arable soils to nitrogen fertilizer.

This study examined the effects of NH(4)NO(3) fertilizer on the size and activity of nitrifying, autotrophic, ammonia-oxidizing populations of the beta subdivision of the class Proteobacteria in arable soils. Plots under different long-term fertilizer regimes were sampled before and after NH(4)NO(3) additions, and the rates of nitrification were determined by (15)N isotopic pool dilution assays. Ammonia-oxidizing populations in the plots were quantified by competitive PCR assays based on the amoA and ribosomal 16S genes. Prior to fertilizer addition, ammonium concentrations and nitrification rates in the plots were comparatively low; ammonia-oxidizing populations were present at 10(4) to 10(5) gene copies g of soil(-1). Three days after the application of fertilizer, nitrification rates had risen considerably but the size of the ammonia-oxidizing population was unchanged. Six weeks after fertilizer treatment, ammonium concentrations and nitrification rates had fallen while the ammonia-oxidizing populations in plots receiving fertilizer had increased. The rapidity of the rise in nitrification rates observed after 3 days suggests that it results from phenotypic changes in the ammonia-oxidizing bacterial population. Associated increases in population sizes were only observed after 6 weeks and did not correlate directly with nitrifying activity. Phylogenetic analyses of PCR products from one of the plots revealed a population dominated by Nitrosospira-type organisms, similar to those prevalent in other soils.

Betaproteobacteria↗
PubMed2000

Kinetic study of addition of volatile organic compounds to a nitrifying sludge.

The effects of different concentrations of several volatile organic compounds (VOC) such as ethanol, acetate, propionate, and butyrate ranging from 0 to 2000 mg/L as well as a mixture of volatile fatty acids (MVFA) at a 4:1:1 (acetate:propionate:butyrate) ratio on the nitrification rate in batch cultures were studied. The results showed that ethanol and acetate were consumed in a mixotrophic way by the nitrifying sludge. At a concentration of 500 mg/L, the nitrification rate of inhibition was different for each compound in which propionate and butyrate were the most inhibitory. At 2000 mg/L the inhibition was 80% with ethanol and 100% with acetate, propionate, and butyrate. With similar concentrations of MVFA, the inhibition was also similar to that in acetate. The effect of the addition of pulses of MVFA at a ratio of 4:1:1 during 14 h on the performance of the continuous nitrifying process with a hydraulic retention time of 3 d was also studied. No inhibition of the nitrification process was observed with pulses of 750-3000 mg of MVFA/L in the input of the reactor. The results in batch cultures suggest that the different degrees of inhibition of the nitrification process were related to the type of organic matter added. The noninhibitory effect of the organic matter in the continuous cultures on the nitrification efficiency of the nitrifying sludge might be related to the feeding pattern.

Acetates↗
PubMed2006

Frequent fire alters nitrogen transformations in ponderosa pine stands of the inland northwest.

Recurrent, low-severity fire in ponderosa pine (Pinus ponderosa)/interior Douglas-fir (Pseudotsuga menziesii var. glauca) forests is thought to have directly influenced nitrogen (N) cycling and availability. However, no studies to date have investigated the influence of natural fire intervals on soil processes in undisturbed forests, thereby limiting our ability to understand ecological processes and successional dynamics in this important ecosystem of the Rocky Mountain West. Here, we tested the standing hypothesis that recurrent fire in ponderosa pine/Douglas-fir forests of the Inland Northwest decreases total soil N, but increases N turnover and nutrient availability. We compared soils in stands unburned over the past 69-130 years vs. stands exposed to two or more fires over the last 130 years at seven distinct locations in two wilderness areas. Mineral soil samples were collected from each of the seven sites in June and July of 2003 and analyzed for pH, total C and N, potentially mineralizable N (PMN), and extractable NH4+, NO3-, PO4(-3), Ca+2, Mg+2, and K+. Nitrogen transformations were assessed at five sites by installing ionic resin capsules in the mineral soil in August of 2003 and by conducting laboratory assays of nitrification potential and net nitrification in aerobic incubations. Total N and PMN decreased in stands subjected to multiple fires. This loss of total N and labile N was not reflected in concentrations of extractable NH4+ and NO3-. Rather, multiple fires caused an increase in NO3 sorbed on ionic resins, nitrification potential, and net nitrification in spite of the burned stands not having been exposed to fire for at least 12-17 years. Charcoal collected from a recent fire site and added to unburned soils increased nitrification potential, suggesting that the decrease of charcoal in the absence of fire may play an important role in N transformations in fire-dependent ecosystems in the long term. Interestingly, we found no consistent effect of fire frequency on extractable P or alkaline metal concentrations. Our results corroborate the largely untested hypothesis that frequent fire in ponderosa pine forests increases inorganic N availability in the long term and emphasize the need to study natural, unmanaged sites in far greater detail.

Ecosystem↗
PubMed2005

Use of microelectrodes to investigate the effects of 2-chlorophenol on microbial activities in biofilms.

In order to assess the applicability of using microelectrodes as a tool for inhibition tests, temporal and spatial inhibitory effects of 2-chlorophenol (2-CP) on O(2) respiration and nitrification activities in municipal wastewater biofilms were investigated using microelectrodes for O(2) and NH(4)(+). The time-course microelectrode measurements demonstrated that 2-CP inhibited O(2) respiration and nitrification activities within 6-18 min. The microbial activities were inhibited only in the upper 400 microm of the biofilms by 2-CP, and the bacteria present in the deeper parts of the biofilms were still active, probably due to limited penetration of 2-CP. These results could reasonably explain the difference in inhibitory ratios of the O(2) respiration and nitrification activities in the biofilms. O(2) respiration activity was incompletely inhibited, which was attributed to the presence of O(2) respiration activities in the deeper parts of the biofilm. In contrast, nitrification activity was significantly inhibited because ammonia-oxidizing bacteria were present in the upper parts of the biofilm. These results indicate that the microelectrodes with a very quick response time and a high spatial resolution are useful tools to study temporal and spatial inhibitory effects of inhibitors on in situ microbial activities in biofilms.

Bacterial Physiological Phenomena↗