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PubMed2006

Nitrogen removal in a small constructed wetland: an isotope mass balance approach.

The nitrogen (N) removal potential of constructed wetlands is increasingly used to lower the N load from agricultural nonpoint sources to inland and coastal waters. To determine the removal efficiency and key factors limiting wetland N removal, N fluxes were studied in a small constructed wetland in Central Switzerland. With an isotope mass balance approach integrating the natural isotope signature of nitrate (NO3-, ammonium (NH4+), and particulate nitrogen (PN), the N transformations such as assimilation, mineralization, nitrification, and denitrification were quantified. On average, the wetland removed 45 g m(-2) yr(-1) N during the studied 2.5 years, corresponding to a removal efficiency of 27%. Denitrification contributed 94% to the N removal, while only 6% of the removed N accumulated in the sediments. Denitrification was most efficient during periods with an oxic water column overlying anoxic sediments, as NH4+ released during mineralization of sediment organic matter was completely nitrified and subsequently denitrified at the sediment-water interface. During water column anoxia, NH4+ accumulated in the water and fueled assimilation by duckweed and internal recycling. The NO3-N isotope signature in the wetland mainly reflected the mineralization of sediment organic matter and subsequent nitrification, while denitrification at the sediment-water interface produced no fractionation.

Ammonia↗
PubMed1997

Emerging principles of inorganic nitrogen metabolism in Paracoccus denitrificans and related bacteria.

The taxonomy of Paracoccus denitrificans and related bacteria is discussed. Evidence is given which shows that the physiological differences between P. denitrificans and Thiosphaera pantotropha are less fundamental than previously thought. A proposal to consider a species P. pantotropha is mentioned. The properties of the denitrifying enzymes and the genes involved in their formation in P. denitrificans is discussed. The synthesis of the membrane-bound-nitrate reductase is regulated by FNR, that of the nitrite- and nitric oxide reductase by NNR. Evidence is given that FNR acts as a redox sensor rather than an oxygen sensor. The occurrence of aerobic denitrification and coupled heterotrophic nitrification-denitrification in the original strain of Thiosphaera pantotropha are explained by a limiting respiratory activity which activates FNR. Aerobic denitrification leads to a lower growth yield and an increase in mumax in batch culture when a limiting respiratory activity is assumed and when excess substrate is present. Coupled heterotrophic nitrification-denitrification gives a smaller increase in mumax and a more drastic reduction in yield. Both processes are thus advantageous to the organism. In a chemostat with limiting substrate these processes are disadvantageous. T. pantotropha has lost the ability for aerobic denitrification during extended cultivation. Possibly the substrate concentration was limiting during extended cultivation giving a selective advantage to variants which have lost these properties. The calculations predict that P. denitrificans should be able to grow chemolithotrophically with hydroxylamine.

Aerobiosis↗
PubMed2000

Significance of gaseous NO for ammonia oxidation by Nitrosomonas eutropha.

Nitrification by the obligately lithoautotrophic ammonia oxidizer Nitrosomonas eutropha was significantly inhibited when nitric oxide was removed from the culture medium by means of intensive aeration and turbulence. Nearly complete recovery of ammonia oxidation could be achieved by adding 100 ppm NO to the supplied air. Inhibition of ammonia oxidation occurred also upon addition of the NO binding agent 2,3-Dimercapto-1-propane-sulfonic acid (DMPS). Recovery of ammonia oxidation occurred within 3 h in the presence of 100 ppm NO and within 76 h in the absence of externally added NO. In co-cultures of N. eutropha and the NO detoxifying bacterium Pseudomonas PS88, hardly any nitrification was detectable and release of NO was extremely low when the heterotroph was provided with an organic substrate. When cells of Pseudomonas PS88 were added to a mixotrophically nitrifying culture of N. eutropha the release of NO decreased drastically upon the addition and ammonia oxidation ceased. These results confirm for the first time the significance of NO in the course of ammonia oxidation by N. eutropha.

Ammonia↗
PubMed2002

Investigation of organic nitrogen and carbon removal in the aerobic digestion of various sludges.

Nitrification and carbon removal are investigated in aerobic batch digestion of various sludges. The experiments are carried out with activated sludge (Test 1) and with a mixture of activated and primary settling sludge (Test 2). The nitrification rate was monitored, measuring the NO2- concentration. At the 3rd day of the digestion 40.7 mgNO2-N/l and 3.89 mgNO2-N/l were found in Tests 1 and 2 respectively. In a digestion process, the degradation of biomass indicates the beginning of the endogenous phase. Our measure for biomass content of the sludge was protein analysis. In Test 1, the first day values of 50.93 mgTOC/ g(dry) matter/day and 138.53 mg(protein)-C/g(dry) matter/day for specific TOC and protein-C removal rates showed, that the digestion process began in the endogenous phase. For Test 2, since the endogenous phase began after removal of raw organic matter in primary settling sludge, specific TOC and protein-C removal rates were observed to be 60.12 mgTOC/g(dry) matter/day and 26.72 mg(protein-C/g(dry)matter/day, respectively.

Agriculture↗
PubMed2000

Ecological study of a bioaugmentation failure.

A nitrifying sequencing batch reactor was inoculated twice with the aerobic denitrifying bacterium Microvirgula aerodenitrificans and fed with acetate. No improvement was obtained on nitrogen removal. The second more massive inoculation was even followed by a nitrification breakdown, while at the same time, nitrification remained stable in a second reactor operated under the same conditions without bioaugmentation. Fluorescent in situ hybridization with rRNA-targeted probes revealed that the added bacteria almost disappeared from the reactor within 2 days, and that digestive vacuoles of protozoa gave strong hybridization signals with the M. aerodenitrificans-specific probe. An overgrowth of protozoa, coincident with the disappearance of free-living bacteria, was monitored by radioactive dot-blot hybridization only in the bioaugmented reactor. Population dynamics were analysed with a newly developed in situ quantification procedure of the probe-targeted bacteria. The nitrifying groups of bacteria decreased in a similar way in the bioaugmented and non-bioaugmented reactors. Other bacterial groups evolved differently. The involvement of different ecological parameters are discussed separately for each reactor. These results underline the importance of predator-prey interaction and illustrate the undesirable effects of massive bioaugmentation.

Animals↗
PubMed2003

Activity and population structure of nitrifying bacteria in an activated-sludge reactor containing polymer beads.

Photo-crosslinked polymer beads were introduced into a laboratory activated-sludge unit containing municipal sewage sludge and the effect on nitrifying capacity was examined. The ammonia load started at a nitrogen-loading rate of 0.02 kg m(-3) day(-1) and was increased stepwise. It was found that the bead-containing unit could almost completely oxidize ammonia (over 95%) up to a nitrogen-loading rate of 0.216 kg m(-3) day(-1), whereas the maximum loading rate of the control unit (without polymer beads) was 0.096 kg m(-3) day(-1). The nitrifying potential of suspended and bead-associated organisms in the bead-containing unit was measured under different loading conditions. It was found that the bead-associated organisms exhibited high specific activities under high loading conditions and that the contribution of the bead-associated organisms to nitrification was greater than that of the suspended solids under these conditions. The bacterial population dynamics in the suspended solids and bead-associated organisms were analysed by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments and by fluorescence in situ hybridization with group-specific probes. Among the known nitrifying organisms, ammonia-oxidizing beta-proteobacteria and Nitrospira-related organisms were detected by these approaches. A comparison of the activity dynamics and population dynamics, however, suggested a possibility that other organisms may also have been involved in the nitrification process under high loading conditions.

Ammonia↗
PubMed2003

Effects of temperature and fertilizer on activity and community structure of soil ammonia oxidizers.

We investigated the effect of temperature on the activity of soil ammonia oxidizers caused by changes in the availability of ammonium and in the microbial community structure. Both short (5 days) and long (6.5, 16 and 20 weeks) incubation of an agricultural soil resulted in a decrease in ammonium concentration that was more pronounced at temperatures between 10 and 25 degrees C than at either 4 degrees C or 30-37 degrees C. Consistently, potential nitrification was higher between 10 and 25 degrees C than at either 4 degrees C or 37 degrees C. However, as long as ammonium was not limiting, release rates of N2O increased monotonously between 4 and 37 degrees C after short-term temperature adaptation, with nitrification accounting for about 35-50% of the N2O production between 4 and 25 degrees C. In order to see whether temperature may also affect the community structure of ammonia oxidizers, we studied moist soil during long incubation at low and high concentrations of commercial fertilizer. The soil was also incubated in buffered (pH 7) slurry amended with urea. Communities of ammonia oxidizers were assayed by denaturant gradient gel electrophoresis (DGGE) of the amoA gene coding for the alpha subunit of ammonia monooxygenase. We found that a polymerase chain reaction (PCR) system using a non-degenerated reverse primer (amoAR1) gave the best results. Community shifts occurred in all soil treatments after 16 weeks of incubation. The community shifts were obviously influenced by the different fertilizer treatments, indicating that ammonium was a selective factor for different ammonia oxidizer populations. Temperature was also a selective factor, in particular as community shifts were also observed in the soil slurries, in which ammonium concentrations and pH were better controlled. Cloning and sequencing of selected DGGE bands indicated that amoA sequences belonging to Nitrosospira cluster 1 were dominant at low temperatures (4-10 degrees C), but were absent after long incubation at low fertilizer treatment. Sequences of Nitrosospira cluster 9 could only be detected at low ammonium concentrations, whereas those of Nitrosospira cluster 3 were found at most ammonium concentrations and temperatures, although individual clones of this cluster exhibited trends with temperature. Obviously, ammonia oxidizers are able to adapt to soil conditions by changes in the community structure if sufficient time (several weeks) is available.

Ammonia↗
PubMed2003

In situ distribution and activity of nitrifying bacteria in freshwater sediment.

Nitrification was investigated in a model freshwater sediment by the combined use of microsensors and fluorescence in situ hybridization with rRNA-targeted oligonucleotide probes. In situ nitrification activity was restricted mainly to the upper 2 mm of the sediment and coincided with the maximum abundance of nitrifying bacteria, i.e. 1.5 x 107 cells cm-3 for ammonia-oxidizing Beta-proteobacteria (AOB) and 8.6 x 107 cells cm-3 for Nitrospira-like nitrite-oxidizing bacteria (NOB). Cell numbers of AOB decreased more rapidly with depth than numbers of NOB. For the first time, Nitrospira-like bacteria could be quantified and correlated with in situ nitrite oxidation rates in a sediment. Estimated cell-specific nitrite oxidation rates were 1.2-2.7 fmol NO2- cell-1 h-1.

Bacteria↗
PubMed2003

Comparison of suspended growth and hybrid systems for nitrogen removal in ammonium bisulfite pulp mill wastewater.

A series of bench-scale nitrification/denitrification tests were carried out with both suspended growth and hybrid bioreactors. The hybrid reactor was filled with plastic (polyethylene) media to evaluate the effects of biofilm. Two types of reactor configurations were tested; 4-compartment and 6-compartment modes. The experiments were initiated with a half-strength pulp and paper wastewater and its strength increased stepwise to the raw wastewater. Solid retention time was fixed at 10 days after a start-up period while hydraulic retention time was extensively varied from 3.5 to 0.5 days. The results from each type of reactor were compared in terms of nitrification/denitrification efficiency and stability. Experimental results demonstrate that the hybrid system showed greater stability in nitrification and higher denitrification efficiency than the suspended growth system. In the hybrid system, attached volatile solids formed 61- 72% of total volatile solids in the reactor and the amount of attached volatile solids insignificantly varied with the organic loading rate (0.37 - 2.76 kg COD M(-3) d(-1)) after initial biomass attachment. Under the conditions tested (0.1 - 2.8 kg COD m(-3) d(-1)), organic loading rate insignificantly influenced the nitrification. Better performance was obtained in denitrification when the anoxic zone was better isolated from the aerobic compartments (6-compartment mode). Overall, the hybrid system with fixed-film growth had better resistance to upset caused by transients such as changes in influent composition or hydraulic retention time.

Biofilms↗
PubMed2003

Performance evaluation of leachate treatment system using innovative sulfur circulation method.

A pilot-scale experimental study was carried out to evaluate the performance of an innovative method for early stabilization of landfill. This method employs sequential processes of: leachate collection; nitrification through aeration; sulfate addition in effluent tank; and leachate injection back to the landfill. This study focused on: 1) decomposition of recalcitrant organic matters, 2) the characteristics of denitrification, 3) sulfide oxidation for sulfate recovery, and 4) nitrification by aerating discharged leachate. It was found that, when sulfate (SO4(2-)) added leachate was introduced inside the landfill, sulfate-reducing bacteria decomposed recalcitrant organic matters like lignocellulose by using SO4(2-) as an electron acceptor and simultaneously sulfur-oxidizing bacteria denitrified the leachate using sulfides (H2S, HS-, S2-) as electron donors. These two types of bacteria existed not competitively but symbiotically on substrate utilization. Sulfate-reducing bacteria produced S2- while sulfur-oxidizing bacteria oxidized S2- to SO4(2-). During aeration, the concentration of NO3(-)-N increased from near zero up to 925 mg l(-1). Eventual denitrification efficiency in the simulated waste landfill was observed to be approximately 92.3%. Also, S2- present in the discharged leachate was converted to SO4(2-) again in the aeration process. Sulfate needed in this process could be recirculated. Therefore, the amount of sulfate required in the operation of this method could be maintained marginal after the initial addition of sulfate in the effluent tank. Decomposition of recalcitrant organic matters and denitrification hastened the stabilization of landfill. The results of this study indicated that this innovative method was effective and economic.

Nitrogen↗
PubMed2001

The effect of clay particles on the activity of suspended autotrophic nitrifying bacteria and on the performance of an air-lift reactor.

Clay minerals have some properties, namely a high surface area and the ability of ion exchange that may exert some effects on microbial systems. It is often difficult to know the way the clay is exerting its influence and whether its presence improves a given metabolic process. The present work concerns the study of the effect of the addition of powdered kaolin to autotrophic nitrification systems, and includes the study of the effects of the particles on the activity of a suspended nitrifying bacteria consortium and on the performance of an air-lift biofilm reactor used for tertiary nitrification. Concerning the suspended culture, kaolin particles produced stimulation on the specific endogenous and exogenous respiration rates of the bacteria, probably due to a nutritional effect supplied by the clay. This effect was more pronounced for the ammonia oxidation rates, although nitrite oxidation was also enhanced but to a lesser extent. In respect to the presence of kaolin particles in the air-lift reactor, the results obtained indicate that the clay particles become incorporated in the biofilm pellets, but do not change significantly their thickness or their shape. However, nitrate production decreased when the concentration of particles increased. The low adsorption of ammonia by the kaolin indicated that the clay particles embedded in the biofilm did not probably retain the ions. Although it was not proved, precipitation of salts may have occurred.

Adsorption↗
PubMed2002

The monitoring of a two step aerobic-anoxic process with separate biomass to enhance performance in the treatment of liquid industrial wastes.

The paper presents the results of a one-year study of the performance of a full scale plant for the treatment of industrial liquid wastes adopting the alternate cycle process. The carbon and nitrogen removal performances were discussed according to the experimental measurements of maximum nitrification and denitrification rates. It was demonstrated that the nitrification process was the limiting step: it worked with a rate in the range 0.002 - 0.02 KgNH4-N kg(-1)VSS d(-) at 20 degrees C. This was because of inhibition phenomena due to the presence of both complex organic compounds and heavy metals which were not removed by the chemical-physical pre-treatment step. The denitrification process was characterized by a maximum rate ranging from 0.015 to 0.056 Kg NO3-N kg(-1)VSS d(-1) at 20 degrees C, according to the available amount of readily biodegradable COD in the treated wastes. The reliability of the aerobic-anoxic process was determined on the basis of the percentage of successful cycles compared with the performed ones. It was shown that the actual cycles ranged from 50 to 100% of the expected ones, while effective cycles were up to 84% in the first step and up to 60% in the second one. These were related to the carbon to nitrogen ratio. Even if at times the nitrogen and carbon removal yields were not satisfactory, the two step aerobic-anoxic process operated in the alternate cycle mode seems a successful solution for the treatment of liquid industrial wastes.

Bacteria, Aerobic↗
PubMed2005

Missing aerobic-phase nitrogen: The potential for heterotrophic reduction of autotrophically generated nitrous oxide in a sequencing batch reactor wastewater treatment system.

Several biochemical pathways can induce nitrogen loss from aerated, aerobic wastewater treatment bioreactors. These pathways include "traditional" simultaneous nitrification-denitrification (SND) (i.e. autotrophic nitrification - heterotrophic denitrification), autotrophic denitrification, and anaerobic ammonia oxidation. An oxygen limitation, often expressed in terms of low dissolved oxygen (DO) concentration, is a common element of these pathways. The presented research investigated the effect of mixed liquor DO concentration and biomass slowly degradable carbon (SDC) utilization rate on the heterotrophic nitrous oxide (N2O) reduction rate, for biomass cultured in an anoxic/aerobic wastewater treatment bioreactor. Biomass oxygen and SDC availability-limitation, expressed in terms of DO concentration and SDC ultilization rate, respectively, were found to significantly impact the observed heterotrophic N2O reduction rate. The findings support the hypothesis that nitrogen lost from the mixed liquor of an aerobic bioreactor could result from simultaneous autotrophic N2O generation (i.e. autotrophic denitrification) and heterotrophic N2O reduction. The results also support the idea that autotrophic N2O generation could be occurring in a bioreactor, although N2O may not be measurable in the reactor off-gas. Therefore, this autotrophic N2O generation - heterotrophic N2O reduction mechanism provides an alternative explanation to nitrogen loss, when compared to "conventional" SND, where heterotrophic organisms are assumed to reduce autotrophically generated nitrite and nitrate to dinitrogen (N2). In addition, nitrogen loss speculatively attributed to N2 formation via anaerobic ammonia oxidation in oxygen-limited environments, again because of the absence of measurable N2O, may in fact be due to the autotrophic N2O generation - heterotrophic N2O reduction mechanism.

Aerobiosis↗
PubMed2005

A novel approach to remove nitrogen in a biological aerobic filter (BAF).

Laboratory study on nitrogen removal was carried out using biological aerobic filter (BAF) fed with synthetic domestic wastewater in the temperature range of 20.5-26.5 degrees C in order to gain insight into the mechanism and the influences of operation parameters on nitrite accumulation in the biological nitrogen removal process. Influent loading with 0.26-0.62 kg (m(3)d(-1)) NH4+-N, 0.28-0.63 kg (m(3)d(-1)) TN, 1-2 m h(-1) hydraulic loading and air/ water ratio 3:1, resulted in the removal of NH4+-N and TN by 0.15-0.52 kg (m(3)d(-1)) and 0.18-0.42 kg (m(3)d(-1)) respectively. Hence BAF seems to be a promising nitrogen removal technique. The investigation of nitrite concentrations in the bulk and effluent, the profiles of inorganic nitrogen compounds and the spatial distribution of microbial populations and activity indicated that the nitrite accumulation and shortcut nitrification-denitrification had taken place in the bioreactor. No clear relationships were observed between the nitrite accumulation with the influent loading, temperature and pH value except that nitrite concentrations in the bulk increased with high back washing frequency. The results suggested that the filter structure and operation pattern were the principal factors that cause the nitrite accumulation and shortcut nitrification-denitrification occurring in the biological aerobic filter.

Bacteria↗
PubMed2005

Nitrogen elimination mechanisms in an organic media aerated biofilter treating pig manure.

Biofilters using organic media are known to procure efficient treatment for different types of wastewater, but the nitrogen removal pathways implied are still not well understood. In this study, a lab-scale aerated biofilter using peat and treating pig manure was operated for 180 days, in order to quantify the nitrogen transformations occurring in it. It was shown that stripping was important during the start-up, until nitrification took place. Simultaneous nitrification and denitrification, proved by N2 production, became the principal mechanism after some time. The production of N2O did not seem to come only from heterotrophic denitrification, but also from chemodenitrification and autotrophic denitrification. It has also been found that part of the influent nitrogen was retained in the system during the first 150 days, due to filtration, sorption and assimilation. During the last periods of operation, the nitrogen previously retained has been used by microorganisms, leading to an excessive N2 discharge.

Animals↗
PubMed2006

Backwash based methodology for the estimation of solids retention time in biological aerated filter.

The concept of solids retention time (SRT) was used for describing the growth of biofilm in a biological aerated filter (BAF) system. The SRT profile was obtained from the change in solids accumulation, estimated from the head loss profile data before and after backwash using the Carmen-Kozeny equation. The SRT profile along the filter bed depth showed the SRT of about 2 days for the lower layer and about 6 days for the upper layer. The overall SRT was determined by the direct estimation of excess solids mass during backwash and of solids retained in the filter bed. The ideal characteristic SRT distribution was maintained by regular backwash, for organic removal and nitrification. The SRT for high organic removal and nitrification is demonstrated by the SRT distribution along the filter bed in this BAF process.

Biofilms↗
PubMed2006

Activated sludge diffusion for odour removal --effects of H2S on the biomass.

The removal of odours from wastewater treatment plants through diffusion of odour-containing air volumes into the aerated basins was investigated in a bench scale experimental campaign which lasted more than 200 days. Hydrogen sulphide was selected as a model odorous compound and its removal efficiencies were experimentally evaluated along with its effects on the biomass and on the main biochemical processes. Two bench scale sequencing batch reactors were fed in parallel on real primary sewage and monitored for chemical oxygen demand removal, nitrification and denitrification. The balance of H2S was also monitored after adding to one of them a Na2S liquid solution of 17 mgS l(reactor)(-1) d(-1), corresponding to a gas-phase concentration of 240 mgS (Nm3)(-1). Results showed an average sulphide removal of 94% in the reactor supplied with Na2S. Moreover, microbial composition did not show relevant variations after the addition of sulphide, and the good features of activated sludge flocs were maintained also in terms of sludge settleability. No relevant effects of sulphide were detected on carbon and nitrogen metabolism and chemical oxygen demand removal, nitrification and denitrification efficiencies were always above 75%, 95%, and 50% respectively, and comparable across the two reactors.

Ammonia↗
PubMed2006

Biological nutrient removal using an IACOD process: determining the combined effects of low temperature and long solids retention time.

This study was undertaken using an intermittently aerated cylindrical oxidation ditch (IACOD) process for biological nutrient removal. The kinetic aspects of nitrification, denitrification, and phosphorus release/uptake were investigated by conducting a pilot-scale operation under various contact times for the aerobic/anoxic reactor, SRTs, and HRTs. The effects of temperature were also evaluated. The results of the study revealed that a cycle time of 180 min. (i.e., the aerobic contact time of 60 mim. followed by the anoxic contact time of 120 min.) enhanced the biological nutrient removal at an aerobic SRT of 8.3 days and an HRT of 24 hours in the aerobic/anoxic reactor. Even during the winter months with mixed liquor temperatures between 9.6 degrees C and 12 degrees C at an aerobic SRT of 10 days, the IACOD process was capable of almost completely nitrifying the influent NH4- -N. The IACOD process was also capable of denitrifying the NO3- -N in the aerobic/anoxic reactor, yielding effluent NO3- -N concentrations of less than 2.0 mg l(-1) N. Furthermore, the release and abundant uptake of phosphorus successfully occurred at this low temperature range. The enhanced biological phosphorus removal rates increased steadily as the temperature increased from 9.6 degrees C to 22 degrees C. However, an inhibition of phosphorus release was observed at a temperature range of 18 degrees C to 20 degrees C. This inhibition might have been caused by the sudden increase in the NO3- -N concentration of the return sludge, which was induced by the rapid nitrification of the influent NH4+ -N at a relatively elevated temperature. The inhibition was not prolonged due to the subsequent increase in the denitrification rate as the temperature increased further to 20 degrees C and above.

Aerobiosis↗