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PubMed2006

Assessment of nitrification potential in ground water using short term, single-well injection experiments.

Nitrification was measured within a sand and gravel aquifer on Cape Cod, MA, using a series of single-well injection tests. The aquifer contained a wastewater-derived contaminant plume, the core of which was anoxic and contained ammonium. The study was conducted near the downgradient end of the ammonium zone, which was characterized by inversely trending vertical gradients of oxygen (270 to 0 microM) and ammonium (19 to 625 microM) and appeared to be a potentially active zone for nitrification. The tests were conducted by injecting a tracer solution (ambient ground water + added constituents) into selected locations within the gradients using multilevel samplers. After injection, the tracers moved by natural ground water flow and were sampled with time from the injection port. Rates of nitrification were determined from changes in nitrate and nitrite concentration relative to bromide. Initial tests were conducted with (15)N-enriched ammonium; subsequent tests examined the effect of adding ammonium, nitrite, or oxygen above background concentrations and of adding difluoromethane, a nitrification inhibitor. In situ net nitrate production exceeded net nitrite production by 3- to 6- fold and production rates of both decreased in the presence of difluoromethane. Nitrification rates were 0.02-0.28 mumol (L aquifer)(-1) h(-1) with in situ oxygen concentrations and up to 0.81 mumol (L aquifer)(-1) h(-1) with non-limiting substrate concentrations. Geochemical considerations indicate that the rates derived from single-well injection tests yielded overestimates of in situ rates, possibly because the injections promoted small-scale mixing within a transport-limited reaction zone. Nonetheless, these tests were useful for characterizing ground water nitrification in situ and for comparing potential rates of activity when the tracer cloud included non-limiting ammonium and oxygen concentrations.

Bromides↗
PubMed2005

Nitrification-denitrification via nitrite accumulation for nitrogen removal from wastewaters.

The biological nitrification-denitrification process is used extensively for removal of ammonia nitrogen from wastewaters. Saves in aeration, organic matter (for denitrification) and surplus sludge are achievable if nitrite accumulation is possible in the nitrification step. In this paper, operational parameters were studied for each process for maximum nitrite accumulation in the nitrification step and nitrite adaptation in the denitrification step. Nitrite accumulation during nitrification can be controlled by the dissolved oxygen (DO) concentration, presenting a maximum of 65% at around 0.7 mg DO/L. Denitrification can be adapted to nitrite and the process is stable if nitrite in the reactor is keep low. The performance of a continuous stirred tank reactor (CSTR) and an up flow sludge blanket reactor (USB) were compared. Once the operational parameters were established, a CSTR for nitrification and an USB reactor for denitrification were operated in series for 25 days. The process was stable and a steady state was maintained for 20 days, and 93.5% of overall nitrogen removal was achieved in the nitrification-denitrification via the nitrite process.

Ammonia↗
PubMed2005

Dynamics of viable nitrifier community, N-mineralization and nitrification in seasonally dry tropical forests and savanna.

The study was conducted in Vindhyan region, to assess the N-mineralization, nitrification and size of viable community of ammonium- and nitrite-oxidizing bacteria as affected by different sites and seasons. Six different ecosystems (four forests and two savannas), which differ in terms of topography, vegetation and moisture status, were selected for the present study. The soils of the study sites differ significantly in its physico-chemical properties. The savanna site had significantly higher pH (7.2), bulk density (1.37 g cm(-3)) and silt content (67.80%) but lower water holding capacity (1.37%), total-C (16,356 microg g(-1) dry soil), N (1090 microg g(-1) dry soil) and P (213 microg g(-1) dry soil) than forest sites. The soil moisture content, N-mineralization, nitrification rates and numbers of ammonium- and nitrite-oxidizing bacteria were highest in the wet season and lowest in dry season, while the size of mineral-N (NH4(+)-N and NO3(-)-N) showed a reverse trend at the sites. The N-mineralization, nitrification and nitrifier population size differ significantly across the site and season. The numbers of free-living cells of ammonium- and nitrite-oxidizing bacteria were significantly related to each other and to N-mineralization, nitrification, soil moisture and mineral-N components. The N-mineralization, nitrification and the viable number of nitrifying cells were consistently higher for forest soils compared to savanna sites. It was concluded that soil microbial process (N-mineralization and nitrification) and nitrifier population size were dependent on site topography, vegetation cover and soil moisture status.

Bradyrhizobiaceae↗
PubMed2004

Macroscale and microscale analyses of nitrification and denitrification in biofilms attached on membrane aerated biofilm reactors.

A membrane aerated biofilm reactor (MABR), in which O(2) was supplied from the bottom of the biofilm and NH(4)(+) and organic carbon were supplied from the biofilm surface, was operated at different organic carbon loading rates and intra-membrane air pressures to investigate the occurrence of simultaneous chemical oxygen demand (COD) removal, nitrification and denitrification. The spatial distribution of nitrification and denitrification zones in the biofilms was measured with microelectrodes for O(2), NH(4)(+), NO(2)(-), NO(3)(-) and pH. When the MABR was operated at approximately 1.0 g-COD/m(2)/day of COD loading rate, simultaneous COD removal, nitrification and denitrification could be achieved. The COD loading rates and the intra-membrane air pressures applied in this study had no effect on the start-up and the maximum rates of NH(4)(+) oxidation in the MABRs. Microelectrode measurements showed that O(2) was supplied from the bottom of the MABR biofilm and penetrated the whole biofilm. Because the biofilm thickness increased during the operations, an anoxic layer developed in the upper parts of the mature biofilms while an oxic layer was restricted to the deeper parts of the biofilms. The development of the anoxic zones in the biofilms coincided with increase in the denitrification rates. Nitrification occurred in the zones from membrane surface to a point of ca. 60microm. Denitrification mainly occurred just above the nitrification zones. The COD loading rates and the intra-membrane air pressures applied in this study had no effect on location of the nitrification and denitrification zones.

Biofilms↗
PubMed2005

Effect of salinity and inorganic nitrogen concentrations on nitrification and denitrification rates in intertidal sediments and rocky biofilms of the Douro River estuary, Portugal.

The regulatory effects of salinity and inorganic nitrogen compounds on nitrification and denitrification were studied in intertidal sandy sediments and rocky biofilms in the Douro River estuary, Portugal, over a 12-month period. Nitrification and denitrification rates were measured in slurries of field samples and enrichment experiments using the difluoromethane and the acetylene inhibition techniques, respectively. Salinity did not regulate denitrification in either environment, suggesting that halotolerant bacteria dominated the denitrifier communities. However, nitrification rates were stimulated when salinity increased from 0 to 15 practical salinity units. NO3- addition experiments revealed that NO3- availability stimulates denitrification rates in sandy sediments, but not in rocky biofilms; however, in rocky biofilms a positive and linear relationship was observed between denitrification rates and water column NO3- concentrations (r=0.92) during the monthly surveys. The N2O:N2 ratios increased rapidly when NO3- increased from 63 to 363 microM; however, results from monthly surveys showed that environmental parameters other than NO3- availability may be important in controlling the variation in N2O production via denitrification. Ammonium additions to sandy sediments stimulated nitrification rates by 35% for the 20 microM NH4+ addition, but NH4+ appeared to inhibit nitrification at high concentration addition (200 microM NH4+). In contrast, rocky biofilm nitrification was stimulated by 65% when 200 microM NH4+ was added.

Bacteria, Aerobic↗
PubMed2002

The inhibition of marine nitrification by ocean disposal of carbon dioxide.

In an attempt to reduce the threat of global warming, it has been proposed that the rise of atmospheric carbon dioxide concentrations be reduced by the ocean disposal of CO2 from the flue gases of fossil fuel-fired power plants. The release of large amounts of CO2 into mid or deep ocean waters will result in large plumes of acidified seawater with pH values ranging from 6 to 8. In an effort to determine whether these CO2-induced pH changes have any effect on marine nitrification processes, surficial (euphotic zone) and deep (aphotic zone) seawater samples were sparged with CO2 for varying time durations to achieve a specified pH reduction, and the rate of microbial ammonia oxidation was measured spectrophotometrically as a function of pH using an inhibitor technique. For both seawater samples taken from either the euphotic or aphotic zone, the nitrification rates dropped drastically with decreasing pH. Relative to nitrification rates in the original seawater at pH 8, nitrification rates were reduced by ca. 50% at pH 7 and more than 90% at pH 6.5. Nitrification was essentially completely inhibited at pH 6. These findings suggest that the disposal of CO2 into mid or deep oceans will most likely result in a drastic reduction of ammonia oxidation rates within the pH plume and the concomitant accumulation of ammonia instead of nitrate. It is unlikely that ammonia will reach the high concentration levels at which marine aquatic organisms are known to be negatively affected. However, if the ammonia-rich seawater from inside the pH plume is upwelled into the euphotic zone, it is likely that changes in phytoplankton abundance and community structure will occur. Finally, the large-scale inhibition of nitrification and the subsequent reduction of nitrite and nitrate concentrations could also result in a decrease of denitrification rates which, in turn, could lead to the buildup of nitrogen and unpredictable eutrophication phenomena. Clearly, more research on the environmental effects of ocean disposal of CO2 is needed to determine whether the potential costs related to marine ecosystem disturbance and disruption can be justified in terms of the perceived benefits that may be achieved by temporarily delaying global warming.

Ammonia↗
PubMed2005

Model demonstrating the potential for coupled nitrification denitrification in soil aggregates.

A model of reactive, multi-species diffusion has been developed to describe N transformations in spherical soil aggregates, emphasizing the effects of irrigation with reclaimed wastewater. Oxygen demand for respiratory activity has been shown to promote the establishment of anaerobic conditions. Aggregate size and soil respiration rate were identified as the most significant parameters governing the existence and extent of the anaerobic volume in aggregates. The inclusion of kinetic models describing mineralization, nitrification, and denitrification facilitated the investigation of coupled nitrification/denitrification (CND), subject to O2 availability. N-transformations are shown to be affected by effluent-borne NH4+-N content, in addition to elevated BOD and pH levels. Their incremental contribution to O2 availability has been found to be secondary to respiratory activity. At the aggregate level, significant differences between apparent and gross rates of N-transformations were predicted (e.g., NH4+ oxidation and N2 formation), resulting from diffusive constraints due to aggregate size. With increasing anaerobic volume, the effective nitrification rate determined at the aggregates level decreases until its contribution to nitrification is negligible. It was found that the nitrification process was predominantly limited to aggregates <0.25 cm. Assuming that nitrification is the main source for NO3- formation, denitrification efficiency is predicted to peak in medium-sized aggregates, where aerobic and anaerobic conditions coexist, supporting CND. In effluent-irrigated soils, the predicted NO2- formation rate in small aggregates is enhanced when compared to freshwater-irrigated soils. The difference vanishes with increasing aggregate size as anaerobic NO2- consumption exceeds aerobic NO2- formation due to the coupling of nitrification and denitrification.

Aerobiosis↗
PubMed2004

Quantification of nitrification and denitrification rates in algae and duckweed based wastewater treatment systems.

Nitrification and denitrification rates at three different depths (0.1, 0.45 and 0.9m from the water surface) in two series of four algae and duckweed based waste stabilisation ponds (ABPs and DBPs) were measured using nitrate reduction techniques in laboratory batch incubations. The effects of temperature and BOD5 loading were investigated. In situ measurements over the ponds' depths were also done for confirmation of laboratory results. Higher dissolved oxygen (DO) concentrations in ABPs, especially during the warm season, favoured higher nitrification in ABPs over DBPs. Organic surface loading also affected the rate of nitrification in the ponds. Nitrification rates did not increase along the treatment line despite the decrease in organic matter content. Adsorption of nitrifiers to available suspended particles and subsequent sedimentation was assumed to be the main reason for the similar nitrification rates in most ponds. In both systems, the presence of DO in the water column resulted in very low denitrification rates (5-45 mg-N m(-2)d(-1)). Higher denitrification rates (160-560 mg-N m(-2)d(-1)) were measured in the sediments when anoxic conditions prevailed in the overlaying water. The absence of nitrite or nitrate accumulation suggested sufficient nitrite and nitrate diffusion within the water column to allow full denitrification. The nitrification and denitrification rates in both systems were higher at high temperature. The range of nitrogen loss via denitrification in ABPs and DBPs corresponded to 15-25% of total influent nitrogen.

Biofilms↗
PubMed2004

The effect of volatile fatty acids on the nitrification of a saline effluent.

Anaerobically produced volatile fatty acids (VFA) may affect the nitrification yield. The effect of the type of VFA (acetic, propionic and butyric acid) on nitrification of a saline (24 g NaCl l(-1)) medium was studied. Nitritation (40 mg N-NH4+ l(-1)) and nitratation (100 mg N-NO2- l(-1) were assessed in batch cultures fed with different VFA (32 mg TOC l(-1)). The effect of increasing VFA concentrations on nitrification was studied in batch reactors fed with an initial concentration of 40 mg N-NH4+ l(-1) and C/N ratios of 0, 2, 4, 8 and 16 as well as in a continuous mixed flow reactor operated at 30 degrees C and pH 7.5 and fed with 500 mg N-NH4+ l(-1) and 500, 1000, 2000, and 4000 mg TOC l(-1). Nitritation and nitratation rates were decreased by organic matter; inhibition increased with the VFA size. A non-competitive inhibition model fitted the experimental data on nitrification rate reduction at increasing acetic add concentrations; inhibition constants were 685 mg acetic acid l(-1) for ammonia oxidation and 74.3 mg acetic acid l(-1) for nitrite oxidation. The continuous reactor's nitrifying ability decreased from 82% to 40% at C/N ratios 1 and 4, respectively. Loss of nitrification, but a 50% ammonia removal was found at a C/N of 8. It was concluded that the nitrification rate reduction is proportional to the VFA molecular weight and that an increase in VFA concentration diminishes the nitrifying ability due to kinetic limitations.

Acetates↗
PubMed2003

Combined carbonaceous removal and nitrification with biological aerated filters.

This paper describes the use of a submerged biological aerated filter (BAFs), on a pilot plant scale, in the secondary nitrification of low strength domestic wastewater. The results, obtained throughout three months of tests, confirmed the ability of BAFs to obtain simultaneous carbonaceous removal and nitrification. In fact, alter a start-up period of 5 weeks, a remarkable steady state condition in the removal of suspended solids (TSS), chemical oxygen demand (COD) and nitrification was reached. For a hydraulic loading rate of 1.6 m3 m(-2) h(-1), the mean efficiency of the process in the removal of TSS and COD was 85% and 83% respectively. Mean concentrations in the influent flow of around 114 mg(TSS)/L and 140 mg(COD)/L were reduced to average values of below 17 mg(TSS)/L and 25 mg(COD)/L. Secondary nitrification was achieved with a mean efficiency of 85% for a mean volumetric loads of 0.45 kg(N-Namm) m(-3) d(-1) (25 degrees C). Through an intensive activity of nitrification, in the steady state condition, mean influent concentrations of around 12 mg(N-Namm)/L were reduced to average values of below 2 mg(N-Namm)/L. The removal loading rate increased linearly with the applied loading rate for volumetric loads of up to 0.7 kg(N-Namm) m(-3) d(-1). The nitrification was not sensitive to the applied COD loads because of the low level of carbon substrate.

Bioreactors↗
PubMed1993

Microscale distribution of nitrification activity in sediment determined with a shielded microsensor for nitrate.

Microprofiles of O(2) and NO(3) were measured simultaneously in freshwater sediment with microsensors which were completely free from electrical interference because of coaxial designs. Depth profiles of nitrification (NO(3) production) and denitrification (NO(3) consumption) were subsequently determined by computer simulation of the measured microprofiles. The nitrifying bacterial community responded very quickly to changes in environmental conditions, and new steady-state microprofiles of O(2) and NO(3) were usually approached within a few hours after perturbation. Nitrification started quickly after introduction of O(2) in previously anoxic layers, suggesting prolonged survival of the nitrifiers during anaerobiosis. Changes in the availability of O(2) and NH(4) greatly affected the nitrification profile, and there was a high rate of coupled nitrification-denitrification under conditions in which nitrification occurred right above the oxic-anoxic interface. Addition of C(2)H(2) rapidly removed the NO(3) peaks, indicating that NO(3) production was due mainly to autotrophic nitrification.

Journal Article↗
PubMed1994

Simulation Model of the Coupling between Nitrification and Denitrification in a Freshwater Sediment.

A model was constructed to simulate the results of experiments which investigated nitrification and denitrification in the freshwater sediment of Lake Vilhelmsborg, Denmark (K. Jensen, N. P. Sloth, N. Risgaard-Petersen, S. Rysgaard, and N. P. Revsbech, Appl. Environ. Microbiol. 60:2094-2100, 1994). The model output faithfully represented the profiles of O(2) and NO(3) and rates of nitrification, denitrification, and O(2) consumption as the O(2) concentration in the overlying water was increased from 10 to 600 muM. The model also accurately predicted the response, to increasing O(2) concentrations, of the integrated (micromoles per square meter per hour) rates of nitrification and denitrification. The simulated rates of denitrification of NO(3) diffusing from the overlying water (D(w)) and of NO(3) generated by nitrification within the sediment (D(n)) corresponded to the experimental rates as the O(2) concentration in the overlying water was altered. The predicted D(w) and D(n) rates, as NO(3) concentration in the overlying water was changed, closely resembled those determined experimentally. The model was composed of 41 layers 0.1 mm thick, of which 3 represented the diffusive boundary layer in the water. Large first-order rate constants for nitrification and denitrification were required to completely oxidize all NH(4) diffusing from the lower sediment layers and to remove much of the NO(3) produced. In addition to the flux of NH(4) from below, the model required a flux of an electron donor, possibly methane. Close coupling between nitrification and denitrification, achieved by allowing denitrification to tolerate some O(2) ( approximately 10 muM), was necessary to reproduce the real data. Spatial separation of the two processes (no toleration by denitrification of O(2)) resulted in too high NO(3) concentrations and too low rates of denitrification.

Journal Article↗
PubMed1994

Effects of methane metabolism on nitrification and nitrous oxide production in polluted freshwater sediment.

We report the effect of CH(4) and of CH(4) oxidation on nitrification in freshwater sediment from Hamilton Harbour, Ontario, Canada, a highly polluted ecosystem. Aerobic slurry experiments showed a high potential for aerobic N(2)O production in some sites. It was suppressed by C(2)H(2), correlated to NO(3) production, and stimulated by NH(4) concentration, supporting the hypothesis of a nitrification-dependent source for this N(2)O production. Diluted sediment slurries supplemented with CH(4) (1 to 24 muM) showed earlier and enhanced nitrification and N(2)O production compared with unsupplemented slurries (</=1 muM CH(4)). This suggests that nitrification by methanotrophs may be significant in freshwater sediment under certain conditions. Suppression of nitrification was observed at CH(4) concentrations of 84 muM and greater, possibly through competition for O(2) between methanotrophs and NH(4) -oxidizing bacteria and/or competition for mineral N between these two groups of organisms. In Hamilton Harbour sediment, the very high CH(4) concentrations (1.02 to 6.83 mM) which exist would probably suppress nitrification and favor NH(4) accumulation in the pore water. Indeed, NH(4) concentrations in Hamilton Harbour sediment are higher than those found in other lakes. We conclude that the impact of CH(4) metabolism on N cycling processes in freshwater ecosystems should be given more attention.

Journal Article↗
PubMed2005

Nitrification in activated sludge batch reactors is linked to protozoan grazing of the bacterial population.

Protozoa feed upon free-swimming bacteria and suspended particles inducing flocculation and increasing the turnover rate of nutrients in complex mixed communities. In this study, the effect of protozoan grazing on nitrification was examined in activated sludge in batch cultures maintained over a 14-day period. A reduction in the protozoan grazing pressure was accomplished by using either a dilution series or the protozoan inhibitor cycloheximide. As the dilutions increased, the nitrification rate showed a decline, suggesting that a reduction in protozoan or bacterial concentration may cause a decrease in nitrification potential. In the presence of cycloheximide, where the bacterial concentration was not altered, the rates of production of ammonia, nitrite, and nitrate all were significantly lower in the absence of active protozoans. These results suggest that a reduction in the number or activity of the protozoans reduces nitrification, possibly by limiting the availability of nutrients for slow-growing ammonia and nitrite oxidizers through excretion products. Furthermore, the ability of protozoans to groom the heterotrophic bacterial population in such systems may also play a role in reducing interspecies competition for nitrification substrates and thereby augment nitrification rates.

Ammonia↗
PubMedDate not supplied

Nitrification and denitrification rates of Everglades wetland soils along a phosphorus-impacted gradient.

Little information is available on the effect of phosphorus (P) enrichment on nitrogen (N) biogeochemical cycling in wetland soil. Of particular importance are the coupled nitrification-denitrification reactions that regulate the microbially mediated loss of N from wetland systems. Soils from the northern Florida Everglades have been affected by P loading from surface waters over the past 40 years. Elevated P levels have been show to have an effect on the size and activity of the microbial pool and a decrease in the N to P ratio of the microbial biomass. The objective of the study was to determine if P enrichment in soils affected microbial activities related to nitrification and denitrification in these flooded, peat soils. Potential nitrification rates of soil and detritus were determined using constantly stirred reactors under aerobic conditions while denitrification rates were determined from anaerobic incubations of slurry. Nitrification rates showed two distinct linear phases, a slower initial rate, signifying activity of nitrifiers present, followed by a sharp increase in the NH4+ conversion rate indicative of maximum potential rates. Initial rates of nitrification were highest in the surficial detrital layer decreasing with soil depth and did not correlate to soil total P. The potential rates of nitrification were 13 times greater than the initial rates. Potential denitrification rates were highest in the detritus and 0- to 10-cm soil interval with significantly lower values in the 10- to 30-cm soil interval, significantly correlated to total P of the soil. A significant (P < 0.01) relationship was seen between potential denitrification rates and soil total P suggesting an increased rate of N removal from P-enriched regions of the northern Everglades.

Conservation of Natural Resources↗
PubMedDate not supplied

Quantification of the effect of fumigation on short- and long-term nitrogen mineralization and nitrification in different soils.

The effect of soil fumigation on N mineralization and nitrification needs to be better quantified to optimize N fertilizer advice and predict NO(-)(3) concentrations in crops and NO(-)(3) leaching risks. Seven soils representing a range in soil texture and organic matter contents were fumigated with Cyanamid DD 95 (a mixture of 1,3-dichloropropane and 1,3-dichloropropene). After removal of the fumigant, the fumigated soils and unfumigated controls were incubated for 20 wk and N mineralization and nitrification were monitored by destructive sampling. The average short-term N mineralization rates (k(s)) were significantly larger in the fumigated than in the unfumigated soils (P = 0.025), but the differences in k(s) between fumigated and unfumigated soils could not be related to soil properties. The average long-term N mineralization rates (k(l)) were slightly larger in the fumigated soils but the difference with the unfumigated soils was not significant. Again, the differences in k(l) values could not be related to soil properties. Nitrification was inhibited completely for at least 3 wk in all soils, and an effect on nitrification could be observed up to 17 wk in one soil. An S-shaped function was fitted to the nitrification data corrected for N mineralization, and both the rate constant (gamma) and the time at which maximum nitrification was reached (t(max)) were strongly correlated to soil pH. However, since no correlations were found between the effect of fumigation on N mineralization and soil properties, taking into account the effects of fumigation in fertilizer advice and in the prediction of NO(-)(3) leaching risks will need further research.

Allyl Compounds↗
PubMedDate not supplied

Influence of chemical oxygen demand/total Kjeldahl nitrogen ratio and sludge age on nitrification of nitrogenous wastewater.

Four laboratory-scale biological nitrification units (influent total Kjeldahl nitrogen [TKN] = 1002 to 1062 mg/L) were operated at chemical oxygen demand (COD)/TKN ratios of approximately 0.5, 1.0,15, and 2.0 and at three different sludge ages of 30, 20, and 10 days to study the influence of COD/TKN, sludge age, COD loading, and TKN loading on nitrification and nitrifiers. Percent nitrification was found to increase with decreases in COD/TKN and increases in sludge age. The average nitrifier concentration increased from 460 mg/L at a COD/TKN of 2.22 and a sludge age of 10 days to 706 mg/L at a COD/TKN of 0.676 and a sludge age of 30 days. The nitrifier fraction was found to be higher at a lower COD/TKN and lower at a higher COD/TKN. The nitrifier fraction increased with the decrease in sludge age and COD loadings and the increase in TKN loadings. The effect of sludge age on the nitrifier fraction was amplified at a COD/ TKN of approximately 0.5 rather than at approximately 2.0. The nitrification rate (kilograms TKN oxidized per kilograms nitrifiers per day) was shown to be dependent on COD/TKN and sludge age. The activity performed by Nitrobacter was affected at all COD/TKN ratios studied as well as at a sludge age of 10 days. This was manifested by the accumulation of high levels of nitrite-nitrogen in the nitrified effluent. The presence of heterotrophs did not affect nitrification rates and the growth of nitrifiers, which were found to be beneficial. High sludge age and COD loadings resulted in a higher sludge volume index of more than 200 mL/g mixed liquor suspended solids. Microscopic examination showed filamentous structure of sludge under these conditions. It is concluded from the investigations that a sludge age of 30 days and a COD/TKN of approximately 1.0 are optimal to yield maximum nitrification and nitrifier growth rates for treating high-strength nitrogenous wastewater.

Bioreactors↗
PubMed2002

Soil microbial toxicity of eight polycyclic aromatic compounds: effects on nitrification, the genetic diversity of bacteria, and the total number of protozoans.

Eight polycyclic aromatic compounds (PACs) were tested for their toxic effect on the soil nitrification process, bacterial genetic diversity, and the total number of protozoans (naked amoebae and heterotrophic flagellates). After four weeks of exposure in a well-characterized agricultural soil, toxic effects were evaluated by comparison to uncontaminated control soils. All PACs affected the nitrification process, and the calculated no-observed-effect concentrations (NOECs) for nitrification were 79 mg/kg for pyrene, 24 mg/kg for fluoranthene, 26 mg/kg for phenanthrene, 72 mg/kg for fluorene, 23 mg/kg for carbazole, 22 mg/kg for dibenzothiophene, 75 mg/kg for dibenzofuran, and 1,100 mg/kg for acridine. For all substances but acridine, nitrification was the most sensitive of the three toxicity indicators evaluated. No effect of the tested substances on bacterial diversity was found, as measured by denaturant gradient gel electrophoresis. In general, only weak effects at very high concentrations were found for the protozoans. However, for acridine, protozoan numbers were reduced at lower concentrations than those that affected the nitrification process, that is, with a 5% reduction at 380 mg/kg. For effects on nitrification, toxicity (NOEC values) expressed as soil pore-water concentrations (log10(micromol/L)) showed a significant inverse relationship with lipophilicity (log octanol-water partition coefficient) of the substances (r2 = 0.69, p = 0.011, n = 8). This finding could indicate that the toxicity of substances similar to those tested might be predicted by a quantitative structure-activity relationship with lipophilicity as the predictor variable.

Animals↗