Maximum Nitrification Rate Research Articles

The influence of macrofaunal burrow spacing and diffusive scaling on sedimentary nitrification and denitrification: An experimental simulation and model approach

The influence of burrow spacing on nitrification and denitrification was simulated experimentally using sediment plugs of different thicknesses immersed in aerated seawater reservoirs. Different plug thicknesses mimic different distances between oxygenated burrow centers and produce similar changes in aerobic–anaerobic reaction balances as a function of diffusive transport scaling. The thicknesses used were roughly equivalent to transport scales (interburrow spacing) that could be produced by burrow abundances of ~400 to 50,000 m-2, depending on burrow lumen radii (e.g., 0.05–1 cm). Following the exposure of anoxic sediment plugs to aerated water, an efficient aerobic nitrification zone was established within the first ~2–3 millimeters of sediment. At pseudo-steady state, the thinnest plug (2 mm) simulating highest burrow density, was entirely oxic and the denitrification rate nil. Denitrification was stimulated in anoxic regions of the thicker plugs (5, 10, and 20 mm) compared to the initial value in experimental sediment. Maximum nitrification rates and the highest denitrification/nitrification ratio between oxic nitrification and adjacent denitrification zones occurred for the intermediate plug thickness of 5 mm. Of the oxic/anoxic composites, the thickest plug showed the least efficient coupling between nitrification/denitrification zones (lowest denitrification/nitrification ratio). Both the thickness of the oxic layer and the total net remineralization of dissolved inorganic N varied inversely with plug thickness. A set of diffusion–reaction models was formulated assuming a range of possible nitrification kinetic functions. All model forms predicted optimal nitrification–denitrification and ammonification–denitrification coupling with relative oxic–anoxic zonation scales comparable to intermediate plug thicknesses (5–6 mm). However, none of the commonly assumed kinetic forms for nitrification could produce the observed NO-3 profiles in detail, implying that natural sediment populations of nitrifiers may be less sensitive to O2 than laboratory strains. Our experimental and model results clearly show that rates of N remineralization and the balance between stimulation/inhibition of denitrification are highly dependent on sedimentary biogenic structure and the particular geometries of irrigated burrow distributions.

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−1VSS d−1 at 20°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−1VSS d−1 at 20°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.

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 NH 4 +-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/m 3 d in the anaerobic reactor while the maximum NH 4 +-N removal rate and maximum nitrification rate were 0.84 kg NH 4 +-N/m 3/d and 0.50 kg NO 3 −-N/m 3/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 m 3/kg COD and the biogas compositions of CH 4, CO 2, and N 2 were kept relatively constant, 66–75, 22–32, and 2–3%, respectively.

Nitrification in a membrane bioreactor (MBR) for wastewater treatment

Nitrification of the MBR process for sewage treatment was investigated with a pilot scale plant in this study. Complete nitrifcation occurred where the sludge retention time (SRT) was over 5 days. The maximum nitrification rate (Rmax) of the biomass was determined with batch tests and was found to be around 1.71 – 2.0 mgNO3--N/gVSS-h. Nitrification was affected more by the influent C/N ratio than SRT.

Nitrification of anaerobically pretreated municipal landfill leachate at low temperature

Nitrification of anaerobically pretreated municipal landfill leachate (270–1000 mg COD l −1, 53–270 mg NH 4–N l −1) was studied in laboratory-scale activated sludge reactors without (AS) and with (ASC) the addition of plastic carrier material. The reactors were run at 10°C (149 d), 7°C (21 d) and 5°C (16 d). With a loading rate of 0.027 g NH 4–N g MLVSS −1 d −1 and a hydraulic retention time of ca. 3 d, at 10°C, complete nitrification was obtained in both reactors. At 7°C, and in loading rate of 0.023 g NH 4–N g MLVSS −1 d −1, both reactors appeared to be overloaded and ammonium removal was only ca. 93%. At 5°C, with a lower loading rate of 0.010 g NH 4–N g MLVSS −1 d −1, complete nitrification was obtained in the ASC reactor but in the AS reactor only 61% of ammonium was removed. Aerobic posttreatment produced effluent with 150–500 mg COD l −1, less than 7 mg BOD 7 l −1, and, on average, less than 13 mg NH 4–N l −1. In batch assays at 24 and 10°C, maximum nitrification rates were 0.13 and 0.03 g NO 3–N g MLVSS −1 d −1, respectively, while ammonium removal rates were twice as high. The nitrification rates were higher with than without carrier material, suggesting that a large fraction of nitrifying micro-organisms was attached on the surface of the carrier material. The results show that nitrification of anaerobically treated leachate is feasible at temperatures down to 5–10°C. Benefits of the carrier reactor were evident only at low temperatures and under varying loading conditions.

The influence of dietary oxolinic acid on fluidised bed biofilter performance in a recirculation system for rainbow trout ( Oncorhynchus mykiss)

The effect of medicated feed, containing 2.35±0.01 mg oxolinic acid (OA) g −1, upon the performance of fluidised bed (FB) biofilters was examined over a 29-day period. Rainbow trout were used as stock animals in duplicate recirculation systems. OA was detectable within the systems throughout the period of study, with bulk water OA concentrations reaching 1.24 mg l −1 at their highest point. Sludge levels of OA were measured at 60 mg day −1 at peak. A mass balance for OA was undertaken on day 21 of the study. Seventy-two percent of the antibiotic could be recovered from the trout, sludge and water, with fish being of minimal significance at trial termination. The treated feed did not effect biofilter performance, either during the feeding period (7 days duration) or for 14 days post-feeding, with respect to nitrification rates. In separate studies, which employed a scale model of the recirculation system, maximum nitrification rates (MNR) were examined using media from each of the biofilters and four doses of OA (0.1–100 mg l −1). OA did not effect MNR, but water turbidity and bacterial count increased.

Effect of Environmental Parameters on Autotrophic Decay Rate (bA).

Activated sludge treatment systems for industrial wastewater effluents, or mixtures of industrial and urban wastewater, can be subjected to nitrifying nitrogen starvation periods. Because of the autotrophic decay, the maximum nitrification rate could be significantly reduced after a few days of nitrogen starvation. As published data on the autotrophic decay rate (bA) are scarce, little is known about the parameters influencing its value. The autotrophic decay rate of nitrifiers (bA) was estimated in an activated sludge pilot plant treating industrial wastewater under stable conditions of load, temperature and hydraulic parameters. The effect of environmental parameters on bA was investigated. Influent quality had a significant impact on bA: at 30°C, under aerobic conditions, changes in the quality of an industrial effluent from the same source induced bA variations from 0.08 to 0.16 d−1. The bA value doubled when small amounts of urban wastewater were added to the pilot plant influent. When 30% of the load was composed of urban wastewater, bA reached a value of 0.36 d−1. Microfauna grazing of autotrophic bacteria was shown to be partly responsible for bA variations, explaining why the bA value was found to decrease by at least 50% under anoxic conditions.

Effect of sludge retention time (SRT) on nutrient removal in sequencing batch reactors

Two bench‐scale activated sludge Sequencing Batch Reactors (SBR's), with working volumes of 100 liters each, operated on synthetic wastewater at sludge retention times (SRT) of 7 days (Reactor 1) and 15 days (Reactor 2) respectively. Biological phosphorus and nitrogen removals were applied in the systems to study nitrification, denitrification, and phosphorus removal kinetics during the start‐up phase. Excellent enhanced biological phosphorus removal was achieved in both reactors within 21 days. The maximum phosphorus release rate in each reactor was 10‐mg PO4‐P/ g.MLSS.h at 20°C and phosphorus contents of about 5% dry weight of biomass were achieved. In Reactor 2, very good nitrification was achieved with 100% ammonia removal within initial two weeks of operation. The maximum nitrification rate was 3.0 mg NO3‐N/g. MLSS.h, but later phosphorus release rates continued to decline, due to the elevated remaining nitrate concentrations from preceding cycles in the initial fill and mix phase. Remaining nitrate consumes influent organic during the fill and mix phase, decreasing the availability of organic matter for phosphorus removing bacteria, thus deteriorating their activity. For SBR 1, phosphorus release rates didnl shows any decline, as incomplete nitrification led to much lower nitrate during the initial fill and mix phase. The present study implied that higher SRT is beneficial for phosphorus removal. But later, SRT should be reduced to decrease the nitrification activity, if the target is phosphorus removal, otherwise remaining elevated nitrate concentration diminishes phosphorus removal.

Full scale evaluation of nitrification performance in an integrated fixed film activated sludge process

The nitrification performance of an integrated fixed film activated sludge (IFAS) process was compared to a parallel control system at full scale. The IFAS process utilized the Ringlace and Biomatrix looped cord media products. Monitoring and evaluation of the retrofit was divided into two periods. The first monitoring period was from October 3, 1995 to June 20, 1996. The second monitoring period was started on December 2, 1996 and was completed on March 28, 1997. During the first operating period, the maximum media nitrification rate was estimated to be 0.42 kg/d/1000 m of media at an average temperature of 10°C. Settling was also improved. To correct flow short circuiting observed during the first operating period additional aerators were mounted below the media frames and baffles were mounted above existing diffusers. Nitrification performance of the media during the second operating period was found to be marginal. Although the nitrification performance in the control train was not stressed to the same degree as in the 1995/96 period, the likely main cause of the deteriorated performance of the media was a proliferation of bristle worm in the biofilm. The results of this study indicate that proper aeration design, and the prevention and treatment of worm blooms are two important issues in the application of the IFAS process.

Factors affecting nitrogen removal from domestic wastewater using immobilized bacteria

The parameters affecting the nitrogen removal process by the immobilized bacteria in the anoxic-oxic process have been studied by investigating two bench scale Runs A and B. The hollow polypropylene pellets have been dosed into the anoxic reactor in Run A and into the oxic reactors of both Runs up to 24% of volume. Run B was operated with no pellets in the anoxic reactor as a control. The maximum nitrification rate of 0.4 kg NH4-N/m3d was achieved in sufficient DO (6.5 mg/l) at 15°C in the reactor with both activated sludge and immobilized micro-organisms. The volumetric nitrification rate was found to be greatly dependent on bulk oxygen concentration especially when the DO was maintained below 4 mg/l. A mathematical model developed successfully simulated the experimental results showing the variation of nitrification rate with DO. In the case of denitrification, the contribution of immobilized bacteria was prominent when lesser concentration of MLSS was present in the activated sludge in the combined immobilized and activated sludge system. The presence of immobilized bacteria in the anoxic reactor will be effective when higher nitrate nitrogen loadings are expected and the maintenance of higher MLSS than 2 g/l in an activated sludge facility is not feasible.

High rate of aerobic nitrification and denitrification by Nitrosomonas eutropha grown in a fermentor with complete biomass retention in the presence of gaseous NO2 or NO.

A pure culture of the obligately lithoautotrophic ammonia-oxidizer Nitrosomonas eutropha was grown in a laboratory-scale bioreactor with complete biomass retention. The air supply was supplemented with nitrogen dioxide (NO2; 25 or 50 ppm) or nitric oxide (NO; 25 or 50 ppm). Compared to cultures grown without these nitrogenous oxides, the addition of NO2 or NO to the culture resulted in a significant increase of the nitrification rate, specific activity of ammonia oxidation, growth rate, and maximum cell densities. In contrast, the growth yield slightly decreased in the presence of NO or NO2. Maximum cell densities of about 2 x 10(10) cells ml-1 and a maximum nitrification rate of about 221 mmol NH4+ l-1 day-1 were obtained after 3 weeks in the presence of 50 ppm NO2. Furthermore, in the stationary phase about 50% of the nitrite produced was aerobically denitrified to dinitrogen (N2) and traces of nitrous oxide (N2O). When cells were supplemented with NO, a high rate of aerobic denitrification occurred only during the first days of the exponential growth phase.

Nitrification limitation in animal slurries at high temperatures

Nitrification rates in two types of animal slurry were measured at temperatures between 20 and 60°C. The rates were assessed in rapid laboratory assays using samples from aeration tanks of large-scale treatment plants for pig or veal-calf slurry. Maximum nitrification rates for the two slurries were observed around 35 and 40°C. For veal-calf slurry, the observed maximum rate was 1.5 mmol NH + 4 per gram volatile suspended solids per hour. The maximum rate for digested pig slurry was 0.11 mmol g −1h −1). For digested pig slurry, a sharp drop in nitrification rate was observed at temperatures higher than 40°C. The rate in veal-calf slurry dropped at temperatures higher than 45°C. No nitrification was observed above 45°C in digested pig slurry and above 50°C in veal-calf slurry.

Identification of activated sludge and wastewater characteristics using respirometric batch-experiments

This paper presents a procedure to obtain activated sludge kinetics and wastewater characteristics from respirometric batch-experiments. For identification of state variables and model parameters a modified version of the ASM no. 1 that describes the oxygen uptake rate of the nitrification process and organic matter elimination was used. It is demonstrated that the maximum nitrification rate of activated sludge and the concentration nitrifiable nitrogen, and the rapid hydrolysis rate together with the concentration slowly biodegradable organic compounds can be estimated accurately. Suggestions to improve identifiability problems are given. It is concluded that the proposed method offers possibilities to follow changes in sludge capacities, for both heterotrophic and autotrophic micro-organisms, and wastewater composition.

Full scale evaluation of nitrification performance in an integrated fixed film activated sludge process

The nitrification performance of an integrated fixed film activated sludge (IFAS) process was compared to a parallel control system at full scale. The IFAS process utilized the Ringlace and Biomatrix looped cord media products. Monitoring and evaluation of the retrofit was divided into two periods. The first monitoring period was from October 3, 1995 to June 20, 1996. The second monitoring period was started on December 2, 1996 and was completed on March 28, 1997. During the first operating period, the maximum media nitrification rate was estimated to be 0.42 kg/d/1000 m of media at an average temperature of 10°C. Settling was also improved. To correct flow short circuiting observed during the first operating period additional aerators were mounted below the media frames and baffles were mounted above existing diffusers. Nitrification performance of the media during the second operating period was found to be marginal. Although the nitrification performance in the control train was not stressed to the same degree as in the 1995/96 period, the likely main cause of the deteriorated performance of the media was a proliferation of bristle worm in the biofilm. The results of this study indicate that proper aeration design, and the prevention and treatment of worm blooms are two important issues in the application of the IFAS process.

Factors affecting nitrogen removal from domestic wastewater using immobilized bacteria

The parameters affecting the nitrogen removal process by the immobilized bacteria in the anoxic-oxic process have been studied by investigating two bench scale Runs A and B. The hollow polypropylene pellets have been dosed into the anoxic reactor in Run A and into the oxic reactors of both Runs up to 24% of volume. Run B was operated with no pellets in the anoxic reactor as a control. The maximum nitrification rate of 0.4 kg NH4-N/m3d was achieved in sufficient DO (6.5 mg/1) at 15°C in the reactor with both activated sludge and immobilized micro-organisms. The volumetric nitrification rate was found to be greatly dependent on bulk oxygen concentration especially when the DO was maintained below 4 mg/1. A mathematical model developed successfully simulated the experimental results showing the variation of nitrification rate with DO. In the case of denitrification, the contribution of immobilized bacteria was prominent when lesser concentration of MLSS was present in the activated sludge in the combined immobilized and activated sludge system. The presence of immobilized bacteria in the anoxic reactor will be effective when higher nitrate nitrogen loadings are expected and the maintenance of higher MLSS than 2 g/1 in an activated sludge facility is not feasible.

Nitrification of landfill leachate using suspended-carrier biofilm technology

The possibility of nitrifying municipal landfill leachate using suspended-carrier biofilm technology was studied in three laboratory-scale reactors filled with three different types of carrier media. The effects of the temperature and the hydraulic retention time (HRT) on the volumetric nitrification rate were investigated. Steady-state nitrification rates were obtained in the processes after approximately 1 month of operation. The nitrification rate showed a rather weak dependence on the temperature, the rate at 5°C being approximately 77% of the rate at 20°C. The HRT had a more pronounced effect on the rate of nitrification, showing a considerable increase in nitrification rate with a decreased HRT. The highest efficiency was achieved for a carrier media consisting of small cubes of macroporous cellulose. A maximum nitrification rate of 40 g (NH + 4-N)/(m 3 reactor h) was obtained by use of this carrier at 20°C, an HRT of 14 h and a carrier filling degree of 10% of the reactor volume.

Combined biological nitrification and denitrification of high-salinity wastewater

The focusing on the discharge of nitrogen compounds to aquifers has put pressure on power plants to look into removal of nitrogen compounds from the gas scrubbing liquors (DESOx and DENOx). The scrubber liquor has a high salinity, a high chloride content and a temperature of about 40°. Initial laboratory tests to evaluate the possibility of performing biological nitrification and denitrification showed promise and a pilot-scale test unit was established at one of the Danish coal-fired combined heat and power plant (AVEDØRE 1). The pilot plant was operated under varying conditions with regard to temperature and chloride concentration. Maximum nitrification and denitrification rates were measured. At 30°C and 20 g Cl−/l, maximum nitrification and denitrification rates of 2 and 3 mg N/g VSS·h respectively were measured. In the effluent, concentrations of inorganic nitrogen were below 8 mg N/l. Twice during the test period, inhibition of the biomass activity was caused by high concentrations of heavy metals. The high content of heavy metals was due to malfunction of pH control in the heavy metal removal plant. The nitrification process was more sensitive to heavy metals than the denitrification process, and during the two toxic events the nitrification rate decreased to zero. The influence of rapid changes in the chloride and nitrite contents on nitrification was also examined. The results from the performed tests can be applied on other wastewaters with similar characteristics as these scrubber liquors i.e. with salinity. As an example fertilizer and pharmaceutical industries can be mentioned.

Bioconversion of Methylamine in Biofilters

Bioconversion of methylamine (MA) was studied using two sets of biofilters arranged in three stages and packed with inoculated peat-based media of initial pH 7.89 and 4.77, respectively. Tests were made to compare effects of initial media pH on the performance of the filter and on the variation of physicochemical properties of the medium for treating MA. A MA loading of 3.50 g nitrogen per m3 medium per hour was kept in the first stages of both filters. Results indicated that all the influent MA was hydrolyzed to ammonia in the pH range of 7.5 to 8.5. About 1/3 of the ammonia nitrogen was nitrified to nitrate and 1/3 was converted into organic or cell nitrogen. Properties of the media varied over time and with the height of the packing. The neutral medium performed well compared with the acid one. Maximum absorption capacities of 40 g ammonia-N and 42 g nitrate-N per kilogram of dry medium were observed for the neutral medium. Maximum rate of nitrification was 0.69 g nitrogen per m3 medium per hour, which occurred in the middle stage of the filter with the medium at a pH of 7.6 and containing a moisture of 55%.

Combined biological nitrification and denitrification of high-salinity wastewater

The focusing on the discharge of nitrogen compounds to aquifers has put pressure on power plants to look into removal of nitrogen compounds from the gas scrubbing liquors (DESO x and DENO x ). The scrubber liquor has a high salinity, a high chloride content and a temperature of about 40°. Initial laboratory tests to evaluate the possibility of performing biological nitrification and denitrification showed promise and a pilot-scale test unit was established at one of the Danish coal-fired combined heat and power plant (AVEDORE 1). The pilot plant was operated under varying conditions with regard to temperature and chloride concentration. Maximum nitrification and denitrification rates were measured. At 30°C and 20 g Cl − /l, maximum nitrification and denitrification rates of 2 and 3 mg N/g VSS·h respectively were measured. In the effluent, concentrations of inorganic nitrogen were below 8 mg N/l. Twice during the test period, inhibition of the biomass activity was caused by high concentrations of heavy metals. The high content of heavy metals was due to malfunction of pH control in the heavy metal removal plant. The nitrification process was more sensitive to heavy metals than the denitrification process, and during the two toxic events the nitrification rate decreased to zero. The influence of rapid changes in the chloride and nitrite contents on nitrification was also examined. The results from the performed tests can be applied on other wastewaters with similar characteristics as these scrubber liquors i.e. with salinity. As an example fertilizer and pharmaceutical industries can be mentioned.

Nitrification of Ammonium Nitrogen in Soils Treated with XDE‐474

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