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PubMed2006

The effect of landfill leachate composition on organics and nitrogen removal in an activated sludge system with bentonite additive.

A pre-denitrification activated sludge system (AS) without internal recycle was used in lab-scale studies of landfill leachate treatment. A bentonite supplement at a ratio of 1:4 (mineral : biomass) was used to ensure high sludge settling levels and to serve as a micro-organisms carrier. The system was operated within different parameters such as hydraulic retention time (HRT), ammonia loading rate (ALR) or external recycle ratio, which was adapted to treat varying leachate concentrations of COD and ammonia, ranging from 1020 to 2680 mgO(2)l(-1) and 400-890 mgNH(4)-Nl(-1) respectively. The nitrification was complete and ammonia oxidation reached 99%; this was obtained while the ALR did not exceed 0.09 g NH(4)(+)-Ng(-1)MLVSS d(-1) and HRT was not lower than 1 day (in the aeration reactor). The performance of denitrification was successfully improved by controlling the external recycle rate, when the BOD(5)/N ratio in the raw leachate was 4.1. Consequently, N-removal of up to 80% was achieved. A 10-fold decrease in the denitrification rate was obtained at a BOD(5)/N ratio of 0.5. The efficiency of COD removal varied significantly from 36% to 84%. The positive effect of bentonite addition was determined and is discussed based on preliminary studies. The experiments were carried out in fill-and-draw activated sludge with bentonite; the biomass ratio was 1:2. The activated sludge with bentonite was fed with a synthetic high ammonia and organic-free medium.

Bentonite↗
PubMed2006

Some properties of a sequencing batch reactor for treatment of wastewater containing thiocyanate compounds.

Thiocyanate (SCN) compounds in photo-processing wastewater (PPWW) could be treated by an SBR system without any release of thiocyanate to the atmosphere during the aeration step. An SCN loading greater than 84 g m(-3)d(-1) showed negative effects on the growth of bio-sludge and removal efficiencies of the system. The acclimatization period of the system was increased with an increase in SCN concentration or loading. The COD, BOD(5), TKN, and SCN removal efficiencies were 96.0 +/- 1.6%, 72 +/- 2%, 49 +/- 5%, and 82 +/- 3%, respectively, under an SCN loading of up to 84 g m(-3)d(-1). The removal efficiency of the system was repressed by SCN due to the repressed growth rate of nitrification bacteria. However, the removal efficiency could be increased with an increase in HRT or a decrease in SCN loading. Also, increases in HRT or decreases in SCN loading led to increased sludge age or solid retention time (SRT) and decreased the sludge volume index (SVI) value. The SRT and SVI of the system with synthetic wastewater containing 840 mg l(-1) SCN under an HRT of 3 days (SCN loading of 280 g m(-3)d(-1)) were 3.9 +/- 0.7 days and 65 +/- 4 ml g(-1), respectively, while they were 11.2+/-0.8 days and 55 +/- 6 ml g(-1), respectively under an HRT of 10 days (SCN loading of 84 g m(-3)d(-1)).

Bioreactors↗
PubMed2005

A novel two-stage MBR denitrification process for the treatment of high strength pet food wastewater.

A novel paradigm using pre-denitrification process is presented to optimize an existing system of two-stage MBRs treating high strength pet food wastewater. Successive reduction of organics in the 1st stage and almost complete nitrification in the 2nd stage generated effluent meeting stringent surface discharge criteria i.e. BOD5, TSS and NH4+ -N of < 10 mg/L at an overall HRT of 6.3 days. Pre-anoxic zone was created by a submerged coil in the path of influent to the 1st stage. Final effluent and the 1st stage mixed liquor were recirculated to the coil. With prevailing high denitrification rates, more than 94% of the recirculated nitrates were denitrified in less than 15 min of effective anoxic residence time. At a recycle ratio of 3:1, total nitrogen was reduced by 84%, aeration energy by 25% and the external alkalinity requirement by 65%, enhancing economical viability of the system.

Animal Feed↗
PubMed2006

Activated sludge ozonation to reduce sludge production in membrane bioreactor (MBR).

Total experimental period was divided into two stages. At first stage, a series of batch studies were carried out to get an understanding of the effect of ozonation on sludge properties. At the following stages, three membrane bioreactors (MBRs) with different amounts of activated sludge to be ozonated were run in parallel for a long period to evaluate the influence of sludge ozonation on sludge yield and permeate quality. Through batch study, it was found that ozone could disrupt the cell walls and cause the release of plasm from the cells, then the amounts of soluble organics in the solution increased with ozonation time. With the rise of soluble organics, the amount of soluble organics to be mineralized increased as well, which would reduce the soluble organics content. For the counteraction between these two aspects, a pseudo-balance could be achieved, and soluble organics would vary in a limited range. Sludge ozonation also increased the contents of soluble nitrogen and phosphorus in the solution. On the basis of batch study, a suitable ozone dosage of 0.16 kg O(3)/kg MLSS was determined. Three systems were run in parallel for a total period of 120 days; it was demonstrated that a part of activated sludge ozonation could reduce sludge production significantly, and biological performance of mineralization and nitrification would not be inhibited due to sludge ozonation. Experimental results proved that the combination of ozonation unit with MBR unit could achieve an excellent quality of permeate as well as a small quantity of sludge production, and economic analysis indicated that an additional ozonation operating cost for treatment of both wastewater and sludge was only 0.096 Yuan (US$ 0.0115)/m(3) wastewater.

Bioreactors↗
PubMed2006

Study of the aerobic biodegradation of coke wastewater in a two and three-step activated sludge process.

A laboratory-scale biological plant composed of two aerobic reactors operating at 35 degrees C was used to study the biodegradation of coke wastewater. The main pollutants to be removed are organic matter, especially phenols, thiocyanate and ammonium nitrogen. The concentrations of the main pollutants in the wastewater during the study ranged between 922 and 1,980 mg COD/L, 133 and 293 mg phenol/L, 176 and 362 mg SCN/L and 123 and 296 mg NH(4)(+)-N/L. The biodegradation of these pollutants was studied employing different hydraulic residence times (HRT) and final effluent recycling ratios in order to minimize inhibition phenomena attributable to the high concentrations of pollutants. During the optimisation of the operating conditions, the removal of COD, phenols and thiocyanate was carried out in the first reactor and the nitrification of ammonium took place in the second. The best results were obtained when operating at an HRT of 98 h in the first reactor and 86 h in the second reactor, employing a recycling ratio of 2. The maximum removal efficiencies obtained were 90.7, 98.9, 98.6 and 99.9% for COD, phenols, thiocyanate and NH(4)(+)-N, respectively. In order to remove nitrate, an additional reactor was also implemented to carry out the denitrification process, adding methanol as an external carbon source. Very high removal efficiencies (up to 99.2%) were achieved.

Bioreactors↗
PubMed2006

The performance of BAF using natural zeolite as filter media under conditions of low temperature and ammonium shock load.

Natural zeolite and expanded clay were used as filter media for biological aerated filter (BAF) to treat municipal wastewater in parallel in whole three test stages. The stage one test results revealed that zeolite BAF and expanded clay BAF have COD and NH(3)-N removals in the range of 84.63-93.11%, 85.74-96.26%, 82.34-93.71%, and 85.06-93.2%, respectively, under the conditions of water temperature of 20-25 degrees C and hydraulic load of 2-3m(3)/(m(2)h). At the following stage two, the influent NH(3)-N concentration was increased to about double value of the stage one, and it was investigated that the effluent NH(3)-N of expanded clay BAF increased significantly and then gradually restored to normal condition in 2 weeks, while the effluent NH(3)-N of zeolite BAF kept stable. At stage three, the low reactor temperature has also different effects on these two BAFs, under conditions of water temperature of 7-10 degrees C, hydraulic load of 2-3m(3)/(m(2)h), zeolite BAF and expanded clay BAF have COD and NH(3)-N removals in the range of 74.5-88.47% (average of 81.57%), 71.73-88.49% (average of 81.06%), 71.91-87.76% (average of 80.49%), and 38.41-77.17% (average of 65.42%), respectively. Three stages test results indicated that the zeolite BAF has a stronger adaptability to NH(3)-N shock load and low temperature compared to expanded clay BAF. In addition, the detection of the amounts of heterobacteria and nitrobacteria of two biological aerated filters in three stages also showed the zeolite filter media was more suitable to the attached growth of nitrobacteria, which is helpful to the improvement of nitrification performance in zeolite BAF.

Bioreactors↗
PubMed2006

Trimethylamine (TMA) biofiltration and transformation in biofilters.

Bioremoval of trimethylamine (TMA) in two three-stage biofilters packed with compost (A) and sludge (B), respectively, was investigated. Both biofilters were operated with an influent TMA concentration of 19.2-57.2mgm(-3) for 67 days. Results showed that all of the inlet TMA could be removed by both biofilters. However, removal efficiency and transformation of TMA in each section of both biofilters was different. In the Introduction section, TMA removal efficiency and maximum elimination capacity of the compost medium were greater than those of sludge medium under higher inlet TMA concentration. In comparison with biofilter A, considerably higher NH(3) concentrations in effluent of all three sections in biofilter B were observed after day 19. Although, NO(2)(-)-N concentration in each section of biofilter A was relatively lower, NO(3)(-)-N content in each section of biofilter A increased after day 26, especially in the Materials and method section which increased remarkably due to a lesser amount of TMA and higher ammonia oxidation and nitrification in compost medium. In contrast, neither NO(2)(-)-N nor NO(3)(-)-N were detected in either section of biofilter B at any time throughout the course of the experiment. The cumulative results indicated that compost is more favorable for the growth of TMA-degrading and nitrifying bacteria as compared to the sludge and could be a highly suitable packing material for biodegradation and transformation of TMA.

Ammonia↗
PubMed2005

The water quality of the Ria de Aveiro lagoon, Portugal: from the observations to the implementation of a numerical model.

Ria de Aveiro is a very important area of the Portuguese coast, which has been under an increasing anthropogenic pressure for several decades and, contributes to the degradation of the lagoon's water quality. This work presents both a characterisation of the water quality of the Ria de Aveiro lagoon, using physical, chemical and biological experimental data, and an implementation of a numerical model for the water quality of the lagoon. The ultimate goal is to obtain an accurate numerical model able to simulate major water quality features of the lagoon under the influence of different forcing conditions. Data analysis reveals good correlations between the salinity and almost all the water quality variables as well as between the different variables. The maximum biochemical oxygen demand concentration (BOD) depends on the light intensity, the temperature and the river inputs. The main vulnerable areas of the lagoon, from the water quality point of view, seem to be the far end of the main channels, where low dissolved oxygen concentration (DO) and high BOD concentrations are observed. The numerical model of the Ria de Aveiro has reproduced both winter-spring and spring-summer events related to the lagoon water quality as well as its main pattern. Both data and modelling results show that the BOD5 concentrations (where the subscript '5' means that the BOD measurements were conducted for five days, without inhibitor of nitrification) are driven by the river influence, during the winter-spring period, and by the biological activity during the spring-summer period. The DO concentrations show high values in the spring-summer period and smaller concentrations in the winter-spring period at the far end of the lagoon. The application of the model to the study of scenarios has demonstrated the role of nutrients and light in the phytoplankton growth, the relationship between DO and phytoplankton concentrations, as well as the effect of the BOD degradation in the ammonia (NH4) regeneration.

Environmental Monitoring↗
PubMed2004

Influence of long-term diesel fuel pollution on nitrite-oxidising activity and population size of nitrobacter spp in soil.

Previous investigations have shown that ammonia oxidation is not inhibited by diesel fuel in a soil with a long history of contamination contrary to a non-contaminated soil. As a consequence, ammonia oxidation does not constitute a Limited step in nitrification process (Appl. Environ. Microbiol. 65 (1999) 4008). Moreover, this type of soil also has had the opportunity to develop an abundant microbial population able to metabolise the diesel hydrocarbons. Whether the properties of soil with a long history of diesel fuel contamination may affect the activity of nitrite-oxidising bacteria was investigated. It was observed that re-exposure of soil to diesel fuel apparently stimulated the proliferation of nitrite-oxidising bacteria, as determined by most probable number (MPN) culture technique and MPN-polymerase chain reaction technique. The potential of nitrite-oxidising activity in soil treated with diesel fuel was about 4 times higher than in the control without addition. In the presence of diesel fuel and ammonium, the potential nitrite-oxidising activity was 40% higher than in presence of ammonium only. However, in the presence of hydrocarbon only, low proliferation of Nitrobacter was observed, probably because the heterotrophic bacteria were strongly limited by lack of nitrogen and did not produce sufficient organic metabolites that could be used by the Nitrobacter cells.

Ecosystem↗
PubMed2005

Environmental pH as an important factor for the distribution of urease positive ammonia-oxidizing bacteria.

The effect of pH on ureolytic activity of a number of chemolithotrophic ammonia-oxidizing bacteria (AOB) has been studied in context with distribution patterns of these species. The pH-optima for urea-based nitrification were found to differ clearly among the examined species. Pronounced optima ranged between pH 5.0 and 8.0. Urease is an intracytoplasmic enzyme and should therefore be independent of the external pH. Our first results indicated the presence of a pH-dependent uptake system for urea. Simultaneous oxidation of free ammonia, possible only at high pH values, led to a strong intensification of ureolysis. The lag-phase of growth on urea as the sole energy source was clearly prolonged compared to free ammonia. Our results point on the existence of an active, most likely energy-linked urea-uptake system in addition to a possible passive diffusion of urea. The different pH-optima of urea-uptake agree with known distribution patterns of distinct AOB. It might be a reason for the shift of dominant Nitrosospira populations along pH gradients in acid soils as observed by others in molecular analyses of natural AOB populations.

Ammonia↗
PubMed2004

Purification capacity of a highly loaded laboratory scale tidal flow reed bed system with effluent recirculation.

The purification capacity of a laboratory scale tidal flow reed bed system with final effluent recirculation at a ratio of 1:1 was investigated in this study. In particular, the four-stage reed bed system was heavily loaded with strong agricultural wastewater. Under the hydraulic and organic loading rates of 0.43 m3/m2.d and 1055 gCOD/m2.d, respectively, the average removal efficiencies obtained for COD, BOD5, SS, NH4-N and P were 77%, 78%, 66%, 62% and 38%, respectively. Even with the high loading rates, approximately 30% of NH4-N was converted into NO2-N and NO3-N from the mid-stage of the system where nitrification took place. The results suggest that the multi-stage reed bed system could be employed to treat strong wastewater under high loading, especially for the substantive mass removal of solids, organic matter and ammoniacal-nitrogen. Tidal flow combined with effluent recirculation is a favourable operation strategy to achieve this objective.

Agriculture↗
PubMed2005

Distribution of estrogens, 17beta-estradiol and estrone, in Canadian municipal wastewater treatment plants.

The distribution of female hormones, 17beta-estradiol and estrone, was determined in effluents of 18 selected municipal treatment plants across Canada. Replicate 24-h composite samples were collected from the influent and final effluent of each treatment plant, and the removal efficiency compared to the operational characteristics of the plants. In conventional activated sludge and lagoon treatment systems, the mean concentrations of 17beta-estradiol and estrone in influent were 15.6 ng/l (range 2.4-26 ng/l) and 49 ng/l (19-78 ng/l). In final effluents, the mean concentrations of both 17beta-estradiol and estrone were reduced to 1.8 ng/l (0.2-14.7 ng/l) and 17 ng/l (1-96 ng/l), respectively. 17beta-estradiol was removed effectively, >75% and as high as 98%, in most of the conventional mechanical treatment systems with secondary treatment. The removal of estrone was much more complex with removal varying from 98% to situations where the concentrations in the effluent were elevated above that detected in the influent. The estrogenicity, measured using a transfected estrogen receptor in yeast (YES) assay, was also variable, ranging from high removal to elevations of estrogenicity in final effluent. Although the apparent removals were not statistically correlated with either hydraulic (HRT) or solid (SRT) retention times, plants or lagoons with high SRT were very effective at reducing the levels of hormones. Well-operated plants that achieved nitrification also tended to have higher removal of hormones than those that did not nitrify. Laboratory aerobic reactor experiments confirmed the rapid removal of 17beta-estradiol, estrone, and estrogenicity when exposed to sewage slurries.

Biological Assay↗
PubMed2005

Nutrient and organic carbon trends and patterns in the upper Rio Grande, 1975-1999.

Nutrient patterns and trends were analyzed using USGS water quality data collected from 1975 to 1999 along the uppermost 600 km of the Rio Grande in Colorado and New Mexico. Data on discharge, pH, organic carbon (total), N-NH(4+)+organic N (total), NH4+ (dissolved), N-NO(2-)+N-NO3- (dissolved), phosphorus (total), and P-orthophosphate (dissolved) came from six USGS stations--Lobatos, Taos Junction, Otowi, San Felipe, Isleta and Bernardo--ranging from the Colorado-New Mexico border to about 80 km below Albuquerque, NM. Kendall's S and Seasonal Kendall's S' were used to measure trend, and ANOVA and Tukey's multiple comparison test were used to analyze spatial differences between stations. Temporal trend analyses show widespread decreases in N and P concentrations at most stations, likely due to improvements in sewage treatment and dilution from increasing discharge. N-NO(2-)+N-NO3- (dissolved) and total nitrate load increases at Isleta and Bernardo, likely due to improved nitrification in sewage treatment and to increasing human population. Spatial analyses show large increases for most parameters at Isleta. All parameters show decreases again at Bernardo, about 50 km downstream from Isleta, except for N-NO(2-)+N-NO3- (dissolved), which continues to increase. Urbanization in the Albuquerque area significantly impacts downstream river nutrient levels.

Colorado↗
PubMed2006

Short- and medium-term effects of three fire fighting chemicals on the properties of a burnt soil.

The impact of three fire fighting chemicals (FFC) on 11 chemical soil properties and on soil recovery (0-2 cm depth) was evaluated 1, 30, 90 and 365 days after a prescribed fire. Five treatments were considered: unburnt soil (US) and burnt soil with 2 l m(-2) of water alone (BS) or mixed with the foaming agent Auxquímica RFC-88 at 1% (BS+Fo), Firesorb at 1.5% (BS+Fi) and FR Cross ammonium polyphosphate at 20% (BS+Ap). At t=1 day, soil pH increases in the order US<BS</=BS+Fo, BS+Fi<BS+Ap, which was most likely due to the accumulation of ashes, the reduction of organic acids and the cations supplied by FFC. In all burnt treatments, soil pH remained significantly higher than in US up until t=90 days. SOM richness remained similar and constant until t=90 days in all plots, but, probably due to fire-triggered erosion, at t=365 days it was significantly lower in BS+Ap (C, N), BS and BS+Fo (C) than in US. Immediately after the fire, soil delta(15)N decreased in all burnt soils (significatively in BS+Ap) due to the inputs of (15)N depleted ashes from leguminous vegetation. Compared with US, soil delta(15)N increased significantly in all burnt plots between t=90 days (30 days in BS+Ap) and t=365 days, suggesting a medium-term fire-triggered increment of N outputs ((15)N depleted). As is habitually the case, there was a transient post-fire increase of NH(4)(+)-N levels (significative for BS+FFC plots) that lasted for 30 (BS, BS+Fo and BS+Fi) to 90 days (BS+Ap). The high initial NH(4)(+)-N levels in BS+Ap (200x that of US; 9-18x those of BS, BS+Fo and BS+Fi), and its persistence can delay the post-fire vegetation recovery due to the toxicity of NH(4)(+) to seeds and seedlings. NO(3)-N levels changed significantly only in BS+Ap between t=30 and t=90 days due to the nitrification of its large NH(4)(+)-N pool. Except in BS+Ap, whose soil P levels were 70-140x (t=1 days) and 10-20x (t=365 days) higher than in the other treatments, available P content in BS and BS+FFC was not significatively higher than in US. The concentrations of available cations in BS and BS+FFC were higher (not always significatively, except for K) than in US until t=90 days, likely due to ashes- and FFC-derived cations. Contrarily to divalent cations, monovalent cations (more soluble and easily leached) decreased slowly until t=90 days.

Cations↗
PubMed2006

Removal of nutrients in various types of constructed wetlands.

The processes that affect removal and retention of nitrogen during wastewater treatment in constructed wetlands (CWs) are manifold and include NH(3) volatilization, nitrification, denitrification, nitrogen fixation, plant and microbial uptake, mineralization (ammonification), nitrate reduction to ammonium (nitrate-ammonification), anaerobic ammonia oxidation (ANAMMOX), fragmentation, sorption, desorption, burial, and leaching. However, only few processes ultimately remove total nitrogen from the wastewater while most processes just convert nitrogen to its various forms. Removal of total nitrogen in studied types of constructed wetlands varied between 40 and 55% with removed load ranging between 250 and 630 g N m(-2) yr(-1) depending on CWs type and inflow loading. However, the processes responsible for the removal differ in magnitude among systems. Single-stage constructed wetlands cannot achieve high removal of total nitrogen due to their inability to provide both aerobic and anaerobic conditions at the same time. Vertical flow constructed wetlands remove successfully ammonia-N but very limited denitrification takes place in these systems. On the other hand, horizontal-flow constructed wetlands provide good conditions for denitrification but the ability of these system to nitrify ammonia is very limited. Therefore, various types of constructed wetlands may be combined with each other in order to exploit the specific advantages of the individual systems. The soil phosphorus cycle is fundamentally different from the N cycle. There are no valency changes during biotic assimilation of inorganic P or during decomposition of organic P by microorganisms. Phosphorus transformations during wastewater treatment in CWs include adsorption, desorption, precipitation, dissolution, plant and microbial uptake, fragmentation, leaching, mineralization, sedimentation (peat accretion) and burial. The major phosphorus removal processes are sorption, precipitation, plant uptake (with subsequent harvest) and peat/soil accretion. However, the first three processes are saturable and soil accretion occurs only in FWS CWs. Removal of phosphorus in all types of constructed wetlands is low unless special substrates with high sorption capacity are used. Removal of total phosphorus varied between 40 and 60% in all types of constructed wetlands with removed load ranging between 45 and 75 g N m(-2) yr(-1) depending on CWs type and inflow loading. Removal of both nitrogen and phosphorus via harvesting of aboveground biomass of emergent vegetation is low but it could be substantial for lightly loaded systems (cca 100-200 g N m(-2) yr(-1) and 10-20 g P m(-2) yr(-1)). Systems with free-floating plants may achieve higher removal of nitrogen via harvesting due to multiple harvesting schedule.

Biodegradation, Environmental↗
PubMed2006

Evaluating the sources and fate of anthropogenic dissolved inorganic nitrogen (DIN) in two contrasting North Sea estuaries.

Nitrogen isotope ratios (delta(15)N) were used to help elucidate the sources and fate of ammonium (NH(4)(+)) and nitrate (NO(3)(-)) in two northeastern English estuaries. The dominant feature of NH(4)(+) in the heavily urbanised Tyne estuary was a plume arising from a single point source; a large sewage works. Although NH(4)(+) concentrations (ranging from 30-150 microM) near the sewage outfall varied considerably between surveys, the sewage-derived delta(15)N-NH(4)(+) signature was remarkably constant (+10.6+/-0.5 per thousand) and could be tracked across the estuary. As indirectly supported by (15)N-depleted delta(15)N-NO(3)(-) values observed close to the mouth of the Tyne, this sewage-derived NH(4)(+) was thought to initiate lower estuarine and coastal zone nitrification. In the more rural Tweed, NH(4)(+) concentrations were low (<7 microM) compared to those in the Tyne and delta(15)N-NH(4)(+) values were consistent with mixing between riverine and marine sources. The dominant form of dissolved inorganic nitrogen (DIN) in the Tweed was agricultural soil-derived NO(3)(-). A decrease in riverine NO(3)(-) flux during the summer coinciding with an increase in delta(15)N-NO(3)(-) values was mainly attributed to enhanced watershed nutrient processing. In the Tyne, where agricultural inputs are less important compared to the Tweed, light delta(15)N-NO(3)(-) (ca. 0 per thousand) detected in the estuary during one winter survey pointed to a larger contribution from precipitation-derived NO(3)(-) during high river discharge. Regardless of the dominant sources, in both estuaries most of the variability in DIN concentrations and delta(15)N values was explained by simple end-member mixing models, implying very little estuarine processing.

Agriculture↗
PubMed2006

Simulation of the treatment performance of outdoor subsurface flow constructed wetlands in temperate climates.

Numerical models are a means to increase the understanding of the processes occurring in the "black box" constructed wetland. Once reliable models for constructed wetlands are available they can be also used for evaluating and improving existing design criteria. The paper shows simulation results for outdoor experimental subsurface vertical flow constructed wetlands using CW2D, a multi-component reactive transport module developed to simulate transport and reactions of the organic matter, nitrogen and phosphorus in subsurface flow constructed wetlands. The surface area of the experimental vertical flow bed was 20 m(2). The organic load applied was 27 g COD m(-2) d(-1) (corresponding to a specific surface area of 3 m(2) per person). The aim of the work is to calibrate the model for temperature dependency that has been implemented in CW2D. Water temperature during the investigation period varied between 4 degrees C and 18 degrees C. The measured effluent concentrations during summer could be simulated using the standard CW2D parameter set when the flow model was calibrated well. However, the increasing effluent concentrations at low temperatures could not be simulated with the standard CW2D parameter set where temperature dependencies are considered only for maximum growth, decay, and hydrolysis rates. By introducing temperature dependencies for half-saturation constants for the hydrolysis and nitrification processes it was possible to simulate the observed behaviour. The work presented is a step on the way to validate the CW2D module. Model validation is a necessary step before numerical simulation can be finally used in practice, e.g. for checking existing design guidelines.

Computer Simulation↗
PubMed2007

Nitrous oxide emissions from an intensively cultivated maize-wheat rotation soil in the North China Plain.

N2O emissions from a maize-wheat rotation field were monitored in the Fengqiu State Key Agro-Ecological Experimental Station (Fengqiu County, Henan Province, China) from June 2004 to June 2005. The experiment included four treatments: a bare (crop-absent) soil treated with 150 kg N ha-1 (WN150) and soils fertilized with 0 (N0), 150 (N150), and 250 (N250) kg N ha-1 and cropped with maize or wheat. The bulk of the N2O emissions occurred in pulses following the application of fertilizer N at soil temperatures of 15 degrees C or more. The application of fertilizer N significantly increased the N2O emission, from 636 g N2O-N ha-1 year-1 in the N0 treatment to 4480 g N2O-N ha-1 year-1 in the N250 treatment. However, this increase primarily occurred during the maize growing season. The emission factor of applied fertilizer N as N2O was 1.05-1.34% and 0.24-0.26% during the 105-day maize and 241-day wheat growing seasons, respectively, and was on average 0.61-0.77%. Increasing the rate of fertilizer application increased the emission factor during the maize growing season. The presence of maize appears to increase N2O emission by 45% versus bare soil during the maize growing season. And, N2O emission during the maize season were significantly related to CO2 production (R=0.43-0.81, n=30, P<0.05). N2O emission was greatly affected by soil moisture during the maize growing season and by soil temperature during the wheat growing season. The maximum rates of nitrification occurred when soil moisture was in the range of 45-60% WFPS, with the optimum value being approximately 50%. However, soil moisture influenced N2O emission only when the soil temperature was at the optimum level. It is suggested that reducing the application rate of basal fertilizer N during the maize growing season could decrease N2O emission.

Agriculture↗