Nitrogen Mass Balance Research Articles

Infiltration Mechanism Controls Nitrification and Denitrification Processes under Dairy Waste Lagoon

Earthen waste lagoons are commonly used to store liquid wastes from concentrated animal feeding operations. The fate of ammonium (NH) and nitrate (NO) was studied in the vadose zone below earthen-clay dairy farm waste lagoons using three independent vadose zone monitoring systems. The vadose zone was monitored from 0.5 to 30 m below land surface through direct sampling of the sediment porewater and continuous measurement of the sediment profile's water content variations. Four years of monitoring revealed that wastewater infiltration from the lagoon is controlled by two mechanisms: slow (mm d), constant infiltration from the lagoon bed; and rapid (m h) infiltration of wastewater and rainwater via preferential flow in desiccation cracks formed in the unsaturated clay sediment surrounding the lagoon banks. The preferential flow mechanism is active mainly during wastewater-level fluctuations and intensive rain events. The vadose zone below the waste sources remained unsaturated throughout the monitoring period, and all infiltrating NH was oxidized in the upper 0.5 m. The NH oxidation (nitrification) was coupled with NO reduction (denitrification) and depended on the sediment water content, which was controlled by the infiltration mechanism. Coupled nitrification-denitrification (CND) resulted in 90 to 100% reduction in the total nitrogen mass in the vadose zone, with higher removal under high water content (∼0.55 m m). Mass balance of nitrogen and isotopic composition of NO indicated that CND, rather than cation exchange capacity, is the key factor regulating nitrogen's fate in the vadose zone underlying earthen waste lagoons.

Importance of the ammonia volatilization rates in shallow maturation ponds treating UASB reactor effluent

This study aimed at determining the influence of ammonia volatilization on nitrogen removal in polishing (maturation) ponds treating sanitary effluent from upflow anaerobic sludge blanket (UASB) reactors in the city of Belo Horizonte, Brazil. An apparatus for the capture and absorption of volatilized ammonia in three polishing ponds in series was installed. Volatilized ammonia was captured by a chamber on the surface of the ponds and dissolved in boric acid solution, in order to estimate the amount of ammonia per unit surface area of each pond. Low rates of volatilization, below 0.2 kg/ha.d, in about 75% of samples from all the ponds, were observed. The mass balance of ammonia nitrogen of the ponds showed that the volatilization represented only about 2% of the total removal of nitrogen from the polishing ponds. The results obtained suggest that ammonia volatilization was a mechanism of little importance in nitrogen removal in the investigated polishing ponds.

Modeling the potential benefits of catch-crop introduction in fodder crop rotations in a Western Europe landscape

Among possible mitigation options to reduce agricultural-borne nitrate fluxes to water bodies, introduction of catch crop before spring crops is acknowledged as a cost-efficient solution at the plot scale, but it was rarely assessed at the catchment level. This study aims to evaluate a set of catch crop implantation scenarios and their consequences in a coastal catchment prone to eutrophication. The objectives are (i) to discuss the potential benefits of catch crop introduction taking into account the limitations due to the physiographic and agricultural context of the area (ii) to propose a multicriteria classification of these scenarios as a basis for discussion with stakeholders.We used the distributed agro-hydrological model TNT2 to simulate 25 scenarios of catch crop management, differing in length of catch crop growing period, place in the crop rotation and residue management. The scenarios were classified considering the variations in main crop yields and either nitrogen fluxes in stream or the global nitrogen mass balance at the catchment level.The simulations showed that in the catchment studied, little improvement can be expected from increasing the catch crop surface. Catch crop cultivation was always beneficial to reduce nitrogen losses, but led to adverse effects on main crop yields in some cases. Among the scenarios involving additional catch crop surface, introducing catch crop between two winter cereals appeared as the most promising. The classification of scenarios depended on the chosen criteria: when considering only the reduction of nitrogen fluxes in streams, exporting catch crop residues was the most efficient while when considering the global nitrogen mass balance, soil incorporation of catch crop residues was the most beneficial.This work highlights the interest, while using integrated models, of assessing simulated scenarios with multicriteria approach to provide stakeholder with a picture as complete as possible of the consequences of prospective policies.

Nitrogen mass balance in the Brazilian Amazon: an update

The main purpose of this study is to perform a nitrogen budget survey for the entire Brazilian Amazon region. The main inputs of nitrogen to the region are biological nitrogen fixation occurring in tropical forests (7.7 Tg.yr(-1)), and biological nitrogen fixation in agricultural lands mainly due to the cultivation of a large area with soybean, which is an important nitrogen-fixing crop (1.68 Tg.yr(-1)). The input due to the use of N fertilizers (0.48 Tg.yr(-1)) is still incipient compared to the other two inputs mentioned above. The major output flux is the riverine flux, equal to 2.80 Tg.yr(-1) and export related to foodstuff, mainly the transport of soybean and beef to other parts of the country. The continuous population growth and high rate of urbanization may pose new threats to the nitrogen cycle of the region through the burning of fossil fuel and dumping of raw domestic sewage in rivers and streams of the region.

Use of geomorphic, hydrologic, and nitrogen mass balance data to model ecosystem nitrate retention in tidal freshwater wetlands

Abstract. Geomorphic characteristics have been used as scaling parameters to predict water and other fluxes in many systems. In this study, we combined geomorphic analysis with in-situ mass balance studies of nitrate retention (NR) to evaluate which geomorphic scaling parameters best predicted NR in a tidal freshwater wetland ecosystem. Geomorphic characteristics were measured for 267 individual marshes that constitute the freshwater tidal wetland ecosystem of the Patuxent River, Maryland. Nitrate retention was determined from mass balance measurements conducted at the inlets of marshes of varying size (671, 5705, and 536 873 m2) over a period of several years. Mass balance measurements indicate that NR is proportional to total water flux over the tidal cycle. Relationships between estimated tidal prism (calculated water volume) for spring tides and various geomorphic parameters (marsh area, total channel length, and inlet width) were defined using measurements from air photos and compared to field data. From these data, NR equations were determined for each geomorphic parameter, and used to estimate NR for all marshes in the ecosystem for a reference spring (high) tide. The resulting ecosystem NR estimates were evaluated for (a) accuracy and completeness of geomorphic data, (b) relationship between the geomorphic parameters and hydrologic flux, and (c) the ability to adapt the geomorphic parameter to varying tidal conditions. This analysis indicated that inlet width data were the most complete and provided the best estimate of ecosystem nitrate retention. Predictions based on marsh area were significantly lower than the inlet width-based predictions. Cumulative probability distributions of nitrate retention indicate that the largest 3–4% of the marshes retained half of the total nitrate for the ecosystem.

Carbon and nitrogen mass balance during flue gas treatment with Dunaliella salina cultures

The biotreatment of flue gases with algae cultures is a promising option to sequestrate CO2, yet the emission of other greenhouse gases (GHG) from the cultures can hamper their environmental benefit. Quantitative data on the sequestration potential for CO2 and NO (x) in relation to the direct production of CH4 and N2O are urgently required. The present study assessed the flows of carbon (C) and nitrogen (N) through cultures of the green alga Dunaliella salina, supplied with biodiesel flue gas, by means of mass balancing. D. salina was grown in artificially lighted, field- (42-L bubble column reactor) and laboratory-scale cultures (23 A degrees C, pH 7.5). In the bubble column reactor, algae grew with an average specific growth rate of 0.237 day(-1) under flue gas supplementation (6.3 % (v/v) CO2, 1.2 ppmv NO (x) ), and CO2 was retained to 39 % in the system. The specific sequestration rate for CO2 was low, with 0.13 g CO2 L-1 day(-1). Cultures emitted up to 13.03 mu g CH4 L-1 day(-1) and 4261 mu g N2O L-1 day(-1). The moderate retention of NO (x) -N was outweighed by emissions of N2O-N, and total N in the system decreased by 15.48 % during the 9-day trial. Results suggest that GHG production was mainly the outcome of anaerobic microbial processes and their emission was lower in pre-sterilized cultures. Under the tested conditions, up to six times more CO2 equivalents were emitted during flue gas treatment. Therefore, the direct GHG emissions of algae culture systems, intended for flue gas treatment (i.e. open ponds) need to be reviewed critically.

Effects of five macrophytes on nitrogen remediation and mass balance in wetland mesocosms

Five macrophyte species, Carex elata All., (Cae), Juncus effusus L. (Jue), Typhoides arundinacea (L.) Moench (syn. Phalaris arundinacea L.) (Pha) var. picta, Phragmites australis (Cav.) Trin. (Phr), and Typha latifolia L. (Ty), have been grown in mesocosms fed with a synthetic wastewater to acquire information on nitrogen balance and assess their capacity to abate nitrogen. The experiment, conducted during the growing seasons 2008–09 with four replicates, also included an unvegetated control. The mesocosms, filled with gravel, were fed with a solution of 105ppm of NO3–N and 100ppm of NH4–N in 2008 for a cumulative nitrogen load of 86g/m2 and with increased concentration in 2009 from 104ppm of NO3–N and 119ppm NH4–N, to 200ppm of NO3–N and 207ppm of NH4–N for a cumulative nitrogen load of 222g/m2. At the end of the experiment plants were harvested and N content in the above and belowground biomass was determined along with the amount of N contained in the roots and gravel microbial communities.In the first growing season (8 months) Ty removed 82g/m2 (96% of the cumulative load) of TOT N, followed by Cae (94%), Jue (82%), Pha (81%), Phr (77%) and the control (48%). In the second growing season (6 months) all the vegetated treatments, except Jue, increased their efficiency, with Pha removing 216g/m2 (98% of the cumulative load) of TOT N, followed by Phr and Ty (97%), Cae (93%), Jue (75%) and the control (63%). Jue showed lower tolerance than the other species to high N concentration. Depending on the species, plants absorbed 53–75% of the two-seasons load and allocated 51–83% of this amount in the aerial tissues, showing the benefit of harvesting to remove N from the treatment site, at least in the medium short term. Application of the N balance allowed the gaseous losses to be estimated, giving values ranging from 51g/m2 in Ty to 114g/m2 in Pha, 17% and 37% of the total load respectively. If the target is the definitive elimination of the maximum amount of N from the treatment site, the sum of nitrogen harvested in the aerial part and the gaseous losses has to be considered. This value was maximum with Cae, with 227g/m2 over the two years.

Effect of stocking density on soil, water quality and nitrogen budget inPenaeus monodon(Fabricius, 1798) culture under zero water exchange system

Soil and water interactions and their influence on growth and production in different densities (SD8 & SD16) under zero water exchange were studied in two successive crops of Penaeus monodon in Tamil Nadu, India during 2007 and 2008. Scraping and tilling during pond preparation increased the mineralization rate than scraping only. During crop, there was no significant difference in soil organic carbon and total nitrogen between the SDs. However, as the crop progressed, organic carbon and total nitrogen content of the soil showed significant difference under both the SDs. Between the SDs, nitrate and phosphate content in water significantly differed, whereas the progress of the crop significantly increased both available and total nutrients. Mass balance of nitrogen indicated that applied feed contributed to 97.4–98.5% of input nitrogen, of which nitrogen in sediment accounted for 16.5–27.3%, nitrogen recovery in shrimp was 34.2–43.6% and the nitrogen lost through denitrification and volatilization varied from 4.7% to 34.7%. Zero water exchange system is highly efficient as nitrogen recovery is higher in shrimp and lower in discharge water. Lack of significant difference in metabolites between the SDs indicates the role of aeration and probiotics in sustaining SD16 cultures.

Electrochemical Decoloration of Synthetic Wastewater Containing Rhodamine 6G: Behaviors and Mechanism

Dye wastewater has posed a great threat to our aqueous environment. In this study, the treatment of synthetic wastewater containing Rhodamine 6G by electrochemical technology using RuO2-coated Ti mesh as anode was investigated. The effects of solution pH, temperature, and dye auxiliaries on the performance were investigated. Carbon and nitrogen mass balance analyses, UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) were used to elucidate the working mechanism. It was found that lower solution pH and lower temperature facilitated the decoloration of the wastewater. The addition of dye auxiliaries did not significantly affect the decoloration. Under optimal condition, complete decoloration of the synthetic wastewater was obtained within 5 min, and 42.3% of the dye was mineralized. The amine and methyl groups were first detached from the dye molecule, leading to a change in the dye structure from polar into nonpolar to fo...

Reactive Uptake of HONO to TiO2 Surface: “Dark” Reaction

The interaction of HONO with TiO(2) solid films was studied under dark conditions using a low pressure flow reactor (1-10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The reactive uptake of HONO to TiO(2) was studied as a function of HONO concentration ([HONO)(0) = (0.3-3.3) × 10(12) molecules cm(-3)), water concentration (RH = 3 × 10(-4) to 13%), and temperature (T = 275-320 K). TiO(2) surface deactivation upon exposure to HONO was observed. The measured initial uptake coefficient of HONO on TiO(2) surface was independent of the HONO concentration and showed slight negative temperature dependence (activation factor = -1405 ± 110 K). In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficient: γ(0) = 1.8 × 10(-5) (RH)(-0.63) (calculated using BET surface area, 40% uncertainty) at T = 300 K. NO(2) and NO were observed as products of the HONO reaction with TiO(2) surface with sum of their yields corresponding to nearly 100% of the nitrogen mass balance. The yields of the NO and NO(2) products were found to be 42 ± 7% and 60 ± 9%, respectively, independent of relative humidity, temperature, and concentration of HONO under experimental conditions used. The contribution of aerosol to the total HONO loss in the boundary layer (calculated with initial uptake data for HONO on TiO(2) surface) showed the unimportance of this process in the atmosphere. In addition, the diffusion coefficient of HONO in He was determined to be D(HONO-He) = 490 ± 50 Torr cm(2) s(-1) at T = 300 K.

Interaction of NO2 with TiO2 Surface Under UV Irradiation: Products Study

The interaction of NO(2) with TiO(2) solid films was studied under UV irradiation using a low pressure flow reactor (1-10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. HONO, NO, and N(2)O were observed as the products of the reactive uptake of NO(2) to the illuminated TiO(2) surface with the sum of their yields corresponding nearly to 100% of the nitrogen mass balance. The yield of the products was measured as a function of different parameters such as irradiance intensity, relative humidity (RH), temperature, and concentrations of NO(2) and O(2). The yield of N(2)O was found to be 0.15 ± 0.05 independent of the experimental conditions. The distribution of the products between NO and HONO was found to be independent of temperature in the range T = 280-320 K and was governed by relative humidity: increase in RH led to lower NO and higher HONO yield, with a maximum of nearly 65% reached at ~5% RH. Presence of molecular oxygen was shown to shift the HONO/NO distribution to HONO at low RH (<5%) with no effect at higher RH where the HONO yield is maximum. The following values for the yield of the products of NO(2) interaction with pure TiO(2) under real atmospheric conditions can be recommended from this work: 0.65 ± 0.10, 0.05 ± 0.05, and 0.15 ± 0.05 for HONO, NO, and N(2)O, respectively. The mechanism of the photoinitiated heterogeneous reaction and possible atmospheric implications of the obtained results are discussed.

Nitrogen balance and fate in a heavily impacted watershed (Oglio River, Northern Italy): in quest of the missing sources and sinks

Abstract. We present data from a comprehensive investigation carried out from 2007 to 2010, focussing on nitrogen pollution in the Oglio River basin (3800 km2, Po Plain, Northern Italy). Nitrogen mass balances, computed for the whole basin with 2000 and 2008 data, suggest a large N surplus in this area, over 40 000 t N yr−1, and increasing between 2000 and 2008. Calculations indicate a very large impact of animal husbandry and agricultural activities in this watershed, with livestock manure and synthetic fertilizers contributing 85% of total N inputs (about 100 000 t N yr−1) and largely exceeding crop uptake and other N losses (about 60 000 t N yr−1). Nitrogen from domestic and industrial origin is estimated as about 5800 and 7200 t N yr−1, respectively, although these loads are overestimated, as denitrification in treatment plants is not considered; nonetheless, they represent a minor term of the N budget. Annual export of nitrogen from the basin, calculated from flow data and water chemistry at the mouth of the Oglio River, is estimated at 13 000 t N yr−1, and represents a relatively small fraction of N inputs and surplus (∼12% and 34%, respectively). After considering N sinks in crop uptake, soil denitrification and volatilization, a large excess remains unaccounted (∼26 000 t N yr−1) in unknown temporary or permanent N sinks. Nitrogen removal via denitrification was evaluated in the Oglio riverbed with stable isotope techniques (δ15N and δ18O in nitrate). The downstream final segment of the river displays an enriched nitrate stable isotope composition but calculations suggest a N removal corresponding to at most 20% of the unaccounted for N amount. Denitrification was also evaluated in riverine wetlands with the isotope pairing technique. Areal rates are elevated but overall N removal is low (about 1% of the missing N amount), due to small wetland surfaces and limited lateral connectivity. The secondary drainage channel network has a much higher potential for nitrogen removal via denitrification, due to its great linear development, estimated in over 12 500 km, and its capillary distribution in the watershed. In particular, we estimated a maximum N loss up to 8500 t N yr−1, which represents up to 33% of the unaccounted for N amount in the basin. Overall, denitrification in surface aquatic habitats within this basin can be responsible for the permanent removal of about 12 000 t N yr−1; but the fate of some 14 000 t remains unknown. Available data on nitrate concentration in wells suggest that in the central part of the watershed groundwater accumulates nitrogen. Simultaneously, we provide evidences that part of the stored nitrate can be substantially recycled via springs and can pollute surface waters via river-groundwater interactions. This probably explains the ten fold increase of nitrate concentration in a reach of the Oglio River where no point pollutions sources are present.

Fate of nitrogen during volume reduction of human urine using an on-site volume reduction system

This study was carried to assess the effect of a mixture of salts, urea and creatinine on water evaporation from urine using an on-site volume reduction system in long-term experiments. Subsequently, the fate of nitrogen during volume reduction of urine was also assessed. The water evaporation rate, salt accumulation in the gauze sheet, concentrations of urea and ammonia-N, and pH of urine were measured periodically. Based on the results, a mass balance of nitrogen in concentrated urine was calculated for a moderate evaporating condition. The results revealed that steady-state evaporation was observed throughout the experiment period without any inhibition due to salt accumulation. Salt concentration in the gauze sheet reached steady-state illustrating the possibility of salt falling back to the tank from the sheet. No significant reduction of urea was observed for a moderate evaporating condition, which indicates inhibition of urea hydrolysis by the high concentration of the mixture of salts, urea and creatinine in the urine. In contrast, for a low evaporating condition, the pH of the urine increased to 8.9, which indicates early urea hydrolysis, causing an offensive odour and ammonia loss to the air. In simple storage experiments, a mixture of salts, urea and creatinine amounting to 227–334 g L−1 in urine inhibited urea hydrolysis, even with faecal contamination, at 25°C, while urine samples containing a mixture of salts, urea and creatinine at less than 227 g L−1 did not provide strong inhibition of hydrolysis.

Simulation of the Anaerobic Digestion of Microwave Pre-Treated Waste Activated Sludge with ADM1

AbstractThe disposal of sludge originating from municipal waste water treatment is a major issue and represents up to 50% of the operating costs of wastewater treatment plants (WWTP). (Appels et al., 2008) This sludge, a by-product of the treatment processes, however, has the potential to be converted into an energy rich biogas, i.e. a mixture of ca. 65% CH4 and 35% CO2, which can be utilized for the sustainable production of heat and/or electricity. Various pre-treatment methods have been suggested in literature for improving the solids reduction and biogas production rate by enhancing the digestion's rate limiting step, i.e. organic matter hydrolysis. They all induce the solubilization of complex particulate matter so this is more rapidly and completely consumed during the anaerobic digestion process. Methods that have been shown to have a positive effect on anaerobic digestion include chemical, mechanical, biological and thermal processes. Microwave disintegration is one of the more recently applied pre-treatment methods. The disintegration is caused by the combination of thermal and athermal effects and may hence provide superior results compared to a heat treatment (Eskicioglu et al., 2007).The application of mathematical models for the optimization of the digestion process is widely acknowledged. Due to the complexity of the microbial process, accurate modelling of anaerobic digestion is, however, a daunting task. A major stride countering this problem was achieved by the development of the Anaerobic Digestion Model no 1 (ADM1) by the corresponding IWA task group (Batstone et al. 2002). This model is ever since, considered to be the state of the art in modelling of anaerobic digestion and has been the platform for further refinements and numerous applications (Batstone et al. 2006).The main aim of this work is to investigate the ability of ADM1 to describe anaerobic digestion of microwave pre-treated sludge. Compared to untreated sludge, the composition and structure of the sludge is changed dramatically due to the treatment. The recorded data and digester performances were compared with the results of a modelling in ADM1 (Batstone et al., 2002). Practically, the ADM1 implementation as described by Rosen & Jeppsson (Rosen and Jeppsson (2005)) is chosen as it effectively completes the mass balance for COD, carbon and nitrogen.

Transport and Fate of Nitrogen-Containing Compounds in Gas-Phase Biofilters: A Swing Test to Mitigate Ammonia

This work carried out a three-month experiment to study the transport, transformation, and fate of nitrogen (N) in two gas-phase ammonia mitigation biofilters using agricultural products (a mixture of wood chips and compost) as the packing media. Two nitrogen enriching steps and one nitrogen depleting step were included as a swing test. In the first nitrogen enriching step, a high ammonia inlet concentration (~70 ppm) was applied. The ammonia removal efficiencies reached 94%, and 73.5% to 86.6% of N-NH3 was transformed into NH4+-N, NO2--N, or NO3--N. The nitrogen depleting step partially cleaned nitrogen compounds with limited disturbance to the media and restored ammonia removal efficiency for a short time. The second nitrogen enriching step used a lower (40 ppm) ammonia inlet concentration. Only 33.4% to 46.2% of NH3-N was transformed into NH4+-N, NO2--N, or NO3--N in the media, and the ammonia removal efficiency fell quickly after ten days. The pH values in the biofilter media were high and changed only slightly during the test (8.5 to 8.2). The free ammonia concentration reached 784 mg L-1 in the media moisture. The nitrogen mass balance analysis showed that the NH4+-N, NO2--N, and NO3--N accumulated in the media accounted for 50% to 100% of the nitrogen captured from the inlet gas. The nitrification process was modeled as consecutive first-order reactions. The kinetic time constants of the two first-order reactions decreased with time and with accumulated nitrogen in the media, suggesting a decline of the nitrogen transformation rates. One very likely reason that caused the decrease of ammonia removal efficiency and kinetic time constants is the accumulated free ammonium in the biofilter media.

Waste stabilization mechanism by a recirculatory semi-aerobic landfill with the aeration system

The main purpose of this research is to clarify and compare the mechanism of waste stabilization by a recirculatory semi-aerobic landfill with the aeration system. Our research is proposing the semi-aerobic landfill system for developing countries because of the simple and low-cost technology for the final disposal. Moreover, this system with leachate recirculation can be a more effective system for waste stabilization because of the improvement of leachate quality as an organic pollutant and, also, nitrogen removal. In this research, five different systems of landfill (Ae: aerobic, An: anaerobic, Se: semi-aerobic, SeR: recirculatory semi-aerobic landfill, and SeRA: recirculatory semi-aerobic landfill with aeration system) are compared with lysimeters which are 1 m high with a diameter of 0.3 m. The results of the leachate quality shows that the leachate treatment effect of the SeRA system can be observed to be as high as the Ae system. To determine the mechanism of this process, all lysimeters are dismantled after 1,100 days in the experimental period and the waste composition, the dissolution test, the mass balance of carbon and nitrogen, the determination of bacterial counts, etc., were analyzed. In this research, it was proven that the SeRA system has an optimal leachate treatment effect that is the same as the Ae system. And, from the results of the mass balance of carbon and nitrogen, the SeR and SeRA systems show higher waste stabilization effectiveness and nitrogen removal than the other systems. Moreover, the number of the aerobic bacteria can be observed to be higher in the SeR and SeRA systems. To determine these results, the waste stabilization mechanism is considered by the results of leachate quality, the mass balance of carbon and nitrogen, and, also, the bacterial numbers.

Effects of exogenous enzymes on apparent nutrient digestibility in rainbow trout (Oncorhynchus mykiss) fed diets with high inclusion of plant-based protein

Plant-based protein ingredients are increasingly used in feed for carnivorous fish as replacement for fish meal. This study investigated if supplementing diets with high inclusion levels of plant-based protein with three different enzymes could improve the apparent nutrient digestibility in juvenile rainbow trout (Oncorhynchus mykiss). Three diets with high inclusion levels of either de-hulled, solvent extracted soybean meal (344g/kg), sunflower meal (246g/kg), or rapeseed meal (264g/kg) were produced and feed batches were coated post-extrusion with the different enzymes: β-glucanase at 67mg/kg, xylanase at 208mg/kg, protease at 228mg/kg, or a combination of the three enzymes at the same doses. Three consecutive digestibility trials were carried out using a flow-through, modified Guelph System. Each trial was designed to include five dietary treatment groups: a non-supplemented control diet and 4 diets supplemented with either β-glucanase, xylanase, protease or a combination of the three enzymes. Diets were fed to triplicate tanks and two faecal sampling periods for digestibility measurements for each tank were scheduled. Each experiment comprised a 10-day digestibility trial succeeded by a water sampling period for measuring the dissolved nitrogen (N) output. Each experiment lasted 17–19 days in total.Apparent digestibility coefficients (ADCs) of protein, fat, ash, phosphorus and dry matter (DM) were derived from the three digestibility trials, along with calculations of the specific growth rate (SGR, %/d) and feed conversion ratio (FCR). Nitrogen mass-balance and energy retention were evaluated for each dietary treatment group to elucidate on the utilization of digested nutrients and energy.Enzyme supplementation had only moderate effect on apparent nutrient digestibility in the sunflower and rapeseed experiments, while β-glucanase and protease improved the apparent digestibility of all dietary nutrients in the soybean experiment (P<0.05). The effect was more pronounced for lipid than for other nutrients. β-Glucanase had a positive effect on energy retention in the soybean experiment (P<0.05), while there were no effects on nitrogen retention or fish performance in any of the three experiments (P>0.05) during the short feeding periods. The study thus provides preliminary results on the potential of β-glucanase and protease to increase apparent nutrient digestibility of soybean meal in fish feed.

Soil Budget, Net Export, and Potential Sinks of Nitrogen in the Lower Oglio River Watershed (Northern Italy)

AbstractA nitrogen mass balance, realized for the lower Oglio River basin (Po River Plain, northern Italy), suggested an elevated impact of agricultural activities in this watershed. Livestock manure, synthetic fertilizers, biological fixation, atmospheric deposition, and wastewater sludge contributed 51, 34, 12, 2, and 1% of total N (TN) input, respectively (basin average 450 kg N ha−1 arable land (AL) year−1, overall input 100 115 t N year−1). Crop uptake, ammonia volatilization and denitrification in soils contributed 65, 21, and 14%, respectively, of TN output (basin average 270 kg N ha−1 AL year−1, overall output 60 060 t N year−1). N inputs exceeded outputs by 40 056 t N year−1, resulting in a basin average surplus of about 180 kg N ha−1 AL year−1. About 34% of the N surplus was exported annually from the basin while the remaining amount (about 26 800 t N year−1) underwent other unaccounted for processes within the watershed.The relevance of nitrogen removal via denitrification in aquatic compartments within the watershed was evaluated. Denitrification in the secondary drainage network can represent a relevant nitrogen sink due to great linear extension (over 12 500 km), with estimated nitrogen loss up to 8500 t N year−1. Denitrification in the riverbed and in perifluvial wetlands have the potential to remove only a small fraction of the nitrogen surplus (&lt;3%). Evidence suggests the relevance of groundwater as a site of nitrogen accumulation.

Seasonal Changes of Nitrogen and Phosphorus Content of Aquatic Plant (Zizania latifolia) and Mass Balance of Nitrogen and Phosphorus in the Water Culture System of Zizania latifolia

Seasonal Changes of Nitrogen and Phosphorus Content of Aquatic Plant (Zizania latifolia) and Mass Balance of Nitrogen and Phosphorus in the Water Culture System of Zizania latifolia

Effects of Organic Carbon Addition in Controlling Inorganic Nitrogen Concentrations in a Biofloc System

The daily addition of tilapia feed and tapioca starch at the C : N weight ratio of 16:1 was conducted to examine the effectiveness of biofloc‐mediated assimilation and nitrification in the zero‐water exchange tilapia cultivation tanks. Inorganic nitrogen concentrations in treatment tanks receiving feed and tapioca starch indicated profiles, which resembled the start‐up of biofilters. Assimilation was essential for the control of inorganic nitrogen concentrations prior to the occurrence of complete nitrification as confirmed by an increase in suspended solids concentration from 52 to 1180 mg SS/L, a slower rate of total ammonia nitrogen (TAN) and nitrite accumulation, and lower concentrations of TAN and nitrite relative to those in control tanks receiving only feed addition. Effective control of inorganic nitrogen concentrations (i.e., TAN and NO2‐N &lt;1.0 mg N/L) was observed in both systems when complete nitrification was established after approximately 6–7 wk regardless of starch supplementation. Results from the nitrogen mass balance suggested that nitrification and, to a lesser extent, assimilation were responsible for inorganic nitrogen control in treatment tanks.