Changes In Ammonia Concentrations Research Articles

Regime shift in secondary inorganic aerosol formation and nitrogen deposition in the rural United States

Secondary inorganic aerosols play an important role in air pollution and climate change, and their formation modulates the atmospheric deposition of reactive nitrogen (including oxidized and reduced nitrogen), thus impacting the nitrogen cycle. Large-scale and long-term analyses of secondary inorganic aerosol formation based on model simulations have substantial uncertainties. Here we improve constraints on secondary inorganic aerosol formation using decade-long in situ observations of aerosol composition and gaseous precursors from multiple monitoring networks across the United States. We reveal a shift in the secondary inorganic aerosol formation regime in the rural United States between 2011 and 2020, making rural areas less sensitive to changes in ammonia concentrations and shortening the effective atmospheric lifetime of reduced forms of reactive nitrogen. This leads to potential increases in reactive nitrogen deposition near ammonia emission hotspots, with ecosystem impacts warranting further investigation. Ammonia (NH3), a critical but not directly regulated precursor of fine particulate matter in the United States, has been increasingly scrutinized to improve air quality. Our findings, however, show that controlling NH3 became significantly less effective for mitigating fine particulate matter in the rural United States. We highlight the need for more collocated aerosol and precursor observations for better characterization of secondary inorganic aerosols formation in urban areas.

Mathematical modeling of ammonia emission rate in newly constructed buildings

A rapid growth in monolithic residential construction over recent decades has created a problem associated with ammonia contamination inside newly constructed buildings. Absence of substantiated preventive actions aimed at minimizing ammonia emissions hinders commissioning of new residential buildings and may create an unfavorable sanitary-epidemiological situation with obvious olfactory-reflex and irritating effects on public health. The aim of this study was to develop a scientifically grounded method to predict when ammonia concentrations emitted from concrete constructions would reach their permissible levels in air inside contaminated premises in newly constructed buildings. Ammonia emissions were estimated based on data of laboratory tests that involved analyzing indoor air samples taken in Saint Petersburg and the Leningrad region. Indoor air was analyzed in 4 newly constructed residential buildings (165 premises, 57 test protocols, 893 air samples tested to identify ammonia in them). Relationships between changes in ammonia concentrations and ventilation time were obtained by using regression analysis (regression equation, least square method). To establish reproducibility of the results and a possibility to compare them, we tested variances for homogeneity by using Fisher criterion. Sampled populations were compared with Student’s t-test in case the data fitted to a normal distribution (Kolmogorov – Smirnov test, Shapiro – Wilks test). Critical significance was taken at 0.05 in all the statistical comparisons. We have developed a method for predicting when ammonia concentrations that occurred in indoor air inside newly constructed buildings due to multi-day emissions from building materials would reach their permissible levels. The method involves multi-day measurements (y, mg/m3) of ammonia concentrations sequentially in each premise inside a newly constructed building on any day of measurements during the time period t; building up relationships between averaged ammonia concentrations (yav, mg/m3) and a time moment t; mathematical analysis of the obtained relationships by parameterization and statistical analysis of the obtained kinetic parameters.

Математическое моделирование скорости эмиссии аммиака во вновь выстроенных зданиях

A rapid growth in monolithic residential construction over recent decades has created a problem associated with ammonia contamination inside newly constructed buildings. Absence of substantiated preventive actions aimed at minimizing ammonia emissions hinders commissioning of new residential buildings and may create an unfavorable sanitary-epidemiological situation with obvious olfactory-reflex and irritating effects on public health. The aim of this study was to develop a scientifically grounded method to predict when ammonia concentrations emitted from concrete constructions would reach their permissible levels in air inside contaminated premises in newly constructed buildings. Ammonia emissions were estimated based on data of laboratory tests that involved analyzing indoor air samples taken in Saint Petersburg and the Leningrad region. Indoor air was analyzed in 4 newly constructed residential buildings (165 premises, 57 test protocols, 893 air samples tested to identify ammonia in them). Relationships between changes in ammonia concentrations and ventilation time were obtained by using regression analysis (regression equation, least square method). To establish reproducibility of the results and a possibility to compare them, we tested variances for homogeneity by using Fisher criterion. Sampled populations were compared with Student’s t-test in case the data fitted to a normal distribution (Kolmogorov – Smirnov test, Shapiro – Wilks test). Critical significance was taken at 0.05 in all the statistical comparisons. We have developed a method for predicting when ammonia concentrations that occurred in indoor air inside newly constructed buildings due to multi-day emissions from building materials would reach their permissible levels. The method involves multi-day measurements (y, mg/m3) of ammonia concentrations sequentially in each premise inside a newly constructed building on any day of measurements during the time period t; building up relationships between averaged ammonia concentrations (yav, mg/m3) and a time moment t; mathematical analysis of the obtained relationships by parameterization and statistical analysis of the obtained kinetic parameters.

Detection of NH3 in poultry housing based on tunable diode laser absorption spectroscopy combined with a micro circular absorption cell

Accurate monitoring of ammonia has decisive significance for the environmental control of poultry housing. Existing sensors based on semiconductor or electrochemistry have the defects of short life, severe baseline drift and delayed response when facing the harsh environment of poultry housing. In this work, we developed a portable sensor based on tunable diode laser absorption spectroscopy with a micro circular absorption cell for sensitive detection of ammonia in poultry housing. The micro circular absorption cell has a volume of only 25 ml, but the effective absorption path is up to 5 m, which allows the sensor to achieve the ability of less than 15 s response time and 0.2 ppm measurement accuracy. The results of continuous monitoring for 6 days showed that the ammonia concentration in the range of 0–6 ppm was accurately detected in a poultry house with 36 roosters. Through analyzing dynamic changes in ammonia concentration, we successfully identified some abnormal activity caused by humans or weather. Therefore, our sensor has performances of accurate, stable, real-time measurement of ammonia and can provide strong technical support for environmental control of poultry housing.

Influence of Micro- and Macrostructure of Atomised Water Jets on Ammonia Absorption Efficiency

Ammonia has a very wide range of applications. Its worldwide production exceeds 230 million tonnes per year. Due to its properties, ammonia causes a serious threat to human life and health when released uncontrolled into the environment. Research carried out in the word shows that this substance may be effectively neutralised by absorption in water. The aim of research described in this paper is to determine the influence of key parameters of the micro- and macrostructure of water streams on the course of the ammonia absorption process. During the studies, different types of water nozzles were used, with similar efficiency and supply pressure, but characterised by different parameters of the micro- and macrostructure of the produced stream. The experiments were divided into two stages. In the first one, the macro- and microparameters of the streams were measured, while in the second one, the changes in ammonia concentration were established during delivering spray jet generation by different nozzles. Among the basic parameters of the macrostructure, the spray angle and liquid distribution in the jet (spray intensity) were determined, while for the microstructure, the droplet size distribution and mean droplet diameters were measured. Ammonia concentration was measured by means of a photoionisation detector (PID). In order to evaluate the absorption efficiency of different water spray jets, the apparent absorption rate (kp) and the half-time of concentration reduction (t½) in the kinetic range were established. The study has confirmed that atomised water jets are an effective method for neutralising ammonia released into the environment. The research has a practical aspect and shows that the structure of atomised water streams influence the course of the absorption process. Increasing the spray angle in a conical stream leads to an improvement in the quality of water atomisation and helps increase ammonia absorption. Moreover, it was also observed that for the absorption of spatial ammonia clouds, use should be made of nozzles generating streams with full spray cones and high uniformity of spray and dispersion.

Modeling of Environmental Pollution by Ammonia Emission from a Damaged Pipeline

Purpose. This work provides for the development of a hydraulic model for calculating the unsteady ammonia outflow from a damaged pipeline and the implementation of this model into a numerical model for predicting emergency air pollution. Methodology. To solve the problem, the calculated dependencies of the pressure flow hydraulics were used. An empirical model to calculate the evaporation of ammonia from a damaged pipeline was also used. To calculate the process of spreading ammonia in atmospheric air, a three-dimensional equation of convective-diffusion transfer of impurities was used. Mathematical modeling of the spread of ammonia from a damaged pipeline takes into account the change with height of the wind flow velocity, as well as the change with height of the vertical coefficient of atmospheric diffusion, the dynamics of changes over time in the intensity of ammonia leakage from the damaged pipeline. For the numerical solution of the three-dimensional differential equation for the transfer of ammonia in atmospheric air, its physical splitting is carried out: an equation that describes the transport of an impurity due to convection is singled out separately, an equation that describes the transport of an impurity due to atmospheric diffusion and separately an equation that describes a change in the ammonia concentration in air due to the action of the emission source. The McCormack method is used to numerically integrate the equation for the convective transfer of ammonia in air. The Richardson method is used to numerically integrate the equation of diffusion transfer of an impurity. The Euler method is used to numerically integrate the equation that describes the change in ammonia concentration under the influence of an emission source. Findings. Based on the developed model of unsteady ammonia outflow from the damaged pipeline and the created numerical model of ammonia propagation in the atmospheric air, a computational experiment was carried out to assess the level of atmospheric air and underlying surface pollution in the event of an emergency ammonia outflow in the section where the Tolyatti – Odessa ammonia pipeline crosses the Dnipro River. Data on non-stationary environmental pollution were obtained. Originality. A mathematical model that allows calculating the unsteady process of ammonia outflow from a damaged pipeline has been developed. A numerical model is proposed to determine the areas of contamination during an emergency ammonia outflow from the Tolyatti – Odessa ammonia pipeline. Practical value. Based on the developed model, a code has been created that makes it possible to promptly predict the environmental pollution dynamics during an emergency ammonia outflow. The proposed mathematical model can be used in the development of emergency response plan for chemically hazardous facilities.

Flexible ammonia sensor integrated with polyaniline/zinc oxide/graphene composite membrane materials

In this work, three composite membrane materials based on polyaniline (PANI), zinc oxide (ZnO), and graphene were fabricated using chemical oxidative polymerization and integrated with interdigitated electrodes on the flexible printed circuit of an ammonia sensor. This flexible ammonia sensor operates based on changes in membrane resistance with changes in ammonia concentration. The surface morphology and elemental analysis of the sensing composite materials were observed through scanning electron microscopy and energy-dispersive spectroscopy, respectively. The characteristics of the ammonia sensor, such as the thickness effect, response, response time, recovery time, repeatability, and selectivity, were investigated. The planar structure of graphene effectively increased the specific surface ratio and gas reaction surface of the sensor. The fabricated PANI/ZnO/graphene ammonia sensor achieved the highest response of 205% at an ammonia concentration of 20 ppm.

Quantitative analysis of ammonia adsorption in Ag/AgI-coated hollow waveguide by mid-infrared laser absorption spectroscopy

The adsorption effect of ammonia gas molecules on the inner surface of silver and silver iodide-coated hollow waveguides (Ag/AgI-HWGs) was studied by using a direct absorption spectrometry system with a 9.56-µm quantum cascade laser as the light source. The dynamic changes in ammonia concentration in the Ag/AgI-HWG during the process of NH3 influx and N2 purge were measured with a high time resolution. The adsorption and desorption processes of ammonia were quantitatively analyzed. The results indicate that the density of ammonia molecules adsorbed on the inner wall surface of the Ag/AgI-HWG was 1015 molecules/cm2, characterized as multilayer adsorption, and the corresponding F value (a dimensionless number commonly used to characterize influence of the adsorption effect) was about 5.89. The adsorption capacity increased with the pressure and decreased with the temperature, which is consistent with Le Chatelier's principle. The differential heats of adsorption were deduced to be 7.6 and 6.1 kJ/mol for monolayer and multilayer adsorption, respectively, and the Brunauer-Emmett-Teller model was established and agreed well with our measurement results. The adsorption kinetic process also fit well to both the pseudo-first-order and pseudo-second-order kinetic model. This study fills in the gap in the research of Ag/AgI-HWGs adsorption and is meaningful for accurate gas detection using HWG-based spectroscopy systems.

Ammonia-weighted imaging by chemical exchange saturation transfer MRI at 3T.

Hepatic encephalopathy (HE) is triggered by liver cirrhosis and is associated with an increased ammonia level within the brain tissue. The goal of this study was to investigate effects of ammonia on in vitro amide proton transfer (APT)-weighted chemical exchange saturation transfer (CEST) imaging in order to develop an ammonia-sensitive brain imaging method. APT-weighted CEST imaging was performed on phantom solutions including pure ammonia, bovine serum albumin (BSA), and tissue homogenate samples doped with various ammonia concentrations. All CEST data were assessed by magnetization transfer ratio asymmetry. In addition, optical methods were used to determine possible structural changes of the proteins in the BSA phantom. In vivo feasibility measurements were acquired in one healthy participant and two patients suffering from HE, a disease associated with increased brain ammonia levels. The CEST effect of pure ammonia showed a base-catalyzed behavior. At pH values greater than 5.6 no CEST effect was observed. The APT-weighted signal was significantly reduced for ammonia concentrations of 5mM or more at fixed pH values within the different protein phantom solutions. The optical methods revealed no protein aggregation or denaturation for ammonia concentrations less than 5mM. The in vivo measurements showed tissue specific and global reduction of the observed CEST signal in patients with HE, possibly linked to pathologically increased ammonia levels. APT-weighted CEST imaging is sensitive to changes in ammonia concentrations. Thus, it seems useful for the investigation of pathologies with altered tissue ammonia concentrations such as HE. However, the underlying mechanism needs to be explored in more detail in future in vitro and in vivo investigations.

In-situ study of migration and transformation of nitrogen in groundwater based on continuous observations at a contaminated desert site

The objective of this study was to explore the controlling factors on the migration and transformation of nitrogenous wastes in groundwater using long-term observations from a contaminated site on the southwestern edge of the Tengger Desert in northwestern China. Contamination was caused by wastewater discharge rich in ammonia. Two long-term groundwater monitoring wells (Wells 1# and 2#) were constructed, and 24 water samples were collected. Five key indicators were tested: ammonia, nitrate, nitrite, dissolved oxygen, and manganese. A numerical method was used to simulate the migration process and to determine the migration stage of the main pollutant plume in groundwater. The results showed that at Well 1# the nitrogenous waste migration process had essentially been completed, while at Well 2# ammonia levels were still rising and gradually transitioning to a stable stage. The differences for Well 1# and Well 2# were primarily caused by differences in groundwater flow. The change in ammonia concentration was mainly controlled by the migration of the pollution plume under nitrification in groundwater. The nitrification rate was likely affected by changes in dissolved oxygen and potentially manganese.

Bacterial and protist community changes during a phytoplankton bloom

The present study aims to characterize the change in the composition and structure of the bacterial and microzooplankton planktonic communities in relation to the phytoplankton community composition during a bloom. High-throughput amplicon sequencing of regions of the 16S and 18S rRNA gene was undertaken on samples collected during a 20 day (d) mesocosm experiment incorporating two different nutrient addition treatments [Nitrate and Phosphate (NPc) and Nitrate, Phosphate and Silicate (NPSc)] as well as a control. This approach allowed us to discriminate the changes in species composition across a broad range of phylogenetic groups using a common taxonomic level. Diatoms dominated the bloom in the NPSc treatment while dinoflagellates were the dominant phytoplankton in the control and NPc treatment. Network correlations highlighted significant interactions between OTUs within each treatment including changes in the composition of Paraphysomonas OTUs when the dominant Chaetoceros OTU switched. The microzooplankton community composition responded to changes in the phytoplankton composition while the prokaryotic community responded more to changes in ammonia concentration.

COMPOSITIONAL AND MARKETABLE QUALITY OF FRESH-CUT FLORETS OF FOUR SPECIALTY BRASSICAS IN RELATION TO CONTROLLED ATMOSPHERE STORAGE

Brassica vegetables are consumed year-round as raw salad or cooked ingredients. Four Brassica species were selected for this study, broccoli (Brassica oleracea var. italica), broccoli raab (Brassica rapa L.), choisum (Brassica rapa var. parachinensis), and gailan (Brassica oleracea var. alboglabra). While there is abundant information about broccoli, research on gailan, choisum and broccoli raab is very limited. The effect of CA (3% O2 alone or in combination with 7 or 15% CO2, 1% O2 alone or combined with 15% CO2) and air on marketable quality (overall visual, yellowing, discoloration, decay) and chemical parameters (antioxidant activity, chlorophyll, sugar, fermentative volatiles, and ammonia content) during storage at 5°C was evaluated. Products were obtained from a wholesaler, washed in chlorinated water, trimmed into florets and placed in unsealed polyethylene bags that were held in polycarbonate chambers through which humidified air or the controlled atmospheres flowed. Visual quality was evaluated after 0, 8, 12, 16 and 20 days, while chemical parameters were measured after 0, 8, 16 days. Generally, CA treatments did not affect the antioxidant activity, chlorophyll or sugar concentrations in any of the specialty brassicas studied. On the other hand, both ammonia content and visual quality evaluations were affected by atmosphere composition. Florets stored in low oxygen (3% O2) often had the best visual quality but generally all atmospheres maintained better marketable quality than air storage. The 3% oxygen CA improved marketability to about 16 days. Low oxygen delayed postharvest and post-cutting deterioration of florets from all Brassica species, and based on changes in ammonia concentrations, was considered beneficial to maintain quality of fresh-cut brassicas stored at 5°C.

The evidence based practice for optimal sample quality for ammonia measurement

ObjectivesPre-analytical factors are a major source of variability in laboratory results. Failure to identify these factors can lead to falsely increased or decreased results and to erroneous clinical decisions. We aimed to investigate several pre-analytical factors influencing ammonia measurement, and to quantify their effect on the apparent increase in ammonia concentration. Design and methodsBlood samples were taken from 20 healthy volunteers and submitted to five different sets of conditions: placing sample on ice vs. room temperature immediately after phlebotomy; centrifugation at room temperature vs. 0°C; measurement at 60min vs. 30min after sampling; storing sample at room temperature vs. 4°C; and use of stopper (i.e. open vs. closed tube). Ammonia was measured in all samples. Additionally, alanine aminotransferase (ALT), gamma glutamyltransferase (GGT), free hemoglobin, and complete blood count were determined. ResultsSamples placed on ice immediately after centrifugation, samples spun at 0°C, and samples stored at 4°C all had lower changes in ammonia concentration than samples with less favorable treatments (P=0.008; P=0.033, and P=0.001, respectively). The observed biases exceeded clinically relevant acceptance criteria. Most of the tested parameters were significantly associated with increased ammonia. Multiple linear regression analysis identified only three variables that contributed significantly to the prediction of the dependent variable (i.e. increased NH3): ALT, GGT, and storage. ConclusionPre-analytical factors cause significant errors in ammonia measurement. An increase in ammonia concentration is most strongly associated with ALT and GGT activity and with storage temperature.

The Potential of Quercetin in <i>Psidium guajava L.</i> Leaves Extract as Bioinhibitor for Controlled Released Fertilizer

This study was done to investigates the usage of natural products as one of the materials in fertilizer application. Urease inhibitors that are commonly used in agriculture are usually chemical based which affects the environment. Introducing natural products will ensure biodegradability of the material. Psidium Guajava L. (guava) has been reported to have properties such as antibacterial, anti-oxidant, anti-cancer, and anti ulcer for medical purposes. Guava leaves extract contains an active compound named quercetin that was successfully reported to exhibit significant urease inhibitory activities. Spectrophotometric method was used in this study with the theory of Beers Law in order to measure the changes in ammonia concentration. Small reduction of ammonia (NH3) concentration with different about 0.1 mol/L was calculated and the releasing was almost equal till the end of incubation time. The guava leaves extract prepared showed the potential to reduce the release of NH3 concentration during urea application.

Pigeon peas as a supplement for lactating dairy cows fed corn silage-based diets

Holstein rumen-cannulated cows [n=7; initial body weight (BW) 640.56±71.43kg] were fed a corn silage basal diet with 1 of 3 concentrates (C=control; P10=10% pigeon peas; P20=20% pigeon peas). Cows were randomly assigned to treatments in a replicated 3×3 Latin square and individually fed using Calan gates. Each experimental period was 21 d with 7 d for adaption and 14 d for sample collection. Ruminal fluid samples were taken the last day of each experimental period and analyzed for pH, ammonia, long-chain fatty acids, and volatile fatty acids (VFA). Consecutive a.m. and p.m. milk samples were taken during the last 2 wk of the 21-d period and analyzed for fat, protein, long-chain fatty acids, and somatic cell count. Dry matter intake (kg/d) was reduced during the second period and was greater for P10 diets. Milk protein was greater for cows fed P20 compared with P10. Energy-corrected milk was greater for cows fed the control diet compared with P10. Treatment had no effect on milk yield. Ruminal fluid pH decreased over sampling times; however, pH remained at or above 5.5. Diets did not affect ruminal fluid pH; however, pH was different for sampling periods. Ruminal ammonia decreased until 8h postfeeding at which time it peaked consistent with changes in ammonia concentrations that usually peak 3 to 5h postfeeding on diets high in plant proteins. Dietary treatments altered ruminal fluid VFA with reduced concentrations of acetate and greater concentrations of propionate for control diet, resulting in reduced acetate:propionate ratio. Isobutyrate exhibited an hour by treatment interaction, in which isobutyrate decreased until 8h postfeeding and then tended to be greater for P10 than for other treatments. Animals fed the P10 diet had greater concentrations of ruminal isovalerate. Ruminal cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid (CLA) isomers were not affected by dietary treatments. The P10 diet had greatest ruminal synthesis of cis-9,trans-11, but control cows had greatest ruminal synthesis of trans-10,cis-12. Milk CLA isomers were similar among treatments. Trends were observed for greater cis-9,trans-11 and trans-10,cis-12 for the P10 diet. Pigeon peas may be used as a protein supplement in dairy diets without affecting milk production, dry matter intake, or ruminal environment when they replace corn and soybean meal.

Polytungstate clusters on zirconia as a sensing material for a selective ammonia gas sensor

Tungstated-zirconia has been tested as a functional material for a selective ammonia gas sensor. The sensor has been found to respond consistently and rapidly to changes in concentration of ammonia in the oxygen rich and moist gas mixture at 673 K. The sensor showed negligible cross-sensitivity to propene, CO, and NO. From characterizations of tungstated-zirconia by XRD, Raman, UV–vis, high-resolution TEM, and ammonia-TPD, it was found that subnano-sized polytungstate clusters are uniformly supported on the zirconia surface, and the strong acid sites derived from the polytungstate clusters are suggested to effectively work as selective adsorption sites for ammonia. The fabricated ammonia sensor utilizing tungstated-zirconia is expected to be useful for controlling the injection amount of ammonia in urea-SCR systems.

Detecting changes in epiphytic lichen communities at sites affected by atmospheric ammonia from agricultural sources

Lichens were recorded on Quercus petraea trunks and twigs near ammonia recording stations in ‘continental’ Norfolk, and ‘oceanic’ Devon in order to test indicator values developed for epiphytic lichens in areas of high atmospheric ammonia in the Netherlands. Lichens on trunks in Norfolk showed a similar correlation of nitrophyte indices with ammonia concentration and bark pH as those in Holland, whereas in Devon there was no correlation with nitrophyte indices on trunks and a negative correlation with acidophyte indices. Results on twigs in both sites suggest that lichens on twigs respond more rapidly to recent changes in ammonia concentrations while trunks may maintain relict lichen communities due to either a legacy of previous acidification or ecological continuity. The results suggest that loss of acidophytes is taking place prior to the establishment of nitrophytes indicating the importance of establishing levels of ammonia at which sensitive communities are at risk.

Impact of rapid impulse operating disturbances on ammonia removal by trickling and submerged-upflow biofilters for intensive recirculating aquaculture

Biofilters are regularly used in aquaculture production systems to remove ammonia and nitrite and are the only economically feasible ammonia removal devices in saltwater systems. Six identical 5.23L biofilters, three trickling and three submerged-upflow filters, were operated at predetermined water quality conditions (pH 7.5, temperature 25°C, salinity 5ppt, TAN 1mg/L), and then perturbed to simulate a number of possible operating disturbances, e.g. increased fish load, flushing of culture tanks, closing off of valves. Each disturbance was a controlled impulse change in ammonia concentration, temperature, pH or salinity. The maximum water quality ranges were pH 6–9, TAN 0.5–4.0mg/L, temperature 15–35°C, and salinity 0–10ppt. After each disturbance, the water quality was immediately returned to the predetermined (baseline) values. The ammonia removal across the filters was monitored during the disturbance and the recovery period for loss and subsequent restoration of biofilter removal efficiency. Baseline nitrification rates resumed within 1–2h after cessation of the shock. Some impulse shocks were temporarily detrimental to both filter types—especially low pH (−29% efficiency), low salinity (−13% to −18% efficiency), and low temperature (−11% to −13% efficiency). Raising the temperature (+9% to +12% efficiency) and TAN concentration (+0.30 to +0.36mg/L of filter additional TAN removal) appears to be beneficial to the biofilter.

Impact of positive ramp short-term operating disturbances on ammonia removal by trickling and submerged-upflow biofilters for intensive recirculating aquaculture

Biofilters are regularly used in freshwater aquaculture production systems to remove ammonia and nitrite and are the only economically feasible ammonia removal devices in saltwater systems. Six identical 5.23l biofilters, i.e., three trickling and three submerged-upflow filters, were operated at predetermined baseline water quality conditions (pH 7.5, temperature 25°C, salinity 5ppt, TAN 1mg/L), and then perturbed to simulate a number of possible operating disturbances, e.g. increased fish load, flushing of culture tanks, closing off of valves. Each disturbance was a controlled positive ramp short-term change in ammonia concentration (with other water quality parameters held constant) or temperature or pH or salinity. Ammonia removal across the biofilters was monitored during the disturbance and recovery period for loss and subsequent restoration of ammonia removal efficiency. Baseline water quality to the filters was resumed at the end of each disturbance and baseline ammonia removal occurred within 1 to 2h after end of disturbance. Ranges of variation in water quality were pH 7.5–9, TAN 1.0–4.0mg/L, temperature 25–35°C, and salinity 5–35ppt. Salinity increases over a 5–10h period reduced biofilter removal efficiency (−12 to −30% TAN removal); temperature increases, over a 1.6–10h period, offered about a 5% increase in TAN removal while gradual TAN increases, over a 3–12h period, although providing an approximately extra 1mg/L of removal did not significantly change removal efficiency; and gradual pH increases, over a 3–7.5h period, did not change biofilter removal efficiency significantly.

Modeling Inorganic Aerosols and Their Response to Changes in Precursor Concentration in Mexico City

Based on data from the 1997 Investigación sobre Materia Particulada y Deterioro Atmosférico-Aerosol and Visibility Evaluation Research (IMADA-EVER) campaign and the inorganic aerosol model ISORROPIA, the response of inorganic aerosols to changes in precursor concentrations was calculated. The aerosol behavior is dominated by the abundance of ammonia and thus, changes in ammonia concentration are expected to have a small effect on particle concentrations. Changes in sulfate and nitrate are expected to lead to proportional reductions in inorganic fine particulate matter (PM2.5). Comparing the predictions of ISORROPIA with the observations, the lowest bias and error are achieved when the aerosols are assumed to be in the efflorescence branch. Including crustal species reduces the bias and error for nitrate but does not improve overall model performance. The estimated response of inorganic PM2.5 to changes in precursor concentrations is affected by the inclusion of crustal species in some cases, although average responses are comparable with and without crustal species. Observed concentrations of particle chloride suggest that gas phase concentrations of hydrogen chloride may not be negligible, and future measurement campaigns should include observations to test this hypothesis. Our ability to model aerosol behavior in Mexico City and, thus, design control strategies, is constrained primarily by a lack of observations of gas phase precursors. Future campaigns should focus in particular on better understanding the temporal and spatial distribution of ammonia concentrations. In addition, gas phase observations of nitric acid are needed, and a measure of particle water content will allow stable versus metastable aerosol behavior to be distinguished.