Average Ammonia Concentration Research Articles

Influence of Backwashing Time on Iron, Manganese, Ammonia and Turbidity Removal Using a Pilot-Scale Biological Filter

Backwashing time is one of the most critical operational parameters for biological filter. In order to investigate the effect of backwashing time on iron, manganese, ammonia and turbidity removal, three backwashing time (5 min, 4 min and 3 min) were adopted. Results showed that the average concentration of total iron, manganese and ammonia in effluent was 0.025 mg/L, 0.007 mg/L, and 0.022 mg/L; 0.012 mg/L, 0.001 mg/L and 0.017 mg/L; 0.013 mg/L, 0.000 mg/L and 0.016 mg/L, respectively, which illustrated varying backwashing time had little influence on the removal efficiency of them. The turbidity in effluent was 0.28 NTU, 0.38 NTU, 0.57 NTU, respectively. The shorter backwashing time, the higher turbidity in effluent. Turbidity was almost completely removed in 0~0.4m of the media. After backwashing, the turbidity in effluent was decreased to less than 1 NTU in 40 min, droped to less than 0.5 NTU in 90 min.

Biological Nutrient Removal using Porous Media

This study aims to examine the modified A 2 /O process is useful to reduce the environmental pollution caused by nutrient in wastewater. Specific results are as follows: The removal rate was evaluated at each time period, ie., 18h, 8h, 6h, and 3h after the reaction started. The anoxic rate was more than 94-97% from 18h to 6h but was less than 50% before 6h. Thus, the test of nitrification was done using 6h as the optimal anoxic retention time and the aerobic retention time set at 24h. When the flow change was 1:1, the average ammonia concentration inputted was 30㎎/l. Returned top nitric acid solution and the concentration of ammonia solution falling into the anoxic reactor was about 50% of the initial concentration, and the flow change was 1:2, the concentration of ammonia falling into the anoxic reactor was about 62% of that of influxed ammonia. And the results of this study showed that the nitrogen removal rate can be improved by inputting untreated nitric acid and changing the flow of top nitrate solution using the modified A 2 /O method.

Biodrying of municipal solid waste under different ventilation modes: drying efficiency and aqueous pollution

Ventilation is very important during the biodrying process because it affects the biodrying efficiency and secondary pollution. In this study, three ventilation modes-intermittent negative ventilation (IN), continuous negative ventilation (CN) and intermittent positive ventilation (IP)-were used to provide the same amount of total air during biodrying of municipal solid waste (MSW). During the entire 16-day experiment, 68.4%, 68.7% and 67.2% of water contained in the initial waste was removed under IN, CN and IP trials respectively. The ratio of water loss to volatile solid loss was used to evaluate the biodrying efficiency, with values of 5.35, 5.93 and 4.82 being observed for IN, CN and IP trials respectively. The total organic carbon concentrations of the leachate generated from the biodrying of waste were as high as 25,000 mg/l, while those of the condensate were not higher than 3500 mg/l. During the entire process, the average ammonia concentrations of leachate and condensate were 1350 mg/l and 2140 mg/l respectively. From the aspect of biodrying efficiency, continuous negative ventilation was the most preferable ventilation mode for biodrying of MSW, while special care should be taken to prevent aqueous pollution if it is used in a MSW treatment plant.

Trends in atmospheric ammonia and particulate ammonium concentrations in Sweden and its causes

Daily average air concentrations of ammonia plus particulate ammonium, nitric acid plus particulate nitrate, sulphur dioxide and particulate sulphate have been measured at four EMEP (European Monitoring and Evaluation Programme) sites in Sweden since 1986. From 1993 sampling was made with a filter pack that separates the gaseous and particulate forms. The separation is not perfect, but fairly good when compared to a denuder. The same filter pack was used for monthly measurements at four high altitude sites in the Swedish mountain areas. The concentration of particulate ammonium decreases more rapidly than the ammonia emissions in Sweden and neighbouring countries while the ammonia concentration increases. Particulate ammonium is mainly long-range transported from the continent to the southern parts of Sweden, while gaseous ammonia comes from all directions. The particulate ammonium concentrations are charged balanced with particulate sulphate and nitrate concentrations and the long-range transport is therefore limited by the availability of these anions.

Spatial and temporal variability of ammonia and other inorganic aerosol species

Nitrogen deposition to the sensitive ecosystems in Rocky Mountain National Park (RMNP) has been increasing. Ammonia has been shown to be a large fraction of this nitrogen deposition, and sources in northeastern Colorado were found to be a significant contributor. In this work we report on the results from a small network of Radiello passive samplers to investigate the temporal and spatial variability of ammonia gas concentrations in northeastern Colorado. A URG denuder/filter-pack sampler was collocated with a Radiello passive sampler to provide a check on the accuracy of passive ammonia measurements and to provide information about complementary aerosol and trace gas species. These measurements showed seasonal variations in the concentrations of both particulate- and gas-phase aerosol components. The highest concentrations of ammonia occurred during summer months. These were almost twice the lowest concentrations, which occurred during spring and fall months. Ammonia also exhibited higher than expected concentrations during winter. There was considerable spatial variability in average ammonia concentrations, with May–August averages ranging from 3 μg m−3 in rural grasslands to 4–11 μg m−3 at suburban-urban sites to almost 30 μg m−3 in an area of intensive livestock feeding and farming operations. The large ammonia gradients near sources are expected for this primary pollutant with high deposition rates. The overall concentrations in this region are significantly larger than those measured in RMNP, which were around 0.5 μg m−3, and represent a large reservoir of ammonia that can be transported to RMNP with easterly winds.

Experimental Study on the Treatment of Low Concentration Domestic Sewage in a Zeolite Biological Aerated Filter

The present paper describes the performance and the feasibility of the zeolite biological aerated filter applied to treat the low concentration sewage as recalaimed water reuse as cooling tower make-up water in the thermal power plant. The result showed that average removal rate of COD, turbidity and ammonia was 79%, 86% and 50% respectively, under the conditions of hydraulic loading L=4.4m3/m2•h, gas-water ratio=2:1, HRT=0.63h, t=8.5~14.5oC and backwashing in 48 hours. The average concentration of COD, turbidity and ammonia in effluent was 13.0mg/l, 4.2NTU and 1.95mg/l, respectively. The effluent quality met the water quality standards of the reuse of urban recycling water-water quality standard for industrial uses GB/T19923-2005.

Environmental comfort in constructions for Sindi and Guzera calves in the agreste region of the State of Paraiba, Brazil

The objective of this study was to evaluate the quality of air, bioclimatic indexes of facilities and physiological indices of Guzera and Sindhi calves, reared in climatic conditions of Agreste. The study was conducted at the experimental station of Alagoinha, PB, Brazil, using 16 calves of Sindi and Guzerá races. The average concentration of oxygen (20.85%), ammonia (1.99 ppm), carbon monoxide (<0.01 ppm), methane (0.13 ppm) and hydrogen sulfide (<0.01) within facilities, were within the limits established by the Brazilian and international standards, for both animals and workers. The bioclimatic index of temperature and humidity and the temperature of the black globe and humidity index were within the thermal comfort zone for cattle in most of the experimental period, the mean values of respiratory frequency (26.0 min mov-1) and skin temperature (32.3 °C) were higher in the hottest time of the day (1 pm) and rectal temperature (39.3 ºC) in the late afternoon (5 pm), but remained within normal ranges for the studied races. The races have good adaptability to climatic conditions in the region of the Paraibano Agreste, Brazil.

A semi-continuous measurement of gaseous ammonia and particulate ammonium concentrations in PM2.5 in the ambient atmosphere

Ammonia has a short residence time in the atmosphere and rapidly neutralizes acid gases that occur near its source, requiring a rapid measurement system for ammonia and particulate ammonium concentrations to better understand their sources, temporal variation of ammonia emissions, and the formation of secondary ammonium aerosols. A semi-continuous measurement system, consisting of a diffusion scrubber, a particle growth chamber, an air-liquid separator, and a fluorescent detector, was developed to determine both gaseous ammonia (NH3) and particulate ammonium (NH4+) in PM2.5 in the ambient atmosphere of Gwangju, South Korea, during the months of March, April, July, and September of 2007. During the sampling periods, the average concentrations of ammonia and ammonium were found to be 2.33 ± 1.29 μg/m3 and 1.89 ± 0.99 μg/m3, respectively. Although the average gaseous ammonia concentration was highest in March, the particulate ammonium concentration was higher during the warmer season, reaching 2.08 ± 1.07 μg/m3 and 2.32 ± 0.94 μg/m3 in April and July, respectively, while only 1.68 ± 0.61 μg/m3 in March and 1.24 ± 0.99 μg/m3 in September. It is proposed that the higher availability of acid species during the warmer months produced a significant amount of particulate ammonium sulfate. Diurnal fluctuation of ammonia and ammonium during the warmer months showed that their peak time occurred at approximately 10:00 am. Both ammonia and ammonium concentrations were better correlated during the warmer months than during the cooler months. Further, the data suggest that the ammonia and ammonium were measured under well dispersed conditions, and multiple sources contributed to the ammonia at the sampling site.

Cyclic properties and ammonia by-product emission of Li/Mg–N–H hydrogen storage material

A magnesium amide-based hydrogen storage material, 3 Mg(NH 2) 2 + 8LiH, was subjected to cycling tests of dehydrogenation and hydrogenation, in which the cyclic trend in the hydrogen storage capacity as well as the amount of the ammonia by-product contained in the desorbed hydrogen gas were recorded. After 300 cycles at 473 K, the initial hydrogen capacity of 4.2 mass% dropped to 3.6 mass%, corresponding to the decay rate of 0.0004 per cycle. The average ammonia concentration through the 300 cycles was determined to be 0.05 ± 0.01 mol%(NH 3/H 2) which is entirely responsible for the hydrogen capacity decay because the ammonia emission leads to the loss of elemental nitrogen from the system. When the dehydrogenation temperature was raised to 573 K, the hydrogen capacity decay became more significant and the ammonia concentration increased to 0.27 ± 0.06 mol%(NH 3/H 2). The reaction kinetics also severely deteriorated during cycling at the higher temperature.

Modelling deposition and air concentration of reduced nitrogen in Poland and sensitivity to variability in annual meteorology

The relative contribution of reduced nitrogen to acid and eutrophic deposition in Europe has increased recently as a result of European policies which have been successful in reducing SO2 and NOx emissions but have had smaller impacts on ammonia (NH3) emissions. In this paper the Fine Resolution Atmospheric Multi-pollutant Exchange (FRAME) model was used to calculate the spatial patterns of annual average ammonia and ammonium (NH4+) air concentrations and reduced nitrogen (NHx) dry and wet deposition with a 5 km × 5 km grid for years 2002–2005. The modelled air concentrations of NH3 and dry deposition of NHx show similar spatial patterns for all years considered. The largest year to year changes were found for wet deposition, which vary considerably with precipitation amount. The FRAME modelled air concentrations and wet deposition are in reasonable agreement with available measurements (Pearson’s correlation coefficients above 0.6 for years 2002–2005), and with spatial patterns of concentrations and deposition of NHx reported with the EMEP results, but show larger spatial gradients. The error statistics show that the FRAME model results are in better agreement with measurements if compared with EMEP estimates. The differences in deposition budgets calculated with FRAME and EMEP do not exceed 17% for wet and 6% for dry deposition, with FRAME estimates higher than for EMEP wet deposition for modelled period and lower or equal for dry deposition. The FRAME estimates of wet deposition budget are lower than the measurement-based values reported by the Chief Inspectorate of Environmental Protection of Poland, with the differences by approximately 3%.Up to 93% of dry and 53% of wet deposition of NHx in Poland originates from national sources. Over the western part of Poland and mountainous areas in the south, transboundary transport can contribute over 80% of total (dry + wet) NHx deposition. The spatial pattern of the relative contribution of national sources to total deposition of NHx may change significantly due to the general circulation of air.

The Effect of Hydraulic Loading Rates on Nitrogen Removal by Using a Biological Filter Proposed for Ventilated Improved Pit Latrines

No on-site sanitation system treats both urine and faecal matter in one process. A laboratory scale biological filter was fed with high concentration of urea (4 g N/L) and 17.1 g COD/L to determine if it will be possible to treat liquid that leach from a ventilated improved pit latrine. The HLR in the proposed biological filter system was calculated to be ca 36 L/m2/d, significantly lower than the rates that are typical applied in standard rate biological filters (in the range of 1000 – 4000 L/m2/d) used to treat domestic wastewater. However, the TKN and COD concentrations in standard rate biological filters are significantly lower, namely ca 60 mg N/L and 500 mg COD/L, compared to the typical nitrogen and COD concentrations of faecal sludge, namely 3 - 5 g N/L and 20 – 50 g COD/L, respectively. The biological filter was operated at 13.0, 23.9, 35.7 and 62.3 L/m2/d, until stable state conditions were obtained. It was possible to remove most of the nitrogen and COD at the applied hydraulic loading rates by a combination of volatilization, nitrification and de-nitrification processes. However, at 62.3 L/m2/d the column efficiency (1.5 m long column) decreased and ammonia concentration in the effluent increased again. The best performance was achieved at a hydraulic loading rate of 35.7 L/m2/d, with an average ammonia concentration of 285.5 (± 9.1) mg N/L.

Characterization and electrocaogulative treatment of nanofiltration concentrate of a full-scale landfill leachate treatment plant

In this study, characterization and electrocoagulative treatability of nanofiltration concentrate from a full-scale landfill leachate treatment plant (Istanbul, Turkey) were investigated. The average concentrations of COD, TKN and ammonia were determined as 6200, 587.5, and 110 mg/L, respectively. Membrane concentrate also have almost neutral pH, high conductivity and color. Besides, nanofiltration concentrate contains low metal concentrations. After the characterization of the concentrate, treatment of the concentrate by electrocoagulation method with aluminum plate electrodes was investigated. The effects of electrode type, current intensity and treatment time on the treatment of nanofiltration concentrate by EC process were investigated. According to the results, the most acceptable current intensity for COD, color, and phosphorus removal was determined to be 15.9 mA/cm 2 and the most acceptable treatment time was determined to be 30 min. The treatment efficiencies for COD, color, and phosphorus at 15.9 mA/cm 2 and 30 min were determined as 45%, 60%, and 91.8%, respectively. According to the results of this study, EC process may be an acceptable solution for the treatment of leachate nanofiltration concentrate. More detailed studies however need to be done for the determination of the optimum operational parameters of the electrocoagulative treatment of membrane concentrate.

Spatial and temporal distribution of ambient nitric acid and ammonia in the Athabasca Oil Sands Region, Alberta

Monthly average ambient concentrations of gaseous nitric acid (HNO3) and ammonia (NH3) were monitored at the Athabasca Oils Sands Region (AOSR), Alberta, Canada, between May 2005 and September 2008. Generally, concentrations of both pollutants were elevated and highly variable in space and time. The highest atmospheric concentrations occurred in the vicinity of the major mining and oil extraction activities of Fort Murray and Fort McKay. Maximum monthly average concentrations of HNO3 decreased from >6 μg m–3 2005 and 2006 to <4 μg m–3 in 2007 and 2008. While the HNO3 summer seasonal averages in 2005 and 2006 approached ~2 μg m–3 at some sites, in the subsequent summers and during winter seasons it rarely exceeded 1 μg m–3 and no clear differences between summer and winter occurred. Concentrations of NH3 were elevated during the entire study and frequently reached 6 μg m–3. Generally, NH3 stayed higher in summer than in winter; the summer seasonal averages often exceeded 4 μg m–3 while those for winter only on two occasions were above 3 μg m–3. In summer 2008, an expansion of the area with elevated NH3 levels was observed extending to remote locations. Ammonia is of a much higher concern from a perspective of possible biological effects, because of its potential for direct toxic effect on lichens and its contribution to the elevated N dry deposition with possible negative consequences for forests and other ecosystems.

Effects of diurnal emission patterns and sampling frequency on precision of measurement methods for daily ammonia emissions from animal houses

Ammonia concentrations and airflow rates are the main parameters needed to determine ammonia emissions from animal houses. It is possible to classify their measurement methods into two main groups according to the sampling frequency: semi-continuous and daily average measurements. In the first method, ammonia concentrations and airflow rates are monitored during a certain period and instant emission rates are calculated. When using daily average methods, 24-h average ammonia concentrations and airflow rates are used to determine the average daily emission rate. As less information is used in the second method, an error may be expected. The aim of this work was to determine the nature and magnitude of this error. Three databases containing data from semi-continuous ammonia emissions measurements from different animal houses (pigs, poultry and rabbits) in three European countries (Denmark, The Netherlands and Spain) were used to characterise this error. An average systematic deviation between methods of 1.5% was found. The magnitude of this bias was directly related to the daily variation of ammonia concentration and airflow rate. The magnitude of this bias, and also the random component of the error, were modelled. The developed model adequately described variation in bias in the studied dataset (R2 = 0.85) and can be used as a tool to decide which type of measurement methods can be used.

In vitro ruminal degradation of ricin and its effect on microbial growth

Ricin is a toxic protein found in castorseed ( Ricinus communis L.). We hypothesized that ruminal microbiota are capable of degrading ricin, and that the toxin inhibits ruminal microbial growth. Therefore, first we evaluated the in vitro ruminal degradation of ricin from solvent castorseed meal (SCM) by SDS-PAGE and densitometry analysis of culture medium (Experiment 1). Culture medium (three replicates) were collected after 0, 3, 6, 12, 24 and 48 h of incubation content initially 0, 61, 122 and 244 μg of ricin/mL or 122 μg of ricin/mL (without ruminal inoculum). No protein compounds were detected by SDS-PAGE in the culture medium without ricin, indicating an absence of interference from the ruminal inoculum. Ricin chains remained intact in the absence of rumen inoculum, but they were degraded at rates of 0.2725, 0.1504 and 0.0648 h −1 with ruminal inoculum, at initial ricin concentrations of 61, 122 and 244 μg/mL. Next, the effect of ricin denaturation on rumen microbial specific growth rate (SGR) (OD-600 nm) and the average ammonia concentration at the same time of incubation were investigated (Experiment 2). This experiment had a completely randomized design in a 3 × 3 factorial (three replicates) arrangement, with three sources of protein (trypticase-control; crude extract of soluble protein at pH 3.8 buffer of solvent castorseed meal (CEP) intact, containing 1.46 mg of ricin/mL; and denatured CEP with calcium oxide, containing 0.04 mg of ricin/mL) and three protein levels (0.42, 0.84, and 1.68 mg/mL). There was interaction (P=0.021) between protein level and protein source for SGR. A linear increase (P<0.001) of SGR was observed with increase of trypticase level, but there was a quadratic effect (P=0.023) with increase of intact CEP level, with a minimum value of SGR of −0.004 h −1 at a protein level of 1.45 mg/mL (210 μg of ricin/mL) of intact CEP. There was no effect (P=0.099) of denatured CEP level, but SGR increased (P<0.001) 3.2 times with denaturation of intact CEP. Ruminal microbial growth was inhibited by 50% with 89 μg of ricin/mL. Ammonia concentration was 91% lower (P<0.001) for the CEP source when compared to trypticase, but the denaturation of intact CEP had no effect (P=0.9560) on the ammonia concentration. Although ruminal microbiota was able to degrade ricin in in vitro conditions, the toxin inhibits ruminal microbial growth. Therefore, complete detoxification of CSM before using it to feed ruminants is recommended. The denatured CEP presents potential of use as modifier of rumen microbial fermentation.

Ammonia emission rates from dairy livestock buildings in Eastern Canada

Gaseous ammonia emissions from livestock production are deemed responsible for the acidification of several ecosystems and for the formation of PM 2.5 . The latter induces adverse health effects in humans, mostly respiratory ailments. In this study, ammonia emission rates from two tie-stall commercial dairy buildings were monitored in Canada where little data is currently available. Buildings studied were mechanically ventilated and livestock management practices were typical of Eastern Canada. Ammonia emission measurements made at building A during the months of February and March 2007 ranged from 3.77 to 6.80 g day −1 animal −1 while those performed at building B during summer 2007 ranged from 11.33 to 18.20 g day −1 animal −1 . These values fall within the range of ammonia emission rates found in the literature for studies completed in Western Europe: 0.1625 g day −1 AU −1 to 23.38 g day −1 animal −1 . A titration method, using acid traps, was used at building B to measure average ammonia concentrations while an electrochemical ammonia analyser was used at building A for continuous measurements. Propeller anemometers were developed to measure building ventilation flow rates. The precision of the equipment used to measure building ventilation rates and gaseous ammonia concentrations inside the building were evaluated at both locations.

Milk House Wastewater Flows and Characteristics for Small Dairy Operations

Water meters were used to indicate milk house wastewater flow rates in the milk houses of 16 dairy operations with between 41 and 130 milking cows. Wastewater samples (7 to 21) were taken from the first septic tank providing primary treatment of the milk house water to measure pH, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), fats, oils and grease (FOG), total phosphorus, total Kjeldahl nitrogen (TKN), and ammonia nitrogen concentrations. Average water flow rates across the 14 dairy operations without parlors ranged from 8.6 to 35.3 L/d/cow. Milk house water use per cow per day on individual farms varied by between 146% and 400%. Overall average BOD5 concentration across all sixteen operations was 1.44 g/L while individual farm averages ranged from 0.50 to 4.52 g/L. Overall average COD concentration was 2.26 g/L; farm averages ranged from 0.72 to 6.28 g/L. Overall average TSS concentration across all operations was 686 mg/L, farm averages ranged from 181 to 1,537 mg/L. Average FOG concentration was 477 mg/L, farm averages ranged from 45 to 1,334 mg/L. Median average pH level was 6.8, farm levels ranged from 5.9 to 8.0. Average phosphorus concentration across all operations was 56 mg/L, farm averages ranged from 18 to 101 mg/L. Average TKN concentration was 81 mg/L, farm averages ranged from 33 to 179 mg/L. Average ammonia concentration was 34 mg/L, farm averages ranged from 12 to 98 mg/L. Based on these results the authors recommend using 19 L/d/cow for the design milk house wastewater flow rate for milk houses for dairy operations with 130 or fewer cows. For sizing aerobic treatment units and infiltration systems, the authors recommend using 1.5 g/L for the design effluent BOD5 concentration for a milk house only. For designing irrigation land application systems based on annual TKN and P per cow for milk house only sites, the authors recommend using 0.6 and 0.35 kg/cow/yr, respectively.

Microbial ecology and performance of ammonia oxidizing bacteria (AOB) in biological processes treating petrochemical wastewater with high strength of ammonia: effect of Na2CO3 addition

This study evaluated nitrification performance and microbial ecology of AOB in a full-scale biological process, powder activated carbon treatment (PACT), and a pilot-scale biological process, moving bed biofilm reactor (MBBR), treating wastewater collected from a petrochemical industry park. The petrochemical influent wastewater characteristics showed a relative low carbon to nitrogen ratio around 1 with average COD and ammonia concentrations of 310 mg/L and 325 mg-N/L, respectively. The average nitrification efficiency of the full-scale PACT process was around 11% during this study. For the pilot-scale MBBR, the average nitrification efficiency was 24% during the Run I operation mode, which provided a slightly better performance in nitrification than that of the PACT process. During the Run II operation, the pH control mode was switched from addition of NaOH to Na(2)CO(3), leading to a significant improvement in nitrification efficiency of 51%. In addition to a dramatic change in nitrification performance, the microbial ecology of AOB, monitored with the terminal restriction fragment length polymorphism (T-RFLP) molecular methodology, was found to be different between Runs I and II. The amoA-based TRFLP results indicated that Nitrosomonas europaea lineage was the dominant AOB population during Run I operation, while Nitrosospira-like AOB was dominant during Run II operation. To confirm the effects of Na(2)CO(3) addition on the nitrification performance and AOB microbial ecology observed in the MBBR process, batch experiments were conducted. The results suggest that addition of Na(2)CO(3) as a pH control strategy can improve nitrification performance and also influence AOB microbial ecology as well. Although the exact mechanisms are not clear at this time, the results showing the effects of adding different buffering chemicals such as NaOH or Na(2)CO(3) on AOB populations have never been demonstrated until this study.

Ammonia and carbon dioxide concentrations in disposable and reusable static mouse cages

The value of a static mouse cage is partially determined by the cage's ability to dissipate carbon dioxide and ammonia. The authors compared the concentrations of ammonia and carbon dioxide produced by mice housed in two types of static isolator cages: a newly introduced disposable cage and a conventional reusable cage. Female mice were housed in three disposable and three reusable cages (n = 5 per cage). After 7 d, groups that were housed in disposable cages were rehoused in fresh reusable cages and vice versa. Intracage carbon dioxide, ammonia, temperature and relative humidity were measured daily. Overall, there were no significant differences in carbon dioxide or ammonia concentrations between the cage types. Within 30 min of placing mice in cages, carbon dioxide concentrations rose to more than 10,000 ppm in both cage types and rarely dropped below 8,000 ppm during both phases of the study. Ammonia concentrations rose slowly until day 4 and then began to rise rapidly. The maximum average ammonia concentration was 710 ppm. There was a highly significant relationship between increasing levels of humidity and ammonia production in the disposable cages (r = 0.88). For the reusable cages, the correlation was not as strong (r = 0.68). Both cage types were similar in their ability to dissipate carbon dioxide and ammonia. The suggested frequency of cage changing can only be estimated; on the basis of existing literature, it seems prudent to change cages when the ammonia concentration reaches 50 ppm.

Nitrogen removal from agricultural runoff by full-scale constructed wetland in China

We aimed at indicating some regularities of a constructed wetland treating agricultural runoff in China. The regularities, including the nitrogen removal capacity all year round, the nitrogen distribution pathways, and the nitrogen species removal kinetics, of a free water surface constructed wetland (2,800 m2) in the Dianchi Valley, which has been in operation for 27 months, were studied. The planted Phragmites australis and Zizania caduciflora were harvested biannually. The average inflow rate was recorded by an ultrasonic flow instrument, and then the hydraulic loading rate (HLR) and hydraulic retention time (HRT) were calculated. The average inflow and outflow concentrations of total nitrogen (TN), ammonia, and nitrate were measured, while the corresponding removal rates were calculated, showing better results than other constructed wetlands. Then the distribution pathways of nitrogen were analyzed, which indicated that plant harvesting was more important in wetland-treated agricultural runoff than in domestic wastewater. The reason for a good nitrogen removal capability and the obvious function of plants in the present wetland is the sound climate and intermittent inflow in the wetland. Results showed that inflow load had significant correction with both TN and ammonia removal efficiency. HLR, inflow rate, inflow nitrogen concentration, and temperature had significant and positive correction with both TN and ammonia removal. However, HRT had negative correction with both TN and ammonia removal, and the nitrate removal efficiency and parameters mentioned earlier were not significantly correlated. The rate constant values for nitrate and ammonia in summer were obviously larger than in winter. It is possible that bacterial and microbial activities were more active in summer than winter, and more conducive to bacterial and vegetative growth in summer than winter. Since this study was a pioneer for the implementation of constructed wetlands in China treating agricultural runoff, it has proved that this eco-technology could be used effectively for water quality enhancement in China and other areas with a similar climate.