Venkata K Vaddella

Measuring concentrations of ammonia in ambient air or exhaust air stream using acid traps.

Strong acid solutions have been widely used in acid traps to determine concentrations of ammonia in ambient air or exhaust air stream. A literature survey indicates the method has a long history and a wide variation in use. Through a series of studies, this paper examines several factors including volume of the acid, depth of the acid, and airflow rate; that might affect the efficiency of sulfuric acid traps and recommends steps researchers and other users may take to ensure reliable results from this method. The results from these series of studies indicate: (i) an inverse relationship between the efficiency of the acid traps and the amount of ammonia to be trapped even when the capacity of the acid trap is excessively greater than the maximum theoretical stoichiometric capacity needed to dissolve all of the ammonia, (ii) for the same volume of acid, the efficiency of the acid trap increased with the acid depth but overall, the efficiency at any given acid depth decreased as the amount of ammonia through the trap increased, and (iii) at the two airflow rates examined in this study (0.5 and 1.0 L/min) the efficiency of the acid traps decreased at similar rates as the concentration of ammonia in the sample air increased but the efficiency of the trap was significantly higher at the lower airflow rate. To obtain reliable measurements from this method, therefore, multi-point calibrations within the entire range of target measurements is recommended to provide accurate corrections of the measurements.

Simulation of Ammonia Emissions from Scrape and Flushed Dairy Manure Post-Collection Storages

Manure scraping and flushing are the two common manure handling systems in concentrated animal feeding operations (CAFOs) in the United States. Previous studies have reported on the impacts of these two manure handling systems on ammonia emissions within barns. There are no studies comparing the impacts of the two manure handling systems on ammonia emissions during post-collection storages in lagoons and other similar manure storages although these facilities are known to account for the largest portion of ammonia volatilization in CAFOs. A series of bench scale experiments were conducted for a period of 23 days in controlled laboratory conditions to quantify and compare ammonia losses from typical storages of simulated scraped manure, and simulated flushed manure. Ammonia emission fluxes estimates (with cumulative ammonia emissions in the parentheses) over a 23-day period were 2.25±0.08g/m2/day (2034±106.5 mg) from the simulated scraped manure storage, 2.04±0.04g/m2/day (1739.3±53.3 mg) from the simulated flushed manure storages with 411 cm2 exposed surface area each, and 4.62±0.13g/m2/day (1752±56.3 mg) from the simulated scraped manure with 183 cm2 exposed surface area, respectively. These results indicate that ammonia emission fluxes from scraped manure storage would be more than from flushed manure storage by at least two times if both manure post-storages had approximately the same exposed surface area to the volume ratio. However, results also revealed significantly higher cumulative ammonia emissions from simulated scraped manure storage with 411 cm2 than from both the simulated flushed manure storage with 411 cm2 and the simulated scraped manure storage with 183 cm2 exposed surface areas.

A Model for Overall Mass Transfer Coefficient of Ammonia from Dilute Dairy Manure Slurries

Available data indicate that about 75-80% of total nitrogen (N) entering a dairy operation is lost as ammonia (NH3) from an anaerobic dairy lagoon and other similar manure storages. Direct measurement of NH3 emissions from manure holding systems can be complicated and expensive. Process-based emission models can be used to provide a cost effective alternative method for NH3 emissions estimation. The overall mass transfer coefficient (KoL) of NH3 is an important component of any NH3 emission process-based model. Models relying on purely theoretically derived KoLs of NH3 from livestock manures have not adequately predicted NH3 emissions. In this study, the KoL of NH3 from dilute dairy manure slurries was modeled empirically, in a laboratory convective emission chamber (CEC), to determine realistic NH3 KoL values under typical conditions of the Pacific Northwest. The KoL of NH3 increased with both liquid temperature (TL), and air velocity (Vair), but decreased with increase in both air temperature (Tair), and concentration of total solids (TS). The KoLs of NH3 ranged from 1.41×10-6 to 3.73×10-6 m/s. The obtained non-linear empirical model of KoL of NH3 from dilute dairy manure slurries had a coefficient of determination (R2) of 0.83. This model is thus reliable for determining KoL of NH3 in NH3 emissions process-based models over the range of the experimental conditions considered in this study. The sensitivity of the KoL of NH3 to the four model parameters, in descending order was: TL, Tair, Vair and TS concentration, respectively.

A Model of Ammonium Ion Dissociation in Liquid Dairy Manure

Emission of Ammonia (NH3) from lagoons and other similar structures holding liquid dairy manures contributes to environmental pollution and also lowers the fertilizer-value of the liquid-effluent. In general, NH3 volatilization from these facilities depends on the concentration of free NH3 in the liquid, which is a function of the dissociation of ammonium ion (NH4+). The dissociation of NH4+, on the other hand, is dependent on the: liquid temperature, liquid pH, and concentration of total solids (TS). In this study the ammonium ion (NH4+) dissociation constant (Kd) was empirically modeled at a pH of 9; at four temperatures (5, 15, 25, and 35°C), generally experienced in the US Pacific Northwest, and at five TS concentrations (0.5, 1.0, 1.5, 2.0, and 2.5%; w/w) common in flushed-dairy manure. The Kd of NH3 increased 1.61 times for every 10 oC rise in temperature. The data also indicated a linear decrease in the Kd of NH4+ with increase in the concentration of TS in the liquid. The resulting empirical model of the Kd of NH4+ as a function of temperature and TS had a coefficient of determination, R2, of 0.97; demonstrating a good fit to the experimental data. The Kds of NH4+ in the dairy manure liquid were 117%, 87%, 61%t, and 54% compared to the theoretical Kds of NH4+ in pure water at 5, 15, 25, and 35°C, respectively. The results of this study emphasize the need for: (i) including both the liquid-TS and the liquid-temperature in models of Kd of NH4+ in livestock wastewaters, and (ii) covering the entire ranges, of both parameters, encountered in the region where the model will be used.

A Process-based Model for Ammonia Emission from Storages of Flushed Dairy Manure

Ammonia (NH3) is one of the major gaseous pollutants emitted from livestock facilities. Estimates indicate that the largest portion (about 80%) of the total nitrogen entering a dairy facility is lost as NH3 from manure storages; such as anaerobic lagoons. Direct measurements of NH3 emissions from these storage structures are not only tedious but also quite complex and expensive exercises. Process-based models offer an alternative cost-effective approach of making emissions estimations. This research coupled theoretical and empirical analyses of NH3 emissions mechanisms to increase the reliability of process-based NH3 emission models. A process-based model was developed to predict NH3 emission from dilute dairy manure via incorporation of two newly developed empirical sub-models of: the overall mass transfer coefficient (KoL) of NH3 from liquid dairy manure; and the dissociation constant (Kd) of ammonium (NH4+) in liquid dairy manure. The KoL was modeled based on lagoon liquid temperature (TL), air velocity, air temperature, and total solids (TS) concentrations. The Kd was modeled based on TL, and TS concentrations. The model predictions were validated with directly measured NH3 emissions using an open-path ultra-violet differential optical absorption spectroscopy (UV-DOAS) technique. Directly measured NH3 emission fluxes from our study lagoon ranged from 16.1 to 41.2 µg/m2/s, which compared well against our model predicted fluxes with a normalized mean error (NME) of 15%. Sensitivity analyses showed NH3 emission is most sensitive to the lagoon-liquid temperature compared to the other factors (air temperature, air velocity, and total solids concentrations) examined in this study.

A Process-based Model for Ammonia Emissions from Storages of Flushed Dairy Manure

Ammonia (NH3) is one of the major gaseous pollutants emitted from livestock facilities. Estimates indicate that the largest portion (about 75-80%) of the total nitrogen entering a dairy facility is lost as NH3 from manure storages; such as anaerobic lagoons. Direct measurements of NH3 emissions from these storage structures are not only tedious but also quite complex and expensive exercises. Process-based models offer an alternative cost-effective approach of making emissions estimations. This research coupled theoretical and empirical analyses of NH3 emissions mechanisms to increase the reliability of NH3 emission process-based models. A process-based model was developed to quantify NH3 emissions from dilute dairy manure via incorporation of two newly developed empirical sub-models of: the overall mass transfer coefficient (KoL) of NH3 from liquid dairy manure; and the dissociation constant (Kd) of ammonium ion (NH4+) in liquid dairy manure. The KoL was modeled based on lagoon-liquid temperature (TL), air velocity, air temperature, and total solids (TS) concentrations. The Kd was modeled based on TL, and TS concentrations. The model predictions were validated with directly measured NH3 emissions using an open-path ultra-violet differential optical absorption spectroscopy (UV-DOAS) technique. Directly measured NH3 emission fluxes from our study lagoon ranged from 16.1 to 41.2µg/m2/s, which compared well against our model predicted fluxes with a normalized mean error (NME) of 15%. Sensitivity analyses showed NH3 emission is most sensitive to the lagoon-liquid temperature compared to the other factors (air temperature, air velocity, and total solids concentrations) examined in this study.

Ammonia Emissions from Manure Storages using Urine-feces Separation Systems

About 80% of dairy cattle N intake is excreted as urine and feces. Urinary-N is about 75% urea and fecal-N is mostly organic. Ammonia can only be volatilized when urinary urea is hydrolyzed by the urease enzyme present in the feces (urease is not present in the urine). Minimizing contact between urine and feces may be an effective approach to reducing urea hydrolysis and thus subsequent ammonia emissions; indeed, previous studies have reported 5 to 99% ammonia emissions mitigation within barns through separation of feces and urine. The objective of this study was to compare the efficacy of ammonia mitigation by separation of urine and feces in the waste stream against a conventional scrape manure handling method where urine and feces are comingled. Laboratory scale simulation studies were conducted to evaluate ammonia emissions from post-collection storages of three waste streams: i) idealistically separated feces and urine (no contact between urine and feces), ii) realistically separated urine and feces, and iii) conventionally scraped manure. From the results of this study, ammonia losses ranking in descending order was: aggregate of idealistically separated waste streams, aggregate of realistically separated urine and feces, and the scrape manure, respectively. Based on the results of our studies, therefore, the extra effort of separating the waste streams would not enhance mitigation of ammonia loss from the post-collection storages of the separated waste streams compared to the conventional scrape manure collection system.