Modeling hydrogen sulfide emissions across the gas–liquid interface of an anaerobic swine waste treatment storage system

doi:10.1016/j.atmosenv.2008.03.016

Atmospheric Environment

Volume 42, Issue 22, July 2008, Pages 5602-5611

https://doi.org/10.1016/j.atmosenv.2008.03.016 Get rights and content

Abstract

Hydrogen sulfide (H₂S) is a colorless gas emitted during decomposition of hog manure that produces an offensive “rotten egg” smell and is considered a toxic manure gas. In the southeastern United States, anaerobic waste treatment lagoons are widely used to store and treat hog excreta at commercial hog farms. Hydrogen sulfide is produced as manure decomposes anaerobically, resulting from the mineralization of organic sulfur compounds as well as the reduction of oxidized inorganic sulfur compounds by sulfur-reducing bacteria. The process of H₂S emissions from anaerobic waste treatment lagoons are investigated utilizing a two-film model with three different modeling approaches: Coupled Mass Transfer with Chemical Reactions Model with the assumption (1) pH remains constant in the liquid film (MTCR Model I) and (2) pH may change throughout the liquid film due to diffusion processes that occur within the film (MTCR Model II); and (3) a Mass Transfer Model which neglects chemical reactions (MTNCR Model) in the gas and liquid films.

Results of model predictions are consistent with previous works, which show that flux is largely dependent on the physicochemical lagoon properties including sulfide concentration, pH, and lagoon temperature. Air temperature and low wind velocities (e.g., <3.25 m s⁻¹) have negligible impact on flux. Results also indicate that flux values decrease with increased film thickness. The flux was primarily influenced by variations in the liquid film thickness, signifying that the H₂S flux is driven by liquid-phase parameters. Model results were compared with H₂S flux measurements made at a swine waste treatment storage lagoon in North Carolina using a dynamic emission flux chamber system in order to evaluate model accuracy in calculating lagoon H₂S emissions. The MTCR Model II predicted the highest increase in emission rates as aqueous sulfide concentration was increased. The MTNCR Model showed the highest dependence on pH. All three models showed good agreement in diurnal comparison with flux measurements; however, each model significantly over predicted the measured flux rates. The MTNCR Model estimates were closest to experimental values, predicting 3–35 times the actual measured values.

Introduction

Hydrogen sulfide (H₂S) is a colorless, potentially harmful gas released from swine manure (US EPA, 2001a). It is produced as manure decomposes anaerobically, resulting from the mineralization of organic sulfur compounds as well as the reduction of oxidized inorganic sulfur compounds such as sulfate by sulfur-reducing bacteria (US EPA, 2001a). With a low odor threshold ranging from 0.0005 to 0.3 ppm (ATSDR, 2004), it is also one of the primary gases released from swine facilities that is associated with odor complaints due to its characteristic “rotten egg” smell.

Over the last few years, changes in livestock production methods in the US have led to the emergence of large-scale commercial livestock operations, substantially increasing the number of animals in geographically concentrated areas (Aneja et al., 2006). As emissions of trace gases (i.e., nitrogen and sulfur species) likely increase in parallel with the growth and consolidation of this industry, it is important to ensure that these operations do not exceed state regulatory levels for gases such as H₂S.

To date, few studies have reported H₂S emissions from waste storage treatment lagoons (Zahn et al., 2002; Lim et al., 2003; Blunden and Aneja, 2008). Arogo et al. (2000) studied the concentration and production of H₂S from stored liquid hog waste in a laboratory experiment. Arogo et al. (1999) have investigated the effects of environmental parameters (wind speed and air temperature) and manure properties (solids content and liquid temperature) in the laboratory and developed an overall mass transfer coefficient for emission of H₂S from liquid swine manure. The US Environmental Protection Agency (EPA) has developed a comprehensive model, WATER9, Version 2.0 (US EPA, 2001b) for estimating emissions of individual waste constituents in wastewater collection, storage, treatment, and disposal facilities.

In this study, a two-layer model of gas–liquid interchange for exchange between air and water is used to predict H₂S flux across an air–water interface. The interface between the two layers is often considered a two-layer film system (Whitman, 1923; Danckwerts, 1970; Liss and Slater, 1974). The two-film layer consists of well-mixed gas and liquid films adjacent to the interface. The rate of transfer is controlled by molecular diffusion through the stagnant boundary layer.

Similar models have been developed to predict emissions of ammonia (Aneja et al., 2001), dimethyl sulfide (Aneja and Overton, 1990), sulfur dioxide, nitrogen oxide, methane, carbon monoxide (Liss and Slater, 1974), and carbon dioxide (Quinn and Otto, 1971). It is noted that other modeling approaches may be utilized to predict gas exchange at the air–liquid interface (e.g., Danckwerts, 1970).

For comparison, three process-based models have been developed in order to predict the rates of H₂S flux from swine waste storage and treatment lagoons based on different conditions in the gas and liquid films. Two coupled Mass Transfer and Chemical Reactions Models based on the concept of simultaneous mass transfer and equilibrium chemical reaction were developed. One model considers flux based on the assumption of constant pH throughout the liquid film (MTCR Model I) and a second model considers a possible pH gradient in the liquid film due to diffusion processes (MTCR Model II). A third mass transfer model considers the hydrogen sulfide concentration in the bulk gas and liquid phases, neglecting chemical reactions in the gas and liquid films (MTNCR Model). Field experiments to measure H₂S emissions from an anaerobic waste treatment lagoon were previously conducted at a commercial swine finishing operation in North Carolina over each of the four predominant seasons (Blunden and Aneja, 2008). These experimental results are used to evaluate the model's accuracy in calculating lagoon H₂S emissions.

Section snippets

Experimental flux measurements

Hydrogen sulfide flux measurements were made at a commercial swine finishing operation in eastern North Carolina (Blunden and Aneja, 2008). Waste from the eight on-site animal confinement houses were flushed out with recycled lagoon effluent and discharged into the anaerobic lagoon from each house approximately once per week (varying days for each house).

Hydrogen sulfide flux was measured using a dynamic flow through chamber system (Aneja et al., 2000), consisting of a fluorinated ethylene

Sensitivity analysis

The three modeling approaches provide flux dependence for hydrogen sulfide emissions on lagoon temperature, lagoon pH, and aqueous sulfide content in the lagoon as well as atmospheric environmental factors such as ambient air temperature, wind speed, and the concentration of H₂S in the ambient air. Practical ranges of these parameters have been considered for the sensitivity analysis. The effect of each parameter was examined by varying the values of the parameter throughout a given range while

Conclusions

A processed-based mass transport model has been developed in an effort to predict hydrogen sulfide flux from anaerobic waste treatment systems. Different conditions were considered, resulting in three variations of the model. The MTNCR Model considers mass transport and neglects chemical reactions. Two models consider mass transport coupled with chemical reaction in the gas and liquid phases (MTCR). The MTCR Model I assumes pH to be constant for mass transport though the liquid film, while the

Acknowledgments

Funding for this research project was provided by the US Department of Agriculture (USDA) as a part of the National Research Initiative (NRI) under Contract No. 2003-05360. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

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Modeling hydrogen sulfide emissions across the gas–liquid interface of an anaerobic swine waste treatment storage system

Abstract

Introduction

Section snippets

Experimental flux measurements

Sensitivity analysis

Conclusions

Acknowledgments

Atmospheric Environment

Biophysical Journal

Evaluation of Henry's constant for H2S in water and sewage effluents

Journal of Environmental Science and Health A

Respiration and Circulation

The emission rate of dimethyl sulfide at the atmospheric–oceanic interface

Chemical Engineering Communications

Characterization of atmospheric ammonia emissions from swine waste storage and treatment lagoons

Journal of Geophysical Research

Measurement and modelling of ammonia emissions at waste treatment lagoon–atmospheric interface

Water, Air, and Soil Pollution

Emerging national research needs for agricultural air quality

EOS Transactions

Mass transfer coefficient for hydrogen sulfide emission from aqueous solutions and liquid swine manure

Transactions of the ASAE

Hydrogen sulfide production from stored liquid swine manure: a laboratory study

Transactions of the ASAE

Comparing ammonium ion dissociation constant in swine anaerobic lagoon liquid and deionized water

Transactions of the ASAE

Diffusion: Mass Transfer in Fluid Systems

Gas–Liquid Reactions

Diffusivity of Bisulfide Ion in Aqueous Solution

Principles of gas absorption

Industrial and Engineering Chemistry

Evaluation of Henry's constant for H₂S in water and sewage effluents