Xiaorong Dai

Research output: ThesisPh.D. thesis

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Airborne contaminants and odor from animal manure and municipal wastewater can affect human physical and psychological health, and the environment. The estimation of gas emission rates and development of technologies to reduce the release of noxious gases from wastewater is limited by current knowledge on the production pathways of gases and the release mechanisms from various sources. The overall objective of this PhD project was to assess the production and release of noxious gases from animal manure and municipal wastewater by giving emphasis on the effects of waste management (such as, surface disturbances during storage, acidification and aeration), the hydrolysis of urea by bacteria, the waste types and wastes physicochemical characteristics.
Animal wastewater stored in under-floor deep pit is characterized by the frequent occurrence of surface liquid disturbances caused by the urine and feces that fall into the pit, and alter the chemical equilibrium of the liquid surface. A laboratory study was conducted in manure reactors with simulated in-barn storage conditions for determining the NH3, H2S and CO2 emissions as affected by liquid surface disturbances.
To extend knowledge about quantification and release behavior of pollutant gases from various waste sources, NH3, CO2, H2S, and SO2 emissions during storage of five types of wastewater (i.e., swine manure, dairy manure, beef manure, layer hen manure and municipal wastewater) were studied and compared.
Ammonia is a gas pollutant generated from animal manure (mixture of urine and feces) by hydrolysis of urinary urea catalyzed by microbial urease present in feces. To better understand the enzymatic process of ammonia formation in manure, experiments based on Michaelis-Menten kinetics were conducted to obtain accurate estimates of the kinetic parameters of urease activity of feces and manure from pig and cattle, and to investigate the effects of pH on animal fecal urease by individual ammonium generation rate determination at five pH levels.
Investigating the gas production and release mechanisms is important not only for estimating better gas emissions from wastewater, but also for improving gas emission abatement technologies, such as slurry acidification. Experiments of slurry aeration and acidification were conducted in animal wastewater reactors which acted as dynamic flux chambers. Ammonia, hydrogen sulfide, and carbon dioxide emissions during the storage were measured and their relations to the chemical compositions of the slurry were analyzed.
The results of this PhD study suggest that future estimation of gas emissions should consider transient-state conditions, especially in the case of H2S, as occupational exposures and the associated health risks will be highly underestimated if the evaluation of exposures to H2S is based on emissions from slurries stored under undisturbed conditions. The convective mass transfer governed NH3 release, while bubble-release was dominant in the releases of CO2, H2S, and SO2.The physicochemical characteristics of different types of wastes (e.g., the total nitrogen, total ammoniacal nitrogen, dry matter, and pH) had great influence on the releases of NH3, CO2, H2S, and SO2. The investigation of kinetic parameter showed that the maximum urease activity for pig feces is at around pH 7, while that for the cattle feces is around pH 8, indicating that the predominant fecal ureolytic bacteria species differ between the animal species. The study on urease activity determination in animal feces contributed to a better understanding of the urea hydrolysis process in manure, and provides the basis for further studies of enzymatic degradation process in manure, and the obtained enzyme-kinetic parameters can be utilized in prediction modeling of ammonia production rates and thus ammonia release from animal productions. The results of the acidification study showed that slurry acidification can reduce ammonia emissions by 50-77% and has no significant effect on CO2 and H2S emissions during treatment and subsequent storage.
Original languageEnglish
  • Blanes-Vidal, Victoria, Principal supervisor
  • Karring, Henrik, Co-supervisor
Place of PublicationOdense
Publication statusPublished - 2014

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