Civil Engineering ETDs


Meghan Preut

Publication Date



Activated sludge is one of the most commonly applied biological treatment processes for wastewater treatment. The microorganisms grown in activated sludge systems are responsible for the removal and transformation of wastewater contaminants. These bacterial populations are sensitive to wastewater characteristics, plant design and operational parameters. Because the effectiveness of activated sludge relies on microbial activity, a better understanding of the microbial communities and how they respond to constraints may be useful for improving plant performance. Environmental conditions in the activated sludge process are complex and the identification and classification of the communities present has proven a challenge for engineers as well as microbiologists and ecologists. Many bacteria in activated sludge cannot be cultured and conventional culture dependent techniques are not adequate in defining these populations in depth. Recent molecular methods have advanced the understanding of this complicated ecosystem, yet much remains unclear due to plant specific dynamics that influence community structure. Sequencing techniques are a novel approach to the identification of the microbial populations of activated sludge. This new technology allows researchers to ask exploratory questions about specific and distinct wastewater treatment processes that could not be efficiently completed with other methods. One such unique wastewater treatment plant that may benefit from the use of pyrosequencing techniques is the Los Alamos National Laboratory Sanitary Wastewater System (LANL SWWS) located in Los Alamos, New Mexico. This plant experiences highly variable flow and utilizes glycerin as a supplemental carbon source due to low-strength carbon influent. In addition, the plant experienced an upset in 2012 with respect to excessive tardigrade growth. In response introduced sludge from another wastewater treatment plant (seed event) to help improve the microbial populations. 454-pyrosequencing was used as a method to identify and analyze the microbial populations of this glycerin enriched activated sludge wastewater treatment plant. The objectives of this research were to 1) determine the differences between LANL SWWS activated sludge population and that in other plants, 2) identify and evaluate the effects of glycerin as a supplemental carbon source on the microbial population, 3) identify any adaptive characteristics or population changes due to the seeding event, 4) determine if there were certain operational conditions or environmental factors that influence specific microbial populations. In order to accomplish these objectives, samples were taken from LANL SWWS and other nearby wastewater treatment plants. These samples were pyrosequenced and the results were analyzed with various bioinformatics tools. The microbial communities were compared between LANL SWWS and other plants that did not utilize an external carbon source. Analysis of the activated sludge population before and after the seed event was performed and contrasted with the microbial structure and distribution of the activated sludge used to inoculate LANL SWWS. Wastewater characteristics and plant parameters were investigated to determine bacterial responses to environmental and operational conditions. There was a distinction between the microbial populations of LANL SWWS and conventionally fed wastewater treatment plants. The relative abundance of the dominant taxa found in the samples exposed to glycerin as an external carbon source exhibited a different distribution compared to the samples obtained from conventional treatment facilities. It was also apparent that the introduction of foreign biomass into the LANL SWWS activated sludge via the seed event had no direct influence on the microbial community. The main contributing parameter that affected the microbial population of LANL SWWS appeared to be the solids residence time, which was likely the cause of the tardigrade proliferation and could also justify the distribution of the consortia within the activated sludge.


Wastewater, Microbial populations, 454-pyrosequencing, supplemental carbon source, Glycerin, Los Alamos National Laboratory


Office of the Vice President for Research, Grant 456355, and Los Alamos Laboratory Directed Research and Development

Document Type




Degree Name

Civil Engineering

Level of Degree


Department Name

Civil Engineering

First Advisor

Schuler, Andrew

First Committee Member (Chair)

Thomson, Bruce

Second Committee Member

Takacs-Vesbach, Cristina

Third Committee Member

Wingo, Robert