Characterization of the spatial variations in the structure and diversity of microbial communities within and between the stages of a wastewater treatment plant based on passive methods

Abstract

Wastewater is frequently discharged directly to water bodies without any treatment in developing countries. Despite the efforts to treat a higher percentage of sewage, wastewater treatment plants (WWTP) often end up abandoned due to the high maintenance and operational costs. Consequently, untreated wastewater often reaches water bodies and causes several pollution problems, such as eutrophication, affecting the communities' public health. To achieve the Sustainable Development Goal (SDGs) number six of the United Nations, which seeks to substantially improve water quality by 2030, lowering the release of pollutants and toxins into wastewater and safe reuse and recycling of treated water. It is crucial to switch from centralized to decentralized WWTP systems that require less maintenance and operation costs. Microorganisms are essential in wastewater treatment since they are involved in nutrient and organic matter removal through several metabolic pathways. However, microbial communities are susceptible to environmental variation, design and operational features of WWTP. Moreover, few studies have been performed focusing on the microbial communities within the treatment stages of complete decentralized systems. Therefore, this work's general objective was to characterize the spatial variations of the bacterial communities occurring in a decentralized wastewater treatment plant. This work is composed of three chapters. Chapter one describes the problem statement and context, research question, solution overview, and main contributions. Chapter two describes the types of constructed wetlands (CW) and the pollutant removal processes that occur within them. Additionally, this chapter discusses the effect of environmental parameters as well as operational and design factors on the structure, diversity, and activity of microbial communities. Chapter three presents the characterization of bacterial communities of a decentralized WWTP (the system under analysis) composed of a ST, an UAF, and a HFCW. Microbial characterization was carried out by high-throughput sequencing of 16S rRNA (V3-V4 region) to evaluate the spatial distribution of bacteria communities within a septic tank (ST), an up-flow anaerobic filter (UAF), and a horizontal flow constructed wetland (HFCW). Moreover, the effect of physicochemical parameters on the structure and diversity of bacterial communities was analyzed. Finally, chapter four describes future perspectives of this work and the importance of investigating the mechanisms to remove pathogenic microorganisms in the CW and the influence of iron in microbial communities' behavior during wastewater treatment.