Constructed Wetlands for Sustainable Wastewater Treatment in the UAE: Microbiology Study, Performance Evaluation & Life-Cycle Assessment

Abstract

Constructed wetlands (CWs) for wastewater treatment are an attractive alternative to conventional wastewater treatment for selective application in the United Arab Emirates. Despite the relatively geographically disparate communities, the UAE is still overly reliant on centralized treatment systems. Thus, the implementation of energy efficient and decentralized wastewater treatment alternatives has great potential for beneficial impact. The treatment performance of constructed wetlands for the removal of organic matter and nutrients is thought to be largely dependent on microbially-mediated processes. In this study, the focus is a full-scale start-up CW (vertical subsurface flow type) operating under arid climate conditions in the UAE. Soil core samples were frequently collected after initial sewage feeding start-up. The spatial distribution was retained during sampling with the aim of revealing the microbial community development and shifts over depth as well as time both during the system’s start-up and throughout its stabilization period. Genomic DNA quantification and qPCR were used to assess the development of microbial biomass whereas PCR-DGGE of the 16S rRNA gene was used to study the population shifts. Genomic DNA concentrations were found to be low during the system’s start-up indicating low amounts of biomass. The results demonstrated that an increasing genomic DNA concentration with time is an expected outcome. DGGE profiles showed an initial undifferentiated profile that culminated in a clearly differentiated profile with an increasing diversity with depth. The study of the microbial community structure and diversity in CWs is necessary to achieve a sound understanding of the variables involved in an adequate performance and should lead to enhanced system design and a deeper understanding of treatment subtleties. A survey that analysed the major design and performance indicators of CWs operating in the UAE was conducted. Analysis of the results indicated a shift over recent years from designs initially conceived for other regions to more tailored design addressing the specific water re-use quality limits of the UAE with the mitigation of excessive solids handling. Finally, life-cycle assessment (LCA) was used as an environmental impact assessment tool to compare two decentralized wastewater treatment options for Masdar City: the existing membrane bioreactor (MBR) and a proposed equivalent CW. The impact assessment was utilized to identify major impact categories and their causes and what modifications can be introduced to alleviate them.

Date of Award	Jun 2013
Original language	American English
Supervisor	Jorge Rodriguez (Supervisor)