Microbial characterization in municipal wastewater treatment and QMRA of edible crop irrigated with treated effluent

  • Yamrot Mulugeta Amha

Student thesis: Master's Thesis


The use of treated wastewater for the irrigation of edible crops in the UAE presents an opportunity to enhance food security while overcoming water scarcity issues due to the arid climate and a growing water demand in the region. Developing reliable Quantitative Microbial Risk Assessment (QMRA) procedures is crucial for setting recommendations on reuse applications of treated wastewater. In this study, a comprehensive microbial diversity analysis of the municipal wastewater treatment process and a QMRA was carried-out using molecular biology tools and stochastic modeling. In contrast to previous studies, in which common pathogens or their indicator organism were directly targeted, this study focused on the analysis of the overall microbial community profiles. This was done to understand the microbial ecology in the warm climate of Abu Dhabi and to detect non-targeted pathogens present in the treated wastewater. Furthermore, samples from three stages of the treatment i.e., pre-treated, pre-chlorinated and post-disinfected, were studied at two different seasonal time-points, to analyze the efficiency of the treatment facility in removing pathogens. The microbial diversity at different stages of the treatment process was determined using PCR-DGGE with subsequent DNA-band sequencing, as well as direct next generation sequencing i.e., Illumina sequencing. The results from Illumina sequencing revealed the presence of 21 untargeted pathogens, such as sequences indicating Mycobacterium tuberculosis, Bacillus anthracis, Escherichia coli O157:H7 and other bacteria that are known human pathogens, in different stages of the treatment, including post-disinfected samples. Additionally, the micro-diversity of E. coli was studied at different stages of the treatment using a newly developed molecular technique. Quantitative-PCR (qPCR) was used to enumerate Salmonella spp. in post-disinfected samples. A QMRA model was constructed to estimate the disease burden of salmonella infection from raw consumption of vegetables (lettuce, cabbage and cucumber) irrigated with treated wastewater. Exposure models were developed and simulated using Monte Carlo analysis using 10,000 iterations per simulation, to account for variability and uncertainty of model input parameters. The results showed elevated median disease burden, when compared with acceptable disease burden set by WHO, which is 10-6 disability adjusted life years (DALYs) per person per year. The results of this study showed the need to incorporate modern molecular methods for pathogen detection to monitor treated wastewater and advanced disinfection processes for application in edible crop irrigation.
Date of Award2014
Original languageAmerican English
SupervisorFarrukh Ahmad (Supervisor)


  • Wastewater Treatment; Purification; Mycobacterium Tuberculosis.

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