English

 

Name of the Student : Rateb Hussein
Name of the supervisor/s :

Dr. Khaled Swaileh

Title of the thesis :

Molecular Identification of Microbial Communities in Wastewater Treatment Systems

Abstract :  

The microbial communities in samples from three wastewater treatment systems have been examined using modern molecular techniques. The samples included a scum layer of Al Bireh Wastewater Treatment Plant secondary sedimentation tank, Pilot-scale Upflow Anaerobic Sludge Blanket (UASB) sludge and a biofilm of a Biofilter. The three samples origin is a municipal wastewater. The goal of the study was to identify the microbial content of the scum sample in order to control scum formation and to improve the efficiency of the UASB and Biofilters. The molecular techniques applied to achieve these goals were PCR, DGGE and 16S rRNA sequencing. DNA was extracted from the three samples and small regions of the 16S rRNA genes of both Archaea and Bacteria were amplified via the polymerase chain reaction (PCR). Thereafter, samples were analyzed via Denaturing Gradient Gel Electrophoresis (DGGE), a technique that allows for the separation and visualization of individual PCR products that are of the same size, based on differences in their sequence. About 500bp of the 16S rRNA genes were amplified for the determination of dominant PCR product by DGGE. The whole 16S rRNA genes were amplified and cloned in pCRII® – TOPO vector. Dominant clones were sequenced and compared to a published database for identification using Basic Local Alignment Search Tool (BLAST search).

Several filamentous bacteria were identified including Microthrix parvicella, Nocardia sp., Hyphomicrobium facilis, Chloroflexi, Candidates TM7 and Nocardioides oleivorans. These filamentous bacteria are thought to be the reason behind scum formation in the BWWTP. The low F/M ratio and high grease and oil load in the aeration tank could be the main reasons behind the spread of these groups of bacteria in the system. These groups of microorganisms exhibit seasonal variation depending on temperature and oil load. Solving the problem of scum formation could be based on the idea that the F/M ratio must be increased and the oil/grease loads in the influents must be reduced.

The methanogenic community of the UASB analyzed by PCR based DGGE and FISH analysis showed the presence of highly diverse methanogens including Methanospirillum hungatei, Methanosarcina barkeri, Methanosarcina mazei, Methanobrevibacter arboriphilus and other methanogen clones. The abundance of these methanogens is low and this may result from high oil and grease load (municipal wastewater) which contains long chain fatty acids (LCFA) that are toxic to methanogens. All these conditions result in 60% removal for COD which is lower than other studies done at the same conditions and achieved 88% COD removal for domestic wastewater.

The chemical analysis of the UASB shows that the reactor removal efficiency for COD is 60% and that for BOD is 56%. The reactor needs further adjustment to increase the microbial content and achieve higher removal efficiency.

The microbial community in the Biofilter composed of mostly uncultured bacteria of soil origin. This could originate from the packing material of the system (rocks, sand and PVC). In addition, the biofilm was not yet developed as the system was in its startup phase. The presence of Zoogloea ramigera is promising as this microorganism plays a role in the biofilm formation.