Doctor of Philosophy
School of Civil, Mining and Environmental Engineering
Phan, Hop Van, Nutrients and trace organic contaminants removal by an anoxic-aerobic membrane bioreactor (mbr): lab-, pilot- and full-scale investigations, Doctor of Philosophy thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2015. http://ro.uow.edu.au/theses/4564
Increasingly stringent environmental regulations and freshwater shortage are key drivers for a worldwide trend of introducing advanced technologies for wastewater treatment, particularly in removing nutrients (i.e., nitrogen and phosphorous) and trace organic contaminants (TrOCs). Membrane bioreactor (MBR) is a compact process that employs membranes for effective solid-liquid separation, which in turn brings about additional advantages such as decoupling of hydraulic retention time (HRT) and sludge retention time (SRT), maintenance of higher mixed liquor solids concentration (MLSS) than the conventional activated sludge (CAS) process and potentially better removal of resistant contaminants in a single step. The anoxic-aerobic MBR process combines bioreactors harbouring different redox conditions and thus facilitates efficient removal of nutrients, and potentially that of TrOCs. This thesis aims to evaluate the performance of an anoxic-aerobic MBR in terms of nutrient and TrOC removal at lab-, pilot- and full-scale installations. The dynamics of bacterial communities in the MBR system and the corresponding removal performance under different operating conditions have been assessed. The robustness of the anoxic-aerobic MBR during simulated ‘hazardous events’ i.e., deviations in operating conditions is also evaluated.
Simultaneous nitrogen and TrOC removal (a set of 30 TrOCs) by a laboratory scale anoxic-aerobic MBR was demonstrated. In this study, biodegradation was demonstrated as the main TrOC removal mechanism, with aerobic degradation playing a major role. Low oxidation reduction potential (ORP) regimes (i.e., anoxic) were conducive to biodegradation of some TrOCs, but it may only aid in biosorption in absence of internal recirculation between the anoxic-aerobic zones. Metagenomic approach using pyrosequencing of 16S rRNA genes revealed the bacterial communities developed in the anoxic-aerobic MBR system. Internal recirculation between the aerobic and anoxic bioreactors was observed to be a key driving force shaping the bacterial communities in the anoxic-aerobic MBR. Insights into the shifts in bacterial communities along with the changes in removal efficiencies under different operating conditions have been provided. A more diverse bacterial community was noted during operation without sludge withdrawal (‘infinite’ SRT) than during an SRT of 25d. However, with a few exceptions, the bulk organic, nitrogen and TrOC removal performance were similar under the SRTs investigated, suggesting that the shorter SRT investigated in this study (25 d) was adequate for the development of functional bacterial groups in the MBR. Potential bacterial groups participating in TrOC degradation were identified.