Impact of hydraulic retention time and organic matter concentration on performance of side-stream aerobic granular membrane bioreactor
Date
2019-07-16
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Abstract
Widespread membrane bioreactors (MBRs) application has been limited due to an undesirable yet inherent phenomenon named membrane fouling. Membrane fouling can be defined as unfavorable attachment of organic and inorganic matter inside (pore clogging) or onto (cake layer) membrane pores. Aerobic granulation biotechnology has become a promising substitute for activated sludge process (ASP) by offering advantages including high biomass retention, good settleability, high resiliency to high strength wastewater and shock loading and strong and round shape structure. Aerobic granulation technology is attributed to cell-to-cell interaction between microorganism consisting physical, chemical and biological phenomena. An integration of aerobic granulation technology (AG) and membrane bioreactors (MBRs) leading to the advent of aerobic granulation membrane bioreactor (AGMBR) method, has been able to suppress fouling rate. It was believed that large particle size, high density and more compact and dense structure of granules can significantly control and reduce membrane fouling compared to conventional MBRs method which are operated by activated sludge. However, granules instability in long term operation is a detrimental obstacle which is followed by delayed irreversible (i.e., irrecoverable) fouling in AGMBR application. Operational parameters majorly contributed to granule formation and membrane fouling. Hence, optimum selection of operational factors plays significant role in granules stability leading to fouling control in AGMBR application. This study investigated the effect of hydraulic retention time (HRT) and chemical oxygen demand (COD) concentration on membrane fouling in aerobic granular membrane bioreactor (AGMBR) in a systematic approach. Changes in HRT (7, 10, and 15 h) and COD (500, 1000 and 1500 mg/L) were applied in five operational phases, corresponding to different organic loading rates (OLRs), to determine the most significant parameters to control membrane fouling for enhanced AGMBR performance. Membrane fouling was associated with two critical points: initial flux reduction (primary fouling) and maximum transmembrane pressure (TMP) (secondary fouling). Membrane permeability loss was significantly intensified with increase in HRT from 7.5 to 15 h and COD from 500 to 1000 mg/L (OLR of 1.6 kg COD/m3.d). The highest polysaccharide content of loosely bound EPS (0.41 mg PS/mg VSS) and soluble microbial products (SMPs) (27 mg PS/L) occurred alongside poor AGMBR performance at this phase. Variations in membrane fouling was accompanied with considerable changes in Flavobacterium, Thauera and Paracoccus populations. Membrane performance deteriorated with reduction in Flavobacterium and Thauera relative abundances, while system recovery coincided with Paracoccus proliferation. Generally, OLR diminution from 3.6 kg COD/m3.d (phase I) to 1.6 kg COD/m3.d (phase IV) resulted in severe granules breakage alongside intensified membrane fouling. HRT and HRT and COD interaction were identified as the most significant parameters in controlling membrane fouling.
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Keywords
Aerobic Granulation, Side-stream aerobic granular membrane bioreactor
Citation
Tavana, A. (2019). Impact of hydraulic retention time and organic matter concentration on performance of side-stream aerobic granular membrane bioreactor (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.