Investigation of the impact of zinc oxide (ZnO) nanoparticles (NPs) on soluble microbial product (SMP) formation and characteristics in membrane bioreactor (MBR)

• Main Author: Eng, Chin Yee
• Other Authors: Zhou Yan
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/68142
• Institution: Nanyang Technological University

In recent years, membrane bioreactors (MBRs) are increasingly popular in wastewater treatment industry. In MBR, soluble microbial products (SMP) are a key factor that contribute to membrane fouling. In this research study, the production, characteristics and behavior of SMP in the presence of zinc oxide (ZnO) nanoparticles (NPs) were investigated in order to clarify the impact of environmental nanoparticle pollutants (ENPs) on SMP behavior in MBRs. Conventional chemical analysis (phenol-sulfuric acid method and Lowry method) showed that the SMP production was elevated as ZnO NPs concentration increased. However, acclimation of microorganisms to ZnO NPs had taken place as the exposure time increased. The increase in SMP concentration was found to be due the inhibition of SMP biodegradation, cell lysis and secretion of SMP by microorganisms to alleviate the toxicity of ZnO NPs. Further examination of bound extracellular polymeric substances (EPS) demonstrated that hydrolysis of EPS had occurred and contributed to SMP accumulation. High Performance Size Exclusion Chromatography (HP-SEC) analysis confirmed the enhanced production of SMP especially high molecular weight (MW) organic matters in the presence of ZnO NPs. Florescence Excitation Emission Matrix (FEEM) analysis further demonstrated that the concentration of organics that constituted SMP were generally increased in the presence of ZnO NPs especially amino acid-like, protein-like and polysaccharide-like matters. The production of these organics would help in the adaptation of microorganisms to the toxic ZnO NPs. The fluorescence regional integration (FRI) analysis also showed that composition of SMP were slightly affected by ZnO NPs where the percentage distribution of amino acid-like and protein-like organics were enhanced. These protein substances had greater potential to clog the pores of the membrane, leading to membrane fouling.