Long term effects of zinc oxide nanoparticles on wastewater treatment in a membrane bioreactor (MBR) process

LONG-TERM EFFECTS OF ZINC OXIDE NANOPARTICLES ON WASTEWATER TREATMENT IN A MEMBRANE BIOREACTOR (MBR) PROCESS TAN SIEW YEN, MAGDALENE (B.Eng.(Hons.), NUS A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2015 i i ACKNOWLEDGEMENTS I would hereby like to express my deepest gratitude to my Project Supervisor, Associate Professor Ting Yen Peng for his invaluable advice and guidance throughout the course of this project Special thanks are also extended to Dr Qiu Guang Lei who did his utmost in supervising and guiding me throughout the project I am truly grateful by his support and assistance offered in the course of this project I would also like to express appreciate to all my laboratory mates, namely Divya Shankari Srinivasa Ragha, Shruti Vyas, Subhabrata Das, Thulasya Ramanathan and Gayathri Natarajan, and laboratory officer, Sylvia Wan, for their constant help and support while conducting the study in the laboratory Lastly, I would like to express my sincere gratitude to my family and friends for their constant support and encouragement ii This page is intentionally left blank iii TABLE OF CONTENTS DECLARATION i ACKNOWLEDGEMENTS ii TABLE OF CONTENTS iv SUMMARY vii LIST OF TABLES ix LIST OF FIGURES x NOMENCLATURE xii INTRODUCTION 1.1 Nanoparticles 1.2 Zinc oxide nanoparticles 1.3 Membrane bioreactors 1.4 Objectives of research 1.5 Scope of research 1.6 Schedule of various experimental phases LITERATURE REVIEW 2.1 Zinc oxide nanoparticles 10 11 11 2.1.1 Environment relevant concentrations 12 2.1.2 Stability of zinc oxide nanoparticles in aqueous environment 17 2.2 Ecotoxicity effects of zinc oxide nanoparticles 19 2.2.1 Mechanisms of zinc oxide nanoparticles 21 2.2.2 Effects of zinc oxide nanoparticles on bacteria 23 2.2.3 Effects of zinc oxide nanoparticles on wastewater treatment 25 2.3 Membrane bioreactors 29 iv 2.3.1 Introduction 29 2.3.2 ZnO nanoparticles in MBRs 34 2.3.3 Membrane fouling 39 2.3.4 Membrane fouling control 44 MATERIALS AND METHODS 47 3.1 Experimental setup 47 3.2 Operating conditions in the MBR system 49 3.3 Synthetic municipal wastewater feed 50 3.4 Analytical methods 51 3.4.1 Wastewater characteristics 52 3.4.2 Sludge characteristics 54 3.4.3 Membrane fouling rate 55 3.4.4 Zinc phosphate precipitate in mixed liquor 55 3.4.5 Soluble Microbial Products (SMP) and Extracellular Polymeric Substances (EPS) 56 3.4.6 Bacterial community dynamics 57 3.4.7 Zn content in wastewater and activated sludge 59 RESULTS AND DISCUSSION 60 4.1 Standard curves 60 4.2 Effect of ZnO nanoparticles on wastewater treatment 60 4.2.1 Wastewater characteristics 61 4.2.2 Sludge characteristics 71 4.2.2.1 MLSS, MLVSS, SVI and Sludge morphology 71 4.2.2.2 Soluble microbial substances (SMP) and Extracellular polymeric substances (EPS) 78 4.3 Fate of ZnO nanoparticles 4.3.1 Solubility of ZnO NPs 88 88 v 4.3.2 Removal behaviour of ZnO NPs 89 4.3.3 Mass balance of Zn 92 4.4 ZnO nanoparticles effect on bacterial community 96 CONCLUSIONS 100 5.1 Effects of ZnO NPs on removal efficiencies 100 5.2 Effects of ZnO NPs on sludge characteristics 101 5.3 Effects of ZnO NPs on bacteria community in MBR 101 5.4 Fate of ZnO NPs in MBR 102 FURTHER STUDIES 103 6.1 Effect of ZnO NPs in MBR using municipal wastewater 103 6.2 Transformation of ZnO NPs in MBR system 104 6.3 Impact of ZnO NPs on MBR bacterial community 105 6.4 Effect of ZnO NPs on physiochemical stability of MBR activated sludge flocs 105 6.5 Impact of ZnO NPs on membrane fouling 106 REFERENCES 107 APPENDIX 123 Appendix A1: Standard Curves 123 Appendix A2: EDX Analysis 127 vi SUMMARY In recent years, the growing release of zinc oxide nanoparticles (ZnO NPs) from consumer-products in various sectors into sewage systems has raised concerns on the potential adverse impact on wastewater treatment plants MBR systems, which have been widely used since 1990s for municipal wastewater treatment, are traditionally not designed to cope with the removal of nanoparticles At present, the effect of this new emerging pollutant, ZnONPs, on the performance of MBR system is still largely unknown In this study, the effect of zinc oxide nanoparticles (ZnO-NPs) on the system performance and its removal behaviour in an MBR system were investigated A lab-scale submerged MBR system was operated continuously for 242 days Three experimental phases were conducted, with 0, mg/L and 10 mg/L of ZnO NPs added into the system over the whole duration Significant changes in COD, TN and phosphorous removal efficiency of the system were observed with the addition of mg/L and 10 mg/L ZnO NPs Concentrations of proteins and polysaccharides in SMPs showed significant changes while that of EPSs were affected to a smaller extent The MBR system was efficient in removing ZnO-NPs from the wastewater, achieving higher than 95% removal efficiency on almost all days Sorption onto biomass works well as the main removal mechanism at low ZnO-NPs vii concentration while membrane rejection also plays a part in the removal of Zn when concentration was increased to 10 mg/L ZnO-NPs caused a major shift in the bacterial community structure but no significant change in community diversity as revealed from 16S rRNA genebased PCR-DGGE analysis In addition, the type of EPS also changed from those enveloping the sludge to those forming a dense matrix around the bacteria cells KEYWORDS Membrane bioreactor; municipal wastewater treatment; zinc oxide nanoparticles; membrane fouling; extracellular polymeric substances (EPS), bacterial community dynamics viii LIST OF TABLES Table 2.1 Potential fate of nanoparticles in aquatic systems 13 Table 2.2 Concentration of nanomaterials in consumer products (in g/kg or mg/kg product) and the consequent added concentration and releases in the Dutch reaches of the Rhine and Meuse 14 Table 2.3 Modeled concentrations of ZnO nanoparticles released into environmental compartments in different countries, shown as mode (most frequent value) and as range of the lower and upper quantiles (Q0.15 and 0.85) 15 Table 2.4 Some common nanoparticles, their respective applications, and some estimates of their potential environmental size concentrations 16 Table 2.5 Typical MBR effluent quality 31 Table 3.1 Composition of synthetic wastewater 50 Table 4.1 Summary of effects of ZnO NPs on nutrient removal in 70 wastewater Table 4.2 Shannon-Wiener diversity index of the bacterial community in MBR 98 ix 100 Markus, A.A., Parsons, J.R., Roex, E.W.M., Kenter, G.C.M., Laane, R.W.P.M., 2013 Predicting the contribution of nanoparticles (Zn, Ti, Ag) to the annual metal load in the Dutch reaches of the Rhine and Meuse Science of the Total Environment 456–457, 154–160 101 Martinew-Castanon, G.A., Nino-Martinez, N., Martinez-Gutierrez, F., Martinez-Mendoza, J.R., Ruiz, F., 2008 Synthesis and antibacterial activity of silver nanoparticles with different sizes J Nanopart Res 10, 1343-1348 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curve for NO3 N Figure A1.6 Standard curve for PO43 P 125 Figure A1.7 Standard curve for Polysaccharides Figure A1.8 Standard curve for Proteins 126 Appendix A2: EDX Analysis Figure A2.1: Elemental content of sludge on Day 69 127 Figure A2.2 Elemental content of sludge on Day 140 128 Figure A2.3 Elemental content of sludge on Day 214 129 Figure A2.4 Elemental content of sludge on Day 240 130 [...]... reported ZnO NP concentrations of 10 ng/l in natural surface water and 430 ng/l in treated wastewater in Europe, 1 ng/l in natural surface water and 300 ng/l in treated wastewater in US and 13 ng/l in natural surface water and 440 ng/l in treated wastewater in Switzerland, as shown in Table 2.3 14 Table 2.3 Modeled concentrations of ZnO nanoparticles released into environmental compartments in different... micron sized pollutants, but very 6 little information is currently available on the fate of nanoscale materials in treatment processes Several studies had confirmed that a considerable amount of the NPs, including zinc oxide, released into the activated sludge process can be absorbed by the activated sludge, resulting in a reduction of NPs in the effluent and an accumulation in the biomass (Kaegi et al.,... products are retained by wastewater treatment plants (Benn and Westerhoff, 2008; Kiser et al., 2009; Tiede et al., 2010) However, the fate of ZnO-NPs during and after wastewater treatment remains largely unknown Conventional wastewater treatment plants are not designed to remove nanoparticles from wastewater stream, and the effect of nanoparticles on the treatment efficiencies of wastewater process also... main advantages of choosing MBR over the conventional activated sludge system (CAS) in wastewater treatment are lower sludge production and smaller carbon footprint Conversely, the main challenges are in higher energy and equipment costs and membrane fouling In wastewater treatment using MBR, ultrafiltration (UF) membranes of pore size 0.1-0.4 µm are typically used, and thus able to remove bacteria... bacteria and other micron-sized pollutants from wastewater The question of how effective MBR is in removing nanoparticles, specifically ZnO-NP, now arises Typical wastewater treatment systems, MBRs included, are not designed to treat wastewater containing significant amounts of nanoparticles The mechanisms of particle transport and the impact of particle size during wastewater treatment have traditionally... shown in Table 2.1 12 Table 2.1 Potential fate of nanoparticles in aquatic systems (Klaine et al., 2008, Weinberg et al., 2011) Various properties of ZnO-NPs have made them attractive constituents in many consumer products In European Union countries alone, annual production of ZnO-NPs in 2012 was 1600 tonnes (Sun et al., 2014) Zinc oxide is used mainly in sunscreens and paints or coatings Usage data published... et al (2011) indicate that about 40% of the German population can be expected to use sunscreen, for about 20 days a year Combining the scarce available data which included indicative figures on the content of nanomaterials in various products and usage profiles, an estimate on the contribution of nanoparticles to the annual metal load of two Dutch rivers was reported by Markus et al., 2013 It was predicted... occur in wastewater and the potential toxicity, if any In view of these issues, it is important that the fate and transformation of ZnO-NPs during the wastewater treatment process be examined in detail Lastly, it is also important to study the changes in bacteria community structure due to longterm exposure of ZnO-NPs in order to gain more insight into the microbialNPs interaction in wastewater treatment. .. Wilson Database, 2011) Occasionally, accidental spillages or permitted release of industrial effluents in aquatic systems could also lead to direct exposure to nanoparticles for humans via inhalation of water aerosols, skin contact and direct ingestion of contaminated drinking water or particles adsorbed on vegetables or other foodstuffs (Moore, 2006) More indirect exposure could arise from ingestion of. .. hindered aggregation of both morphologies Chaúque et al., 2013 discussed the impacts of stability of ZnO-NPs in wastewater treatment It was found that the release of zinc from ZnO-NPs in wastewater was more significant under acidic conditions and low ionic strength, but the release of zinc from ZnO-NPs in wastewater is lower compared to de-ionized water, indicating the role of biomass present in wastewater ... of zinc oxide nanoparticles 19 2.2.1 Mechanisms of zinc oxide nanoparticles 21 2.2.2 Effects of zinc oxide nanoparticles on bacteria 23 2.2.3 Effects of zinc oxide nanoparticles on wastewater treatment. .. of this project I would also like to express appreciate to all my laboratory mates, namely Divya Shankari Srinivasa Ragha, Shruti Vyas, Subhabrata Das, Thulasya Ramanathan and Gayathri Natarajan,... industrial effluents in aquatic systems could also lead to direct exposure to nanoparticles for humans via inhalation of water aerosols, skin contact and direct ingestion of contaminated drinking water