Polyaluminum Chloride and Chitosan Composite Coagulant for Natural Organic Matter Removal

Transcription

1 Polyaluminum Chloride and Chitosan Composite Coagulant for Natural Organic Matter Removal 1,A. Liana 1, S. Liu 1, M. Lim 1, C. Chow 2, D. Wang 3, M. Drikas 2, R. Amal 1 1 ARC Centre of Excellence for Functional Nanomaterials, School of Chemical Engineering, The University of New South Wales, Sydney, Australia 2 Australian Water Quality Centre (AWQC), South Australian Water Corporation, Adelaide, Australia 3 SKLEAC, Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China mega@student.unsw.edu.au

2 Natural Organic Matter NOM is water pollutant produced from the decomposition of plant and animal materials. Heterogeneous, complex mixture of organic compounds. Slide 2 of 32

3 Removal of NOM from Water Removal of NOM from drinking water is desirable. Negative impacts of NOM in drinking water : Colour, taste and odour Complex with heavy metals, pesticides and herbicides Promote microbiological regrowth Precursor of Disinfection By-Products (DBPs) NOM + Cl 2 DBP CHCl 3 CHCl 2 Br CHClBr 2 CHBr 3 Slide 3 of 32

4 Polyaluminum Chloride NOM can be removed by polyaluminum chloride (PACl). PACl hydrolyse to form different aluminium species. PACl Monomeric (Al 3+ ) Oligomeric Colloidal hydroxides (Al(OH) 3 ) (Al 13 O 4 (OH) 24 (H 2 O) 12 ) 7+ Al Keggin Structure of Al 13 Slide 4 of 18 Slide 4 of 32

5 PACl Composite Coagulant PACl outperforms conventional coagulant like alum but its efficiency can still be improved. Performance of PACl can be enhanced by addition of organic polymer to create a new composite coagulant. Slide 5 of 18 Slide 5 of 32

6 PACl Composite Coagulant What is Chitosan? Chitosan is a natural, biodegradable and non toxic cationic polymer extracted from crustaceans, shrimps and crabs. Slide 6 of 18 Slide 6 of 32

7 Preparation of PACl-Chitosan Preparation of PACl Stock Chitosan NaOH Stock Preparation of Chitosan Stock Chitosan Water HCl AlCl PACl 3 HEAT SPEED Slow Titration at 55 C 75 C Composite Coagulant Al (PACl Chitosan) PACl HEAT SPEED Mix for 1 h Chitosan n Slide 7 of 18 32

8 Testing of PACl-Chitosan Composite Coagulant Natural Water NW Water sourced from Myponga Reservoir, South Australia Synthetic Water SW Milli-Q water Humic acid (Aldrich) 10 mg/l DOC 4 mg/l KCl 96 mg/l NaHCO 3 60 mg/l CaSO 4. 2H 2 O 60 mg/l MgSO 4 Slide 8 of 17 32

9 Testing of PACl-Chitosan Composite Coagulant Coagulation studies at ph 6 in standard jar test apparatus Measure the removal efficiency by: Dissolved Organic Carbon (DOC) indicator of total organic UV-Visible Absorbance (UV 254 ) indicator of aromatic organic matters Slide 9 of 17 Slide 9 of 32

10 Effects of Al Concentration on Removal Efficiency Similar NOM removal efficiency (UV 254 ) at lower concentration of Al for composite coagulant. NOM removal for SW water is higher than that for NW. SW PACl-Chi SW PACl NW PACl-Chi NW PACl Slide 10 of 32

11 Why is the optimum removal of NOM from synthetic water better than that from natural water? To understand why, we study the chemical characteristics of NOM from two water sources. Slide 11 of 18 Slide 11 of 32

12 Functional Group NOM Characteristics Synthetic Water [1] Natural Water [2] Carboxyl 16% 17.4% Aromatic 45% 17.2% Aliphatic 33% 61.8% Carbonyl % Literature has shown that aromatic compounds are easier to be removed compared to aliphatic compounds [3] 1. Pelekani, C., et al. Environmental Science & Technology, : p Niederer, C., R.P. Schwarzenbach, and K.-U. Goss. Environmental Science & Technology, : p Liang, L. and P.C. Singer. Environmental Science & Technology, : p Slide 12 of 18 32

13 NOM Characteristics High performance size exclusion chromatography analysis : Synthetic Water Natural Water Different apparent molecular weight for two water samples Slide 13 of 18 32

14 NOM Characteristics NOM characteristics affect removal performance. NOM with high aromatic content is easier to be removed than NOM with high aliphatic content. Better removal was achieved for NOM with higher molecular weight. Slide 14 of 32

15 Effects of Al Concentration on DOC Removal For SW Chitosan addition reduced the amount of Al required SW PACl-Chi SW PACl NW PACl-Chi NW PACl Slide 15 of 32

16 What is the role of Chitosan in composite coagulant? Why addition of Chitosan improved the removal at lower [Al] for SW but NOT for NW? Slide 16 of 18 Slide 16 of 32

17 NOM Characteristics HPSEC analysis for water samples after coagulation with 2.16 mg Al.L -1 Slide 17 of 18 32

18 Method developed by Chow et al., 2004: Filtered with 0.45 µm membrane then adjusted to ph 2 NOM (ph 2) Hydrophobic NOM Characteristics Hydrophilic VHA : Very Hydrophobic acids VHA DAX-8 SHA XAD-4 IRA-958 CHA SHA : Slightly Hydrophobic acids CHA : Charged Hydrophilics NEU : Neutral Hydrophilics Adjust to ph 8 NEU Effluent concentrations determined using DOC analyser Chow et al. (2004) - Journal of Water Supply: Research and Technology 53(2): Slide 18 of 32

19 NOM Characteristics Rapid fractionation for samples after coagulation with 2.16 mg Al.L -1 Natural Water Synthetic Water VHA : Very Hydrophobic acids SHA : Slightly Hydrophobic acids CHA : Charged Hydrophilics NEU : Neutral Hydrophilics Majority of VHA components in SW samples are removed after treatment with composite coagulant compared to PACl only. Slide 19 of 18 32

20 1 H NMR Analysis NMR Analysis of Coagulants : δ 1 H/ppm Signal at 3.65 ppm in PACl coagulant refers to Al 13 decomposition products Signal not observed in PACl Chi chitosan hinder the decomposition of polymeric Al species Slide 20 of 32

21 NOM Characteristics UV Vis analysis for very hydrophobic acids (VHA) component in water samples : Chitosan in composite coagulant helps in removing VHA components in SW but not so effective in NW Slide 21 of 32

22 Zeta Potential Analysis Slide 22 of 32

23 Predominant Mechanism of Coagulation Charge Neutralisation/ destabilisation Slide 23 of 32

24 Flocs size analysis Measured using Malvern Mastersizer For SW samples : Coagulant Confirmed that chitosan helps in forming larger flocs better removal D 50 : 50 % distribution of the particle size Flocs Size Analysis Al concentration of 2.16 mg/l D 50 (µm) Al concentration of 4.32 mg/l D 50 (µm) PACl 77 ± 3 [Chi]:[Al]= ± ± 5 Slide 24 of 18 32

25 Microscope Images of Flocs Flocs formed for synthetic water samples after coagulation : PACl PACl - Chi 100 µm 100 µm Note : Samples taken before settling process in jar test experiment Slide 25 of 18 32

26 Zeta Potential Analysis Predominant Coagulation Mechanism for NW is NOT Charge Neutralisation Slide 26 of 32

27 Flocs size analysis for NW samples : Coagulant Flocs Size Analysis Al concentration of 2.16 mg/l D 50 (µm) Al concentration of 4.32 mg/l D 50 (µm) PACl 150 ± ± 15 [Chi]:[Al]= ± ± 5 Greater average flocs size in NW compared to SW due to presence of particulates. D 50 : 50 % distribution of the particle size Slide 27 of 18 32

28 Microscope Images of Flocs Flocs formed for natural water samples after coagulation : PACl PACl - Chi Note : Samples taken before settling process in jar test experiment Slide 28 of 32 18

29 What is the role of Chitosan in composite coagulant? Chitosan in composite coagulant contributes to positively charged species that helps charge neutralisation. Chitosan aids the removal process via polymer bridging, thus forming larger flocs. Why addition of Chitosan improved the removal at lower [Al] for SW but NOT for NW? Different organics in VHA fractions in the two waters, thus varying their interaction with chitosan in composite coagulant. Slide 29 of 18 Slide 29 of 32

30 Trihalomethane Formation Potential Excess chlorine dosage (20 mg/l); 4 h 35 C and quenched with excess ascorbic acid. Residual chitosan in the treated water did not significantly affect the THM formation potential. Slide 30 of 32

31 Conclusions Successfully synthesize PACl-Chi composite coagulant NOM characteristics affect the removal mechanisms and coagulation efficiencies. Better removal efficiency at lower [Al] for SW treated with composite coagulant compared to PACl No improvement in removal efficiency for NW when treated with composite coagulant. Different removal behavior in the two water samples might be due to difference in organic characters of the VHA fractions. NOM that can be removed by charge neutralisation would experience the benefit from composite coagulant. Slide 31 of 32

32 Acknowledgement University of New South Wales (UNSW) ARC Centre of Excellence for Functional Nanomaterials (ARCCFN) Australia Water Quality Centre (AWQC) and South Australia (SA) Water Dr. Yijiao Jiang, Particle and Catalysis Research Group, UNSW All members of Particle and Catalysis Research Group, UNSW Slide 32 of 32

33 Effect of ph Effect of ph tested with coagulant dose of 4.32 mg Al.L -1 Synthetic water Best removal efficiency obtained at ph 6 Natural Water

34 NOM Characteristics HPSEC analysis for VHA component in water samples Slide 34 of 18

35 Residual Turbidity Studies Residual Turbidity Analysis for SW and NW samples Synthetic Water Natural Water Slide 35 of 18