Wastewater Recovery & Reuse Technologies

Transcription

1 Wastewater Recovery & Reuse Technologies Presented at: MWQA Convention by Peter S. Cartwright, PE October 11,

2 Introduction 2

3 This educational offering is recognized by the Minnesota Department of Labor & Industry as satisfying credit towards water conditioning and plumbing continuing education requirements. 3

4 Global Water Supplies 4

5 Industrial/ Commercial Discharges 5

6 Effluent likely to be unique to a specific manufacturing process 6

7 Membrane Technologies 7

8 Membrane Technologies Microfiltration (MF) Ultrafiltration (UF) Nanofiltration (NF) Reverse Osmosis (RO) 8

9 Membrane Technologies Advantages Continuous process, resulting in automatic and uninterrupted operation Low energy utilization involving neither phase nor temperature changes Modular design no significant size limitations Minimal moving parts with low maintenance requirements No effect on form or chemistry of contaminants Discrete membrane barrier to ensure physical separation of contaminants No chemical addition requirements to effect separation 9

10 Conventional vs. Crossflow 10

11 Crossflow Filtration Feed Concentrate Membrane Permeate 11

12 Membrane Process 12

13 Microfiltration 13

14 Microfiltration (MF) Particle (suspended solids) removal only. Pore sizes in the submicron range (<1.0µ). Removal mechanism is sieving. 14

15 Ultrafiltration 15

16 Ultrafiltration (UF) Dissolved organic (macromolecule) removal. Pore sizes in the submicron range, and generally smaller than MF. Removal mechanism is sieving. 16

17 MF and UF Membranes operate based on sieving What is to big to pass through the pores is held back ( rejected ) 17

18 Nanofiltration 18

19 Nanofiltration (NF) Loose RO Rejects salts as with RO - But - Rejects multivalent salts to a much higher degree than monovalent salts 19

20 Reverse Osmosis 20

21 RO Removes dissolved organic contaminants by a process of SIZE EXCLUSION: What s too big to go through the membrane is held back. Function of both the size and shape of the organic molecule. 21

22 Dissolved organics with a molecular weight greater than ~100 Daltons are rejected by RO 22

23 Membrane Technologies 23

24 Thin Film Composite Vast majority of RO membranes are Thin Film Composite: High Rejection Excellent Thermal Stability Bacteria Resistant ph Stable 24

25 HOWEVER They are chemically attacked by oxidizing agents: Chlorine compounds Hydrogen peroxide Potassium permanganate Others 25

26 Microfiltration & Ultrafiltration Materials of Device Configuration Construction Hollow Fiber Tubular Plate & Frame Spiral Wound Polymeric PS X X X X PES X X X X PAN X X X X PE X PP X X X PVC X PVDF X X PTFE X X PVP X X CA X Non-Polymeric Coated 316LSS X None a-alumina X X None Titanium Dioxide X None Silicon Dioxide X None PS = Polysulfone PES = Polyethersulfone PE = Polyethylene PP = Polypropylene PAN = Polyacrylonitrile PVDF = Polyvinylidene Fluoride PTFE = Polytetrafluoroethylene CA = CelluloseAcetate PVP = Polyvinylpyrrolidone TF = Thin Film Composite 26

27 Nanofiltration & Reverse Osmosis Materials of Device Configuration Construction Hollow Fiber Tubular Plate & Frame Spiral Wound Polymeric PS* X X X PES* X X X CA X X X TF X X X Non-Polymeric None * Base polymer below TF polymer PS = Polysulfone PES = Polyethersulfone CA = CelluloseAcetate TF = Thin Film Composite 27

28 Membrane Element Devices Plate & Frame Tubular Hollow (Capillary) Fiber Spiral Wound 28

29 Membrane Element Devices 29

30 Membrane Elements Plate & Frame Tubular Hollow Fiber Spiral Wound 30

31 Membrane Elements 31

32 Plate & Frame 32

33 Plate & Frame 33

34 Tubular 34

35 Tubular 35

36 Hollow (Capillary) Fiber 36

37 Hollow Fiber Membranes Hollow fiber membranes are manufactured from the unsupported polymer spinneret process. 37

38 Hollow (Capillary) Fiber 38

39 Hollow (Capillary) Fiber 39

40 Spiral Wound 40

41 Spiral Wound Courtesy of Mike Grigus 41

42 Spiral Wound Courtesy of Mike Grigus 42

43 Spiral Wound 43

44 Membrane Element Configuration Comparison Element Configuration Packing Density * Fouling Resistance ** Plate & Frame Low High Hollow (Capillary) Fiber High High Tubular Low Very High Spiral Wound Medium Low * Membrane area per unit volume ** Tolerance to suspended solids 44

45 System Design 45

46 Membrane System Schematic 46

47 Terminology Feed Influent Concentrate Brine Permeate Product Bank Array Reject Filtrate 47

48 Definition of Flux Flux = Total Permeate Rate Total Membrane Area Specific Flux = Flux NDP (net driving pressure) 48

49 Rejection Solute removal from the feed water 49

50 Percent Rejection % Rejection: The degree of removal of solute by the membrane process. For RO: Rejection (%) = Feed Conductivity Permeate Conductivity Feed Conductivity x

51 RO always rejects a percentage of salts. Therefore, permeate quality a function of feedwater quality. 51

52 If feedwater TDS é, Permeate TDS é 52

53 Ion exchange technologies do not work this way; resins are more absolute. 53

54 Recovery 54

55 Definition of Recovery % Recovery: The percentage of feedwater that passes through the membrane as product water (i.e. how efficiently water is converted into product water). Permeate Rate Recovery (%) = Feed Rate x 100 Part of system design 55

56 Definition of Concentration Factor The degree to which contaminants in the concentrate stream are concentrated Recovery 56

57 Effect of Recovery on Concentration 57

58 Effect of Recovery on Concentration Factor 58

59 Typical RO Spiral Membrane Element 59

60 High Recovery Advantages Lower flow rate (smaller diameter piping, etc.) Smaller high pressure pump 60

61 High Recovery Hazards Precipitation Fouling For RO/NF High p For RO/NF As Recovery Permeate TDS Discharge Issues 61

62 Water Temperature 62

63 Feedwater temperature will affect RO permeate rate: As temperature ê, Permeate rate ê 63

64 Colder water has a higher viscosity than warm water, so more pressure is required to force it through the membrane. 64

65 Osmotic Pressure 65

66 Osmotic Pressure (p) The pressure, due to the effect of TDS in the feedwater, that must be overcome in order to generate product water flow. pis a function of the specific salt, as wel as its concentration. 66

67 Osmotic Pressure p= 1.19 (T + 273) SM i Where: p = Osmotic Pressure (psi) T = Water Temperature ( o C) M i = Molar Concentration of individual ions (gmol/l) 67

68 Typical Osmotic Pressure at 25 C Osmotic Pressure Compound Conc. (mg/l) Conc. (mol/l) (psi) (bar) NaCl 35, NaCl 1, NaHCO 3 1, Na 2 SO 4 1, MgSO 4 1, MgCl 2 1, CaCl 2 1, Sucrose 1, Dextrose 1,

69 Osmotic Pressure Simplified Calculations For monovalent salts: assume 1 psi of osmotic pressure per 100 mg/l of TDS. For multivalent salts: assume ½ psi of osmotic pressure per 100 mg/l of TDS. 69

70 RO pump pressure directly affects permeate rate. 70

71 As pump pressure é, Permeate rate é 71

72 Membrane manufacturers specify the maximum recommended pump pressure. If the pressure is too high, the membrane will foul more quickly. 72

73 System Design Criteria Feedwater Quality Permeate Quality Requirements Membrane Technology (MF, UF, NF, RO) Membrane Polymer Membrane Element Configuration Pretreatment Requirements 73

74 Feedwater Quality General Parameters Total Solids Content Suspended (TSS) Dissolved Organic (TOC, MBAS, COD, BOD) Dissolved Inorganics (TDS) 74

75 Feedwater Quality (cont.) Chemicals of Concern Oxidizing Chemicals Organic Solvents Saturated Solutes 75

76 Feedwater Quality (cont.) Other Factors ph Operating Temperature Osmotic Pressure as a Function of System Recovery Variation in Chemistry as a Function of Time 76

77 System Design Factors Optimum Membrane Element Configuration Total Membrane Area Specific Membrane Polymer Optimum Pressure Maximum System Recovery Flow Conditions (turbulent, etc.) Membrane Element Array Pretreatment Requirements 77

78 Membrane Element Array 78

79 Membrane Fouling 79

80 Fouling The bane of all membrane systems 80

81 81

82 Fouling Plugging - Particulate materials (suspended solids) Scaling - Precipitated materials Organic Fouling - Coating and plugging by organics Microorganisms - Bacterial biofilm 82

83 Fouling Summary Foulant Primary Mechanism Examples Suspended Solids (plugging) Filtration Dirt, clay, silt, dust, hydrous metal oxides, e.g. Fe(OH) 3 Inorganic Salts (scaling) Concentration effects, Adsorption CaCO 3, MgCO 3, BaSO 4, CaSO 4, SiO 2, and other salts Organics (plugging) Adsorption, Film Formation Oils, grease, surfactants, coagulants, antiscalants, humic and fulvic acids Microorganisms (Biofouling) Adhesion, Adsorption, Biofilm Formation Bacteria

84 Fouling Mitigation Pretreatment System Design Membrane Polymer Membrane Device Configuration Chemical Addition System Operation 84

85 Membrane Element Cleaning Capability Element Configuration Available MembraneTechnology Backwashable? MF UF NF RO Plate & Frame Yes Yes Yes Yes No (except for inorganic membrane) Tubular Yes Yes Yes Yes Yes Hollow Fiber Yes Yes Yes No Yes SpiralWound Yes Yes Yes Yes No (NF, RO) Yes (MF, UF) 85

86 Case Histories 86

87 Zero Liquid Discharge of Cooling Tower Blowdown 87

88 Cooling Tower Blowdown Treatment System 88

89 Tubular MF 89

90 Tubular MF 90

91 Continuous Deionization (CDI)

92 Porex Module Specifications Modules Housing Diameter 6" Schedule 40 Permeate Port (Qty2) 2.875"Æ x 1.89" L pipe stub Concentrate Ports 6"Æ pipe Anvil Gruvlok groove Mounting Required Horizontal; 2 point Module Length 72" Tubes Number of Tubes 10 Nominal ID 1" Nominal OD 1.34" Total Active Surface Area 15.2 ft 2 Permeate Volume Concentrate Volume Total Volume Potting Internal Supports Gasket Material Preservative (Shipping) Membrane Internal Liquid Volume Materials of Construction 4.33 gallons 2.45 gallons 6.78 gallons Solvent Cement Polypropylene None Propylene Glycol PVDF 92

93 MF System Schematic 93

94 MF System Performance 94

95 RO Membrane Systems Flows and Recoveries First Stage RO Polishing RO Second Stage RO Feed Rate (gpm) Permeate Rate (gpm) System Recovery(%) 73% 75% 67% 95

96 Membrane Element Backwashing/Backpulsing Element Configuration Tubular MF Spiral Wound RO Backwashable? Yes No 96

97 To Minimize MF Fouling High Velocity (12-15 ft/sec) Chlorine Addition Backpulsing

98 Cleaning 98

99 MF Acid Cleaning 15 minutes - 3-5% HCl Recirculation 45 minutes - Soak 45 minutes - Recirculation with Rinse Water

100 MF Caustic Cleaning NaOH + Bleach (12-15% NaOCl) ph minutes - Recirculation 150 minutes - Soak 30 minutes - Recirculation with Rinse Water

101 RO Cleaning <6 months

102 Conclusions MF Protects Spiral RO Membranes: Low Cleaning Frequency High System Recovery MF Facilitates Zero Liquid Discharge MF Eliminates Traditional Clarification 102

103 Orange County Ground Water Replenishment System 103

104 Orange County Ground Water Replenishment System 104

105 Microfiltration System 144 MGD Evoqua CS Microfiltration System Tiny, straw like hollow fiber polypropylene membrane Removes bacteria, protozoa, and suspended solids 0.2 micron pore size Backwash every 22min, CIP every 21 days (no maintenance wash 10 e 5 s)

106 Reverse Osmosis System 100 MGD Reverse Osmosis System 3 stage: array 21, 5 mgd units, 12 gfd flux Hydranautics ESPA-2, CSM FLR and Dow XFRLE Membranes Recovery Rate: 85% Removes dissolved minerals, viruses, and organic compounds (incl. CECs) Pressure range: psi

107 Advanced Oxidation Disinfection 100 MGD Trojan UVPhox System Low Pressure High Output lamp system Destroys trace organics Uses Hydrogen 3 mg/l Peroxide to create an Advanced Oxidation Process 13, 8.75 mgd trains (1 acts as standby) 6 reactors per train housed in 3 vessels 432 lamps per train (5616 total lamps)

108 Project Funding and Timing Capital Cost: approximately $481 million Split equally between OCWD and OCSD Expandable to 130,000 afy (438,500 m 3 /day) Operational since January

109 Food Processing Wastewater Recovery & Reuse 109

110 Background Bakery Wastewater 15,000 gpd BOD 50,000 mg/l TSS 5,000 mg/l POTW Limits: 250 mg/l BOD 250 mg/l TSS Hauling/Treatment Charges $50,000/month 110

111 Conceptual Design Prescreening large suspended solids Microfiltration almost all suspended solids Reverse osmosis polish for discharge or reuse Evaporation concentrate disposal 111

112 Prescreen Testing Vibrating screen vs. automatic backwashing filter 100µ automatic backwashing continuous filter selected 112

113 Prescreen Testing Collected filtrate Observed settled solids 113

114 Prescreen Filter 114

115 Microfiltration Testing 115

116 Ceramic MF Membrane Silicon Carbide 0.05µ Pore Size 116

117 Ceramic MF Membrane 117

118 Permeate Rate 118

119 Polymeric MF Membrane PVDF Material 0.05µ Pore Size 119

120 Flux Rate 120

121 Applications Testing Results Continuous Automatic Backwashing Filter Polymeric MF Tubular Membrane 121

122 Polish with RO Standard Thin Film Membrane 122

123 Concentrate Treatment Prescreen filter solids to Vapor Compression Evaporator MF concentrate back to feed tank RO concentrate to Vapor Compression Evaporator 123

124 Vapor Compression Evaporator 124

125 Results ND = NonDetectable Plant Efflu ent MF Permeate RO Permeate Distillate TDS (mg/l) TSS (mg/l) ND ND BOD (mg/l) ND 125

126 Total Treatment System 126

127 Contact Information Peter S. Cartwright, PE 1/