Optimizing Chemical Phosphorus Removal

Size: px

Start display at page:

Download "Optimizing Chemical Phosphorus Removal"

Gregory Casey
7 years ago
Views:

1 Optimizing Chemical Phosphorus Removal JB Neethling HDR Engineering 2013 Technical Conference and Exposition Ohio Water Environment Association (OWEA) Mason, OH June 18-20, 2013 Copyright 2013 HDR Engineering, Inc. All rights reserved.

2 Agenda Chemical Phosphorus Removal Basics Phosphorus Species Performance Opportunities for Optimization

3 Phosphorus Species Total P Dissolved P Particulate P Ortho P (Reactive P) Inorganic Condensed P Soluble Organic P Particulate Reactive P Particulate Acid Hyd P Particulate Organic P

4 Fundamental Principle of Phosphorus Removal There is no airborne (gaseous) form of phosphorus

5 Fundamental Principle of Phosphorus Removal There is no airborne (gaseous) form of phosphorus The exception

6 Convert to Particulate SolP Liquid Soluble P Particulate P Solid Particulate P

7 Typical Chemical Treatment Opportunities Primary Secondary Tertiary Polish Solids Processing

8 Chemical Chemicals used for Phosphorus Aluminum Sulfate (Alum) Formula Precipitation Al 2 (SO4) (H 2 O) M.W. = Ferric Chloride FeCl 3 M.W. = Poly Aluminum Chloride Ferrous sulfate (pickle liquor) Al n Cl (3n-m) (OH) m Al 12 Cl 12 (OH) 24 Removal mechanism Metal hydroxides Metal hydroxides Metal hydroxides Effect on ph removes alkalinity removes alkalinity none Fe 2 SO 4 Metal hydroxides Removes alkalinity Lime CaO, Ca(OH) 2 Insoluble precipitate Raises ph to above 10

9 Ferric Reaction with Phosphorus The following illustrates a stoichiometric reaction of Fe +++ with P FeCl 3 + H 3 PO 4 = FePO 4 + 3HCl 3 1 mole of Fe reacts with 1 mole P 5.2 mg ferric per mg P 0.92 mg alkalinity per mg of ferric

10 Alum Reaction with Phosphorus The following illustrates a stoichiometric reaction of Al +++ with P Al 2 (SO 4 ) 3. 14H 2 O+ 2H 3 PO 4 2AlPO 4 + 3H 2 SO H 2 O 2 mole of Al reacts with 2 mole P (or 1 mole Al per mole P) 9.6 mg alum per mg P 0.5 mg alkalinity per mg of Alum

11 Phosphorus Concentration Phosphorus Removal Initial removal - Stoichiometric 1:1 Equilibrium control need higher dose Break ~ 1 mg/l Chemical Dose

12 Al/P (mol/mol) Fe/P (mol/mol) Molar Dose Ratio From Tests Full Scale Lab data ph 6 Lab data ph Lab data ph 6.5 Lab data ph 6.8 Lab data ph 7.2 Lab data ph Full Scale data ortho P res (mg/l) ortho P res (mg/l) Slav Hermanowicz, Chemical Fundamentals of Phosphorus Precipitation, WERF Boundary Condition Workshop, Washington DC, 2006

13 Exact Molar Ratios Versus Effluent Soluble P will Vary with Applications 1.5 to 2.0 Molar ratios for percent removal 5.0 to 7.0 Molar ratios for higher efficiency and to reach low minimal soluble P concentrations Ratios are higher with PAC Factors that influence ratios ph Mixing method Wastewater characteristics Colloids and solids effect P-metal hydroxide complexations Organic subtrates Iron and aluminum can react with humic substances

14 Kinetics and Mixing of Phosphorus / Alum Reaction Szabó et al. (2006) The Importance Of Slow Kinetic Reactions In Simultaneous Chemical P Removal, WEFTEC 2006

15 Photomicrographs of Phosphate Precipitants

16 ph 7--> Scott Smith, Wilfrid Laurier University ph 3

17 Scott Smith, Wilfrid Laurier University Fresh HFO

18 Young HFO FePO 4 precipitant After 4 days. Scott Smith, Wilfrid Laurier University

19 Aged HFO HFO precipitant After 2 years. Hard!! Scott Smith, Wilfrid Laurier University

20 Metal Hydroxide Removal of P Found for Ferric Addition Metal hydroxide formed Co precipitation of P into hydrous ferric oxides structure Fe(OH) 3, Fe(OH) 4 - Surface complexation between P and metal hydroxide compounds Phosphorus and Iron share oxygen molecule: FeOOH + HOPO 3 = FeOOPO 3 + H 2 O Hydroxide formation can be simply represented: FeCl 3 + 3H 2 O => Fe(OH) HCl Al 2 (SO 4 ) 3.14H 2 O + 3 H 2 O => 2Al(OH) 3(s) + 3H 2 SO 4

21 Closer Look at the Chemical Species 33

22 Phosphorus Speciation and Removal in Advanced Wastewater Treatment L. Liu, D. S. Smith, D. Houweling J.B. Neethling, H.D. Stensel S. Murthy, Amit Pramanik and A. Z. Gu

23 Analytical Definitions of Phosphorus Species Filterable/nonfilterable (soluble?) Passing through filter paper Could be colloidal (very small particles) Reactivity to analytical procedure Measure for orthophosphate Pretreatment (acid hydrylosis, digestion, etc) Convert larger molecules to be reactive (orthophosphate)

24 Phosphorus Species Categories Total P Dissolved P Particulate P Ortho P (Reactive P) Inorganic Condensed P Soluble Organic P Particulate Reactive P Particulate Acid Hyd P Particulate Organic P

25 Effluent ortho-p (mg/l) Particulate Chemical Precipitant Measures as Reactive P 0.35 Combined Secondary Effluent- Jar Testing Results P in=0.31mg/l unf iltered Filtered Alum Dose-Al 2 (SO 4 ) 3.14H 2 O (mg/l)

26 Method Analytical Definition Based Phosphorus Fractions/Species Total P Dissolved P Particulate P Sol Reactive P SRP Sol Acid Hydrolyzable Sol Dig. PRP Part Acid H. Particle Digestible Ortho P Inorganic Condensed P Sol Org Particulate Organic P Colloidal P Chemical particulate P

27 Nonreactive Phosphorus Total P Dissolved P Particulate P Sol Reactive P SRP Sol NonReactive P SNRP PRP Particulate NonReactive P Total Reactive P Total NonReactive P

28 Analytical Definition Based Phosphorus Fractions/Species Total P Dissolved P Particulate P Sol Reactive P SRP Sol Non Reactive P snrp Ortho P Acid Hydrolyzable P Sol Org Part Chemical P Part Organic P Colloidal P

29 Particulate Nonreactive Phosphorus, ug/l Secondary Effluent TSS adds to Particulate NRP % % TSS, mg/l 1.0% 1.5% 2.0% 2.5% 3.0% 5

30 Particulate Nonreactive Phosphorus, ug/l Filtered Effluent TSS adds to Particulate NRP 35 ug/l % % TSS, mg/l 1.0% 1.5% 2.0% 2.5% 3.0% 1 mg/l

31 Phophorus [mg/l] Pilot Study Results Illustrated Challenges at Limits of Technology No Treatment Technology Available for SNRP Portion May Not Be Bioavailable / Biodegradable 0.00 DSBP THS-1 ZW-500 DSD2 srp snrp pp Particulate P Soluble NonReactive P Neethling et al, 2007 Soluble Reactive P

32 P Concentration, mg/l Effluent P Fractions From Advanced Tertiary Treatment Processes Sedimentation Filtration Membrane Filtration pahp pop prp sahp DOP srp Lui, Gu, et al. (ongoing) Phosphorus Speciation and Removal in Advanced Wastewater Treatment, WERF Report

33 P concentration (mg/l) P fractions at Plant N pop pahp prp DOP sahp 0.0 BNR INF BNR Chemical P removal sahp seems to remain after BNR, associated with biomolecules Chemical addition converts srp into prp Chemical srp (PO 4 ) removal relies prp removal Mono/Dual media Filtration srp

34 P concentration (mg/l) Comparison of P fractions at Plant P BNR INF BNR Eff BNR Trident HS pop pahp prp DOP sahp srp Plant P and N are similar as (BNR+sedimentation +Filtration): composition very different DOP dominant soluble fraction; pahp major particulate form Multi stage barrier remove TP to lower level

35 Opportunities for Optimization

36 Opportunities for Improvement Improve understanding of chemical kinetics Dose relationships Reuse formed metal hydroxides Enhance solids separation

37 Al/P (mol/mol) Fe/P (mol/mol) Molar Dose Ratio From Tests Full Scale Lab data ph 6 Lab data ph Lab data ph 6.5 Lab data ph 6.8 Lab data ph 7.2 Lab data ph 8 Full Scale data ortho P res (mg/l) ortho P res (mg/l) Slav Hermanowicz, Chemical Fundamentals of Phosphorus Precipitation, WERF Boundary Condition Workshop, Washington DC, 2006

38 Single Step Chemical Addition Requires High Dose One Step P entering mg/l 5 P residual mg/l 0.1 Alum/P dose mol/mol 5 Alum/P dose mg/mg 48 Alum dose mg/l 235

39 Two Step Chemical Addition Reduce Dose One Step Step 1 Step 2 Two Steps P entering mg/l P residual mg/l Alum/P dose mol/mol Alum/P dose mg/mg Alum dose mg/l

40 Two Step Chemical Addition Reduce Dose One Step Step 1 Step 2 Two Steps P entering mg/l P residual mg/l Alum/P dose mol/mol Alum/P dose mg/mg Alum dose mg/l

41 Reuse Chemical Sludge to Reduce Dose and Increase Reliability Return chemical sludge to upstream process Build solids inventory operate in solids contact mode

42 Conventional Tertiary Chemical P Removal Al/Fe PCL AS SCL Al/Fe SCL Filter

43 ReUse Chemical Sludge Upstream Al/Fe PCL AS SCL Al/Fe SCL Filter

44 Contact Clarification in Tertiary Al/Fe PCL AS SCL Al/Fe ANX SCL Filter

45 Coeur d Alene: Microfiltration and Solids Recycle PCL Al/Fe AS SCL Al/Fe ANX TMF

46 Implications for Design and Operation Coeur d Alene Pilot No Solids Inventory Loss of Alum feed

47 PO4-P [mg/l] SE PO4-P [mg/l] Implications for Design and Operation Coeur d Alene Pilot With Solids Inventory Alum Off Alum On Jun 10-Jun 11-Jun 11-Jun 12-Jun 12-Jun 13-Jun 13-Jun 14-Jun 14-Jun 15-Jun TMF Effluent PO4-P Secondary Effluent PO4-P

48 Summary and Conclusion - I Chemical reactions for phosphorus removal with ferric or alum is a primarily a surface complexation reaction Good mixing and contact time is needed to maximize chemical efficiency Preformed Metal Hydroxides retain the ability to react and remove phosphate

49 Summary and Conclusion - II Target phosphorus species for effective removal: Precipitate Reactive Phosphorus Phosphate Increased dose can improve removal Filter particulate fractions High efficiency filters Soluble Non-Reactive P remains difficult to remove Reuse metal hydroxides to reduce chemical use

50 Optimizing Chemical Phosphorus Removal JB Neethling HDR Engineering 2013 Technical Conference and Exposition Ohio Water Environment Association (OWEA) Mason, OH June 18-20, 2013 Copyright 2013 HDR Engineering, Inc. All rights reserved.

Occurrence and implication of dissolved organic phosphorus (DOP) in

Occurrence and implication of dissolved organic phosphorus (DOP) in tertiary wastewater effluents L. Liu 1, D. S. Smith 2, M. Bracken 3, J.B. Neethling 4, H.D. Stensel 5 and S. Murthy 6, A. Pramanik 7