Phosphorous removal by physicochemical and biological means

Transcription

1 Phosphorous removal by physicochemical and biological means Dr. Mathias Ernst Technische Universität Berlin Head of Centre for Water in Urban Areas 1

2 Outline EU and German wastewater legislation Relevant phosphorous compounds Physico-chemical removal methods Surface water treatment plant Tegel (Berlin) Enhanced biological P removal process Conclusion 2

3 European Requirements 91/271/EEC municipal wastewater BOD 5 (mg/l) Removal rate (%) Sensitive waters < 25 mg/l COD (mg/l) Removal rate (%) < SS removal rate [%] Nitrogen TN l (mg/l) P.E > P.E. Phosphorus TP (mg/l) P.E. > P.E. < < 15 (70-80%) < 10 (70-80%) < 2 < 1

4 Implementaion in Germany Wastewater ordinance (AbwV) Parameter Class 1 Class 2 Class 3 Class 4 Class 5 Ruhleben BOD5 (mg/l) COD (mg/l) NH4-N (mg/l) Nitrogen, N-total (Kjeldahl) (mg/l) Phosphorus, total (mg/l) Class 1: <40 kg BOD 5 /d Class 2: Class 3: Class 4: Class 5: > P.E.= 60 g BOD 5 /d

5 Typical Concentrations of Total Phosphorus in Water Domestic wastewater 3 15 mg/l TP Agricultural drainage mg/l TP Lake surface water mg/l TP Table 6-4 Mesotropher Bereich TP mg m -3 Chl a mg m -3 [Vollenweider, 1982] 5

6 Forms of Phosphorus Total P (TP) consists of Total organic P (TOP) (e.g., phospholipids), Total inorganic P (TIP) (ortho- and poly-phosphates); Raw wastewater: TP, TOP, TIP 10, 3, 7 mg/l;

7 Phosphoric acid system 7

8 Forms of Phosphorus Total P (TP) consists of Total organic P (TOP) (e.g., phospholipids), Total inorganic P (TIP) (ortho- and poly-phosphates); Raw WW: TP, TOP, TIP 10, 3, 7 mg/l; Relevant for TP removal Particulate/Colloidal (cell fragments) Dissolved phosphorous 8

9 Rapid Sand Filtration (RSF): a DW technology applied to AWWT (III Filtration) Single media (sand or anthracite) vs. Multi Media (sand and anthracite); (sand and granular active carbon) Particle size < 0.5 mm up to > 2 mm 9

10 Particle Size Removal Efficiency: III Filtration of Activated Sludge Effluent 10

11 III- Filtration with Chemical Addition Chemicals Added: Metal coagulants (Al(III), Fe(III)), organic polymers, lime Metal Coagulants: Al 3+ (or Fe 3+ ) + 3 OH - Al(OH) 3 (or Fe(OH) 3 ) In AWT, generally operate in sweep flock Also Al 3+ (or Fe 3+ ) + PO 4 3- AlPO 4 (or FePO 4 ); Al:P (molar): 1.4, 1.7, %, 85 %, 95 % P removal

12 Log C vs. ph Diagram: Equilibrium Phosphate and Aluminum Concentrations Figure

13 Lg c(al, Fe) vs. ph (Al-, Fe-Hydroxids) Stabilitätsdiagramm für Eisen und Aluminium

14 III- Filtration with Chemical Addition Chemicals Added: Metal coagulants (Al(III), Fe(III)), organic polymers, lime Metal Coagulants: Al 3+ (or Fe 3+ ) + 3 OH - Al(OH) 3 (or Fe(OH) 3 ) In AWT, generally operate in sweep flock Al 3+ (or Fe 3+ ) + PO 4 3- AlPO 4 (or FePO 4 ); Al:P (molar): 1.4, 1.7, %, 85 %, 95 % P removal Organic Polymers: Primary coagulants (cationic, anionic, non-charged polymers) 14

15 Polymer flocculation Highmolecular compounds adsorb on two particles Highmolecular polymers (0, +, -) as flocculation aid

16 III- Filtration with Chemical Addition Chemicals Added: Metal coagulants (Al(III), Fe(III)), organic polymers, lime Metal Coagulants: Al 3+ (or Fe 3+ ) + 3 OH - Al(OH) 3 (or Fe(OH) 3 ) In AWT, generally operate in sweep flock Al 3+ (or Fe 3+ ) + PO 4 3- AlPO 4 (or FePO 4 ); Al:P (molar): 1.4, 1.7, %, 85 %, 95 % P removal Organic Polymers: Primary coagulants (cationic, anionic, non-charged polymers) Lime (Ca(OH) 2 Ca OH - ): Ca 2+ + CO 2-3 CaCO 3 Mg OH - Mg(OH) 2 3 Ca PO 3-4 Ca 3 (PO4) 2 5 Ca PO OH - Ca 5 (PO 4 ) 3 OH (hydroxyapatite) 16

17 III- Filtration with Chemical Addition Point of application for P removal : III-Filtration relatively low doses; In-Line, Static Mixer, Rapid Mixer or Flocculator Before I-Sedimentation (High Doses); Before Biological Process (interaction with biology); Before II-Sedimentation (Higher Doses) 17

18 Badegewässerrichtlinie Water management at Berlin

19 Tegel Lake

20 Tegel Lake Area: Average depth: Max depth: 4 km² 8 m 16 m At its banks: wells and water work to produce dw from bank filtrate Three inflows: Nordgraben (with Panke), Tegeler Fließ, Oberhavel 70 s: 2.88 mg/l PO 3-4 in Tegel Lake 1985: p-elimination plant put into operation, capacity 6 m 3 /s 2003: 0.05 mg/l PO 3-4 in Tegel Lake

21 two pipes: DN 1000 each flocculant: Fe 2 (SO 4 ) 3 Fe 3+ + PO 4 3- FePO 4 ph=5-5.5 Fe OH - Fe(OH) 3 ph 8-9 coagulation (destabilisation, microflocs: mm) complexation with organic compounds adsorption reactions residual time 30 s (time for coagulation) pipe flocculation β-factor: PO 4 c c Fe PO 4 Addition of flocculation aid: weak anionic polyacrylamide macroflocs: agglomeration faster, bigger sink faster

22 Sedimentation and Filtration Processes B C D Sedimentation Post-precipitation, coagulation, and -flocculation Filtration Double bed filter: pumice stone / sand Backwash every 24h

23 Phosphate elimination plant Tegel Feed concentration mg/l TP (mixture of three feed waters) Effluent: µg TP/L (required: 25 µg TP/L) P-removal of 96% - 99% Present costs of treatment: 7 cent/m³ (incl. depreciation)

24 Green: class II Yellow: class III Tegel Lake Water quality class II Other waters in Berlin: Class II-III or Class III

25 Second P removal plant in Berlin: Chain of the Grunewald lakes (drinking water assurance)

26 III- Filtration with Chemical Addition Clarification / Sedimentation before filtration if high doses Performance: Up to 95 % P removal; turbidity 1 NTU Other benefits of chemical clarification: 1) High-Ph disinfection by lime; 2) Physical removal of pathogens by III Filtration; Enhanced microbial removals: >2-log protozoa and bacteria; >1-log viruses 3) Chemical precipitation of metals (e.g., Zn(OH) 2, or adsorption onto Al(OH) 3 flock) (flock sweep effect) 26

27 Q I Enhanced biological Phosphorous Removal Review: C and N removal two stages N - Aerobic NH 4 ~> NO 3 BOD 5 ~> CO 2 External Carbon Source DN - Anoxic NO 3 ~> N 2 Q E Q R (Return Activated Sludge) Q R Q W Q W C-Source Energy-Source Autotroph B. (aerobic) Heterotroph B. BOD 5 Removal (aerobic) Denitrification Denitirfication (anoxic) inorg C (CO 2 ) ~> org C (Biomass) NH 4 + O 2 ~> NO 3 org C (BOD) ~> org C (Biomass) org C + O 2 ~> CO 2 org C (BOD) ~> org C (Biomass) org C + NO 3 ~> CO 2 + N 2 27

28 Review: C and N removal one stage Q I DN - Anoxic NO 3 ~> N 2 N - Aerobic NH 4 ~> NO 3 BOD 5 ~> CO 2 Q E Q IR (Internal Recirculation) Q R (Return Activated Sludge) Q W C-Source Energy-Source Autotroph B. (aerobic) Heterotroph B. BOD 5 Removal (aerobic) Denitrification Denitirfication (anoxic) inorg C (CO 2 ) ~> org C (Biomass) NH 4 + O 2 ~> NO 3 org C (BOD) ~> org C (Biomass) org C + O 2 ~> CO 2 org C (BOD) ~> org C (Biomass) org C + NO 3 ~> CO 2 + N 2 28

29 Review: C and N removal one stage max. 80 % N-Removal Q I 100 l/s 500 l/s DN - Anoxic NO 3 ~> N 2 N - Aerobic NH 4 ~> NO 3 BOD 5 ~> CO l/s Q E 300 l/s Q IR 100 l/s Q R Q W O 2 BOD 5 NH 4 NO 3 29

30 Enhanced biological Phosphorous Removal Q E Q I Anae PO 4 Rel. DN - Anoxic NO 3 ~> N 2 N - Aerobic NH 4 ~> NO 3 PO 4 Uptake Q IR Q R Q W Autotroph B. (aerobic) Heterotroph B. BOD 5 Removal (aerobic) C-Source inorg C (CO 2 ) ~> org C (Biomass) Energy-Source NH 4 + O 2 ~> NO 3 org C (BOD) ~> org C (Biomass) org C + O 2 ~> CO 2 Denitrification Denitirfication (anoxic) org C (BOD) ~> org C (Biomass) org C + NO 3 ~> CO 2 + N 2 PAOs Storage Consumption Storage Consumption Step 1 (mainly anaerobic) org C ~> Intrac. C Poly-P ~> PO 4 Step 2 (mainly aerobic, anoxic) growth on In. C PO 4 ~> Poly-P Cons. of In. C 30

31 Enhanced biological Phosphorous Removal Q I Anae PO 4 Rel. DN - Anoxic NO 3 ~> N 2 N - Aerobic NH 4 ~> NO 3 PO 4 Uptake Q E Q IR Q R Q W O 2 NO 3 BOD 5 PO 4 31

32 Enhanced biological Phosphorous Removal Q I Anae PO 4 rel. DN - Anoxic NO 3 ~> N 2 N - Aerobic NH 4 ~> NO 3 PO 4 Uptake Q E Q IR Q R Q W Optional: Al 3+ Fe 3+ salts 32

33 Advantages of EBPR Only slight increase of waste sludge production as P is stored intracellular Less chemical precipitation necessary Reduced chemical demand Reduced waste sludge production in comparison with chemical removal only Only small anaerobic volumes necessary (option for retrofitting possible) 33

34 Conclusions P removal of municipal wastewaters is necessary to avoid eutrophication in receiving surface waters Required P removal rates are high (up to 99%) as concentrations > 50µg/L TP already cause eutrophication in freshwater Physico-chemical P removal requires effective coagulants (Fe, Al, lime, polymers), subsequent tertiary filtration and ph control P/C methods produce considerable amounts of sludge waste EBPR shall be applied where ever appropriate (lower sludge production, higher cost effectiveness, combination with C and N removal) 34

35 Thank you for your attention!