Phosphorous removal by physicochemical and biological means

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

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

European Requirements 91/271/EEC municipal wastewater BOD 5 (mg/l) Removal rate (%) Sensitive waters < 25 mg/l 70-90 COD (mg/l) Removal rate (%) < 125 75 SS removal rate [%] Nitrogen TN l (mg/l) 10.000-100.000 P.E >100.000 P.E. Phosphorus TP (mg/l) 10.000-100.000 P.E. >100.000 P.E. < 35 90 < 15 (70-80%) < 10 (70-80%) < 2 < 1

Implementaion in Germany Wastewater ordinance (AbwV) Parameter Class 1 Class 2 Class 3 Class 4 Class 5 Ruhleben BOD5 (mg/l) 40 25 20 20 15 4 COD (mg/l) 150 110 90 90 75 45 NH4-N (mg/l) - - 10 10 10 0.3 Nitrogen, N-total (Kjeldahl) (mg/l) - - 10 18 13 8 Phosphorus, total (mg/l) - - - 2 1 0.2 Class 1: <40 kg BOD 5 /d Class 2: 40-200 Class 3: 200-400 Class 4: 400-4000 Class 5: >4000 1 P.E.= 60 g BOD 5 /d

Typical Concentrations of Total Phosphorus in Water Domestic wastewater 3 15 mg/l TP Agricultural drainage 0.05 1 mg/l TP Lake surface water 0.01 0.04 mg/l TP Table 6-4 Mesotropher Bereich TP 14.5-49 mg m -3 Chl a 3-7.4 mg m -3 [Vollenweider, 1982] 5

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;

Phosphoric acid system 7

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

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

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

Log C vs. ph Diagram: Equilibrium Phosphate and Aluminum Concentrations Figure 6-13 12

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

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, 2.3 75 %, 85 %, 95 % P removal Organic Polymers: Primary coagulants (cationic, anionic, non-charged polymers) 14

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

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

Badegewässerrichtlinie Water management at Berlin

Tegel Lake

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

two pipes: DN 1000 each flocculant: Fe 2 (SO 4 ) 3 Fe 3+ + PO 4 3- FePO 4 ph=5-5.5 Fe 3+ + 3 OH - Fe(OH) 3 ph 8-9 coagulation (destabilisation, microflocs: 0.01-0.05 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

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

Phosphate elimination plant Tegel Feed concentration 0.2 0.5 mg/l TP (mixture of three feed waters) Effluent: 18-22 µg TP/L (required: 25 µg TP/L) P-removal of 96% - 99% Present costs of treatment: 7 cent/m³ (incl. depreciation)

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

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

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

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

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

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 2 100 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

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

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

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

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

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

Thank you for your attention! Mathias.ernst@tu-berlin.de