Struvite recovery options in conventional wastewater treatment plants (WWTPs)

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1 Burgas Asen Zlatarov University Department of Water Treatment technology Struvite recovery options in conventional wastewater treatment plants (WWTPs) Nenov V., Jemendjiev H., Peeva G., Bonev B., Burgas Asen Zlatarov University, Dept. Water Treatment, Y.Yakimov str.1, Burgas 8010, Bulgaria

2 P issue The issue of Phosphorus (P) attracts the world attention in two aspects, namely the eutrophication caused by the nutrient pollution and its depletion as an important nutrient element

3 Number of publications per year related to phosphorus as a nutrient, pollutant and resource

4 Phosphorus flows in the environment

5 Eutrophication effects Reductions in oxygen can kill wildlife or force animals to leave the affected area Adverse impacts on the water quality Secondary pollution The major concern is that nutrients (including phosphorus) can push aquatic ecosystems beyond natural thresholds causing irreversible shifts in ecosystem structure The annual cost of eutrophication in the US could be as high as $2.2 billion

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7 Geographic distribution of resources 74% Morocco World reserves estimated for years

8 Other sources of P needed Wastewater works as an important secondary source of P 56,700 t P yr-1 (56% of all raw material fertilizers), the sewage sludge has the major role among the secondary raw materials in Germany t dry sewage sludge is obtained annually in Bulgaria Globally, 1.3 Mt P/year is treated in MWWTPs worldwide

9 P recovery One of the most promising technologies is the phosphorus precipitation as magnesium ammonium phosphate, Mg NH4PO4.6H2O (struvite) Struvite is valuable fertilizer Sludge dewatering liquor (SDL) from MWWTPs PO mg/l; NH mg/l

10 Most common methods for P removal Chemical Phosphorus Removal (CPR) Biological P removal (BPR) Type of Advantage Disadvantage treatment CPR Low residual P can be reached Increased sludge volume; Reduced P plant availability; Limited P recovery BPR Highly economical; Good opportunity for P recovery from SDL* as struvite Removal of P up to 60% *SDL sludge dewatering liquor

11 Aim of the work To clarify the potential of P recovery as struvite in applying the combination of CPR + Bio-removal and solely BPR To show the potential of Microbial Fuel Cell in extracting P from the CPR sludge

12 Case studies CPR/BPR removal is a conventional method for MWWT Municipal WWTP PE P-removal Stabilization Dewatering Burgas CPR/BPR Anaerobic open Centrifuges Pomorie BPR Anaerobic open Centrifuges

13 Monthly influent flow rate and influent/effluent P concentrations MWWTP Burgas (CPR/BPR) 2014 Q * av P ** av m 3 /month mg/l Influent l effluent MWWTP Pomorie (BPR) Q av m 3 /month P av mg/l Influent / effluent January February March April May June July August September October November December

14 Doses of FeCl3 MWWTP Burgas 2014 Jan Feb March April May June July Aug Sept Oct Nov Dec Qav m 3 /month FeCl 3, m3/month Dose, mgfe 3+ /mg P

15 P balance MWWTP Burgas (CPR/BPR) 78% of Pinfl

16 P balance MWWTP Pomorie (BPR) 48% of Pinfl

17 Phosphate and ammonia levels in the centrate Centrate Average concentration of PO 4 3-, mg/l Average concentration of NH 4+, mg/l WWTP Pomorie (BPR) WWTP Burgas (CPR +BPR)

18 P precipitation from Sludge Dewatering Liq Mg sources - Sea water brine and MgCl2 Brine Mg=59.5 g/l) Ca= 3.5 g/l Conditions of precipitation Mg:PO 4 2:1 ph = 9.5. Phosphate removal rate, % ,6 MgCl₂.6H₂O as magnesium source 92,1 Brine as magnesium source Phosphate removal rate at different magnesium sources (Initial concentration: PO mg/l

19 Phosphate removal rate, % Phosphate removal rate. % P removal rate at different ph and Mole ratio 90 Centrate from MWWTP Burgas Centrate from MWWTP Pomorie ,5 9 9,5 10 ph Mg/PO₄ = 1:1 Mg/PO₄ = 2:1 Mg/PO₄ = 3: ,5 9 9,5 10 ph Mg/PO₄ = 1:1 Mg/PO₄ = 2:1 Mg/PO₄ = 3:1 Microscopic observation of struvite crystals (400 XS) (left) and the dry precipitated product

20 Microbial Fuel Cell Anode half reaction C 6 H 12 O 6 + H 2 O = 6CO H e - Cathode half reaction 12O H e - = 12H 2 O

21 Bio - ELECTROCHEMICAL DISSOLUTION OF ORTHO- PHOSPHATES FROM FERRIC PHOSPHATES R A MFC reactor used B

22 ELECTROCHEMICAL DISSOLUTION OF ORTHO-PHOSPHATES FROM FERRIC PHOSPHATES Bio-electrochemical mobilization process summary Organic matter CO 2 Fe 3+ PO e - Fe 2+ + o-po H + Fe(OH) 2 COD removal Electricity generation Increasing phosphate concentration

23 o-po4 concentration, mg/l Potential difference, mv ELECTROCHEMICAL DISSOLUTION OF ORTHO-PHOSPHATES FROM FERRIC PHOSPHATES o-po4 CONCENTRATION ( ) and VOLTAGE ( ) vs. TIME INITIAL STATUS OF THE SYSTEM Dissolved phosphates mg/l Suspended phosphates 450 mg/l Time, hours Q max 7.08 mgpo 4.h -1. L- 1 Q aver 4.06 mgpo 4.h -1.L -1

24 Real sludge containing FePO4

25 MEC principle COD removal Hydrogen production Consumption of the H + in the cathode compartment result in ph elevation Anode half reaction C 6 H 12 O 6 + H 2 O = 6CO H e - Cathode half reaction 24H e - = 12H 2

26 ph elevation by electrochemical processes (Microbial Electrolysis Cell)

27 ph elevation by electrochemical processes (Microbial Electrolysis Cell) ph

28 ph ph elevation by electrochemical processes (Microbial Electrolysis Cell) struvite precipitation 1200 mv mg/l mv ,2 mg/l 24,2mg/l Tim e, hours

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30 CONCLUSIONS Sea water brine as a source of Mg can be viewed as another step for more economical production of struvite from SDL The P balance studies show that in case of CPR/BPR plant the prevailing part of P is chemically bonded, i.e. the chemical precipitate can be considered as an important secondary source of P The application of MFC for P extraction which enables mobilizing the phosphate constituents and their subsequent conversion into valuable chemicals with fertilizing properties (struvite) The results obtained with the MFC show a way for low energy mobilization of phosphates locked in FePO4 precipitates P recovery was successfully applied with real fluids obtained from sewage sludge containing FePO 4.

31 Thank you for your attention