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Phosphorus recovery and VFAs production from sewage sludge fermentation

• D. Crutchik, N. Frison, A. Jelic and F. Fatone

Natalia Herrero García

• Municipal wastewater contains around 100‐120gCOD/(inhabitant per day);
• Up to now, the utilization of sewage sludge has been limited mainly to the

production of biogas for co‐production of thermal and electric energy and compostable material;

• The sewage sludge might be considered as a challenging feedstock to be

processed for bio‐based applications (waste‐to‐chemicals and bio‐product value chain);

• Volatile Fatty Acids (VFAs) could be considered intermediates for a wide range
• f applications

Background Background

Production & Application of Waste‐derived VFAs Production & Application of Waste‐derived VFAs

Lee et al., 2014. Chemical Engineering Journal. The operating conditions for VFAs production should be addressed based on the final application of the VFAs Proper process control can manipulate the type

• f VFA produced, which is critical to the

performances of the downstream applications.

Organic‐rich Wastes Pretreatment of Waste Anaerobic technologies for VFA production

Volatile fatty acids (VFA)

‐ph ‐Temperature ‐Hydraulic retention time ‐Solids retention time ‐Organic loading rate ‐Additives

Applications: ‐Polyhydroxyalkanoates ‐Electricity ‐Biogas ‐Hydrogen ‐Lipids for Biodiesel ‐Biological nutrient removal

Operating conditions

Fermentation

• f Sewage

Sludge

Struvite (MgNH4PO4∙6H2O)

Magnesium hydroxide Mg(OH)2 To anaerobic digester PS&WAS WAS PS ‐Acetic Acid; ‐Propionic Acid; ‐Butyric Acid; ‐Others

Scenario: Integration of VFA Production and Phosphorus Recovery Scenario: Integration of VFA Production and Phosphorus Recovery

S/L (After Dynamic Thickening)

SCFAs (SSFL)

T=37ºC

Role of SCFAs in Wastewater Treatment Role of SCFAs in Wastewater Treatment

• SCFAs are rbCOD and help the denitrification

processes;

• Enhanced Bio‐P removal (4‐5 mgVFA are required for

each mg P removed);

• Hydrogen production;
• Biological Nutrients Removal;
• Lipids for biodiesel;
• Polyhydroxyalkanoates (PHAs).

Lee et al., 2014. Chemical Engineering Journal.

Addition of Mg(OH)2 as magnesium ion source and struvite seed crystals (5 g/L) to promote reaction.

Mg2+ + NH4

+ + HnPO4 n‐3 + 6 H20

MgNH4PO4∙6H20 + nH+

Struvite: High comercial value as slow release fertilizer

Phosphorus Recovery Via Struvite Cristallyzation Phosphorus Recovery Via Struvite Cristallyzation

Crutchik et al,. 2013 Initial pH fixed at pH 8.5 by addition NaOH

Objective Objective

• To study the effect of the sludge type and the initial

fermentation pH on the production and composition of SCFAs;

• To evaluate the feasibility of phosphorus recovery (as

struvite, NH4MgPO4∙6H2O) from sewage sludge fermentation liquid (SSFL);

• To validate effect of initial pH and sludge type in propionate

production and phosphorus recovery, best

• perating

conditions were evaluated in a bench‐scale sequencing batch fermentation reactor

Parameter Units PS PS&WAS WAS TS g/L 29.7 ± 0.6 39.1 ± 0.8 58.1 ± 0.4 VS g/L 23.6 ± 0.5 33.5 ± 0.7 45.9 ± 0.5 Total COD mgCOD/gTVS 846.4 ± 4.0 914.8 ± 3.8 997.4 ± 6.1 Total Nitrogen (TN) mgN/gTVS 32.5 ± 0.8 41.9 ± 0.7 56.2 ± 0.5 Total Phosphorus (TP) mgN/gTVS 17.2 ± 0.4 17.5 ± 1.6 18.7 ± 1.1 COD/N ratio gCOD/gN 26.6 21.8 18.7

Origin: WWTP of Verona municipality (North of Italy); Type of Dynamic Thickening:

• Gravity Belt thickening for Primary Sludge;
• Screw Drum for Waste Activated Sludge (6‐8 g polyacrilamide /kgTS)

Characteristics of the PS, WAS and PS&WAS Characteristics of the PS, WAS and PS&WAS

N° Experiment Sludge Type COD/N (gCOD/gN) Initial fermentation pH 1‐5 PS 26.6 4.96 (Uncontrolled),8,9,10,11 6‐10 PS&WAS 21.8 5.76 (Uncontrolled),8,9,10,11 11‐15 WAS 18.7 6.19 (Uncontrolled),8,9,10,11

The response surface methodology (RSM) was applied y b bx bx bxx b x

bx

• Outline of the Batch Fermentation Experiments

Outline of the Batch Fermentation Experiments

18.75 23.75 0,0 10,0 20,0 30,0 40,0 5,5 7,0 8,5 10,0 Ratio COD/N %HPr on SCFAs Initial pH 0,0‐10,0 10,0‐20,0 20,0‐30,0 30,0‐40,0 18.75 23.75 40 80 120 160 200 240 280 5,5 7,0 8,5 10,0 Ratio COD/N SCFAs Efficiency (mgCOD/gVSS) 120‐160 160‐200 200‐240 240‐280

3D Surface plots: Maximal SCFA Production Efficiency and Percentage of Propionic Acid 3D Surface plots: Maximal SCFA Production Efficiency and Percentage of Propionic Acid

Initial pH

Initial fermentation pH<8.5 & higher fraction of PS promote highest % HPr Low initial pH & higher fraction of PS favoured the production of the SCFA

18.75 23.75 0,0 2,0 4,0 6,0 8,0 10,0 5,5 7,0 8,5 10,0 Ratio COD/N PO4‐P release (mgP/gVSS) Initial pH 0,0‐2,0 2,0‐4,0 4,0‐6,0 18.75 23.75 25 50 75 100 5,5 7,0 8,5 10,0 Ratio COD/N %PO4‐P recovered (mgP/gVSS) Initial pH 0‐25 25‐50 50‐75 75‐100

3D Surface Plots: P Released and Percentage of P Recovered 3D Surface Plots: P Released and Percentage of P Recovered

Increase of PO4 ‐P release observed at higher initial pH Higher PO4‐P recovery noted at low initial pH & higher fraction of WAS

0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 0,0 20,0 40,0 60,0 80,0 100,0 120,0 140,0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

pH Propionate production (mgCOD/gVSS)

Time (d)

PERIOD I (WAS) PERIOD II (WAS+PS) PERIOD III (PS) Yield of propionate pH effluent

Period Sludge Type COD/N (gCOD/gN) Initial fermentation pH I WAS 26.6 8.5 II PS&WAS 21.8 5.76 (Uncontrolled) III PS 18.7 6.19 (Uncontrolled)

SBFR: SCFA Production Yield of Propionic Acid SBFR: SCFA Production Yield of Propionic Acid

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 10 20 30 40 50 60 70

HPr/ HAc (gCOD/ gCOD)

Time (d)

WAS WAS+PS PS

SBFR: SCFAs Composition Acetic acid/ Propionic acid (HPr/HAc) SBFR: SCFAs Composition Acetic acid/ Propionic acid (HPr/HAc)

PERIOD I PERIOD II PERIOD III

0,2 0,4 0,6 0,8 1 1,2 1,4 (mgPO4

3‐‐P/gVSS)

PS+WAS

0,4 0,8 1,2 1,6 2 2,4 (mgPO4

3‐‐P/gVSS)

WAS

0,2 0,4 0,6 0,8 1 (mgPO4

3‐‐P/gVSS)

PS

96 %

Recovery

55%

Recovery

PO4

3‐‐P released

(mgP/gVSS) Final PO4

3‐‐P recovered

(mgP/gVSS) % PO4‐P recovered WAS

2.11 1.43

55.0 PS+WAS 1.27 1.22 96.0 PS 0.96 0.85 89.0

SSFL: PO4

3‐ Release & Recovery by Struvite Crystallization.

SSFL: PO4

3‐ Release & Recovery by Struvite Crystallization.

Before After

89 %

Recovery

Before After Before After

Conclusions Conclusions

• Fermentation of sewage sludge provide a suitable source of SCFAs and

PO4

3—P for a wide range of applications;

• The sewage sludge type and the initial fermentation pH affect the

production and composition of SCFA;

• Higher

production

• f

Propionic acid was

• bserved

at an initial fermentation pH in a range between 5.5‐8 and with higher fraction of PS (high COD/N ratio);

• The alkaline fermentation of WAS enhanced the release of nutrients (N

and P), which can be recovered by struvite crystallization up to 11 mg Struvite/gVSS.

Phosphorus recovery and VFAs production from sewage sludge fermentation

• D. Crutchik, N. Frison, A. Jelic and F. Fatone

Thank you for your attention

Natalia Herrero García