Phosphorus recovery and VFAs production from sewage sludge - PowerPoint PPT Presentation

Phosphorus recovery and VFAs production from sewage sludge fermentation Natalia Herrero García D. Crutchik, N. Frison, A. Jelic and F. Fatone

Background Background 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 of applications

Production & Application of Waste ‐ derived VFAs Production & Application of Waste ‐ derived VFAs Organic ‐ rich Wastes Pretreatment of Waste Anaerobic technologies for VFA production Operating conditions ‐ ph The operating conditions for VFAs production ‐ Temperature ‐ Hydraulic retention time should be addressed based on the final ‐ Solids retention time application of the VFAs ‐ Organic loading rate ‐ Additives Volatile fatty acids (VFA) Proper process control can manipulate the type Applications: ‐ Polyhydroxyalkanoates of VFA produced, which is critical to the ‐ Electricity performances of the downstream applications. ‐ Biogas ‐ Hydrogen ‐ Lipids for Biodiesel ‐ Biological nutrient removal Lee et al., 2014. Chemical Engineering Journal.

Scenario: Integration of VFA Production and Scenario: Integration of VFA Production and Phosphorus Recovery Phosphorus Recovery Magnesium hydroxide T=37ºC Mg(OH) 2 PS Fermentation S/L SCFAs (SSFL) PS&WAS of Sewage Sludge WAS ‐ Acetic Acid; ‐ Propionic Acid; (After Dynamic ‐ Butyric Acid; Thickening) ‐ Others Struvite (MgNH 4 PO 4 ∙ 6H 2 O) To anaerobic digester

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 biodiese l; • Polyhydroxyalkanoates (PHAs). Lee et al., 2014. Chemical Engineering Journal.

Phosphorus Recovery Via Struvite Cristallyzation Phosphorus Recovery Via Struvite Cristallyzation Mg 2+ + NH 4 + + H n PO 4 n ‐ 3 + 6 H 2 0 MgNH 4 PO 4 ∙ 6H 2 0 + nH + Addition of Mg(OH) 2 as magnesium ion source and struvite seed crystals (5 g/L) to promote reaction. Initial pH fixed at pH 8.5 by addition NaOH Crutchik et al,. 2013  Struvite: High comercial value as slow release fertilizer

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, NH 4 MgPO 4 ∙ 6H 2 O) from sewage sludge fermentation liquid (SSFL); • To validate effect of initial pH and sludge type in propionate production and phosphorus recovery, best operating conditions were evaluated in a bench ‐ scale sequencing batch fermentation reactor

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

Outline of the Batch Fermentation Experiments Outline of the Batch Fermentation Experiments N° Sludge COD/N Initial fermentation pH Experiment Type (gCOD/gN) 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 � � b �� x � � y � b � � b � x � � b � x � � b �� x � x � �b �� x �

3D Surface plots: Maximal SCFA Production 3D Surface plots: Maximal SCFA Production Efficiency and Percentage of Propionic Acid Efficiency and Percentage of Propionic Acid 40,0 280 %HPr on SCFAs 240 30,0 SCFAs Efficiency (mgCOD/gVSS) 200 20,0 160 120 10,0 80 0,0 40 0 5,5 5,5 7,0 7,0 8,5 8,5 23.75 23.75 Initial pH 10,0 10,0 Initial pH Ratio COD/N Ratio COD/N 18.75 18.75 0,0 ‐ 10,0 10,0 ‐ 20,0 20,0 ‐ 30,0 30,0 ‐ 40,0 120 ‐ 160 160 ‐ 200 200 ‐ 240 240 ‐ 280 Low initial pH & higher fraction of PS Initial fermentation pH<8.5 & higher fraction of PS promote highest % HPr favoured the production of the SCFA

3D Surface Plots: P Released and Percentage of P 3D Surface Plots: P Released and Percentage of P Recovered Recovered %PO4 ‐ P recovered (mgP/gVSS) PO4 ‐ P release (mgP/gVSS) 10,0 100 8,0 75 6,0 50 4,0 25 2,0 0 0,0 5,5 5,5 7,0 7,0 8,5 23.75 8,5 Initial pH 10,0 Initial pH 23.75 Ratio COD/N 10,0 18.75 Ratio COD/N 18.75 0,0 ‐ 2,0 2,0 ‐ 4,0 4,0 ‐ 6,0 0 ‐ 25 25 ‐ 50 50 ‐ 75 75 ‐ 100 Increase of PO 4 ‐ P release observed at higher Higher PO 4 ‐ P recovery noted at low initial initial pH pH & higher fraction of WAS

SBFR: SCFA Production SBFR: SCFA Production Yield of Propionic Acid Yield of Propionic Acid Sludge COD/N Period Initial fermentation pH Type (gCOD/gN) I WAS 26.6 8.5 II PS&WAS 21.8 5.76 (Uncontrolled) III PS 18.7 6.19 (Uncontrolled) 9,00 140,0 PERIOD I (WAS) PERIOD II (WAS+PS) PERIOD III (PS) Propionate production 8,00 120,0 7,00 (mgCOD/gVSS) 100,0 6,00 5,00 80,0 pH 4,00 60,0 3,00 40,0 2,00 20,0 1,00 0,0 0,00 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 Time (d) Yield of propionate pH effluent

SBFR: SCFAs Composition SBFR: SCFAs Composition Acetic acid/ Propionic acid (HPr/HAc) Acetic acid/ Propionic acid (HPr/HAc) PERIOD I PERIOD II PERIOD III 1,8 WAS PS WAS+PS HPr/ HAc (gCOD/ gCOD) 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 0,0 0 10 20 30 40 50 60 70 Time (d)

3 ‐ Release & Recovery by Struvite Crystallization. 3 ‐ Release & Recovery by Struvite Crystallization. SSFL: PO 4 SSFL: PO 4 3 ‐ ‐ P released 3 ‐ ‐ P recovered PO 4 Final PO 4 % PO 4 ‐ P recovered (mgP/gVSS) (mgP/gVSS) 2.11 1.43 WAS 55.0 PS+WAS 1.27 1.22 96.0 PS 0.96 0.85 89.0 89 % 55% 96 % PS+WAS PS Recovery WAS Recovery Recovery 1,4 1 2,4 1,2 2 0,8 3 ‐ ‐ P/gVSS) 3 ‐ ‐ P/gVSS) 3 ‐ ‐ P/gVSS) 1 1,6 0,6 0,8 1,2 (mgPO 4 (mgPO 4 (mgPO 4 0,6 0,4 0,8 0,4 0,2 0,4 0,2 0 0 0 Before After Before After Before After

Conclusions Conclusions Fermentation of sewage sludge provide a suitable source of SCFAs and • 3— P for a wide range of applications ; PO 4 • The sewage sludge type and the initial fermentation pH affect the production and composition of SCFA; • Higher production of Propionic acid was observed 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 Natalia Herrero García Thank you for your attention D. Crutchik, N. Frison, A. Jelic and F. Fatone