8 phosphorus recovery and vfas production from...
TRANSCRIPT
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 theproduction of biogas for co‐production of thermal and electric energy andcompostable material;
• The sewage sludge might be considered as a challenging feedstock to beprocessed for bio‐based applications (waste‐to‐chemicals and bio‐productvalue chain);
• Volatile Fatty Acids (VFAs) could be considered intermediates for a wide rangeof applications
BackgroundBackground
Production & Application of Waste‐derived VFAsProduction & Application of Waste‐derived VFAs
Lee et al., 2014. Chemical Engineering Journal.
The operating conditions for VFAs productionshould be addressed based on the finalapplication of the VFAs
Proper process control can manipulate the typeof VFA produced, which is critical to theperformances 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
Ope
ratin
g cond
ition
s
Fermentation of Sewage Sludge
Struvite (MgNH4PO4∙6H2O)
Magnesium hydroxideMg(OH)2
To anaerobic digester
PS&WASWAS
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 TreatmentRole of SCFAs in Wastewater Treatment
• SCFAs are rbCOD and help the denitrificationprocesses;
• Enhanced Bio‐P removal (4‐5 mgVFA are required foreach 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 CristallyzationPhosphorus Recovery Via Struvite Cristallyzation
Crutchik et al,. 2013
Initial pH fixed at pH 8.5 by addition NaOH
ObjectiveObjective
• To study the effect of the sludge type and the initialfermentation pH on the production and composition ofSCFAs;
• To evaluate the feasibility of phosphorus recovery (asstruvite, NH4MgPO4∙6H2O) from sewage sludge fermentationliquid (SSFL);
• To validate effect of initial pH and sludge type in propionateproduction and phosphorus recovery, best operatingconditions were evaluated in a bench‐scale sequencing batchfermentation reactor
Parameter Units PS PS&WAS WASTS 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&WASCharacteristics 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 b x b x b x x b x b x
Outline of the Batch Fermentation ExperimentsOutline of the Batch Fermentation Experiments
18.7523.75
0,010,020,030,040,0
5,57,0
8,510,0 Ratio COD/N
%HPr on SCFAs
Initial pH
0,0‐10,0 10,0‐20,0 20,0‐30,0 30,0‐40,0
18.7523.75
04080
120160200240280
5,57,0
8,510,0 Ratio COD/N
SCFAs E
fficiency (m
gCOD/gVS
S)
120‐160 160‐200 200‐240 240‐280
3D Surface plots: Maximal SCFA Production Efficiency and Percentage of Propionic Acid3D Surface plots: Maximal SCFA Production Efficiency and Percentage of Propionic Acid
Initial pH
Initial fermentation pH<8.5 & higherfraction of PS promote highest % HPr
Low initial pH & higher fraction of PS favoured the production of the SCFA
18.7523.75
0,02,0
4,0
6,0
8,0
10,0
5,57,0
8,510,0
Ratio COD/N
PO4‐P release (m
gP/gVS
S)
Initial pH
0,0‐2,0 2,0‐4,0 4,0‐6,0
18.7523.75
0
25
50
75
100
5,57,0
8,510,0 Ratio COD/N
%PO
4‐P recovered (m
gP/gVS
S)
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 higherinitial 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
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
pH
Prop
ionate produ
ction
(mgCOD/gV
SS)
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 8.5II PS&WAS 21.8 5.76 (Uncontrolled)III PS 18.7 6.19 (Uncontrolled)
SBFR: SCFA ProductionYield of Propionic AcidSBFR: SCFA ProductionYield of Propionic Acid
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
0 10 20 30 40 50 60 70
HP
r/H
Ac
(gC
OD
/gC
OD
)
Time (d)
WAS WAS+PS PS
SBFR: SCFAs CompositionAcetic acid/ Propionic acid (HPr/HAc)
SBFR: SCFAs CompositionAcetic acid/ Propionic acid (HPr/HAc)
PERIOD I PERIOD II PERIOD III
0
0,2
0,4
0,6
0,8
1
1,2
1,4
(mgPO
43‐‐P/gVS
S)PS+WAS
0
0,4
0,8
1,2
1,6
2
2,4
(mgPO
43‐‐P/gVS
S)
WAS
0
0,2
0,4
0,6
0,8
1
(mgPO
43‐‐P/gVS
S)
PS96 %
Recovery 55%
Recovery
PO43‐‐P released
(mgP/gVSS)Final PO4
3‐‐P recovered (mgP/gVSS)
% PO4‐P recovered
WAS 2.11 1.43 55.0PS+WAS 1.27 1.22 96.0
PS 0.96 0.85 89.0
SSFL: PO43‐ Release & Recovery by Struvite Crystallization. SSFL: PO43‐ Release & Recovery by Struvite Crystallization.
Before After
89 % Recovery
Before AfterBefore After
ConclusionsConclusions
• Fermentation of sewage sludge provide a suitable source of SCFAs andPO4
3—P for a wide range of applications;
• The sewage sludge type and the initial fermentation pH affect theproduction and composition of SCFA;
• Higher production of Propionic acid was observed at an initialfermentation 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 (Nand P), which can be recovered by struvite crystallization up to 11 mgStruvite/gVSS.